By Michael Microbi
A primary goal of enhancing biological treatment led to another important goal of controlling overflows for the 2015 Shamokin Coal Township (Pa.) Joint Sewer Authority’s treatment plant upgrade and expansion. Adding sequencing batch reactors (SBRs) to the plant’s existing trickling filters sufficiently improved the effluent quality to lessen the eventual impact on the Chesapeake watershed. However, the addition required upgrading the existing headworks to fully protect the new SBRs.
Grit removal was historically a problem at the plant, which operated an Archimedes screw device that augured grit from two chamber wells. During wet weather events, incoming grit included sediment and other fine particles especially harmful to plant pumps and processes. The older grit system was unable to remove the large amount of grit entering the system during these overflow events, requiring costly, multi-day cleanouts four times a year.
“It was very labor intensive,” said Paul Petrovich, general manager of the Sewer Authority.
Designers from Great Valley Consultants evaluated various grit removal technologies for the expansion project based on two key criteria: grit particle removal efficiency and ability to handle surge events. They visited real installations nearby and spoke with operators. Ultimately, the PISTA® 360™ with V-FORCE BAFFLE™ from Smith & Loveless was selected because of its high efficiencies, high turndown and low life cycle cost.
Unlike conventional vortex-type systems, the PISTA 360 maintains ideal velocity during low-flow and surge events, ensuring consistent grit removal at all times. The system’s patented hydraulic design is comprised of a carefully positioned inlet flume and integral flow control baffle inside a 360-degree, flat-floor grit chamber. This design creates a forced vortex flow path that sweeps the incoming grit along the chamber floor toward the center opening for removal. As flows fluctuate, the baffle causes the water level to properly adapt to maintain ideal velocities. It features a 10:1 turndown with no additional downstream control devices.
The upgraded Shamokin Coal Township Joint Sewer Authority plant was officially commissioned in 2015. Project leaders report exceptional service from the system, which has provided more than a year of dependable grit removal with minimal O&M requirements, including during combined sewer overflow events.
“It’s removing 99 percent of the grit, pre-storm and during storm events,” Petrovich said. “We don’t see any grit downstream, including in the motors where grit can tear them up.”
That’s significant because of the heavy flows encountered during wet weather.
“We are a combined sewer system so during storm events flows can actually reach 13.5 MGD,” Petrovich said, adding that the new 12 MGD grit chamber “wasn’t missing a beat. It pulls out all of the grit.”
The performance of the system is especially impressive, according to Petrovich, when you consider that it requires significantly less O&M than the previous unit. The recommended maintenance schedule consists primarily of periodic lubrication, he said.
“There has been very little trial and pain,” Petrovich remarked. “After start-up, we had to adjust certain settings, but since then we have had basically no other maintenance.”
To learn more about Smith & Loveless, visit smithandloveless.com.
