Effect of Ultrasound in Improving Dewatering and Stabilization of Anaerobic Digested Sludge

Large quantities of sludge are produced in biological wastewater treatment.This kind of sludge or biosolids are very putrescible. The primary sludge being produced in primary sedimentation tank is very putrescible, odorous, and grey, from which 60 -70 percent is volatile solids. The secondary sludge being produced in primary sedimentation tank is brown, odourless and highly microbial containing 70-80 percent volatile solids. The sludge with these properties has problems not less than domestic wastewater. Therefore, the sludge should be stabilized for safe utilization and disposal in environment.In large wastewater treatment plants high quantities of sludge are produced. Therefore, prior to disposal, solids must be processed for dewatering and reduction of its volatile solids. The processes prior to sludge disposal are thickening, dewatering and stabilization. Dewatering of sludge is reducing transfer and disposal costs. Typical methods for dewatering are filtering, centrifuge and drying sludge bed. At the present time, sludge undergoes many important technical challenges and about 50% of the investments and operation costs are associated with sludge treatment. Usually for the stabilization of sludge, biological digestion processes are used. The digestion methods could be aerobic or anaerobic process. The anaerobic digestion has been studied many years ago and was used for sludge stabilization. This process includes degradation of organic and inorganic compounds in the absence of molecular oxygen. The main application of stabilization process is thickening of sludge from wastewater treatment plants and treatment of industrial wastes. The anaerobic process is a standard technique for sludge stabilization. With regard to the limitation in hydrolysis phase, anaerobic degradation of sludge is a very slow process. This process requires a high fermentative microorganism mass with typical detention time of more than 20 days for sludge digestion. The rate of degradation of organic compounds is in the range of 50 to 60%. Investigation showed that for a better sludge hydrolysis, the following processes is suggested: 1) Chemical solubilisation, 2) thermal pre-treatment, 3) mechanical sludge degradation, and 4) ultrasonic cell degradation.Some advantages of ultrasound pre-treatment of sludge are as below:- Low cost and efficient operation compared to other pre-treatment processes.- Complete process automation.- Potential to control filamentous bulking and foaming in the digester.- Better digester stability.- Improved volatile solid destruction.- Better sludge dewatering ability.- Improved sludge quality.The Usage of ultrasonic process for pollutant degradation in water and wastewater treatment was an advanced oxidation process, which is developed as an efficient technology in different fields of environmental engineering science in order to protect the environment from pollutants and as a key technology for future in the world.