Learn about the comparison between Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) by microorganisms and organic matter present in water.
Comparison # Biological Oxygen Demand (BOD):
1. It may be defined as the amount of oxygen used for biochemical oxidation by microorganisms in a unit volume of water. This test has been developed for five days at 20°C.
2. As BOD value approximates the amount of oxidizable organic matter, it is therefore, used as a measure of degree of water pollution and waste strength.
3. BOD values have been useful in process design and loading calculations, measure of treatment efficiency and operation, stream pollution control and in evaluating self-purification capacity of a stream.
4. Types of microorganisms, pH presence of toxins, some reduced mineral matter and nitrification process have been the important factors that influence the BOD test.
Comparison # Chemical Oxygen Demand (COD):
1. It may be defined as the amount of oxygen required by organic matter in a sample of water for its oxidation by a strong chemical oxidant, and is expressed as ppm of oxygen taken from a solution of potassium dichromate in two hours.
2. This value has been a poor measure of strength of organic matter as oxygen also get consumed in the oxidation of inorganic matter such as nitrates, sulphates, reduced metal ions, and also that some organic materials like benzene, pyridine and few other cyclic organic compounds do not get oxidized by this test.
3. It has been a very important parameter in management and design of the treatment plants due to its rapidity in determination. Values are taken as basis for calculation of efficiency of treatment plants and also figure in the standards for discharging industrial domestic effluents in various kinds of waters.
4. Presence of toxins and other such unfavourable conditions for the growth of microorganisms are not able to effect COD values.