A Novel Liquid-Solid Circulating Fluidized-Bed Bioreactor for Biological Nutrient Removal from Municipal Wastewater

Biological nutrient removal (BNR) using a novel liquid-solid circulating fluidized-bed (LSCFB) bioreactor was assessed with and without particle recirculation. The LSCFB employs attached microbial films for the biodegradation of both organics and nutrients within a single circulating fluidized-bed unit. This new technology combines the more compact and efficient fixed-film process with the BNR process that provides the additional removal of nitrogen and phosphorous. A lab-scale LSCFB was demonstrated to treat degritted municipal wastewater (MWW), operated at an empty-bed contact time of 0.82 h. The system removed 94, 80 and 65 % of organic (chemical oxygen demand, COD), nitrogen (N), and phosphorous (P), respectively, without particle recirculation, whereas with particle recirculation the system removed excess phosphorus and achieved overall removal efficiencies of 91, 78 and 85 % for C, N, and P, respectively. The system generated effluent characterized by <5 mg biological oxygen demand/L, <5 mg total suspended solids/L, <1 mg NH4-N/L, <7 mg total nitrogen/L, and <1 mg PO4-P/L. Combination of nitrification, denitrification and enhanced biological phosphorus removal in one unit saves space, reduces energy consumption, and also produces less sludge at approximately 0.12-0.13 g volatile suspended solids/g COD consumed. Excellent lab-scale results led to the establishment of a pilot-scale LSCFB for MWW treatment at a capacity of 5000 L/day. Initial results of the pilot-study showed a similar trend in BNR as observed in the lab-study.