Pumped flow biofilm reactors (PFBR) for treating municipal wastewater

A novel laboratory bench-scale sequencing batch biofilm reactor ( SBBR) system was developed for the treatment of synthetic domestic strength wastewater, comprising two side-by-side 18 l reactor tanks, each containing a plastic biofilm media module. Aerobic and anoxic conditions in the biofilms were effected by intermittent alternate pumping of wastewater between the two reactors. With a media surface area loading rate of 4.2 g chemical oxygen demand ( COD) m(2). d, the average influent COD, total nitrogen ( TN) and ammonium- nitrogen ( NH4- N) concentrations of 1021 mg l, 97 mg l and 54 mg l, respectively, reduced to average effluent concentrations of 72mg COD l, 17.8mg TN l, and 5.5mg NH4- N l. Using a similar alternating biofilm exposure arrangement, a 16 person equivalent pilot ( PE) plant was constructed at a local village treatment works to remove organic carbon from highly variable settled municipal wastewater and comprised two reactors, one positioned above the other, each containing a module of cross-flow plastic media with a surface area of 100m(2). Two different pumping sequences ( PS) in the aerobic phase were examined where the average influent COD concentrations were 220 and 237 mg l for PS1 and PS2, respectively, and the final average effluent COD was consistently less than 125 mg l - the European Urban Wastewater Treatment Directive limit - with the best performance occurring in PS1. Nitrification was evident during both PS1 and PS2 studies. A 300 PE package treatment plant was designed based on the bench-scale and pilot-scale studies, located at a local wastewater treatment works and treated municipal influent with average COD, suspended solids ( SS) and TN concentrations of 295, 183 and 15 mg l, respectively resulting in average effluent concentrations of 67mgCOD l, 17mg SS l and 9mg TN l. The SBBR systems performed well, and were simple to construct and operate.