Abstract: The separation of fungal suspension Trichoderma reesei was studied by using cross-flow filtration(CFF)with re-versed-flow cleaning(RFC)technique.The advantage of this technique is demonstrated in comparison with other filtra-tion techniques.The filtration rate is influenced by different frequencies of RFC.For optimum combination of CFF andRFC,both experimental and theoretical considerations are necessary and are discussed.An expression has been derivedfor the optimum filtration time needed to maximize the flux for a given RFC period assuming that the filtration stage canbe approximated by Ruth’s equation.The practical usefulness of this calculation is demonstrated on a batch thickening op-eration.