Biodegradation Mechanisms of Linear Alcohol Ethoxylates under Anaerobic Conditions

The anaerobic biodegradation mechanisms of linear alcohol ethoxylates (LAE) were studied in incubation experiments with anoxic sewage sludge. Sophisticated analytical techniques were applied, such as solid-phase extraction (SPE) followed by reversed phase high performance liquid chromatography (HPLC) procedures based on the derivatization of LAE and poly(ethylene glycol) (PEG). During the degradation of LAE C 12 (EO) ∼9, a technical dodecanol ethoxylate with an average of nine ethoxy (EO) units, and LAE C 12 (EO) 8, a single ethoxymer, alcohol ethoxylates with shortened EO chains were released as the first identifiable metabolites, but no PEG products were observed. From our results it was concluded that the first step of anaerobic microbial attack on the LAE molecule is the cleavage of the terminal EO unit, releasing acetaldehyde stepwise, and shortening the ethoxy chain until the lipophilic moiety is reached. In contrast to the aerobic degradation pathway, where central scission prevails (the cleavage of the ether bond between alkyl and ethoxy chains), such a primary attack on the surfactant molecule is very unlikely in an anaerobic community of fermenting bacteria.