Effects of nano zero-valent iron nanoparticles on membrane fouling mitigation in a submerged anaerobic membrane bioreactor for landfill leachate treatment

A laboratory-scale anaerobic membrane bioreactor (AnMBR) for landfill leachate (LFL) was operated to investigate the effects of nano zero-valent iron (nZVI) (without nZVI addition, 50-300 mg/L) on contaminant removal and membrane fouling. nZVI can be a potential additive to improve AnMBRs' performance by regulating LFL treatment, microbial community structure, and especially membrane fouling. Therefore, this study evaluated the role and effectiveness of nZVI in enhancing AnMBRs' performance for wastewater treatment and membrane fouling mitigation. Results show that nZVI addition could improve AnMBR performance in removing pollutants and reducing membrane fouling. The optimal condition was found to be nZVI at 100 mg/L, corresponding to a membrane fouling rate of 0.012 mbar/min. However, since membrane fouling rate worsens at higher concentrations, the optimal nZVI concentration for pollutant removal was determined to be 200 mg/L. The results indicated removal efficiencies of 68% for chemical oxygen demand (COD), 31% for colour, and 47% for dissolved organic carbon (DOC). As a result, transmembrane pressure (TMP) decreased by 68%, and permeate flux showed a slight improvement at 100 mg/L nZVI. Additionally, adding nZVI reduced the ratios of protein to polysaccharide in both extracellular polymeric substances (EPS) and soluble microbial products (SMP), thereby mitigating membrane fouling. <i>Firmicutes, Bacteroidetes,</i> and <i>Proteobacteria</i>, which showed relatively high abundance, played important roles in pollutant removal in LFL. Also, bacteria associated with membrane fouling were identified as <i>Alphaproteobacteria, Sphingobacteria,</i> and <i>Flavobacteria</i> in the AnMBR. Results indicate that nZVI addition can enhance AnMBR performance in both pollutant removal and membrane fouling reduction.