The Water and Sewer Authority of Cabarrus County (WSACC) serves selected water and sewer needs for five jurisdictions in south-central North Carolina. One of WSACC’s primary facilities is the Rocky River Regional Wastewater Treatment Plant in Concord. This two-stage 26.5 mgd biological wastewater treatment facility processes domestic and industrial wastewater.
In early 2016, maintenance staff determined that the four existing 1970s-era bar screens at Rocky River’s main pump station needed to be replaced to address serious operational challenges — safety, cost and time — that WSACC had been dealing with for years.
The problem
The bar screens were deep — about 40 feet from the deck level to the bottom and about 55 feet total — making them difficult to access at the bottom of the 4-foot-wide channel. The coarse screens are used to remove debris from wastewater prior to entering the dry pit submersible influent pumps that convey the water to WSACC’s headworks facility. The main problem at WSACC was profound grit buildup at the screen. Grit is not an unusual issue with aging U.S. infrastructure, but it can, and did, wreak havoc at WSACC.
During a rain event, when water flow picked up, grit would inundate the old screens and jam the sprockets at the bottom of the system. To get the screen moving again, a maintenance crew of six or more would need to access a dark, 4-by-8-foot pit to shovel the grit out of the pit and into buckets to be hauled back up to the deck. After unburying the screens, the crew would replace any broken components. This would happen three to four times each month, according to WSACC officials.
“The old screens constantly broke,” says maintenance manager Chris Carpenter. “Access was so hard, and it was a tremendous amount of staff time — and permits for confined space entry — to deal with the grit backup.”
Engineering firm Black & Veatch worked with WSACC staff to select the best option to replace their problematic equipment. The new screens needed to be unfailingly reliable during weather events and keep their maintenance crew out of the channel.
The solution
The team agreed that the technology that would fully address their concerns was the FlexRake FP-M 1-inch full-penetration coarse screens from Duperon Corp. The stainless steel, link-driven mechanical bar screens are front-clean, front-return, mechanically cleaned screens with no lower sprockets, bearings or tracks that can jam below the deck. The FlexRake FP-M is suitable for vertical and near-vertical applications, such as the one at Rocky River, because the Flexor technology allows the screen to be vertical without adding submerged maintenance components into the channel.
Cost savings
Time and employee safety aren’t the only benefits WSACC is experiencing with their new equipment. The cost of maintaining the old equipment was significant, including $100,000 to rebuild each screen every five or six years. Carpenter estimates that 10% of the WSACC maintenance budget was spent on the previous bar screens.
Duperon Corp. is a leader in simple, adaptive screening technologies and provides solutions for coarse screening, fine screening, low-flow screening, ultrascreening, washing, compacting and conveying.
800-383-8479 | info@duperon.com | www.duperon.com
