Decomplexation of Cu-1-hydroxyethylidene-1,1-diphosphonic acid by a three-dimensional electrolysis system with activated biochar as particle electrodes

The feasibility of decomplexation removal of typical contaminants in electroplating wastewater,complexed Cu(Ⅱ)with 1-hydroxyethylidene-1,1-diphosphonic acid(Cu-HEDP),was first performed by a three-dimensional electrode reactor with activated biochar as particle electrodes.For the case of 50 mg/L Cu-HEDP,Cu(Ⅱ)removal(90.7%)and PO_(4)^(3−)conversion(34.9%)were achieved under the conditions of electric current 40 mA,initial pH 7,acid-treated almond shell biochar(AASB)addition 20 g/L,and reaction time 180 min,with second-order rate constants of 1.10×10^(−3) and 1.94×10^(−5) min^(−1) respectively.The growing chelating effect between Cu(II)and HEDP and the comprehensive actions of adsorptive accumulation,direct and indirect oxidation given by particle electrodes accounted for the enhanced removal of Cu-HEDP,even though the mineralization of HEDP was mainly dependent on anode oxidation.The performance attenuation of AASB particle electrodes was ascribed to the excessive consumption of oxygen-containing functionalities during the reaction,especially acidic carboxylic groups and quinones on particle electrodes,which decreased from 446.74 to 291.48μmol/g,and 377.55 to 247.71μmol/g,respectively.Based on the determination of adsorption behavior and indirect electrochemical oxidation mediated by in situ electrogenerated H_(2)O_(2) and reactive oxygen species(e.g.,•OH),a possible removal mechanism of Cu-HEDP by three-dimensional electrolysis was further proposed.