Characterization of arsenic species in the anaerobic granular sludge treating roxarsone-contaminated wastewater

Abstract

Roxarsone (4-hydroxy-3-nitrophenylarsonic acid), an organoarsenic feed additive, has been widely used in animal feed. Significant amount of arsenic enters into anaerobic granular sludge (AGS) in roxarsone-contaminated wastewater treatment process. However, the characterization of bonded and precipitated organoarsenic and inorganic arsenic in the AGS is still not clear. The characterization of arsenic species in the AGS treating roxarsone-contaminated wastewater was investigated in this study. Total arsenic concentration in the AGS was 8246.69μg·g−1. A series of extraction processes were performed to analyze arsenics in the AGS. As(III) (1384.71μg·g−1) and 4-hydroxy-3-aminophenylarsonic acid (HAPA, 439.05μg·g−1) were the dominant inorganic and organic soluble arsenic species, respectively. Similar arsenic species were detected in the cellular bonded arsenics. Field emission scanning electron microscope coupled with energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscope (XPS) and X-ray diffraction (XRD) analysis confirmed that the precipitated arsenic was in form of realgar (AsS). Cellular bonded arsenic had the highest percentage (42.2%), followed by soluble arsenic (32.4%) and precipitated arsenic (25.4%). The result from this study suggests that most of arsenics in the AGS could be leached out and has risk to the environment, and arsenic precipitation could be used as a remediation technique in bioreactors treating organoarsenic-contaminated wastewater.