The double-edged effects of La2O3 and CeO2 on the performance of high-rate anaerobic sludge bed reactors and microbial mechanisms

Industrial wastewaters, generated from such as abrasive and catalyst-producing processes, usually contain rare earth oxides: La 2 O 3 and CeO 2 . When employing anaerobic methanogenesis technology to treat these industrial wastewaters, the impacts of La 2 O 3 and CeO 2 cannot be ignored. This study thoroughly investigated the long-term effects of La 2 O 3 or CeO 2 in high-rate anaerobic expanded sludge bed (EGSB) reactors. When compared to the control reactor, it was found that the addition of La 2 O 3 led to an 11% decrease in chemical oxygen demand (COD) removal efficiency and 38% decrease in methane production rate ( MPR ). Similarly, the introduction of CeO 2 resulted in a 9% in COD removal efficiency and a 17% decrease in MPR . Both La 2 O 3 and CeO 2 had positive influences on enhancing methanogenic activity of anaerobic granular sludge (AnGS). Through the results of quantitative polymerase chain reaction (qPCR) and high-throughput sequencing analysis, it was revealed that La 2 O 3 and CeO 2 contributed to a balanced microbial community by promoting the growth of methanogens and suppressing anaerobic propionate and butyrate-producing bacteria. Meanwhile, La 2 O 3 and CeO 2 stimulated the proliferation of electroactive species: Geobacter and Methanospirillum . However, the results of quantification and characterization of Extracellular Polymeric Substances (EPS) of AnGS showed both La 2 O 3 and CeO 2 reduced the presence of tryptophan substances in EPS and decreased the protein/polysaccharide ratio. This led to the disintegration of AnGS into smaller zoogloea complexes. The findings of this study offer valuable insights for early-warning and optimization of anaerobic methanogenesis treatment in dealing with industrial wastewater containing La 2 O 3 and CeO 2 .