Simultaneous removal of phosphorus and nitrogen from sewage using a novel combo system of fluidized bed reactor–membrane bioreactor (FBR–MBR)

A FBR–MBR combo system was designed as a novel approach for simultaneous phosphorus and nitrogen removal from sewage. The combo system was evaluated more than 7 months under variable pH (7.5–9.5), hydraulic retention times (HRT = 2–10 h), intermittent aeration cycles (IAC) (on/off = 60/60–15/45 min) and sludge retention times (SRT = 10–60 d). Prior recovery of phosphorus as struvite in the FBR enhanced nitrogen and COD removal efficiency in MBR. Under optimum operating conditions (pH = 9, HRT = 6 h and IAC = 45/15 min), PO43−–P, NH4+–N and COD removal efficiencies were 92.6 ± 4.2, 98.7 ± 1.2 and 99.3 ± 0.5%, respectively. Stable mixed liquor suspended solid concentration (3.0–5.0 g/L); enhanced nitrification–denitrification activity (78–92%) and reduced transmembrane pressure were also achieved. Compared to soluble microbial products, extracellular polymeric substances (EPS) showed strong correlation with fast membrane fouling. Among EPS components, carbohydrate rather than protein was associated with membrane fouling. Except HRT, all parameters considered (pH, IAC, SRT) showed a significant effect on removal efficiency.