CHEMICAL OXYGEN DEMAND (COD)
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Chemical oxygen demand (COD) is used as a measure of oxygen requirement of a sample that is susceptible to oxidation by strong chemical oxidant. The dichromate reflux method is preferred over procedures using other oxidants (eg potassium permanganate) because of its superior oxidizing ability, applicability to a wide variety of samples and ease of manipulation. Oxidation of most organic compounds is 95-100% of the theoretical value.
Dichromate Reflux Technique Standard Method.
Equipment Required
1. 500-millilitre (ml) Erlenmeyer flask with standard (24/40) tapered glass joints
2. Friedrichs reflux condensers (12-inch) with standard (24/40) tapered glass joints
3. Electric hot plate or six-unit heating shelf
4. Volumetric pipettes (10, 25, and 50ml capacity)
5. Burette, 50 ml - 0.1 ml accuracy
6. Burette stand and clamp
7. Analytical balance, accuracy 0.001gram (g)
8. Spatula
9. Volumetric flasks (1,000ml capacity)
10. Boiling beads, glass
11. Magnetic stirrer and stirring bars
Chemicals Required
1. Potassium dichromate (K2Cr2O7) 0.25N
2. Sulphuric acid (H2SO4) / silver sulphate (Ag2SO4) solution
3. Mercuric sulphate (HgSO4) crystals
4. Ferrous ammonium sulphate (FAS) [Fe(NH4)2(SO4)2], approximately 0.01N
5. Ferroin indicator (1, 10-phenanthroline and ferrous ammonium sulphate)
Caution: In carrying out the following procedures, use proper safety measures, including protective clothing, eye protection, and a fume hood. Reagents containing heavy metals (HgSO4 and Ag2SO4) should be disposed of as toxic wastes.
Chemical Preparation
1. Dissolve 12.259g of oven-dried (primary standard grade dried at 103oC to a constant weight) potassium dichromate in distilled water and dilute to 1 litre volume in a volumetric flask.
2. Add 22g of reagent grade silver sulphate to a 4kg bottle of concentrated sulphuric acid (H2SO4) and mix until the silver sulphate goes into solution.
3. Use 1 g of mercuric sulphate (HgSO4) to complex 100 mg chloride (2,000 mg/l).
4. Dissolve 1.485g of 1,10-phenanthroline monohydrate and 0.695g of ferrous ammonium sulphate heptahydrate in distilled water and dilute to approximately 100ml. (Alternatively, this indicator may be purchased as Ferroin Indicator from most scientific suppliers.)
5. Dissolve 39g reagent grade ferrous ammonium sulphate hexahydrate in distilled water. Add 20ml of concentrated sulphuric acid (H2SO4). Cool and dilute to exactly 1 litre in a volumetric flask using distilled water. The ferrous ammonium sulfate (FAS) titrant must be standardized daily by the following procedure:
Dilute 10ml of standard potassium dichromate (K2Cr2O7) solution to 100ml with distilled water. Slowly add 30ml of concentrated sulphuric acid and cool to room temperature. Titrate with ferrous ammonium sulphate titrant, using 2 to 3 drops (0.10 to 0.15 ml) of Ferroin indicator.
Normality of FAS = (ml K2Cr2O7)(0.25)
ml FAS required
The deterioration of FAS can be decreased if it is stored in a dark bottle.
Procedure
1. Place a 50ml sample or an aliquot diluted to 50ml in a 500ml refluxing flask. The blank is prepared using 50ml of distilled water. This is a precise measurement and a 50ml volumetric pipette should be used. Refer to COD Range and Sample Size below for dilution.
2. Add 5 to 7 glass boiling beads.
3. Add 1g of mercuric sulphate (HgSO4), 5ml of concentrated sulphuric acid / silver sulphate solution, and mix until the HgSO4 is in solution. The function of the mercuric sulphate is to bind or complex chlorides. One gram may not be required if the chloride concentration is low. (Caution: Always add acid slowly down the side of the flask while mixing to avoid overheating. It may be necessary to use gloves because of the heat generated.)
4. Accurately add 25ml of 0.25 N potassium dichromate (K2Cr2O7) and mix.
5. Add while mixing, an additional 70ml of concentrated sulphuric acid-silver sulphate solution.
6. After thorough mixing, attach the flask to the reflux condenser, apply heat, and reflux for 2 hours. Refluxing time can be decreased depending on the ease of oxidation of organic materials. This time may be determined by refluxing for periods from 15 minutes to 2 hours and comparing the results.
7. A reagent blank containing 50ml of distilled water treated with the same reagent as the sample should be refluxed with each set of samples.
8. Cool the apparatus to room temperature after the refluxing period. Wash down the interior of the condenser and flask twice with approximately 25ml portions of distilled water.
9. Remove flask from the condenser and dilute to a final volume of approximately 350ml with distilled water.
10. Add 4 to 5 drops of Ferroin indicator and a magnetic stirring bar.
11. Place flask on a magnetic stirrer and rapidly titrate with 0.1 N ferrous ammonium sulphate to the first red-brown endpoint.
Caution: Use care in titration. The endpoint is very sharp and may be reached rapidly.
Formula to determine COD:
COD (mg/l) = (a-b)(N) x 8,000 / sample size (ml)
Where:
a = ml Fe(NH4)2(SO4)2 used for blank
b = ml Fe(NH4)2(SO4)2 used for sample
N = normality of FAS titrant (Fe(NH4)2(SO4)2)
ml sample = the actual volume of sample used before dilution
Sources of Error
1. The largest error is caused by using a nonhomogeneous sample. Every effort should be made to blend and mix the sample so that solids are never excluded from any aliquot.
2. Always use the largest sample practical and use the largest glassware that is in keeping with good laboratory practice.
3. Use volumetric flasks and volumetric pipettes with a large bore.
4. The K2Cr2O7 oxidizing agent must be precisely measured. Use a volumetric pipette and use the same one each time if possible.
5. When titrating, be certain that the burette is clean and free of air bubbles.
6. Always read the bottom of the meniscus and position the meniscus at eye level.
COD Range and Sample Size
COD Range (mg/l) 50-800 100-1500 240-3700 480-7500 1200-18800 2400-3700 40000-375000
Volume of Sample (ml) 50 25 10 5 2 1 0.1
All samples high in solids should be blended for 2 minutes at high speed and stirred when an aliquot is taken. Sample volumes less than 25ml should not be pipetted directly, but serially diluted and then a portion of the diluent removed:
1. 500ml of sample diluted to 1,000 ml = 0.5 ml sample/ml of diluent, .: 50 ml of diluent = 25 ml of sample.
2. 100 ml of sample diluted to 1,000 ml = 0.1 ml sample/ml diluent, .: 50 ml of diluent = 5 ml of sample.
Elimination of Interference
One gram of mercuric sulphate (HgSO4) will complex 100mg of chloride in a 50ml sample (2,000 mg/l). For samples higher in chloride more HgSO4 should be used in the ratio of 10:1 HgSO4.
Interference from nitrites can be prevented by the addition of 10:1 ratio of sulfamic acid:nitrite. The addition of the silver sulphate (AgSO4) concentrated sulphuric acid (H2SO4) refluxing acid will aid in the oxidation of some organic nitrogen compounds, but aromatic hydrocarbons and pyridine are not oxidized to any appreciable amount.
© 2006 Oasis Environmental Ltd
sIn Lesson 1 and 2, it was emphasized that Bald Eagles need to live near and hunt from unpolluted, high quality water. Water quality is sometimes difficult to determine. Some people think that if water is clear; it is clean, and if it is cloudy or colored, the water is dirty or polluted....unfortunately, it is not that simple.
The only way to determine the health of a lake or river is to test the water. This part of Lesson 3 will walk you through ten different water quality tests that you can perform on a lake, pond or river in your area. At the end of this section, you will be able to take your data and calculate the overall quality of the water you have been testing. Depending on the results, you can decide if the lake or river would be a good place for a Bald Eagle to live and hunt.
A majority of the information, charts, and tables in this section came from an excellent book titled Field Manual for Water Quality Monitoring : An Environmental Education Program for Schools. If you would like more complete information on this subject, this book would be a great resource.
Introduction
Have you ever looked into the flowing waters of a stream or river and wondered where it began, or to where it flowed? There are some features that are unique to rivers and lakes.
• All rivers and lakes have flowing water. Depending on their size and shape, the water flow might be fast or very slow.
• Rivers and lakes are inseparable from the land through which they flow. The land area that drains rain and snowmelt to a river is called a watershed. Everything that happens in a watershed affects the water quality to some degree. Every person on earth lives within a watershed. Do you know what your watershed looks like? How does land use affect your river?
• Rivers are some of the oldest natural features on Earth. Rivers stretch back in time millions of years. Just imagine the age of the Colorado River, as it has cut a channel almost a mile deep called the Grand Canyon.
• Rivers and lakes are some of the most used and abused natural features on Earth. Many watersheds have been altered as a result of human needs for water, food, recreation, transportation, manufactured foods and other amenities. These growing demands have led to pollution of streams and rivers and unwise land uses that further degrade water quality.
How to Measure Water Quality Using a Water Quality Index
Many factors can affect water quality. The conditions of a river or lake can fluctuate periodically, so you must measure water quality periodically to look for trends. Water that is determined to be safe for one use may be unacceptable for another purpose or species. This part of Lesson 3 will use biological, chemical and physical measurements to determine the health of a body of water.
The information in this part of the lesson has been divided into three main sections. You should start with "Water Quality Index." It will describe the process and what type of information you will need to collect to calculate a Water Quality Index (WQI) for a body of water.
The next section, the largest, involves information on the nine tests that go into the WQI. Each section contains background information on the tests and its significance. Detailed instructions are also included on how to perform the tests. Some of the tests have kits that can be purchased, and their instructions should be followed. If some of the tests are more involved than you prefer, maybe you can team up with a science club or a high school science class and share the information.
The information in "Calculating the WQI" will allow you to take your tests results and make a scientific conclusion about the quality of the water. Although many factors affect where a Bald Eagle lives, you will be able to determine if the water would be a positive factor in its selection of a home.
There are other ways to evaluate the quality of water. You don’t always have to use test tubes and chemicals, sometimes all you have to do is look at what critters already live there. There are some animals that can be used as indicator species. For example, black fly larva can tolerate a higher level of pollution than a caddisfly larva. Using the Critter Scorecard, you can determine the quality of the water by what type of creatures you find.
And finally, the last thing you need to do before you get started is to select a lake, stream or river you would like to test !
Biochemical Oxygen Demand (BOD)
When organic matter decomposes, it is fed upon by aerobic bacteria. In this process, organic matter is broken down and oxidized (combined with oxygen). Biochemical oxygen demand is a measure of the quantity of oxygen used by these microorganisms in the aerobic oxidation of organic matter.
When aquatic plants die, they are fed upon by aerobic bacteria. The input of nutrients into a river, such as nitrates and phosphates, stimulates plant growth. Eventually, more plant growth leads to more plant decay. Nutrients, then, can be a prime contributor to high biochemical oxygen demand in rivers.
Sources of Organic Matter
There are natural sources of organic material which include organic matter entering lakes and rivers from swamps, bogs, and vegetation along the water, particularly leaf fall.
There are also human sources of organic material. When these are identifiable points of discharge into rivers and lakes, they are called point sources. Point sources of organic pollution include:
1. pulp and paper mills;
2. meat-packing plants;
3. food processing industries;
4. wastewater treatment plants.
Nonpoint pollution comes from many sources that are difficult to identify. Nonpoint sources of organic pollution include:
1. Urban runoff of rain and melting snow that carries sewage from illegal sanitary sewer connections into storm drains; pet wastes from streets and sidewalks; nutrients from lawn fertilizers; leaves, grass clippings, and paper from residential areas;
2. Agricultural runoff that carries nutrients, like nitrogen and phosphates, from fields;
3. Runoff from animal feedlots that carries fecal material into rivers.
Changes in Aquatic Life
In rivers with high BOD levels, much of the available dissolved oxygen is consumed by aerobic bacteria, robbing other aquatic organisms of the oxygen they need to live. Organisms that are more tolerant of lower dissolved oxygen may appear and become numerous, such as carp, midge larvae, and sewage worms. Organisms that are intolerant of low oxygen levels, such as caddisfly larvae, mayfly nymphs, and stonefly nymphs, will not survive. As organic pollution increases, the ecologically stable and complex relationships present in waters containing a high diversity of organisms is replaced by a low diversity of pollution-tolerant organisms.
Sampling Procedure
A dissolved oxygen bottle strapped to the extended rod sampler can be used to take a BOD sample. Remember, samples taken near the river bottom may hold more oxygen-demanding materials and organisms; therefore, to get a representative sample it is best to sample between the surface and river bottom, and away from the shore.
One of the dissolved oxygen bottles should be blackened or purchased as a "dark bottle." One approach is to wrap the bottle with black electrical tape. It is always a good idea if several bottles are available to run several BOD samples.
Like the dissolved oxygen tests, it is important to run all tests for comparison at the same time of day.
Biochemical Oxygen Demand Testing Procedures
1. Fill two dissolved oxygen bottles (one clear and one black) with sample water, holding them for two to three minutes between the surface and the river bottom. If sampling by hand remember to use gloves.
2. Prepare the clear sample bottle according to the directions for the dissolved oxygen test. Determine the DO value for this sample in mg/L.
3. Place the black sample bottle in the dark and incubate for five days at 68'F (20'C). This is very close to room temperature in many buildings. If there is no incubator, place the blackened sample bottle in a "light-tight" drawer or cabinet.
4. After five days, determine the level of dissolved oxygen (in mg/L) of this sample by repeating steps four through eleven of the DO testing procedure.
5. The BOD level is determined by subtracting this DO level from the DO level found in the original sample taken five days previously:
• BOD=mg/LDO(original sample)-mg/LDO(after incubation)
• The BOD measure is, the amount of oxygen consumed by organic matter and associated microorganisms in the water over a five-day period.
In waters suspected of carrying large amounts of organic waste/ sewage, the oxygen demand may be so great that all oxygen is consumed before the 5-day period. The above approach would not reveal the true oxygen demand over the 5-day period.
Alternative approaches require the use of a dissolved oxygen meter to periodically measure dissolved oxygen levels, and re-saturate the sample with oxygen. Another alternative is to make buffered dilution water and dilute the sample until oxygen demand is more in balance with oxygen supply.
For further information about testing procedures, please consult Standard Methods For The Examination of Water And Wastewater 16th edition, American Public, Health Association, New York, 1985.
After the test is completed and the results are recorded, the Water Quality Index (WQI) for the body of water can be computed. To formulate a WQI, you must first compute a Q- value for the results you obtained. The Q-values of all nine tests will be used together to determine the health of the river or lake. See Water Quality Index page. To compute the Q-value for the BOD test, follow these steps:
1. Find the weighting curve chart at the end of this page;
2. Locate your test result on the bottom (horizontal or “x” axis) of the chart;
3. Interpolate the Q-value for your test result using the following steps;
a. From your test result value on the horizontal (“x”) axis of the chart, draw a vertical line up until it intersects the weighting curve line;
b. From this point of intersection, draw a horizontal line to the left hand side (the vertical or “y” axis) of the chart;
c. Where this horizontal line intersects the vertical (“y”) axis of the chart, read off the value. This is the Q-value for this test; it should be recorded in Column B on the WQI chart on the Water Quality Index page.
The Q-value for each test should then be multiplied by the weighting factor listed in the chart on the Water Quality Index page. Record the product of this calculation in Column D of the chart.
BOD : mg/L Note: if BOD5>30.0, Q=2.0
Phosphorus is usually present in natural waters as phosphate .Organic phosphate is a part of living plants and animals, their by-products, and their remains. Inorganic phosphates include the ions (H2PO-2, HPO=4, and PO-4) bonded to soil particles and phosphates present in laundry detergents.
Phosphorus is an essential element for life. It is a plant nutrient needed for growth, and a fundamental element in the metabolic reactions of plants and animals. Plant growth is limited by the amount of phosphorus available. In most waters, phosphorus functions as a "growth-limiting" factor because it is usually present in very low concentrations.
The natural scarcity of phosphorus can be explained by its attraction to organic matter and soil particles. Any unattached or “free" phosphorus, in the form of inorganic phosphates, is rapidly taken up by algae and larger aquatic plants. Because algae only require small amounts of phosphorus to live, excess phosphorus causes extensive algal growth called "blooms." Algal blooms are a classic symptom of cultural eutrophication. (Eutrophication means when a body of water has an increased amount of minerals and nutrients. This change favors the growth of plants over animals.)
Cultural eutrophication is the human-caused enrichment of water with nutrients, usually phosphorus. Most of the eutrophication occurring today is human-caused. Natural eutrophication also takes place, but it is insignificant by comparison. Phosphorus from natural sources generally becomes trapped in bottom sediments or is rapidly taken up by aquatic plants. Forest fires and fallout from volcanic eruptions are natural events that cause eutrophication. Lakes that receive no inputs of phosphorus from human activities age very slowly
Sources of Phosphorus
Phosphorus comes from several sources: human wastes, animal wastes, industrial wastes, and human disturbance of the land and its vegetation.
Sewage from wastewater treatment plants and septic tanks is one source of phosphorus in rivers. Sewage effluent (out flow) should not contain more than 1 mg/ L phosphorus according to the U.S. Environmental Protection Agency, but outdated wastewater treatment plants often fail to meet this standard. Also, some types of industrial wastes interfere with the removal of phosphorus at wastewater treatment plants.
Storm sewers sometimes contain illegal connections to sanitary sewers. Sewage from these connections can be carried into waterways by rainfall and melting snow. Phosphorus-containing animal wastes sometimes find their way into rivers and lakes in the runoff from feedlots and barnyards.
Soil erosion contributes phosphorus to rivers. The removal of natural vegetation for farming or construction for example, exposes soil to the eroding action of rain and melting snow. Soil particles washed into waterways contribute more phosphorus.
Fertilizers used for crops, lawns, and home gardens usually contain phosphorus. When used in excess, much of the phosphorus in these fertilizers eventually finds its way into lakes and rivers.
Draining swamps and marshes for farmland or shopping malls releases nutrients like phosphorus that have remained dormant in years of accumulated organic deposits. Also, drained wetlands no longer function as filters of silt and phosphorus, allowing more runoff -and phosphorus- to enter waterways.
Impacts of Cultural Eutrophication
Shallow lakes and impounded river reaches, where the water is shallow and very slow-moving, are most vulnerable to the effects of cultural eutrophication. Phosphorus stimulates the growth of rooted aquatic vegetation. These plants, in turn, draw phosphorus previously locked within bottom sediments and release it into the water, causing further eutrophication. Eventually, the entire lake or river stretch may fill with aquatic vegetation.
The first symptom of cultural eutrophication is an algal bloom that colors the water a pea-soup green. As eutrophication increases, algal blooms become more frequent. Aquatic plants that normally grow in shallow waters become very dense. Swimming and boating may become impossible.
The advanced stages of cultural eutrophication can produce anaerobic conditions in which oxygen in the water is completely depleted. These conditions usually occur near the bottom of a lake or impounded river stretch, and produce gases like hydrogen sulfide, unmistakable for its "rotten egg" smell.
Changes in Aquatic Life
As with other types of water pollution, cultural eutrophication causes a shift in aquatic life to a fewer number of pollution tolerant species. The many different species that exist in clean water are replaced by a fewer number of species that can tolerate low dissolved oxygen levels-carp, midge larvae, sewage worms (Tubifex), and others. For example, waters that once supported bass, walleye, pike, and bluegill may only be able to support carp under eutrophic conditions.
Reversing the Effects of Cultural Eutrophication
Aquatic ecosystems have the capacity to recover if the opportunity is provided by:
1. Reducing our use of lawn fertilizers (particularly inorganic forms) that drain into waterways;
2. Encouraging better farming practices: low-till farming to reduce soil erosion; soil- testing to match the amount of fertilizer applied to soil needs, thus preventing excess fertilizer from finding its way into waterways; building storage or collecting areas around cattle feedlots, so that phosphorus containing manure is not carried away with surface runoff;
3. Preserving natural vegetation whenever possible, particularly near shorelines; preserving wetlands to absorb nutrients and maintain water levels; enacting strict ordinances to prevent soil erosion;
4. Supporting measures (including taxes) to improve phosphorus removal by wastewater treatment plants and septic systems; treating storm sewer wastes if necessary; encouraging homeowners along lakes and streams to invest in community sewer systems;
5. Requiring particular industries to pretreat their wastes before sending it to a wastewater treatment plant.
Can you think of any other actions that would prevent or reduce the effects of eutrophication?
Sampling Procedure
It is important that glassware used for measuring total phosphate be “acid-washed," that is, soaked in diluted HCI, and then rinsed thoroughly with distilled water. Please wear protective gloves when handling this glassware. WARNING: Never wash this glassware with phosphorous-containing detergents.
Total Phosphate (PO-4-P) Testing Procedure
Total Phosphate test kit items
1. Fill the 50 ml graduated cylinder to the 50 ml line with the water sample. Pour into a 125 ml Erlenmeyer flask. Use gloves if drawing the sample by hand.
2. Use a 1ml pipette to add 1ml, of Sulfuric Acid, 36% to the flask. Swirl to mix.
3. Use the 0.05 g spoon to add one measure of Ammonium Persulfate. Swirl to dissolve.
4. Add a few boiling stones. Place the flask on a hot plate, small backpacking stove or Sterno and boil gently for 30 minutes. Add deionized water to the sample during the boiling to maintain a volume between 10 and 50 ml. Permit the volume to decrease to approximately 10 ml (about 1/4 inch of water) at the end of the boiling step, but do not allow the sample to go to dryness or to dense white sulfur trioxide fumes. Remove from the hot plate and cool.
If inside, please boil sample in a well-ventilated place; if outside, please stay upwind of the boiling sample.
5. Add one drop of Phenolphthalein Indicator, 1% to the cooled sample.
6. While swirling the flask, use a 1 ml- pipette to add Sodium Hydroxide dropwise until the solution turns faint pink. A volume of slightly less than 3 ml is required.
7. While swirling the flask, add Sulfuric Acid, 36%, one drop at a time, until the pink color disappears.
8. Quantitatively transfer the sample, which should be at room temperature, to the 50 ml graduated cylinder. After transferring the solution from the flask to the graduated cylinder, wash the flask with a little deionized water and add it to the solution in the graduated cylinder. Dilute the solution in the graduated cylinder to exactly 50 ml using deionized water and mix well.
9. Fill a test tube to the 10 ml line with the test sample from step 9.
10. Use the 1.0 ml pipette to add 1.0 ml of Phosphate Acid Reagent. Cap and mix.
Use of the Axial Reader
11. Use the 0.1 g spoon to add one level measure of Phosphate Reducing Reagent. Cap and mix until the powder has dissolved. Wait 5 minutes.
12. Remove the stopper from the test tube. Place the tube in the Phosphate Comparator with Axial Reader. Match the sample color to a color standard. Record the result as mg/L (ppm) Total Phosphate.
Note: Total phosphate concentrations of non-polluted waters are usually less than 0. 1mg/ L.
After the test is completed and the results are recorded, the Water Quality Index (WQI) for the body of water can be computed. To formulate a WQI, you must first compute a Q-value for the results you obtained. The Q-values of all nine tests will be used together to determine the health of the river or lake. See Water Quality Index page. To compute the Q-value for the Phosphate (PO4-P) test, follow these steps:
1. Find the weighting curve chart at the end of this page;
2. Locate your test result on the bottom (horizontal or “x” axis) of the chart;
3. Interpolate the Q-value for your test result using the following steps;
a. From your test result value on the horizontal (“x”) axis of the chart, draw a vertical line up until it intersects the weighting curve line;
b. From this point of intersection, draw a horizontal line to the left hand side (the vertical or “y” axis) of the chart;
c. Where this horizontal line intersects the vertical (“y”) axis of the chart, read off the value. This is the Q-value for this test; it should be recorded in Column B on the WQI chart on the Water Quality Index page.
The Q-value for each test should then be multiplied by the weighting factor listed in the chart on the Water Quality Index page. Record the product of this calculation in Column D of the chart.
Phosphate (PO4-P): mg/L Note: PO4-P>10.0, Q=2.0
One way to determine the quality of lake, river or creek water is to observe what type of animals live there. The Critter Countdown consists of a scorecard (located at the end of the page) and an identification guide. Go to a body of water and start hunting. You might want to take a net, something to use as a scope, a bucket and a magnifying lens. Use the scorecard to judge the quality of the water. Remember you may not find all the critters listed. When you are done hunting, make sure you return all the critters (unharmed) back to the water.
One Point Critters
Pollution-tolerant organisms can be in any quality of water
Aquatic Earthworms and other Worms 1/4” - 2”, can be very tiny; thin worm-like body. Tubifex worms shown.
Blackfly Larva Up to 1/4”, one end of body wider; black head, suction pad on end.
Midge Fly Larva Up to 1/4”, dark head, worm-like segmented body, 2 tiny legs on each side. Bright red or green body. Red ones also called bloodworms.
Leech 1/4” - 2”, brown, slimy body, ends with suction pads.
Other Snails No operculum (hard end cover), breathe air; snail shell coils in one plane
Pouch Snail and Pond Snail No operculum (hard end cover). Breathe air; shell usually opens on left.
Rat-tailed Maggot 1/4” to 1”; the The body is covered with fine hairs and is wrinkled. The long tube is used to breathe.
Mosquito Larva and Pupa Fused segments makes the thorax thicker than the rest of body. They feed on algae and other bits of organic debris. Larva (top) pupa (bottom)
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Two Point Critters Somewhat pollution tolerant organisms can be in good to fair quality water
Crayfish Up to 6”, 2 large claws, 8 legs, resembles small lobster
Damselfly Larva 1/2” - 1”, large eyes, 6 thin hooked legs, 3 broad oar-shaped tails, positioned like a tripod. Smooth (no gills ) on sides of lower half of body.
Fingernail Clam Small
Crane Fly Larva 1/3” -2”, milky green or light brown, plump caterpillar-like segmented body, 4 finger-like lobes at back end.
Scud 1/4”, white to gray, body higher than it is wide, swims sideways, more than 6 legs, resembles small shrimp.
Dragon Fly Larva 1/2” -2”, large eyes, 6 hooked legs; wide oval to round abdomen.
Alderfly larva 1” long; looks like small hellgrammite but has 1 long, thin, beached tail at back end (no hooks). No gill tufts underneath.
Fishfly larva Up to 1 1/2” long; looks like small hellgrammite, but often a lighter reddish-tan color, or with yellowish streaks. No gill tufts underneath.
Sowbug 1/4”-3/4”, gray oblong body wider than it is high, more than 6 legs, long antennae.
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Three Point Critters Pollution sensitive organisms found in good quality water.
Stonefly Larva 1/2” - 1 1/2”, 6 legs with hooked tips, antennae, 2 hair-like tails. Smooth (no gills) on lower half of body.
Mayfly Larva 1/4” -1”, brown, moving, plate-like or feathery gills on sides of lower body, 6 large hooked legs, antennae, 2 or 3 long, hair-like tails. Tails may be webbed together.
Dobsonfly Larva (Hellgrammite) 3/4” - 4”, dark-colored, 6 legs, large pinching jaws, eight pairs feelers on lower half of body with paired cotton-like gill tufts along underside, short antennae, 2 tails and 2 pairs of hooks at back end.
Caddisfly Larva Up to 1”; 6 hooked legs on upper third of body, 2 hooks at back end. May be in a stick, rock or leaf case with its head sticking out. May have fluffy gills tufts on lower half.
Water Penny 1/4” flat saucer-shaped body with a raised bump on one side and 6 tiny legs on the other side. Immature beetle.
Gilled Snail Shell opening covered by thin plate called operculum. Shell usually opens on right.
Riffle Beetle 1/4” oval body covered with tiny hairs, 6 legs, antennae. Walks slowly underwater, does not swim on surface.
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Nitrogen is an element needed by all living plants and animals to build protein. In aquatic ecosystems, nitrogen is present in many forms.
Nitrogen is a much more abundant nutrient than phosphorus in nature. It is most commonly found in its molecular form (N2), which makes up 79 percent of the air we breathe. This form, however is useless for most aquatic plant growth.
Blue-green algae, the primary algae of algal blooms, are able to use N2 and convert it into forms of nitrogen that plants can take up through their roots and use for growth: ammonia (NH3) and nitrate (NO-3).
How do aquatic animals obtain the nitrogen they need to form proteins? In two ways: they either eat aquatic plants and convert plant proteins to specific animal proteins, or they eat other aquatic organisms which feed upon plants.
As aquatic plants and animals die, bacteria break down large protein molecules into ammonia. Ammonia is then oxidized (combined with oxygen) by specialized bacteria to form nitrites (NO-2) and nitrates (NO-3). These bacteria get energy for metabolism from oxidation.
Excretions of aquatic organisms are very rich in ammonia, although the amount of nitrogen they add to waters is usually small. Duck and geese, however, contribute a heavy load of nitrogen (from excrement) in areas where they are plentiful. Through decomposition of dead plants and animals, and the excretions of living animals, nitrogen that was previously "locked up" is released.
There even exist bacteria that can transform nitrates (NO-3) into free molecular nitrogen (N2). The nitrogen cycle begins again if this molecular nitrogen is converted by blue-green algae into ammonia and nitrates.
Because nitrogen, in the form of ammonia and nitrates, acts as a plan nutrient, it also causes eutrophication. As you learned in the Total Phosphate Test, eutrophication promotes more plant growth and decay, which in turn increases biochemical oxygen demand. However, unlike phosphorus, nitrogen rarely limits plant growth, so plants are not as sensitive to increases in ammonia and nitrate levels.
Sources of Nitrates
Sewage is the main source of nitrates added by humans to rivers and lakes. Sewage enters waterways in inadequately treated wastewater from sewage treatment plants, in the effluent (outflow) from illegal sanitary sewer connections, and from poorly functioning septic systems.
Septic systems are common in rural areas. Unlike large, centralized urban sewer systems that collect waste from many households, septic systems are generally used to treat the waste from only a single household.
In a septic system, household wastewater from toilets, sinks, bathtubs, and washing machines flows through a main pipe into a box called a septic tank. After larger waste materials settle and floating grease is skimmed off, the remaining liquid then flows through a grid of perforated pipes. The holes in these pipes allow the liquid to trickle out onto a layer of stone, gravel, and soil known as the "drain field".
In properly functioning septic systems, soil particles remove nutrients like nitrates and phosphates before they reach groundwater. However, two factors often keep septic systems from working like they should.
Septic systems must be properly located. When septic system drainfields are placed too close to the water table, nutrients and bacteria are able to percolate down into the groundwater where they may contaminate drinking water supplies. They may also find their way into lakes or rivers via groundwater flow.
Also, septic tanks must be emptied periodically, to function properly. If the tank is full, household wastes go directly to the drain field instead of settling in the tank. When this happens, the drain field pipes may become plugged, and household sewage may start to pool on the ground and enter water through surface runoff.
Water containing high nitrate levels can cause a serious condition called methemoglobinemia (met-hemo-glo-bin-emia), if it is used for infant milk formula. This condition prevents the baby's blood from carrying oxygen; hence the nickname "blue baby" syndrome.
Two other important sources of nitrates in water are fertilizers, and the runoff from cattle feedlots, dairies, and barnyards. High nitrate levels have been discovered in groundwater beneath croplands due to excessive fertilizer use, especially in heavily irrigated areas with sandy soils. Storm water runoff can carry nitrate-containing fertilizers from farms and lawns into waterways. Similarly, places where animals are concentrated, such as feedlots and dairies, produce large amounts of wastes rich in ammonia and nitrates. If not properly contained, these can seep into groundwater or be transported in runoff into surface waters.
As discussed in the Total Phosphate section, people have created the eutrophication problem that threatens to limit organism diversity, recreational opportunities, and property values. Only we can reverse eutrophication through thoughtful action.
Sampling Procedure
Again, any sampling device might be used for this water quality test to obtain representative samples. It is also important to have spotless glassware, rinsed with demineralized water. Always use demineralized water during the nitrate test, Distilled water contains ammonia (NH3) ions that will interfere with the test.
Nitrate Testing Procedure
Nitrate test kit items
Note: Use the following procedure for suspected nitrate nitrogen in the 0.25- 10.0 mg/L range. A low range test 0-1 mg/L Nitrate test is also available.
1. Fill the sample bottle with sample water. Use gloves if drawing the sample by hand.
2. Rinse and fill one test tube to the 2.5 ml line with water from the sample bottle,
3. Dilute to the 5 ml line with the Mixed Acid Reagent, Cap and mix. Wait 2 minutes.
4. Use the 0.1 g spoon to add one level measure (avoid any excess) of Nitrate Reducing Reagent. Cap and invert gently 50-60 times in one minute. Wait 10 minutes.
5. Insert the test tube into the Nitrate Nitrogen Comparator. Match the sample color to a color standard. Record the result as mg/L, (ppm) Nitrate Nitrogen (NO3-N). To convert to mg/L Nitrate (NO3), multiply by 4.4.
6. Place the reacted sample in a clearly marked container. Arrangements should be made with toxic material handlers for safe disposal. Please wash your hands after this water test is completed.
For Your Information
Nitrate Test Kits which do not require the use of cadmium are also available.
After the test is completed and the results are recorded, the Water Quality Index (WQI) for the body of water can be computed. To formulate a WQI, you must first compute a Q- value for the results you obtained. The Q-values of all nine tests will be used together to determine the health of the river or lake. See Water Quality Index page. To compute the Q-value for the nitrate (NO-3) test, follow these steps:
1. Find the weighting curve chart at the end of this page;
2. Locate your test result on the bottom (horizontal or “x” axis) of the chart;
3. Interpolate the Q-value for your test result using the following steps;
a. From your test result value on the horizontal (“x”) axis of the chart, draw a vertical line up until it intersects the weighting curve line;
b. From this point of intersection, draw a horizontal line to the left hand side (the vertical or “y” axis) of the chart;
c. Where this horizontal line intersects the vertical (“y”) axis of the chart, read off the value. This is the Q-value for this test; it should be recorded in Column B on the WQI chart on the Water Quality Index page.
The Q-value for each test should then be multiplied by the weighting factor listed in the chart on the Water Quality Index page. Record the product of this calculation in Column D of the chart.
Nitrate: mg/L Note: If NO-3>100.0, Q=1.0
Water (H20) contains both H+ (hydrogen) ions and OH- (hydroxyl) ions. The pH test measures the H+ ion concentration of liquids and substances. Each measured liquid or substance is given a pH value on a scale that ranges from 0 to 14.
Pure deionized water contains equal numbers of H+ and OH- ions, and has a pH of 7. It is considered neutral, neither acidic nor basic. If a water sample has more H+ than OH- ions, it is considered acidic and has a pH less than 7. If the sample contains more OH- ions than H- ions, it is considered basic with a pH greater than 7.
It is important to remember that for every one unit change on the pH scale, there is approximately a ten-fold change in how acidic or basic the sample is. For example, the average pH of rainfall over much of the northeastern United States is 4.3, or roughly ten times more acidic than normal rainfall of 5.0-5.6. Lakes of pH 4 (acidic) are roughly 100 times more acidic than lakes of pH 6.
Human-Caused Changes in pH
In the U.S., the pH of natural water is usually between 6.5 and 8.5, although wide variations can occur. Increased amounts of nitrogen oxide (NOx) and sulfur dioxide (SO-2), primarily from automobile and coal-fired power plant emissions, are converted to nitric acid and sulfuric acid in the atmosphere. These acids combine with moisture in the atmosphere and fall to earth as acid rain or acid snow.
Acid rain is responsible for thousands of lakes in eastern Canada, northeastern United States, Sweden, and Finland becoming acidic. In many areas of the United States, the type of rocks and minerals present determine the acidity of the local water. If limestone is present, the alkaline (basic) limestone neutralizes the effect the acids might have on lakes and streams.
The areas hardest hit by acid rain and snow are downwind of urban/industrial areas and do not have any limestone to reduce the acidity of the water.
Changes in Aquatic Life
Changes in the pH value of water are important to many organisms. Most organisms have adapted to life in water of a specific pH and may die if it changes even slightly. This has happened to brook trout in some streams in the Northeast.
At extremely high or low pH values (e.g., 9.6 or 4.5) the water becomes unsuitable for most organisms. Serious problems occur in lakes with a pH below 5, and in streams that receive a massive acid dose as the acidic snow melts in the spring. Immature stages of aquatic insects and young fish are extremely sensitive to pH values below 5.
Very acidic waters can also cause heavy metals, such as copper and aluminum, to be released into the water. Heavy metals can accumulate on the gills of fish or cause deformities in young fish, reducing their chance of survival.
pH Sampling Procedure
Like the sample collected for the dissolved oxygen test, the water sample for the pH test should be collected away from the river bank and below the surface. If possible, use an extension rod sampler.
The sample must be measured immediately because changes in temperature can affect the pH value. If pH must be measured later, the sample should be placed on ice and measured as soon as possible.
If the pH of the same water sample is tested more than once, the most common pH value (the mode) should be reported, not the average value.
pH Testing Procedure
1. Rinse each test tube with the water sample. Gloves should be worn to avoid skin contact with the water.
2. Fill the tube to the 5 ml line with sample water.
3. While holding dropper bottle vertically, add 10 drops of Wide Range Indicator Solution.
4. Cap and invert several times to mix.
5. Insert the tube into the Wide Range pH Comparator. Hold the comparator up to a light source. Match the sample color to a color standard.
6. Record the pH value.
7. Wash your hands.
After the test is completed and the results are recorded, the Water Quality Index (WQI) for the body of water can be computed. To formulate a WQI, you must first compute a Q- value for the results you obtained. The Q-values of all nine tests will be used together to determine the health of the river or lake. See Water Quality Index page. To compute the Q-value for the pH test, follow these steps:
1. Find the weighting curve chart at the end of this page;
2. Locate your test result on the bottom (horizontal or “x” axis) of the chart;
3. Interpolate the Q-value for your test result using the following step;:
a. From your test result value on the horizontal (“x”) axis of the chart, draw a vertical line up until it intersects the weighting curve line;
b. From this point of intersection, draw a horizontal line to the left hand side (the vertical or “y” axis) of the chart;
c. Where this horizontal line intersects the vertical (“y”) axis of the chart, read off the value. This is the Q-value for this test; it should be recorded in Column B on the WQI chart on the Water Quality Index page.
The Q-value for each test should then be multiplied by the weighting factor listed in the chart on the Water Quality Index page. Record the product of this calculation in Column D of the chart.
The water temperature of a river is very important for water quality. Many of the physical, biological, and chemical characteristics of a river are directly affected by temperature. For example, temperature influences:
1. the amount of oxygen that can be dissolved in water;
2. the rate of photosynthesis by algae and larger aquatic plants;
3. the metabolic rates of aquatic organisms;
4. the sensitivity of organisms to toxic wastes, parasites, and diseases.
Remember, cool water can hold more oxygen than warm water, because gases are more easily dissolved in cool water.
Human-Caused Changes in Temperature
One of the most serious ways that humans change the temperature of rivers and lakes is through thermal pollution. Thermal pollution is an increase in water temperature caused by adding relatively warm water to a body of water. Industries, such as nuclear power plants, may cause thermal pollution by discharging water used to cool machinery. Thermal pollution may also come from stormwater running off warmed urban surfaces, such as streets, sidewalks, and parking lots.
People also affect water temperature by cutting down trees that help shade the river, exposing the water to direct sunlight.
Soil erosion can also contribute to warmer water temperatures. Soil erosion can be caused by many types of activities, including the removal of streamside vegetation, overgrazing, poor farming practices, and construction. Soil erosion raises water temperatures because it increases the amount of suspended solids carried by the river, making the water cloudy (turbid). Cloudy water absorbs the sun's rays, causing water temperature to rise.
Changes in Aquatic Life
As water temperature rises, the rate of photosynthesis and plant growth also increases. More plants grow and die. As plants die, they are decomposed by bacteria that consume oxygen. Therefore, when the rate of photosynthesis is increased, the need for oxygen in the water (BOD) is also increased.
The metabolic rate of organisms also rises with increasing water temperatures, resulting in even greater oxygen demand. The life cycles of aquatic insects tend to speed up in warm water. Animals that feed on these insects can be negatively affected, particularly birds that depend on insects emerging at key periods during their migratory flights.
Most aquatic organisms have adapted to survive within a range of water temperatures, Some organisms prefer cooler water, such as trout, stonefly nymphs, while others thrive under warmer conditions, such as carp and dragonfly nymphs. As the temperature of a river increases, cool water species will be replaced by warm water organisms. Few organisms can tolerate extremes of heat or cold.
Temperature also affects aquatic life's sensitivity to toxic wastes, parasites, and disease. For example, thermal pollution may cause fish to become more vulnerable to disease, either due to the stress of rising water temperatures or the resulting decrease in dissolved oxygen.
Sampling Procedure
The temperature test measures the change in water temperature between two points, the test site and a site one mile upstream. By detecting significant temperature changes along a section of the river, we can begin to uncover the sources of thermal pollution.
Because the temperature test compares the difference in water temperature at two different stream sites, it is important to match as closely as possible the physical conditions at these sites - current speed, amount of sunlight reaching the water, and the depth of the stream.
To reduce errors, the same thermometer should be used at both sites. Rubber gloves should be worn if there is any chance that hands might come in contact with the water.
Temperature Testing Procedure
1. At the site where the other water quality tests are being performed, lower the thermometer four inches below the water surface.
2. Keep the thermometer in the water until a constant reading is attained (approximately two minutes).
3. Record your measurement in Celsius.
4. Repeat the test approximately one mile upstream as soon as possible.
5. Subtract the upstream temperature from the temperature downstream using the following equation: temp. downstream - temp. upstream = temp. change
6. Record the change in temperature.
After the test is completed and the results are recorded, the Water Quality Index (WQI) for the body of water can be computed. To formulate a WQI, you must first compute a Q- value for the results you obtained. The Q-values of all nine tests will be used together to determine the health of the river or lake. See Water Quality Index page. To compute the Q-value for the temperature test, follow these steps:
1. Find the weighting curve chart at the end of this page;
2. Locate your test result on the bottom (horizontal or “x” axis) of the chart;
3. Interpolate the Q-value for your test result using the following steps;
a. From your test result value on the horizontal (“x”) axis of the chart, draw a vertical line up until it intersects the weighting curve line;
b. From this point of intersection, draw a horizontal line to the left hand side (the vertical or “y” axis) of the chart;
c. Where this horizontal line intersects the vertical (“y”) axis of the chart, read off the value. This is the Q-value for this test; it should be recorded in Column B on the WQI chart on the Water Quality Index page.
The Q-value for each test should then be multiplied by the weighting factor listed in the chart on the Water Quality Index page. Record the product of this calculation in Column D of the chart.
Change in Temperature: 'C
Turbidity is a measure of the relative clarity of water: the greater the turbidity, the murkier the water. Turbidity increases as a result of suspended solids in the water that reduce the transmission of light. Suspended solids are varied, ranging from clay, silt, and plankton, to industrial wastes and sewage.
Sources of Turbidity
High turbidity may be caused by soil erosion, waste discharge, urban runoff, abundant bottom feeders (such as carp) that stir up bottom sediments, or algal growth. The presence of suspended solids may cause color changes in water, from nearly white to red-brown, or to green from algal blooms.
Changes in Aquatic Life
At higher levels of turbidity, water loses its ability to support a diversity of aquatic organisms. Waters become warmer as suspended particles absorb heat from sunlight, causing oxygen levels to fall (Remember, warm water holds less oxygen than cooler water). Photosynthesis decreases because less light penetrates the water, causing further drops in oxygen levels. The combination of warmer water, less light, and oxygen depletion makes it impossible for some forms of aquatic life to survive.
Suspended solids affect aquatic life in other ways. Suspended solids can clog fish gills, reduce growth rates, decrease resistance to disease, and prevent egg and larval development. Particles of silt, clay, and organic materials settle to the bottom, especially in slow-moving stretches of rivers. These settled particles can smother the eggs of fish and aquatic insects, as well as suffocate newly-hatched insect larvae. Material that settles into the spaces between rocks makes these microhabitats unsuitable for mayfly nymphs, stonefly nymphs, caddisfly larvae, and other aquatic insects living there.
Sampling Procedures
Turbidity can be measured using a simple device called a Secchi disk, or a more precise instrument known as a turbidimeter.
A Secchi disk is an 8" diameter (23 cm.) black and white disk attached by a chain or rope that is marked in foot increments. Because Secchi disk measurements are based upon the disk being lowered until it disappears, it cannot be used in rivers which are shallow or have low turbidity. In these cases the Secchi disk reading may need to be estimated as accurately as possible.
It may be difficult to use the Secchi disk in fast river currents because the current will push the disk downriver, preventing an accurate measurement. A weight may have to be added to the disk in this situation. A turbidimeter is an optical device that measures the scattering of light, and provides a relative measure of turbidity in nephelometer turbidity units (NTUs). Secchi disk measurements and turbidimeter results can be roughly equated.
Turbidimeters are relatively expensive, but are the most accurate method for measuring turbidity. If multiple schools are involved in a watershed monitoring program, then one turbidimeter might be purchased for the program. Samples from throughout the watershed could then be read on the one turbidimeter. It may also be possible to use a local college's turbidimeter.
Another option is to use an inexpensive turbidity test available from the LaMotte Company. Like the original Jackson Tube, this test involves viewing an object located at the end of a tube; in this case, the object is a black dot rather than a flame. As the turbidity of a sample increases, the dot becomes increasingly blurred. The turbidity of the sample is then compared with an identical amount of clear water to which a standardized turbidity reagent has been added.
Turbidity Testing Procedures: Secchi Disk
1. Lower the Secchi disk from a bridge, boat, or dock into the water until it disappears. It is important that the disk travels vertically through the water and is not "swung out" by the river current. Note the number of feet/inches on the chain or rope.
2. Drop the disk even further (until it disappears) and then raise it until you can see the disk again, Note the number of feet/inches on the chain.
3. Add the results of step I and step 2 and divide by two. This is your turbidity level using the Secchi disk.
The Relationship Among Feet, JTU'S, and NTU's
The Secchi disk measurement in feet has been roughly correlated with Jackson Turbidity Units (JTU's). These units were based upon a standard suspension of 1000 parts per million diatomaceous earth in water. By diluting this suspension, a series of standards was produced.
Jackson Turbidity Units (JTU's) are the application of these standards to the original device for measuring turbidity called the “Jackson tube.” The Jackson tube is a long glass tube suspended over a lit candle. A sample of water was slowly poured into the tube until the candle flame as viewed from above could no longer be seen. This device is no longer used because it is not sensitive to very low turbidities.
A turbidimeter measures turbidity as nephelometer turbidity units (NTU). Instruments such as the turbidimeter that measure the scattering of light are called nephelometers. Both NTU's and JTU s are interchangeable units. They differ only in that their name reflects the device used to measure turbidity.
Please note that the weighted curve chart in Calculating a WQI uses NTU's/JTU's. Because feet have been roughly correlated with JTU'S, the numerical value obtained from the weighted curve chart should be viewed cautiously when using a Secchi disk. The weighting factor for turbidity, however, is quite small (0.08) and does not affect the overall water quality index as heavily as most of the other water quality parameters.
After the test is completed and the results are recorded, the Water Quality Index (WQI) for the body of water can be computed. To formulate a WQI, you must first compute a Q-value for the results you obtained. The Q-values of all nine tests will be used together to determine the health of the river or lake. See Water Quality Index page. To compute the Q-value for the turbidity, follow these steps:
1. Find the weighting curve chart at the end of this page;
2. Locate your test result on the bottom (horizontal or “x” axis) of the chart;
3. Interpolate the Q-value for your test result using the following steps;
a. From your test result value on the horizontal (“x”) axis of the chart, draw a vertical line up until it intersects the weighting curve line;
b. From this point of intersection, draw a horizontal line to the left hand side (the vertical or “y” axis) of the chart;
c. Where this horizontal line intersects the vertical (“y”) axis of the chart, read off the value. This is the Q-value for this test; it should be recorded in Column B on the WQI chart on the Water Quality Index page.
The Q-value for each test should then be multiplied by the weighting factor listed in the chart on the Water Quality Index page. Record the product of this calculation in Column D of the chart.
Turbidity: NTU’s/JTU’s Note: If Turbidity > 100.00, Q=5.0
Dissolved oxygen (DO) is essential for the maintenance of healthy lakes and rivers. The presence of oxygen in water is a good sign. The lack of oxygen is a signal of severe pollution. Rivers range from high to very low levels of dissolved oxygen. Sometimes the level gets so low that there is little aquatic life.
Most aquatic plants and animals need oxygen to survive. Fish and some aquatic insects have gills to collect oxygen from the water. Some aquatic organisms, like pike and trout, require medium-to-high levels of dissolved oxygen to live. Other animals, like carp and catfish, flourish in waters of low dissolved oxygen. Waters of consistently high dissolved oxygen are usually considered healthy and stable ecosystems capable of supporting many different kinds of aquatic organisms.
Where Does the Oxygen Come From?
Much of the dissolved oxygen in water comes from the air. Oxygen can also be mixed into the water by waves on lakes or the tumbling of water on fast-moving rivers. Algae and rooted aquatic plants also deliver oxygen to water through photosynthesis.
In general, rooted aquatic plants are more abundant in lakes and slow-moving rivers. In bodies of water with lots of plants, there will a large daily fluctuation in dissolved oxygen. Dissolved oxygen levels rise from morning through the afternoon as a result of photosynthesis, reaching a peak in late afternoon. Photosynthesis stops at night, but plants and animals continue to respire and consume oxygen. As a result, dissolved oxygen levels fall to a low point just before dawn. Dissolved oxygen levels may dip below 4 mg/liter in such waters- the minimum amount needed to sustain warm water fish like bluegill, bass, and pike.
Physical Influences on Dissolved Oxygen
Water temperature and the volume of water moving down a river (discharge) affect dissolved oxygen levels. Gases, like oxygen, dissolve more easily in cooler water than in warmer water. In temperate areas, rivers respond to changes in air temperature by cooling or warming.
River discharge is related to the climate of an area. During dry periods, flow may be severely reduced, and air and water temperatures are often higher. Both of these factors tend to reduce dissolved oxygen levels. Wet weather or melting snows increase flow, with a resulting greater mixing of atmospheric oxygen.
Human-Caused Changes in Dissolved Oxygen
The main factor contributing to changes in dissolved oxygen levels is the build- up of organic wastes. Organic wastes consist of anything that was once part of a living plant or animal, including food, leaves, feces, etc. Organic waste can enter rivers in many ways, such as in sewage, urban and agricultural runoff, or in the discharge of food processing plants, meat packing houses, dairies, and other industrial sources.
A significant ingredient in urban and agricultural runoff are fertilizers that stimulate the growth of algae and other aquatic plants. (See the sections in this chapter on biochemical oxygen demand, nitrate, and total phosphate for more information.) As plants die, aerobic bacteria consume oxygen in the process of decomposition. Many kinds of bacteria also consume oxygen while decomposing sewage and other organic material in the river.
Changes in Aquatic Life
Depletions in dissolved oxygen can cause major shifts in the kinds of aquatic organisms found in water bodies. Species that cannot tolerate low levels of dissolved oxygen-mayfly nymphs, stonefly nymphs, caddisfly larvae, and beetle larvae-will be replaced by a few kinds of pollution-tolerant organisms, such as worms and fly larvae. Nuisance algae and anaerobic organisms (that live without oxygen) may also become abundant in waters with low levels of dissolved oxygen.
Calculating Percent Saturation
The percent saturation of water with dissolved oxygen at a given temperature is determined by pairing temperature of the water with the dissolved oxygen value, after first correcting your dissolved oxygen measurement for the effects of atmospheric pressure. This is done with the use of the correction table and the percent saturation chart.
Rivers that consistently have a dissolved oxygen value of 90 percent or higher are considered healthy, unless the waters are supersaturated due to cultural eutrophication. Rivers below 90 percent saturation may have large amounts of oxygen-demanding materials, i.e. organic wastes.
To calculate percent saturation, first correct your dissolved oxygen value (milligrams of oxygen per liter) for atmospheric pressure. Look at the correction chart. Using either your atmospheric pressure (as read from a barometer) or your local altitude (if a barometer is not available), read across to the right hand column to find the correction factor. Multiply your dissolved oxygen measurement by this factor to obtain a corrected value.
________________________________________
Correction Table for Dissolved Oxygen Measurements
Atmospheric Pressure (mmHg) Equivalent Altitude (ft.) Correction Factor
775 -540 1.02
760 0 1.00
745 542 .98
730 1094 .96
714 1688 .94
699 2274 .92
684 2864 .90
669 3466 .88
654 4082 .86
638 4756 .84
623 5403 .82
608 6065 .80
593 6744 .78
578 7440 .76
562 8204 .74
547 8939 .72
532 9694 .70
517 10,472 .68
Level of Oxygen Saturation Chart
Now look at the percent saturation chart. Draw a straight line between the water temperature at the test site and the corrected dissolved oxygen measurement, and read the saturation percentage at the intercept on the sloping scale.
Example:
Let's say that your dissolved oxygen value was 10 mg/L, the measured water temperature was 15'C, and the atmospheric pressure at the time of sampling was 608 mmHg. From the table in Figure 8, the correction factor is 80 percent, which multiplied by 1 0 mg/L gives a corrected dissolved oxygen value of 8 mg/L. Drawing a straight line between this value and 15’C gives a percent saturation of about 80 percent.
How might you interpret these results? At the relatively cool temperature of 15'C, one would expect a river to have a dissolved oxygen value higher than 80 percent. It would appear that something is using up oxygen in the water.
Sampling Procedures
Because DO levels vary so much according to time, weather, and temperature, this test should be run during the same period (week and time of day) if yearly comparisons are to be made. In rivers, there is usually adequate mixing of water from the surface to the river bottom. However, in impounded river reaches or in very large deep rivers there may be little mixing of the water. This could cause differences in DO measurements from the surface to the river bottom.
It is best to sample away from shore and below the water surface. In free- flowing rivers with good mixing, samples taken beneath the surface and in the current will probably be representative samples. In slow-moving river reaches and in impounded river areas with little mixing, it is very important to sample away from shore and to sample at various depths. Shore sampling will probably not provide a representative sample in these waters. Nor will a sample taken from only one depth, since aquatic vegetation produces oxygen near the surface, while decaying vegetation on the bottom consumes oxygen through the respiration of aerobic (oxygen-dependent) bacteria.
The extended rod sampler with an elastic strap or wire basket can be used to hold a dissolved oxygen bottle. If no bridge is available to sample from, or if the bridge carries too much traffic to be used safely, or is too high above the water, perhaps a boat may be found. If neither a bridge nor a boat are available, the best option is to extend the rod sampler from shore as far as possible and take a sample beneath the river surface. A dissolved oxygen sample can be obtained near shore without a sampling device, but keep in mind that it is probably not a representative sample. Remember that the dissolved oxygen test should be run immediately after sampling.
Warning:
Please wear protective gloves. If your skin comes into contact with any reagent, rinse this area liberally with water. First aid directions are included on the reagent containers. SAFETY GOGGLES SHOULD BE WORN WHILE SHAKING THE DISSOLVED OXYGEN BOTTLE
Dissolved Oxygen Testing Procedure
1. If you have a barometer, record the atmospheric pressure. Remove the cap and immerse the DO bottle beneath the river's surface. Use gloves to avoid contact with the river.
2. Allow the water to overflow for two to three minutes. (This will ensure the elimination of air bubbles.)
3. Make sure no air bubbles are present when you take the bottle from the river.
4. Add 8 drops of Manganous Sulfate Solution and 8 drops of Alkaline Potassium Iodide Azide.
5. Cap the bottle, making sure no air is trapped inside, and invert repeatedly to fully mix. Be very careful not to splash the chemical-laden water. Wash your hands if you contact this water. If oxygen is present in the sample, a brownish-orange precipitate will form (floc). The first two reagents "fix" the available oxygen.
6. Allow the sample to stand until the precipitate settles halfway. When the top half of the sample turns clear, shake again, and wait for the same changes.
7. Add 8 drops of Sulfuric Acid 1:1 Reagent. Cap and invert repeatedly until the reagent and the precipitate have dissolved. A clear yellow to brown-orange color will develop depending on the oxygen content of the sample.
Dissolved Oxygen Test Kit Items
Note: Following completion of step 7, contact between the water sample and the atmosphere will not affect the test result. Once the sample has been "fixed" in this manner, it is not necessary to perform the actual test procedure immediately. Several samples can be collected and 'fixed" in the field, and then carried back to a testing station or laboratory where the titration procedure is to be performed.
8. Fill the titration tube to the 20 ml line with the "fixed" sample and cap.
9. Fill the Direct Reading Titrator with Sodium Thiosulfate 0.025N Reagent. Insert the Titrator into the center hole of the titration tube cap. While gently swirling the tube, slowly press the plunger to titrate until the yellow-brown color is reduced to a very faint yellow.
Note: If the color of the fixed sample is already a very faint yellow, skip to step 10.
10. Remove the cap and Titrator. Be careful not to disturb the Titrator plunger, as the titration begun in step 8 will continue in step 11. Add 8 drops of Starch Indicator Solution. The sample should turn blue.
11. Replace the cap and Titrator. Continue titrating until the sample changes from blue to a colorless solution. Read the test result where the plunger tip meets the scale. Record as mg/L (ppm) dissolved oxygen.
Note: Each minor division on the Titrator scale equals 0.2 mg/L (0.2 ppm).
Note: If the plunger tip reaches the bottom line on the Titrator scale (10) before the endpoint color change occurs, refill the Titrator and continue the titration. When recording the test result, be sure to include the value of the original amount of titrant dispensed.
After the test is completed and the results are recorded, the Water Quality Index (WQI) for the body of water can be computed. To formulate a WQI, you must first compute a Q- value for the results you obtained. The Q-values of all nine tests will be used together to determine the health of the river or lake. See Water Quality Index page. To compute the Q-value for the dissolved oxygen test, follow these steps:
1. Find the weighting curve chart at the end of this page;
2. Locate your test result on the bottom (horizontal or “x” axis) of the char;
3. Interpolate the Q-value for your test result using the following steps;
a. From your test result value on the horizontal (“x”) axis of the chart, draw a vertical line up until it intersects the weighting curve line;
b. From this point of intersection, draw a horizontal line to the left hand side (the vertical or “y” axis) of the chart.
c. Where this horizontal line intersects the vertical (“y”) axis of the chart, read off the value. This is the Q-value for this test; it should be recorded in Column B on the WQI chart on the Water Quality Index page.
The Q-value for each test should then be multiplied by the weighting factor listed in the chart on the Water Quality Index page. Record the product of this calculation in Column D of the chart.
Nitrate: mg/L Note: If NO-3>100.0, Q=1.0
Fecal coliform bacteria are found in the feces of humans and other warm-blooded animals. These bacteria can enter rivers directly or from agricultural and storm runoff carrying wastes from birds and mammals, and from human sewage discharged into the water.
Fecal coliform by themselves are not dangerous (pathogenic) . Pathogenic organisms include bacteria, viruses, and parasites that cause diseases and illnesses. Fecal coliform bacteria naturally occur in the human digestive tract, and aid in the digestion of food. In infected individuals, pathogenic organisms are found along with fecal coliform bacteria.
If fecal coliform counts are high (over 200 colonies/100 ml of water sample) in the river, there is a greater chance that pathogenic organisms are also present. A person swimming in such waters has a greater chance of getting sick from swallowing disease-causing organisms, or from pathogens entering the body through cuts in the skin, the nose, mouth, or the ears. Diseases and illness such as typhoid fever, hepatitis, gastroenteritis, dysentery, and ear infections can be contracted in waters with high fecal coliform counts.
Pathogens are relatively scarce in water, making them difficult and time-consuming to monitor directly. Instead, fecal coliform levels are monitored, because of the correlation between fecal coliform counts and the probability of contracting a disease from the water.
Cities and suburbs sometimes contribute human wastes to local rivers through their sewer systems. A sewer system is a network of underground pipes that carry wastewater.
In a separate sewer system, sanitary wastes (from toilets, washers, and sinks) flow through sanitary sewers and are treated at the wastewater treatment plant. Storm sewers carry rain and snow melt from streets, and discharge untreated water directly into rivers. Heavy rains and melting snow wash bird and pet wastes from sidewalks and streets and may "flush out" fecal coliform from illegal sanitary sewer connections into the storm sewers.
In a combined sewer system, sanitary wastes and storm runoff are treated at a wastewater treatment plant. After a heavy rain, untreated or inadequately treated waste may be diverted into the river to avoid flooding the wastewater treatment plant. To avoid this problem, some cities have built retention basins to hold excess waste water and prevent untreated wastes from being discharged into rivers. Without retention basins, heavy rain conditions can result in high fecal coliform counts downstream from sewage discharge points. That is why it is important to note weather conditions on the days before a fecal coliform measurement.
Fecal and total coliform standards for water used for drinking, recreation, and treated sewage
Sampling Procedures
1. Remove the stopper or cap just before sampling and avoid touching the inside of the cap.
2. If sampling by hand, use gloves and hold the bottle near its base. Plunge it (opening downward) below the water surface, then turn the bottle underwater into the current and away from you.
3. Avoid sampling the water surface because the surface film often contains greater numbers of fecal coliform bacteria than is representative of the river.
4. Also, avoid sampling the sediments for the same reason, unless this is intended. The same general sampling procedures apply when using the extended rod sampler.
5. When collecting samples, leave some space in the sample container (an inch or so) to allow mixing of the sample before-pipetting.
It is a good idea to collect several samples from any single location on the river to minimize the variability that comes with sampling for bacteria. If possible, sterilization should occur between sampling sites. Ideally, all samples should be tested within one hour of collection. If this is not possible, the sample bottles should be placed in ice and tested within six hour
Testing Procedure (the Quick and Easy way)
Detection of Water Born Coliform and Fecal Coliforms with Coliscan Easy Gel
This new process for coliform and fecal coliform testing does not require an incubator or water bath.
1. Use a sterile calibrated dropper to collect a 1 ml water sample and deposit the sample into bottle containing liquid coliscan medium (this procedure may be done in the field and the coliscan-water mix can be kept on ice until returning to the lab).
2. Pour the coliscan water mix into a pre-treated petri dish and swirl to cover entire bottom of petri dish.
3. Place the petri dish containing the coliscan-water mix in a warm place and incubate for 24-48 hours (this is best done in a place such as an incubator which holds the temperature in a range of 850-950' F).
4. Count the red colonies in the petri dish as coliforms and the purple colonies as fecal coliforms (E. coli). (White or blue-green colonies should be noted, but they are not classified as coliforms or fecal coliforms).
Gels can be attained through:
Traditional Fecal Coliform Testing Procedure
1. First, sanitize the forceps by dipping forceps in alcohol, then burning alcohol off with a flame (an alcohol lamp works well). Do not place the hot forceps back into the alcohol.
2. Using the sanitized forceps, place an absorbent pad in the sterile petri dish. Be careful not to touch the pad with your fingers.
3. Unscrew the neck of the broth plastic tube (ampoule) or use an ampoule breaker if needed, and drain the broth onto the pad (The broth is liquid food for fecal coliform bacteria). Put the top on the petri dish and set aside.
Fecal Coliform Test Equipment Items
4. Sanitize forceps with alcohol and flame again,
5. Unscrew the top half of the filtration system and place a sterile filter paper on top of the filtration system's membrane with forceps; grid side up. Be sure the filter lies completely flat with no wrinkles.
6. Screw on the top half of the filtration system to the bottom half.
7. Before taking a sample, use a pipette to rinse the filtration system with a small amount of distilled water. Add the water through the hole in the top of the system. (There should be two or three rubber stoppers on top of the filtration system, and one hole without a stopper. See Figure 3.8).
8. Determine the desired volume of water (in ml) to be tested based upon the water source (See chart below for suggested sample volume sizes). Place the pointed end of the pipette into the water to be sampled and lower into the water until the desired sample size, as shown by volume markings on the side of pipette, has been drawn into the pipette. A rubber bulb attached to the top of the pipette may be required to obtain the desired volume. When there are high numbers of fecal coliform, a proper sample should not exceed 60 colonies on the petri plate. The higher range affects the colony sheen or color development resulting in errors in making a proper count.
Adapted from Standard Methods for the Examination of Water and Wastewater.
9. Place the end of the pipette into the open hole on top of the filtration system, and release the water sample into the funnel.
10. With the filtration system level, use the suction pump and draw all of the sample and distilled water through the filter while swirling so that the number of bacteria adhering to the upper filtration system is reduced. (Warning: be careful when pushing the plunger back into the syringe; you want to avoid pushing air back into the filtration unit and forcing the filter off the membrane.) Draw the water through the filter until it appears dry.
11. Unscrew the top half of the funnel, and carefully remove the filter with the sanitized forceps.
If you do not have a water bath, one might be available at a local university, community sewage treatment plant, or local laboratory. If no water bath is available in your community you might try a hot air incubator if it holds temperature. Recognizing that a water bath is relatively expensive, multiple schools within a watershed involved in a water monitoring program might want to purchase one water bath for the entire program.
12. Open the top of the petri dish, and slide the filter across and into the dish, with the grid side up. Petri dishes should be incubated within 30 minutes of filtering the sample; this will ensure heat shock of any non-fecal coliform organisms. Be sure to record the date, site, and volume of sample on the frosted part of the petri dish.
13. Enclose the petri dish in a waterproof bag (to avoid leakage) and then put into the water bath. Dishes may also be sealed with waterproof tape (freezer tape) to avoid leakage. Incubate for 24 hours (+/- 2 hours) at 44.5'C. (Temperature must be maintained within a range of ±0.25'C to 44.5'C.) Petri dishes should be inverted during incubation to avoid condensation. Please wash your hands after this test.
14. After incubation, carefully count the bacterial colonies on the filter, using a magnifying glass (10 x) or unaided eye. You might want several people to verify the bacterial count. Each bluish spot is counted as one fecal coliform colony. Cream or gray-colored colonies are nonfecal coliform. Fecal coliform colonies should be examined within 20 minutes to avoid color changes that occur with time. Some common fecal coliform culture problems can be seen below.
15. It is important to report the highest fecal coliform value rather than an average value.
When the experiment is done correctly there should be
20-60Coliform colonies evenly dispersed
Growth around sealing edge means
unclean filter holder or poor seal
A dry spot without growth shows improper seating
of filter
Sample size too large
Uneven distribution os from not swirling the
sample while filtering or not adding distilled
water to sample
A word about sterilization ...
It is essential to sterilize sample bottles, pipettes, and filtration system before sampling. Sterilization can be accomplished by using an autoclave; 121' C for 15 minutes. If an autoclave is not available, the home economics department may have a pressure cooker that they might be willing to lend to the water quality monitoring program. If a pressure cooker is used, please be sure that it has a working pressure gauge. The gauge may be checked with the county cooperative extension service. The pressure cooker should be ran at 15 psi. to properly sterilize sample bottles, pipettes and filtration system.
If these two pieces of equipment are unavailable, an oven can be used. The oven must attain a temperature of 170' (±10 ‘C) for not less than 60 minutes. The plastic filtration system cannot, however, be placed in a dry oven because the system will melt. The same holds true for plastic sampling bottles. The filtration system can, however, be placed in boiling water for 5 minutes to sanitize it. Petri(I dishes, culture media, absorbent pads, and filters are sterilized and packaged. Equipment that has been inadequately sterilized may interfere with fecal coliform growth.
... and sampling design
If the purpose of sampling is to determine fecal coliform levels at a river reach, then samples should be taken beneath the water surface and in the current (if there is one). If the purpose of sampling is to confirm suspected sources of fecal coliform contamination, then samples should be taken just downriver from the source (like the mouth of a storm drain), and other samples should be taken upriver from the source for comparison.
There is also wet-weather sampling and dry-weather sampling. Wet-weather sampling involves sampling during and just after a rainstorm, often at timed intervals. It is done if fecal coliform contamination is suspected from storm drains carrying urban storm water runoff. Wet-weather samples can then be compared to samples taken during a period of dry weather (dry-weather samples). The bottles used for the dissolved oxygen test might also be used for the fecal coliform test.
Try to avoid sampling stagnant areas of rivers. The extended rod sampler is an effective device for obtaining a sample in the current. If sampling rivers in which little current exists, push the sample bottle underwater away from your body, thereby creating a current.
After the test is completed and the results are recorded, the Water Quality Index (WQI) for the body of water can be computed. To formulate a WQI, you must first compute a Q-value for the results you obtained. The Q-values of all nine tests will be used together to determine the health of the river or lake. See Water Quality Index page. To compute the Q-value for the fecal coliform test, follow these steps:
1. Find the weighting curve chart at the end of this page;
2. Locate your test result on the bottom (horizontal or “x” axis) of the chart;
3. Interpolate the Q-value for your test result using the following steps;
a. From your test result value on the horizontal (“x”) axis of the chart, draw a vertical line up until it intersects the weighting curve line;
b. From this point of intersection, draw a horizontal line to the left hand side (the vertical or “y” axis) of the chart;
c. Where this horizontal line intersects the vertical (“y”) axis of the chart, read off the value. This is the Q-value for this test; it should be recorded in Column B on the WQI chart on the Water Quality Index page.
The Q-value for each test should then be multiplied by the weighting factor listed in the chart on the Water Quality Index page. Record the product of this calculation in Column D of the chart.
Fecal coliform (FC): colonies/100ml Note: if FC>100,000, Q=2.0
If you remember from Lesson 1, fish are the favorite food of Bald Eagles. Since fish live in the water and can be affected by what is in the water, it is important to know if a lake or river is “healthy.”
In an attempt to devise a system to compare rivers and lakes in various parts of the country, the National Sanitation Foundation (NSF) created and designed a standard index called the Water Quality Index (WQI). The WQI is one of the most widely used of all existing water quality procedures. The overall results of nine separate tests can be used to determine if a particular stretch of river is healthy.
The WQI consists of nine tests:
Dissolved Oxygen
Fecal Coliform
pH
BOD (Biochemical Oxygen Demand)
Temperature
Total Phosphate
Nitrates
Turbidity
Total Solids
After completing the nine tests, the results are recorded and transferred to a weighting curve chart where a numerical value is obtained. For each test, the numerical value or Q-value is multiplied by a “weighting factor.” (See individual tests for more information on Q-value.) For example, dissolved oxygen has a relatively high weighting factor (.17); because it is more significant in determining water quality than the other tests. The nine resulting values are then added to arrive at an overall water quality index (WQI). The highest score a body of water can receive is 100.
Water Quality Index Ranges
90-100 Excellent
70-90 Good
50-70 Medium
25-50 Bad
0-25 Very Bad
If you are unable to run all nine tests and you want to estimate the “Overall Water Quality Index,” students could determine the Q value of missing data by examining known data. For example , if the “fecal coliform” test were not run, the results or Q-value of three related tests (dissolved oxygen, nitrates, total phosphate) could be averaged to get a score for that test. Using the table below as an example, the average Q-value of the three tests is 62 - or a fecal coliform count of 20 colonies per 100 ml of water.
So is this water excellent, good, medium, bad or very bad?
________________________________________
the following table to enter your own data.
Note on Sampling
It is important to exercise care in the way samples are collected for analysis. A collected sample should be representative of the river or lake being tested. Near-shore samples may not be representative of the river at that location. If possible, water samples should be collected from a bridge spanning the river, from a boat, or off the end of a dock. A rule of thumb for sampling is to sample midway across the river and below the surface.
A simple device can be constructed from a series of metal rods that can be extended and rubber tubing attached that holds the sample bottle. This device might be extended out from shore if no bridges are available and particularly if the river is narrow or shallow. A golf ball retriever can also be adapted very easily for this purpose.
INTERPRETING WATER ANALYSIS
TEST RESULTS
1. Alkalinity: This is the sum of components (mainly bicarbonate, carbonate, and hydroxide) in the water that tend to elevate the pH of the water above 4.5. These factors are characteristic of the source of water and the natural processes taking place at any given time. Alkalinity represents the buffering capacity of water and its ability to resist a change in pH. Alken-Murray recommends alkalinity above 75 mg/L to offset acid produced by bacteria nitrifying ammonia.
The acceptable range for most finfish is 20-200 mg/1 (ppm).
CHEMetrics kits recommended K-9810: 10 - 100 ppm & K-9815: 50 - 100 ppm
2. Ammonia: Ammonia nitrogen (N) is present in variable concentrations in many surface and ground water supplies. A product of microbiological activity, ammonia when found in natural water is regarded as indicative of sanitary pollution.
Ammonia is rapidly oxidized by certain bacteria, in natural water systems, to nitrite and nitrate--a process that requires the presence of dissolved oxygen. Ammonia, being a source of nitrogen is also a nutrient for algae and other forms of plant life and thus contribute to overloading of natural systems and cause pollution.
In fish, ammonia represents the end-product of protein metabolism and what is important is whether it is present in the un-ionized form as free ammonia, NH3, which is toxic to fish (both freshwater and marine) at >0.03 mg/L (ppm), or in the ionized form, NH4+, in which it is innocuous. The relative concentration of each is pH and temperature dependent. The higher the pH, the more of the NH3 will be present. Ammonia can block oxygen transfer in the gills of fish, thereby causing immediate and long term gill damage. Fish suffering from ammonia poisoning will appear sluggish and come to the surface, as if gasping for air. In marine environments, the safe level of NH4+ is between 0.02 and 0.4.
The USEPA recommends a limit of 0.02 ppm as NH3 in freshwater or marine environments. Total ammonia levels, at this limit, can range from 160 ppm at pH 6 and temperature of 5 degrees C to 0.06 ppm at pH 9 and temperature of 25 degrees C.
If large quantities of fish are suddenly added to the water body (such as during stocking), the ammonia level can spike because the natural bacteria that degrade ammonia are slow to reporduce (having a 14 day cycle), so it is best to add a seeding quantity of Alken Clear-Flo 1100 or Alken Clear-Flo 1200 at the same time you add your new fish, to avoid this problem.
CHEMetrics kits recommended: K-1510: 0-1 ppm & 1 - 10 ppm
3. Carbon Dioxide: Carbon dioxide (CO2) is present in water supplies in the form of a dissolved gas. Typically, surface waters contain less than 10 ppm free carbon dioxide while ground waters may have much higher concentrations. Dissolved in water, CO2 forms carbonic acid which lowers pH.
Aquatic plant life, from phytoplankton to large rooted plants, depends upon carbon dioxide and bicarbonates in water for growth. Of significance for fish is the fact that when the oxygen concentration falls (e.g. through the degradation of organic wastes), the carbon dioxide concentration rises. This increase in carbon dioxide makes it more difficult for fish to use the limited amount of oxygen present. To take in fresh oxygen, fish must first discharge the CO2 in their blood stream, a process which is slowed down considerably when there are high concentrations of CO2 in the water itself. Unfortunately the CHEMetrics test kits do not measure below 10 mg/L, so if you get a reading on this test, you know your water body is in trouble.
The acceptable range of carbon dioxide for most finfish is <2.0 mg/L (ppm).
CHEMetrics kit recommended: K-1910: 10 - 100 ppm
4. Chloride: Chloride is one of the major anions to be found in water and sewage. Its presence in large amounts may be due to natural processes such as the passage of water through natural salt formations in the earth or it may be an indication of pollution from sea water intrusion, industrial or domestic waste or deicing operations. Potable water should not exceed 250 mg/L of chloride. When calcium or magnesium is the cation, up to 1000 mg/L can be tolerated without a salty taste to the water.
CHEMetrics kit recommended: K-2002: 2 - 20 ppm
5. Dissolved Oxygen: Vital to aquatic life, oxygen enters the water by diffusion from the atmosphere or through plant photosynthesis. Actual solubility is directly proportional to the partial pressure in the gas phase, to salt concentration and temperature. The dissolved oxygen level in water is constantly changing and represents a balance between respiration and decomposition that deplete oxygen and photosynthetic activity that increases it. Organic waste may overload a natural system causing a serious depletion of the oxygen supply in the water that in turn leads to fish kills. Likewise, eutrophic waters, that is those rich in nutrients, achieve the same result through causing massive proliferation of algae (algal blooms) whose eventual decomposition uses up the available dissolved oxygen.
Recommended minimum dissolved oxygen levels for fresh water fish are as follows:
warm water fish .......... 5.0 mg/L (ppm)
cold water fish .......... 6.0 mg/L (ppm)
Koi........... 8.0 mg/L (ppm)
Marine fish......5.0 mg/L (ppm)
Marine Shrimp....> 5.0 mg/L (ppm), close to saturation*
* Reference for shrimp is page 124 Marine Shrimp Culture: Principles and Practices edited by Arlo W. Fast & L.James Lester
CHEMetrics kit recommended: K-7510: 0 - 10 ppm & K-7512: 1 - 12 ppm. A dissolved oxygen meter can be used, if calibrated according to manufacturer's instructions. Self-stirring DO probes are easier to work with, if this option is available, but the test kits are often preferred by consumers treating a single pond.
6. Nitrites: Nitrites occur in water as an intermediate product in the biological breakdown of organic nitrogen, being produced either through the oxidation of ammonia or the reduction of nitrate. The presence of large quantities of nitrites is indicative of waste water pollution. The level considered ideal for marine fish is between 0.01 and 0.04 ppm.
Levels exceeding 0.55 mg/L (ppm) nitrite-nitrogen can cause 'brown-blood' disease in finfish.
CHEMetrics kit recommended: K-7002: 0 - 0.4 ppm & 0.4 ppm - 4 ppm
7. Nitrates: Nitrates occur in water as the end product in the biological breakdown of organic nitrogen, being produced through the oxidation of ammonia . Although not particularly toxic to fish, excess nitrates in the water is often used as an indicator of poor water quality. Under anaerobic conditions, such as in the sludge or soil at the botton of a pond, lake or aquarium, denitrification can be used to convert nitrate back to nitrite and from there to nitrogen gas, removing total nitrogen from the aquatic system. In marine environments, levels of 0.1 to 0.2 are considered ideal.
Levels exceeding 50 mg/L (ppm) nitrate-nitrogen are considered unhealthy for lakes.
Levels from 10 mg/l to 40 mg/l indicate poor water in aquariums, depending on the species being raised.
CHEMetrics kit recommenended: K-6902: 0 - 1 ppm & 1 - 5 ppm
For larger, seriously polluted ponds, lakes, etc., also use: K-6902D: 0 - 25 ppm & 25 - 125 ppm
8. pH: By definition, pH is the negative logarithm of the hydrogen ion concentration. It is in effect an "Index" of the amount of hydrogen ion present in a substance and is used to categorize the latter as acid, neutral, or alkaline (basic).
Most natural waters will have pH values from pH 5.0 to pH 8.5 (compare the range in which Alken Clear-Flo products work best: 6.0-8.5). Fresh rain water may have a pH of 5.5 to 6.0. The carbon dioxide produced by respiration of animals and plants in water have the effect of lowering pH. Carbon dioxide and bicarbonate removed from the water by the photosynthetic processes of aquatic plants raises pH. The same processes alter the dissolved oxygen content; oxygen drops during respiration and decomposition; it rises with photosynthetic activity. A pH that is too high is undesirable because free ammonia increases with rising pH.
The acceptable pH range for most finfish and shellfish species is 6.8-8.5
9. Total Hardness: The Total Hardness of a water represents primarily the total concentration of Calcium and Magnesium ions expressed as calcium carbonate. Hardness may range from zero to hundred of parts per million, depending on the origin of the water or the treatment to which the water has been subjected.
Waters containing hardness concentrations of up to 60mg/L (ppm) are referred to as "soft", those containing 120-180 mg/L (ppm) as "hard".
Recommended level: >130 mg/L (ppm)
CHEMetrics kit recommended: K-4502: 2 - 20 ppm & K-452: 20 - 200 ppm
10. Density: The amount of crowding each species of finfish and shellfish will tolerate varies between species. For the majority of finfish, the limit is 0.2 to 0.5 lbs of fish per inch of body length per cubic foot of rearing space. When the tolerable limit is exceeded, fish will exhibit signs of stress including darkening of body color, "clubbing" of gills, fin nipping or loss of tissue between the fin rays and reduced immunity to disease. Shrimp and prawns will also become more susceptible to disease when over-crowded.
Revised 8/25/2006
Interpreting Tests - part 1
Interpreting Tests - part 2
Interpreting Tests - part 3
In addition to your standard tests, there are circumstances which suggest that additional tests may be required before Alken Clear-Flo® can be prescribed.
These include:
1. Chlorine: Because of its strong oxidizing properties, chlorine acts as a BIOCIDE. The test for this should read "0" (zero), before Clear-Flo® is added. If this is a problem in your natural waterbody, someone is likely backwashing a swimming pool into your influent water or else there is an industrial or municipal effluent in your influent water. If the problem is a swimming pool nearby, have a talk with your neighbor and encourage them to dump elsewhere. If you cannot locate the source of this problem, contact Ken at Alken-Murray to prescribe a chemical de-chlorination solution for you. Fish, plants, algae and bacteria can all be killed by Chlorine.
CHEMetrics kit recommended: K-2505: 0 - 1 ppm & 1 - 5 ppm
2. Copper (total soluble): Copper sulfate is often added to water to control algae. This is toxic to both fish AND bacteria. DO NOT APPLY Alken Clear-Flo® when the copper test measures levels above 0.5 ppm (mg/l). Lethal concentrations of copper for marine organisms is 5.8 to 600 ppm, depending on species. Copper is toxic to Mysid shrimp at 77 ppm.
CHEMetrics kit recommended: K-3510: 0 - 1 ppm & 1 - 10 ppm
3. Detergents: Where detergents (anionic surfactants) are used to clean machinery, animals, and the household, the runoff may be contaminated. The Clear-Flo® 1200 will work to eliminate this contaminant when its concentration is less than 1 mg/L. Alken Clear-Flo® 7004 should be used to treat detergents greater than 1 mg/L. Some surfactants can be lethal in quantities as small as 10 to 12 mg/L (Triton-X114), so this is an important parameter if you suspect runoff from animal washing or other industrial effluent. The U.S. drinking water standard prohibits levels above 0.5 mg/L.
CHEMetrics kit recommended: K-9400: 0 - 3 ppm
4. Iron: Concentrations above 1 mg/L will impart a foul taste to the water. High concentrations can indicate runoff from mining operations or industrial effluent and indicate the need for further investigation before prescribing a treatment regimen. The US drinking water standard prohibits levels above 0.3 mg/L.
CHEMetrics kit recommened: K-6010: 0 - 1 ppm & 1 - 10 ppm
5. Lead: Lead is a poison whose effects are cumulative. Drinking water should not exceed 20 ppb. When groundwater contains a higher level, it may indicate contamination from the discharges of smelting or mining operations, or leachate from municipal sewage sludge fertilizer. Lead is toxic to freshwater species at 1.3 to 8.7 ppm, while marine species are more tolerant. The LC50 of lead for diatoms is 7940 ug/L. (Test needs to be performed by a suitable independent laboratory)
6. Mercury. Mercury is a common trace metal used in industry as a biocide. Acutely toxic to marine organisms in the range of 3.5 to 1678 ppm. Organomercuric compounds may be toxic to marine organisms in the range of 0.1 to 2.0 ppm. Alken-Murray's current formulas cannot withstand high levels of mercury, so alternative treatment options must be considered to decrease the level of mercury.(Test needs to be performed by a suitable independent laboratory)
7. Tributyl Tin. This substance has been declared, by the California Department of Fish and Game, to be "the most toxic substance ever released in the marine environment." This substance, which can be toxic in concentrations as low as 50 parts per trillion in water, is found in marine paints and antifouling coatings. Fortunately, Tributyl tin appears to be less bioavailable in sediment than it is in seawater, so higher levels may have less effect on benthic biota (bottom dwelling creatures) than might be expected, were the substance suspended in water. If you suspect this substance, obtain testing from an environmentally certified laboratory. We are not aware of any test kits for this substance. (sometimes mispelled as tributylin tin)
8. Sulfite: Sulfite is not normally found in natural waters. Its presence, therefore, usually indicates contamination from pulp and paper industrial effluent, or food canning (used as a preservative). An excess of sulfite can lower the pH and render the water corrosive.
CHEMetrics kits recommended: K-9602: 2 - 20 ppm
For seriously polluted water, you may also need kit K-9610: 10 - 100 ppm
9. Phosphate: High phosphate concentrations in surface waters may indicate fertilizer runoff, domestic waste discharge, or the presence of industrial effluents or detergents. If high phosphate levels persist, algae and other aquatic life will flourish, eventually decreasing the level of dissolved oxygen due to the accelerated decay of organic matter. Algae blooms are encouraged by levels of phosphate greater than 25 micrograms/L. Obtain tests in the 0 to 25 ppm and 25 to 200 ppm ranges. To combat waste accumulation, in the presence of high phosphate levels, you must double the initial dose of Alken Clear-Flo® normally prescribed for the size of the pond/lake/waste treatment plant.
Phosphorous Discharge Standards
1) Total Phosphorous for discharge < 100 micrograms/L
2) Where stream enters lake < 50 micrograms/L
3) Discharge into a lake < 25 micrograms/L
4) Algae blooms are encouraged by levels of phosphate > 25 micrograms/L
5) Phosphate phosphorous - > 100 micrograms/L may interfere with coagulation process in water treatment plant
CHEMetrics kit recommended: K-8510: 0 - 1 ppm & 1 - 10 ppm & K-8510D: 0 - 25 ppm & 25 - 250 ppm
10. Phenol. Phenol is usually found in a waterbody if pine cleaners and phenolic sanitizers are used and then washed into the drain system. If water has more than 1 ppm, add Alken Clear-Flo® 7002 to your Clear-Flo 1000 line prescription.
CHEMetrics kit recommended: K-8012: 0 - 1 ppm & 1 - 12 ppm
11. Hydrocarbons. Although most people know that petroleum spills are toxic to aquatic life, they are often unaware that rinsing used motor oil into the storm sewer or pond is also harmful. Benzene, Toluene, Xylene and Benz(a)Pyrene should not exceed 0.1 ppm. Smaller amounts can be handled by Clear-Flo formulas, but amounts exceeding 0.1 ppm should be treated with Clear-Flo 1006. Botryococcus braunii, a chlorophyte order of Chlorococcales algae produces C34 hydrocarbons with characteristics similar to crude petroleum. When it blooms, this algae appears as a slimy bright green scum on the surface of the water. B. braunii grows especially well in the presence of high nitrates., and will test positive on a hydrocarbon test when present. Clear-Flo 1006 should be prescribed to clean the water, eliminating both the food for this algae and its exudate.
(Kit for this is more expensive than to have TPH tested by an independent lab, so we only recommend CHEMetrics K-9310, along with equipment, for distributors to monitor treatment of soil for their clients.)
12. Cyanide. Cyanide is used in many chemical and refining processes. Effluent from electroplating and metal cleaning operations, coke ovens, steel manufacturing, etc. can end up in lakes and ponds if the factory is not careful. Levels above 0.01 ppm are unsafe for marine species. . If the waterbody does contain fish, you can apply Alken Clear-Flo 1015, but request that Yucca schidigera be omitted, to allow application of higher dosages, with safety. For wmunicpal or industrial astewater with cyande problems, you can apply Alken Clear-Flo 7015, which is currently available or ask Alken-Murray to augment whatever bacteral product has been selected, to remediate other pollutants in your system, with a serious percentage of Alken-Murray's cyanide-degrading Bacillus megaterium, AMC 300. Fortunately, B.megaterium AMC 300 has demonstrated remarkable compatibility with a wide assortment of strains in the Alken-Murray microbial collection, but any new combinations should be verified with Valerie Anne Edwards.
A chemical solution for cyanide in wastewater that does not also contain high levels of ammonia is alkaline chlorination to safely remove cyanide, but if ammonia levels are high, you could end up with undesirable levels of chloramines.
CHEMetrics kit recommended: K3810: 0 - 0.1 & 0.1 to 1.0
13. COD. Chemical Oxygen Demand measures organic and inorganic content as indicators of the amount of dissolved oxygen that will be removed from the water column or sediment due to bacterial and/or chemical activity. Normal COD in a pond should be less than 10 mg/L. A COD of 60 mg/L in a natural pond or lake or aquaculture pond or tank is in emergency need of treatment.
CHEMetrics kit recommended to distributors only, as equipment is needed too:K-7351(0 - 150 ppm), K-7361 (0 - 1500 ppm), & K-7371 (0 - 15000 ppm) plus Hach COD Reactor model 45600, Lab-Guard or Hach Safety Shield, Hach DR-890 datalogging colorimeter and Eppendorf Electronic pipettor (100 l - 5 ml).
14. BOD. Biological Oxygen Demand measures the amount of oxygen utilized by organisms in the biochemical oxidation of organic matter in a wastewater sample in a specified time (usually 5 days), and at a specified temperature. BOD measurements are used as a measure of the organic strength of the water. Although it is not identical to COD, the speed with which one can obtain COD test results, often dictates that this test is used for prescription purposes. Typical natural water has a BOD from 0.8 to 5 mg/L. Anything above 6 mg/L needs to be treated as it will rob the water of needed oxygen for the fish.
Testing for BOD should be performed by an outside lab unless distributor has appropriate equipment. The BOD test performed independently is fairly inexpensive for an individual pond owner.
15. Pesticides. Although the USA banned the use of DDT since the early 1970's, nondegraded DDT can still be found in water, released by erosion and storm runoff. Levels as low as 14 ppm in the water are acutely toxic to marine organisms. Chlordane is acutely toxic between 2.4 and 260 ppm. Heptachlor epoxide is acutely toxic at 0.04 ppm. Endrin is acutely toxic from 0.037 to 1.2 ppb. Dieldrin is toxic above 0.1. Alken-Murray's formulas can withstand and degrade small amounts of these substances, but a large scale contamination may require alternative treatment options. Independent laboratory tests are required if you suspect pollution from particular pesticides.
16. FOG, aka Fats, Oils, and Grease (from natural plants, fish and animal feed etc) can cause stress to aquatic animals if the level is above 0.1 mg/L. Sudden die-offs will occur if this level reaches 85 - 100 mg/L. Most Alken Clear-Flo 1000 line aquatic products contain some degraders of fats and greases, but if the level exceeds 6 mg/L, you should add Clear-Flo 1003 to your regimin of pond water treatment.
Independent laboratory tests are recommended for this only if you suspect this to be high in your pond or lake, such as from kitchen waste runoff (illegal in the USA), fatty diet fed to cultured fish showing an oily layer at the top of the water.
17. Silicate, often contributes to pond water turbidity and helps diatoms and algae to proliferate. Higher levels of microbial assistance are needed when silicate levels are high (up to 100 mg/L has been found). Adding sand to a formula, adds silica, which can feed algae. Ideal levels to discourage algae should be low, < 15 mg/L.
CHEMetrics kit recommended: K-9010: 0 - 1 ppm & 1 - 10 ppm & K-9011: 0 - 0.2 ppm
When the waterbody contains a variety of toxins, a custom blended formula will be created, taking into consideration the levels of the each contaminant.
Interpreting Tests - part 1
Interpreting Tests - part 2
Interpreting Tests - part 3
We have been asked for addition toxicity information on other compounds and have given them below. If some industry is suspected to be dumping contaminated effluent, we may ask for these elements to be tested, but this is rare.
These include:
1. Selenium: No specific toxicity data is available, but the USEPA 1986 has set 54 - 410 ppb (parts per billion) as an action level for this compound in marine environments. This element is necessary in small amounts in feeds.
If you suspect a large contamination, have an independent laboratory test this parameter for you.
2. Chromium: Chromium is toxic to marine organisms at 2000 to 105,000 ppm. The most toxic form, hexavalent chromate, is produced in pickling and plating operations, anodizing aluminum, leather tanning, manufacturing of paints, dyes and explosives. Also used to inhibit corrosion in open and closed system cooling towers. After PG&E lost a lawsuit over hexavalent chromium discharged to drinking water of the plant's neighbors, causing major health problems and a movie, named Erin Brockovich became a huge hit, most manufacturers of chemical water treatment for cooling towers can easily convince their clients to use other corrosion inhibitors with less hazardous environmental consequences attendant to accidental release from holding lagoons, so hopefully we will see less hexavalent chromium in ground water, reservoirs and recreational ponds and lakes.
I recommend CHEMetrics kits K2810B (measures 0 to 120 mg/L and 120 to 1200 mg/L) and K2810C (measures 0 to 1200 mg/L and 1200 to 12, 000 mg/L), but you can also purchase K2810D to measure 0 to 30 mg/L and 30 to 300 mg/L and K2810A to measure 0 to 60 mg/L and 60 to 600 mg/L, if you want to test the entire range possible with visual test kits, using the Diphenyl Carbazine method, APHA Standard Methods for Analysis of Water and Wastewater, method 3500-Cr-D (approved in 1995) Alternatively, you can ask an accredited USEPA laboratory to perform this test for you, especially valuable if you intend to sue the company discharging hexavalent chromium to a source that could end up in your lake, pond or reservoir.
3. Nickel: Nickel is toxic to marine organisms at 141 ppm. Get an EPA lab to test for this, if you suspect it to be causing fish deaths.
4. Zinc: Zinc causes acute marine toxicity at 192 to 320,000 ppm, depending on the species and is chronically toxic at levels of 120 ppm. The average acceptable level of zinc in potable water is 1 mg/L.
Although CHEMetrics offers test kits that measure up to 6 mg/L, to test for serious contamination, send sample to an accredited USEPA laboratory that tests water and wastewater.
5. Cadmium: Cadmium is acutely toxic to freshwater species at 10 ppb - 1 ppm. Cadmium is acutely toxic to marine species at 320 ppb to 15.5 ppm. If suspected, send a water sample to a USEPA accredited lab that tests water and wastewater.
6. Manganese: Manganese is required by aquatic species and no toxicity data is available. Surface and ground water rarely contain more than 1 ppm of manganese. Acceptable levels in potable water is less than 0.05 mg/L.
7. Inorganic Arsenic: Arsenic is toxic to marine organisms at the level of 2000 mg/L. If this is suspected, send sample to an accredited USEPA laboratory, testing water and wastewater samples. If a massive fish kill or human death is suspected to be caused by Arsenic, contact your local police department for forensic testing for arsenic. If only minor toxicity is suspected, a USEPA accredited laboratory will test water and wastewater samples.
8. Hydrogen Sulfide: Hydrogen sulfide inhibits aerobic respiration, inhibits muscle contractions, including breathing, and promotes excess breakdown of glucose. Hydrogen sulfide develops when sulfate-reducing bacteria grow up in the anaerobic sludge of a pond, and no harm is noticed shrimp, prawns, catfish and other bottom-feeders disturb the sludge layer, releasing hydrogen sulfide into the water, where it is first noticed when dead shrimp, prawns or fish float to the surface and a rotten egg odor, is observed. The rotten egg odor will be noticed when as little as 0.25 micrograms of unionized hydrogen sulfide is present in each 1 Liter of pond water. Levels of unionized H2S in ponds is toxic above 0.033 mg/L are toxic to shrimp and many fish. Some researchers suggest that H2S above 0.005 mg/L should be considered toxic and treated with ALKEN CLEAR-FLO 1005
If a pond owner attempts mechanical dredging to recover pond depth taken up by organic sludge, this process can accidentally release sufficient hydrogen sulfide gas to cause human deaths, unless workers wear NIOSH approved SCBA (self-contained breathing apparatus). See Biodredging to learn about biological dredging of ORGANIC sludge, another option for recovering pond depth lost to an accumulation of organic sludge. If sufficient percentages of inorganic sludge are present (sand, rocks, dirt, etc.) washed down due to soil erosion, mechanical dredging may be the only option to recover pond depth, but to avoid issues with hydrogen sulfide, sludge should be pre-treated with ALKEN ENZ-ODOR 6 to avoid the risk of releasing dangerous levels of hydrogen sulfide when the mechanical dredging begins. This pre-treatment is especially important if the pond is located close to the owner's home. Alkalinity and nitrate levels should be tested to determine if addition of sodium nitrate or ALKEN ENZ-ODOR 9 are also needed or if pond pollution levels are sufficient to prevent formation of acid during oxidation of unionized hydrogen sulfide in the sludge layer of the pond.
CHEMetrics test kit recommended by Alken-Murray for pond testing is: K-9510: 0 - 1 ppm & 1 - 10 ppm., since any level above 10 ppm will have killed everything in the pond and be obvious due to severe rotten egg odor coming frrom the pond. For wastewater testing, Alken-Murray recommends CHEMetrics kits K-9510D for 0 - 30 and 30 - 300 ppm, K9510A for 0 - 60 ppm and 6 0 - 600 ppm, K9510B for 0 to 120 and 120 to 1200 ppm, and 9510C for 0 - 1200 and 1200 to 12,000 ppm, providing you the entire possible range of sulfide in water. The protocol for all of these kits is the APHA Standard Methods method 4500-S-2D, which uses methylene blue methodology to detect sulfides in solution in water.
9. Sulfate: I have not found any aquatic limits for sulfate, but the US Public Health has set 250 mg/L as the limit allowed in drinking water.
This test requires an independent laboratory to test. . We usually do not test for this parameter in natural waterbodies, but it is of interest in wastwater treatment.
10. Salt: The average acceptable levels for freshwater fish are 0 - 5 ppt. Seawater averages 25 to 70 ppt.The level that is toxic varies with the species of aquatic animal, from 205.5 ppb for Zebra danio to 3,412,000 ppb for pond snails. LaMotte offers a test kit that measures 0 - 20 ppt of salt. A Sper Scientific Refractometer, measures 0 - 28% Salinity, and this is the instrument Alken-Murray uses to test salinity.
11. Magnesium: The US Public Health has set 150.3 mg/L as the acceptable level of magnesium in drinking water. I cannot find any limits for aquatic applications.
When the waterbody contains a variety of toxins, a custom blended formula will be created, taking into consideration the levels of the each contaminant.
Interpreting Tests - part 1
Interpreting Tests - part 2
Interpreting Tests - part 3
Water Analysis
Why do we need to analyze water?
If water is badly polluted-- like raw sewage--- it might be obvious from its appearance or odor.
It might be colored or turbid (cloudy), or have solids, oil or foam floating on it.
It might have a rotten odor, or smell like industrial chemicals.
A lot of dead fish floating on the surface of a lake would be a clear sign that something was wrong.
But many harmful-- and beneficial-- materials in water are invisible and odorless. In order to go beyond the obvious, to determine what materials are in the water, and how much, we need to be able to conduct chemical or microbiological analyses.
Analysis of a natural body of water will tell us how clean or polluted it is. If there is damage to wildlife, the measurements will help pinpoint the cause-- and the source. In a wastewater treatment plant, analyses are necessary for monitoring the effectiveness of the treatment processes. In the United States, the Clean Water Act requires wastewater dischargers to have permits. These permits set limits on the amounts of specific pollutants which can be discharged, as well as a schedule for monitoring and reporting the results. Usually, the reports must be filed monthly, while the measurement frequency for a particular parameter (measurable property) can run anywhere from "continuously" to just once a year. Only standard analytical procedures specified in the "Code of Federal Regulations" may be used, so that the government agencies can feel reasonably confident that results from different laboratories are comparable.
Similar considerations apply to drinking water. The purity of the water we drink is of more concern to the average person than the quality of the wastewater discharged by the sewage plant. But we should not forget that in many places, especially along a river, one town's wastewater discharge may be part of the next town's water supply...
There are two aspects to water analysis that we need to consider:
1. what substances or organisms are we interested in testing for-- and why?
2. what procedures and equipment do we use to make the measurements, and how do they work?
Let's look at the "procedures and equipment" first:
(If you want to read about the "substances and organisms" first,
click here,-- or here for no-frames version-- but the procedures on that page refer to methods discussed below.)
Analytical Methods
Water analyses are done by several methods. The most common types of measurements are gravimetric (weighing), electrochemical (using meters with electrodes) and optical (including visual). Instrumental methods are becoming increasingly popular, and instrumentation is getting "smarter" and easier to use with the inclusion of microprocessors. In the simplest case, a sample may just be placed in an instrument and a result read directly on a display. More often some physical separation technique or chemical procedure is needed before a measurement is made, in order to remove interferences and transform the analyte-- the target of the analysis-- into a form which can be detected by the instrument.
Since even raw sewage is generally more than 99.9% water, most environmental analyses are measuring very low concentrations of materials. The results of these measurements are usually expressed in the units "milligrams per liter," abbreviated as mg/L. Since a milligram is one thousandth of a gram, and a liter of water weighs about a thousand grams, a mg/L is approximately equal to one part per million by weight. A part per million ("ppm") is only one ten thousandth of one percent. For toxic metals and organic compounds of industrial origin, measurements are now routinely made in the part per billion (microgram per liter) range or even lower. At such low levels, sensitive equipment and careful technique are clearly necessary for accurate results. Avoiding contamination of the sample and using methods which prevent interferences from other substances in the water are crucial requirements for successful analyses.
Separation Techniques:
Some measurements require separating the analyte from other substances in the water which may interfere with the measurement. Some measurements even require separating the analyte from the water entirely. Separation techniques include:
• Filtration: The water is passed through a fine-pore filter which can be made of paper, glass fibers, a cellulose acetate membrane, etc. Filtration through a filter of some agreed-upon standard pore size can be used to separate "suspended" from "dissolved" portions of the analyte. The analyte may be the suspended matter which is captured on the filter-- or the filter may be used to clarify the water for analysis of a dissolved material. Often, the filtration is assisted by applying a vacuum below the filter, which is supported on a porous holder in some type of funnel.
• Distillation: If the analyte can be boiled out of the water, or along with the water, then the vapors can be cooled and re-condensed or trapped in a liquid form in a different container. This way the analyte can be removed from the interfering substances in the original water sample. Often the sample is made acidic or alkaline, or treated chemically in some other way before distillation, to convert the analyte into a volatile (easily evaporated) form, and to immobilize or neutralize interfering substances.
• Extraction: Some analytes may be much more soluble in an organic solvent than in water. If the solvent does not mix with water, and the sample is shaken with portions of the solvent, almost all of the analyte may be transferred from the water into the solvent, leaving interfering substances behind. This is known as a "liquid-liquid" extraction. The analysis may be completed using the organic portion. There are also continuous versions of this process for use with liquid or with dry samples.
Another type of extraction is called "solid-phase extraction." In this kind of procedure, the sample is passed through a column or filter containing a powdered or granulated material which retains (adsorbs) the substances of interest and allows other types of dissolved materials to pass through. Then a solvent, or an acid or alkaline solution, can be passed through to de-sorb and redissolve the analytes, a process known as elution.
Either type of extraction can also be used to concentrate the analyte into a smaller total volume, which increases the sensitivity of the analysis. This can be true for distillation or filtration, as well.
Measurement Techniques:
• Gravimetric analysis or, simply, weighing:
Analytical balances routinely used for gravimetric analysis are sensitive to one tenth of a milligram, or one ten-thousandth of a gram. Most laboratories use electronic balances with direct digital readouts. For a measurement of the milligrams per liter of solids in the water, a measured volume of sample can be dried in a tared (pre-weighed) dish; the dish plus solids are weighed after the water has evaporated off; the weight of solids is calculated by subtraction, and the concentration figured by dividing the weight of solids by the volume of the sample. For a filtered sample, the tared filter itself is dried along with the solids it captured, and the suspended solids (those captured on the filter) calculated in the same way. In some chemical analyses, a precipitate is formed by reacting the analyte of interest with another chemical reagent (reacting chemical); then the precipitate can be filtered, dried, and weighed as a suspended solid. This type of analysis is more common with water solutions that are more concentrated than environmental samples, though, such as chemicals purchased for use in water or wastewater treatment.
• Electrochemical:
The outer portions of all atoms and molecules consist of "shells" of electrons, and all chemical reactions involve interactions with these outer electrons-- sharing or transfer, or something in between. It is not surprising,, then, that electricity and chemistry are interrelated (just think of batteries), and that electrical measurements can be used to detect and determine some substances of interest. The procedures involve placing electrodes in a water sample and measuring either an electrical potential (voltage), in millivolts, or a current, in milliamperes, which is related to the concentration of analyte. Depending on what they are designed to measure, electrodes can be simple pieces of metals such as gold, silver, platinum, copper, etc.; or they may be elaborate systems with semi-permiable membranes and several internal electrodes and filling solutions. The instrumentation may be capable of reading out directly in concentration units. Usually some sort of calibration procedure is necessary, using one or more standard solutions of known concentration.
• Colorimetry or spectrophotometry:
This method involves measuring the intensity of a color in a solution and relating it to the concentration of the analyte. While some materials of interest are already colored, most of these analyses require the analyst to add some chemical reagents (reacting chemicals) to a sample to produce a characteristic color.
The simplest type of measurement is visual comparison of the intensity of the color to a set of color standards which represent various concentrations of the analyte. While this is method does not require any expensive equipment, color perception is rather subjective-- and many people have some degree of color-blindness.
A more precise measurement can be made using a colorimeter. A colorimeter is a device consisting of 1) a light source, which can be as simple as tungsten-filament light bulb; 2) some optics for focusing the light 3) a colored filter, which passes light of the color which is absorbed by the treated sample; 4) a sample compartment to hold a transparent tube or cell containing the sample, 5) a light-sensitive detector, like the light meter on a camera, which converts the light intensity into an electric current, and 6) electronics for measuring and displaying the output of the detector. Some colorimeters may be designed to read out directly in concentration units, while others may show the results in units of light absorbance which need to be compared to a calibration curve. (An interesting point is that the filter is not the same color as the solution being tested, but rather the complementary color. We want to use a filter which transmits light of the color which the solution absorbs. A yellow solution looks yellow because it absorbs blue light, so a blue filter would be used.)
If we want to get more precise and more interference-free measurements, we can use a spectrophotometer. This is very similar to a colorimeter, except that instead of using a filter to select the color of light to pass through the sample, we instead break the white light up into a rainbow (spectrum) of colors using a prism or a diffraction grating. The light is passed through a narrow opening (slit) before reaching the sample. By rotating the prism or grating, the color {"wavelength") of light can be selected more precisely and we can better match the color with that absorbed by the sample. The principle is shown in the diagram below. Needless to say, spectrophotometers cost more than colorimeters, and are likely to be more delicate and less portable, as well. While many tests are done using visible light, some analyses also make use of the invisible ultraviolet or infrared portions of the spectrum. Scanning spectro photometers can also be used to identify some types of analytes by the wavelengths or colors of the light they absorb.
There is a variation of this type of testing, usually referred to as atomic spectroscopy, which is used mostly for trace metal analysis. The sample is converted to a gas by one of several methods-- usually involving heating. Then the light from a lamp containing the same metal is passed though the gas and the absorbance measured just as with a liquid sample (atomic absorption spectrophotometry). Alternatively, the intensity of the light emitted from the heated atoms of the metal in the gas can be used as a way of measuring the concentration (atomic emission spectrophotometry). A very popular atomic emission method in use today is called inductively coupled plasma spectrometry. The sample is carried in a stream of argon gas surrounded by coils which emit radio frequency energy that converts some of the gas into a very hot, ionized (electrically charged) form. An advantage of this method is that many elements can be measured simultaneously, or in rapid succession.
• Titration:
Titration depends on using a well-defined chemical reaction to measure the amount of a standard solution needed to react with certain amount of the sample. A known volume, such as 100 mL, of sample is placed into a flask or beaker. The standard reagent is dispensed from a graduated tube called a burette so the volume used can be measured. The "end point" of the reaction is usually determined by observing a color change in an indicator solution, which is added to the flask before the start of the titration. End points are also often determined using electrochemical equipment. Once we know how much of the standard reagent was needed, we can calculate the amount of the analyte that is in the sample, because the reaction will always use the same proportion of the two materials. A common example is measuring the concentration of an acid by titrating with a standard base, such as sodium hydroxide.
• Chromatography:
This technique got its name, which means "color picture", because it was first used to separate colored pigments from a single spot on a piece of paper. A solvent, such as alcohol, is allowed to move slowly across the paper, and the different components of the pigment travel at different rates. The result is a series of separated spots of different colors. They move at different rates because of differences in the pigments' relative attraction to the paper (the "stationary phase") and their solubility in the solvent (the "mobile phase"). This principle is used in modern instrumentation to separate mixtures of organic chemicals or inorganic ions. The components can be identified by their retention times,-- i.e., how long it takes them to pass through the instrument-- and detectors can be used to measure the amount of each component.
In gas chromatography, (or, simply, "GC") the mixture of substances is injected into a narrow, coiled column, several feet long, made of an inert material like glass, silica or stainless steel. The sample has usually been extracted into an organic solvent and concentrated by evaporation as a pretreatment step. The column may be filled with an oil-coated, powdered mineral, which forms the stationary phase. In the narrower capillary columns, the stationary phase is bonded directly to the wall of the tubing. The columns are usually contained in an oven, which may be programmable to raise the temperature at a controlled rate over time. Heating the column allows analysts to use this technique on many substances which are not gases at room temperature, including solvents and toxic chemicals like pesticides and PCB's. A continuous flow of an inert gas, such as argon, helium, or sometimes nitrogen, carries the evaporated mixture through the column. The substances are detected as they exit the column, usually by a technique that converts them into ions (electrically charged atoms or molecules), although one method uses heat conduction. The ions are produced by means such as flames, ultraviolet light, or radioactive materials. They are detected by being attracted to charged plates, where they produce an electrical current proportional to the amount present. The output of the detector usually is shown as a chart of "peaks" vs. time, called a chromatogram, often with the retention time and the intensity of the peak printed out. The retention time is used to identify the substance, while the height or area of the peak is used to quantify its concentration. A more positive identification is possible using a mass spectrometer (see below) as the detector.
For substances which cannot easily be vaporized because of high boiling point or instability at higher temperatures, there is a liquid version of this technique know as HPLC (High pressure or high performance liquid chromatography). Organic solvents are used as the mobile phase. Ultraviolet (UV) light absorption is often used for detection. Herbicides and pharmaceuticals are common types of substances analyzed by this technique. Another variation of LC is ion chromatography, (IC), where the target analytes are charged inorganic or organic substances. The mobile phase is an aqueous (water-based) solution, and the stationary phase is made up of an ion exchange resin. The detectors usually measure electrical conductivity, although UV absorption can also be used. This technique can be used to measure the concentrations of several important inorganic anions, such as fluoride, sulfate, phosphate, and nitrate all in one analysis
• Mass Spectrometry:
In a mass spectrometer, an ionized vapor is passed between magnets or radio frequency coils which separate the ions by mass (actually by charge to mass ratio). The pattern produced is characteristic of the particular substance, which can be identified by comparison with computerized "libraries" of mass spectra. While the instrumentation can be used alone, for environmental analyses it is usually used in tandem with another technique. Used as a "detector" for gas chromatography ("GC-MS"), it can positively identified components which have already been separated from a mixture. There is some use with liquid chromatography, as well (LC-MS). As a detector for metal ions produced in an ICP (see above), it provides very high sensitivity and is being used to determine very low levels of metal in drinking water, and may soon be approved for wastewater effluents and receiving waters.
Parameters / Analytes
The previous page described some of the techniques and equipment used in water and wastewater analysis. This page discusses what things we want to measure, what their significance is, and what methods are used for each of them. Click on the parameter in the left frame to view information here.
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pH is a measure of how acidic or alkaline a solution is. In pure water at room temperature, a small fraction (about two out of every billion) of the water molecules (H2O, or really, H-O-H) splits, or dissociates, spontaneously, into one positively charged hydrogen ion (H+) and one negatively charged hydroxide ion (OH-) each. There is an equal number of each ion, so the water is said to be "neutral".
Some materials, when dissolved in water, will produce an excess of (H+), either because they contain these ions and release them when they dissolve, or because they react with the water and cause it to produce the extra hydrogen ions. Substances which do this are called acids. Likewise, some chemicals, called bases or alkalis, produce an excess of hydroxide ions.
The scale which is used to describe the concentration of acid or base is known as pH, for power or potential of the Hydrogen ion. A pH of 7 is neutral. pH's above 7 are alkaline (basic); below 7, acidic. The scale runs from about zero, which is very acidic, to fourteen, which is highly alkaline. The scale is logarithmic, meaning that each change of one unit of pH represents a factor of 10 change in concentration of hydrogen ion. So a solution which has a pH of 3 contains 10 times as many (H+) ions as the same volume of a solution with a pH of 4, 100 times as many as one with a pH of 5, a thousand times as many as one of pH6, and so on. Some common materials and their approximate pH's are: Acids--- carbonated beverages, 2 to 4; lemon juice, about 2.3; vinegar,about 3; Bases: baking soda, 8.4; milk of magnesia.10.5; ammonia,11.7;lye,14 to 15. (Some of these figures are from the Handbook of Chemistry and Physics, 56th ed., CRC Press,1976)
While the pH measures the concentration of hydrogen or hydroxide ions, it may not measure the total amount of acid or base in the solution. This is because most acids and bases do not dissociate completely in water. That is, they only release a portion of their hydrogen or hydroxide ions.
A strong acid, like hydrochloric acid, HCl, releases essentially all of its H+ in water. The concentration of H+ is the same as the total concentration of the acid. A weak acid, like acetic acid (the acid in vinegar), may release only a few percent of the hydrogen that it has available.
If you are trying to neutralize an acid by adding a base, like sodium hydroxide, the amount you would need to neutralize a strong acid could be calculated directly from the pH of the acid solution. But for a weak acid, the pH does not tell the whole story; the total amount of base needed would be a lot more. This is because as the OH- from the base reacts with the H+ in solution to form water, more H+ will break loose from the undissociated portion of the acid to take its place. The neutralization will not be complete until all of the weak acid has dissociated. To measure the total acidity, also called base-neutralizing capacity (BNC) of a water sample, it has to be titrated with base. That is, a solution of a base whose concentration is known must be added to the water sample slowly until the neutralization is complete. By measuring the volume of the base added, you can figure out the original concentration of acid.
In a similar way, the acid-neutralizing capacity (ANC), or alkalinity of a water sample has to be determined by titrating it with a solution of a strong acid of known concentration.
For a more technical explanation of pH and alkalinity, look at this "mini-tutorial", which includes formulas, reactions, examples, and titration curves.
Significance: Although there are some microorganisms which can function at extreme pH's, most living things require pH's close to neutrality. Many enzymes and other proteins are denatured by pH's which differ much from pH7, which disrupts the functioning of the organism and may kill it. Besides the harm to aquatic life in natural waters, pH imbalances can inhibit-- or completely wipe out-- biological processes in wastewater treatment plants, resulting in incomplete treatment and pollution of the receiving waters. Low (acidic) pH's also cause corrosion in sewers systems and increase the release of toxic and foul-smelling hydrogen sulfide gas. (This gas has been responsible for the deaths of numerous sewer workers.) Low pH's also increase the release of metals, some toxic, from soils and sediments. Alkalinity is an important parameter because it measures the water's ability to resist acidification, for instance, to acid rain. In wastewater treatment, some processes produce acidity. If there is not enough alkalinity to neutralize it, the pH of the process can drop and cause it to become inhibited. Alkalinity can be supplemented by chemical addition to avoid this.
Measurement: There are indicator solutions which change color in different pH ranges, and these can be used for approximate estimation of pH in solutions which contain high enough concentrations of pH-determining ions. "pH paper", impregnated with such indicators, are commonplace in testing laboratories. For accurate measurements and use in dilute solutions, electrochemical measurement (a "pH meter") is required. Alkalinity and acidity are determined by titration with strong base or acid, respectively, using either indicators or a pH meter to mark the endpoint.
Dissolved Oxygen (D.O.): Like solids and liquids, gases can dissolve in water. And, like solids and liquids, different gases vary greatly in their solubilities, i.e, how much can dissolve in water. A solution containing the maximum concentration that the water can hold is said to be saturated. Oxygen gas, the element which exists in the form of O2 molecules, is not very water soluble. A saturated solution at room temperature and normal pressure contains only about 9 parts per million of D.O. by weight ( 9 mg/L). Lower temperatures or higher pressures increase the solubility, and visa versa.
Significance: Dissolved oxygen is essential for fish to breathe. Many microbial forms require it, as well. The oxygen bound in the water molecule (H2O) is not available for this purpose, and is in the wrong "oxidation state", anyway. The low solubility of oxygen in water means that it does not take much oxygen-consuming material to deplete the D.O. As mentioned before, the biodegradation products of bacteria which do not require oxygen are foul-smelling, toxic, and/or flammable. Sufficient D.O. is essential for the proper operation of many wastewater treatment processes. Activated sludge tanks often have their D.O. monitored continuously. Low D.O.'s may be set to trigger an alarm or activate a control loop which will increase the supply of air to the tank.
Measurement: D.O. can be measured by a fairly tricky wet chemical procedure known as the Winkler titration. The D.O. is first trapped, or "fixed", as an orange-colored oxide of manganese. This is then dissolved with sulfuric acid in the presence of iodide ion, which is converted to iodine by the oxidized manganese. The iodine is titrated using standard sodium thiosulfate. The original dissolved oxygen concentration is calculated from the volume of thiosulfate solution needed.
Measurements of D.O. can be made more conveniently with electrochemical instrumentation. "D.O. meters" are subject to fewer interferences than the Winkler titration. They are portable and can be calibrated directly by using the oxygen in the air.
(Click to enlarge)
Oxygen Demand: The biochemical oxygen demand, abbreviated as BOD, is a test for measuring the amount of biodegradable organic material present in a sample of water. The results are expressed in terms of mg/L of D.O. which microorganisms, principally bacteria, will consume while degrading these materials. As this method is a fairly long-term bioassay test (5 days), a more rapid (2 hour) test is often used to estimate the BOD; it is known as the COD, or chemical oxygen demand test. An even more rapid test, known as the TOC, or total organic carbon test takes only a few minutes, but requires expensive instrumentation. In the United States, most regulatory agencies specify the BOD test for permit reporting, especially for biological treatment plants.
Significance: For reasons discussed earlier, the depletion of oxygen in receiving waters has historically been regarded as one of the most important negative effects of water pollution. Preventing these substances from being discharged into our waterways is a key purpose of wastewater treatment. Monitoring BOD removal through a treatment plant is necessary to verify proper operation. However, because the test takes too long to be useful for short-term control of the plant, the chemical or instrumental surrogate tests are often used as guides.
Measurement: The BOD test is performed in a specially designed bottle with a flared cap which forms a water seal to keep out air. The bottle is filled completely with sample, which must be near neutral pH and free of toxic materials. After an initial measurement of the D.O., the bottle is sealed and stored in a dark incubator at 20C for five days. The D.O. is measured again after this incubation period. The difference is the BOD. (The bottles are kept in the dark because algae which may be present in the sample will produce oxygen when exposed to light.) Since most wastewaters have BOD's which are much higher than the limited solubility of oxygen in water, it is necessary to make a series of dilutions containing varying amounts of sample in a nutrient-containing, aerated "dilution water." The measured BOD's are then multiplied by the appropriate dilution factors. A variation of this test, called the carbonaceous BOD, adds an inhibitor which prevents the oxidation of ammonia, so that the test is a truer measure of the amount of biodegradable organic material present. Samples which do not contain enough bacteria to carry out the BOD test can be "seeded" by adding some from another source. Examples of samples which would need seeding are industrial wastewaters which may have been at high temperatures or high or low pH, or samples which have been disinfected. (If there is residual disinfectant present, it must be neutralized before testing.)
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The COD test is done by heating a portion of sample in an acidic chromate solution, which oxidizes organic matter chemically. The amount of chromate remaining (measured by a titration), or the amount of reduced chromium produced (measured spectrophotometrically), is translated into an oxygen demand value. Biodegradability, toxins, and bacteria are not important, and the test is complete in about two hours. The figure will be higher than the BOD.
The TOC is done instrumentally. The organic carbon is oxidized to carbon dioxide by burning or by chemical oxidation in solution. The carbon dioxide gas is swept out and measured by infrared spectrometry or by redissolving it in water and measuring the pH change (the gas is acidic.) Both COD and TOC can often be correlated with BOD for a specific wastewater sample, but each wastewater is different. As a rough guide, the COD of a raw domestic wastewater is about 2.5 times the 5-day BOD.
Solids: Water, a liquid, can contain quite a bit of solid material, both in dissolved and suspended forms. The term "dissolved" implies that the individual molecules of a substance are mixed in among the water molecules. In practice, solids are classified as "dissolved" if they pass through a standard glass-fiber filter with about one micrometer pore size. Solids captured on the filter are, by definition, "suspended" solids..
Solids which settle out of a water sample on standing for a period of an hour are defined as "settlable." .
Solids are also further classified as "fixed" or "volatile." Fixed solids are basically the ash left over after burning the dried solids; volatile solids are those that are lost in this procedure. The sum of the two is referred to as "total". (This can be confusing, as the word "total" is also used in describing the sum of suspended and dissolved solids.) Volatile solids are often used as an estimate of the organic matter present.
Significance: Solids in wastewater contribute to sediment formation; volatile solids may be associated with oxygen demand.
Measurement: Total solids (TS) are determined by drying a known amount of a sample at a temperature of 103 to 105 C in a tared (pre-weighed) vessel, such as a porcelain dish, cooling in a dry atmosphere (in a container known as a desiccator), weighing on an analytical balance, subtracting the tare weight, and dividing by the original amount of sample. Results can be expressed in mg/L if the sample was originally measured out by volume; or percent by weight, if the sample was originally weighed. If the sample is then burned in a furnace at about 500 C, cooled, and weighed, the fixed (FS) or volatile solids (VS) can be determined. .
If the original sample is filtered through a tared glass-fiber filter, which is then dried, the weight of the material captured on the filter is used to figure the total suspended solids (TSS). Burning the filter in the furnace allows measurement of volatile suspended solids (VSS) or fixed suspended solids (FSS).
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The dissolved solids (DS) can be estimated from the difference between the total solids and the total suspended solids, but the official method calls for drying the filtrate (the liquid which passes through the filter) in a dish at 180C. (And, of course, there are TDS, FDS and VDS).
An estimate of total suspended solids can be obtained by an optical/instrumental measurement known as turbidity. The sample is placed in a glass tube; a beam of light is shined through it, and the light scattered at right angles to the beam is measured photometrically. In the same way that COD can be correlated with BOD, turbidity can be correlated with TSS; but the correlation will hold only for the particular sample from which it was derived.
Similarly, an estimate of dissolved solids is often made by measuring the water's electrical conductivity. Pure water does not conduct electricity. If substances which dissociate into electrically charged ions are dissolved in the water, they will conduct a current, roughly proportional to the amount of dissolved substances. Conductivity can be used to track sewage pollution. Note, however, that many organic materials dissolve in water without producing ions. So, while a salt solution may have a high electrical conductivity, a concentrated solution of sugar would go undetected by this method.
Nutrients: Nutrients are usually thought of as compounds of nitrogen or phosphorus, although certainly other elements, such as iron, magnesium, and potassium are also necessary for bacterial and plant growth.
Nitrogen occurs primarily in the oxidized forms of nitrates (NO3-) and nitrites (NO2-) or the reduced forms of ammonia (NH3) or "organic nitrogen"-- where the nitrogen is part of an organic compound such as an amino acid, a protein, a nucleic acid, or one of many other compounds. All of these can be used as nutrients, although the organic nitrogen first needs to decompose to a simpler form .
Phosphorus is biologically important in the form of phosphate, the most highly oxidized state of the element. The most biologically available form is dissolved orthophosphate, (PO4-3). (In solution, there are up to three hydrogens attached to the molecule, each one decreasing the negative charge of the ion by one. How many hydrogens are attached depends on the pH.) There are also condensed forms of phosphate, with more than one phosphorus atom per ion, such as pyrophosphate and polyphosphates. There are also organic phosphates, and all of these forms can be either dissolved or particulate (i.e., insoluble). The sum of all the forms is known as total phosphorus.
Significance: These nutrients are important in natural waters because, in excess, they can cause nuisance growth of algae or aquatic weeds. In wastewater treatment, a deficiency of nutrients can limit the effectiveness of biological treatment processes. In some plants treating industrial wastewaters, ammonia or phosphoric acid must be added as a supplement.
Measurement: Ammonia can be measured colorimetrically, by the Nessler or phenate methods, after distillation from an alkaline solution to separate it from interferences. It can also be determined by an electrode method, sometimes without distillation, since there are fewer interferences. Organically-bound, reduced nitrogen can be determined by the same methods after a digestion (the Kjeldahl digestion) which converts the nitrogen in those compounds to ammonia. The combination of ammonia and organic nitrogen is known as "Total Kjeldahl Nitrogen," or TKN. (TKN analysis is used for measuring protein content of animal feeds, as well.) Nitrite is determined colorimetrically. Nitrate can also be determined this way; the most popular way is by first reducing nitrate to nitrite chemically using cadmium, then analyzing the nitrite. There is an electrode method for nitrate, but it is not considered too accurate. Finally, ammonia (as the positively charged ammonium ion, NH4+), nitrate, and nitrite can be measured by ion chromatography, as well.
Phosphate can be measured by ion chromatography, also. Greater sensitivity, at lower cost, is obtained by colorimetric methods which measure dissolved orthophosphate. Some insoluble phosphates and condensed phosphates-- so called "acid-hydrolyzable phosphate"-- can be included by heating the sample with acid to convert these forms to orthophosphate. If the organic phosphate is to be included, to measure "total phosphate", then the sample must be digested with acid and an oxidizing agent, to convert everything to the orthophosphate form.
Chlorine: The pure element exists as the molecule, Cl2, which is a gas or a liquid at normal temperatures, depending on the pressure. When dissolved in water, most of it reacts to form hypochlorous acid (HOCl) and hydrochloric acid (HCl) which make the water more acidic. The HOCl dissociates, to some extent, to form H+ and OCl-, called hypochlorite ion. (The HCl dissociates completely.) If there is enough alkalinity to react with the hydrogen ions produced and keep the pH around neutral, most of the chlorine will be in the form of hypochlorous acid and hypochlorite ion. Disinfection can be done using solutions of sodium hypochlorite, which produce the same substances in solution. Hypochlorite ion is not considered as strong a disinfectant as HOCl, so the pH can affect the disinfectant efficiency. Dissolved chlorine, hypochlorous acid, and hypochlorite ion, taken together, are all known as "free chlorine". Free chlorine can react with ammonia in solution to form compounds called chloramines, which are weaker disinfectants than free chlorine, but have the advantage of not being used up by side reactions to the extent that free chlorine is. Free chlorine (and chloramines) also react with organic nitrogen compounds to form organic chloramines, which are even weaker disinfectants. The chloramines are termed "combined chlorine," and the sum of the free and combined forms are called "total chlorine." (Note that a large enough amount of chlorine can oxidize ammonia to nitrogen gas; this can be used as a chemical means of destroying ammonia.)
Significance: Chlorine is the most commonly used disinfecting agent for drinking water and wastewater. It is coming into some disfavor because of toxic and carcinogenic byproducts, such as chloroform, which are formed when it reacts with organic matter present in the water. Unless reduced to chloride, chlorine itself is toxic to aquatic life in receiving waters. Pure chlorine liquid or gas is also a storage and transportation hazard because of the possibility of accidental releases to the atmosphere. Some treatment plants are switching to hypochlorite solution because it is safer to handle. Others are eliminating it entirely and using UV light or ozone for disinfection.
Measurement: There are several choices for chlorine measurement, some of which can distinguish between free chlorine and the various chloramines. There are titrations involving visual, color-indicator endpoints, as well as electrochemically measured endpoints. Some of them can be used to differentiate among the various forms of chlorine depending on whether iodide ion is added to the testing mixture. The indicator known as DPD (full name, N,N-diethylparaphenylenediamine) can be used to measure free or total chlorine both colorimetrically or as a titration indicator. "Amperometric titration" is a sensitive electrochemical method.
Oil and Grease is the name given to a class of materials which can be extracted from water using certain organic solvents. They can be of biological origin (animal fat, vegetable oil); they can be "mineral" (petroleum hydrocarbons); or they can be synthetic organic compounds. Fats and greases from restaurants and food processing industries can clog sewers, causing blockages and backups. Petroleum products can be toxic and flammable, and can coat surfaces and interfere with biodegradation by microorganisms in wastewater treatment plants. They are mostly biodegradable, especially biological oils and greases, but are a problem due to forming a separate phase from the water.
Measurement: The major method of analysis is liquid-liquid extraction. Currently, the chlorofluorocarbon known as CFC-113 is used, but is due to be phased out in favor of the hydrocarbon, hexane, because of the damage done by CFC's to the stratospheric ozone layer. In the procedure, the sample is acidified, and then shaken several times with the solvent. The solvent portions are combined and evaporated, and the residue is measured by weight. In a CFC solution, the concentration of the oil/grease can also be measured by infrared spectrophotometry without having to evaporate the solvent. To determine petroleum hydrocarbons alone, the extract solution can be treated with the material, silica gel, which absorbs the more polar biological compounds. A newer method, solid phase extraction, passes the water sample through a small column or filter containing solid sorbent material which absorbs the oil and grease. It is then desorbed from the sorbent using a solvent and analyzed as above.
(Click the picture to see a
flame atomic absorption spectrophotometer in use.)
Metals: Chemically, metals are classified as elements which tend to lose electrons in a chemical reaction. As solids, they have easily movable electrons, which makes them good conductors of electricity and reflectors of light. In compounds, they tend to be positively charged, because they have lost electrons (which carry a negative charge), and they tend to bind with non-metals. This tendency makes some of them, such as iron and magnesium, biologically useful as part of biochemically active compounds like enzymes. Others, such as lead, cadmium, and mercury are highly toxic because they interfere with the normal operation of these biological compounds. The US EPA lists nine metals used in industry (arsenic, cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc) as toxic "priority pollutant" metals.
Measurement: There are numerous colorimetric methods for metals. Most of them are more useful in a purer medium, such as drinking water, than they are in wastewater, because of the presence of interfering substances. The most popular methods in use today involve one form or another of atomic spectroscopy, as described previously. Another technique, X-ray spectroscopy, is useful primarily for solid samples. There are also electrochemical methods, like polarography and "anodic stripping voltametry" (ASV) which are quite sensitive; but due to their complexity, they are usually thought of as being confined mostly to research purposes. (However, click here to see information from a company that sells a small, portable field instrument that uses ASV for sensitive lead and copper measurements. Similar equipment for these and other metals is also sold by another company.)
Cyanide: Cyanide is the name of an ion composed of carbon and nitrogen, CN-. It is used in the mining and metal finishing and plating industries-- usually as the sodium or potassium salts, NaCN or KCN-- because of its ability to bind very strongly to metals to form water-soluble complex ions. This same property makes it highly toxic to living things because it prevents the normal activity of biologically important, metal-containing molecules. It is, however, biodegradable by some bacteria in low concentrations; and they can become acclimated to higher concentrations if given enough time. For unacclimated microorganisms in a wastewater treatment plant, however, a cyanide "dump" by an industry can lead to inhibition or even death, which can cause a severe "plant upset."
Measurement: Cyanides are usually measured by a sensitive colorimetric/ spectrophotometric procedure which can detect levels down to about 5 parts per billion in water. Since much of the cyanide in a sample is likely to be bound to metal ions, a digestion/distillation procedure is necessary to measure "total" cyanide. Cyanide can also be measured by ion chromatography or an electrode method, though the latter is not considered too accurate.
Toxic Organic Compounds: An organic compound is any compound which contains carbon, with the exception of carbon monoxide and carbon dioxide, carbonates, or cyanides. Organic compounds contain chains and/or rings of connected carbon atoms, often with other elements attached. There are millions of possible compounds, with many useful properties. Many are biologically active, since all living things are made up of organic molecules. Industries use and produce thousands of organic compounds in manufacturing such items as plastics, synthetic fibers, rubber, pharmaceuticals, pesticides, and petroleum products. Some of the compounds are starting materials; some are solvents; some are byproducts. The US EPA lists 116 of them as toxic "priority pollutants"; many states have longer lists. One of the major groupings is volatile organic compounds (VOC's), many of which are chlorine-containing solvents. There are also petroleum hydrocarbons and starting materials for plastics, dyes, and pharmaceuticals. The "semi-volatile" group include solvents, PAH's (polycyclic aromatic hydrocarbons, like naphthalene and anthracene which are coal tar constituents), as well as pesticides (especially chlorinated pesticides) and PCB's (polychlorinated biphenyls, which were formerly used in electrical transformers and other products).
Measurement: Most of these are analyzed routinely by gas chromatography (GC), often followed by mass spectrometry (MS) for identification. HPLC is also used for some analytes. A technique which is becoming available for field measurements for some of these compounds is immunoassay, sometimes called ELISA, for "enzyme-linked immunosorbent assay." This method, which produces a color reaction related to the concentration of the target compound, or family of compounds, is portable, relatively inexpensive and does not require a great deal of training. It is in use more for surveying hazardous waste sites, however, than for water analysis.
Pathogenic microorganisms: Sewage contains large numbers of microbes which can cause illness in humans, including viruses, bacteria, fungi, protozoa and worms (and their eggs or ova). They originate from people who are either infected or are carriers. While many of these can be measured directly by microscopic techniques (some after concentration), the analyses most commonly performed are for so-called "indicator organisms." These organisms, while not too harmful themselves, are fairly easy to test for and are chosen because they indicate that more serious pathogens are likely to be present. For instance, wastewater treatment plants are often required to test their effluents for the group known as "fecal coliforms," which include the species E. coli, indicative of contamination by material from the intestines of warm-blooded animals. Water supplies test for a more inclusive group called "total coliforms", and in some cases, for general bacterial contamination (heterotrophic plate count, or HTP.)
Measurement: The two most commonly used methods of analysis for indicator organisms are the multiple tube fermentation technique and the membrane filter procedure.
In the first method, a number of tubes containing specific growth media are innoculated with different amounts of the sample and incubated for a particular time at a prescribed temperature. The appearance of colors, fluorescence, or gas formation indicates the presence of bacteria belonging to the target group. The number of organisms per 100 mL in the original sample is estimated from most probable number (MPN) tables, which list the values of MPN for different combinations of positive and negative results in tubes which contained different initial volumes of the sample. Often, positive results must be confirmed by further innoculation of small amounts of material from the positive tubes into tubes containing a different media, which can extend the test to several days.
The second technique involves filtering a known volume of sample through a membrane filter (made of a material such as cellulose acetate) which has a small enough pore size to retain the bacteria. The filter is then placed in a dish of sterile nutrient media, either soaked into an absorbent pad or in a gel such as agar, and sealed. The dish is incubated for the prescribed time and temperature. The media contain a colored indicator which will identify the target bacteria. Each bacterium in the original sample will result in a colony after incubation, which is large enough to see without a great deal of magnification. The concentration in the sample can be determined by direct count of the colonies, knowing the volume of sample used. In some cases, these colonies require further confirmation.
Detection and enumeration of HTP or of specific pathogenic bacteria, such as Salmonella, E. coli, or Enterococcus can be done by similar methods, but utilizing specific growth media for each type. Viruses are usually measured by concentration, followed by addition to cultures of cells which they infect and counting the number of plaques formed due to cell destruction. Pathogenic protozoa and ova of multicelled organisms are determined by concentration and direct counting under the microscope, often with the aid of fluorescent staining compounds.
Besides, direct observation, identification of pathogenic microorganisms can be done by standard techniques used in clinical laboratories involving observing reactions in a battery of different indicating media. Some newer methods use chromatography to identify patterns of compounds which serve as "fingerprints" for certain bacteria; DNA analysis is another recent innovation. Most wastewater treatment plants, however, confine their testing to simply counting the numbers indicator bacteria.
Reference: http://findebookee.com/w/water-analysis
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