A Process for treating a microorganism -containing stream includes the step of passing the stream (12) through a chamber (14), pressurizing the stream (12) in the chamber to a pressure greater than 14.7 p.s.i.g., introducing a feed gas (16) into the pressurized stream (12) such that the feed gas (16) is soluble within the microorganisms, and depressurizing the stream (12) so as to cause the soluablized feed gas (16) to expand within the microorganisms so as to rupture the cell walls of the microorganisms. The feed gas (16) can be carbon dioxide, air, nitrogen, methane of mixtures thereof.
