Chennai awaits more bio-CNG plants to enable switch to clean energy

Expanding bio-CNG generation with more plants can help business tap into clean energy and the civic body reduce landfilling of wet waste.

It has been a year since the launch of a bio-CNG (Compressed Natural Gas) plant in Chetpet by Greater Chennai Corporation (GCC) in partnership with Srinivas Waste Management Solutions Pvt Ltd. Around 100 tons of vegetable and food waste from Koyambedu market and hotels are processed every day and converted into bio-CNG. This renewable source of energy is sold to the Gas Authority Of India Limited (GAIL) and various hotels whose reliance on conventional energy has drastically reduced as a result. 

A similar plant at Madhavaram was inaugurated about six months ago but is yet to be functional as it awaits the arrival of some machinery. Five more such plants for which tenders were released by the GCC two years ago are set to take longer to be established.

Delays to the bio-CNG project of the civic body continue even as 1300 – 1600 tonnes of wet waste ends up in Chennai’s two landfills every day.

Functioning of the bio-CNG plant in Chennai

About 100 tonnes of food and vegetable waste collected every day from bulk waste generators –  hotels and the Koyambedu market – is segregated at the plant in Chetpet.

The segregated waste is loaded in bio-grinders, where waste is ground and liquefied by adding the right proportion of water. Soil and other untreatable substances from the liquid get settled at the bottom of an aerobic tank. The organic content, stored in the feeding tank is pumped into two digestors for anaerobic treatment.

“In the absence of oxygen, microorganisms feed on the organic content, reducing its biological oxygen demand and chemical oxygen demand. In 21 days, biogas which is a combination of Methane, Carbon Dioxide, negligent amount of Oxygen and Hydrogen Sulfide, is formed from the liquid,” says M Manikandan, Senior Manager Operation – Bio CNG, Srinivas Waste Management Solutions Pvt Ltd.

Hydrogen Sulfide, a corrosive gas, is segregated through chemical scrubbers and Carbon Dioxide is removed through high pressure. The result is 93% pure Methane that is compressed and filled in cascades under the right pressure as bio-CNG.

The 100 tonnes of biodegradable waste can be processed into 10,000 m3 of biogas, which is again compressed to 4000kg of bio-CNG. 

bio-cng plant waste processing
JCBs compress waste and ensure there is no inorganic waste. Pic: Laasya Shekhar

Read more: How to produce biogas from kitchen waste and reduce your LPG bills


Benefits of bio-CNG plants

Restaurant chains in Chennai have cut down their fuel expenditure after replacing LPG cylinders with bio-CNG.

“A kilo of commercial LPG cylinder is about Rs 104 while a kilo of bio-CNG is Rs 74 (as of 23rd February). We save about 30% of the expenditure after switching to bio-CNG,” said B Loganathan, Area Manager of Saravana Bhavan.

About 1.5 tonnes of waste is collected from nine main branches of Saravana Bhavan every day to be converted into bio-CNG. 

While LPG is taxed at 18% GST, bio-CNG, a cleaner form of energy, has 5% GST. 

Using bio-CNG also makes the kitchen environment bearable.

“As more burners are put to use in restaurant kitchens at the same time, the formation of ice on LPG cylinders is common. One has to pace down the cooking or sprinkle hot water on the cylinders to prevent it. There is no such problem with CNG,” adds Loganathan.

Saravana Bhavan has replaced LPG with CNG at two out of 22 branches in Chennai. 

Wastage of gas can be avoided with CNG, say consumers.

As multiple stoves function at full blast in restaurant kitchens, enduring high temperatures becomes an occupational hazard for chefs. “I notice that, with CNGs, kitchens no longer get as hotter as LPGs. As I stand to fry the dals, I no longer feel the wave of heat on my stomach,” says a worker from Aachi Masala. 

“When cooking using the full flame, there is a wastage of gas. But even in the full flame, CNG’s flame is balanced and doesn’t come out of the vessel,” says Rajan JJM, Projects and Automation head of Aachi Masala.

Aachi Masala purchases about 400kg of bio-CNG from the Chetpet plant every day. 

About 10-12 tonnes of cow dung which was earlier dumped in the city’s stormwater drains are now processed into this renewable form of energy through the bio-CNG plant. 

Roadmap for bio-CNG plants in Chennai

This project of converting waste to a meaningful resource was conceived more than three years ago, as an attempt to recycle 100% of the wet waste generated in the city.

“We spent a lot of time researching and zeroing in on the land for setting up the plants,” says an official from the Greater Chennai Corporation, who sought anonymity.

Of the seven bio-CNG plants conceptualised to treat 700 tonnes of waste per day, only one plant is currently functional.

“Madhavaram plant is all set to run soon. Work is in progress to set up six other plants at Koyambedu, Sholinganallur and Madhavaram. We have identified the land for all the plants except for Koyambedu. We are holding talks with the Metro Water Department to use their land at Koyambedu for the purpose,” says the official, adding that all seven plants will be functional in about five months. 

Under the proposed Public-Private Partnership (PPP) model for operation, GCC is in charge of providing land and resources (waste) to the private organisation. The civic body also gets a royalty of Rs 35 per tonne of waste.  

  • Chennai generates about 2500 – 2800 tonnes of wet waste per day. 
  • Around 1200 tonnes of wet waste gets treated at the Micro Composting Centres (MCC) and vermicompost plants. 
  • A total of 100 tonnes of waste is converted to bio-CNG at Chetpet. Once the six other plants function, another 600 tonnes of waste will be repurposed.
  • GCC aims to set up two bio-CNG plants with 500 tonnes capacity each at Perungudi and Kodungaiyur dump yards respectively.

“The amount of bio-CNG produced per tonne of waste is different in different places and is dependent on the nature of waste. Only if the yield is good can we go ahead with the project. So, we hired a consultant to study the characteristics of the waste at Kodungaiyur and Perungudi,” says the GCC official.


Read more: Ambitious budget for Chennai’s waste management but no coherent strategy


Challenges in waste management

Despite various measures by the GCC to streamline segregation, only 30% of the waste is segregated in the city, according to the workers at the Chetpet plant. A total of 30 workers work through various shifts at the Chetpet bio-CNG plant to segregate the waste.

“We manually remove the plastic and other inorganic waste so that the digestors are not damaged. JCBs crush the collected waste, making it easy for segregation,” says a sanitary worker at the Chetpet bio-CNG plant. 

As GCC aims to expand its bio-CNG initiatives, it is could learn valuable lessons from the experience of other cities.

Non-availability of feedstock is a roadblock for bio-CNG plants. In Visakhapatnam, Vyzag Bio Energy Fuel Pvt Ltd has tied up with the city corporation to process waste to bio-CNG. “We set up a plant of about 30 tonnes of capacity, as more than 300 tonnes of wet waste is generated in Vizag every day. But, we barely get 4 tonnes of waste every day from which we produce about 100 kilos of bio-CNG,” says K S Raja, CEO of Vyzag Bio Energy Fuel Pvt Ltd.  

Business-wise, operating large capacitated bio-CNG plants can help avail government subsidies and incur profits. Under the SATAT scheme launched by the Ministry of New and Renewable Energy (MNRE) last year, entities that produce 2000 kilos of biogas a day, can sell it directly to Indian Oil Corporation at 80% of the CNG price.

“This is a revolutionary subsidy by MNRE as it eases our pain of finding the market for bio-CNG. It is only irony that the central government issues subsidies and the local governments are incapable of source segregation,” says K S Raja. 

Having realised the cost benefits, businesses in Chennai are interested to make a switch to bio-CNG. However, the absence of an adequate number of bio-CNG plants in the city increases transportation costs for consumers.

“Even though I am a crusader of cleaner energy, I cannot make a profit if I transport bio-CNG from Chetpet to Ennore, which is 23 km away. Decentralisation of bio-CNG plants is a viable solution to promote this green energy,” says Parameswar Rao, who owns a chain of hotels in North Chennai. 

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