n-Propanol production during ethanol degradation using anaerobic granules

n-Propanol formation and consumption during ethanol oxidation by anaerobic brewery granules was investigated. The granules were taken from an UASB reactor fed with a synthetic brewery waste water. Ethanol degradation assays and an isotopic assay using 13C-labeled ethanol and bicarbonate were performed. Intermediate products propionate, n-propanol, acetate, hydrogen, formate and carbon monoxide were observed. Results have shown a consistent and reproducible trend of ethanol being converted to, primarily intermediates propionate and acetate with some accumulation of n-propanol. Hydrogen and carbon monoxide concentration accumulated to 1120 and 50 ppm in the gas phase, respectively. Methane and carbon dioxide were the terminal products. Bicarbonate was not a significant contributor of carbon for n-propanol production based on 13C assay results. From reaction energetics analysis and ethanol degradation assays, reactions of hydroformylation of ethanol with carbon monoxide and hydrogen, ethanol condensation, propionate reduction, and, ethanol oxidation coupled with propionate reduction are potentially responsible for the formation of propanol during anaerobic ethanol oxidation. Carbon monoxide is likely an additional carbon to ethanol during the formation of n-propanol. Hydrogen appeared to play a strong role as a driving force governing reactions involving propionate.