Basic Research On Ultrasonic Pretreatment Of Sewage Sludge

The high water content of sewage sludge has engendered many inconveniences in transportation, disposal, sanitation and other areas. Ultrasound has the unique advantage in improving the sludge drying rate with its energy compaction, high penetrating power and the cavitation. The ultrasound in improving the sewage sludge drying rate and pre-treatment technics were experimental studied.The effects of pretreatment time, the density of ultrasound, and the water content of the sewage sludge on the sludge drying rate were researched by sludge drying experiments. The results show that ultrasonic pretreatment can effectively improve the sludge drying rate, speed up the evaporation of the free water in sludge surface and help to end the constant drying stage. It was found that the low density (3W/mL), short time (4min) and the low water content (84.7%) are the best operation condition for improving the sludge drying rate. However, when the density of ultrasonic and the water content are too high that will not be conducive to the ultrasonic crack and the evaporation of the free water.The mechanical dehydration of the pretreated sewage sludge was simulated, and the influence of water content on the pretreatment was studied. The results show that when the water content is low, the effect of dehydration is very obvious under different ultrasonic densities and different time and the water content is decreased to 70%-81%, which greatly increase the efficiency of the mechanical dehydration. But continuing to increase the water content, most energy is absorbed by water, which reduces the efficiency of the ultrasonic crack.The main factors that affect the ultrasonic pretreatment were analyzed by using the gray theory. The order of correlation degree on various factors affecting sludge drying rate was: the water content of sludge> the density of ultrasonic >radiation time.The pretreatment by the ultrasonic, improving the sludge drying rate and the pre-treatment technics were affected by a lot of factors, for example, radiation time, the density of ultrasonic, the sewage sludge factors, etc. In order to make the ultrasonic pretreatment play a full role, only when these factors combine to the best condition can reduce the cost of the sewage plants, ameliorate the technics of the sludge treatment, and find a new way for the sewage sludge resource recovery, innocuity and reduction.