Patent ID: 7560027

Claim:
A method for treating a wastewater comprising: (a) treating a wastewater biologically in a biological treatment tank; (b) separating a solid from a liquid in the wastewater treated biologically from step (a), to obtain a treated wastewater and a sludge; (c) withdrawing a portion of the sludge from step (b) to obtain a withdrawn sludge; (d) treating the withdrawn sludge from step (c) by an alkali-treatment to reduce the volume of the sludge; (e) biologically solubilizing and decomposing the withdrawn sludge from step (d), under an anaerobic, an anoxic or a microaerophilic condition and in the presence of a sludge decomposing microorganism to produce a solubilized sludge; and (f) returning the solubilized sludge from step (e) to the biological treatment tank of step (a).