Dumping fatty food waste down the drain — not good

Fat dumped down the drain plugs up sewage pipes as well as causing flooding, corrosion, and increased operating and maintenance expenses

Every holiday season, the Oslo Water and Sewerage Works runs a campaign to reduce the amount of fat from food, cooking oil and food scraps dumped down the kitchen sink or in the toilet.

This awareness-building campaign intends to expand the knowledge around proper food disposal while exposing the vulnerabilities of our household wastewater systems.

Fat dumped down the drain plugs up sewage pipes as well as causing flooding, corrosion, and increased operating and maintenance expenses.

In Norway, almost all municipalities encounter plugged sewers as a result of fat being dumped down the kitchen sink and in the toilet.

It is both convenient and regarded as harmless to dispose of fats in this way; however, as these liquids cool, they coat the inside of the sewer pipes that over time leaves a layer of fat.

Fat is not the only culprit guilty of plugging the sewers. Food scraps such as coffee grinds, eggshells and rice along with items such as ear swabs, baby wipes, and feminine hygiene products get trapped in the fat and accelerate the blockage.

The accumulation of fat in the sewers is similar to how cholesterol builds up in our arteries. As fat builds up in the sewer, the flow of wastewater becomes restricted causing a sewer pipe to back up and overflow untreated wastewater into basements, streets, and watersheds.

Corrosion and poisonous gas

Blocked sewers are only one of many problems caused by fat.

Fat is acidic and corrodes the pipe network, in particular, pipes constructed of concrete — also the most common material for sewer pipes. Pumps needed to transport the sewerage to the treatment plant also get plugged with fat.

Fat also contributes to the formation of hydrogen sulfide, a potentially harmful gas to employees working in manholes.

How is fat removed? And how much?

To tackle the problem of blocked sewers and clogged pumps, the Water and Sewerage Works in Oslo flushes the city’s sewer pipes approximately 200 days of the year — some areas requiring multiple flushes per month.

If the problem is a clogged pump, an employee has to scrap the fat off the pump. Not a sought-after job but one that garners respect.

Up to 30 pounds can be removed from certain pumps at any one given time. An average of 140 tons of fat is removed from the sewers and pumps in Oslo each year.

The maintenance cost connected to flushing and scraping runs an annual cost of anywhere between $170,000 and $340,000.

Change in awareness, change in behavior

Restaurants are required to install fat separators under their main kitchen sink drain, sanctioned in the Pollution Control Act. This Act gives the Agency authority to regularly inspection restaurants to ensure that fat separators have been properly installed.

Private homeowners are required to accept the terms and conditions outlined by the agency. These non-negotiable terms are sanctioned in municipal bylaws governing water and wastewater services.

Yet, the agency has no jurisdiction to enter private homes to inspect whether or not fat has been dumped down the drain or flushed down the toilet. To get private homeowners to stop improperly disposing of fat, food scraps and other non-flushables, a public relations campaign aimed at creating awareness about the sensitive nature of the sewage treatment system has been initiated.

A city sewer rat has been chosen as the mascot to represent improper handling of the sewer system. Tips are also offered on how to properly treat the waste disposal system, for example, wipe your pots and pans with a paper towel and throw it in the compost instead of washing the grease off and letting it run down the drain.

While fat is in a liquid-state when warm and easily washed out of sight in soapy water, it eventually hardens and leaves layer upon layer of hardened fat inside the collection pipes.

In Oslo, there is also a municipal food scrap pickup service that turns the scraps into bio-fuel for city busses and landscape fertilizer. Recycling depots will also accept fat from private homes.

These services make it easy to adhere to the terms and conditions outlined by the Oslo Water and Sewerage Works. At 340,000 private kitchens in Oslo, there is a lot of potential fat to clog up the sewers!

Next time you find yourself in Oslo — or in front of any kitchen sink and toilet — think before you dump and flush.

Sonya Jenssen previously worked for the Union Bay Improvement District and Wedler Engineering LLP in Courtenay. She is away on assignment as a project co-ordinator for the City of Oslo at the Water and Sewerage Works.

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