Where The Magic Happens: Portlands wastewater treatment plant
Where The Magic Happens: Portland's wastewater treatment plant City of Portland

Everyone in City Council Chambers had themselves a nice chuckle Wednesday, when an item came up about turning the emissions from Portland's collective shit into natural gas that can fuel vehicles—"poop into power" as Commissioner Nick Fish put it.

The deal is that Portland will stop burning off more than 100 million cubic feet of biogas—mostly methane because, you know, shit—that it can't use. (Hundreds of millions more cubic feet are already used to generate electricity at the city's Columbia Boulevard Wastewater Treatment Plant, or to help make shingles at a local roofing company.)

Rather, the city will spend $9 million to build a facility that can turn the waste in to renewable natural gas (RNG), which can then be sold on the market to power vehicles that otherwise might run on high-polluting diesel.

Portland will also spend about $3 million more building a local fueling station to distribute the gas to a city fleet that currently has no vehicles that run on RNG, and to connect its methane processing facility to the gas distribution system of NW Natural.

All told, the city plans to spend about $15.5 million on the project, which it's been considering for years. But officials' estimates suggest that money could be made back fairly quickly.

"At the current market prices of RNG for the volume range, the gross revenue to BES [the Bureau of Environmental Services] would be $3 million to $10 million a year, and the payback would be less than 3 years," reads an "impact statement" submitted to council members. That estimate differed from a presentation BES gave Wednesday, which said the project would be paid off in between 4 and 8 years.

The gas the city plans to sell, of course, will still be burned in vehicle engines, and therefore still find its way into the atmosphere. But the city says it's making a big difference for fossil fuel emissions because those engines might otherwise be running on diesel fuel, a problematic pollutant.

According to figures presented to the Portland City Council on Wednesday, the natural gas Portland sells could eliminate 21,000 tons of carbon dioxide emissions per year, and supply enough gas to run 154 garbage trucks.

"Diesel fuel is particularly a problem in North and Northeast Portland in terms of particulates," Susan Anderson, director of the Bureau of Planning and Sustainability, said at a council meeting on Wednesday.

One thing that wasn't much pointed out during the presentation? Most of those emissions reductions aren't going to benefit Portland—at least in the near term.

"We do need some more activity in the Northwest with respect to CNG [compressed natural gas] fueling," BES engineer Paul Suto told council.

Not enough companies have vehicle fleets that run on natural gas in the Portland area for the majority of the RNG to be used here. Suto says the city hopes to sell "up to 30 percent" of the gas locally, when the project is completed late next year, and hopefully work toward 100 percent in coming years.

The rest will likely be sold in California (which, like Oregon, has a renewable fuels program that make it more lucrative to sell there).

"The whole point is to have the air quality benefits locally," Suto says.

There's also the matter of Portland's vehicle fleet. The city is planning to build an RNG fueling station near the wastewater treatment plant, but currently doesn't have vehicles that run on the fuel.

How the city moves its fleet toward natural gas in unclear. Suto says some of the conversion occur as vehicles are cycled out of use, but that "there are some vehicles we’ve identified we’d like to do sooner than later."

Portland officials will need to decide how much revenue from RNG sales they should use to convert vehicles to run on the fuel, Suto says. And there could be trickier questions around converting vehicles that don't belong to BES. The utility bureau faces strict limitations on how it can use ratepayer money, so officials need to figure out what, if any, revenues could be spent creating a cleaner city fleet for, say the Portland Bureau of Transportation.

"That’s where it’s been tricky," Suto says. "The attorneys need to get together and say what's in the code."