Biodegradation of poly(vinyl alcohol) with different molecular weights anddegree of hydrolysis

The biodegradability of poly(vinyl alcohol) (PVA) was investigated under di fferent conditions by respirometric determinations, iodometric analysis, an d molecular weight evaluation. Microbial inocula derived from the sewage sl udge of municipal and paper mill wastewater treatment plants were used. A r ather active PVA-degrading bacterial mixed culture was obtained fr om the p aper mill sewage sludge. Significant biodegradation levels within quite sho rt incubation times were obtained in liquid cultures in the presence of acc limated microbial populations. The influence of some polymer properties suc h as molecular weight and degree of hydrolysis on the biodegradation rate a nd extent was investigated in the presence of either the acclimated mixed b acterial culture or its sterile filtrate. Kinetic data relevant to PVA mine ralization and to the variation of PVA concentration, molecular weight, and molecular weight distribution revealed a moderate effect of the degree of hydrolysis. The molecular weight appeared to be not a limiting factor of mi crobial attack. Comparison of the degradation process in the presence of ei ther bacterial cells or their culture filtrate highlighted the ability of s ome microbial strains to utilize polymer chains having 5-10 kD molecular we ight. This result suggests the occurrence of two PVA degradation mechanisms : a random-type attack and a terminal unzipping depolymerization process of polymer chains. Copyright (C) 2000 John Wiley & Sons, Ltd.