A Biomethanation Plant comprising of desuldge means as herein described desuldge loops providing at the bottom in each compartment, said means having holes on rooftop for monitoring level of sludge, means are provided for improving gaseration efficiency, a digester having multi compartment for multistage biodegradation with additional stream controllers between partition walls, said stream controllers having opening at the bottom, a spent wash feed means provided with valves on branch pipe lines on roof top with cleaning mechanism, a complete liquid mixing means provided, a gas pressure releaser installed on roof top with cleaning mechanis, a complete liquid mixing means provided, a gas pressure releaser installed on rooftop near gas dome for releasing high pressure inside digester.