Maryland shares more information about Back River Wastewater Treatment Plant explosion

The “working theory” on the explosion last week at a building on the Back River Wastewater Treatment Plant campus is that it might have been ignited after hot oil escaped from a leaking pipe, according to an inspection report from the Maryland Department of the Environment.

The explosion blew holes in three walls of the building, which is operated by a private contractor called Synagro, and the firefighting efforts covered the first floor in 6 to 8 inches of water, according to the state’s report. No one was injured, but the building remains closed.

Inside the fire-damaged building, Synagro dried sewage sludge into pellets, which are then used as agricultural fertilizer. The sludge is removed during the treatment process, so that the liquid can be cleaned and discharged into the river.

To dry out the sludge, Synagro heated it up by circulating mineral oil in a closed loop of pipes held at temperatures of 350 to 370 degrees Fahrenheit, according to the state’s report.

When state inspectors arrived on the day of the explosion, the chief of the Baltimore Department of Public Works’ Environmental, Regulatory and Compliance section told them that their theory is that some of the oil escaped through a hole and hit the pellets, causing the blast, according to the state’s report.

But the Baltimore City Fire Department, which is investigating the explosion and subsequent two-alarm fire, has not determined an official cause.

A Synagro spokesman did not comment on the theory presented by the Department of the Environment, saying that a cause has yet to be determined.

The fire is the latest setback for an already troubled wastewater plant, which is the largest in Maryland.

The state dispatched a team last year to take over Back River, warning that the facility could be approaching “catastrophic failure.” Since then, the plant’s discharge into the river has come into compliance with pollution limits, though internal issues with machinery have persisted, according to inspection reports from the state.

The state is to remain at the plant through April 30, under its most recent agreement with the city of Baltimore, which owns and operates the Back River plant, though it accepts waste from thousands of households and businesses in both the city and the county.

The loss of the pelletizing plant means that the sludge will need to be processed another way. If that isn’t done quickly enough, sludge could start to build up in the plant. Such buildups contributed heavily to the plant’s pollution issues over the past few years.

Normally, about 70% of the biosolids from the plant are routed to Synagro’s building.

In its report, the MDE calls for Baltimore to submit a plan explaining how it will handle the sludge while the Synagro pelletizer is down.

“There appears to be no impact to the liquid stream of the wastewater treatment process operations, but the solids processing will be affected, and an alternate plan needed,” reads the report from MDE.

The city did not respond to questions about whether it has submitted a plan.

According to the state’s report, the city can dry out the sludge using its own centrifuges, though it can’t create pellets the way Synagro would have.

Synagro is finding alternative applications for the resulting product, said the company’s vice president for government affairs Layne Baroldi. It can be spread on fields or used in composting, he added.

The city’s centrifuges function similarly to a clothes dryer, said Doug Myers, Maryland senior scientist from the Chesapeake Bay Foundation, who has been following the sewage treatment issues at Back River.

According to the state’s report, two of the four centrifuges are functioning.

“The big question mark in my mind is: Is that enough?” Myers said. “We haven’t seen any quantification of the amount of biosolids produced every day and the capacity of those centrifuges.”

Baroldi said Synagro has portable dewatering equipment at Back River and is working to bring it online to help process the sludge, though there is sufficient capacity as of now.

Synagro also is working to bring some of the dewatering equipment inside its building back online by early April, though the pelletizing equipment will remain offline.

In a statement Wednesday, Jason Mitchell, director of the city’s Department of Public Works, said the agency is working to optimize its own centrifuges in the meantime.

“As we continue our efforts to successfully restore the Synagro support services to the plant, we will continue optimizing the operation of our city-owned centrifuges,” Mitchell’s statement read. “These processes have not impacted DPW’s waste disposal.”