Degradation of Organic Matter of Municipal Sewage Sludge Using Ultrasound Treatment in Shiraz Wastewater Treatment Plant

Abstract

Background: Nowadays, the reduction of sludge production in the activated sludge process as well as disposal restrictions have drawn much attention. Objectives: The purpose of this study was to evaluate the feasibility of using ultrasound treatment in increasing the degradation of organic matter in sewage sludge from Shiraz Municipal Wastewater Treatment Plant and also to assess its effect on sludge dewatering. Materials and Methods: The samples were collected from the anaerobic digester of the Shiraz Wastewater Treatment Plant. The present study was conducted at the bench-scale method. The influence of different pH (3-9) and the effect of contact time (10-120 min) at the constant ultrasonic treatment (37 kHz) on degradation of organic matter were investigated. Since ultrasound is a cyclic sound pressure with a frequency greater than the upper limit of the human hearing range, this limit is approximately 20 kilohertz (20,000 hertz). In addition, the effect of ultrasonic treatment on the total solids (TS), volatile solids (VS), sludge volume index (SVI) and specific resistance to filtration (SRF) were determined. Results: The results of this study showed that the release of soluble chemical oxygen demand (SCOD) in the supernatant and SRF were in the range of 127.9-831 mg/L and 12.48-36.55 m/kg at 10 to 120 min ultrasonic contact time, respectively. In addition, TS and VS decreased from 57.98 and 56.31 to 52.69 and 49.87 mg/L, respectively. Despite the significant reduction in the solids, there was no considerable variation in SVI. Conclusions: This method can be used as a pretreatment method for the treatment of the sewage sludge. Moreover, a complementary treatment is necessary to reach the standard limit.