Experimental study of polyvinyl alcohol degradation in aqueous solution by UV/H2O2 process

Water-soluble polymers contaminating industrial effluents create potential pollution concerns in water resources. In particular, polyvinyl alcohol (PVA), which is quite abundant in wastewater effluents, is toxic and cannot be effectively treated by biological processes. The present study investigates the photo-oxidative degradation of aqueous PVA solutions in a UV/H2O2 photochemical reactor and the effect of hydrogen peroxide feeding strategies on the photoreactor performance. The total organic carbon (TOC) removal and the reduction of polymer molecular weights are determined for different initial polymer and hydrogen peroxide concentrations. By treating an aqueous solution containing 500 mg/L of a 130 kg/mol PVA and H2O2/PVA mass ratio of 10, the results show that nearly 87% of TOC removal was achieved when the photoreactor was operated for 2 h in stepwise operation (semi-batch). Accordingly, the number average molecular weight of the polymer is reduced to 10.9 kg/mol (91.6%). The oxidation reaction without UV light, however, is much less effective and results in merely 43% TOC removal and 21% reduction of polymer molecular weights. As for the case where the UV reactor was operated with no hydrogen peroxide, almost no PVA polymer degradation is achieved. This study also shows that the feeding strategy of hydrogen peroxide can have a significant impact on the degradation of PVA molecules in the UV/H2O2 process.