Optimization of moving bed membrane bioreactor process for improved water and nutrient recovery from domestic wastewater

Hybridizing moving bed biofilm reactor (MBBR) and membrane bioreactor (MBR) processes has been reported to enhance wastewater treatment performance, but there remains a lack of knowledge on the optimal process configuration for water and nutrient recovery, which is important in the design of the process. This study aims to optimize MBBR+MBR (MBMBR) process configuration in terms of minimizing membrane fouling together with maximizing N&P recovery rather than removal, comparing three different MBMBR configurations under various loadings. The studied configurations were MBBR+MBR, two serially connected MBBRs+MBR, and two serially connected MBBRs+MBR with sludge recycling from the MBR to the second MBBR. In all the configurations, the first MBBR showed high COD removal rates (up to 24 g-COD/m(2).d), whereas nitrification was not detected due to high COD loading. Nitrification rates in the second MBBR reached 0.65 and 0.92 g-NH4+-N/(m(2).d), in the absence and the presence of sludge recycling from the MBR, respectively. Hence, hybridizing suspended and attached growth by applying sludge recycle (last configuration) improved the nitrification rate and process stability. In the MBR, complete nitrification was attained throughout the study, together with increasing N&P recovery due to biomass decay at long SRTs. The serial arrangement of MBBRs may allow for a more economical design, as the attached biomass in the first MBBR increased appreciably (>20 g-SS/m(2)) under high COD loadings. The last configuration gave the best performance in terms of N&P recycling and minimizing membrane fouling among the studied alternatives.