Simultaneous Removal of BOD and Nitrogen with Anoxic/Oxic Porous Biomass Support Systems

Abstract

To protect the public water, there is a growing demand to treat domestic gray water as well as night soil using onsite wastewater treatment systems (OWTS) in Japan. Therefore, to meet this demand, we seek the potential of the technology of the system with porous biomass support particles (BSP) using large number of small, open-cell foam pads to support high concentration of biomass in an aeration tank. From aneconomic point of view, durability of pads is an important factor of this process. Polyurethane foam with certain physical characteristics was chosen for pads. To attain simultaneous removal of BOD and nitrogen in an aeration tank, optimum pore size and pads dimensions were chosen in terms of diffusion. To aim for steady and further removal of nitrogen with biomass both on BSP and in suspension, we applied intermittent anoxic/oxic porous biomass support systems process to a full-scale field test, operated in the manner of 1.5 hours aeration and subsequent 0.5 hours agitation. For 330 days of the experiment, less than 20 mg/L and 15 mg/L of effluent BOD and nitrogen are achieved regardless of water temperature between 13 and 31 degrees centigrade.