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Kochi: On February 19, Prime Minister Narendra Modi virtually inaugurated India’s newest bio-CNG plant in Indore – touted to be Asia’s largest. When it reaches full capacity in less than a month, the plant is expected to process 550 tonnes of organic solid municipal waste per day to produce 17,000 kg of bio-CNG and 100 tonnes of organic compost.
As many as 75 municipalities across India are slated to get such bio-CNG plants over the next two years, according to the PM’s Office.
But while the Indore plant is an important step forward, according to experts in the waste management sector, its success is not guaranteed. A glaring problem in the way of bio-CNG’s success in India is waste segregation at source. If this is not properly implemented, they said, bio-CNG may not confer any benefits wherever it’s being implemented.
CNG stands for ‘compressed natural gas’. Bio-CNG is a renewable fuel obtained by purifying biogas – in contrast to CNG, a non-renewable source of energy. Biogas is produced when microbes break down organic matter like food, crop residue, waste water, etc.
When he inaugurated the Indore bio-CNG plant, Prime Minister Modi called the wet waste from households and agricultural and livestock farms “gobar dhan” – Hindi for ‘cattle dung/manure wealth’. More Gobar Dhan bio-CNG plants are slated to come up in towns and villages as well, he added.
“This campaign will go a long way in making Indian cities clean, pollution free and in the direction of clean energy,” he said.
This claim is directly tied to India’s climate pledges under several international treaties. And according to Modi, tackling the disposal of wet waste is the latest focus of the national Swachh Bharat Mission.
In rural areas, kitchen and food waste in rural areas are often fed as fodder to livestock; they’re a bigger problem in urban areas, where they are produced in larger quantities and usually disposed of highly polluting landfills.
Urban households generate approximately five to ten times more waste per day than rural ones, Divya Tiwari, principal scientist and advisor at Saahas, an NGO that has been working in the waste management sector since 2001, told The Wire Science.
According to one estimate, 80-90% of municipal waste in India ends up in landfills. A 2017 analysis underscored how landfills have numerous environmental and public health consequences. Food waste in dump-sites releases methane, a strong greenhouse gas, into the atmosphere. Leachates from landfills contaminate groundwater resources. The odour and other noxious emissions affect the health of people and cattle living or working nearby.
In this milieu, bio-CNG plants look like a silver bullet.
The by-product of organic compost is better for soil health than chemical fertilisers (and will save India forex as well). Bio-CNG units in the transport sector offer the prospect of cleaner and greener fuel.
However, the success rate of biogas technologies based on municipal solid waste has been poor, Tiwari said. The principal problem is that waste that is fed to biogas plants is not segregated – into organic and inorganic parts – at the source.
The composition of waste also keeps changing. This is an issue for the digester, according to her. This is a container at the biogas plant in which the organic waste is placed and allowed to decompose, releasing biogas. The digester’s internal conditions, like temperature and composition of bacteria, need to be closely controlled to ensure usable biogas is produced in meaningful quantities.
For these two reasons, the bio-CNG plant in Indore may be more successful than similar units are likely to be in other parts of the country. According to Tiwari, Indore has achieved high levels of waste segregation at source.
In fact, since 2016, the Indore Municipal Corporation (IMC) has ensured 100% household-waste segregation, IndiaSpend has reported.
The research team at the Indore plant has also tested and analysed the quality of waste coming in for the past year, Nitesh Tripathi, project head of the new plant, told The Wire Science.
“We are paying a royalty of Rs. 2.52 crore per annum to ensure that the IMC supplies waste of at least 90% purity,” he said, adding that incoming waste will also be tested first before entering the digester.
Put another way, these are the measures that will have to be in place if bio-CNG facilities in other parts of the country can expect to be successful.
The Indore plant has been set up on a public-private partnership model, between the IMC and the private Indo-Enviro Integrated Solutions Ltd.; the latter made a capital investment of Rs 150 crore in the plant.
The IMC will buy half of the bio-CNG produced to run 400 city buses, according to the Union government. The rest will be sold in the open market at competitive rates – currently fixed at Rs 77 per kg. According to Tripathi, the local demand for bio-CNG is high, including from numerous industrial units around Indore.
Size and tech matter
There are two more factors that predict success: the size of a plant and its technology.
Larger biogas plants have been found to be more efficient than smaller ones. Tiwari recalled an example in Bengaluru: the city installed around 15 plants – each capable of processing upto 5 tonnes of waste per day – in 2016. All of them are now defunct, she said, primarily because they became economically infeasible due to low returns, and because their technology was not suitable for municipal solid waste.
Biogas plants require significant capital investment. Their economic viability depends most on the revenue earned from the gas, Tiwari said. If the gas can be used directly for cooking, the economic viability is good. However most plants operating in the 1-20 tonnes per day range convert biogas to electricity instead. Returns on this are lower: supplying power to the grid is less gainful than selling the gas as bio-CNG or as a replacement for LPG. Some gas is also wasted in the conversion process.
Small plants can’t afford the costly infrastructure required to bottle the biogas. Nor can they handle the slurry – a thick, semi-liquid produced as a by-product of the waste treatment process. They simply discharge this into the sewage, adding to the load of sewage treatment plants. So larger plants, with a capacity of 50 tonnes per day or above, that include bottling facilities have a higher success rate, Tiwari explained.
Methane leaks are also a concern in these small plants, she added. And research has been clear: methane leaks from plants can contribute to global warming, compromising the very environmental benefits they claim to deliver.
Large plants – like the one in Indore – are a better bet in such scenarios. The technology they have also makes a difference. The Indore plant, for example, is of German design; its tanks are made of glass-fused steel, which, Tiwari said, doesn’t allow leaks.
And large-scale biogas plants are the need of the hour – because maintaining and monitoring large reactors is much easier, apart from them being more economically feasible, said professor Ajay S. Kalamdhad and researcher Prakash Singh of IIT Guwahati. They have studied the prospects of bio-CNG in the vehicle sector in India.
Bio-CNG potential in India
Their research has found that there is big scope for bio-CNG in India – but that we’re using less than 2.5% of our net bio-CNG potential when it comes to municipal solid waste and wastewater energy alone. If “harnessed correctly”, they wrote, bio-CNG from these sources can replace around 4,000 tonnes of India’s diesel consumption per day.
In fact, biogas potential from agricultural residue and livestock dung is around 75 billion cu. m a year – which is around 80,000 tonnes of Bio-CNG per day, they told The Wire Science.
“If bio-CNG is produced from all biomass – agricultural residue, livestock dung, municipal solid waste and wastewater – we can replace about 50% of our current total diesel usage in the transport sector,” they said. This could also reduce India’s dependence on foreign oil imports.
Meanwhile, the demand for CNG vehicles in India has been increasing. Gujarat alone reported a 143% spike in demand for such vehicles between 2017 and 2020, Times of India reported in September 2021. And according to AutocarIndia, sales of CNG cars in India grew by 97% between April and September 2021. This bodes well for bio-CNG use in the country too, because vehicles that can run on CNG can also use bio-CNG without additional mechanical modifications.
The Sustainable Alternative Towards Affordable Transportation, an initiative of the Ministry of Petroleum and Natural Gas, encourages entrepreneurs to set up compressed biogas plants. But only 14 such plants have been commissioned thus far around the country. And of them, only three process municipal solid waste.
The biggest challenge ultimately is that there is no segregation of waste at source. Without waste segregation at source, no bio-CNG plant can function efficiently.
“The willpower of the government and the municipal authority with public participation in waste segregation is crucial here,” Tripathi said. “The Solid Waste Management Rules 2016 clearly state that there must be source segregation. The rule is already there. But we’re not following it. Implementation is poor.”
According to some estimates, only five of 29 states in India segregate waste at the source. Until waste segregation is more widespread, bio-CNG plants in cities, towns or villages – where segregation at source is still not happening – are unlikely to succeed.
Tiwari herself is hopeful. “Hopefully the Indore [project] will give confidence to municipalities and private players to implement these sustainable waste management solutions that also offer economic gains,” she said.