Municipal Solid Waste as an Alternate Source of Energy: A Review

Abstract

Municipal solid waste (MSW) is a big environmental challenge. However; it is a potential source of recycling materials, heat and energy. In developed countries this waste is used as resource to produce energy and compost; whereas in developing countries like India, collection, transportation and disposal of MSW are a big task. Wastes to energy technologies (WTE-T) play important role in sustainable management of MSW throughout the world. These technologies reduce the amount of waste as well as produce energy, which can be used to generate electricity. These include thermochemical treatment technologies, biochemical treatment technologies and utilization of landfill gas. Thermochemical techniques include Incineration, Gasification, Pyrolysis, Plasma arc gasification and Hydrothermal carbonization. Incineration is the most common technique used for treatment of MSW. It reduces 70% mass and 90% volume of MSW and sterile ash remains as byproduct. Gasification is advantageous over incineration, as gases are not released into atmosphere. Pyrolysis is the anaerobic thermal degradation of MSW, carried out in an oxygen free environment, producing gases (syngas), liquid and solid residuals. Syngas is composed of methane, hydrogen, carbon mono oxide and carbon dioxide. It can be used in engines, boilers, turbines, fuel cells and heat pumps. Plasma arc gasification also involves partial oxidation of MSW. Syngas and high quality producer gas is obtained that can be used as transport fuel, heat and to generate electricity. Hydrothermal Carbonization (HTC) is a complex process through which hydro-char is produced, which is similar to coal and can be used as a solid fuel for heat and power generation. Organic fraction of MSW is biodegradable and has high energy content. Biochemical treatment technologies are designed to utilize this fraction of MSW. Anaerobic digestion of organic waste is performed by microbes in absence of oxygen in a closed container (biogas digester), resulting in the reduction of waste and production of a combustible gas, biogas, a mixture of methane and carbon dioxide. Landfill gas is rich in methane and must be used to produce heat and energy. It usually consists of 50% methane and 50% CO2. Gas is collected by pipes and reaches the wells installed inside the landfills.