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The sewage-to-energy exchange building, in foreground with angled white roof, and the CSU Spur and National Western Center buildings it serves just to the north, in April, 2022. (Photo by Matthew Staver for Colorado State University)

As long as humans are around, there’s vast renewable energy to be had from the results of their daily living. 

The National Western Center and Colorado State University’s growing Denver Spur campus are now heated every day by energy that experts in renewables were tired of seeing literally flushed down the drain. In a squeaky-clean building in the shadow of Interstate 70, energy is pulled from one of Denver’s main sewage lines and transferred to clean water pipes shooting out to buildings on the National Western Center campus next door.

It’s the largest sewage heat recovery system in North America, online since April, and an offshoot of the 72-inch sewage main provides 90% of the energy needed to heat and cool local buildings. In winter, the 65- to 70-degree sewage heats water in the exchanger. In summer, the sewage flow cools the exchange water well below ambient air temperature on a 95-degree downtown day. 

Sewage-loaded institutions from Canadian cities to Las Vegas hotels are studying the project for lessons as the budding renewable technology takes hold among carbon-conscious customers. 

The interior of a wastewater heat recovery system, the Central Utility Plant, is seen on Dec. 12, 2022, at the National Western Center in Denver. Heat is transferred from used sewer water by a plate and frame heat exchanger within the plant. Distribution pipes create a heat exchange to loop around nearby buildings, usually between 51 and 77 degrees Fahrenheit, creating a low-carbon campus. (Olivia Sun, The Colorado Sun via Report for America)

The attraction for CSU was clear, Spur campus Associate Vice Chancellor Jocelyn Hittle said, as the university builds up a complex researching everything from clean water sources, to veterinary medicine, to vertical horticulture. 

“It’s in our ethos to think about sustainability, to think about the long term, and we know that a low-carbon option here was important,” Hittle said. Overall, the building energy costs are a few percent higher than simply connecting to the existing grid, Hittle said, but CSU “is going to be here for a long time. So the benefits accrue, when you think about sustainability and climate over that period.”

Making the sewage-to-heat system even more obvious was the fact it was basically an in-house project. Jim McQuarrie was the director of technology and innovation for Metro Water Recovery, the region’s largest sewer utility, when he pitched the idea to one of his former graduate school engineering advisers at CSU. 

Ambient loop pumps are seen in the Central Utility Plant on Dec. 12, 2022, at the National Western Center in Denver. Heat is transferred from used sewer water by a plate and frame heat exchanger within the plant. Distribution pipes create a heat exchange to loop around nearby buildings, usually between 51 and 77 degrees Fahrenheit, creating a low-carbon campus. (Olivia Sun, The Colorado Sun via Report for America)

Metro Water Recovery wants to off-load heat from sewage before it gets to the treatment plants along the South Platte River, and is then discharged into the stream. Warmer water hurts fish and other wildlife. 

Denver has billion-dollar redevelopment plans for the National Western site, traditional home to the January stock show and other events. The area’s sewer main was above ground on the site, which helped Metro Water Recovery lose heat but blocked ideal site development. 

A closed-loop energy system at National Western Center and the Colorado State University Spur campus takes energy from sewage pipes and transfers it to clean water pipes circulating through local buildings. The design also helps Metro Water Recovery keep effluent cooler before it’s treated and discharged into the South Platte River drainage that can be damaged by hot temperatures. (National Western Center illustration)

The planning coalition that developed around the idea agreed to put the big sewage pipes underground, and run an offshoot pipe to the new exchange building. The gleaming pipes throughout are labeled “sewer” or “ambient water.” Incoming sewage is first screened for large objects, then ground inside the pipes to a slurry that will maintain its flow. 

As in all cities, wastewater temperatures are boosted by hot shower or kitchen drains over 100 degrees and dishwashers that hit 140 degrees. 

In the exchange chamber, the sewage pipes flow next to clean water pipes, which are then pumped to circulate through CSU’s Spur buildings a block away, and the growing complex of National Western Center renovations. Heat pumps in each building add or subtract a few degrees from the piped clean water to create the right indoor temperatures. Then the clean water circles back to the exchange building for another run. 

And the sewage keeps on coming. After leaving the exchange, the sewage flows back into the mains headed over to Metro Water Recovery, having lost energy but gained a purpose. 

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Every two hours, the sewage flow in the pipes is reversed to clean out silt and sand deposits, said Bryan Scott, chief operator on site for CenTrio, which financed, built and manages the exchange complex for Denver and National Western Center. The exchange equipment is built by SHARC, a British Columbia energy firm. 

Developers in Boulder are working on a small system for an apartment complex, as is a slopeside condo at Snowmass Village, among others, CenTrio noted. The U.S. Department of Energy has estimated the energy from all the nation’s sewage could heat 30 million homes if recaptured. 

“Anyone looking to utilize the free energy just going down the drain,” Scott said. 

Besides getting a reliable and low-carbon form of energy, CSU wants its energy and engineering students to continue involvement in the project as part of their education, Hittle said. 

“That’s another opportunity for us from a project of this scale,” Hittle said. “We’re learning as we go.” 

Michael Booth

Michael Booth is a Colorado Sun reporter covering health, health policy and the environment. Email: booth@coloradosun.com Twitter: @MBoothDenver