Improvement of Sludge Dewatering by Ultrasonic Pretreatment

摘要

Nowadays, treatment and dewatering of sludge are one of the most difficult processes in wastewater treatment plants and a major challenge for professionals and officials. Reducing the volume of sludge production in activated sludge method is very important. Dewatering process is responsible for separating excess water from the wasted sludge. It is an important issue to increase the amount of treatment and reduce environmental pollution. The aim of present research was to examine the impacts of ultrasonic wave to improve the dewatering characteristics of sludge such as capillary suction time (CST) and solid contents (SC) in sludge cake and determining the optimal range of variables such as ultrasound density, time and the amount of sludge exposed to sonification by use of ultrasonic method. The present research was a batch experiment performed on a laboratory scale. During two seasons, 12 samples were collected from the treatment plant of South of Tehran (Iran) with an interval of 15 days. The influence of the variables on CST and SC in sludge cake was measured. The effect of ultrasonic waves on the SC was studied by using a particle size sensor. The optimum CST and SC in sludge cake was 86 s and 26.4 when amount of sludge subjected to sonication, time and ultrasonic density were 15, 5 min and 1 kW/mL, respectively. The d(10), d(50), d(90) and mean particle sizes with the application of ultrasonic waves were 6.3, 44.2, 24.4 and 28.84 mu m, respectively. According to the results of this study, ultrasound waves and cavitation phenomenon can improve the sludge dewaterability characteristics and capable of increasing the process efficiency.