Ultrasonic disintegration of sewage sludge

The production of excess sludge is one of the most serious challenges in biological wastewater treatment plants. Treatment and disposal of excess sludge in a biological wastewater treatment system requires high cost which has been estimated to be 50?60% of the total expense of wastewater treatment plant (Metcalf & Eddy, 2004; Egemen et. al., 2001). A common method for the biodegradation of excess sludge is biological treatment by anaerobic digestion. Anaerobic digestion is commonly used for stabilization and solid reduction of treatment plant sludges. Anaerobic digestion is a slow process because of the hydrolysis stage which is the rate-limiting step of the sludge degradation. That disadvantage is prominanced for the treatment of excess sludge which is the final product of the treatment of meat processing sludge due to its high oil and high organic material contents. In order to improve hydrolysis and anaerobic digestion performance, disintegration was developed as the pretreatment process of sludge to accelerate the anaerobic digestion and to increase degree of stabilization (Bougrier et. al., 2005)The main purpose of this thesis was to investigate the effects of ultrasonic pre-treatment on excess sludge disintegration at different specific energy inputs with low ultrasound frequency (20 kHz). Meat processing sludge containing high organic materials and oil content was chosen as sludge sample for the experimental studies which disintegration degree (DD) that used as the main parameter for evaluation of disintegration performance of sludge. Solid reductions with the ultrasonic pre-treatment were monitored total solids (TS), total organic solids, suspended solids (SS), and volatile suspended solids (VSS) measurements. Effects of ultrasonic disintegration on supernatant characteristics on meat processing industry sludges were also investigated. Biochemical methane potential (BMP) assay was carried out in order to monitor methane production as the indicator of improvement anaerobic biological degradation preceding ultrasonic treatment. In addition, the effect of ultrasonic pre-treatment on sludge filterability was evaluated depending on CST measurements of raw and pre-treated sludge samples.The experimental results showed that 30000 kJ/kgTS of supplied energy is efficient for disintegration of meat processing sludge. Higher specific energy inputs then 30000 kJ/kgTS led to a mineralization phenomenon preceding a solubilization phenomenon and because of that disintegration degree (DD) decreased. The protein results showed that sludge solids were hydrolyzing during the ultrasonic pre-treatment. Biochemical methane potential (BMP) results obtained in this study suggest that ultrasonic pre-treatment significantly enhanced the biodegradability of biological sludge than sludges that not pre-treated. Maximum methane production was observed for 30000 kJ/kgT and 136% higher biogas production in pre-treated sludge was obtained comparing to the raw sludge at the end of the 40 days of incubation period. Sludge?s supernatant characteristics were also affected by the ultrasonic pre-treatment. For 30000 kJ/kgTS, the soluble chemical oxygen demand (SCOD), dissolved organic carbon (DOC), total nitrogen (TN), total phosphorus (TP) in sludge?s supernatant increased by 487%, 290%, 3230%, and 870%, respectively. Depending on CST data, there was a negative effect of ultrasonic pre-treatment on sludge filterability even for very low specific energy levels.Keywords: anaerobic digestion, sewage sludge, ultrasonic pre-treatment, disintegration