Degradation of natural and synthetic polyesters under anaerobic conditions

Often, degradability under anaerobic conditions is desirable for plastics c laimed to be biodegradable, e.g. in anaerobic biowaste treatment plants, la ndfills and in natural anaerobic sediments. The biodegradation of the natur al polyesters poly(beta -hydroxybutyrate) (PHB), poly(beta -hydroxybutyrate -co-11.6%-beta -hydroxyvalerate) (PHBV) and the synthetic polyester poly(ep silon -caprolactone) (PCL) was studied in two anaerobic sludges and individ ual polyester degrading anaerobic strains were isolated, characterized and used for degradation experiments under controlled laboratory conditions. In cubation of PHB and PHBV films in two anaerobic sludges exhibited significa nt degradation in a time scale of 6-10 weeks monitored by weight loss and b iogas formation. In contrast to aerobic conditions, PHB was degraded anaero bically more rapidly than the copolyester PHBV, when tested with either mix ed cultures or a single strained isolate. PCL tends to degrade slower than the natural polyesters PHB and PHBV. Four PHB and PCL degrading isolates we re taxonomically identified and are obviously new species belonging to the genus Clostridium group I. The depolymerizing enzyme systems of PHB and PCL degrading isolates are supposed to be different. Using one isolated strain in an optimized laboratory degradation test with PHB powder, the degradati on time was drastically reduced compared to the degradation in sludges (2 d ays vs. 6-10 weeks). (C) 2001 Elsevier Science B.V. All rights reserved.