Simultaneous electrochemical degradation of organophosphorus pesticides and recovery of phosphorus: Synergistic effect of anodic oxidation and cathodic precipitation

To address future phosphorus scarcity and organophosphorus pesticides discharge associated environmental problems, a filter-press type electrochemical system was developed for acephate, a typical organophosphorus pesticide, degradation and simultaneous recovery of phosphorus. In this reaction system, boron-doped diamond (BDD) mediated anodic oxidation could transform acephate into ortho-phosphate (o-PO4) and then o-PO4 was precipitated with Ca2+ at the cathode surface in the form of hydroxyapatite induced by the local basic environment. The phosphorus recovery efficiency raised from 57 % to 92 % within 180 min by elevating current density from 5 to 30 mA/cm(2), accompanying the enhanced acephate mineralization efficiency from 77% to 97%. These enhancement trends were attributed to the increased yield of BDD((OH)-O-center dot) and higher local pH near the cathode, respectively, at higher current density applied. Phosphorus recovery efficiency swelled by 15% with solution pH decreasing from 9.0 to 4.0 since anodic oxidation of acephate into o-PO4 was favorable in the acid solution. Moreover, phosphorus recovery was seriously depressed in the initial reaction stage with the presence of Mg2+, whereas bicarbonate posed the negative effect over the whole reaction process. Unexpectedly, the presence of Cl- inhibited the degradation of acephate since highly oxidative (OH)-O-center dot was consumed by Cl-. In general, the electrochemical strategy of "anodic oxidation-cathodic precipitation" has been demonstrated practicable for phosphorus recovery from the organophosphorus wastewater. (C) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.