Performance and microbial response of anaerobic membrane bioreactor to oil and salt co-occurrence in food wastewater treatment

High concentrations of oil and salt can adversely affect the effectiveness of anaerobic membrane bioreactors (AnMBRs) for food wastewater treatment, yet the impacts of their co-occurrence remain unknown. This study evaluated the performance of an AnMBR in response to simultaneous oil and salt stressors in synthetic food wastewater, in terms of methane production, membrane fouling, and microbial activity. Results show that either 8 g/L of cooking oil or 9 g/L NaCl in food wastewater caused the failure of AnMBR operation with a notable reduction in methane production and severe membrane fouling. However, the co-occurrence of oil and salt achieved a higher methane yield compared to oil stress alone. Additionally, the co-occurrence of oil and salt could alleviate osmotic stress to reduce microbial secretions and form macromolecular precipitates, thereby mitigating membrane fouling, compared to oil and salt alone. Such mitigation was due to the co-occurrence of high oil and salt to reduce long-chain fatty acids, enhancing living cells and their electron transfer activity. Further microbial analysis evidenced that the co-occurrence of oil and salt enriched hydrolytic and acidogenic bacteria (e.g. Bacteroidetes, Proteobacteria, Thermotogae, and Synergistetes) as well as hydrogenotrophic methanogens (e.g. Methanolinea ) to upregulate genes related to methanogenesis for methane production. Furthermore, key enzymes involved in the hydrogenotrophic methanogenesis pathway (M00567) were augmented when 8 g/L of oil was simultaneously added with 9 g/L of salt. • High concentrations of oil or salt individually caused AnMBR performance failure. • Co-occurrence of 8 g/L oil and 9 g/L salt mitigated individual negative effects. • Membrane fouling mitigated due to the co-occurrence of oil and salt. • Co-occurrence enriched hydrolytic bacteria, and hydrogenotrophic methanogens. • Key enzymes were elevated in the hydrogenotrophic methanogenesis pathway (M00567).