Variation of antibiotics in sludge pretreatment and anaerobic digestion processes: Degradation and solid-liquid distribution.

Degradation and solid-liquid distribution of antibiotics in three sludge pretreatments (ultrasonic, alkaline and thermal hydrolysis pretreatment) and subsequent anaerobic digestion processes were investigated. The contamination of fluoroquinolones (FQs) was most serious in the raw sludge, while sulfonamides (SAs) were negligible. Obvious solubilization of antibiotics was observed after sludge pretreatments. The intracellular antibiotics were released after thermal hydrolysis pretreatment, meanwhile tetracyclines (TCs) were thermally decomposed. Compared to TCs and macrolides (MLs), FQs were hardly degraded in anaerobic digestion with removal efficiencies lower than 42.02%, and the residual FQs were mostly adsorbed on the digested sludge. The limiting step for FQs reduction was the biodegradation, rather than desorption of adsorbed antibiotics. Addition of pretreatments had no obvious effect on the degradation and distribution of antibiotics in the anaerobic digested sludge, except that the thermal hydrolysis enhanced the migration of antibiotics to the liquid phase.