ABSTRACT
In conventional methods of wastewater treatment such as activated sludge and trickling filter processes, large volumes of primary sludge is produced in addition to the excess settled secondary sludge. In case of the activated sludge process, the secondary sludge is mainly the microbial biomass produced by the metabolism of the organic material. The microbial yield on settled sewage is about 50 per cent. The principal end products of raw water and wastewater treatment consist of: product water, treatment-plant effluent, and by-product slurry or sludge. The treatment and disposal of sludge is perhaps the most complex problem faced by an environmental engineer in the field. The solids from the sludge are the waste solids derived from the treatment process in which they originate. The large-scale incineration of sludges is an expensive alternative due to high capital costs, and is only a partial disposal option as the ash formed creates further disposal problem.
