Oxidation Of Organoarsenics In Aqueous Solution: Kinetics And Degradation Pathways

Organoarsenic such as arsanilic acid and roxarsone has been widely used as feed additive in animal husbandry to control coccidial intestinal parasites and improve feed efficiency. They are almost excreted unchanged in the manure and urine and they will be biotically and abiotically degraded to the inorganic arsenic in the environment, which may pose potential risks to environment and human health. But, there are few studies on the degradation and transformation of ASA/ROX during wastewater treatment process. We investigated the kinetics, thermodynamics and mechanism of ASA/ROX degradation with traditional oxidation ways in this study.The degradation of ASA with potassium permanganate fitted adjusted pseudo-first-order kinetic model. ASA could be degraded and this degradation process was strongly affected by solution pH. The degradation efficiency was enhanced at lower pH values. The oxidation of ASA with KMnO4 in the presence of HA was strongly promoted. The background ionic strength provided by sodium chloride had little influence on ASA degradation process. ASA could be almost degraded, but the reduction of total organic carbon was not significant. In addition, inorganic arsenic and aniline were identified as degradation products. However, any other forms of organic arsenic were not found. The possible degradation pathways were proposed on the basis of the identified intermediates. The results of present study might provide a feasible and appropriate method of ASA degradation in wastewater treatment.The degradation of ASA with sodium hypochlorite fitted common kinetic model. The degradation of ASA with NaCIO shows strong pH dependence, with the degradation rate constant decreasing with the increase of pH. The oxidation of ASA in the presence of HA was strongly inhibited. The ammonium ion significantly inhibited the ASA degradation process and bicarbonate ion had positive effect on ASA degradation. In real water, the degradation of ASA with sodium hypochlorite was not very ideal. ASA could be almost degraded, but the reduction of total organic carbon was not significant. In addition, inorganic arsenic and trichloroaniline were identified as degradation products. The possible degradation pathways were proposed on the basis of the identified intermediates.The degradation of ROX with sodium hypochlorite fitted pseudo-first-order kinetic model. ROX could be degraded and this degradation process was strongly affected by solution pH. The degradation efficiency was enhanced at lower pH values. The oxidation of ROX in the presence of HA was promoted. The ammonium ion significantly inhibited the ROX degradation process and bicarbonate ion had positive effect on ROX degradation. In real water, the degradation of ROX with sodium hypochlorite is very ideal. ROX could be completely degraded, but the reduction of total organic carbon was not obviously. In addition, inorganic arsenic and 3,4,5-chlorine-2-nitrophenol were identified as degradation products. The possible degradation pathways were proposed on the basis of the identified intermediates.