Clean Your Pipes With Ice

Ice pigging offers an efficient, cost-effective and powerful approach to cleaning force mains

Clean Your Pipes With Ice

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Since it was first deployed in the U.S. seven years ago, ice pigging has proven to be a powerful, sustainable and increasingly popular cleaning method for wastewater force mains and siphons, as well as potable water distribution mains.

The accumulation of sediment fats, oils, greases and debris in wastewater collections systems clogs force mains and siphons, causing pipeline restrictions that increase energy use, lower pump efficiency and lead to sanitary sewer overflows. They can also lead to capital expenditures for increased pumping capacity or force main replacement.

Cleaning approaches like hard pigs and soft swabs present a risk because they can get stuck in the force main, requiring emergency excavation. Excavating to retrieve a hard pig is costly and time-consuming at best, and in some locations such as highways, river crossings and developed areas, it is simply not an option. In cases where redundant systems do not exist, installing temporary bypass systems presents a significant expense.

Other methods such as flushing and waterjetting can be inefficient and at times ineffective. In addition, these processes use a great deal of water, which may not be readily available.

Ice pigging addresses all of these issues.

Glacial action

Developed in the U.K., ice pigging involves pumping a slurry of ice into a main through an existing fitting, using pressure to push the ice pig downstream and discharging the dirty ice and waste material into a gravity sewer or receiving treatment works.

A semisolid material, the ice slurry can be pumped like a liquid, but it behaves like a solid once the pig is formed in the main. As the pig passes through the pipe, it acts like a glacier by scrubbing the pipe and entraining accumulated deposits as it moves downstream, incorporating sediment and biofilm into the ice instead of “bulldozing” it. Unlike traditional hard pigs, an ice pig is not so abrasive that it risks damaging the pipe.

Ice slurry filling 20% to 30% of a pipe’s volume cleans with shear forces up to 1,000 times greater than water alone. This provides more effective cleaning while using significantly less water than traditional flushing methods. In fact, ice pigging uses approximately 50% less water than standard flushing. It also takes significantly less time: Typically, the section of main being cleaned is out of service for no more than 30 to 60 minutes.

Suitable for all pipe materials, ice pigging offers several other benefits. Because the slurry is pumped into the main, specialized launch and retrieval stations are not required as with mechanical pigging or swabbing. Moreover, customer service isolation is not usually needed, and sewer lines can be quickly and easily put back into service after cleaning.

Perhaps most important, since the pig is an ice slurry and not a solid object, it cannot become stuck in the pipe like traditional mechanical pigs or soft swabs. Instead, an ice pig can negotiate pipe bends, partially closed gate valves and in-line butterfly valves without affecting the cleaning process. The ice pig is not affected by changes in the pipe diameter, and any ice that remains behind simply melts.

Simple steps

The first step in using ice pigging to clean sewer force mains is isolating the force main in question. Wet well levels are managed to prepare for interruption. The lift pump is turned off, and the required amount of ice is pumped into the main via a pump bypass or air release valve.

The ice is then pushed along the pipe using a wet well pump or external water supply if the well pump is insufficient. The pig flows through the pipe, cleaning it as it passes through.

The final step is to discharge the dirty ice and waste material. At the collection outlet, the dirty ice and waste material are discharged into a gravity sewer or the receiving treatment plant. The dirty ice can also be collected with a vacuum truck.

The force main is then returned to normal operational service.

Sonoma Water

Based in Santa Rosa, California, Sonoma Water serves communities in the Sonoma area, a world-famous wine growing region and tourist destination.

The agency manages and maintains a water transmission system that delivers naturally filtered water from the Russian River to nine cities and special districts that, in turn, deliver drinking water to more than 600,000 residents of Sonoma and Marin counties. This water system includes 90 miles of underground aqueduct pipes, as well as storage tanks that convey and store approximately 130 million gallons of water for the agency’s clients. In addition, Sonoma Water operates the wastewater collections system for many of the smaller communities in the county.

In 2018, the agency was experiencing a drop-off in pump efficiency in one of its sewer collections systems and force mains. The agency deduced that there was blockage in a force main that’s under pressure from a lift station where wastewater is collected to the treatment plant in Petaluma.

“While we typically don’t have blockages in our force mains due to the lines being under pressure, we recognize that biofilm accumulates on the inside of the lines and thickens over time,” says David Royall, environmental services coordinator for Sonoma Water.

This situation became exacerbated during extreme wet-weather events when the system became susceptible to inflow and infiltration through joints and manholes in the gravity sections of the sewer system. In those instances, the pumps needed to push more water down the line than they were meant to handle. As a result, there were numerous SSOs upstream of the lift station.

After determining that a restriction existed, Sonoma Water decided to move forward with cleaning the line to see if that would solve the problem. An initial strategy involved putting breaches in the force main to provide access points that would allow for manual cleaning of the line. However, it quickly became apparent that this system was going to be problematic and very expensive. Sonoma Water would have to acquire easements in some locations to gain access to its pipeline. Additionally, it would have to factor in excavation costs and the expense of putting valves into each section of the pipe.

“This method was going to be very costly; there had to be another way. I did an internet search to discover other ways to clean sewer force mains without intruding into the pipe itself,” Royall says. “I came across ice pigging from SUEZ Advanced Solutions and, from there, contacted the company. SUEZ’s water system consultant Daniel Eisenberg called me back, and the rest is history.

“Ice pigging was the most unobtrusive means of cleaning these lines that I could find,” Royall adds. “All we had to do was install a 2-inch fitting so the ice pigging truck could tie directly into it. Then the truck pumped the slurry directly into our force main. We didn’t have to cut any pipes or dig anything up — you’re just inserting the ice mixture into your system. Once you empty the truck, you turn the pumps on, and the pumps force the pig down the line. It’s the most efficient and effective means of cleaning a force main that I could find. I must admit, it almost seemed too good to be true: How can something so simple be so effective?”

The effectiveness of the ice pigging solution became evident when one of Sonoma Water’s engineers revisited the efficiency of the pumps. The agency reported an increase in pump efficiency of 12% on the northern section and 15% on the southern section.

In addition, in spite of having an extremely wet winter, Sonoma Water experienced virtually no overflows, avoiding fines and eliminating the time and expense needed to send notices out to customers.

The cost savings over excavation and its related requirements was a big benefit. Sonoma Water estimates that the cost of the ice pigging operation was only 10% of the alternative.


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