A Developmental Research on Upgrading and Practical Application of Anaerobic Contact Process by Using Two-Phase Anaerobic Process

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A biological sludge bulking phenomenon was observed in experimental anaerobic contact processes (ACP) treating wheat starch waste water, and the bulking was caused by filamentously growing anaerobic microorganisms. There are many kinds of anaerobic microorganisms which grow filamentously, like in activated sludge. One species of anaerobic bacteria caused serious sludge bulking, and it had thin rod (around 0.2 m in width) and long chained morphology. When acidogenically fermented starch waste water was fed to the ACP, the thin rod microorganism was eliminated and the biomass concentration of the methanogenic fermentor was recovered. From these results, it is revealed that acidogenic fermentation of waste water containing raw starch prior to treatment by an ACP is effective to prevent the anaerobic sludge bulking and to keep high organic loading of ACPs.The comparison of one-phase and Two-phase anaerobic digestion processes in the characteristics of substrate degradation and the bacterial population levels was investigated by using the chmostate-type reactor to which starch was fed as substrate when both processes were operated under the same experimental conditions. It was found that the two-phase system was more stable to the change in pH than one-phase system. The methane recovery rates and COD removal rates in the two-phase system increased by 4 to 9% and 3 to 10%, respectively. The population levels of acidogenic bacteria in both system were in the same order, but the number of acetate-utilizing methanogenesis in the methanogenesis of the two-phase system were 2 to 10 times higher than in the one-phase system. The phase separation by high dilution rate would strengthen the ecological relationships among the bacteria rather than weaken or destroy these relationships.