a method for the physical and biological treatment of an organic effluent , which is decomposed by microorganisms in a biological treatment zone , includes recovering a fraction of the biomass derived from the biological treatment , filling a compression reservoir with the biomass fraction , isolating the compression reservoir , and subjecting the filled compression reservoir to a very high pressure so to destroy or damage the microorganisms in the biomass fraction . thereafter , the compression reservoir is returned to atmospheric pressure and the treated biomass fraction is reinjected into the biological treatment zone or into another biological treatment zone .