Roxarsone, an extensively used organoarsenical feed additive, is often pooled in livestock wastewater. Sulfate exists ubiquitously in livestock wastewater and is capable for arsenic remediation. However, little is known about impacts of sulfate on roxarsone biotransformation during anaerobic digestion of livestock wastewater. In this study, the biodegradation of 5.0 mg L^-1 roxarsone, and the accumulation and volatilization of the generated arsenical metabolites in a sulfate-spiked upflow anaerobic granular blanket reactor were investigated. Based on the analysis of degradation products, the nitro and arsenate groups of roxarsone were successively reduced to amino and arsenite groups before the C-As bond cleavage. Effluent arsenic concentration was ∼0.75 mg L^-1, of which 82.9-98.5% were organoarsenicals. The maximum arsenic volatilization rate reached 32.6 μg-As kg^-1-VS d^-1. Adding 5.0 mg L^-1 sulfate enabled 66.7% and 45.9% decrease in inorganic arsenic concentration and arsenic volatilization rate, respectively. Arsenic content in the anaerobic granular sludge (AGS) was accumulated to 1250 mg kg^-1 within 420 days. Based on the results of FESEM-EDS and XPS, sulfate addition induced arsenic precipitation in the AGS through the formation of orpiment. Arsenic in the effluent, biogas and AGS accounted for 52.9%, 0.01% and 47.1% of the influent arsenic when the reactor operated stably. The findings from this study suggest that sulfate has effectively regulatory effects on arsenic immobilization and volatilization during anaerobic digestion of organoarsenic-contaminated livestock wastewater.

Roxarsone是一种广泛使用的有机砷饲料添加剂，经常混入牲畜废水中。硫酸盐普遍存在于牲畜废水中，并且能够进行砷修复。然而，关于牲畜废水厌氧消化过程中硫酸盐对洛克沙酮生物转化的影响知之甚少。在这项研究中，研究了5.0 mg L ^-1 roxarsone的生物降解，以及在硫酸盐加标的上流厌氧颗粒毯式反应器中生成的砷代谢物的积累和挥发。基于降解产物的分析，在C-As键裂解之前，将洛克沙酮的硝基和砷酸酯基团连续还原为氨基和亚砷酸酯基团。废水中砷浓度约为0.75 mg L ^-1，其中82.9-98.5％是有机砷。最大砷挥发速率达到32.6μg- Askg ^-1 -VS d ^-1。加入5.0 mg L ^-1硫酸盐可使无机砷浓度和砷挥发速率分别降低66.7％和45.9％。厌氧颗粒污泥（AGS）中的砷含量累积至1250 mg kg ^-1在420天内。根据FESEM-EDS和XPS的结果，硫酸盐的添加通过果皮的形成诱导了AGS中砷的沉淀。当反应器稳定运行时，废水，沼气和AGS中的砷分别占进水砷的52.9％，0.01％和47.1％。这项研究的结果表明，硫酸盐对有机砷污染的家畜废水进行厌氧消化时，对砷的固定和挥发具有有效的调节作用。