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The development of a facile technology for utilizing effectively and/or reducing excess sludge is one of the urgent problems since a large quantity of sewage sludge is formed by activated sludge processes. Excess sludge containing 50mM sucrose was fermented at 50 degrees C using endogenous bacteria in excess sludge, resulting in a high lactic acid production (8.45 g/L) and in an increased sludge reduction (38.2%). Conversion rate to lactic acid was up to 106.0% by standard fermentation at 50 degrees C compared to 43.8% at 30 degrees C and this phenomenon that conversion rate was higher was observed only at 50 degrees C as the fermentation at less or more than 50 degrees C had lower conversion rate than that at 50 degrees C. Lactic acid bacteria increased at 50 degrees C during 1-d fermentation whereas the number of total viable bacteria only increased slightly, indicating that lactic acid bacteria in sludge at 50 degrees C were preferentially able to utilize the sucrose for producing lactic acid. Finally, pH-vibration fermentation at 50 degrees C enabled to completely consume residual sucrose in the normal fermentation, resulting in the maximum production of lactic acid. Lactate fermentation by a purely cultured lactic acid bacterium TS1 with autoclaved excess sludge containing 50mM sucrose had more than 100% of conversion rate to lactic acid, indicating that a part of sludge was converted into lactic acid during the fermentation. Our technique is useful as a facile engineering for reducing excess sludge concomitantly with producing lactic acid by lactate fermentation.

Interest in the production of lactic acid (LA) is increasing in relation to its applications in the synthesis of biodegradable polymer materials. Before kitchen waste is used as substrates in LA fermentation, it must be stored for some days in the waste collection system. This study examined the effects of pH adjustment including initial pH before the storage in terms of the kind and the amount of added acid on preservation of the waste. The optical purity of LA generated during the storage was also analyzed. It was found that antibacterial activity and suppression ability to D-lactic acid (D-LA) were stronger in the order: acetic acid > L-lactic acid (L-LA) > hydrochloric acid ≈ nitric acid. The optimum condition of waste storage was found to be adjusting initial pH to 3.4 by adding acetic acid. It can be expected that preservation of kitchen waste can be realized by inhibiting the growth of putrefactive bacteria, and higher optical purity of L-LA was obtained by adding weak acid to the waste. [ABSTRACT FROM AUTHOR]

Abstract: Since the actual role of Escherichia coli hydrogenases on fermentation from glycerol has not been clear, we evaluated the effect of inactivation of each E. coli hydrogenase on cell growth, hydrogen production, organic acids production, and ethanol production. Inactivation of hydrogenase 2 and hydrogenase 3 reduced cell growth, hydrogen and succinate production as well as glycerol utilization while acetate increased. Inactivation of hydrogenase 2 in minimal medium at pH 7.5 impaired hydrogen production, but no significant effect occurred at pH 6.5 or in complex medium. Inactivation of hydrogenase 3 impaired hydrogen production in minimal and rich medium, pH 6.5 and pH 7.5 accumulating formate in all conditions. Therefore during fermentation from glycerol, hydrogenase 3 is the main hydrogenase with hydrogen synthesis activity through the formate hydrogen lyase complex. Hydrogenase 2 seems mainly required for optimum glycerol metabolism rather than hydrogen synthesis. There were no significant impacts by inactivating hydrogenase 1 and hydrogenase 4. [Copyright &y& Elsevier]