ALCOHOL AND ACID FORMATION DURING THE ANAEROBIC DECOMPOSITION OF PROPYLENE-GLYCOL UNDER METHANOGENIC CONDITIONS

Intermediates formed during the anaerobic decomposition of propylene g lycol under methanogenic conditions were studied using a serum bottle technique. The pathway is similar to the anaerobic decomposition of et hylene glycol as previously reported. For both compounds, the decompos ition is believed to proceed via an initial disproportionation of the glycol to form equal molar amounts of the volatile fatty acid and norm al alcohol of the same chain length. In the case of ethylene glycol, d isproportionation results in the formation of acetate and ethanol, whi le disproportionation of propylene glycol produces propionate and n-pr opanol. Following disproportionation, the alcohols produced from glyco l fermentation are oxidized to their corresponding volatile fatty acid with the reduction of protons to form hydrogen. Ethanol and propionat e oxidation to acetate proceeds via a;well-established syntrophic path way that is favorable only under low hydrogen partial pressures. Subse quent degradation of acetate proceeds via acetoclastic methanogenesis with the production of carbon dioxide and methane. Despite the product ion of hydrogen in the initial steps of glycol degradation, both compo unds are completely degradable under the methanogenic conditions teste d in this study.