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.