Fe3O4 accelerates tetracycline degradation during anaerobic digestion: Synergistic role of adsorption and microbial metabolism

Abstract

Antibiotics contaminants, for example, tetracycline (TC) in the environment have attracted extensive attention around the world, and appropriate treatments for such contaminants are urgently required. In this study, five groups of anaerobic reactors supplemented with different amounts of Fe3O4 were operated periodically to investigate their performance on TC removal. The results showed that Fe3O4 effectively promoted TC removal. Compared with the control reactor, the TC removal efficiency was increased by 7.3% when co-digested with glucose, and increased by 40.4% when mono TC was digested in reactors with 5.0 g/L Fe3O4. Further analysis indicated that the probable mechanism of Fe3O4 promoting TC removal was through TC being adsorbed from the liquid onto Fe3O4, making TC more available for microbes to be biodegraded. Microbial community analysis indicated that the bacteria (Klebsiella, Pseudomonas, and Escherichia) related to TC removal were enriched, which meant more pathways for TC removal were available following the addition of Fe3O4. In addition, in the Fe3O4-supplemented reactors, syntrophic metabolism (between Desulfovibrio and Methanobacterium, Azonexus and Methanobacterium) were possibly established, which played an important role in improving TC removal and CH4 production. The electron transport system data further confirmed these results. The functional gene classification for Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that the dominant functions enhanced by Fe3O4 supplementation was microbial metabolic activities.