Response characteristics of the symbiotic flocs system of bacteria and algae in treating Marine aquaculture wastewater with oxytetracycline.

This study investigated the use of bacterial-algal symbiotic flocs (BASS) to treat marine aquaculture wastewater containing low concentrations of oxytetracycline (OTC). Compared with the activated sludge system (AS) and the Chlorella sp. system (CS), the BASS system was found to consistently remove 82.03 ± 11.53% of ammonia nitrogen without nitrate accumulation, and achieved a consistent removal rate of 85.91 ± 12.49% for OTC. The BASS system achieved a more stable defense mechanism through the gradient accumulation of humic substances under the pressure of different concentrations of OTC, tyrosine-like substances were found in the inner layer of EPS. High concentrations of OTC would inhibit the nitrification, denitrification, and heterotrophic nitrate reduction pathways of the BASS system, reduce the oxidation decarboxylation reaction, and decrease the content of NADH. The spread of ARGs in the BASS system mainly occurred through IS1380, IS66, and recombinase. This study confirmed the potential of the BASS system for treating marine aquaculture wastewater and helped us better understand the resistance mechanism when facing fluctuations in antibiotic concentrations, providing ideas for controlling the spread of ARGs.