Urbanization is an outcome of the changes in the pattern of livelihood and the consequent change in the nature of habitation. From its earliest days, the urban economy in most parts of the world has been dominated by trade and commerce, supported by artisanal and other specialized activities.
As industrialization gained pace, an economic activity increasingly shifted away from farming to factories and to the service industries causing a rapid increase in urbanization.
Levels of urbanization in Brazil and Malaysia can be compared with Western Europe and North America and by 2025; even China and Indonesia are likely to have two-thirds of their population residing in urban areas.
The slower pace of urbanization over the past six decades in the case of India is the result of the slow pace of economic growth and slower growth of employment opportunities in the non-agriculture sector. However, it is estimated that by 2025, 37% of the population of India i.e., 450 million will live in urban areas.
According to the World Health Organization (WHO) report in 2015, it has observed that 22 types of diseases are associated with improper management of municipal solid waste. Also, there are social implications of improper waste management which disproportionately affect the poorer communities living in slums and areas nearer to landfills and dumpsites.
Millions of waste pickers are exposed to hazardous substances while collecting waste in the dumpsites seriously impacting their health and life expectancy. The improper waste management largely contributes to air, land and water contamination.
Rapid urbanization across the globe results in growing volumes of waste, depleting landfill spaces, volatile energy prices and of course growing concerns for air pollution that have given rise to Waste-to-Energy (WTE) as a leading solution for a cleaner future.
Urban solid and liquid waste has two principal components. One is the municipal solid waste (MSW) which includes commercial and residential waste generated in municipal or notified areas in either solid or semi-solid form excluding industrial hazardous waste, e-waste and including treated bio-medical waste. The other is the liquid waste, that is, sewerage.
Various components of MSW have an economic value and can be recovered, reused or recycled cost effectively. Currently, the informal sector picks up part of the resources from the streets and bins to earn their living in India. However, a sizeable portion of organic waste, as well as recyclable material, go to landfills untreated.
According to Report of Task Force on Waste to Energy in India, an estimated 62 Million tonnes2 of MSW waste is generated annually by 377 Million people in India’s urban areas, of which 80% is disposed of indiscriminately at dump yards in an unhygienic and unscientific manner by the municipal authorities leading to problems of health and environmental degradation.
If the estimated 62 Million tonnes annual generation of MSW continues to be dumped without treatment, it would need 3, 40, 000 cubic meters (1240 hectares per year at 10-meter height and density of 500 kg/m3) of landfill space every day.
Considering the projected waste generation of 165 Million tonnes by 2031, the land consumed by landfills for 20 years could be as high as 45,400 hectares of precious land, which the country cannot afford. The task force report considers it imperative to minimize the waste going to landfills by at least 75% through processing of MSW using appropriate technologies.
In addition to increasing waste generation, the global demand for energy will increase by 56 percent between 2010 and 2040, with the greatest demand in the developing world (US Energy Information Administration 2013).
According to the World Bank, there are currently 1.2 billion people (20% of the world’s population) without access to electricity (World Bank-Energy Facts). In India alone, 300 million people lack any access to power and another 400 million Indians have limited access to power.
Projected Municipal Waste Generation for the Urban Population in India
WTE Tangible Benefits:
- A sustainable solution for residual waste disposal or MSW, with up to 90 percent reduction in the volume of waste disposed of compared to landfill.
- Complementary to resource reuse and recycling.
- A reliable source of renewable energy in the form of electricity and steam generated, reducing carbon footprint and dependence on fossil fuels. It produces, biodiesel, metal, biochar (fertilizer) and ashes (building substrate)
- Zero emissions (Eco-friendly)
- Favourable Economic aspect
Some of the main Waste to Energy (WTE) thermal technologies for MSW is being used in the world that creates energy in the form of electricity, fuel or heat such as gasification, pyrolysis incineration or mass burning of municipal solid waste. These technologies are described briefly below:
Pyrolysis uses heat to break down combustible polymeric materials in the absence of oxygen, producing a mixture of combustible gases (primarily methane, complex hydrocarbons, hydrogen, and carbon monoxide), liquids and solid residues.
Gasification is the main technology for biomass conversion to energy and an attractive alternative for the thermal treatment of solid waste. Gasification produces combustible gas such as hydrogen, synthetic fuels and is a process that converts dry organic or fossil-based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide at elevated temperature (500-1800 deg. C).
The syngas can be used as a feedstock for the chemical industry (through some reforming processes, or as a fuel for efficient production of electricity and/or heat. The number of different uses of gas shows the flexibility of gasification and therefore allows it to be integrated with several industrial processes, as well as power generation systems.
Incineration and Mass Burning
Incineration technology is complete combustion of waste with the recovery of heat to produce steam that in turn produces power through steam turbines. There are a number of combustor designs used to burn a combustible fraction of MSW. Complete combustion optimally involves a two-stage transformation of fuel, in this case, solid waste, into CO2 and water vapor.
The secondary phase of incineration (combustion) takes place as the combustible materials (e.g., paper, plastics, organic materials containing carbon, hydrogen, and oxygen) combine with oxygen to form carbon dioxide and water vapor (oxidizes).
Pelletization and Fluff as an RDF to Support Combustion Technology
Refuse Derived Fuel (RDF) is a segregated combustible fraction of MSW. The combustible fraction of the waste is transformed into fuel pellets by the compaction of waste or shredded and converted into fluff, enriched in its organic content by the removal of inorganic materials and moisture. Due to the reduction in fuel particle size noncombustible material, RDF fuels are more homogeneous and easier to burn than the gross MSW feedstock.
Combustion of the RDF from MSW is technically sound and is capable of generating power. RDF can be fired at a temperature above 900 deg. C along with the conventional fuels like coal without any ill effects for generating heat. Operation of the thermal treatment systems involves higher costs and a relatively higher degree of expertise.
Syngas is a mixture of carbon monoxide (CO) and hydrogen (H2) or very little quantity of CO2, which is the product of high-temperature steam or oxygen gasification of organic material such as biomass and MSW. In the gasification reactors, the feedstock is converted into a mixture of H2, CO, and CO2, which produces a variety of downstream energy carriers.
Bio-automotive fuels and chemicals can be produced from high-quality syngas (mainly H2 and CO) which is obtained by gasification of biomass and wastes. Syngas plays an important role as an intermediate in the production of several industrial products, such as methanol and ammonia.
Currently, syngas is produced from fossil fuels, mainly coal, natural gas, and naphtha. Syngas from renewable resources, such as biomass, exhibits a promising prospect.
Catalytic conversion of waste plastic to liquid fuel
Besides conventional WTE technologies, new technologies are emerging in India for converting polymeric wastes to liquid fuel. Catalytic conversion and pyrolysis are the two technologies currently used for converting plastic waste to liquid fuel. Large size conversion plants are based on pyrolysis while catalytic conversions are used in small batch / cyclic operation.
Similarly, soiled plastic wastes are being used for strengthening roads by blending chopped polymeric waste with molten bitumen which reported enhancing the life of the road by 30%. These emerging technologies appear to be promising and need to be explored in conjunction with other MSW processing technologies to create viable alternatives.
As the world’s population increases, so does the demand for energy and products, and so will the amount of waste generated. This waste represents both a threat to the environment and human health, but also a potential source of energy. These WTE technologies can help address and solve these problems.
The selection of technologies is based on the factors like the desired form of the energy, economic conditions, quantity and characteristics of feedstock, end-user requirements and environmental standards.
The MSW conversion into energy is important from the energetic as well as economics point of view because it reduces the direct load on fresh resources and provides energy at reasonably low cost.