Bio-compressed natural gas (bio-CNG) is a purified form of biogas as all unwanted gases are removed to produce a high amount of pure methane gas. Due to its high level of methane and low level of carbon dioxide, bio-CNG is environmentally friendly with very low emission levels. Bio-CNG has commercial, industrial and automotive uses, and can be used in restaurants, cement factories, public transport and CNG-fitted vehicles. It also holds promise for efficient municipal solid waste management and for tackling the issue of urban air pollution. At present, India has 17 bio-CNG producing plants, of which one is in Tamil Nadu. The state, especially its capital city of Chennai, is moving forward in this space with extensive plans of setting up bio-CNG plants in the coming year.
Initiatives for production
The Tamil Nadu government wants to replace CNG used as automotive fuel in buses, tractors and as cooking fuel with bio-CNG, while at the same time reducing the trash generated in the city as it expands. Of the 5,500 tonnes of waste generated in the state every day, 55 per cent is wet waste. About 450-500 tonnes wet waste is processed through composting and 250 tonnes of dry waste is sold every day. The city corporation is also planning to convert up to 15 per cent of wet waste by bulk waste generators into compost. The corporation plans to set up incinerators for dry waste after sorting at Madhavaram, Thiruvotriyur and Manali. To facilitate efforts in the processing of wet waste, the Greater Chennai Corporation gave work orders in February 2020 to construct four bio-CNG plants. The earlier plans included setting up of only three bio-CNG plants. The 50 tonne per day plants were to be set up in a public-private partnership where the private company would be in charge of operations and maintenance of the facility. The final approved projects will come up in Chetpet, Madhavaram, Pallikaranai and Sholinganallur. These are expected to be completed by June. While the total estimate is Rs 373.1 million, each plant will be constructed at a cost of Rs 93.3 million. While the Chetpet plant will have a capacity of 50 metric tonnes, the other three will be of 100 metric tonne capacity each. In Sholinganallur, Pallikaranai and Madhavaram, work is under way to set up bio-CNG plants. In Kannagi Nagar, which is under Zone 15, Sholinganallur, a unit to derive by-products from plastic waste has been established. Here, plastic sheets and tablecloths are made out of plastic waste. In Manali, a trial run of a plant, where incinerated ash from dry waste will be used to create concrete blocks, is under way. Five areas across Chennai have been earmarked for setting up of units that would derive by-products such as soft-wood blocks out of garden waste processing.
Mahindra World City
The bio-CNG plant that is currently operational in Chennai has been set up at Mahindra World City as a joint corporate social responsibility initiative between Mahindra Research Valley and Mahindra World City Developers Limited. Spread over an area of 1,000 square metres, the bio-CNG plant aims to create a carbon-neutral ecosystem in Mahindra World City, Chennai. The bio-CNG plant converts 100 per cent of the 8 tonnes of food and kitchen waste generated daily in the area into 1,000 cubic metres of raw biogas. This raw biogas can be enriched to yield 400 kg of purified CNG grade fuel per day, which is equivalent to a 200 kW power plant. As a by-product, 4 tonnes of organic fertiliser is produced each day. The bio-CNG produced is effectively used to replace CNG as an automotive fuel for CNG buses and tractors and liquefied petroleum gas (LPG) for cooking purposes, as well as to power street lights at Mahindra World City. The organic fertiliser is used by farmers to enhance soil fertility. Further, the power generated is used by buses for free shuttle service and by tractors for cultivation.
The road ahead
Bio-CNG has the potential to replace LPG and CNG at a utility-scale level and to be a truly renewable fuel owing to the abundance of biomass in the country. Moreover, biomass residue, which includes the stubble being burnt, can be redirected to produce bio-CNG. Bio-CNG production is still picking up and is at present expensive to carry out, especially in terms of the capital costs involved in installing bio-CNG plants. Preliminary processes like collection, transportation and segregation may also limit its adaption. As an alternative to large-scale plants, the Citizen Consumer and Civic Action Group suggested the installation of decentralised biogas plants, which may help in reducing waste transportation costs and offer the possibility of direct biogas supply to private customers at a comparatively lower cost. Decentralised units such as bio-methanisation plants close to canteens, anganwadis and on rooftops of restaurants near kitchens can further reduce carbon emissions.
Summing up, scalable business models and enabling policy frameworks can provide a much-needed boost to this bio-CNG segment, which is not only renewable and non-polluting but also a potential solution to the country’s growing waste disposal problem.