Is bio-CNG the right green fuel for public transportation?


The transport sector is one of the major contributors to greenhouse gas emissions. As per the UN World Meteorological Organization, global temperatures will rise by 3.5 degrees Celsius in this century if urgent measures are not adopted. Nations have been focusing on exploring renewable energy sources to reduce the transport sectors’s environmental impact. But the question that arises is, which source is the most effective alternative? Could cow dung or vegetable peels be the answer to this problem?

By Ayushee Sharma

A recent study by IFPEN (the French Institute of Petroleum) has revealed that the bio-gas sector can contribute to decarbonising transportation. The study collated data about the complete life cycle of compressed natural gas (CNG), bio-methane, gasoline, diesel and electric vehicles, and it concluded that bio-methane is the best option for maintaining air quality. The study recommends using a mix of bio-methane and CNG till 2030 to power vehicles, so that they have a climate impact equivalent to that of an electric car, as a mid-term solution.

Agricultural residues, food waste, organic municipal waste, bio-waste from industries, etc, are the common sources of biomass. Raw bio-gas (consisting of methane, carbon dioxide and impurities such as hydrogen sulphide and water vapour) is produced from biomass in the absence of oxygen. It can be converted into different automobile fuels like bio-Compressed Natural Gas (bio-CNG) or compressed bio-gas (CBG), gasoline, syngas and liquefied bio-gas. For example, US-based Cornerstone, a Tetra Tech Company, has invented BioCNG, which is a bio-gas conditioning system to convert methane obtained from the decomposition of organic waste materials into a renewable natural gas (RNG) that can be used as a transportation fuel.

The amount of carbon dioxide produced when bio-CNG is used is equivalent to the amount captured in the formation of biomass, making it carbon neutral. Bio-CNG offers numerous advantages as a renewable vehicle fuel, such as high calorific value and cost savings over conventional fuels. It is similar to natural gas in terms of composition and properties.

Bio-gas, when purified to get bio-methane by absorbing or scrubbing the contaminants, and pressurised for storage in high-pressure cylinders, gets upgraded to bio-CNG. Without proper purification, using bio-gas can lead to erosion of the metal parts in the vehicles. The purity of bio-CNG reserves in automobiles can be tracked using software and data analysis tools.

In India, there is immense scope for bio-CNG due to the abundance of biomass. Built in 2016, the bio-CNG plant at Mahindra World City, Chennai, converts 100 per cent of the food and kitchen waste generated daily, into raw bio-gas. The bio-CNG thereby produced is used for cooking purposes, as a fuel for buses and tractors, as well as to power streetlights in the area. In 2017, Tata Motors showcased the nation’s first bio-CNG bus at the bio-energy programme ‘Urja Utsav’. In the food industry, Amul Dairy has become the first business to start a fully automated bio-CNG generation and bottling plant to generate energy from its plant’s waste. Even educational institutions like IIT-Delhi, for instance, are converting bio-gas to bio-CNG using a water scrubbing technique and supplying this to the CNG refuelling stations.

Government policies are further boosting these initiatives of creating wealth from waste and can curb the nation’s dependence on imported oil and gas. The National Policy on Bio-fuels, approved by the Union Cabinet in May 2018, targets the blending of 20 per cent of ethanol in petrol and 5 per cent of bio-diesel in diesel by 2030. Bio-CNG, bio-hydrogen, second-generation ethanol, drop-in fuels from municipal solid waste (MSW), bio-methanol, etc, have been included in the list of target bio-fuels for use in the transport and energy sectors. In October 2018, the Sustainable Alternative Towards Affordable Transportation (SATAT) scheme was launched by the Ministry of Petroleum and Natural Gas, under which 15 million tonnes of CBG will be produced from 5,000 plants by 2023. Besides this, the Galvanising Organic Bio-Agro Resources Dhan (GOBAR-DHAN) scheme, aimed at converting solid waste and cattle dung into compost, fertiliser, bio-gas and bio-CNG, was announced in the Union Budget 2018-19.

The global adoption of bio-CNG depends on several economic, environmental and technical factors. The capital cost for the installation of bio-CNG plants is high. The sources for feed materials are not consistent and setting up refuelling stations is more complex than conventional stations. Due to the low mileage it yields, vehicles may need additional fuel cylinders. There is also a shortage of skilled professionals for the production processes in this field. And there is a lack of proper standards and regulations in many countries when it comes to installation, operation and maintenance of plants.

However, the plethora of advantages will drive the growth of bio-CNG vehicles, primarily trucks and buses, in the future. This will strengthen the role of public transport in both urban and rural India. As per Renewable Watch Research, there are 17 bio-CNG plants in India (as of 2019), with a combined capacity of 46.18 tonnes per day. Maharashtra and Gujarat are the states with the highest capacity. In Sweden, bio-CNG is already being used on a large scale to run buses. John Lewis, a department store chain in the UK, plans to switch all its heavy delivery trucks to bio-methane-powered versions by 2028.

Petrol as well as diesel vehicles can be powered by bio-CNG through retrofitting. The large scale generation of bio-CNG can help with the problem of the solid waste that is dumped in landfills as well as the air pollution caused by stubble-burning. Simultaneously, it can lead to technological advancements as well as create new employment opportunities. There is a need to create awareness about the benefits of bio-gas to maximise its use for various purposes, including transportation, in order to achieve sustainable development.


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