Insights into the ambient temperature startup of an anaerobic ceramic membrane bioreactor with thermally hydrolyzed inoculum for domestic wastewater treatment

An anaerobic ceramic membrane bioreactor (AnCMBR) with thermally-hydrolyzed sewage sludge as the inoculum was started up at the ambient temperature (26.97 ± 4.23 °C) for treating simulated domestic wastewater. The AnCMBR was operated for 60 days under 24 h hydraulic retention time (HRT), 50 days sludge retention time (SRT), and the mean organic loading rate (OLR) of 0.42 kgCODm−3d−1. Soluble chemical oxygen demand (SCOD) removal evaluation, volatile fatty acid (VFA), and Alkalinity (ALK) analyses, and the microbial community evaluation by polymerase chain reaction (PCR) were conducted. The reported maximum and mean SCOD removals were 62%, 43.54% ± 11.61 respectively. The total volatile fatty acids/alkalinity (TVFA/ALK) ratio was 0.59 indicating system instability. Microbial community analysis revealed significant shifts during the start-up process. The Bacteroidetes were well acclimatized throughout the start-up. The Firmicutes had suppressed during the start-up while Proteobacteria, Epsilonbacteraeota, Spirochetes phylum newly emerged in the system. The thermally-hydrolyzed inoculum was not established as a successful microbial community for treating domestic wastewater at the ambient conditions in this AnCMBR. The findings provided insights on microbial mechanisms and the basis of anaerobic digestion process instability. In comparison with previous studies, the potential countermeasures to address this were identified as proper selection and frequent addition of inoculum, and process monitoring.