Anoxic phosphorous uptake in circulating fluidized bed bioreactor

In this study, biological phosphorous removal in circulating fluidized bed bioreactor (CFBBR) using real municipal wastewater as feed with two entirely separate aerobic and anoxic beds was investigated. With an average influent total phosphorous concentration of 4.6 mg/L, the system achieved average effluent total phosphorous concentration of 1.4 mg/L, translating into 70% total phosphorous removal at a total hydraulic retention time (HRT) of 2.0 hours over a temperature range of 20 °C to 25 °C. P concentration in the biomass was determined at 4 - 5 % of volatile suspended solids (by wt). In addition, the system consistently achieved effluent TSS, BOD₅, NH₄-N, and NO₃-N concentrations of <10, <, 1, and 4-6 mg/l respectively. This phosphorous removal was achieved without recirculation of bioparticles between anoxic and aerobic beds. The presence of phosphorous accumulating organisms (PAOs) and denitrifying phosphorous accumulating organisms (DPAOs) was confirmed by carrying out various batch tests on attached and detached biomass from anoxic and aerobic bed. The tests confirmed P uptake under anoxic condition in the presence of nitrate. Phosphorous release was observed only after nitrates dropped to <1 mg/L. Under anaerobic conditions, 0.16 mg of PO₄-P was released per mg of COD consumed on an average, whereas after addition of nitrates, P uptake was 0.31 mg PO₄-P per mg of NO₃-N consumed on an average. The detachment rate coefficients (b_s) of PAOs in aerobic and anoxic biofilm were 0.1-0.11 d ^-1, and 0.17-0.19 d^-1, respectively.