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A Brief History of Wastewater Treatment in the City of Coeur d’Alene

| October 18, 2020 1:10 AM

As a community grows, so too does the need to treat the bi-products of living close to one another. One of those biproducts, wastewater, can be devastating to the community if not treated. Outbreaks of diseases such as cholera drove many of the developments of sewage collection and treatment in the mid-19th and early 20th centuries.

In our community, the first sewage collection pipes were installed in 1906. This original system consisted of 8 miles of various size vitrified clay piping. At this time, there was no treatment of the sewage. The system was installed to convey the city’s sewage to the Spokane River.

By the late 1930s the city’s population was between 9,000 and 10,000 people and the city was looking to expand it’s collection system further. By this time, centralized treatment of wastewater was beginning to be seen as appropriate for protection of the population.

On Aug. 1, 1939, the “sewage disposal plant” was completed, built in the same location as the original outfall pipe. This spot had the advantage of not only existing infrastructure but was at a very low elevation and most future collection pipes would flow here without the aid of pumps.

This original plant included multiple processes including both primary and secondary levels of treatment. Secondary treatment was still quite new and wouldn’t become a standard method of treatment for decades to come. Included with these two main methods of treatment were several “side stream” treatment processes that we’re still using today including grit separation and sludge digestion. There was even beneficial re-use of the digested and dried solids on local crops.

Although much has been added since the first sewer system was installed more than 100 years ago, the basic concept remains the same. We continue to utilize gravity rather than pumps to convey the wastewater through the community. Our system has grown from 8 miles of pipe to more than 220 miles!

Our “sewage disposal plant” is now a “Water Resource Recovery Facility” but it still uses primary clarifiers (the original one plus two more) for settling out the solid matter in wastewater and trickling filters for biological, secondary treatment.

In 2009, the Wastewater Department began a trial of several methods to further treat the wastewater, targeting phosphorous and ammonia nitrogen. Membrane technology came out as the clear winner and since 2018, all of the wastewater has received a third (tertiary) level of treatment where it is passed through “ultra-filtration” membranes. This treatment removes 99% of the phosphorous, 90% of the ammonia (99.9% in the summer), and virtually 100% of the suspended solids from the wastewater before disinfection and discharge into the Spokane River. The ammonia is removed through a biological process that is more efficient as the temperature rises in the summer. This is the reason for the variance from summer to winter performance.

The end result of this treatment is treated water that is cleaner than the river it is discharged into.

What can you do to help protect our environment? Flush wisely! Only the 3 Ps should go in the toilet: pee, poop, and toilet paper. Wipes, garbage, single-use plastics, prescriptions, and chemicals all have an appropriate disposal method that does not involve a toilet.

For more information, visit the Coeur d’Alene Wastewater website, https://cdaid.org/wastewater.

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Mike Anderson is the Superintendent of the City of Coeur d’Alene Waste Water Utility Department. This article is one of a series presented by the Our Gem Coeur d’Alene Lake Collaborative; a team of professionals working to protect our local water resources. Participating entities include University of Idaho Community Water Resource Center, Coeur d’Alene Tribe Lake Management Department, Idaho Department of Environmental Quality, Kootenai Environmental Alliance, the CDA Chamber of Commerce, and CDA 2030. Other articles in this series are available at www.uidaho.edu/ourgem.