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Unraveling solutions to overwhelmed sewer systems

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photo of clogged pump
A common sight for wastewater operators, a pump clogged with garbage.

By Peter Davey

 

If people got a good sniff of a ragged wastewater pump and had to untangle a snarled mess of entwined fabric, pumping stations might get a break from the onslaught of “flushable” wipes and products clogging their systems.

Yet, there is not much preventing people from using the toilet as a waste disposal unit. While some personal hygiene companies have started to change their marketing and product instructions, there is no definition of what is “flushable.”

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“You can write flushable on anything,” said Robert Haller, executive director of the Canadian Water and Wastewater Association (CWWA). “Anything that disappears when you pull the handle can be called flushable.”

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The Association of the Nonwoven Fabrics Industry defines a flushable product as one that will pass through toilets and drainage pipes without adversely impacting plumbing or wastewater infrastructure and operations.

According to Joe Gemin, an engineer with AECOM, the problem is that once these fabrics are in the sewerage system, or worse, spun inside a pump, they intertwine to form a rope-like mass. This can result in a stalled pump or a sewage backup.

The CWWA has been working for some time, trying to push through regulations governing the labeling and disposal of wipes. However, the demand for these products is huge and growing. It is estimated that sales of disposable wipes is growing at 5% a year in North America and will reach $2.5 billion in 2016.
Haller estimates that municipalities in Canada face $250 million in costs related to removing garbage from sewerage systems, adding that this estimate is “on the low end.”

Making matters worse, consumer habits and efficient fixtures have reduced water consumption. This means that wastewater volume is becoming smaller, while the solids content is remaining the same or increasing.
Sometimes weekly unclogging of pumps, screens and private drains is now just part of the job for operators and treatment plants.

“Everyone is impacted by this, even if they don’t know it,” said Barry Orr, spokesperson for the Municipal Enforcement Sewer Use Group (MESUG). “If beaches were covered with wipes and feminine hygiene products, there would be an outcry.”

Municipalities have a tougher time rousing public awareness and action, compared to other growing concerns such as micro plastics or medicines. At a recent community event discussing micro plastics in the Great Lakes, some 100 people filled the presentation room in Toronto and spoke loudly about protecting waterways.

photo of clogged pump
A common sight for wastewater operators, a pump clogged with garbage.

“Unplugging a pump or grinder doesn’t carry the same weight as environmental concerns over personal care products (cleansers using micro plastics) or medicine,” said Haller. Indeed an image of a seabird, its stomach full of plastic drew an emotional response from the crowd in Toronto. An intertwined pile of pump debris may not do the same.

Fabric manufacturers have published a guidance document for flushable wipes and a proposed ISO committee has been launched to provide a definition on what is “flushable” and/or “dispersible.”
On the treatment side, wastewater equipment manufacturers have introduced new technologies to move wastewater without clogging pumps.

According to KSB Pumps, there are two basic methods to transport wastewater containing solids. One way is to use pumps with a large enough free passage, so that the solids will not clog up the pump. Another is to keep the solids away from the pump or to reduce the size of the solids.

This summer, KSB celebrated 25 years working in Canada with a media open house. During the event KSB introduced the AmaDS3 (dry solids separation) system to overcome clogged sewage pumps. Interestingly, the system was described to the event attendees as a “reverse toilet,” emulating the main entrance point for the problem it aims to address.

Raw wastewater first flows into a separator where a grate separates solids from liquids. The solids-free wastewater then runs into a collecting tank where it remains until a pre-set water level is reached. When the system is activated, the collecting tank is pumped out to the discharge pipe, carrying away the solids contained by the grate. Once the minimum water level in the collecting tank is reached, the pump set is stopped. At this point the inflow check valve opens again automatically, allowing the next flow of wastewater to enter the system.

According to KSB, the system is well suited for remote mountain communities that use a lot of lift stations to transport a small amount of sewage. As the pumps in the AmaDS3 system are isolated from solids carried in wastewater, they can use higher efficiency impellers and enjoy a longer service life with less maintenance.
The system is being used in Europe, in such countries as Germany, Slovenia, Poland, Italy and Denmark. It is ideal for any pumping station struggling with garbage and debris.

Peter Davey is the assistant editor of Environmental Science & Engineering. This article appeared in ES&E’s November/December 2014 issue.

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