The increasing quantum of waste generation has forced authorities to find sustainable methods of waste treatment. Waste-to-energy (WtE) plants offer one such alternative by converting waste into energy, generally through combustion. This method is being viewed as a potential energy diversification strategy and is being exploited by many countries, including India, where 201 WtE plants with a cumulative capacity of 330.93 MWeq have been installed so far.
WtE plants work alongside the recycling process, as the materials that are utilised for combustion are not recyclable. Waste materials are thus segregated before being processed in a WtE plant. WtE plants are efficient sources of energy generation – in terms of value, they incinerate around 80-90 per cent of waste. The residue ash can also be utilised in various processes for example as a raw material for road construction.
Green fuels such as biogas, bio-CNG, biodiesel and green diesel, which are derived from biomass, are also being promoted as cost-effective and environmentally benign alternatives to petroleum and other fossil fuels. This is particularly true in India, which has an abundance of biomass. Tamil Nadu has the highest capacity of agricultural, urban and industrial effluent-based off-grid power plants, generating around 150,218 m3 per day of biogas. Gujarat, on the other hand, has the highest generation capacity for bio-CNG in the country at 28,338 kg per day.
Existing treatment technologies
WtE technologies are primarily based on biological or thermal methods. The biological method, which involves biomethanation, produces biogas. Thermal methods include incineration and more advanced methods that involve little or no supply of oxygen, such as plasma gasification and plasma pyrolysis respectively.
The combustible technologies include incineration, plasma gasification and plasma pyrolysis. Incineration is a process in which energy is recovered through complete oxidation and involves mass burning of waste. Heat- and refuse-derived fuel (RDF) are the by-products of this technology. Plasma pyrolysis technology uses steam and radiation to convert mixed waste into energy through a turbine. It takes place in the absence of oxygen. Biofuels are the by-products of this technology. Plasma gasification technology involves a combustible process that uses plasma to make a slurry of the entire waste and then extract water, fuel and electricity. The by-product derived from this technology is fly ash.
Non-combustible technologies include biomethanation, which is an anaerobic process of breaking down waste particles using fermentation. The by-product of this technology are compost and biogas.
The preferred technology in India at present is mass incineration, as most gases are burnt during the incineration process and the waste is reduced to less than 10 per cent of its volume. This leads to a significant reduction in the transportation cost.
Government initiatives
The government has been working towards promoting WtE plants as an alternative source of energy and has formulated various policies to give an impetus to the development of these plants. In April 2016, the government notified the revised Solid Waste Management Rules, 2016, which laid emphasis on the development of WtE projects.
The Ministry of Power has been granted the authority to decide the tariffs or charges for the power generated from WtE plants based on solid waste. It also has the responsibility of ensuring compulsory purchase of power generated from such plants by distribution companies. The Ministry of New and Renewable Energy (MNRE) will facilitate infrastructure creation for WtE plants and provide appropriate subsidies or incentives. All industrial units using fuel and located within 100 km of solid waste-based RDF plants are expected to make appropriate arrangements to replace at least 5 per cent of their fuel requirement with RDF.
NTPC Limited has been showing interest in WtE plants. It opened 100 tenders for such plants under the government’s Swachh Bharat Mission in 2019. In its endeavour to transform solid waste to energy, NTPC has collaborated with the East Delhi Municipal Corporation (EDMC) along with the municipalities of Kawas, Varanasi, Indore and Mohali. In June 2020, NTPC incorporated a joint venture firm, NTPC EDMC Waste Solutions, for developing and operating a WtE plant.
In February 2020, the MNRE revised the guidelines for its WtE programme to promote the setting up of projects for the recovery of energy in the form of biogas/bio-CNG/power from urban, industrial and agricultural waste, as well as for captive power and thermal use through gasification in industries. The ministry has introduced a central financial assistance facility for different categories of WtE and biomass gasifier projects.
Market potential and opportunities
In India, there is immense scope for bio-CNG due to the abundance of biomass. Bio-CNG offers numerous advantages as a renewable vehicle fuel as compared to conventional fuels. Bio-CNG has a significantly higher calorific value and a lower content of carbon dioxide, making it an ideal option for the automobile and fuel industries. Ve-hicular emissions of carbon monoxide, hydrocarbon, nitric oxide and other suspended particles are also significantly lower in the case of bio-CNG, making it environmentally viable.
A bio-CNG plant built in 2016 at Mahindra World City, Chennai, converts 100 per cent of the food and kitchen waste generated daily at the property into raw biogas. The bio-CNG thereby produced is used for cooking purposes, as a fuel for buses and tractors, as well as to power stree lights in the area. In the food industry, Amul Dairy has become the first business to start a fully automated bio-CNG generation and bottling plant, which uses waste from Amul’s plant to generate energy.
According to the MNRE, the potential of biogas in India is around 71,137.60 million m3 per year, in which the share of municipal solid waste is expected to be 8,550 million m3 per year. The potential of compressed biogas (CBG) is around 32,011.76 million m3 per year, with the share of municipal solid waste in its production expected to be 3,847.50 million m3 per year.
The Sustainable Alternative Towards Affordable Transportation (SATAT) initiative has been introduced to promote CBG or bio-CNG as an alternative, green transport fuel. The SATAT initiative aims to guarantee production offtake with public sector oil marketing companies buying CBG at a fixed rate; set up CBG plants, mainly by independent entrepreneurs; provide an additional revenue source to farmers; and reduce natural gas imports.
Challenges faced by WtE plants
Energy generation from waste in India has the potential to produce nearly 5,600 MW of electricity, which is enough to meet the entire power demand of Delhi. However, WtE technology has faced several roadblocks, due to which it is still not considered the most viable renewable source of energy. Cost recovery is one such issue that has hampered the growth of WtE plants in the country. These plants have high setting-up and operational costs, due to which they are not able to attract many developers. WtE plants sell electricity at about Rs 7 per kWh, as compared to Rs 3-Rs 4 per kWh for coal and solar plants. Discoms are, therefore, not interested in buying such expensive electricity when cheaper alternatives are available. These plants also receive public backlash with activists flagging the health risks arising from the huge amount of bottom ash being generated by these plants.
The lack of waste segregation also causes a hindrance in the efficient operation of WtE plants, adversely affecting power generation and leading to the emission of pollutants. Even segregated waste has a low calorific value and high moisture content, making it unsuitable for burning and requiring additional fuel, thus raising operation costs. Of the 55 million tonnes of municipal solid waste generated every year, only about 15 per cent can be classified as non-biodegradable, non-recyclable, high-calorific-value waste.
All these issues have restricted the growth of WtE plants as an alternative source for energy generation in India.
Future outlook
The solid waste generated in the cities/towns in India currently has the potential to generate approximately 500 MW of power, which can be further enhanced to 1,075 MW by 2031 and 2,780 MW by 2050. The ministry-level initiatives have given an impetus to public-private partnerships in WtE projects, and they are expected to grow manyfold in the coming years.
Major issues such as lack of waste segregation and scarcity of high-calorific-value waste must be addressed. Local authorities in the cities must take robust action to ensure waste segregation at source. Indore has deployed garbage vehicles that are fitted with segregated bins for wet, dry and sanitary waste. More cities should follow the Indore model to promote waste segregation at source.
Technological advancements are also required to ensure the efficient operation of WtE plants. Some headway has no doubt been made in this area. For instance, POLYCRACK technology, the world’s first patented heterogeneous catalytic process that converts multiple feedstock into hydrocarbon liquid fuels, gas, carbon and water, has been used in the WtE plant commissioned by Indian Railways in Bhubaneswar. More such plants should be developed to ensure that the full potential of converting waste into energy is achieved.