Question

Write a short essay on sewage removal in modern human settlements​

Answer 1

Answer:

In most parts of the world, increases in population, the use of huge quantities of fertilizers and pesticides in modem agriculture, the expansion of food processing industry and the growth of other industrial processes contribute to the volume of sewage and waste water.

Therefore wastewater treatment attempts to remove compounds with a high BOD, pathogenic organisms and harmful chemicals.

The wastewater treatment is done as follows:

Primary Treatment:

Primary processing is done to remove solids and large objects by passing the wastewater through a series of screens. Rapidly sedimentable solid particles (‘grit’) then settle out during flow through a grit chamber. The effluent is then allowed to settle in a sedimentation tank (Fig. 9.1). Primary treatment removes about 60% of settleable solids and about 35% of oxygen-demanding waste. In other words, it results in 35% reduction in BOD.

Secondary Treatment:

Secondary processing is required to degrade the dissolved organic compounds. This is effected by natural aerobic microorganisms. The resulting sludge is either disposed of or sent to a digester. In the activated sludge process, some is returned to the aeration tank (Fig. 9.1). At the end of the secondary treatment the strength of the effluent is reduced to 30 : 20 (i.e., suspended solids 30 mg per litre and BOD 20 mg per litre), which can be discharged into water sources. However, major part of the nitrogen and phosphorus compounds still remains in the effluent.

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