The Problem: Case Studies
Aubrey Strause, P.E.—whose company, Verdant Water, provides services in stormwater management and wastewater infrastructure asset management, and who also is an associate with Fuss & O’Neill, a civil and environmental engineering consulting firm—took an interest in the problem of wipes clogging wastewater systems in 2009 when she became involved in the Maine Wastewater Control Association, now known as the Maine Water Environment Association.
Maine’s wastewater facilities and collection systems operators would complain to her about an ongoing problem with ragging (when wipes clog the system).
“They had to take their pumps down all of the time, taking out piles and piles of what they were calling rags, and it took a little while for me to realize they’re talking about different types of wipes,” says Strause.
The association conducted a study in early 2011 and of the 58 responses from across the state, 90% indicated they were having problems and 40% indicated that they have had more than 10 incidents in the previous year. The estimated cost of addressing it was nearly $600,000 or an average of $37,500 per town.
As the wipes market has grown, the challenges associated with them in wastewater systems have increased, says Strause, adding that the problem is not just domestic, but global, as operators in Europe, Australia, New Zealand, and the Middle East are all working on the issue.
Strause has compiled a Google map dotted with all of the different areas in the US that have reported the problem.
To understand the problem, utilities have to dig deep into the material. Due to limited data on the nature of the interferences, the Maine Wastewater Treatment Association has a standard operating procedure (SOP) for helping utilities evaluate materials in pump clogs and sewer obstructions in order to assist the industry in understanding the extent of the problem, characterize the materials responsible for the interferences, and determine how to ultimately solve the problem.
Details on the SOP are available at www.mewea.org/PumpClogSOP.pdf.
Portland, ME, spent $4.5 million installing screens in two pump stations.
“We estimated based on the capital costs of those screens, and the labor and disposal of the wipes, we were paying $800 per dry pound of wipes,” notes Michelle Clements, a spokeswoman for the Portland (ME) Water District.
Scott Firmin, director of Portland (ME) Wastewater Services, says the reason for the expenditure for the pump upgrades is that one of the stations normally pumps about two million gallons per day, but during wet weather, the flows can increase.
“That pump station is designed to operate at about 15 million gallons per day,” he says. “That required three pumps running. The pumps would plug one after another and we could only keep two pumps running very inefficiently. Instead of pumping 15 million gallons, we would only be pumping something like nine million gallons. That extra six million gallons was overflowing directly into the water. When these materials interfere with a gravity sewer, a pump station, a pump, a treatment plant, or even a residential home septic system, they will cause sewage to go someplace where it wasn’t intended to go. That’s normally the environment.”Add Stormwater Weekly and Water Efficiency Weekly to your Newsletter Preferences and keep up with the latest articles on water: green infrastructure, smart meters, stormwater drainage and management, water quality monitoring and water treatment.