宮永 一彦

Recently, excess sludge from wastewater treatment plant has been one of the serious problems. They are disposed by landfill, incineration, bio-gas production and so on. However, these conventional methods contain drawbacks such as short of landfill, dioxin emissions or inefficient production. A countermeasure against the problems is to minimize the sludge production in the wastewater treatment process. In this study, a biochemical sludge-reduction system was proposed. The microbes were experienced in the aerobic and anaerobic conditions alternately. By the change of microbial growth condition, it is thought that obligate aerobic and anaerobic microbes are to be dead, resulting in their solubilization under alternated anaerobic and aerobic conditions, respectively. The concentrations of organic carbonaceous and nitrogenous substrates and mixed liquor suspended solid (MLSS) were more greatly reduced under the alternate aerobic-anaerobic conditions than under the continuous aerobic or anaerobic conditions. The MLSS mainly consisted of protein (more than 50%w/w) and the amount of protein in the suspension fluctuated during the cultivation without any additions of substrates. These results indicate that the microbial solubilization and utilization of protein lysate seem to take place in this system. So far, however, the effects of growth condition on the microbial viabilities in the solubilization have not been investigated. To clarify them, carboxyfluorescein diacetate (CFDA) that was substrate of intracellular esterase was used as an indicator of microbial viability. As a further experiment, the relationships between sludge solubilization, bacterial viabilities and substrate removal are to be investigated in the continuous wastewater treatment process.