a disc filtration system comprises a filter element containing microporous plastic discs through which liquid effluent such as wastewater is passed for filtration . the filter disc surface material contains an anti - bacterial agent exposed to the liquid being filtered for inhibiting growth of microorganisms on the exterior of the filter element . the exposure to the anti - bacterial agent inhibits microorganism growth to an extent that prolongs the useful operational filtration cycle life of the filter between backwashing cycles . the invention applies to disc filters having automatic backwashing and manually operated disc - type filters .