Baltimore County officials are investigating the cause of a fire Monday night at the Back River Wastewater Treatment Plant.

Firefighters responded to the Dundalk treatment facility on Eastern Avenue around 7 p.m. to respond to a fire.

The fire was at a building used for producing a wastewater sludge product, according to a spokesperson for Baltimore City’s Department of Public Works, which operates the Back River Plant.

The building, leased and operated by Synagro Technologies, one of the country’s leading manufacturers of wastewater sludge, converts sewage at Back River into a cheap substitute for agricultural fertilizer.

It’s not the first time the Synagro building, which can house 12,000 gallons of thermal oil, has caught fire. An on-site explosion and gas-fed fires destabilized the building in 2023, forcing an evacuation on the site of the treatment plant.

More than 100 personnel were on the scene to hose down the machinery that was on fire, according to the Baltimore County Fire Department. Firefighters were able to extinguish the fire at 11:37 p.m., said the department spokesperson Travis Francis.

As of Monday night, there was no threat to the community and the water supply was safe for consumption, the department said. One firefighter was transported to the hospital with minor injuries after a slip and fall.

A spokesperson for the city Department of Public Works did not address questions about the cause or damage of the Monday night fire, and Synagro did not immediately respond to a request for comment.

The Middle River-based Synagro, which is owned by a Goldman Sachs-managed investment fund, handles around 70% of waste that passes through Back River at its facility on the campus, processing it into fertilizer pellets used on cropland around the region.

The Back River Wastewater treatment plant serves about 1.3 million Baltimore city and county residents, according to the Baltimore City Department of Public Works. State regulators took control of the plant in 2022, after an inspection by the Maryland Department of the Environment revealed extensive maintenance problems, multiple permit violations and sewage discharges.

Advocates with Blue Water Baltimore and its attorneys at the Chesapeake Legal Alliance also sued the treatment plant for water pollution violations. The lawsuit was dismissed after the city agreed to a consent decree in November 2023, which included a hefty fine.