Effects Of Ultrasonic Pretreatment On Drying Characteristics Of Sewage Sludge

The dry treatment was the basic treatment technic of municipal sewage sluge. However, the dry treatment was made difficult because of the high water content of the sewage sluge. The high water content of sewage sludge has engendered many inconveniences to its treatment and disposal. While ultrasonic takes on unique advantages on the sludge drying because of its high ultrasonic power, mighty penetrating capability and the ability of causing cavitations. Thus this article studies the characteristics influences of ultrasonic brings to the sludge drying.First of all, after radiated by different ultrasonic conditions, EDTA titration method is used to determine the concentration of the Ca2+ and Mg2+ of the sludge and the results show the ultrasonic pretreatment has obvious effects on the promoting dissolution of Ca2+ and Mg2+. The concentration of the two ions of the pre-treated samples presents an increase in compare with the raw samples, which manifests the ultrasonic's destruction effects on the sludge folcs structure. Especially the ion concentration reach the highest under the operational condition of 250W ultrasonic-power and 15 minutes radiation-time increased by 47% and 5% in contrast with the raw sample.This was followed by sludge drying experiments to determine the influences that ultrasonic processing time, ultrasonic power, water temperatures of ultrasonic generator and drying temperature effect on the sludge drying characteristics. The results show ultrasonic pretreatment can effectively improve the sludge drying efficiency and could be more evident with the rise of the ultrasonic power, ultrasonic temperature and drying temperature. In addition, ultrasonic pretreatment could speed up evaporation of the free water in sludge surface and help to end the drying stage with constant speed. If dried under low temperature such as 105 degree celsius and 110 degree celsius, sludge will have premium drying characteristics when radiated for a shorter time such as 3 minutes by ultrasonic. While if dried under higher temperature, better effect is detected when radiated for a longer time such as 5 to 15 minutes. However, it is inappropriate to pretreat too long time because it may increase the viscosity of sludge which is not conducive to the sludge drying and dewatering.In the end, the ultrasonic treatment is expected to be an effective way to the low-cost sludge drying and also be an important reference to the optimization of the sludge drying process because of its effects on the increase of sludge drying efficiency.