Anaerobic biotransformation of four 3-carbon compounds (acrolein, acrylic acid, allyl alcohol and n-propanol) in UASB reactors

Anaerobic biotransformation of the 3-carbon compounds, namely acrolein, acrylic acid, allyl alcohol, and n-propanol was investigated in upflow anaerobic sludge blanket (:UASB) reactors containing granular cultures. The toxic effects of acrolein, acrylic acid, and allyl alcohol on an acetate-enriched Methanosarcina culture were determined. Furthermore, process staging, effect of operational parameters such as influent concentration, F/M ratio and loading rate were also considered. Acrolein, acrylic acid, and allyl alcohol were found to be inhibitory to acetate-enriched Methanosarcina cultures starting from the concentrations of 20, 60, and 3000 mg/l, respectively. Inhibition is defined as the reduction in the activity (in terms of gas production rate) of a batch reactor relative to its activity before the addition of the test chemical. The results of UASB experiments revealed that granular cultures could be acclimated to utilize acrolein, acrylic acid, allyl alcohol, and n-propanol as the sole substrates. Acrolein concentrations up to 300 mg/l were treated with 90% efficiency. In a single-stage UASB reactor, acrylic acid biotransformation and chemical oxygen demand (GOD) removal efficiencies of 95-99 and 45%, respectively, were achieved at an influent concentration of 3000 mg/l. The low COD removal was due to persistence of acetic and propionic acids, as intermediates of acrylic acid. When a two-stage UASB system was employed at the same acrylic acid influent concentration, the COD removal efficiency increased to 97%. At an F/M ratio of 0.027 g COD/g biomass-day, 1000 mg/l of influent allyl alcohol was removed at an efficiency of about 85% after 30 days of acclimation in a single-stage UASB reactor. n-Propanol was biotransformed to mainly propionic acid with more than 99% efficiency at an influent concentration and F/M ratio of 3000 mg/l and 0.27 g COD/g biomass-day, respectively, in a single-stage UASB reactor. But the COD removal did not exceed 68% because of the propionic acid persistence. However, a two-stage UASB system improved the COD removal to 99% for the same n-propanol influent concentration of 3000 mg/l. (C) 1998 Elsevier Science Ltd. All rights reserved.