Disposable Wipes Threaten Wastewater Systems

While manufacturers claim these wipes are flushable, they have been causing major problems for wastewater facilities, and the problem has only worsened in recent years. New York City alone claims that more than $18 million has been spent during the past five years to remedy wipe-related problems in their 14 wastewater treatment plants. In the Southwest, a Tucson, Arizona-based news crew visited a regional reclamation center and documented that "white wipes were everywhere." The operator suspects the wipes are not biodegrading as fast as the general public is being led to believe. The wipes cake the walls and eventually get stuck in the sewers where they clog pumps and pipes. When blockages occur, there is just one way to clear them—by hand.

In Vancouver, Washington, sewer officials performed their own experiment after spending more than $1 million replacing 11 pumps that regularly became clogged as a result of wipe ingestion. They dyed wipes labeled "flushable" and sent them on a one-mile journey through the system. They did not break up. One major producer of flushable wipes claims that the problem is caused by products not meant to be flushed. They explain that flushable wipes, when used as directed, break up after flushing and clear properly maintained toilets, drain lines, sewers, pumps, and septic and municipal treatment systems. Consumer Reports performed tests that dispute these claims. The magazine ran vortex and mixer tests on several major flushable wipe brands that claimed to be safe for sewer and septic systems. After 10 minutes of agitation, the wipes did not break down. Consumer Reports states that the public must understand what is safe to flush and what is not. Their advice: "Do not flush flushable wipes." Until industry standards for all wipes meet wastewater handling equipment requirements, the public must be informed and responsive to minimize system downtime and the resulting costs to taxpayers. In the meantime, waste-handling equipment must be upgraded to handle a large volume of these wipes in the system.

Facing the Problem

Several pump companies have attacked the problem by developing equipment that will shred wipes and other solids to make them safe for wastewater systems. The engineers at one company have developed dual shredding technology that features radial and axial shredding elements. This design obliterates wipes and other hard-to-handle solids. "Incorporating both radial shredding and axial cutting achieves optimum results on hard, to near impossible to pump liquids containing fibrous solids like wet wipes," said Brian Mitsch, the company's VP of operations and engineering. "The radial shredding is achieved by a rotating cutter bar with serrated edges, which traps and shreds solids against the sharp grooves of the radial cutting ring. Wipes and other fibrous debris are efficiently ripped apart. The complementary axial cutting utilizes dual cutting elements operating in tandem to multiply the shearing action. As the material exits the radial shredding area, the axial cutting components shear any remaining pieces using multiple cutting bars. The impeller design expedites flow and hydraulic performance, preventing wrapping and clogging." These pumps feature shredding elements that are cast in hardened 440C stainless steel (Rockwell hardness above 55C), and the patent-pending design provides excellent solids-passage efficiency through its impeller and volute. Available with 2-, 3- or 5-horsepower (HP) high-torque four-pole motors, these pumps are ideal for smaller wastewater stations.

Case Study

FoxRock Properties owns and operates two massive office and medical complexes in Norwell, Massachusetts. The first of the neighboring properties is Longwater Place, a 27,000-square-foot office building, part of a larger 26-acre campus that includes 84,000 square feet of corporate offices and a 160,000-square-foot wellness center. Longwater Place incorporates a full cafeteria, and fitness center, featuring a gymnasium with squash courts and locker/shower facilities. The adjoining property is South Shore Medical Center, an 85,000-square-foot facility comprised of 100 medical examination rooms, 70 medical offices and a complete range of diagnostic equipment. Because of the expansive size of these buildings, property management faces major wastewater handling challenges. The complex has 30 bathrooms and 64 toilets that pass flow content consisting of sanitary waste, wipes and feminine hygiene products flushed by staff, patients and visitors. All of it travels through the sewer lines of both properties and is funneled into an outside 10,000-gallon overflow tank. The wastewater is then pumped through a 4-inch PVC discharge pipe more than one-eighth of a mile from the tank into the municipal sewer system. Two solids-handling submersible pumps are at the heart of the system. Although not required by local regulations, FoxRock Properties maintains this pumping system to ensure that discharges to the municipal sewer system can be handled effectively by the local treatment facilities. "Given the buildings' populations, professional range of clients and types of services provided, it is expected that we would see more than our fair share of flushables," said Dan Snyder, property manager for FoxRock. "In the past, we experienced frequent failures as wipes blocked screens protecting the pumps and wrapped around impellers, clogging the volute and eventually burning out the pumps' submersible motors. Even with a back-up pump in place, the service interruptions and maintenance costs became unacceptable." The average pump service life was less than 1.5 years. After one of the 460-volt submersible pumps failed again, Snyder asked the water and waste equipment specialists at Williamson New England Electric Motor and Pump Company to examine the problem and recommend a solution. Jae Wilson, service manager at Williamson New England Electric Motor and Pump Company reviewed the system and its hydraulic requirements, including the difficult-to-pump wastewater content. Although numerous solids-handling pumps were available, none presented the perfect solution. Research indicated that the heavy wipe content would still tend to wrap and clog pumps with traditional non-clog impellers. The resulting failure meant lifting the pump, disassembling and manually clearing the blockage, and possibly replacing the motor. Wilson consulted with one of his pump suppliers and decided to install a shredder pump with dual shredding technology. Because it used both radial shearing and axial cutting to pass hard-to-pump items such as wipes, this new design was ideal for the application. One important advantage of the new system was immediately noticeable. Most non-clogs, including the second wastewater sump on the FoxRock property, must be surrounded by a screen. The solids and debris that get caught in that screen must be routinely cleared by hand. The installed pump does not require a screen. A post-installation inspection showed no debris in the sump. "So far, I am very happy with the pump. It was installed in July 2014 and continues to operate without clogging," Snyder said. While preventing non-flushable materials from entering the wastewater system is impossible, FoxRock Properties has a pump that can minimize the possibility of clogging and improve downstream conditions.