Fairfax County discovers many benefits to ultraviolet for wastewater treatment
Fairfax County’s new ultraviolet water treatment facility earned an Envision Gold award for sustainability. The award-winning Noman M. Cole Jr. Pollution Control Plant is a 67-million-gallon-per-day wastewater treatment plant in Fairfax County, Va., that replaces the old sodium hypochlorite disinfection system.
The wastewater treatment plant takes the sewage from the southern half of Fairfax County and reclaims it by removing 99.9% of pathogens.
“Disinfection is a dedicated process to remove pathogens and germs, and ultraviolet is EPA approved,” Michael McGarth, plant manager of the Noman M. Cole Jr. Pollution Control Plant, explained. “It uses light to remove microbes, including those that can cause disease.”
The change in treatment, from bleach to ultraviolet, is not only more sustainable for the county, but safer for customers and for employees.
“Chemicals, added in liquid form, killed the germs,” McGrath said. “Unfortunately, the active ingredient remained and would continue to kill things so we had to add another ingredient, sodium bifluoride.”
These chemicals had to be brought in on tankers to the tune of 200 loads per year, or roughly $750,000.
“The (old) system required what felt like almost continual adjustment of the chemicals to get the right dose,” McGrath continued. “They’ve got to test every two hours to demonstrate to the Department of Environmental Quality that they’re not distributing too much, so it takes a lot of labor to monitor.”
The new system uses an entirely different process.
“It does not completely kill the pathogens, but it changes the DNA so they cannot reproduce,” said Capital Improvement Program engineer Sajana Chitrakar.
The technology has been used in various communities for drinking water since 1910 but has only been implemented in wastewater since the 1980s.
“UV also has the resiliency factor,” Chitrakar continued. “With the chemicals, we had to rely on drivers and availability, and so we have eliminated a portion of that because we don’t need (sodium bifluoride) to reduce the bleach.”
It took nearly 10 years from start to finish, McGrath admitted.
“Our water flow had to be changed,” he said. “(The project) required us to construct some new concrete tanks and channels in order to install the UV equipment. It wasn’t an overnight thing.”
In addition to the actual process, the project took longer because Fairfax County funded it itself. Funding came primarily from the construction improvement fund.
The new system had to be run parallel to the old one until the latter was no longer in use. Then the old system was easily hauled off.
“The old system consisted of relative small pumps about the size of a basketball, so it was fairly easy to dispose of,” McGrath said.
In addition to that, the new design also allowed the facility to need fewer pumps. After redesigning the flow of water throughout the plant, and removing a large pump, administrators discovered that there were significant savings in electrical usage.
“We were spending the equivalent of 100 kilowatts every second,” said McGrath. “It’s equivalent to a year’s use for 100 households. They ended up balancing each other out — the energy-saving from the pump saving and the (UV) lights.”
It was also the county’s first CMAR, or construction manager at risk, project — instead of a low bid contract.
“There was also a challenge because there was nothing we could reference,” said Laurel Xiao, engineer IV of Capital Facilities. It was designed by Hazen and Sawyer and constructed by Ulliman Shicutte Construction.
The design also included retractable covers for the UV system, one of the first of its kind in the United States. The ultraviolet disinfection equipment can be pulled out to be cleaned, while a cover keeps worker safety a top priority.
“The design was pretty innovative,” Xiao said. “We have been running the UV system for about a month with the full flow. It has been running pretty good creating the results that we desire.”
The Envision award evaluates projects based on criteria that include improvement to the quality of life, water consumption and environmental impact, among others.
“We are talking about not only meeting the needs of the project but also contributing to the prosperity of our community from an environmental and developmental perspective,” said Xiao.
McGrath said the green programming award has created positive competition among builders and designers who seek to make their engineering projects more sustainable. “It’s a way to attract and incentivize more sustainable infrastructure,” McGrath noted.
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