The purpose of wastewater treatment plants (WWTPs) is to convert raw sewage into acceptable final effluent and to safely dispose of solids removed in the process. The treatment plant should ideally be constructed at minimum capital cost, have economic maintenance and operating costs and be able to provide a reliable service capable of handling design flows. The primary treatment involves physical processes designed to remove floating material and settleable matter of organic and inorganic origin. The objective of primary sedimentation is to remove readily settleable solids and those floating material that escaped the upstream screens. The biological treatment of wastewater significantly reduces the soluble organic matter through microbial-mediated processes. Biological WWTPs have been employed throughout the world in the treatment of municipal wastewater. Despite the fact that they are efficient in removing organics, large amounts of excess sludge are generated.