Impact of micropollutants and the process configuration on the performance of moving bed membrane biofilm reactor (MBMBR).

This study investigates the removal performance of selected micropollutants (ibuprofen, diclofenac, naproxen, carbamazepine, and triclosan) from domestic wastewater using a moving bed membrane biofilm reactor (MBMBR) process, consisting of two moving bed biofilm reactors (MBBRs) in series followed by a membrane bioreactor (MBR). While the integration of MBBR and MBR processes leverages the advantages of both technologies, systematic studies on determining the optimal configuration, particularly in the presence of micropollutants, remain quite limited in the literature. Within the scope of the research, the effects of sludge recirculation (hybrid growth) from the MBR to different MBBR units on treatment performance were evaluated over 140 days with three different periods. The results showed that the COD removal efficiency, which was initially 98% (permeate COD <10 mg/L), gradually decreased following the introduction of micropollutants. The toxicity of micropollutants led to the accumulation of soluble microbial products (SMPs) and extracellular polymeric substances (EPSs), which increased the average supernatant COD up to 370 mg/L in the MBR unit. The membrane rejected most of the SMPs and EPSs, which improved the permeate quality (with permeate COD averaging <50 mg/L in all configurations) but increased the fouling potential. Nitrification almost entirely ceased (with permeate NH4+-N averaging 40 mg/L) during the second period (biofilm-only growth) as the system suffered from both micropollutant toxicity and the lack of microbial seeding by sludge recirculation. Regarding micropollutant removal, high efficiencies of over 75% were achieved for ibuprofen and triclosan, while removal efficiencies for recalcitrant compounds such as carbamazepine, diclofenac, and naproxen generally remained below 30%. This study highlights the impact of micropollutants on ammonia oxidizing bacteria (AOB), which may have a critical role in micropollutant removal, and demonstrates the advantages of the hybrid growth mode in maintaining process stability.