Self-powered peroxi-coagulation for the efficient removal of p-arsanilic acid: pH-dependent shift in the contributions of peroxidation and electrocoagulation

In this study, the performance of the peroxi-coagulation fuel cell (PCFC) process for p-arsanilic acid (p-ASA) removal and power generation were evaluated at initial pH of 3.0-6.0. It was found that > 94% of p-ASA could be removed within 60 min at pH of 3.0-6.0. The fastest p-ASA removal could be obtained at pH of 4.0, whereas the optimum power density was 98.3 mW m(-2) at 745 mA m(-2) achieved at pH of 3.0. In the PCFC system, p-ASA removal was ascribed to the combined action of the electrostatic attraction between p-ASA(-) and positively charged iron precipitant and the oxidation of p-ASA by (OH)-O-center dot. At pH of 4.0-6.0, approximately 45%-50% of p-ASA could be oxidatively converted to inorganic arsenic and the residual inorganic arsenic concentration in solution was below 10 mu g L-1. Contrastly, although 92% of p-ASA was oxidized into As(V) at pH of 3.0, approximately 11 mu M of As(V) was still remained in the solution. In this case, about 81% of p-ASA was oxidized to p-aminophenol by hydroxylation of (OH)-O-center dot and less than 10% of p-ASA was oxidized into p-benzoquinone after 60 min. Notably, phosphate exerted the significantly inhibited effect on arsenic species immobilization via competing for the adsorptive sites on the iron precipitant. The kinetics study revealed that PCFC process had superior p-ASA removal efficiency as compared to electrocoagulation fuel cell process under the same condition. Generally, the PCFC process holds promise as a feasible option for p-ASA removal at rural/remote area where electricity is not easily available.