Feasibility Study on the Co-incineration of Municipal Solid Waste and Sewage Sludge in Taiwan

Abstract

 The co-incineration of sewage sludge and municipal solid waste (MSW) as a sewage sludge treatment method has a possibility to decrease lifecycle cost, energy consumption and greenhouse gas (GHG) emission. This study aims to clarify the feasibility on co-incineration of sewage sludge and MSW in Taiwan. This study assumes that sewage sludge is transported to MSWI by vehicles for co-incineration. First, we collected information on WWTPs and MSWIs in Taiwan and established a database using Google My Map. Second, we set the necessary conditions through literature and questionnaires for co-incineration: (1) Operating ratio less than 90%, (2) Mixing ratio less than 3% (dewatered sludge) and 1% (dried sludge), and (3) Distance between WWTP and MSWI is within 30 km. Third, four scenarios (dried sludge or dewatered sludge) were conceived and obtained the possible combination by screening out through necessary conditions. All four scenarios have 39 combinations for co-incineration. Regardless of whether the sludge is dewatered or dried in WWTP, the co-incinerable amount of sludge is the same on a dry basis which accounts for 89.7% of the national sludge generation. Since the amount of sludge in Taiwan is much less than that of MSW, the operating and mixing ratio does not affect the potential of co-incineration. The most critical factors affecting co-incineration are the distance between WWTP and MSWI. The dried sludge can reduce GHG emissions from transportation and incineration, and the generated electricity can also offset GHG emissions. However, the energy consumption of the drying process in the WWTP causes a large amount of GHG emissions than other processes. From the perspective of GHG emissions, dewatered sludge (S1) is the best scenario for co-incineration with MSW. If the drying equipment is installed in MSWI instead of WWTP, the energy required for sludge drying process can be provided from the waste heat of incineration.