Adding Fe0 powder to enhance the anaerobic conversion of propionate to acetate

Propionate is an unfavorable substrate for the anaerobic digestion because it is thermodynamically difficult to be decomposed into acetate. An attempt to enhance the decomposition of propionate by adding Fe-0 powder (log) into an acidogenic reactor (A1) with propionate as the sole carbon source was made in this study. The results showed that the propionate conversion rate (67-89%) in A1 were higher than that in a reference reactor (43-77%) without dosing of Fe-0 (A2). The enhanced conversion of propionate caused both chemical oxygen demand removal (COD) (57-79%) and acetate production (178-328 mg/L) in A1 to increase significantly. Although Fe-0 contributed the H-2 production chemically, the H-2 content of A1 was less than that of A2. The reason was ascribed to the enhanced utilization of H-2 for the homoacetogenesis. It was calculated that the Gibbs free energy in the decomposition of propionate was decreased by about 8.0-10.2% with the dosing of Fe-0. Also, the activities of enzymes related to the acetogenesis were enhanced by 2-34-folds. Fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE) analysis indicated that Fe-0 increased the abundance of microbial communities, especially propionate-utilizing bacteria and homoacetogenic bacteria. (C) 2013 Elsevier B.V. All rights reserved.