Dewatering of initially conditioned excess sludge after fermentation

Abstract

Increasingly more sewage sludge which is generated today causes the efficient management based on the economic criteria to become a key issue. Sludge treatment that uses the stabilization process and dewatering are the most important and the most expensive processes. Construction of dewatering devices and stabilization of sewage sludge accounts for almost 50% of the total cost of construction in sewage treatment plants. Stabilized sewage sludge does not decay, has no bad smell, it is safe in sanitary terms and more suitable for dewatering. Previous studies have demonstrated that conditioning of excess sludge with ultrasound field after methane fermentation positively affects the levels of COD and VFA in supernatant liquor. Stabilization initially aided with conditioning improves the process of sludge fermentation and consequently affects the final susceptibility of the sludge to dewatering. The paper presents the investigations carried out for the sludge from communal sludge treatment and the sludge from cellulose industry. The studied sludge was initially conditioned with the ultrasonic field and then stabilized in order to determine the final parameters of their dewatering. Sonication of the sludge contributed to improvement in the degree of thickening. Conditioning caused an increase in the capillary suction time and specific resistance of the sludge. Some improvement regarding those parameters was found in the sludge after the fermentation process.