Effects of roxarsone and sulfadiazine on biogas production and their degradation during anaerobic digestion

Roxarsone and sulfadiazine are typical feed additives and often occur in manure and livestock wastewater. Anaerobic digestion is a common technique for the treatment of manure and livestock wastewater. However, the influence of roxarsone and sulfadiazine on anaerobic digestion and their degradation are still unclear. In this study, the effect of roxarsone and sulfadiazine on the anaerobic digestion of synthetic wastewater and their degradation were investigated. During 70-day incubation, the presence of 200 mg L-1 sulfadiazine exhibited little influence on hydrolysis and acidification, but resulted in a temporary inhibition on methanogenesis, whereas 120 mg L-1 of roxarsone resulted in nearly complete inhibition on methanogenesis. Further, the coexistence of 100 mg L-1 sulfadiazine and 60 mg L-1 roxarsone significantly exacerbated the inhibition on anaerobic digestion. Sulfadiazine exhibited high resistance to the adsorption and biodegradation, while roxarsone was nearly completely degraded during anaerobic digestion. Nearly half of total arsenic was transferred from solution to anaerobic granular sludge. The predominant arsenic species was 4-hydroxy-3-aminophenylarsonic acid in the solution and AS(3+) in the sludge. These results will provide valuable information for anaerobic treatment of livestock wastewater simultaneously contaminated by roxarsone and sulfadiazine.