Antibiotic residues may stimulate or suppress methane yield and microbial activity during high-solid anaerobic digestion

High-solid anaerobic digestion (HSAD) is a promising method to centralizedly dispose dewatered sludge from municipal wastewater treatment plants. Until now, few studies have focused on determining the different effects of antibiotic residues on methane yield and microbial communities over a wide range of antibiotic loads in HSAD system. This study investigated the effects of seven typical antibiotics (oxytetracycline, sulfadimethoxine, sulfamethoxazole, enrofloxacin, ciprofloxacin, ofloxacin and norfloxacin) on HSAD over a wide range of loads (0-500 mg/L). The results showed that 10 mg/L of antibiotics had no obvious effect on CH4 yield. Interestingly, 100 mg/L of antibiotics exhibited a strong stimulating effect on CH4 yield. Antibiotics at a concentration of 500 mg/L generally suppressed CH4 yield at the initial stage of anaerobic digestion, and some systems recovered at the late stage of the process with a much higher daily CH4 yield than other systems. Among the three kinetics models, the modified Gompertz model showed the best fit to the experimental data (R-2: 0.9772-0.9997). Antibiotic residues did not have strong effects on the bacterial community, but did affect the archaeal community. The relative abundance of Methanosarcina increased while that of Methanosaeta and Methanoculleus decreased with the antibiotic concentrations increasing. The heat map showed that the archaeal community in the system with 500 mg/L was characterized by Methanobacteriales and Halobacteriales. This study provides a new insight into the different effects of antibiotics on HSAD.