A US wood pellet plant that supplies Drax, a UK power generator, has been found to have violated air pollution limits in Mississippi.

The Mississippi Department of Environmental Quality (MDEQ) sent a notice of violation to Amite BioEnergy, a company owned by Drax, stating that the plant had breached emissions rules. The violation was discovered after a review of Amite’s monitoring reports, which revealed that the plant had been a “major” source of hazardous air pollutants from January 2021 to late last year, despite being permitted to operate as a minor source.

The wood pellet plant, located in Gloster, Mississippi, converts trees from southern states into wooden pellets that are used as biomass fuel in Drax’s power station in North Yorkshire, England. Drax’s sustainability practices have faced increasing scrutiny from MPs and environmental campaigners.

In 2021, Amite was fined $2.5 million for violating air pollution regulations, but it remains unclear whether this latest breach will result in another financial penalty. The notice of violation, issued in March, revealed that the company’s permitted emissions of hazardous air pollutants were capped at 24 tons (22 tonnes) per year on a rolling 12-month basis. However, between January 2021 and December 2022, the plant emitted as much as 37 tons, with the highest levels recorded in July 2022.

The MDEQ has requested an explanation from Amite regarding the violation and the steps taken to address it. Amite argued that, based on its analysis, it was only non-compliant for a brief period between late October and early November 2021.

In response, Drax argued that pellet production was a relatively young industry, adding: “Several wood pellet facilities, not only Amite BioEnergy, initially underestimated emissions in connection with the permitting of these facilities.

“Amite BioEnergy has a history of acting quickly to update emissions and permits upon discovery of new emission factors and new information pertaining to other pellet production plants.”

Following these developments, Ofgem, the energy regulator in Great Britain, has initiated an investigation into Drax’s operations to assess their alignment with biomass sustainability rules. The investigation will be conducted by the US consulting group Black & Veatch.

Drax has faced previous accusations of “environmental racism” due to government subsidies it received for its operations in the US South. In 2022, the company received £617 million in government subsidies, and its market valuation exceeds £2 billion.

The breach by Drax is a cause for concern, according to John Randall, a former Conservative MP and environmental adviser to Theresa May.

Lord Randall added : “It’s imperative that Drax, which receives millions in bill-payer subsidies, cleans up its act immediately.”

In the US, Matt Williams, a campaigner for Cut Carbon Not Forests and a senior advocate for the Natural Resources Defense Council, said of Drax: “It’s already been fined once. But a $2m fine is pocket change to a company that receives hundreds of millions of pounds in subsidies every year by claiming to be green. And now it’s doing it again.

“Burning trees in power stations should not be part of our energy system. The UK government needs to stop handing billions of pounds in subsidies to companies like this that are poisoning people’s air, making climate change worse, and destroying forests.”

A spokesperson for Drax stated that in January 2022, an environmental consultant reviewed the company’s air pollution calculations and identified discrepancies. As a result, Drax contacted the MDEQ to refine the calculations and update the readings.

The spokesperson said: “Drax took prompt corrective action in response and worked with MDEQ to resolve the issues and provide them with accurate reports and permit applications. We continue to work with leading environmental consultants to ensure that we monitor and report permit compliance in a rigorous and transparent manner.

“Drax is committed to environmental compliance and remains focused on transparency and open communication with the [US] Environmental Protection Agency, MDEQ and the community.

“The safety of our people and the communities in which we operate is our priority, and we take our environmental responsibilities very seriously.”

Despite these issues, Drax reported significant profits, with £731 million in 2022 compared to £398 million the previous year. The company recently announced a £150 million share buyback for its investors and revealed plans for significant expansion in the US.