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

The biodegradability of poly(vinyl alcohol) (PVA) was investigated under different conditions by respirometric determinations, iodometric analysis, and molecular weight evaluation. Microbial inocula derived from the sewage sludge of municipal and paper mill wastewater treatment plants were used. A rather active PVA-degrading bacterial mixed culture was obtained fr om the paper mill sewage sludge. Significant biodegradation levels within quite short incubation times were obtained in liquid cultures in the presence of acclimated microbial populations. The influence of some polymer properties such as molecular weight and degree of hydrolysis on the biodegradation rate and extent was investigated in the presence of either the acclimated mixed bacterial culture or its sterile filtrate. Kinetic data relevant to PVA mineralization 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 microbial attack. Comparison of the degradation process in the presence of either bacterial cells or their culture filtrate highlighted the ability of some microbial strains to utilize polymer chains having 5-10 kD molecular weight. 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.