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Sewage Disposal

Sewage Disposal removal of liquid wastes with suspended solid materials generated from human bodies, factories, cooking, recreational activities etc through a network of channels or sewers. Such organised system of refuse disposal is a feature of towns and cities where population density is so high that such a system becomes a public health imperative. In the rural setting, the sewage of individual households is usually disposed of through septic tank which is an underground brick or concrete tank with an outlet for draining the liquid portion of sewage into the soil where it is decomposed by aerobic microorganisms, while the solid portion settling at the bottom of the tank is decomposed anaerobically through the action of anaerobic microbial flora which become permanent resident of that part of the septic tank.

Dhaka, the capital city of Bangladesh generates a huge quantity of sewage everyday. There is no accurate figure on the total volume, but estimation can be made from the quantity of effluent released after final treatment which is discharged every day into the river buriganga. An average day's discharge is about 40,000 cubic meter which is probably, according to popular belief, just about one half to one-third of what the discharge would have been if the collection of sewage were more complete, that is, not lost due to leakage and other impairments in the sewerage system. The sewage treatment plant of the city is located at a place called Pagla. The place is not far from the metropolis and lies at the bank of the river Buriganga which also carries a belt of different types of industries. Thus, the city sewage may have some industrial sewage also discharged into the system.

In Dhaka city, the sewage largely consists of wastewater from toilet because the system was designed so. Kitchen waste-water and water from bathroom uses such as for shower and washing clothes, is usually not discharged into the sewerage system, but instead is carried through surface drains to the disposal sites that are actually low lying areas adjoining the city. The storm sewerage system made to dispose of rainwater is also not linked with the main sewage system although occasional mixing can occur due to leakage and during flooding. The sewage systems of the country's other major cities are basically designed in the manner of the capital city's system although facilities there are admittedly less extensive and are of relatively poor operating standard. [Zia Uddin Ahmed]