One million fewer gallons of water will undergo treatment at the Sioux Falls Water Reclamation Plant because of a new filtration project.
The project was a collaboration between the South Dakota State University Water and Environmental Engineering Research Center, the City of Sioux Falls and the city’s consulting firm, H.R. Green Engineering of Cedar Rapids, Iowa.
For more than a decade, the City of Sioux Falls has set aside $20,000 each year from its capital improvement program to fund graduate research that will increase the efficiency of its wastewater treatment plant.
In 2010, the Sioux Falls Water Reclamation Plant set out to replace the filters that trap the remaining solids just before wastewater releases into the Big Sioux River.
The goal was to increase the flow rate through the filters and automate the backwash system, said Mark Perry, wastewater superintendent for the City of Sioux Falls. The price tag for replacing the filters was $3 million.
The plant’s dual-media filters, which use a combination of anthracite and sand to filter water, were operating well beyond their design life, said Chris Schmit, director of SDSU’s water research center. The filters would clog and then end up backwashed every 24 hours.
With guidance from Schmit, graduate student Sean Sieler worked with H.R. Green Engineering and the City of Sioux Falls to come up with a filtration system that would meet the city’s needs.
“We used an old technology called a monomedia, unstratified deep bed filter, which utilizes only coal and a deep bed,” Schmit explained. The media, which is much larger than conventional filter media, lets more water through, holds more solids and doesn’t clog as quickly.
The filter only needs to be backwashed once every three days to remove deposits and the process uses half as much water as the previous backwash method, Schmit said.
The plant was able to maximize its hydraulic capacity because the monomedia filters could handle twice the amount of water as the old dual-media filters, Perry said. By doubling its capacity, the plant was able to meet the city’s needs without having to build a second filtration building that would have cost about $10 million.
The filters have to undergo backwashing less often and it only takes 15 minutes, resulting in more than a 50 percent savings in time alone, according to Perry.
Backwash water has to undergo reprocessing, so any water savings essentially doubles, Perry said. The plant also gained 800,000 to 900,000 gallons a day in capacity, “because we don’t have to send that water to the head of the plant again.”
Changes in the filtration system have also improved the quality of the water released into the Sioux River, Perry explained. Essentially, the water that the plant releases is “cleaner than what’s normally in the river.”