Fourteen years ago, the pumps operating at the septage receiving wet well at the Valley Forge Sewer Authority’s (VSFA’s) collection system in Phoenixville, Pennsylvania, were constantly clogging. This created frequent headaches for the operators and cost valuable time and expense for unscheduled maintenance. Unscheduled downtime created delays in unloading for the septage trucks and interrupted the normal plant operations as trucks were unable to off-load upon arrival.
Image 1. About 30 septic dump trucks bring waste into the VFSA pumping station every day. (Images courtesy of KSB)“Our septic receiving area was a dry well/wet well that used chopper pumps,” said Lloyd Knauer, Valley Forge’s maintenance and operations supervisor. “With the pumps we had before, whenever we received rags or anything tough to pump, we were constantly having to tear them apart to remove the rags. Additionally, the grit created premature wear issues. Since upgrading our system 14 years ago to the KSB submersible non-clog pumps, we have not had any clogging problem. Prior maintenance problems have been completely alleviated. We periodically pull the pumps for inspection as part of normal preventive maintenance, and notice that there is absolutely no material build-up inside the pump casing.”
The previous chopper pumps were replaced with wet well mounted non-clog vertical submersible motor pumps that use vortex (recessed) impellers.
Image 2. The VFSA services 22,000 customers in the Phoenixville, Pennsylvania, area.“We bring in 20 to 30 septic dump trucks a day from residential septic tanks and industrial facilities. We are very pleased with the way the new pumps handle the difficult septic fluids,” Knauer said. “They pump a variety of different types of material, including rocks and rags. We change the oil about once a year and the pumps have been working great; and the high alloy hardened impellers show virtually no wear after more than 10 years of continuous service.”
Background of the Site
The VFSA is a utility that is owned by its customers and was incorporated as an operating authority in 1968. VFSA owns and operates 90 miles of sewer pipeline, nine pump stations and a regional treatment plant rated for 10 million gallons per day (gpd), and treats an average of 8 million gpd. VFSA serves approximately 22,000 customers in nine Chester County municipalities: the townships of Charlestown, East Pikeland, Schuylkill, Easttown, East Whiteland, Tredyffrin, Willistown, West Vincent and Malvern Borough. In addition to treating the influent wastewater into clean water for stream discharge, the plant also produces a specialized fertilizer product used by area farmers.
The Problem
Part of the plant includes a dedicated septage receiving wet well. The septage waste is then pumped to an equalization tank, prior to being flow-paced into the treatment plant process.
Knauer said that before the pumping system upgrade in 2002, the wells were overflowing regularly because the truck operators did not realize that the pumps were not transferring the materials that were causing the clogs.
“We would either find out from the operators after an overflow occurred, or from the high-level sensors that we eventually had to install,” Knauer said.
“Whenever the overflows would happen, two mechanics would have to come over and get down inside the dry well, shut off all the valves, pull the pump apart, pull the impeller out, unclog it, and put it back together. In the septic business, downtime means lost money. During emergency shutdown of the pumps, the dumping process was curtailed until the pumps could be returned to service, with the result that septage trucks would be waiting as long as several hours until the pumps were back in service.”
Image 3. The VFSA owns and operates 90 miles of collection line, nine pump stations and a regional treatment plant.Since the installation of the non-clog pumps, the maintenance procedure has been limited to planned, infrequent, preventative maintenance inspections, Knauer said.
“These pumps are very good at pumping out the wet well all the way to empty,” he said. You can see on top of the pumps a lot of buildup of grease and rags, but these pumps handle all that, and are virtually maintenance free.”
A Cycle of Changes in Wastewater
A 23-year veteran of the VFSA, Knauer has seen his share of changes in wastewater pumping, particularly with the use of flushable wipes, and other fibrous materials that can knit and cause pump clogging.
“Fortunately, these non-clog pumps can handle it,” Knauer said.
Over the past 10 to 15 years, the low-flow water toilet has reduced the volumetric flow. There has been an increase in the use of personal wipes, in addition to traditional fabric and fibrous materials. The overall impact has been increased clogging issues in a lot of places.
Additionally, there has also been a steady demise of large industrial and general manufacturing plants with high water effluent volumes, which has greatly increased the percent of solids in the pumpage, given the reduction in dilution water from those large industrial users.
Often, “rag balls” form inside the collection system pipes. This is caused by small fibrous materials that re-knit to create much larger formations.
In this geographic area, there are many homes with on-site septic tanks. When the septic tanks reach a certain level, they must be pumped out. That fluid is difficult for standard sewage pumps to deal with. It has an unusually high percentage of abrasive solids (sand) when compared to sanitary waste streams in wastewater collection systems.
Image 4. Excessive sludge, rocks and rags are no problem for the upgraded pumping system at the VFSA, thanks to the clog-free, maintenance-free submersible pumps with vortex impellers.The fluid also generally has fabric and other undesirable materials that are prone to plug pumps. In this instance, based on operating feedback from the plant operations personnel, and in conjunction with the consulting engineer, a supplier recommended a special hardened alloy material for the impeller and pump volute. The net result of an application-specific (wastewater) pump selection is that the end user experiences uncommon reliability.
The standard mechanical seal for all of the manufacturer’s non-clog pumps is silicon carbide, which offers significant longevity advantages. Silicon carbide is an extremely abrasion resistant material, and also dissipates heat better than most other seal face materials, which further enhances longevity before required maintenance.
Additionally, the conservative shaft design with larger bearings reduces the frequency of premature and unscheduled maintenance due to negligible shaft deflection, even at high operating pressures.
The pumps at Valley Forge feature a hardened alloy vortex impeller, which offers longevity and suffers little wear. This increases the anticipated life cycle of the impeller and the pump. The large recessed impeller passage handles heavy materials, including rags and wipes, without any need to cut the materials into smaller pieces.
The pumps at Valley Forge have created a clog-free, worry-free environment for the operators, requiring limited preventive maintenace. The Valley Forge septage hauling truck drivers are happy since they are no longer inconvenienced by unexpected delays offloading their trucks. It’s a great example of how technology solves challenging hydraulic problems for treatment plant and collection systems operations personnel.