Examination of water

Examination of Water | Physical, Chemical, Biological Test of Water

In this article, we will discuss the examination of water.

 

  1. Introduction  

The examination of water is also known as water analysis which is done in a systematic manner to identify the water quality or the presence of impurities in water. The water analysis or examination is conducted for various purposes as listed below.

a. To ascertain the quality of water and quantity of various impurities.

b. To verify the treated water quality is as per standard or not.

c. To identify the dose of chlorine, coagulant, etc in treatment plants

d. To prescribe the degree of treatment for the required water quality

 

Sampling techniques of water:

1. Fully cleaned bottles or buckets or jerricans can be used for the physical tests but the container should be greater than the capacity of 2 liters for biological and chemical tests.

2. Container should be rinsed before sampling.

3. Sample should be well shaken before the test so certain air in the container should be remain.

4. Tap should be let open for two to three minutes to avoid stagnant water during the sample collection from distribution lines.

5. When the sample is taken from a well with a hand pump, pump water for about 5 minutes then collect it into the clean and sterilize container. If there is no hand pump, take the well water directly from the well.

6. When sample collection is from a river; reservoir, lake, a water sample should be taken from below 40 to 50 cm below the surface and it should not be so far or near the draw-off site.

7. Sample should be tested within 1 hour of sample collection in case of microbiological test, if it is not possible to sample should be kept in ice-chest or in cooler till 24 hours.

 

  1.1. Physical Examination of Water  

The physical examination of water is done in 3 ways.

a. Temperature

The temperature of the water is determined by ordinary thermometers. The temperature of surface water is equivalent to the atmosphere whereas that of groundwater may be slightly more or less than that of atmospheric temperature.

The temperature of the water has an effect on the physical properties of water such as density, viscosity, surface tension, saturation value of gases dissolved in water, biological activity. For public water supply, it should be between 10 °C to 15.6 °C. Temperature greater than 25 t is undesirable and above 35 °C is unfit for public water supply.

 

b. Colour

Pure water is colorless, but water in nature is often a closed foreign substance. It is measured by the ability of the solution to absorb light. Water having partly color due to suspended matter is said to have apparent color.

Colour contributed by dissolved solids that remain after removal of suspended matter is known as true color. While the true color in water is due to dissolved materials only. The organic compounds casing true color may exert a chlorine demand thereby seriously reducing the effectiveness of chlorine as a disinfectant. Color is measured by a tonometer. The intensity of the color is measured on a platinum cobalt scale. One milligram of potassium plus half a milligram of metallic cobalt is dissolved in 1 liter of distilled water is one true color unit. Colored water is aesthetically objectionable for drinking purposes.

For drinking watercolor should not be greater than 5 ppm in the platinum cobalt scale. Greater than 5 is tolerable but rejected greater than that 25 ppm in platinum cobalt scale.

1 platinum cobalt scale = 1 ppm = 1mg/lit

 

c. Turbidity

Turbidity is a measure of the extent to which light is either absorbed or scattered by suspended material in water. Absorption and scattering are influenced by both size and surface characteristics of the suspended material; turbidity is not a direct quantitative measurement of suspended solids. For example, one small pebble in a glass of water would produce virtually no turbidity.

If this pebble gets crushed into thousands of particles of colloidal size, measurable turbidity would result. Turbidity is measured photometrically by determining the percentage of light of a given intensity that is either absorbed or scattered.

The original measuring apparatus called a Jackson turbidity meter was based on light absorption and employed a long tube and standardized candle. The glass tube was calibrated with readings of one JTU being equal to the turbidity produced by 1 mg SiO2, in 1 liter of distilled water. Turbidity of 5[ppm is accepted and rejected if it is greater than 10 NTU.

 

Read More: Sedimentation in Water Treatment

 

  1.2. Chemical examination of water  

The chemical examination of water involves the tests which are undertaken to determine the chemical impurities and the corresponding chemical characteristics of water.

Total Solid

The solids present in water may be either dissolved or suspended solids and sum of these suspended and dissolved solids is total solids. The solids present in water is generally expressed in ppm or mg/lit.

The water sample when ket into the oven for evaporation at 103 ºC -105 ºC for 24 hrs obtained residue is total solids. Further obtained if ignited in a muffle furnace at 600 ºCfor 15-20 minutes, volatile solids escape out and obtained Is fixed or inorganic solid.

Examination of water

 

PH

It is the symbol for the logarithm of the reciprocal of hydrogen ion concentration in gram atoms per liter, used to express the acidity or alkalinity of a solution on a scale of 0 to 1, where less than 7 represents acidity, 7 neutrality, and more than 7 alkalinities. It is determined by electrometric and colorimetric methods. The value of pH drinking water is 6.5 to 8.5.

 

Read More: Water Treatment Process

 

  1.3. Biological examination of water  

Pathogenic bacteria are difficult to detect because of their presence in small numbers. Even in polluted water their present infrequently or at irregular intervals. Hence analysis of pat water for all the known pathogens would be a very time-consuming and expensive proposition.

Test For specific pathogens is usually made only when there are reasons to suspect that particular organism is present. At other times, the purity of water is checked using an indicator organism. An indicator organism is one whose presence Presumes that contamination has occurred and suggests the nature and extent of the contaminant.

Generally, both harmful and harmless bacteria occur together in water, and difficult to detect pathogenic bacteria because their presence may be irregular and less in numbers even in polluted water. Non-pathogenic bacteria (E-coli) are largely found in the large intestine of humans and all and are execrated with their feces.

The evidence of the presence of pathogenic bacteria is indirectly obtained by testing those coliforms are called indicator organisms. The absence of E-coli almost justifies the assumption that the fecal polluted water is free from pathogens.

Escherichia coli (E-coli) is the coil from bacteria that inhabit the intestine of human beings and animals and arc thus excreted in large amounts with their feces. As such the water which has been contaminated with sewage will contain E-coli bacteria. For detecting the presence of bacteria of the coliform group and measuring their concentration in water the following methods are adopted.

 

a) Total count or agar plate count test

It is also known as standard plate count. In this method, 1 ml of a water sample is diluted in 99 ml of sterilized/distilled water and diluted 1 ml water is mixed with 10 ml of agar gelatin (a culture medium used to cultivate bacteria) and incubated at 37 °C for 24 hrs or 48 hrs at 20 °C. The bacterial colonies which are formed, are then counted and the results are computed per 100m1. For drinking water the total count should not exceed 1 per 100 ml.

 

b) Multiple tube fermentation technique/E-coli tests

This test is divided into the following parts;

i) Presumptive test

ii) Conform test

iii) Completed test

i) Presumptive test

The presumptive test is based on the ability of the coliform group to ferment the lactose broth and produce gas.

Procedure: (1) Definite amount of diluted samples of water are taken in multiples of 10, such as 0.1 ml, 1.0 ml, 10 ml etc.

(2) The water sample is placed in standard fermentation tubes containing lactose broth which is incubated at a temperature of 37 °C for a period of 48 hrs. If gas is seen in the tube after this period, it indicates the presence of E-coli group, and the result of the test is positive. If no gas is seen, it indicates the absence of the E-coli group, and the result of text is treated as -ve.

 

Conformed test

The conformed test consists of growing cultures of coliform bacteria as media that suppress the growth of other organisms. The gas produced in the presumptive test does not confirm the presence of bacteria in the coliform group because there may be other bacteria present which also ferments lactose.

so a portion of water from the presumptive test is taken and placed in another fermentation tube containing brilliant green lactose bile as a culture medium. It is brilliant green lactose again kept in an incubator at 37 °C for 48 hrs, the evolution of gas in these tubes would confirm the presence of the organisms of the coliform group and vice-versa. Colonies of bacteria indicate the presence of E-coli and a completed test is necessary.

 

iii) Completed test

This test is based on the ability of the culture grown in the conformed test to again ferment the lactose broth. Colonies of bacteria grown in the conformed test are kept into lactose broth fermentation tubes and agar tubes. The tubes are kept for incubation at 37 °C for 24 hrs to 48 hrs.

If gas is seen in tubes, it indicates the presence of E-coli group, and the result of the test is treated as positive and further detailed tests are carried out to detect the type of bacteria present in water. Again the absence of gas indicates negative results and water is safe for drinking.

 

c) Membrane filter technique

The bacteria present in water are retained on the membrane having microscopic pores. The membrane with the bacteria is then put in contact with a suitable nutrient (M-Endo’s medium) which inhabits the growth of bacteria other than the coliform group.

It is then placed in an incubator at 37 °C for a period of 20 hrs. The bacteria of the coliform group if present in water are developed into visible colonies which can be counted with the help of a microscope.

coliform colony/100 ml = (colony counted/ ml of sample) x100