The National Green Tribunal had given the civic body four months, but the municipal corporation has failed to convert to a better technology than the polluting one it uses to manufacture bitumen mixture needed to make roads.

The tribunal had on December 18, 2018, set the deadline for the Calcutta Municipal Corporation (CMC) to “adopt new technologies for abatement of pollution in place of hot mix plants” at Goragacha near Taratala and Palmer Bazar near Sealdah.

Earlier in September last year, the tribunal ordered shutdown of the two polluting plants that use hot-mix technology. The tribunal had lifted the ban temporarily in December when the CMC said it was not being able to repair damaged roads.

Some experts had then suggested that cold-mix technology was less polluting and the civic body could install it. Hot-mix and cold-mix are two ways of preparing the bituminous mixture that is used to lay asphalt roads.

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.

The CMC also plans to use the hot-mix technology in a new plant that it would set up outside the city limits at Sirakol in South 24-Parganas. “We will use batch-mix technology, which is also a type of hot-mix technology but much more improved and less polluting,” a CMC official said.

The tribunal will hear the matter again on Tuesday and sources in the CMC said that they would seek extension for using the two hot-mix plants.

“We sought opinion of Delhi-based Central Road Research Institute (CRRI) and IIT Kharagpur. Both said that hot-mix was the preferred technology for a city like Calcutta where the bed of the road is not so tough, where rain is very high and where the soil has a lot of moisture,” said a senior CMC official.

Four or six months is not adequate time to shift to cold mix technology, the official quoted the CRRI experts as saying in their report.

Environment activist Subhas Datta, who had petitioned the tribunal about the pollution caused to manufacture the road repairing material, blamed the CMC for not shifting to a new technology.

“The tribunal had first asked the CMC to shift to new technology in November 2017. The tribunal had then said that it was costly and needed time. So it asked the civic body to start the process of shift,” said Datta.

But the CMC sat quietly and didn’t take any steps. “It was in September 2018 that the tribunal ordered a shutdown of the two plants. The ban was lifted for four months in December when the CMC pleaded that it was not being able to repair roads. The tribunal gave it time to shift to a better technology but again it has failed.”