Synergy Of Anodic And Cathodic Reaction For The Treatment Of Organophosphorus Wastewater With Phosphorus Recovery:Performance And Mechanism

Organophosphorus pesticides with high toxicity are widely used in agriculture and forestry.However,the discharge of organophosphorus pesticides wastewater would inevitably cause serious environmental pollution problems.On the other hand,as a non-renewable resource,the global phosphate reserve is decreasing,which may cause the crisis of phosphorus resource shortage in the future.Therefore,the use of induced crystallization technology to recover inorganic phosphorus in wastewater as hydroxylapatite has become a research hotspot in recent years.Unfortunately,induced crystallization to produce hydroxylapatite requires alkaline solution,additional solid-liquid separation and post-treatment.Therefore,there are still certain limitations in practical applications.In addition,induced crystallization can only recover inorganic phosphate in wastewater rather than directly used for organophosphorus.Therefore,the development of effective strategies to realize the resource treatment of organophosphorus wastewater has become a research focus.In the electrochemical advanced oxidation process,the pollutants on anode surface could be degraded by direct oxidation or indirect oxidation.At the same time,the OH-generated by cathodic water electrolysis would create local strong alkaline atmosphere on cathode surface,by which the deposition of hydroxyapatite were promoted.Therefore,the electrochemical advanced oxidation process has great development prospects in resource treatment of organophosphorus wastewater.This paper established an "anode oxidation-cathode precipitation" electrochemical system for simultaneous degradation of pollutants and recovery of inorganic phosphorus in organophosphorus pesticide wastewater.In this study,organophosphorus pollutants were degraded by the indirect oxidation reaction,which was mediated by the release of hydroxyl radicals through BDD anode.Then,orthophosphate,the oxidation product,was co-precipitated with Ca2+ and OH-at cathode in the form of hydroxyapatite.The increase of current density was conducive to hydroxyl radicals release and pollutants degradation,meanwhile,the local strong alkaline atmosphere of cathode was strengthened and the electromigration of Ca2+ to cathode were promoted.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%.The anodic oxidation of acephate was favorable in acid solution,since the electrochemical properties of acephate and BDD were improved and the generation of oxidant groups were promoted.Both Mg2+and HCO3-coexisting in the solution would precipitate on cathode,which did not only inhibit the recovery efficiency of phosphorus but also reduced the purity of hydroxyapatite products.The presence of Cl-would not affect the quality of hydroxyapatite,however,the degradation of organophosphorus were inhibited since highly oxidative hydroxyl radicals was consumed by Cl-.To relieve the influence of Mg2+and HCO3-on the quality of phosphorus products,a longitudinal double-cathode electrochemical system for "Mg2+ and HCO3-removal on the first cathode-HCO3-removal and organophosphorus pollutant oxidation at the anode-precipitation of hydroxyapatite on the second cathode " was established.The effects of current density and flow rate on Mg2+removal,HCO3-removal and phosphorus recovery were investigated by monitoring the various species changes in the solution of first cathode,anode and second cathode.Mg2+ were effectively removed on the first cathode,accompanying the removal of a certain of HCO3-.The H+produced at the anode was effective for HCO3-removal,which converted HCO3-into into CO2 gas.The organophosphorus pollutants were oxidized and degraded into orthophosphate at the anode,and then precipitated with Ca2+ on the second cathode.High current density and low flow rate were beneficial for Mg2+ removal,HCO3-removal and phosphorus recovery.At current density of 15 mA·cm-2 and inlet flow rate of 0.1 mL·min-1,about 16.8 mg·L-1 Mg2+ and 41.4 mg·L-1 HCO3-were removed at the first cathode.70.2 mg·L-1 HCO3-were removed and 7.3 mg·L-1 organophosphorus were degraded at the anode,while 5.2 mg·L-1 phosphorus were recovered at the second cathode.Generally,this study provided an efficient method for organophosphorus wastewater resourcization by the synergism of anodic and cathodic reaction,in which organophosphorus contaminants removal and simultaneous phosphorus recovery.Therefore,the study provided the theories foundation for advancing the electrochemical processes in the resource utilization of organophosphorus wastewater,and provided technical support for the extensive application of electrodes synergistic systems for wastewater treatment.