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Tacoma wants to turn your poop into renewable fuel. Really.

Operations supervisor Mike Patrick stands among the anaerobic digesters at the central wastewater treatment plant in Tacoma, Wash., on Thursday, Dec. 14, 2017. The anaerobic digesters produce methane gas which is moved via the orange lines to a holding tank and then used to heat buildings and water throughout the plant. Excess methane is burned off. The treatment plant wants to use the excess methane to produce renewable natural gas for use as transportation fuel.
Operations supervisor Mike Patrick stands among the anaerobic digesters at the central wastewater treatment plant in Tacoma, Wash., on Thursday, Dec. 14, 2017. The anaerobic digesters produce methane gas which is moved via the orange lines to a holding tank and then used to heat buildings and water throughout the plant. Excess methane is burned off. The treatment plant wants to use the excess methane to produce renewable natural gas for use as transportation fuel. joshua.bessex@gateline.com

The city of Tacoma wants to turn your poop into fuel.

Let that sink in. In a few years, the stuff you flush could be used as green fuel, potentially powering vehicles around the country.

The city’s Environmental Services Department also is hoping to make a little money from the endeavor.

The project they’ve proposed would convert methane, a byproduct of the solid waste that’s processed at the city’s wastewater treatment plant on the Tideflats, into renewable natural gas. The gas would be pumped into Puget Sound Energy’s pipeline and transported and sold. The end product would be used in transportation, meaning that the bio-fuel created could offset the use of diesel or natural gas.

The city would make money from the sale of the gas and renewable-energy “currency,” a type of credit offered by the U.S. Environmental Protection Agency to agencies that use bio-fuel to offset fossil fuels that otherwise would be in the pipeline.

“You’re creating this ability to offset more non-environmentally friendly fuels by creating this,” Environmental Services director Mike Slevin said recently. “We can produce a good environmental outcome. And having worked in this industry for a long time, this is one of the rare opportunities where you can do something really good for the environment, and not only save money, but make some money doing it, so it’s a very unusual opportunity.”

Best-case scenario: The currency from the EPA Renewable Fuel Standard program stays in place and keeps its value, and the project breaks even and maybe even makes money. City officials estimate that a combination of grants, revenue from the sale of the gas and renewable energy currency would allow the project to make about $730,000 in its first year.

Even if the EPA “currency” goes away or loses value, the city estimates the project would break even over its lifetime because it still would make money on the sale of the gas.

Puget Sound Energy spokesman Grant Ringel said the the utility is finalizing an agreement with Tacoma that would allow the city to connect to the PSE pipeline.

“We’re very involved in that renewable project. We’ve been working with the city for a good while and are very supportive of it,” Ringel said. “We’re actually looking at a number of possibilities in the future to provide different renewable gas options for our customers, so down the road it might open some possibilities for that.”

Where is the gas coming from?

Slevin described the wastewater treatment facility as a giant digestive system.

“Our wastewater treatment plant produces methane,” Slevin told the City Council during a recent study session. “It’s the mechanical gut. Everyone in this room, you take in nutrients and you produce methane, and our plant just does it on a much larger basis.”

Some of that methane is being used to help heat the treatment plant’s boilers. The rest is burned off.

Slevin said the project would “displace carbon that’s affecting our climate” with a natural byproduct and would mark an 80-percent reduction in the amount of methane that has to be flared.

The city estimates that converting the methane that the plant flares off each day would yield enough renewable natural gas to equal nearly 450 gallons of diesel per day. In a year, they estimate it could reduce greenhouse gas emissions by 788 tons, and would displace 325,000 gallons of diesel over the course of a year.

Because the end product would be a bio-fuel, retrofitting the plant wouldn’t be subject to the city’s interim land-use regulations for the Tideflats, which prohibit new fossil-fuel businesses from opening shop for at least the next year.

Jim Parvey, the city’s chief sustainability officer, said the project has been in the works since about 2002. Over that time, technology has improved greatly, making the project more viable.

Other places already are using similar technologies to harness the power of human poo.

King County is doing it. Methane produced at its wastewater treatment plants is used to produce bio-gas that’s scrubbed of carbon dioxide and then sold to local utilities.

In Oakland, California, the East Bay Municipal Utility District uses bio-gas created by waste, sewage and food scraps to power the wastewater treatment plant and sells the excess renewable energy back to the electric grid. The city of Phoenix also turns waste into bio-gas and sells it as green energy.

So what’s the downside?

The upfront costs are a major drawback. It’s estimated to cost $8 million to design and build a facility to convert methane into renewable natural gas. Those costs include building a connection to Puget Sound Energy’s pipeline and to upgrade lighting at the wastewater treatment plant to LED technology.

Tacoma officials said they hope money from the renewable-energy currency would help pay for the cost of the project and help offset the need for rate increases in the future. Staff estimate the gas would fetch about $3 per gallon.

It’s an exciting prospect for the folks at Environmental Services, who in interviews repeatedly said their goal is to make the city as green as possible. If it’s approved by the City Council, the city is hoping to break ground on the project in 2018. If that happens, it could be making gas in fall 2019.

“This has been the best project I’ve had a chance to work on,” Parvey said.

Candice Ruud: 253-597-8441, @candiceruud

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