In order to increase the efficiency of the excess sludge reduction system using ozone, the application of an injector-type ozone reactor was investigated. From the studies on laboratory-scale experiments, it was found that the injector-type ozone reactor could secure a high dissolved ozone concentration in its comparison with the conventional diffuser-type ozone reactor, so that a higher biodegradability of ozonated sludge could be obtained. From the excess sludge reduction experiments using actual wastewater, it was found that the amount of ozone required for the excess sludge reduction in the case of the injector-type reactor was decreased to approximately 1/4 that of the case of the diffuser-type reactor, and the increase in DOC concentration of the treated water was almost of the same level as the diffuser-type reactor. However, there was also suggested the possibility that the injector-type reactor had accelerated dispersion of sludge flocks and decreased sedimentation ability. It could be concluded from these results that this reactor was very efficient for reducing the amount of ozone required for the excess sludge reduction, though it was necessary to consider the worsening of the sedimentation ability of the sludge.
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