The authors observed a biological sludge bulking phenomenon which was caused by filamentously growing anaerobic microorganisms in experimental anaerobic contact processes (ACP) treating wheat starch wastewater. 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 µ m in width) and long chained morphology. When acidogenically fermented starch wastewater was fed to the ACP, the thin rod microorganism was eliminated and the biomass concentration of the methanogenic fermentor was recovered. The microorganism which caused bulking phenomenon was enriched in a liquid medium containing raw starch (wheat starch particle). The microorganism grew in long chained filamentous form, degraded raw starch, and fermented mainly volatile fatty acids (acetate, propionate, butyrate and ethanol). From these results, it is revealed that acidogenic fermentation of wastewater containing raw starch prior to treatment by an ACP is effective to prevent the anaerobic sludge bulking and to keep high organic laoding of ACPs.

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