Volumetric methods of testing water

With reference to "Standard Methods of Testing Water", some simple small scale laboratory testing procedures can be adopted for approximate estimation of quality of water, 12 analysis are suitable for describing the water or other water sources which are contaminated with pollutants. These testing operations cannot give as accurate as those of the experiments done by the analytical instruments like UV spectrophotometer, HPLC (High Performance Liquid Chromatography), linked with computer and electronic processor system.
The list of test are used in a way to find out the results on general basis and requires the concepts of concentration calculation and standard solutions preparation.

List of tests:

  1. Total residual chlorine
  2. Chlorides
  3. Total Hardness
  4. Calcium
  5. Magnesium
  6. Alkalinity
  7. Free Carbon dioxide
  8. Sulphites
  9. Sulphates
  10. Dissolved Oxygen
  11. Chemical Oxygen Demand
  12. Biochemical Oxygen Demand


Testing procedures

1) Total residual chlorine determination:


The residual chlorine content of an effluent sample is likely to decrease after collection, especially in hot weather. Hence the test for residual chlorine should preferably be done on the spot where the sample is collected, if the sample contains suspended matters, allows a portion to stand for 15 min and test the supernatant.

Iodometric method:

Principle: Chlorine liberates iodine from potassium iodide which is titrated against std sodium thiosulphate solution. The method is suitable for residual chlorine content between 1 and 10mg/l.
Nitrites, ferric and manganic compounds interfere with this test. When these are present, the titration should preferably be carried out within the pH range 4.5 to 8.0 when the results approximate to the true chlorine equivalent. It shall, however, be stated whether the titrated was made in acid solution or not.

Reagents

  • Dil Sulphuric acid - 4N
  • Potassium iodide solution – 10 percent w/v
  • Acetic acid – glacial.
  • Std potassium hydrogen iodate sol – 0.005N dissolve 0.1625g of potassium hydrogen iodate dried at 105oC in water and make it to 1 lit.
  • Std sodium thiosulphate sol – 0.005N dissolve 1.241g of sodium thiosulphate in freshly boiled and cooled water and make up to 1 lit add 5ml of chloroform or 0.4g sodium hydroxide per liter as a preservative.
  • Starch indicator – triturate 5g of starch and 0.01g of mercuric iodide with 30ml of cold water and slowly pour it with stirring into 1 lit of boiling water. Boil for 3 min. allow the solution to cool and decant the supernatant clear liquid.

Procedure:

Take 500ml of the sample. If the total alkalinity of the sample exceed 400mg/l add sufficient dilute Sulphuric acid to reduce the alkalinity to this value then add 5ml of potassium iodide solution and 5ml of acetic acid. Mix and at once titrate with std sodium thiosulphate solution until the color of iodine is nearly discharged. Add 2ml of starch indicator solution and continue the titration until the blue colour disappears for at least 30 sec.

Calculation:

Total residual chlorine, mg/l = 0.1773×1000×v/500
Where v = volume in ml of std sodium thiosulphate sol required for the titration.

Analysis of particle size of suspended solids:


The particle size of suspended solids is determined by wet screening of the freshly drawn sample through the specified sieve. Since the suspended solids in the sample are likely to coalesce keeping, the test should be carried out on the spot. Leaves, twigs and other wind-blown debris, which are extraneous to the sample, should be removed.

Apparatus :
  • Sieve: 850micron sieve
  • Enamelled pail: of diameter slightly bigger than that of the sieve
Procedure: 

Hold the sieve in one hand and with the other pour gently on the mesh surface of the sieve one liter of well-mixed sample. Pour the sample in such a way that it covers the entire mesh surface. If necessary create a vibration while sieving the sample by a gentle rocking motion of the hand holding the sieve. Fill the enamelled pail with fresh water. Then holding the screen on opposite sides with the two hands bring it to the surface of water in the enamelled pail and wet screen by jigging(up and down motion) . Take care to see that while jigging the sieve is dipped in the water only to half its depth and there is no overflow from the mesh through the sides as suspended solids would be washed out without passing through the screen. If necessary wash the material on the screen with a fine jet of water from a wash-bottle until all lodged particles are loosened.
The suspended matter shall be considered passing through the sieve only if no residue is left on it.

Estimation and determination of Phenolic compounds:

General : The phenols are first isolated by distillation under acidic conditions and then determined either by the aminoantipyrine method or bromination method depending upon the quantity of phenol present
Isolation of Phenols:

Apparatus :
  • Distillation apparatus: all glass assembly with 1-liter distillation flask and preferably, Graham condenser.
  • Separating funnel: with ground glass stoppers
Reagents
  • Copper sulphate solution= 10 percent w/v
  • Phosphoric acid= 1:10 v/v
  • Methyl orange indicator= dissolve 0.01 g of methyl orange in 100 ml of water
  • Sodium chloride
  • Chloroform
  • Sodium hydroxide solution= approximately 1N
Procedure:

To 500 ml of the sample add 5.0ml of copper sulphate solution and acidify to pH less than 4.0 with phosphoric acid, using methyl orange as indicator. Omit this treatment in the case of samples preserved by addition of copper sulphate and phosporic acid. Transfer to distillation apparatus and distill until about 450ml of the distillate is collected. Stop distillation and when boiling ceases add 50 ml of water to the distillation flask. Continue distillation operation until a total of 500 ml has been collected.

Acidify the distillate with 1 ml of phosphoric acid and add 5 ml of copper sulphate solution. Transfer to a separating funnel and add 150 grams of sodium chloride. Extract thrice with chloroform, using 50ml of chloroform for each extraction. Take care that all the sodium chloride goes into solution during the first extraction. Combine the chloroform extracts and discard the aqueous layer. Extract the phenols from the chloroform portion with two successive 75 ml quantities of sodium hydroxide solution. Dilute the combined alkaline extracts to 250 ml with water. Heat on a water bath until the chloroform is driven off completely and dilute with water to 500ml.
Note: when phenol concentration in the sample is know to be high, distill a smaller volume, but collect about 450 ml of distillate by adding water to the sample in the distillation flask towards the end and continuing the distillation as above, preferably use a smaller capacity flask for distillation when the volume taken is small.