Qualitative investigation of sewage sludge composting: effect of aerobic/anaerobic pretreatments

Abstract

Treatment and recycling of organic waste play important roles in an integrated waste management system by producing a stabilized material that can be utilized as a source of nutrients and as a soil conditioner. In this study, the viability of composting for the recycling of sewage sludge and also the possible effects of pretreatment under various conditions on the quality of the end-product were examined. Waste sewage sludge was obtained from a wastewater treatment plant in Hamedan, Iran, and was subjected to aerobic and anaerobic digestions. After analyzing the physicochemical properties of the digest, both treated sludges were composted. A third reactor was also set as control by direct composting of sewage sludge without pretreatment. The composting process was controlled by the measurement of the physicochemical properties of the substrate during and at the end of the process. The results of the analyses showed a substantial decrease in the C/N ratio, pH, volatile solids (VSS), total organic carbon, as well as pathogenic populations; however, a significant increase was observed in the ash and nitrogen contents in the compost obtained after anaerobic digestion. Accordingly, it was decided that the compost obtained, especially after anaerobic digestion, showed adequate degrees of maturity and stability and reflected characteristics, which based on national and international standards made it suitable for agricultural use.