Power plants in several Michigan cities are burning millions of tyres each year to make electricity, prompting some pollution concerns as state officials and plant operators defend the practice.

According to plant operators, tyre-derived power is cheaper and cleaner than burning coal or wood, the Detroit Free Press reported. They say that they are keeping tyres out of landfills and helping the state clean up dump sites.

Wyandotte’s municipal power plant creates electricity for about 10,000 households and 3,000 businesses. Two boilers run off natural gas and the third uses tyre shreds and coal. According to officials, tyres contain more energy than coal, pound-for-pound.

“We burn about 300 tons of fuel per day in this boiler. It generates less waste, lower emissions and more-efficient combustion,” said James French, the former director of the city’s power supply.

Some who live near the eight plants that burn tyres to make power in Michigan, however, have challenged them because of pollution concerns.

In Hillman, a village in Alpena and Montmorency counties, the elementary school is next to the power plant. In 2002, when plant officials applied to increase their use of tyres, people like Donna Baranyai, with two children at the school, asked that the application be rejected.

“It still concerns me,” said Baranyai, who eventually moved her children to a school in a neighboring community. “There’s a community park at the end of the street. There are times when you go there and the playground equipment will be all covered in black.”

Michigan officials say 1991 legislation that gave them the power to regulate and remediate used tyres has fueled an economy centered on tyre reuse and recycling. Shredded bits of tyre are mixed with coal and wood to be burned to create electricity, and it’s is the single largest use of old tyres in Michigan.

“We have all these piles of tyres and they are looking for any use they can get because you can only do so much with tyres,” said Neil Taratuta, supervisor of the tyre- and wood-burning Viking Energy plant in Lincoln, a village in Alcona County, about the state’s scrap tyre programs.

Michigan Department of Environmental Quality data suggest that over 20 years, about 31 million discarded tyres have been reduced to two million and more than 200 known illegal tyre dump sites have been reduced to 55.

“Most things are going to be cleaner when compared to coal in terms of pollutants,” said Steve Weis, environmental engineer for MDEQ in Detroit.