Nanofiltration-Based Membrane Bioreactor Operated under an Ultralow Flux: Fouling Behavior and Feasibility toward a Low-Carbon System for Municipal Wastewater Reuse

Abstract

Compared to a conventional membrane bioreactor (MBR) with a porous microfiltration (MF) membrane (MBRMF), a nanofiltration (NF)-based MBR (MBRNF) shows highly attractive features such as high permeate water quality. However, the practical applications of MBRNF are often hindered by the high driven pressures and severe membrane fouling. To address these two critical issues, this study investigated the feasibility of operating MBRNF at an ultralow flux (ULF, e.g., <5 L·m–2·h–1) toward the reuse of municipal wastewater in a single step. We operated the ULF MBRNF at a flux of 2 L·m–2·h–1 and benchmarked its performance against a conventional system using a MBRMF followed by a subsequent NF treatment (MBRMF + NF, both at a constant flux of 20 L·m–2·h–1). The results show that the ULF MBRNF achieved substantial removal of most pollutants, with low negative impacts of ultralow fluxes on pollutant rejections. Besides, the ultralow-flux operation led to a very low fouling rate (0.18 kPa·d–1). More importantly, the ULF MBRNF reduced carbon emissions by 45.2% compared with the MBRMF + NF, mainly due to less energy consumption by pumping. Our findings highlight the simplicity and great potential of ULF MBRNF for wastewater reuse.