Study On Wastewater Treatment Containing Nitrophenol Using Electrochemical Oxidation Process

Nitrophenol is a typical recalcitrant organic pollutant. It has severe impact onhuman healthy and ecological system, owing to its great toxicity and tendency toaccumulate in food chains. Developing feasible technologies to treat this kind ofcontaminants has been a very active research area. However, traditional methods suchas physical, biological process and chemical treatment cannot treat these contaminantseffectively due to various problems existed in the removal process. Electrochemicaloxidation process has attracted considerable interest in recent years for treatingrecalcitrant organic compounds due to its small area demand, simplicity of operationand no need for secondary treatment.This study investigated the removal of two typical organic pollutants,2,4,6-trinitro-1,3,5-trihydroxybenzene (TNPG) and2,4,6-trinitrophenol (TNP) usingelectrochemical oxidation method.Electrochemical treatment of TNPG was investigated firstly in the study. Ti/IrO2electrode was selected as anode. NaCl was used as supporting electrolyte. The effectsof applied current densities，distance between anode and cathode, concentration ofelectrolyte and initial concentration of TNPG on the removal efficiency of TNPGwere investigated. The removal mechanism and degradation pathway for TNPGremoval was discussed at last. The results demonstrated that electrochemicaloxidation could effectively remove TNPG from water. The greatest removal of TNPGwas obtained when current density was20mA/cm2, electrode distance was10mm,and sodium chloride concentration was0.3g/L. When the initial concentration ofTNPG was400mg/L,65.4%of COD was removed after240min electrolysis in thiscondition, while100%of COD was removed after80min electrolysis when the initialconcentration of TNPG was50mg/L. The primary mechanism for TNPG removalwas indirect oxidation. Elimination of nitro-group of the TNPG and replacement byhydroxyl radical were occurred firstly during the degradation, followed by ringcleavage reaction and conversion to CO2and H2O.Removal of TNP from water using electrochemical oxidation was investigated aswell. The anode and supporting electrolyte were the same as those used in theinvestigation for TNPG removal. Effects of initial pH, applied current densities, andinitial concentration of TNP on TNP removal were investigated. The removalmechanism and degradation pathway for TNP removal was proposed by analyzing the intermediates. The results showed that electrochemical oxidation process couldremove TNP effectively. The greatest removal efficiency was obtained at pH3.Increasing applied current densities increased TNP removal efficiency, whereas initialconcentration of TNP had small effect on its removal. The removal mechanism andthe degradation pathway were almost the same as those of TNPG.