Insights into the microbiological mechanism of antibiotic removal in an aerobic-microaerobic process treating manure-free piggery wastewater

A process integrating the sequencing batch reactor (SBR) and up-flow microaerobic sludge reactor (UMSR) has been innovatively developed to effectively remove antibiotics from manure-free piggery wastewater. This study provides a comprehensive analysis of bacteria, genes, and enzymes crucial for antibiotic biodegradation to reveal the underlying microbiological mechanism of antibiotic removal. During the 230-day operational period, a significant succession of microbial communities was observed in the SBR-UMSR system. Intriguingly, microbial interactions were pivotal in dominating the community succession, accounting for a substantial contribution of 69.12%, while abiotic factors only accounted for 30.88%. The analysis of the microbial community and network revealed that the predominant mechanism for antibiotic biodegradation in the SBR-UMSR system was driven by the metabolic activities of heterotrophic bacteria. More denitrifying bacteria were involved in antibiotic biodegradation than ammonia-oxidizing bacteria. In SBR, most of the potential antibiotic-degrading bacteria (PADB) were Gram-positive and facultatively anaerobic, whereas in UMSR, they were Gram-negative and aerobic. Propioniciclava and Norank_f__AKYH767 were the dominant PADB in the SBR and UMSR, respectively. Network analysis pinpointed redox reactions, transfer processes, and hydrolysis reactions as the core processes facilitating antibiotic biodegradation. Despite a general decrease in the abundance of most antibiotic resistance genes (ARGs) in the activated sludge of both SBR and UMSR over the 230-day operation, there was a notable enrichment in multidrug resistance genes. This underlines the necessity for proper sludge management to prevent secondary contamination by ARGs. This research provides deep insights into the mechanisms of antibiotic removal in intricate microbial ecosystems.