This article throws light upon the eleven parameters to be determined for the analysis of industrial effluents. The parameters are: 1. D. O. (Dissolved Oxygen) 2. Temperature 3. Odour 4. Turbidity 5. pH 6. Nonfiltrable (Suspended) Solids 7. Colour 8. Ammonia 9. Hardness 10. Humidity Meter 11. Velocity Meter.
Parameter # 1. D. O. (Dissolved Oxygen):
(I) Since the DO content of a sample can change rapidly, it must be ‘fixed’ immediately after collecting the sample. This is done by means of an oxidation-reduction reaction brought about by the addition of manganese
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(II) sulphate and potassium hydroxide (which is added along with Potassium Iodide)
4Mn ++ + O2 + 8 OH– + 2H2O = 4Mn (OH)3
The result of fixing is that brown manganese (III) hydroxide is precipitated.
(II) The manganese (III) is converted to its equivalent of iodine. For this the solution is just acidified with some sulphamic acid, as iodide is already present
2 Mn(OH)3 + 3H++ = 2Mn + 3 H2O
2 Mn++ + 2I– = 2 Mn++ + I2
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I2 + I– = I3–
(III) A portion of the solution is titrated with sodium thiosulphate
I3– + 2S2O3 = 3I– + S4O6
thiosulphate tetrathionate
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The indicator of the reaction is starch, which forms a blue complex with iodine
I2 + starch = I2‘ starch
(blue)
Requirements:
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Reagents:
1. Manganese (II) sulphate solution:
Weigh 100 g of MnSO4. 4H2O and dissolve in 200 ml of previously boiled distilled water.
2. Alkaline potassium iodide solution:
Take 200 ml of previously boiled and cooled distilled water and dissolve 100 g of KOH and 50 g of Kl in it
3. Sulphamic acid (NH2SO2OH):
This is a solid substance and is used in that form.
4. Starch solution:
Heat 100 ml of distilled water close to boiling point and dissolve 1 g of soluble starch powder in it. Keep it overnight. Decant the solution and store after adding a few drops of formaldehyde solution.
5. Sodium thiosulphate:
Weigh 6.21 g of Na2S2O3.5H2O and dissolve it in previously boiled and cooled distilled water and make the volume up to 1 litre. Keep the solution in a brown or black bottle after adding a pellet of sodium hydroxide as stabilizer.
Apparatus:
A 250 ml DO bottle (glass bottle with stopper), three syringes (2 ml), one plastic syringe 20 ml, spoon, plastic volumetric flask (100 ml), conical flask 250 ml.
Testing Procedure:
“Fixing” of the sample must be done at the spot immediately after collection. The rest of the process can be done in the laboratory. Rinse the DO bottle 2-3 times with sample water and then fill it with more sample water until it overflows. Put on the stopper after ensuring that no air bubbles are trapped in the bottle.
Draw manganese (II) sulphate solution into a 2 ml plastic syringe, slightly above the top mark. If there is an air bubble, invert and rotate the syringe to bring the bubble at the nozzle. Push the piston gently to expel the bubble. Inject 2 ml manganese (II) sulphate into the sample. Repeat the procedure with alkaline potassium iodide (KOH/KI) solution by using another 2ml syringe.
Wait for a minute, a brown precipitate will be formed. Place the stopper firmly on the bottle. Shake the contents thoroughly by inverting and straightening the bottle about 15 times. Keep the bottle in a safe place for approximately 20 minutes (until the precipitate formed settles in a compact layer at the bottom of bottle).
Open the bottle and add a spoonful of sulphamic acid. Replace the stopper. Shake the bottle thoroughly in the same manner as before, until the brown precipitate dissolves. Draw the solution of sodium thiosulphate up to the top mark in a 20 ml syringe.
Remove the air bubbles and keep the syringe ready for titration. Take 100 ml solution from the bottle in a 250 conical flask. Use the 100 ml volumetric flask to measure the required quantity of the solution.
Hold the conical flask in one hand and add thiosulphate solution drop by drop from the syringe with the other hand, or one chemist may hold the flask and the other do the addition of sodium thiosulphate. Addition must be done slowly. Shake the flask gently while adding the drops. Take care that the contents do not spill out.
When the colour of the contents of the flask becomes pale yellow, stop adding thiosulphate. Set the 20 ml syringe carefully aside without spilling its contents or disturbing the plunger in any way. Add 2ml starch solution to the contents of the conical flask with the help of 2ml syringe. Shake it
The colour of the contents changes to blue. Now take the 20 ml. syringe again. Continue adding sodium thiosulphate solution drop by drop until the blue colour just disappears. End point is blue to colourless. The chemist should note the total volume (i.e., amount before adding starch plus amount after adding starch) of the sodium thiosulphate solution consumed from the syringe.
Volume of sodium thiosulphate consumed, say x ml, is equivalent to the milligram concentration of dissolved oxygen in 0.5 litre. Therefore, 2x ml of sodium thiosulphate is equivalent to DO in mg per litre.
Parameter # 2. Temperature:
The temperature parameter plays an important role in certain biological and chemical processes. At high temperatures solubility of gases in water is low. Therefore, the amount of dissolved oxygen will be less, while odour will be more. The increase in the temperature normally occurs due to the disposal of hot effluents in the river.
Temperature affects aquatic life both directly and indirectly by altering various parameters. There may be diurnal (i.e., through the day) or seasonal changes in river water temperature. Temperature may be high at places where hot effluents enter into the river.
Requirements:
A laboratory thermometer (graduated 0° to 50°C) and a 100 ml beaker.
Testing Procedure:
Temperature should be measured immediately after collecting the sample at the site itself.
Parameter # 3. Odour:
The reasons for odour in water can be natural or man-made. Natural reasons may include decaying weeds and algae, or the presence of microorganisms. When organic matter decomposes, gases like ammonia, hydrogen sulphide, etc. are given off.
These impart odour to water. Sewage and industrial wastes are also sometimes responsible for odour in water, for they may contain halogens, sulphides or other types of chemical compounds.
Odour is undesirable in drinking water, and also in water for certain industrial uses. Since the sense of smell varies from person to person, it is essential at odour is smelled by at least 4-5 persons in order to get a fairly reasonable inference.
Requirements:
Beaker (100 ml).
Testing Procedure:
Take about 75 ml. of the sample water in a 100 ml beaker and smell it for odour. This should be done at the site immediately on collecting the sample. If kept for some time it may lose odour.
A tick (√) mark should be made in the respective columns against the appropriate inference in the following table.
Parameter # 4. Turbidity:
Turbidity is the opposite of clarity. It is due to suspended matter in water. At high levels of turbidity, water loses its ability to support a diversity of aquatic organisms.
It becomes warmer as suspended matter absorbs heat from sunlight proportionate to the concentration of its particles. Warm water holds less oxygen than cool water. Less light penetrating turbid water decreases photosynthesis, which in turn reduces oxygen concentrations.
Suspended solids may clog the gills of fish, reduce their growth rates, decrease resistance to disease and prevent egg and larval development. Particles of silt, clay, and organic materials may settle to the river bottom, especially in impounded and slow-moving rivers. These settled particles can accumulate and smother eggs of fish and aquatic insects resting on the river bottom.
Turbidity may be due to soil erosion, waste discharge, urban runoff, abundant bottom feeders (carp) which stir up bottom sediments, or the presence of excessive nutrients which result in algal growth. Turbidity may affect the colour of the water, from nearly white to red-brown to green from algal blooms.
Secchi’ disk (pronounced Sekki) measurements (see testing procedure below) are based upon the disk being lowered into water until it disappears from view. It cannot be used in rivers which are shallow or deep rivers with low turbidity.
In these cases the reading may need to be estimated as accurately as possible. It may be difficult to use the disk in fast currents because the current will cause the disk to swing preventing accurate measurement. A weight may have to be added to the disk in this situation.
Requirements:
Secchi disk, measuring tap, a 2 to 3 metre length of strong twine.
Testing procedure:
Lower the disk into the water until it just disappears from sight (it is important that the twine hangs vertically in the water and is not “swung out” by the river current). Now measure and note the length of twine that has gone underwater.
Lower the disk further and then raise it until it can just be seen again. Now measure and note again the length of thread that has gone below the surface of the water. Add both the readings and divide by two. This is the turbidity level using the Secchi disk, expressed as the distance of visibility of an object in the water.
Before using the Secchi disk it is necessary to check that the twine is securely tied to the disk and that it is not frayed by abrasion or rust. Failure to observe this precaution may result in loss of the disk in water while in use.
Parameter # 5. pH:
The pH value of a solution is a measure of intensity of its acidity or alkalinity. The range of pH values extends from 0 to 14. Values between 0 and 7 indicate acidity while those above 7 indicate alkalinity. A pH value of 7 is indicative of neutrality. Generally water in nature is slightly alkaline. Domestic sewage is also generally alkaline while industrial waste may be acidic or alkaline.
Amounts of dissolved gases like carbon dioxide, ammonia, hydrogen sulphide etc. affect pH values. Seasonal variations may also change pH value. At night it is slightly low because of carbon dioxide produced by respiration in aquatic plants. Carbon dioxide dissolves in water forming carbonic acid. By day this carbon dioxide is consumed in photosynthesis, thus increasing the pH value.
Values lower than pH 5 impart a sour taste to water, and also a lower pH water starts corroding metal pipes. At the same time, lower pH, helps the chlorination process in disinfection.
Higher pH accelerates scale formation in equipment where water is boiled. The exact measurement of pH can be done by using a pH meter (Beckmann) but for approximate measurements paper strips called pH paper, which contain indicators, are used.
Requirements:
Booklets of pH paper, beaker, thermometer.
Testing Procedure:
Take water in a beaker. Tear a leaflet from the pH paper booklet and dip one end of it briefly into the sample taken. Now take it out and match the colour of the wet portion of the leaflet with the colours printed on the cover of the booklet Read the corresponding number. This number is the pH value of the sample.
Precaution:
It is important to protect the pH paper booklet from contact with any liquid. The paper strips should be torn off with dry hands.
Parameter # 6. Nonfiltrable (Suspended) Solids:
Nonfiltrable residue is the material retained on a filter paper after filtration of a well mixed sample of water. Waters with very high levels of nonfiltrable residues may be unsatisfactory not only for drinking but also for such purposes as bathing and washing.
Requirements:
Funnel filter paper, funnel stand, 500 ml beaker and 250 ml beaker.
Testing procedure:
Keep a funnel lined with a filter paper on a funnel-stand. Filter 250 ml of the sample by pouring into the funnel a 250 ml beaker full of water. After the completion of filtration allow the filter paper to dry. Now carefully remove the filter paper, unfold and observe it for any retained solids. Record the observations in the given worksheet as no residue, less, high or very high levels.
Parameter # 7. Colour:
Colour may result from natural materials like soil particles, or it may be of organic origin. It can be due to decaying organic matter like tannins, peat algae, fungi, weeds etc. Dissolved or suspended clay may also impart colour. Some industries like fertile or leather, which use colours in their manufacturing process, are also sometimes responsible for adding colours to water bodies.
Some of these colours are harmful, some are not. But coloured water is generally not preferred for human use. The types and intensity of colour can be observed by visual inspection. For exact determination of intensity of colour a colourinater is required. Here we are adopting the visual inspection method only.
Requirements:
Two test-tubes, clean water (preferably distilled), a white sheet of paper or plastic.
Testing Procedure:
Take two test-tubes. Fill one test-tube with the sample and the other with clean distilled water from the kit Now inspect the samples in sufficient light by holding the test-tube, with the white sheet in the background. The white background makes it easy to compare the contents of the two test-tubes.
Parameter # 8. Ammonia:
Ammonia in water comes from decaying organic matter. Sewage is rich in nitrogenous matter. Disposal of such wastes increases the ammonia content of water. Ammonia in high concentration is harmful to fish and other aquatic animals, and also to man.
Nessler’s reagent (K2Hgl4) forms a brown precipitate with ammonia in the presence of sodium hydroxide
NH3 + 3 NaOH + 2 K2HgI4 = 4KI + 2NaI + 2H2O + OHg. NH2I Hg
Oxidimercuri amm. iodide
Requirements:
Reagents:
1. Nessler’s reagent. It is readily available in market;
2. Sodium hydroxide solution, 2N: Dissolve 8.0 g of NaOH in distilled water and make up the volume to 100 ml.
Apparatus:
Test-tube and dropper bottle.
Testing Procedure:
Take about a quarter of a test tube full of the water sample. Add about 5 drops of Nessler’s reagent and 10 drops of sodium hydroxide solution. Observe the colour of the contents. If they turn brown to form a brown precipitate, presence of ammonia is inferred.
Parameter # 9. Hardness:
Water is termed “hard” when it produces little or no lather with soap (not synthetic detergents). Chemically soaps are sodium salts of organic acids which are soluble in water and they form good lather.
The presence of some chemical substances, mainly calcium & magnesium carbonates, sulphates, bicarbonates or chlorides make soap insoluble. Certain other ions also contribute to hardness of water, but their role is not as significant as that of calcium and magnesium.
Hard water is unsuitable for laundry purposes, as a large portion of soap is wasted. In equipment where water is boiled, the hardness causing substances get deposited on the walls of the equipment. Such deposits may or may not be advantageous. They are advantageous as they prevent corrosion of metal. The disadvantage is that they form a heat insulating layer, thus increasing the energy consumption in boilers.
Hardness in water can be demonstrated from its low foam forming capacity with soap, but its exact amount is represented by the concentration of calcium and magnesium ions. These ions can be analysed by volumetric method.
The concentration of calcium and magnesium ions is determined by titration with EDTA reagent. The titration is based on the principle that Ca and Mg ions form weak complex with Eriochrome Black-T dye and a more stable and soluble complex with EDTA.
When the dye is added to hard water at pH 10 ± 0.1, it forms a wine red coloured complex. When EDTA is added to this complex, it breaks and forms a more stable complex. The dye is released and thus the solution turns from wine red to blue at the end of the reaction.
Requirements:
Reagents:
1. EDTA solution, 0.01 M:
Weigh 3.723 gm. of disodium salt of EDTA. Dissolve it in distilled water and make up the solution of one litre.
2. Buffer solution:
(a) Dissolve 16.9g ammonium chloride in 143 ml of concentrated ammonium hydroxide,
(b) Dissolve 1.179 g of disodium salt of EDTA and 0.780 g of magnesium sulphate heptahydrate (MgS04.7H2O) in 50 ml distilled water. Mix both, (a) and (b) solutions and dilute to 250 ml with distilled water.
3. Eriochrome Blaek-T indicator:
Take 0.4Q g of Eriochrome Black-T and 100 g of sodium chloride, mix both and grind.
Apparatus:
Conical flask (250 ml), beaker, plastic syringe 20 ml, plastic syringe 2 ml, and measuring cylinder (50 ml).
Testing Procedure:
Take 50 ml of the sample in a 250 ml conical flask with the help of a measuring cylinder. Draw buffer solution up to the 1 ml mark in a 2 ml plastic syringe and transfer this into the conical flask, add 100-200 mg (or one-fifth of a spoon or a pinch) of Eriochrome Black-T indicator to it. The solution will turn wine red in colour.
Now take up the EDTA solution in a 20 ml syringe. Add this solution slowly into the conical flask. While doing so gently rotate the flask, taking care not to spill the contents. When the colour starts becoming violet add the EDTA solution drop by drop. Stop adding when the colour of the contents of the flask just becomes blue.
Note the volume of EDTA solution consumed in the titration and to calculate the hardness of the sample by the formula given below:
Parameter # 10. Humidity Meter:
Through an instrument humidity meter, the humidity can be measured and noted.
Parameter # 11. Velocity Meter:
Through this instrument the velocity of water/effluent can be measured immediately.