ANALYSIS OF ENERGY BALANCES FOR A RECYCLING SYSTEM TO INPUT DEWATERED SLUDGE DILECTLY IN CEMENT KILN

Abstract

 Some rural sewage treatment plants, which are located near a cement plant, select a recycling system to input dewatered sludge dilectly in cement kiln. In terms of energy recovery from organic matter contained in sewage sludge, this system (direct cement feedstock system, DCFS) is not defined as an energy recovery measure. Therefore, there is a potential to consider revising the DCFS. On the other hand, an analysis of energy balances and greenhouse gas emissions for this system was not conducted, so information for deciding whether this system should be continued or not is lacking. In this study, I evaluated the cost-effectiveness [kg-CO₂eq/10³ Yen] for the measures to changing from DCFS to sludge carbonization system (SCS) in Gunma and Tochigi prefectures. The evaluated cost-effectiveness values of measures for changing from DCFS to SCS were smaller than the other GHG reduction measures in the field of sludge recycling. It is concluded that continuation of DCFS in rural area is a responsible decision.