In the absence of any legislative- or industry-driven change, “flushable” wipes continue to plague municipal wastewater infrastructure. Municipalities have been forced to find solutions to the damage caused by the fibers of these products, as well as other “rags” that bind up pump impellers, clog screens, and coagulate other fats, oils, and grease into fatbergs.
The city of Big Lake, in Sherburne County, has resolved to take action to address the problem of wipes and rags in the city’s 14 lift stations. The damage to pumps and the resulting repair call-outs were a cost that was simply too great, according to Charlie Gammon, water and sewer foreman for Big Lake. The city is moving away from the more conventional pumps in lift stations and installing vortex pumps that allow only 15% contact with impellers.
Vortex pumps have proven to be able to eliminate much of the need for call-outs and damage to pumps from wipe and rag fibers. But, it doesn’t come cheap. Gammon said that a 5 horsepower vortex pump can run $8,500; and a 15 to 20 horsepower vortex pump can cost as much as $25,000. Given the 14 lift stations in Big Lake’s collection system, this is a major investment to deal with wipes and rags. In the long run, though, Big Lake will save money in call-outs and pump repairs.
“I’m fortunate that Big Lake has given me a lot of flexibility to address these issues,” Gammon said.
The downside to installing vortex pumps is that wipe and rag fibers pass on to the head works where the current screens are not fine enough to catch them all. As part of a phased reconditioning project, Big Lake will be spending about $600,000 to retrofit new finer screens to the head works, which will prevent fibers from passing through and into more sensitive treatment processes.
Gammon recommends that municipalities that have trouble in collection systems from wipes and rags establish good relationships with their pump representatives. “Pump reps want your business, so they will work with you,” said Gammon. “Demo their pumps. They have loaner pumps that they will let you use for a while to try. See how they work before you invest. I always keep in mind that the rate payer is who I'm watching out for, and while I know a lot of reps and really like them, I’m not their friend at work. Every dollar counts to the rate payer.”