Editor’s note: This story was originally published by H2O Radio and shared via AP StoryShare. Written by Jamie Sudler, Executive Producer, KGNU
We are happy to recycle our aluminum and paper with the expectation that they will be reused into something new. But the idea that our human waste we flush down the toilet will somehow be reused might make us wrinkle our noses. Not so for the people who treat sewage in Boulder City who see sewage as a valuable resource.
Boulder, Colorado. –Toilet cleaning. It’s something we all do multiple times a day. We take a shower, wash our hands, do the dishes and do the laundry. We probably don’t think much about where the water is going and what things are in it after we’re done. It is out of sight and out of mind.
But not for Dr. Sherry Cook, who studies environmental engineering at the University of Colorado, Boulder. Thinking about what is happening is her job and her passion. Dr. Cook calls herself a “wastewater person” and for people in her field, when we gush, “This is where the fun begins.”
Cook sees what we put into the sewage system as a valuable treasure that should not be wasted. She says a recent research study asked adults in the United States to draw a water treatment cycle, and many people stopped at the toilet. “We get rid of it and it’s done, and then they have no idea where it goes from there.”
After water and its content leave our homes and businesses, it used to go through a process we called “treatment.” But Dr. Cook says it’s important for people to realize that we’re not treating our wastewater, but rather managing the resources in it to our advantage.
She says the three resources that have been recovered are nutrients, energy, and of course water. There is carbon in our waste that we can convert into methane or renewable natural gas for energy. We take nitrogen and phosphorous and turn them into fertilizer. The water itself can be cleaned up and returned to the river it came from to support aquatic habitats and for us to drink and irrigate crops.
Recover resources from wastewater
How does waste water magically transform from something with a “bad factor” into a valuable commodity? To get this answer, I take a trip to what was once called a Boulder City Sewage Treatment Plant. However, to reflect the paradigm shift in the industry, its director Cole Sigmon says it is now a water resource recovery facility.
The plant is located at a lower elevation in the northeastern part of the city, which allows gravity to send waste down the hill without requiring energy to pump it. Sigmon explains that when someone in Boulder flushes a restroom, it takes about two hours for their input to get to the facility and begin their recovery journey. Upon arrival, the sewage travels down what looks like small escalators that remove toilet paper and other debris. It’s a noisy, smelly place and a bit disconcerting to look at. Once the operator found a few hundred dollar bills in untreated sewage, and even found a caiman – a baby crocodile – that was quickly turned over to wildlife officials. Toilet paper that looks like rubbish is taken to a landfill after being washed.
Then the liquid part goes to the clarifiers – round concrete pans with long rotating arms that remove grease and other substances that float to the surface. Next, the water is pumped into aeration ponds, where biology takes over the processing and removes not only organic matter but also some compounds such as nitrogen and phosphorous. Ponds are large rectangular ponds that also break down human-produced hormones that can feminize male fish in rivers.
After the aeration ponds, more solids, now called sludge, are removed into another set of circular strainers. The sludge then takes a different route from the effluent and is transported to anaerobic digesters a few hundred meters away. Sludge contains valuable nutrients, more phosphorous and nitrogen.
The effluent, without this sludge, is run through ultraviolet disinfection and returned to Boulder Creek, where it originally came from, which flows north of the facility.
The sludge, which at this point is consistent with tomato soup, is run through centrifuges to remove more water. The result is something Sigmon describes as similar to a chocolate cake mix called bio solids. These vital solids are picked up from the Boulder plant about seven trucks a week and transported to eastern Colorado, where farmers use them as fertilizer.
Energy production for garbage collection
Anaerobic digesters that produce biosolids also produce methane, and after a process carried out by the city of Boulder about a year and a half ago, the natural gas is being put into a pipeline owned by Xcel Energy.
Western Disposal Services is able to run about 65 percent of its trucks with gas produced by the Boulder sewage facility.
Not far from Western Disposal Services, which uses all of the renewable natural gas produced at a water resource recovery facility to power its garbage trucks. Of course, it is impossible to trace the minute methane particles produced by a water facility after they enter the pipeline. However, the city gets money from Western Disposal for the renewable energy the wastewater produces for the residents.
Kathy Carroll, director of communications for Western Disposal, said the company is using 60 trucks to collect garbage, recycling and composting materials all the way from Nederland in western Boulder County, east to Broomfield, and now even in parts of Jefferson County. On a tour of the facility, Carol points out a long line of about a dozen connecting stations where, what we’ve been calling garbage trucks, their tanks are filled with natural gas under the cover of solar panels. About 38 of their trucks run on renewable natural gas produced by the city’s wastewater resource recovery facility.
Western Disposal began converting its diesel to CNG fleet in 2010 and is now complete. Carroll says Western is a locally owned business, and the 160 people who work there also live in the community, raise their families and benefit from cleaner air associated with less diesel pollution. Reducing carbon emissions from switching to CNG is important to Western Disposal, and the company has a long-term contract with the city to purchase all gas produced by the sewage plant.
More possibilities to recover resources
Could there be other resources to be recovered from wastewater? There are many ideas, says the director of the water resource recovery station, Sigmon. First, the water moving through the pipes is often warm and its heat can be harnessed to run the plant. Also, Sigmon says some of the algae that grows in their refineries can be harvested for compost and, one day, surprisingly used to make shoes.
Back at the University of Colorado, Dr. Cook says he loves ideas that look at the big picture. For example, she says, “We can get more methane from human stool and reduce some of the breakdown that occurs. There is a huge benefit, right?”
Despite the challenges that lie ahead for the wastewater treatment industry from emerging pollutants such as PFAS chemicals and microplastics, Dr. Cook sees them as opportunities to find solutions that may provide unique resources to create a truly circular economy where waste is put to work rather than simply circulating around a disposal.
“It might be a little awkward to be so passionate about this waste, but I really love it,” says Cook.
This story was produced as part of a series by community radio KGNU on Zero Waste.