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Treatment system strips 2 million pounds of pollutants from city waste water


Posted June 27, 2019


It is being lauded as one of the largest, most advanced applications of denitrification technology anywhere and Whitman, Requardt & Associates, LLP (WRA) created the system inside a century-old facility without disrupting its ongoing work of processing 180 million gallons of waste water daily.

The City of Baltimore started the Enhanced Nutrient Removal project for the Back River Water Resource Recovery Facility in 2006 as part of the Chesapeake Bay Restoration Program. Although Back River had been outfitted previously with systems capable of removing about 50 percent of nitrogen from waste water, operators were aiming to eliminate more than 90 percent of nitrogen and phosphorous. 


In the preliminary phase of the 12-year project, engineers had to identify the  most appropriate treatment technologies based on performance, space requirements, compatibility with existing equipment, cost, and ease of both installation and operation.

Once the project team selected a treatment technology, “we ran a pilot test over a six-month period with a small-scale unit,” said Per Struck, Vice 

President of WRA. “We used the Back River waste water stream…and tested different waste water loadings, temperatures and other conditions to verify that we could meet the reduction goals and we could scale up.”

WRA concluded the Back River system would need 52 specially designed biological deep-bed Denitrification (DN) filters. Each measuring 12 feet wide by 15 feet deep by 100 feet long, the DN system would be one of the largest ever installed. Additionally, installing the massive, high-tech system would be challenging on a facility built at the turn of the last century.

While the City of Baltimore had good records of previous construction on site, crews had to contend with unexpected discoveries such as unmapped pipes and foundations. They also had to remove large pieces of old, abandoned equipment, such as the systems that once delivered treated waste water to Bethlehem Steel for use as cooling or process water.

The project team also had to ensure that Back River remained fully operational and fully compliant with its effluent permit standards throughout the four-year construction phase.

“We couldn’t just tell the City of Baltimore not to flush the toilets for a period of six months while we installed equipment,” Struck said. 

Consequently, the project team selected equipment that could be almost completely installed before tying into existing systems and carefully phased construction. 

Towards the end of construction, however, “there were some challenges, like cutting into a 12-foot-diameter pipe that was still flowing with waste water,” Struck said. 

A skilled marine construction crew, including divers, built a box around the active pipe to support it and contain leakage. Working in the wee hours when effluent flow is lower, crews placed straps around the pipe, cut through it with a band saw, hoisted a section out and redirected the pipe to tie in with the new treatment facility. 

Activating the new treatment system “couldn’t happen overnight,” Struck said. “Chemicals had to be added, flows had to be pumped and a lot of different functions had to work together to improve treatment performance.”

The system’s nearly three-month startup phase experienced some challenges, such has dealing with heavy rainfalls that can double or triple flow to the Back River facility. However, through close collaboration, the project team, city officials and personnel at Back River got the new system fully operational and hitting its treatment goals. Monitoring shows the technology reduced the nitrogen and phosphorous load discharged into the Chesapeake Bay by nearly 2 million pounds in its first year of operation. 







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