Simultaneous removal of metal ions and oxidation of linear alkylbenzene sulfonate by combined electrochemical and photocatalytic processes

Simultaneous electrochemical removal of Zn⁺₂ and Ni⁺₂ ions and photooxidation of linear alkylbenzene sulfonate (LAS) over TiO₂ particles were investigated. To achieve this objective, first, the effect of different variables such as current density, pH and flow rate on sole electrochemical reduction of metal ions was studied. Both controlling pH in the range of 5.5-6 and increasing the liquid volumetric flux effectively improved the rate of Zn⁺₂ ion reduction, but they did not have any significant effect on the rate of Ni⁺₂ ion reduction. Under optimum operating conditions ... and using total electrolyte volume of 6 L, zinc and nickel were reduced by 86% and 53% respectively, over a 7-hour treatment period. Sole photocatalytic treatment of LAS and controlling pH between 5-5.5 resulted in 60% LAS degradation. However, temperature and flow rate did not have any considerable effect on the rate of LAS degradation compared to the photocatalytic system alone. LAS was degraded in the combined system by 76% compared to 60% in the sole photocatalytic system. However, using the combined system, zinc and nickel were reduced by 81% and 47% respectively, which were slightly less than those obtained in the electrochemical system alone.