In the activated sludge process, between the aeration tank and the final clarifier, offline microscreening is introduced to separate activated sludge and purified water. The intention is to reduce the drifting of activated sludge from the aeration tank into the final clarifier. Sludge drifting usually occurs during wet weather flow loading of the treatment facility and can cause higher concentrations of ammonia and suspended solids in the effluent. Laboratory and half-technical scale experiments demonstrate that microscreening is suitable for this application. It is expected that the operational stability of activated sludge processes could be improved significantly by this process modification.