Synergistic effects of chromium(VI) reduction/EDTA oxidization for PCB wastewater by photocatalysis combining ionic exchange membrane processes

• Published in: Desalination and water treatment 2013-01, Vol.51 (1-3), p.495-502
• Main Authors: Hsu, Hung-Te, Chen, Shiao-Shing, Chang, Wen-Shing, Li, Chi-Wang
• Format: Article
• Language: English
• Subjects: Acetic acid; Acids; Aerated; Aeration; Applied sciences; Argon; Cation exchanging; Cations; Charging; Chromium; Current density; Detention time; Edetic acid; EDTA; Efficiency; Electrodialysis; Electron recombination; Ethylenediaminetetraacetic acids; Exact sciences and technology; Formic acid; Glycine; Glycine (amino acid); Glyoxylic acid; Hexavalent chromium; Holes (electron deficiencies); Iminodiacetic acid; Industrial wastewaters; Intermediates; Ionic exchange membrane; Membrane processes; Membranes; Mineralization; New technology; Nitrilotriacetic acid; Oxalic acid; Oxygen; PCB; pH effects; Photocatalysis; Pollution; Polychlorinated biphenyls; Recombination; Reduction; Removal; Synergistic effect; TiO2; Titanium dioxide; Wastewater; Wastewaters; Water treatment and pollution
• ISSN: 1944-3986; 1944-3994; 1944-3986
• DOI: 10.1080/19443994.2012.693651

A new technology using the TiO2 photocatalysis combining electrodialysis was proposed for the simultaneous oxidization of ethylenediaminetetraacetic acid (EDTA)/reduction of hexavalent chromium (Cr(VI)) by electron–hole (e-–h+) pairs. The application of a cationic exchange membrane in this system was used to enhance the efficiency for the prevention of the recombination of electrons with the electron hole. The following parameters were studied: current density, pH, hydraulic detention time (HRT), EDTA/Cr(VI) molar ratio, and oxygen contents (aerated by argon, air, and oxygen). The result showed that the optimum removal efficiency was observed at 4.0 mA/cm2 and higher removal efficiencies were observed at a lower pH due to electrostatic attractions between the positively charged Ti–OH2+, and the negatively charged Cr(VI) and EDTA. A higher EDTA/Cr(VI) molar ratio enhanced the removal efficiency of Cr(VI) in the photocatalytic system, indicating that EDTA plays the role of a hole scavenger in the system. In addition, the removal efficiency of Cr(VI) was better for the system aerated with argon than those systems aerated with oxygen and air, since a lower direct oxygen or oxygen reduction potential (ORP) favors the reduction of Cr(VI). Moreover, an incomplete EDTA mineralization contributes to the occurrence of intermediates, including iminodiacetic acid, nitrilotriacetic acid, glyoxylic acid, glycine, oxalic acid, acetic acid, and formic acid, as identified by the GC/MS.