BIODEGRADABILITY AND CHEMICAL-STRUCTURE OF POLYETHERS

Biodegradability of polyethers and their derivatives was examined in the biodegradation by activated sludeges from muniipal sewage plants, growth of polyethylene glycol (PEG)- or polypropylene glycol (PPG)-utiliing bacteria and PEG dehydrogenase activities. Free terminal hydroxyl groups were necessary for biodegradation of polyethers. Chemical degradation of PEG by Fenton's reagent suggested endogenous breakdown of the molecule. On the contrary, biodegradation of PEG suggested that metabolism occurs exogenously at the end of the molecule. The maximum molecular weights which can be assimilated by bacteria were expected to be 20000 approximately 30000, but PEG dehydrogenase appreciably oxidized PEG 50000. This suggests that PEG with a molecular weight higher than 20000 approximately 30000 could be metabolized, but the rate was too slow to support the growth of bacteria. The cleavage of an ether bond seemed to occur between the ether oxygen and beta-carbon from the starting point of biodegradation, because a PEG or PPG molecule depolymerized by one glycol unit is produced from carboxylated or carbonyl PEG or PPG.