열적 전처리 공정에 의한 하수슬러지의 가용화

Abstract

An increase of the population and urbanization has contributed to a significant increase of generated sewage sludge. The annual production of sewage sludge is constantly growing and will continue to grow in the future. An important process among facilities that can secure energy in a sewage treatment plant is an anaerobic digester. The pretreatment process for he anaerobic digester was used increasing gas production and reducing sludge in wastewater treatment plant. The pretreatment technology of the anaerobic digester includes physicochemical treatment consisting of ultrasonication, high pressure treatment, microwave, high voltage, mechanical grinding and thermal treatment etc.. The main operating factors of the thermal treatment process in the anaerobic digestion pretreatment process are temperature, pressure and time. By applying heat, the substrate structure changes from insoluble to soluble, increasing the biodegradability of the substrate, breaking the chemical bonds in the cell wall and releasing intracellular water. The release of water within the cell consequently contributes to the improvement of the dewaterability of the sludge. The purpose of this study is that the thermal pretreatment of sewage sludge contributes to the solubilization of soluble COD, which is used as an indicator for improving the efficiency of the digester, and the reduction of energy required for mixing and sludge transfer in the anaerobic digester. The purpose of this study is to present data that thermal pretreatment contributes to the increase in the efficiency of the anaerobic digestion tank and the energy independence of sewage sludge by analyzing the effect on the capillary suction time expressing phosphorus sludge dewatering properties. The thermal pretreatment process of sewage sludge affects the increase rate of soluble COD, which is an indicator of improving the efficiency of the digester, the decrease in viscosity of the sludge that contributes to energy reduction in the sludge mixing and transport process, and the capillary suction time, which is an indicator of dewaterability of sludge . The temperature and reaction time selected as independent variables of the thermal pretreatment process of sewage sludge were designed with central composite design (CCD) among surface reaction analysis methods, and the experimental results are as follows. In the application of sewage sludge in the thermal pretreatment process, the SCOD solubilization rate(%) increased in proportion to the temperature and reaction time in the heat treatment temperature range of 90 – 150 ℃ and the reaction time of 60 – 90 minutes, and the maximum solubilization rate of the primary sludge was determined by the heat treatment temperature. It was found to be 15.3% at 140 ℃ and reaction time of 80 minutes, and the maximum solubilization rate of the secondary sludge was 37.8% at a heat treatment temperature of 150 ℃ and reaction time of 60 minutes, and the solubilization rate of the secondary sludge was higher than that of the primary sludge. In the thermal pretreatment process of sludge, the SCOD solubilization rate, the decrease rate of capillary suction time, and the decrease rate of viscosity showed a positive correlation with each other. It was found that the increase in solubilization rate by thermal pretreatment affects the decrease in viscosity and increase in sludge solubilization.