Can Bio-CNG click: A primer on this coming of age tech that can deal with air pollution at 3 levels

Subject: Environment

About Bio-CNG-

Bio-CNG, also known as Compressed Biogas (CBG), is an upgraded version of the humble biogas, the dung-based version of which serves as cooking fuel in many villages in India.

Process of production-

The first stage of the CBG process is pre-treatment. The waste is passed through a trommel screen to remove hard materials like coconut shells and pieces of wood.
The screened waste is shredded in a hammer mill and made into a slurry with water. This slurry is kept in the pre-digester tank in aerobic conditions for one-two day to attract microbes — the process is called hydrolysis.
It is then transferred to an anaerobic digester where it is retained for 20-25 days. It is at this stage — methanogenesis — that biogas is generated.
This gas contains 65 per cent methane, while the rest is carbon dioxide, hydrogen sulphide and water vapour.
The gas is stored in a balloon and then taken to a gas upgradation area.
It is passed through a wet and dry scrubber to remove hydrogen sulphide and carbon dioxide, respectively.
Methane, purified up to 95 per cent, is obtained here which is then compressed at high pressure in cylinders and sent off to filling stations.
This highly purified methane is similar in chemical properties to CNG derived from petroleum sources and can thus be used in vehicles.
Apart from biodegradable waste, agricultural residue, cow dung and chicken litter and press mud from sugar factories are also used as feedstock in CBG plants.

Need for CBG in India-

India is the third largest importer of crude oil.
In 2020-2021, India imported 54 per cent of its natural gas requirement.
CBG is a decentralised energy form as it is produced closest to the point of consumption and unlike solar and wind energy, can be produced at all hours of the day.
CBG is better than incineration-based waste-to-energy plants that release toxic emissions.
The global warming potential of methane is 28 times more than that of carbon dioxide.
EROI is a ratio that measures the energy used to produce another energy source against the actual energy generated from that new source.
The energy returned on energy invested (EROI) score for large biogas plants is 1.24 to 11.05.

Benefits-

If harnessed correctly, municipal solid waste (MSW) and wastewater energy can replace 4053.47 tonnes of India’s diesel consumption per day, the highest consumed transportation fuel in India.
If CBG potential from all biomass is taken into account, 50 per cent of the current diesel usage in transport can be replaced.
Biomethane is the best transportation option to preserve air quality.
CBG provides a very important service of managing our waste and producing organic manure, which can bring back the bio-content in our soil that has been overly laced with chemical fertilisers over the years.
The calorific value of Bio-CNG is more than other transportation fuels.

Limitations-

Methane pollution-

Fugitive methane emission from openly dumped waste also leads to landfill fires as happened in Delhi earlier this year.
Landfill sites are a source of 20 per cent of the methane emission.