Abstract: A process is provided for sterilizing or pasturizing aqueous fluids by contacting the aqueous fluid with a permeable membrane to separate the fluid into a serum and a residue, separating the serum into two portions, the pH of the first portion is increased and the pH of the second is decreased. The second portion of serum is combined with the residue, maintained at an elevated temperature to reduce the concentration of microbial cells, and combined with the first portion of serum to reconstitute the flowable fluid with a reduced concentration of viable cells.