Leveraging anaerobic biodegradation of tetracycline in anaerobic digestion systems with different operational modes

Antibiotics such as tetracycline in wastewater may cause the operation failure of anaerobic digestion systems. Two operational modes, continuous-flow reactors (CFRs) and sequencing batch reactors (SBRs), were operated with or without the addition of tetracycline to examine the influence of tetracycline on system performance, tetracycline removal, metabolic activity, and microbial communities. Tetracycline inhibited the removal of chemical oxygen demand (COD) by 23.9% in CFRs and 20.5% in SBRs, and led to the accumulation of volatile fatty acids (VFAs). Also, the maximum methane production rate was inhibited by 24.5% in CFRs and 48.8% in SBRs due to the existence of tetracycline, while the maximum methane production was reduced by 32.8% in CFRs and 13.8% in SBRs. CFRs exhibited a better recovery capacity during COD shock loading and demonstrated superior propionate degradation and methane production capabilities. CFRs achieved better tetracycline removal capacity compared to SBRs. Biodegradation was found to be the dominant tetracycline removal pathway, accounting for 88.9% (CFRs) and 82.0% (SBRs). Long-term exposure to tetracycline decreased archaea abundances and inhibited the enrichment of hydrolytic-acidogenic bacteria (Mesotoga and Syner-01). Meanwhile, CFRs provided a more conducive environment for the enrichment of these microorganisms. The presence of Geobacter in conjunction with the detected ethanol in a typical reaction cycle in CFRs suggested the potential presence of direct interspecies electron transfer, elucidating the enhanced pollutant removal of CFRs. Additionally, Trichococcus, a genus associated with tetracycline removal, was found to be highly enriched with the long-term dosage of tetracycline.