The effect of coal alternative fuel from municipal solid wastes employing hydrothermal carbonization on atmospheric pollutant emissions in Zimbabwe

The vast increase of municipal solid waste (MSW) generated in Zimbabwe coupled with a severe energy crisis have made waste-to-energy technology more attractive and necessary. Coal-alternative solid fuel production from MSW though hydrothermal carbonization can play a critical role to improve both waste management and energy supply. Moreover, MSW conversion to a carbon neutral solid fuel that can be burnt in existing coal-fired power stations might reduce greenhouse gas (GHG) emissions despite GHG releases from waste collection, waste conversion to fuel, and fuel transportation processes. The purpose of this paper is to investigate present MSW generation in Zimbabwe, its characteristics as a fuel source, and the impact of coal-alternative solid fuel production from MSW using hydrothermal carbonization technology on GHG and other air pollutant emissions. Four different scenarios based on the balance between fuel supply and demand were tested in this paper. The results suggest 0.54 ± 0.14 kg/capita/day of MSW generation in Zimbabwe and about 1051.7 ± 270.7 Gg of annual MSW generation from the current urban population. 289.3 Gg of coal-alternative solid fuel production was expected from domestic MSW collectable in urban areas. The model predicted that co-burning of alternative fuel in coal-fired power plants could reduce the methane potential of household waste from 62,200 to 15,800 Mg CH4 per year. Under the best possible scenario, it could reduce SOx emissions by 4.2%, CH4 emissions by 4.5%, CO2 emissions by 3.1%, and Global Warming Potential by 2.2%. On the other hand, NOx emissions would increase by 18%. If without additional installation of air pollutant control devices in power plants, waste-to-energy generates a trade-off between global warming and acid rain. In addition, geological locations generate a large demand/supply gap of alternative fuel and regulate maximum available consumption of alternative fuel.