Biological Water Pollution

Biological Water Pollution

	Biological Water Pollution It develops from the microorganisms that enter waters from such sources as human waste, food operations, meat packing plants and medical facilities etc. Under normal conditions, the water body is able to handle biological material, because heterotrophs digest the organic matter to simple phosphates, nitrates and sulphates which fertilise the plants. Carbohydrates are converted to CO2 and water, which are also useful to plants. The plants then release °2 through photosynthesis. Due to rapid movement of water, aeration is more or less constant and the wastes eliminated.
However, there arises the problem when water becomes stagnant or is overloaded with waste. Water is now unable to handle the biological material, and it soon becomes polluted. We have already seen how a lake may turn into a swamp due to overabundance of organic matter. A critical factor operating under such a situation is the biological oxygen demand (BOD). It refers to the oxygen requirement by the metabolising organisms. As the number of organisms increases, the demand for O2 increases proportionally. Depletion of O2 in water may lead to death of fish and other aquatic animals, a flat taste of water, and eventual death of aerobes.
The BOD is therefore an important indication of the levels of biological pollution in the water. In laboratory, BOD is determined by measuring the amount of dissolved oxygen in test samples of water distributed to BOD bottles. Initial determination of dissolved oxygen in sample is made. The bottles are then stoppered and incubated at 20°C for five days, after which the amount of dissolved oxygen is again determined. The difference in the oxygen content represents the amount of oxygen used up in the test sample, which is the BOD. Results are expressed as parts per million (ppm). A BOD of several hundred is taken usually high.

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