P-NP mineralization, total nitrogen removal and toxicity reduction using an alternating-electroreduction-electrooxidation system

Abstract

Electrochemical degradation has emerged as a sustainable technology for treating p-Nitrophenol (p-NP). However, most studies have focused only on electrochemical oxidation or electrochemical reduction, and limited research on alternating-electroreduction-electrooxidation system (AEES). The process of p-NP degradation in AEES system has not been understood. In this work, the effect of AEES on p-NP treatment was investigated by regulating the reduction and oxidation time ratios as well as the alternating cycles. The results indicated that the different modes had a significant effect on p-NP degradation rate and TN removal, while the effect on mineralization was limited. Obviously, the sequential reduction–oxidation system performed better than the sequential oxidation–reduction system, with p-NP degradation rates increasing by 34.2 % and 147.9 % over the oxidation and reduction modes alone, respectively. Moreover, an increase in the number of alternating cycles (R60O120 × 1 to R10O20 × 6) results in the improved mineralization from 84.4 % ± 2.1 % to 88.7 % ± 1.7 % and TN removal from 35.1 % ± 1.9 % to 46.6 % ± 2.1 %. The increased mineralization, decreased nitrogen compounds, and reduced complex by-products also contributed to 10.0 % ± 1.4 % reduction of acute toxicity. On the basis of intermediates identification, a degradation pathway for AEES including free radical substitution and ring opening process were proposed.