By Dr. Solmaz Rezaei
Head of research and consulting department
Urban waste is one of the most important issues of urban management in the world that environmental problems related to this issue, such as greenhouse gas emissions and soil and water pollution, have caused serious attention to this issue. Based on the studies, one of the most important sources of greenhouse gas emissions, in particular methane gas, is the landfill, such that the waste is the source of more than 37 percent of greenhouse gas emissions in the United States and experts also mentioned 32 human diseases as the result of poor solid waste management. Typically, urban waste management imposes many costs on the city, which meanwhile, energy generation from urban waste is one of the most exciting methods to dispose waste economically, socially and environmentally. While providing a large portion of urban waste management costs, this method can properly respond to the growing energy needs of cities.
The global rise in oil prices, particularly between the 1970s and 80s, triggered the alarm due to the need for alternative energy sources. Given the high thermal value, urban waste can be considered as one of these energy sources. At present, energy generation from urban wastes is aimed at generating revenue for waste management, enhancing the security of energy supply and reducing landfill, at a global level. According to the International Energy Agency, the share of urban waste in energy production is 1.2 percent, which is 1.5 times the share of wind energy and 4 times the solar energy produced in the world. Also, the growth rate of energy generated from urban waste is about 4.5 times the increase in energy production from other renewable sources.
At present, there are various methods for generating energy from waste, including waste incineration, landfill, waste gasification, biogas, plasma and refuse-derived fuel or RDF, which the first two methods are more economical and more widely used include than other cases.
Waste Incineration Plants: In this system, urban waste is mixed in the waste incinerator and used to generate heat energy. In waste incinerators, oxide waste and carbon materials are reduced. Today, there are about 600 waste incineration plants in the world with an energy production potential of near 7,000 megawatts. Currently, according to strict EU rules, the landfill of combustible waste is limited and the energy production from this waste has been emphasized.
Power generation from landfill: Using household waste burial and in the absence of oxygen after the decomposition of waste, a mixture of methane, carbon dioxide, hydrogen, and other compounds is produced, which continues 2 to 6 months to years after burial. After certain steps, gas can be set up to power generators. Also, the gas can be injected into the local natural gas network. This method requires lower initial investment and maintenance costs than other existing technologies. The power generation capacity of this method was more than 9,000 megawatts by 2010.
Refuse-derived fuel (RDF): In this method, the fuel-energy containing components of the waste are completely dried after a certain process to become suitable for the combustion process. RDF has the ability to burn in power plants or in cement furnaces and reduce fossil fuel consumption up to 50% in these furnaces.
In metropolises such as Tehran, with an annual waste production of about 8,000 tons, the development of such methods can contribute to the management of urban waste and energy production. According to a study by the German DLR Institute, the energy generation capacity from urban waste in Iran will reach 11.4 terawatt hours or 1630 megawatts by 2020.