Arsenic accumulation and volatilization in a 260-day cultured upflow anaerobic sludge blanket (UASB) reactor

Abstract

Roxarsone has been extensively used as an organoarsenic feed additive. Part of supplemented roxarsone was discharged into wastewater. UASB reactor has been widely applied to treat high concentration of organics wastewater. However, there was little report about the arsenic accumulation from organoarsenic biotransformation in an UASB reactor. In this study, the accumulation and volatilization of arsenic in a 260-day cultured UASB reactor spiked with 13.2mg/L roxarsone were investigated. In the anaerobic granular sludge (AGS), the total arsenic concentrations were 5276.90±366.12mg/kg AGS at the bottom of anaerobic sludge bed and 10,661.92±539.63mg/kg AGS at the top of anaerobic sludge bed. Nearly 50% arsenic in the AGS was extracted under acidic conditions, and the main species of the extracted arsenic was arsenite (As(III)). In the aqueous phases, roxarsone was rapidly transformed into 4-hydroxy-3-aminophenylarsonic acid (HAPA) and an unknown organoarsenic, which was further converted to inorganic arsenic and monomethylarsenate (MMA(V)), in which As(III) was also the main species. Volatile arsenic from the reactor spiked with roxarsone was released at a rate of 134.93±6.61ng/d. Based on the mass balance analysis of arsenic, 23.40% of the influent arsenic was accumulated in the AGS and 0.002% was released in the form of volatile arsenic. The results from this study indicated that the operation of anaerobic digestion reactor treating organoarsenic-contaminated wastewater and the disposal of the residual AGS should be well managed.