Degradation of phthalic acid by anodic oxidation in acidic aqueous solutions with high chromium content using boron-doped diamond anode

Abstract

Mineralization of phthalic acid, a highly refractory organic pollutant was studied by an anodic oxidation process with boron-doped diamond (BDD) anode in a highly acidic chromium medium. Synthetic solutions were composed of Cr(III)/Cr(VI), sulfate, sulfuric acid, and phthalic acid (initial form potassium hydrogen phthalate, KHP). Degradation/mineralization of KHP was carried out by hydroxyl radicals produced on the anode and sulfate radicals generated from the sulfate ions present in the medium. To find appropriate operating conditions, the effects of cathode type, current density, electrolysis time, and presence of Cr(VI)-Cr(III) were investigated. Thereafter, the effect of current density, amount of Cr(VI)-Cr(III) in solution, and electrolysis time on KHP mineralization was realized by using response surface methodology and central composite design. The most effective TOC removal rate was found as 94.8% in the case of 0.675% Cr(VI) and 3.825% Cr(III) content by mass at 80 mA cm−2 of current density and 360 min of electrolysis time, despite a high initial TOC content of 9400 mg L−1. As a result, the organic content of the wastewater was removed by electro-persulfate process via the catalytic effect of Cr species. Additionally, the use of BDD anode avoided metal ion pollution that could dissolve from different anode materials like PbO2 and affect the chromium recovery efficiency.