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.