Direct Solid-Liquid Separation Using Hollow Fiber Membrane in an Activated Sludge Aeration Tank

Direct membrane separation using hollow fibers was applied to wastewater treatment in an activated sludge process. A membrane module with a pore size of 0.1 micron was immersed in the aeration tank and treated water was filtered through the membrane by suction. Various operational modes were applied to investigate stable flux conditions as well as organic and nitrogen removal. The stable treatment with a detention time of 4 hours could be kept for about 120 days at a volumetric organic loading of 1.5 kg COD/(m3 day) using intermittent suction with a low pressure of 13 kPa (1.3 m as water head). The COD removal was higher than 95% and more than 90% of COD supplied was oxidized to keep MLSS almost constant in the reactor without sludge wastage, which suggests that total oxidation of influent biodegradable materials can be achieved in this system. Up to 60% of nitrogen could be denitrified by intermittent aeration. The critical organic loading was estimated as 3 to 4 kg COD/(m3 day) in order to keep both stable flux and aerobic condition. The clogging in the membrane was inevitable to some extent, however, the intermittent suction and low pressure operation without cleaning could prevent the unrecoverable clogging and dead end of operation.