Research On The Condition And Mechanism Of Polyvinyl Alcohol Degradation By Fenton Oxidation

Polyvinyl alcohol (PVA) is a kind of water-soluble polymer that is difficult to be degradedby common microorganism. Because of more and more use of this polymer these years, thewastewater containing PVA results in seriously environment pollution. So it is desirable to findan effective way to treat the wastewater containing PVA.The treatment result is unsatisfactory by using traditional biochemical process, since PVA isnon-biodegradable and its biodegradability is very low. On the other hand, generalphysicochemical technology only contributes a little to remove PVA in the wastewater.In this dissertation, PVA was treated by Fenton oxidation. On the purpose of degrading PVAeffectively and improving its biodegradability, the main factors and mechanism of PVAdegradation were studied. The results obtained are shown as following:⑴ Effects of reaction time, initial pH, mass ratio of H2O2 and COD, mole ratio of H2O2 andFe2+, temperature on the degradation of PVA by Fenton oxidation were studied respectively toimprove its biodegradability. The optimal operation condition was obtained by orthogonal test.The reaction time was 30 min, initial pH was 5, mass ratio of H2O2 and COD was 1.3, mole ratioof H2O2 and Fe2+ was 10 and temperature was 40℃.⑵ The degradation approach of PVA in Fenton oxidation was presumed by the change ofapparent parameters, such as TOC, COD, BOD, pH, and so on. It was found that in acidiccondition, PVA was oxidized by ·OH generated in Fenton reaction, about 60% of its organiccarbon was converted to CO2, a part of the remaining was oxidized to acids. So 80% of CODwas removed from PVA.⑶ The effects of the change of main factors on PVA degradation approach were studied. Thetype of oxidation intermediates of PVA changed with the concentration of H2O2 in the way thatwhen H2O2 was deficient, aldehyde was regarded as the main intermediate, otherwise, aldehydewould be oxidized to organic acid.⑷ The mechanism of PVA degradation was studied with gel permeation chromatography,UV-vis spectrum, FT-IR spectrum and GC-MS. The oxidation approach of PVA was derived asfollowing. Dehydrogenation was occurred by ·OH oxidation, double bond of C=C was formed.And then double bond was broken, PVA molecule was degraded. Finally, the formed aldehyde,ketone or organic acid was degraded to CO2 and H2O. So the COD concentration of PVA wasdecreased greatly.⑸ When different PVA and different simulated wastewater were treated by Fenton oxidation,COD concentration was decreased, the removal efficiency of COD was more than 60% and the ratio ofBOD and COD increased from about 0.10 to above 0.40. It was proved by activated sludge process thatafter Fenton oxidation, PVA was degraded to biodegradable intermediates and itsbiodegradability was improved.