The Research Of Improvement Of Sewage Sludge's Drying Properties Through Ultrasound Treatment

As the by-product of municipal sewage treatment, sewage sludge had brought to cities lots of environmental problems. First of all, although had been dewatered, sewage sludge still contented much water which caused problems in transporting, disposing and also in high investment. Second, when the sewage sludge was under an anaerobic condition, it would release odor gases such as H2S which was deleterious to envrionment. Concerning these tow problems, this article researched the relation between the water content of sewage sludge and the emission rate of H2S. Furthermore, it applied ultrasonic treatment to improve the drying properties of sewage sludge.In the first part, the emission rates of H2S from the sewage sludge with 9 different water contents were researched under anaerobic condition. The results indicated that the emission of H2S from dewatered waste activated sludge (WAS) fluctuated periodically within about 40 days. The affection of water content on H2S emission rate of sewage sludge was mainly during the 5~25 days in which the H2S emission rate from the sewage sludge with a water content of 93.75% was 11.8969 mg/kg dry sludge, and the one from the sewage sludge with a water content of 10.33% was only 1.1131 mg/kg dry sludge which was only 9.4% of the former one. In other periods, the affection of water content was limited.The drying properties of two kinds of sewage sludge, sewage sludge after flocculation and settling (water content was 95.02%) and the one after mechanical dewatered (water content was 82.92%), were tested after ultrasonic treatment in the temperature 250℃, 150℃and natural temperature (12℃~15℃). The results indicated that ultrasonic treatment could improve the drying velocity of these two kinds of sewage sludge under the temperatures of 250℃and 150℃. But in the natural temperature condition, ultrasonic treatment had no effective function.The improvement of drying velocity of sewage sludge and the decrease of the final water content in the same condition made ultrasonic treatment a promising method to cut down the disposing cost of sewage sludge and limit odor pollution from it.