A combined photocatalytic and electrochemical treatment of wastewater containing propylene glycol methyl ether and metal ions

Simulated wastewater containing Ni2+, Zn2+ and propylene glycol methyl ether (PGME), a solvent in polymer solution used in metal coating, was treated by a combined electrochemical and photocatalytic technique. The effect of electrode spacing and corrugated electrodes on the removal of Ni2+ and Zn2+ by electrodeposition was investigated. The solution pH and temperature were kept at 6.0 and 25 °C. The metal removal was almost doubled when the electrode spacing was decreased from 6.4 to 1.3 cm. A further 40% increase was obtained with the corrugated cathode at the electrode spacing of 1.3 cm. A 96% removal of Ni2+ and Zn2+ was obtained after 48 h of treatment at a liquid flux of 0.0334 m3 m−2 s−1.For the combined electrochemical–photocatalytic treatment in a rotary reactor, using immobilized TiO2 at a liquid flux of 0.0148 m3 m−2 s−1, metal concentrations decreased about 35% after 48 h of treatment. Lower metal removal could be attributed to the lower liquid flux and the higher liquid volume of 2.4 times that used in the sole electrochemical treatment. However, the PGME removal of 6.9 mg cm−2 was obtained. This was much higher than the removal amounts of 4.5 mg cm−2 and 1.9 mg cm−2 for the sole photocatalytic method and the sole electrochemical treatment, respectively.