Enhancing Roxarsone Degradation and In Situ Arsenic Immobilization Using a Sulfate-Mediated Bioelectrochemical System

Abstract

Roxarsone (ROX) is widely used in animal farms, thereby producing organoarsenic-bearing manure/wastewater. ROX cannot be completely degraded and nor can its arsenical metabolites be effectively immobilized during anaerobic digestion, potentially causing arsenic contamination upon discharge to the environment. Herein, we designed and tested a sulfate-mediated bioelectrochemical system (BES) to enhance ROX degradation and in situ immobilization of the released inorganic arsenic. Using our BES (0.5 V voltage and 350 μM sulfate), ROX and its metabolite, 4-hydroxy-3-amino-phenylarsonic acid (HAPA), were completely degraded within 13–22 days. In contrast, the degradation efficiency of ROX and HAPA was <85% during 32-day anaerobic digestion. In a sulfate-mediated BES, 75.0–83.2% of the total arsenic was immobilized in the sludge, significantly more compared to the anaerobic digestion (34.1–57.3%). Our results demonstrate that the combination of sulfate amendment and voltage application exerted a synergetic effect on enhancing HAPA degradation and sulfide-driven arsenic precipitation. This finding was further verified using real swine wastewater. A double-cell BES experiment indicated that As­(V) and sulfate were transported from the anode to the cathode chamber and coprecipitated as crystalline alacranite in the cathode chamber. These findings suggest that the sulfate-mediated BES is a promising technique for enhanced arsenic decontamination of organoarsenic-bearing manure/wastewater.

Oxidation of Roxarsone Coupled with Sorptive Removal of the Inorganic Arsenic Released by Iron–Carbon (Fe–C) Microelectrolysis

“…It has been estimated that swine and poultry wastes were responsible for the discharges of 0.9 × 10 2 to 2.5 × 10 4 and 0.8 × 10 2 to 5.7 × 10 3 tonnes of arsenic into soils, respectively, in China in 2009, while approximately 2000 tonnes of ROX and p -ASA (containing about 600 tonnes of arsenic) were once used in swine and chicken farming in China each year . Despite the fact that countries including the United States and China have banned the use of phenylarsenic feed additives, they are still widely used in quite a few developing countries, e.g., India, Brazil, Mexico, and Vietnam . In light of the arsenic pollution risk from the use of phenylarsenic feed additives in concentrated animal feeding operations (CAFOs), there is a significant need to develop low cost and practical treatment methods for these compounds in animal waste to prevent the pollution of farmlands by arsenic.…”

“…While ROX and p -ASA can be removed from aqueous solution through adsorption using nanomaterials, − the phase transfer efficiency is limited, the solid–liquid separation is often difficult, and the operating cost can be quite high. Like most organic pollutants, phenylarsenic feed additives can be degraded by a range of oxidation-based technologies, but their breakdown releases the more toxic and mobile inorganic arsenic species. ,,− Thus, the treatment of these organoarsenicals poses unique challenges, and effective capture of the toxic degradation products is as important, if not more important, than degradation of the parent compounds. Recently, treatment schemes based on oxidative degradation of ROX and p -ASA to arsenate followed by sorptive removal of arsenate using the in situ generated or externally added iron (hydro)­oxides through Fenton, Fenton-like, ferrate oxidation, and photocatalytic oxidation have been developed, but these methods suffer the general limitations of high cost and tedious operation. ,− In particular, the presence of dissolved organic matter (DOM) at high levels in the manure leachate poses a significant challenge for the above-mentioned treatment technologies through competing for the adsorption sites and competitive scavenging of the oxidants. ,− As a result, alternative technologies that have high efficiency, simple operation, and resistance against the impact of the water matrix components should be explored for treating phenylarsenic feed additives in manure leachate.…”

Production of H2S with a Novel Short-Process for the Removal of Heavy Metals in Acidic Effluents from Smelting Flue-Gas Scrubbing Systems

“…Sulfidation is an efficient method for the removal of HMs from acid-scrubbing effluents. − However, the addition of metal sulfide reagents (Na 2 S, NaHS, or FeS) to the acid effluents would not only introduce unexpected metal cations, but also lower acid recovery efficiency. , Adding gaseous H 2 S as the reagent in the liquid-phase can remove HMs by direct sulfidation process (DSP), which can successfully overcome the above problems. − The concentration of HMs is relatively high (up to 10 000 mg/L) while the emission limit of most HMs in these industries is relatively low (0.5 mg/L). , Increasing the H 2 S concentration can shorten HMs removal time and increase removal efficiency. , However, the transportation and storage of high concentrations of H 2 S (HC-H 2 S) are not allowed in many districts because of its high toxicity once released to the environment . In practical applications, there are some interim HC-H 2 S production processes.…”