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Activated Sludge Process

Activated Sludge Process is based on the principle that : (i) adequate amount of oxygen or air is passed through sewage containing aerobes. Complete aerobic oxidation occurs, though slowly. However, if this aeration is carried out in the presence of a part of sludge from the previous oxidation process, the oxidation process is much  quickened. This so-added sludge from the previous process is known as activated sludge, since it contains organic matters inhabit­ed by numerous bacteria’s, etc.

sludge treatment

sludge treatment

The process consist in mixing the sedimented sewage with proper quantity of activated sludge and the mixture is sent to the aeration tank in which the mixed liquor is simultaneously aerated and agitated for 4 to 6 hours. During this aeration process, oxidation of the suspended organic matter takes place. First, oxida­tion of the carbon takes place, followed by that of nitrogen to nitrites and nitrates. After aeration, the effluents is sent to settling or sedimentation tank, where sludge is deposited and clean and non- putrefying liquid (practically free from bacteria3, etc.) is drawn off. A part of the settled sludge is sent back for seeding fresh batch of sewage ; while the remainder is disposed off either by : (i) sea burial (i.e., dumping in sea) or (b) land spreading (i.e., spreading uni­formly over soil followed by ploughing in) or (c) digestion. In this sludge is kept in a closed tank in the absence of air for a prolonged period (about 30 days), when it suffers anaerobic decomposition yielding gases like methane (about 60%), hydrogen sulphide, ammonium sulphide and phosphine. The gas can be used as fuel either for city supply or power generation. Between 400-600 litres of gas are produced from each kg of solid sludge.

Sludge treatment

Sludge treatment

 

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