Evaluation of a membrane bioreactor and nanofiltration for municipal wastewater reclamation: Trace contaminant control and fouling mitigation

A membrane bioreactor (MBR) and nanofiltration (NF) membrane processes were developed for municipal wastewater reclamation, and their performances, in terms of trace contaminant control and fouling mitigation, were evaluated and designed to meet water quality criteria and minimize flux decline. The dissolved contaminants in wastewater were poorly degraded by MBR but the microbial nitrification in MBR could greatly contribute to nitrogen removal in the MBR permeate through the addition of a NF membrane. Furthermore, most dissolved contaminants were efficiently removed by the NF membrane. However, the NF membrane was ineffective in the removal of boron. The org-N/C molar ratio was inversely correlated to SUVA and directly corresponded to the 3D FEEM, structural analysis, and IR spectra of organic matter in raw and treated water, and desorbed foulants. The observations obtained from rigorous characterization revealed that the hydrophilic fractions, which were comprised of polysaccharides and amino groups, played a major role in fouling formation of the MBR–NF system. In addition, strong amide IR peak in the NF-base supported the notion that amino groups were primarily responsible for the fouling formation of the NF membrane relative to the polysaccharides groups. ► Ratio of organic nitrogen to carbon, as index, was used to evaluate fouling problem. ► Micropollutants having different logKow and pKa were removed by tested NF membrane. ► Hydrophilic and N-containing organic matters were major problematic foulants.