Short essay on different aspects of Water Pollution

Biological Oxygen Demand (BOD)

1. Biological Oxygen Demand is an important indication of the amount of organic mattet present in the sewage.

2. Biochemical oxygen demand represents the quantity of oxygen required by bacteria and other microorganism during the biochemical degradation and transformation of organic matter present in wastewater under aerobic conditions.

3. Biological Oxygen Demand Test: The Biological Oxygen Demand test essentially consists of measurement of dissolved oxygen. Content of the sample, before and after incubation at 20°C for 5 days if the sample does not contain any oxygen, it is supplied with oxygen and depletion caused is calculated as the measure of BOD. While carrying out the BOD test, microbial organism (called “seed”) may also have to be provided if necessary.

4. The BOD is usually expressed as mg/1 (5 days at 20°C)

Determination: The determination of BOD of a sewage sample is as follows:

BOD₅ at 20°C (in mg/1) = (D,-D₂) x f. where D, = D₀ of diluted sewage sample before incubation mg/1 D₂= D₀ of diluted sewage sample after 5 days incubation at 20°C mg/l|

f = Dilution factor (Vol. of diluted sample/ Vol. of undiluted sewage sample) Dilution of sewage is carried out by pure aerated water.

Importance

1. BOD test is a very valuable test in the analysis of sewage, industrial effluents and grossly polluted waters.

2. It is best test for assessing the organic pollution.

3. It is best for assessing the organic pollution.

4. It gives valuable information regarding the purification capacity of streams.

Chemical Oxygen Demand (COD)

1. Chemical Oxygen Demand is another index of pollution, which measures the effect of pollution on dissolved oxygen (DO).

2. It gives the amount of oxygen required for chemical oxidation of organic matter, present in the sewage.

Significance of COD over the BOD

1. It takes only 3 hours while BOD takes 5 days.

2. Industrial wastes do not respond to BOD test, so COD test is a must.

3. COD value is not affected by the presence of toxins and other unfavourable conditions for the growth of microorganisms.

Other importance

1. COD values are taken as basic for calculation of efficiency of treatment plants.

2. COD is very important parameter in management and design of the treatment plants.

Limitations

1. Some organic materials like benzene, pyridine and few other cyclic organic compounds do not get oxide by this test.

2. COD test does not differentiate between bio-inert and biodegradable materials.

3. It does not indicate the rate at which the biologically ox disable material stabilize.

Dissolved Oxygen (DO)

Oxygen is one of the most common dissolved gases in water. Oxygen can become dissolved in water in three ways-

(i) It enters the water directly from the atmosphere.

(ii) It is introduced into the water by algae through photosynthesis.

(iii) It is introduced by mechanical equipment.

1. The solubility of atmospheric oxygen in fresh waters ranges from 14.6 mg/1 at 0°C to) about 7mg/l at 35°C under 1 atmospheric pressure.

2. The solubility of Oxygen is directly proportional to the pressure and inversely proportional to the temperature.

Significance

(1) Dissolved Oxygen content in water is generally determined by the Winkler’s meth which is an oxidation-reduction process.

(2) The measurement of (DO) gives a ready assessment of purity of water.

(3) The determination of (DO) content is also essential for maintaining aerobic conditions in the receiving water and also in the aerobic treatment of sewage and industrial was water.

(4) The determination of DO is the basis of BOD test, which is used to evaluate the! Pollution strength of wastewater

(5) Another important area in which DO determinations serve as the means of control is the control of river/ stream pollution. DO is absolutely vital for the support of fish and other aquatic life in water bodies.