Improving Acetate Production From Sewage Sludge By A Novel Coupled Syntrophic Acetogenesis With Homoacetogenesis Process

The fermentation of municipal sewage sludge by a novel coupled syntrophic acetogenesis with homoacetogenesis process was studied. The result demonstrated that this coupling system was able to enhance acetate production by relieving hydrogen inhibition during acidification. Results were shown as follow:(1) The coupling system was used to fermentate sewage sludge, and compared with he non-coupling system. Under the experimental condition, the highest concentration of acetate in the syntrophic acetogenesis phase reached 4.27 g/L. In the homoacetogenesis phase, acetate concentration was 1.07 g/L. Acetate yield and total VFA yield in the coupling system reached 0.42 g/ gVS and 0.69 g/ gVS respectively, 61.5% and 53.3% higher than that in the non-coupling system. This study also indicated that pretreatment by heat-alkali could cause 2.9 times of increase in acetate production.(2) Two control systems was used to be compared with the coupling system in acetate production. The acetate yield in the coupling system was 31.3% and 13.5% higher than the two control systems. Enhancement of acetate production is attributed principally to homoacetogenesis, relief of the products (H2 and CO2) inhibition to acidification and syntrophic acetogenesis, enhancement of the conversion of substrate.(3) The effect of pH control to acetate production was studied. When keeping pH 10.0, the final concentration of acetate in the syntrophic acetogenesis phase reached 7.42 g/L, 44.6% higher than the ordinary system. Acetate yield was 0.46 g/ gVS, 4.6% higher than the ordinary system. The acetate percentage of total VFAs in the syntrophic acetogenesis phase reached 68.1%, also higher than the ordinary system.(4) The fed-batch method helps to balance hydrogen production in the acidification phase and hydrogen consumption in the homoacetogenesis phase of the coupling system, and helps to reduce the shockloading of or ganics at the beginning of the fermentation. After 18 d's fermentation, the concentration of acetate in the syntrophic acetogenesis phase of fed-batch 1,2 reached 8.02 g/L and 7.56 g/L. The total VFAs was 11.52 g/L and 11.43 g/L. The concentration of acetate in the homoacetogenesis phase was 1.76 g/L and 1.45 g/L, 50% and 24% higher than the ordinary system. Acetate yield to SCOD was 0.44 and 0.37, 29.4% and 8.8% higher than the ordinary system.