Application of Fenton pre-oxidation, Ca-induced coagulation, and sludge reclamation for enhanced treatment of ultra-high concentration poly(vinyl alcohol) wastewater

Poly(vinyl alcohol) (PVA) wastewater contains up to 10,000 mg/L dissolved organic carbon. A concentration of this magnitude results in a high chemical oxygen demand (COD), which generates major problems for industrial wastewater treatment in general, and the textile and chemical industries, in particular. Thus, we propose a two-stage treatment process that uses Fenton pre-oxidation, coupled with Ca-induced coagulation, to reduce the PVA and COD wastewater concentration. The optimal concentrations of FeSO4 and CaCl2 per gram of PVA were 0.8 g/g-PVA and 4.0 g/g-PVA, respectively, which is significantly lower than that of other reported treatments. Due to successful oxidation, the long chains of PVA molecules were broken up and the OH groups were partially oxidized to COOH. During the coagulation stage, Ca2+ was able to efficiently bind with the PVA pre-oxidation products, thereby forming insoluble compounds. Given initial COD and PVA concentrations of 20,450 and 10,000 mg/L, respectively, a maximum of 81.3 % COD and 96.0 % PVA was removed following this two-stage procedure. Furthermore, the sludge residue was used to remove Sb(III) from the wastewater, achieving an Sb(III) adsorption capacity of 16.0 mg/g. Thus, this study provides new insight into affordable and effective treatment of high concentration PVA-containing wastewater.