Effects of antibiotics on characteristics and microbial resistance of aerobic granules in sequencing batch reactors

The response of characteristics and microbial resistance of aerobic granules to sulfamethazine, oxytetracycline, and ciprofloxacin at ppb level in swine wastewater was investigated in this study. Results showed that no significant changes in physical strength, average granules size, and settling property of aerobic granules were observed with target antibiotics exposure (p>0.05). However, compared to the control group, the protein/polysaccharide ratio and zeta potential of aerobic granules in treatment groups showed a higher level (p<0.05). Meanwhile, the specific removal rates of organics and ammonia nitrogen in reactors with antibiotics addition all decreased greatly, and the inhibition rates of those were 21-29% and 35-42%, respectively. In terms of microbial resistance, the presence of target antibiotics would obviously increase the relative abundances of antibiotics resistance bacteria and antibiotics resistance genes in aerobic granules, ranging from 0.5 to 5 orders of magnitude; thereby, it concluded that antibiotics at ppb level without effect of other induction factors can actually reach an effective content capable of spreading antibiotic resistance in aerobic granular reactor.