Baffled Bioreactor for Municipal Wastewater Treatment

A novel wastewater treatment configuration-the Baffled Bioreactor (BBR)-was tested for municipal wastewater treatment at pilot-scale. This patented BBR is characterized by a hydraulically driven sludge recycling mechanism in the aerobic zone that eliminates the need for sludge return from a final clarifier, which significantly reduces the overall maintenance needs. Throughout 2009, a pilot-scale BBR with a total effective volume of 8.1 m(3) (2,153 gallons) was operated at the Southeast Wastewater Treatment Plant in Rolla, Missouri. An annual average mixed-liquor suspended-solids (MLSS) concentration of 3.2 g/L was maintained in the aerobic zone without a return pump. During the summer, the treatment capacity reached 37.9 m(3)/d (10,000 gpd), with average effluent concentrations of BOD5, SS, and NH4+-N of lower than 10 mg/L, 10 mg/L, and 1 mg/L, respectively. At 37.9 m(3)/d (10,000 gpd), the total hydraulic retention time in the anoxic and aerobic zones was approximately 4.5 h. However, a significant reduction of biological activity was observed in winter in the above-grade system. At a water temperature in the range of 8-10 degrees C, the treatment capacity decreased to 11.4-15.1 m(3)/d (3,000-4,000 gpd), with average effluent concentrations of BOD5, SS, and NH4+-N of 8.8 mg/L, 10.8 mg/L, and 4.2 mg/L, respectively. An anoxic selector significantly improved the sludge settling characteristics in summer and fall, thereby increasing the total MLSS in the BBR. This research demonstrates that this patented BBR technology can effectively remove BOD, SS, and nitrogen throughout the year with minimal maintenance requirements. DOI: 10.1061/(ASCE)EE.1943-7870.0000410. (C) 2012 American Society of Civil Engineers.