The Research Of Adding Fe~0Powder 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, and only acetate is utilized by methanogens, thus deteriorating the digestion. Thus, the propionate production and/or propionic-type fermentation occurring in the acidogenesis stage should be reduced during the anaerobic digestion. So that could operate the anaerobic system successfully and maintained high performance.In this study, Fe。 powder(10g) was added into an acidogenic reactor (Al) to compare with the performance of the conversion of propionate to acetate in a control reactor (A2), the conclusions of the research were shown as follow:(1) The addition of Fe powder into the acidogenic reactor increased the propionate concersion rate. The increased of propionate concersion rate made the COD removal and acetate production of Al were all higher than that of A2.(2) The addition of Fe。 powder enhanced the homoactogenesis, thus reducing the H2content to create a favourable condition for propionate decomposition. According to the calculation on the Gibbs free energy, that of Al was decreased by about8.0%to10.2%. The key enzymes activities in the conversion of propionate to acetate were analysis, the activities of enzymes related to the acetogenesis were enhanced by2-34folds.(3) Fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE) analysis indicated that Fe。increased the abundance of microbial communities, especially propionate-utilizing bacteria and homoacetogenic bacteria.When the influent condition is varied, such as pH and influent concentration, the operation efficiency of acidogenic reactor with Fe。dosed also keeps unknown. These operation parameters must be clear before the practical engineering application. Thus, Fe。 powder (5g) was adding into an acidogenic reactor (R1), and set up a control reactor (R2) to further research Fe。powder dosing could accelerate the decomposition of propionate and enhance the conversion of propionate to acetate under different conditions in this study. The following conclusions could be drawn:(1) The effluent COD of R1due to the addition of ZVI was always lower than that of R2at acidity and high concentration condition. The concentrations of propionate in R1were always lower than that in R2at every stage. Correspondingly, the concentrations of acetate in R1were higher than that in R2. Although the propionate decomposition was inhibited by the acidic influent, the propionate conversion rate in R1was about two times higher than that in R2. The conversion rate in R1was little affected by the increased influent COD, but the conversion rate in R2was decreased. The results clearly indicated that the addition of ZVI in the acidification reactor could effectively enhance the anaerobic system to adopt the variety of the quality in the influent.(2) Analysis the EPS content of sludge showed that the EPS composition content of sludge with Fe dosed was increased. These all contributed to increase the sludge granule size and a stable double-layer structure.(4) The abundance of propionic-utilizing bacteria and acetate-utilizing methanogenesis bacteria in reactor R1were all higher than that in reactor R2. It proved that the adding Fe。 powder could enhance the conversion of propionate to acetate in the point of microbe.