In this article we will discuss about how to estimate the quality of water.
Parameters Analysed on the Spot for Estimating Water Quality:
i. Hydrogen – Ion Concentration (pH):
ADVERTISEMENTS:
The hydrogen ion concentration (pH) is as important as the total solid content, for the sewage and temperature for ecological studies as a whole. Waste water with an adverse concentration of hydrogen ion is difficult to treat by biological means and if the concentration is not altered before discharge, the waste water can alter the pH of natural waters.
In domestic waste water (containing sewage and septic effluents), the pH value normally varies from 0 to 7.5 and therefore do not affect the receiving water body but an altogether different picture may arise in the case where acidic or alkaline wastes go into the streams. Acidic wastes are corrosive to both metallic and concrete structures.
Besides being toxic to the aquatic life, they react with the natural alkalinity of the water, thereby increasing the carbonate hardness and thus rendering it unfit for future uses in laundry or boiler. On the other hand, water having pH value of more than 8 when discharged into the receiving stream, combines with free carbon dioxide and further increases the alkalinity of the water. The optimum ranges of pH for aquatic life are 6.8 to 9.0.
Estimation:
The pH value of clear water in the field is determined with the help of Lovibond pH comparator disc. Water samples are filled-up in the pH cell upto the marked calibration followed in quick succession with the addition of 3 to 5 drops of phenol red solution as indicator. After shaking the sample, the colour developed is matched in the disc by which the pH value is known. In case of coloured water sample or any coloured solution pH value is estimated by using electronic pH meter.
ii. Dissolved Oxygen (DO):
ADVERTISEMENTS:
The dissolved oxygen (DO) content shows the health and ability of the stream to purify itself through biochemical process. Too high content of dissolved oxygen is an indication of organic pollution, particularly when pollution is contributed by sewage outfall. When DO level drops below approximately 5 ppm, the more desirable species of fishes such as trout and brass leave the area and only the coarse type of fishes predominate.
Further it is reported that at an oxygen level of approximately 2 ppm, fishes disappear and the environment shifts towards anaerobic species. High depletion in oxygen content produces foul odour due to the anaerobic decomposition of organic waste leading to the formation of hydrogen sulphide.
Estimation:
DO is estimated on the spot by adding 2 ml of manganese sulphate solution (prepared by dissolving 364 g MnSO4, 4 H2O, in 1 litre distilled water) to the freshly drawn water samples in glass bottles of 300 ml capacity. The content is mixed by swirline 2 ml of alkaline sodium iodide azide (prepared by dissolving 700 g of sodium hydroxide, 135 g of sodium iodide and 10 g of sodium azide in 1 litre of distilled water), solution is then added. The whole content is thoroughly mixed and the resultant brown flock is allowed to settle for about 5 minutes.
ADVERTISEMENTS:
Thereafter, 2 ml of conc. H2SO4 is added whereby the settled flock gets dissolved and makes yellow solution on mixing 200 ml of the above solution is taken out in another cleaned neutral glass bottle and titrated against N/40 sodium thiosulphate solution using starch as indicator. The amount of titrant used gives the direct reading for DO in ppm.
iii. Temperature (°C):
Temperature is one of the most important parameters for aquatic environment because almost all the physical, chemical and biochemical properties are governed by it. For example, density, viscosity, surface tension and vapour pressure of water, more or less depend on the temperature profile of the system. It is the temperature which limits the saturation values of solids and gases that are dissolved in it.
The rate of chemical reactions and other biological activity such as corrosion or incrustation, BOD, photosynthesis, growth and death of micro-organisms are all dependent upon environmental temperature values. Indian climate provides almost an ideal range of solar temperature which attributes a great self-purification strength in the stream. The rate of biochemical reaction is directly proportional to the environmental temperature in hottest summer months, the oxygen demand increases, leading to serious oxygen depletion problem in the systems concerned.
ADVERTISEMENTS:
Estimation:
The temperature of water measured by using a thermometer, calibrated in °C scale. For measuring the temperature of open water body, the thermometer is dipped into the water and the reading is taken. Thermometer should not be taken out from the water body for reading the temperature. If the thermometer of °C scale is not available, then one of °F may be used.
iv. Turbidity /Transparency:
Turbidity of water is responsible for the light to be scattered or absorbed rather than straight transmission through the sample. It is the size, shape and refractive index of the suspended particulates rather than the total concentration of the latter present in the water samples that are responsible for turbidity.
Turbidity decreases light penetration, limit production of phytoplankton which consequently leads to decrease in photosynthetic activity and depletion of oxygen content. Clear ponds with less than 25 ppm turbidity may have 12.8 times more plankton and 5.5 times more fish production than ponds with a turbidity exceeding 100 ppm. High turbidity closes the door and impairs the lungs by completely blanketing the upper surface of water body.
Since the surface not only acts as window through which it receives radiant energy but it is also like lungs through which it takes in oxygen from the atmosphere and gives out carbon dioxide and other dissolved gases that are generated within the water by microbes. The turbidity and the transparency values are interrelated, just like that of total dissolved solid and conductivity values. The transparency values are expressed in cm or mm and turbidity in ppm.
v. Odour:
Odour in water is caused by volatile substances associated with organic matter, living organisms principally algae and related organisms and gases. Offensive odour causes poor appetite for good food, lowers down the water consumption, impairs general quality and causes nausea and vomiting. Odour can result in marked decline in tax revenues, pay rolls and sales. World Health Organisation (WHO 1961) has recommended that water intended for drinking, bathing and recreational purposes should be completely free from any odour.
vi. Colour:
The dissolved or colloidal substances of vegetable origin which generally consists of tannins, glucoside as well as iron and other substances are responsible for the colour present in water. The colour of sewage reflects its strength and condition. Fresh sewage is grey whereas septic sewage is black in colour. The colour of river water is reduced by storage or ageing of the water and by bleaching action of sunlight.
Estimation:
1 g of cobalt chloride along with 1.245 g of potassium chloroplatinate is dissolved in distilled water and the solution is then diluted to 1 litre when the same has a colour of 500 hazen unit. Maximum permissible colour for drinking purposes is 20 ppm on platinum cobalt scale. Colour is harmless but it cannot be allowed more than the maximum tolerance limit fixed as the consumers feel repellant.
Physio-Chemical Parameters for Estimating Water Quality:
i. Total Dissolved Solids (TDS):
TDS contents of water and waste water are defined as residue left upon evaporation at 103°C to 105°C. It is an aggregated amount of the entire floating, suspended, settable and dissolved solids present in the water sample. Further, in all the three above mentioned physical stages, the solids may be organic or inorganic in nature, depending upon volatility of the substances. The organic fraction is driven off as gas on ignition at 600°C and the inorganic fraction remains as ash.
Thus, the term volatile and non-volatile solids refer respectively to organic and inorganic contents of the water sample. Organic constituents of total solids are responsible for taste, colour, odour, gas and biological problems, whereas most of inorganic materials being non-biodegradable do not cause such environmental pollution problems, although a few of them, in traces, produce acute toxicological problems for aquatic dwellers.
Inorganic mineral contents, present in the water, conduct electric current which is measured by specific conductivity tests. An approximate idea of total dissolved solids (TDS) in natural water can be obtained by multiplying the specific conductance at 25°C by a factor of 0.55 to 0.75 with an average of 0.65. TDS in ppm can also be found out by adding the sum of the determined constituents in ppm except that the bicarbonate concentration should be multiplied by a factor of 0.49.
Osmotic pressure in atoms is known on multiplying the conductivity value of mhos/cm by 0.00036. Studies carried out on the productivity of fishes with respect to conductivity values suggest that electric conductivity above 400 mhos/cm do not limit production. On the other hand, the fish production does not increase proportionately with conductivity.
ii. Alkalinity:
It is an anionic phenomenon. All anions such as CO3–2 (carbonate), HCO3– (bi-carbonate), OH (hydroxyl), PO4–3 (phosphate), SiO4– (Silicate) etc., contribute alkalinity to water. The number of mili-equivalents of acid used in the titration to combine all the hydroxyl ions, is known as total alkalinity. The water supplied with less than 103 ppm of alkalinity as CaCO3 is ideal for domestic use. The ratio of alkalinity to that of alkaline earth metals is a good parameter for determining the suitability of irrigation water.
Estimation:
To 100 ml of water sample, 2 drops of 0.1 per cent phenolphthaloin (P) solution, as indicator, is added and titrated against N/50 H2SO4 solution, until the pink colour disappears. Thereafter, another 2 drops of 0.1 per cent methyl orange solution as indicator is added to the same sample of water. Titration against N/50 H2SO4 is continued until the yellow colour changes to pink. The titrant consumed in ml give the value for total alkalinity. (TA).
The calculation for different types of alkalinity involves some mathematical interplay which is as such:
(i) When P = O, TA is HCO3 alkalinity as CaCO3.
(ii) When P = TA, TA is OH alkalinity as CaCO3.
(iii) When P = 1/2 TA, TA is CO3 alkalinity as CaCO3 and equal to 2 P. But when P is either less or more than half of total alkalinity (TA), then altogether a different situation arises. More than one type of alkalinity exists in the same sample.
(a) When P < 1/2 TA, then CO3 will be 2 P and HCO3 will be T-2P.
(b) When P > 1/2 TA, then 2 P T will be for OH and 2(1/2 –P) will be for carbonate type of alkalinity.
iii. Hardness:
Hardness is caused due to bivalent cations such as Ca++, Sr++ etc. Higher cations also contribute hardness to a lesser degree but monovalent cations never produce hardness. Thus, sodium compounds do not cause hardness from the agricultural, limnological and industrial point of view. The estimation of hardness is of vital significance but has a very limited scope in respect of environmental considerations. Water should have zero hardness specially for boilers operating at high pressure. Limnologically, moderately hard water is desirable.
Estimation:
To 100 ml of water sample, 2 ml of buffer solution (prepared by dissolving 16.9 g NH4 CI in 143 ml of concentrated ammonium hydroxide solution) is added to bring the pH value to 9.0. Then one small spoon (say 0.209) of Erichrome black-T is added as indicator which forms wine red colour. The whole content is stirred and titrated against 0.01 M solution of EDTA (ethylene diamine tetra acetic acid), till the wine red colour changes to blue.
To avoid the possibility of interference by trace elements, if suspected to be present in the water, one ml of 5 per cent sodium sulphide (Na2S) solution is added as inhibitor, prior to the procedure for titration. The titrant consumed in ml on multiplying by factor 10 gives the value for the total hardness in ppm as CaCO3.
Relation between Hardness and Alkalinity:
When the total alkalinity valve is higher than the value for total hardness, then the latter indicates the carbonate type of hardness. If and when the total hardness is higher than the total alkalinity, then the value for total alkalinity is for carbonate hardness and the difference of the two shows the value for non-carbonate hardness.
iv. Calcium:
Calcium is one of the alkaline earth metals, the others being magnesium, barium, strontium etc. It is widely distributed on the earth’s crust and is present nearly in all waters. In presence of CO2, Calcium bicarbonate can normally be dissolved upto 20 ppm (as Ca) at atmospheric pressure and upto 100 ppm at higher pressure. The water coming from limestone zone may contain greater concentration of calcium. As soon as CO2 is released, calcium carbonate (which can be retained in water upto 5 ppm as calcium only) is precipitated out.
Lakes have been classified as poor, medium and rich, depending upon their calcium content, being less than 10 ppm, between 10 to 25 ppm and more than 25 ppm respectively. Calcium is not known to indicate or produce any hazardous effect on human health. Concentration upto 1800 ppm has been reported as not to impart any physiological reaction on human being.
Moderate content of calcium in water is rather desirable because the toxicity of various substances i.e. Pb, Cd, Hg etc. have been observed to be neutralised. Undoubtedly, high concentration of calcium content in water is not desirable at all for laundering and for use in boiler. Calcium, if present with sulphate, inhibits malt fermentation and with chloride, inhibits growth of yeast in distillery industry.
Estimation:
2 ml of 1N NaOH solution is added to 100 ml of water sample, to raise the pH above 10. At such high pH, magnesium is precipitated out as Mg(OH)2 but Ca remains in solution. It is than treated against 0.01 M solution of EDTA, by using muroxide as indicator. The titration is continued till the solution becomes distinctly pink in colour. The titrant consumed in ml, on multiplication by factor 4, gives the concentration of calcium as Ca (in ppm). Calcium as CaCO3 is obtained in ppm by multiplying the titrant value in ml by 10.
v. Magnesium:
Its concentration is known by direct mathematical calculation (in ppm) as Mg.
The formula used is as such:
Magnesium as Mg in ppm = 0.24 * (Total hardness as CaCO3 Calcium as Ca)
Magnesium has ten times the solubility of calcium and being bivalent, it too produces hardness. It is absolutely essential for the chlorophyll bearing bacteria, algae and plants. It is second to calcium in hard water, whereas sodium (Na) becomes second to calcium in soft water. Na is metabolized only by blue green algae but potassium (K) along with magnesium is a necessary requirement for all algae. Under low Mg and K conditions, growth and photosynthesis of algae are poor and respiration is high.
vi. Chloride:
The sudden increase in the concentration of chloride in surface water bodies at abnormally high concentration was previously used as index of pollution through contamination by fecal matters. Human excreta contain chloride equal to the chloride consumed with food and water. Normal human body discharges from 8 to15 g (av 9 g of chloride) a day. Since chloride ions are non-biodegradable, these are not removed from the wastes even after subjecting it to the secondary treatment process. However, it is harmless upto 1500 ppm concentration but produces a salty test at 250-500 ppm level.
Estimation:
100 ml of water sample is taken in white porcelain basin to which 1 ml of 5% potassium chromate solution, as indicator, is added and titrated against standard silver nitrate solution (prepared by dissolving 4.79 g of AgNO3 in one litre). The titrant consumed in ml on multiplying by 10, gives the direct reading for chloride content of water in ppm.
vii. Flouride:
Flouride concentration in water both at levels less than 1.0 ppm and more than 1.5 ppm, are harmful for health. According to UNESCO (1963) and California State Water Pollution Control Board (1952), water containing more than 1.0 to 1.5 ppm of flouride can cause mottled enamel in children and an excess of flouride may eventually cause endemic cumulative flourosis with resultant skeletal damage in both children and adults.
If the flouride concentration in drinking water is less than 0.5 ppm, a high incidence of dental carries is likely to occur. Recent researches by Geological Survey of India have led to the discovery of a natural mineral serpentine which can absorb large quantities of flourides from water and can act as a deflouriding agent with considerable success in the treatment of fluorosis.
Estimation:
50 ml of water sample along with control solutions are taken in different nessler tubes and put on the porcelain based wooden stand. To each of the tubes, 2 ml of zirconium alizarin solution is added. 90 minutes after the addition of reagent, the developed colour is matched with the control solution and accordingly calculated. The colour changes from pink to yellow depending on the concentration of the flouride present in water samples.
viii. Iodine:
About 50 mg of iodine is present in a human body weighing about 70 kg. Probably all the cells of the body contain iodine, but 70 to 80% of total iodine content of the body is concentrated in the thyroid gland alone. When the dietary iodine intake falls below 10 mg/day throxine synthesis becomes, inadequate leading to endemic goitre. Persons suffering from goitre become mentally dull, lethargic and lack motor coordination capacity. Tetraglycine hydroperiodide or galabaline tablets or iodised salt are available in the market for compensating the deficiency of iodine in water and diet.
Estimation:
The method for iodine determination begins with the addition of 1 ml of 5% NaCl solution along with 0.5 ml of 1% of arsenious oxide solution to each of the 10 ml of collected water samples. After thoroughly mixing the content, 1 ml of ceric ammonium sulphate solution (prepared by dissolving 13.38 g of 44 ml conc. H2SO4 and diluted to one litre) is added.
Within 15 minutes, 1 ml of ferrous ammonium sulphate solution (prepared by dissolving 1.5 g in 100 ml distilled water with 4.6 ml of conc. H2SO4) is added till the colour disappears. After one hour, the colour changes from red to yellow, depending on the concentration of iodine present. The control solutions are also run side by side under similar experimental conditions for comparison.
ix. Nitrogen:
The elements, nitrogen and phosphorous, are known as bio- stimulants. Nitrogen is an essential building block element in the synthesis of protein. Therefore, its data are of paramount importance in evaluating the nutritional status of the water bodies. Four forms of nitrogen are present in the sewage and consequently in the receiving aquatic ecosystem. Freshly polluted system, especially by sewage contamination, shows higher concentration of ammonia nitrogen which in an aerobic environment changes to nitrites and then to nitrates.
Barth (1953) calculated that, for the conversion of ammonia into nitrate, 4-5 mg oxygen for one mg ammonia oxidised, would be required. Nitrite nitrogen is relatively unimportant in water pollution studies, because it is unstable and easily oxidised into the nitrate form. Nitrate nitrogen is an indicator of past pollution in the process of stabilization and seldom exceeds 0.1 ppm in surface waters. Nitrate nitrogen as NO3 should not exceed 45 ppm in drinking water, because of its serious and occasionally fatal effects on infant.
High concentration of ammonia nitrogen indicates that the pollution is fresh. With ageing, the concentration of albuminoid nitrogen goes on increasing while free ammonia concentration decreases in more or less the same proportion. 0.01 ppm of free NH3 and 0.1 ppm of albuminoid NH3 concentrations are the maximum allowable limits for water used for public consumption.
Ammonia is one of the major constituents contributing to the toxicity of municipal waters. At high pH free NH3 and its hydrolysis products are toxic in low concentration while at low pH, they are converted into ammonium ions (NH4+1) which are comparatively non-toxic.
Nitrate Nitrogen:
The increasing application of fertilizers in agricultural lands results in water pollution due to the leaching of nutrients like N and P into the drains. The presence of these pollutants only in about 0.3 ppm of nitrate nitrogen concentration and 10 ppb soluble P in water, are needed to support the excessive production of algal blooms and aquatic weeds causing undesirable colour, taste and odour, thereby degrading the aesthetic quality of surface water bodies.
Further, it has been estimated that the nitrate nitrogen content varies from 0.04 to 5.0 ppm in the rivers of the world. A survey of the well waters in low lying areas around Patna, Bihar and elsewhere in India reveals that in certain wells, the nitrate-nitrogen was as high as 240 ppm which is considerably above the WHO limit of 10 ppm nitrate as nitrogen.
Such high amount of nitrogen in well water is enough to produce disease known as methemoglobinemia in infants. 10 ppm of nitrate nitrogen concentrations interact under acidic condition with secondary amine compounds present in the water to produce nitrosoamines which are well known carcinogen. Another serious repercussions of high nitrate nitrogen concentration, is that non-pathogenic bacteria which live freely or in symbiotic association with plants, may get destroyed, resulting in a serious breakdown in the self-purification process of the aquatic ecosystem.
Procedure for Determining Free Ammonia and Albuminoid Ammonia Nitrogen Estimation:
250 ml of water sample is usually distilled off in two different stages for measuring nitrogen in the above explained two forms. Accordingly, 250 ml of water simple is first distilled off at pH higher than 11.0. Such high pH value is achieved by adding 2 pellets of sodium hydroxide (NaOH). The distillation is continued, till 50 ml distillate is obtained (A). Thereafter 50 ml of alkaline potassium permanganate solution is added to the remaining constituents in the distilling flask and the distillation is continued till another 50 ml of distillate is collected in another nessler tube (B).
Both the distillates A and B, along with a series of control samples in separate nessler tubes are arranged on white porcelain based stand. To each of the nessler tubes, 2 ml nessler reagent (K2Hgl4) is added. Nessler reagent is prepared by dissolving 35 g Kl in 100 ml distilled water to which saturated solution of HgCl2 is added. Subsequently, 120 g of NaOH is added, dissolved and diluted to 1 litre. Thereafter, the colour developed is matched with standard solutions. Supposing, if the concentration of ammonia is found to be 0.01 mg in the examined water sample after comparing it with the standard solution of ammonia, the sample examined is 250 ml therefore 1000 ml of water sample will show 0.01 x 4.0 ppm.
4-Hours Oxygen Consumption Test:
This test is used to measure the easily decomposable organic content present in water and waste simples. Mild oxidising agent like potassium permanganate (KMnO4) in acidic medium at 37°C is used to oxidise the organic materials. 125 ml of water sample is taken, to which 25 ml of N/80 potassium permanganate solution is added along with 10 ml of N/2 sulphuric acid. The whole content is kept at 37°C for 4 hours. At the end of the incubation period one spoon of solid potassium iodide (KI) is added and titrated against N/40 sodium thiosulphate (Na2S2O3) solution, using starch as indicator.
The result is calculated as given below:
Where, S is the volume of titrant in ml with sample and C is the volume of titrant in ml consumed in control sample.
x. Bio Chemical Oxygen Demand (BOD):
BOD represents the intensity of bio-degradable matter remaining in the stream at any time and DO (Dissolved oxygen) shows the ability of the stream to purify itself through biochemical process. BOD tests show the amount of molecular oxygen required by bacteria to reduce the carbonaceous materials. It is a bio-assay procedure that measures the oxygen consumed by living organism, while utilizing the organic matter. Bio-chemical oxidation is a slow process and therefore. 20 to 30 days are required for the complete degradation of the waste.
Oxidation is achieved upto 95 to 99% in 5 days in case of glucose, about 65% in case of sewage, while 40 to 50% of the organic matters present in any other industrial waste water samples during the same incubation period. Both, the 20°C incubation temperature, used as an average value for slow moving water bodies in temperature climate and easily reproduce able in an incubator, and the 5 days incubation period, were chosen by British Royal Commission for sewage disposal because none of the rivers in England has a reaching time to the sea of more than 5 days.
Estimation:
For the BOD test to be performed the sample of water from rivers are taken in duplicate without going for any dilution. In case of strong sewage or industrial wastes, the samples drawn are suitably diluted so that the DO present in the sample may not get completely exhausted during incubation period. Dilution is thoroughly aerated and enriched with sewage water nutrients for the microbes.
5 to 10 ml of per litre of diluted water is added as seeding material, prior to subjecting to the process of aeration. After suitably diluting the strong waste water sample in duplicate, one is put under incubator at 20°C for 5 days and the other set is put for DO determination. After the incubation period is over, DO contact in the sample is again estimated. The control sample is also taken to ensure the correct value for BOD.
Finally BOD value is calculated as such:
BOD (ppm) = Depletion in DO (mg) x dilution factor where, the dilution factor is;
sample taken (ml) / % of dilution
xi. Chemical Oxygen Demand (COD):
COD test shows the oxygen equivalent of the organic matter that can be oxidised by using a strong oxidising agents e.g. potassium dichromate in acidic solution, at elevated temperature, for two and half hour Silver sulphate is used as catalyst to oxidise the oxidation resistant organic compounds. In case where BOD test fails, COD succeeds.
For example, when, municipal or industrial waste containing organic compounds that are toxic to biological life produces erroneous BOD results. COD value is in general always higher than that of BOD. The ratio of COD/BOD shows the types of treatment required for the particular waste water sample.
(i) When BOD- COD – 0.6, it means that the waste is rich in putrescible matter. Therefore, the best treatment for such type of waste is biological one.
(ii) When BOD- COD is between 0.3 to 0.6, it means that the waste water requires acclimatization, prior to subjecting it for the biological treatment.
(iii) If and when BOD- COD= 0 3, the chemical treatment is the best for such waste.
Estimation:
COD test is done by adding 20 ml of 0.25 N solution of potassium dichromate along with 75 ml of conc sulphuric acid to 100 ml of waste water sample, in a digestion flask of 250 ml capacity. About 5 g of silver sulphate as catalyst is added to the reaction mixture. The whole set along with reaction mixture is refluxed for two hours. Thereafter, it is cooled under tap water and then titrated against 0.25 N solution of Mohr’s salt (ferrous ammonium sulphate) using 2 to 3 drops of ferroin (prepared by dissolving 1.4 of 1 : 10 phenonthroline monohydiate together with 0.69 g of ferrous sulphate in 100 ml distilled water) solution as indicator, till the end point is reached. A blank sample is also digested in similar experimental condition.
The value of COD is computed in ppm as given below:
(a-b) c x 8000
COD (ppm) = volume of sample (ml)
Where, a = vol. of titrant used (ml) in blank,
B = vol. of titrant used (ml) in sample
O = factor of the titrant
Phosphate as P:
50 ml each of water sample along with a suitable control are taken in a series of nessler tubes. To each of the tube, 2 ml of ammonium molybadate solution prepared by dissolving 25.0 g ammonium molybadate in 175 ml of distilled water (soln. A). In another vessel, 280 ml of conc. H2SO4 is added to 400 ml distilled water (Soln. B). Solutions A and B are then mixed together.
Thereafter, five drops of freshly prepared stannous chloride solution of 2.5% strength are added. The whole content of the tube is mixed, which result in the development of blue colour in water as well as in control sample. The visual colour comparison reveals the concentration of phosphate as (P) in ppm by multiplying with 20.
Silicate as SiO2:
Similar method as that for phosphate estimation is carried oar for silicate estimation in water sample by adding 1.1 HCl and 2.0 ml of ammonium molybadate solution. The whole content is thoroughly mixed and kept for five to ten minutes. Thereafter, 1.5 ml of 10% oxalic acid is added. The yellow colour thus developed, is compared with those of control solutions and accordingly calculated by multiplication with 20. The result is expressed as SiO2 in ppm.
Nitrate as Nitrogen:
To 50 ml of water sample, 2 ml of 30% sodium chloride solution along with 10 ml conc. H2SO4 are added and mixed gently. Brucine reagent (0.5 ml) is then added. The whole reaction mixture is put on water bath for 20 minutes, the colour developed is compared visually with suitable control solution and calculated by multiplying with 20. This gives the valve for nitrate as nitrogen in ppm-
Sulphate as SO4:
100 ml of water sample with not more than 40 ppm of a sulphate is taken in nessler tube. Similarly, a series of control samples is taken in different nessler tubes. To each of the tube, 5 ml of conditioning reagent is prepared by dissolving 76 g NaCl, 30 ml conc. HCl and 100 ml of 95% ethyl or isopropyl alcohol in 300 ml distilled water. After thoroughly mixing the whole content, one spoon (say 200 mg) of barium chloride (BaCl2) crystal is added. The turbidity developed is visually matched with that of the control solution of the sulphate within 5 minutes of the BaCl2 addition.
Bacteriological Parameters for Estimating Water Quality:
i. Most Probable Number (MPN):
MPN count of water samples, drawn from the respective sources is determined by using multi tubes dilution techniques. In the procedure, the Mc Conkey lactose bile salt media are filled up in test tubes of different sizes and sterilized under 15 lbs pressure per square cm at 140 °C for 15 minutes. Thereafter, the tubes are arranged in four to five series, with three tubes in each series, for each sample of water to be examined. To each of this set, water sample is transferred through sterilized pipettes.
Each series contains different volume of original water samples, i e., the three tubes of the first series are inoculated each with 10 ml the second series of three tubes with 1.0 ml each, while 0.1 ml each for the third and so on up to the fifth series by adding 0.01 .ml and 0.001 ml respectively to all the three tubes of fourth and fifth series. Thereafter, all the sets are put at 37 x 2°C for 48+2 hours.
At the end of the incubation period, each tube if examined for gas production in the durhams tube. The tubes having gas production are marked as positive ones and those without gas production are discarded. Numerical values for MPN count present in 100 ml of water sample are enumerated with the help of the already worked out chart, based on the formula developed by Thomas (1942).
Mathematical expression for that formula is given below:
ii. Fecal Coliform Count (FC):
All the positive tubes of MPN count are sub-cultured in duplicate, in brilliant green lactose broth (BGLB) media. One set is put at 37°C for 48 hours and other set at 44 x 0.2°C for 24 hours. The values derived from the former set show the confirmatory number of MPN count/100 ml whereas the latter set shows the numerical values for the fecal coliform counts present in 100 ml of water sample under investigation.
iii. Escherichia Coliform Count (E. Coli):
All positive tubes of either fecal coliform or MPN are further sub cultured in a series of three test tubes of Mc Conkey bile – salt lactose broth and put for incubation at 37°C tor 24 hours. Again, the gas production in each tube is examined. The positive tubes are allowed to proceed for further treatment as –
The turbid inoculum from each of the +ve tube is inoculated through loop of standard size in the Mc Conkey agar plate and put for incubation at 37°C for another 24 hours. At the end of the specified time, the well-developed pinkish, flat and transparent colonies are further inoculated in peptone water and Mc Conkey media. The whole set is again put at 37°C for another 24 hours.
The former, on producing positive reactions with Kovac’s reagent and the latter, showing gas production, are utilized for the numerical assessment of Escherichia coliform count, present in 100 ml of sample under investigation. Kovac’s reagent is prepared by dissolving 5 g para dimethyl amino benzaldehyde in 75 ml of either isoamyl alcohol or absolute alcohol and 150 ml of conc. H2SO4.
iv. Fecal Streptococci Count (FS):
Fecal streptococci count is measured by adopting similar methods as for MPN and other counts, and expressed per 100 ml of water samples. The only difference is the use of non-lactose media in the case of F. streptococci estimation. Therefore, azide dexirose broth (ADB) media are used in the tubes arranged in 4 series of three tubes each. To each of the tube, water sample in different dilution i.e. 1.0, 0.1 and 0.01 ml are inoculated and put at 37°C for 48 hours of period. The tubes showing well marked turbidity are considered as positive tubes.
Further, the positive tubes are subcultured in ethyl violet azide (EVA) media and put to incubation for another, 48 hours at 37 x 2°C. The formation of ring at the bottom of the tube, confirms of fecal streptococci in the sample. The numerical values are ascertained again by using the Thomas chart, as used in evaluation of the MPN and E. coliform counts.