Coagulation and ozonation treatment of biologically treated wastewater from recycled paper pulping industry: effect on the change of organic compounds.

Recycled paper pulping wastewater (RPPW) will cause serious environmental problems due to the high loads of dissolved organic matter (DOM) and toxic components. In the present work, the degradation of DOM in the biologically treated RPPWs (cardboard wastewater (CW) and corrugated container wastewater (CCW)) by a combined coagulation and ozonation process was investigated. The optimal chemical oxygen demand (COD) removal of CW reached 73.64% at aluminum sulfate (Al(SO)) dosage of 800 mg/l, aeration aperture of 10 μm, pH of 9, hydrogen peroxide (HO) dosage of 100 mg/l, and reaction time of 70 min. The optimal COD removal of CCW reached 55.76% at a poly-aluminum chloride (PAC) dosage of 700 mg/l, HO dosage of 140 mg/l, and reaction time of 50 min. This study provided some insights into the change of DOM during the combined treatment through the use of UV-Vis spectroscopy and excitation-emission matrix spectroscopy (EEM). PAC and Al(SO) removed high molecular weight organic such as lignin and lignin-derived compounds to improve the biodegradability of the wastewater. Ozone oxidized high molecular weight organic with complex functional groups to low molecular weight organic with simple functional groups and even mineralization, and this phenomenon resulted in the COD of ozonation effluent significantly reduced. Thus, the results presented in this study support the application of the combined coagulation and ozonation process in treating RPPW.