Could self-healing pipes help solve sewer problems?

August 10, 2011

By Michael Timm

When you cut your arm, it bleeds, clots, scabs, scars, and eventually heals. But when a sewer pipe cracks, we don’t expect the pipe to heal itself—at least not yet.

A team of researchers at the University of Wisconsin-Milwaukee is investigating “self-healing” materials that one day could—emphasis on could—do just that.

Self-healing is one goal of the nascent field of biomimetics, where engineers mimic biology in creating synthetic materials. Bones fuse, skin scabs, blood clots, the reasoning goes. Why not I-beams, aircraft fuselages, and water pipes?

“Can we teach these kinds of tricks to synthetic materials?” asks Pradeep Rohatgi, director of UWM’s Center for Composite Materials. “In fact there is some work with polymers and we’re trying to do it with metals.”

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Significant amounts of water leak into cracked pipes on private property. Also, thousands of homes built before 1954 have foundation drains connected to the private lateral (sanitary sewer line), which sends excess water from under the home to the sanitary sewer system instead of a sump pump. ~imagery courtesy MMSD

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Cracked laterals pose a significant challenge for the sewer system.  ~images courtesy MMSD

Rohatgi makes no promises about success. And the applications for so-called autonomous materials range far beyond crafting a more resilient pipe—the military wants superior armor, doctors want biomedical implants that don’t require multiple surgeries to replace failing parts, electric companies want turbines that never have to shut down for maintenance. But UWM’s Rohatgi, whose house has been flooded five times, most recently in May, believes that self-healing sewer systems are also a worthy pursuit.

“[Ten] years ago if you had talked of self-healing polymer or metal or ceramic, people would have thought you’re out of your mind,” said Rohatgi, who is prepared for failure but unashamed to aim high. “You saw the movie Terminator? I mean that’s the ideal. You are hit by a laser, your metal armor melts, but it remembers its shape so it grows back.”

Self-Healing Strategies

Rohatgi and his colleagues outlined several self-healing strategies for composite cast metals in a recent American Foundry Society paper. One strategy is injecting hollow microtubule balloons into a material’s matrix. The balloons contain a healing agent. If a pipe made of the composite cracks, the balloons rupture, the healing agent escapes, interacts with a catalyst, and seals the crack like glue. This has been demonstrated in polymers, but metal poses a challenge.

Another self-healing strategy involves “shape memory alloys.” These are micro-wires of a special alloy embedded in the composite matrix that “remember their shape.” After a pipe made of the composite is cracked, the wires become stretched. If heat is applied, however, the wires return to their original shape, pulling the crack closed. In the presence of sufficient heat, the matrix partially melts and welds back together.

Rohatgi said another self-healing strategy is being researched by Princeton University’s Illhan Aksay where leaks are sealed by applying electric current that affects nanoparticles dispersed in the liquid inside a pipe. The nanoparticles collect in the crack and electric current triggers metal deposition.

Other self-healing strategies mimic the vascular network or platelets in blood. But it’s a new field and each of the strategies has drawbacks. Rohatgi emphasizes that there are no off-the-shelf answers. UWM is not explicitly working on self-healing sewer pipes.

“At our university we want to build a knowledge base in self-healing systems. And we’ll be very happy to make this knowledge base available to the water industry in Wisconsin, to MMSD.”

Reducing Pipe Infiltration

Pipes that seal their own leaks sound about as ambitious as the Terminator’s self-healing armor, but they could help solve a big problem already costing billions in flood damage, preventative infrastructure, and environmental harm.

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Inside a leaking lateral, as gallons of water pour in, overwhelming conveyance systems. ~photo courtesy MMSD

Water in the ground gets into leaky laterals, the pipes that connect homes and businesses to the sewer. Especially during heavy rains, the system is quickly overwhelmed, which can lead to basement backups or sewer overflows.

It’s a problem the Milwaukee Metropolitan Sewerage District is addressing through a $151 million program through 2020 to reduce “infiltration and inflow” on private property across the 28 municipalities it serves.

MMSD itself maintains 300 miles of sewers. It estimates that Milwaukee-area municipalities maintain about 3,000 miles of sewers; there are another 3,000 miles of privately-owned laterals.

“If we want to address basement backups, we need to address the private-property owners. We really can’t put in the world’s largest pipe and convey it down to MMSD. That’s not the solution,” said Bill Wehrley, city of Wauwatosa engineer, in a July 11 MMSD online video. “The solution is to keep the clear water out of the pipe—the water that doesn’t need to be treated.”

Through 2011, MMSD has allocated $9 million to reduce inflow and infiltration, providing funding that municipalities decide how to use. The city of Milwaukee is the largest recipient so far, with over $3 million allocated.

The city is targeting 562 properties in the area between N. 82nd and N. 92nd streets from W. Center to W. Burleigh streets, according to Cecilia Gilbert, Department of Public Works permits and communications manager. She said MMSD flow monitoring identified that area as having high levels of inflow and infiltration.

“The proposed work consists of sanitary lateral inspection, cured in-place lining (trenchless) of the sanitary sewer lateral, and possible foundation drain disconnections,” according to Gilbert. The program is voluntary and totally funded by the city and MMSD.

A Brief History of Our Sewers

In 1869 engineer E.S. Chesborough designed the city’s combined sewer system, which conveyed both wastewater and stormwater into Milwaukee’s rivers.

Ten years later, a commission formed to address the nuisance that the sewage-laden rivers had become. Through the late 1800s and early 1900s, city engineers built intercepting sewers to convey sewage to Jones Island and flushing tunnels that pumped lake water into the rivers to dilute them.

It’s been a century since the 1911 report that sketched out Milwaukee’s current sewer system, a vast network of intercepting sewers leading to a central treatment plant at Jones Island, whose construction began in 1919. With population growth and urbanization came the need for greater capacity, and in 1968 the South Shore Wastewater Treatment Plant in Oak Creek went online to complement Jones Island.

In 1993 MMSD completed its almost 20-mile, 405-gallon-capacity Deep Tunnel, which provides temporary storage for wastewater prior to treatment, dramatically reducing the volume of sewage dumped untreated into local waterways but not eliminating all overflows.

Storms in 2008 and 2010 led to devastating flooding throughout the area, underscoring the need for a decentralized approach to manage stormwater.

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  1. Could self-healing pipes help solve sewer problems? – Bay View Compass | Sewer Video Inspection on Mon, 1st Aug 2011 6:03 pm 

    […] Could self-healing pipes help solve sewer problems?Bay View Compass“The proposed work consists of sanitary lateral inspection, cured in-place lining (trenchless) of the sanitary sewer lateral, and possible foundation drain disconnections,” according to Gilbert. The program is voluntary and totally funded by the city … […]

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