The Calcutta Municipal Corporation has identified a plot at Sirakol in South 24-Parganas’ Mograhat for a factory to manufacture the bitumen mixture needed to lay a road.

The move comes after the National Green Tribunal asked the civic body in October to shut down its two hot mix plants that produced bitumen.

On December 18, the tribunal had provided a temporary breather by saying the civic body had to stop using hot mix technology for road repairs within four months.

The batch mix plant at Sirakol will use the hot mix technology that releases toxic gases into the air.

But the civic body’s defence is the new plant will be “far away from the city”, something that Delhi did 10 years ago when it was forced to close its hot mix plants within the city.

“The batch mix plant will use the hot mix technology. The civic body must install filters to absorb the carbon released in the air when bitumen is heated and other necessary mechanism to fight pollution,” Sangita, a chief scientist at the Central Road Research Institute in New Delhi, said.

In November, the tribunal had asked the civic body to shut down its two hot mix plants at Goragacha near Taratala and at Palmer Bazar near Sealdah.

Hot mix and cold mix are two ways of preparing the bituminous mixture that is used to lay asphalt roads. The bitumen used in the two technologies are different.

In the hot mix technology, bitumen remains in solid state and has to be heated to turn it into a liquid state so that it can be used to lay roads.

Carbon dioxide, the primary cause of global warming, fine particulate matters that can enter the deepest crevices of lungs and even cause cancer and other toxic fumes are released when bitumen is heated.

In cold mix technology, the bitumen remains in liquid state even in ambient temperature and doesn’t need any heating. That means no toxic fumes are released.

Many environment experts have said the civic body should go for the cold mix technology that is less polluting.

“We have identified a place at Sirakol to build a batch mix plant,” a civic official said.

“This will help with the road repairs in south Calcutta. We are on the lookout for land in districts to the north of Calcutta for another plant,” the official said.

Scientists said that moving the plant away from a populous city to a less populous rural area that would also have a better tree cover meant fewer people would be affected.

Human intervention in preparing the bituminous mixture is far less in a batch mix plant than the plants in Goragacha and Palmer Bazar, the civic official said.

“If the right proportion of materials are not added in the mixture, it will be noted in the computer. This will help prevent theft as well,” he said .

There have been complaints that the right quantity of bitumen has not been added to a mixture, a possible reason why repaired roads wears out quickly, the official said.

“The leak of bitumen from plants can be checked with this batch mix plant,” he said.