Reuse of sewage sludge as a catalyst in ozonation - Efficiency for the removal of oxalic acid and the control of bromate formation

Sewage derived sludge is produced with an annual amount increase of 2% all over the world and it is an urgent issue to be addressed by human being. In the present study, sludge was converted into sludge-based catalyst (SBC) with ZnCl₂ as activation agent and characterized by several methods (e.g., scanning electron microscope, X-ray photoelectron spectroscope and Fourier transform infrared spectroscope). Then it was used as a catalyst to enhance the removal of refractory organic matter, oxalic acid, and to control the formation of bromate (BrO₃^-) in bench semi-continuous ozonation experiments. The effects of various operating parameters on the control of BrO₃^- formation were investigated. Furthermore, the mechanism for the enhancement of organic matter removal and the control of BrO₃^- formation was discussed as well. Results indicate that the combination of SBC with ozone shows a strong synergistic effect, resulting in a notable improvement on oxalic acid removal. A crucial surface reaction mechanism for the enhancement of organic matter removal is proposed on the basis of negative effect of higher pH and no inhibition effect of tert-butanol. The control for BrO₃^- formation was demonstrated and the reason for its control in the process of O₃/SBC is the combined effect of SBC reductive properties, ozone exposure decrease and hydrogen peroxide concentration increase.