抄録
This work experimentally elucidated a system for reducing the amount of excess sludge by solubilization of return sludge using an ultrasonic wave process. In this system, part of the return sludge is sent to an ultrasonic reactor, and solubilized sludge is biodegraded in the aeration tank. This study examined (1) solubilization and destruction characteristics of treated activated sludge by ultrasonic wave under practical conditions;(2) reduction of excess sludge production under various conditions on a laboratory scale;(3) field tests; and (4) greenhouse gas emissions. Consequently, the following results were obtained;(1) Even though some bacteria were destroyed, activated sludge treated by ultrasonic waves are not reduced to single cells, but to the smallest flocs under 5μm. Treated activated sludge was scarcely solubilized and their activity levels were scarcely changed.(2) Laboratory scale experiments showed that this system is available for wastewater treatment system. Maximal reduction ratio of excess sludge is about 80%, and it was shown that its ratio is changed not only by exposure power and time but also by retention time in the aeration tank (3) Field tests showed that this system can reduce excess sludge and the maximal reduction ratio was 85%.(4) Greenhouse gas emissions of this system are about 40% lower than those of commonly used methods of sludge treat.
