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Noble Rot: Denver's Composting Moves Forward

The anaerobic digester near LaSalle is one of the world's largest.

Denver's curbside program delivered more than 3,000 tons to Rattler Ridge in 2015.

About 7,000 homes in Denver currently have green carts.

A worm composting program from Denver Public Works and Denver Urban Gardens.

Denver's curbside compost collection program is expanding from four routes to seven in 2016, but only a fraction of residents' organic waste is currently composted.
A massive industrial digester is turning food waste into marketable methane and compost on the plains about 30 miles northeast of downtown Denver.

"It's North America's largest anaerobic digester," says Bob Yost, VP and chief technical officer at A1 Organics. The Eaton-based company procures organic matter as the input for the EDF Renewable Energy-owned facility.

Yost says the plant is designed to produce 4,700 dekatherms a day. That's roughly enough gas to heat 12,000 homes.

The 10.2-million-gallon unit has been fully operational since September 2015, providing gas for the Sacramento Municipal Utility District on a 20-year contract. The waste it's fed is all food scraps from commercial clients -- processors and the like -- but it's not designed to handle grass clippings and plant material.

Founded in 1974, A1 recycles 100,000 tons of organic waste annually, and Yost says the company could easily double that number with its current facilities. An assist from Denver residents wouldn't hurt.

For all of 2015, the City and County of Denver's curbside compost collection program contributed 3,250 tons of food scraps and green matter to A1's 430-acre Rattler Ridge facility in Keenesburg in 2015, up 73 percent from 1,950 tons in 2014. Christmas trees are also delivered here as part of the city's annual Treecycle program to be mulched, as A1 took in a total of 2,645 cubic yards of leaves and limbs in 2015.

Baby steps

While the trendline is heading in the right direction, A1 still takes in only a tiny fraction of Denver's organic waste.

Denver's curbside program delivered more than 3,000 tons to Rattler Ridge in 2015."Our waste analysis shows that about 50 percent of what is thrown out is compostable," says Charlotte Pitt, operations manager for Denver Public Works' Solid Waste Division. Participants in the city's curbside compost program who also recycle typically throw out "a small amount of plastic film waste, and maybe a little bit of styrofoam."

In 2008 Denver launched its curbside compost collection program with one route and capacity for about 2,500 homes. Budget cutbacks almost immediately pushed it onto the chopping block, but participants saved it in 2010. "They didn't want to see it go away and they were willing to pay for it," says Pitt. As a result, a $107 annual fee covers the costs of curbside collection.

With a $2 million loan from the Denver Department of Environmental Health, Public Works expanded the program to four routes in 2013. The program currently has about 7,000 participating households out of about 60,000 that are eligible, meaning the adoption rate is around 12 percent. (That number is markedly lower than the recycling program's 75 percent participation rate.) After three more routes come online in 2016, capacity will approach 10 percent of the city's total solid waste customer base of 174,000 homes.

While residents not on the route map can drop off compost at a facility at Cherry Creek Drive South and Quebec Street, only a tiny percentage of Denver's compostable waste ultimately ends up at A1.

And the city's residential recycling and composting programs combine to divert only 16 percent of the city's waste stream from the landfill, reported the Denver Post, and most of that can be attributed to recycling. San Francisco diverts 80 percent. The national average is 35 percent.

Sure, the statistics are sobering. The flip side: There's plenty of room for growth.

"If it was a perfect world and everybody composted and recycled, we could probably keep 75 percent of waste out of landfills," Pitt says. "We'd be able to start taking trash trucks off the street. We'll convert them into composting trucks."

A closed-loop yard

A worm composting program from Denver Public Works and Denver Urban Gardens.Beyond the curbside collection program, Denver also promotes backyard composting. Public Works has teamed with Denver Urban Gardens to offer an educational program to train master composters for more than 20 years. Pitt describes it as a "train-the-trainer program" with 30 workshops and as many as 1,000 participants a year.

The rationale? "If we can keep it out of our waste stream, that's a positive for the city," says Pitt.

Plenty of cities and states have mandates to reduce landfill shipments, and composting is an obvious starting point. About a third of waste at landfills nationwide is food waste, and roughly 70 percent of it is organic.

"All of that waste produces methane at the landfill, which is 23 times more potent of a greenhouse gas than carbon dioxide," says Yost. And even though it produces methane, composting is a carbon sink, he adds. "It absorbs way more carbon than it creates" -- and you have the compost replacing less environmentally friendly fertilizers.

The big picture: Some reports say universal composting and recycling could significantly cut greenhouse gas emissions, as landfills are the top source of anthropogenic methane in the U.S.

All things considered, composting represents an unbelievable amount of low-hanging fruit in terms of greenhouse gas reduction.

"It's huge," says Pitt. "If you look at the total cost of composting versus transportation or LEED, it's relatively inexpensive for the impact. Dollar by dollar for reducing greenhouse gases, it's by far the cheapest option." But to fulfill its potential, she adds, it requires buy-in on a mass scale.

After starting in commercial composting in 2009, Denver-based Waste Farmers sold its routes to Alpine Waste & Recycling in 2011 and started bagging its own brands of soil products for hobbyists and professionals. Sales grew by a dizzying 80 percent in 2015.

Now that he's out of the compost-collection business, Waste Farmers CEO John-Paul Maxfield says commercial growth has outpaced residential composting locally for several reasons. "Part of the challenge is that it's really cheap to throw stuff away," he says. Denver also earns royalties from city-owned landfills, he adds, providing a "disincentive" to diversion.

To foster participation in the curbside program, the city "needs to do a better job of letting people know they can compost," Maxfield adds. Another piece of compost-collection advice: "Subcontract it out to a private company. That'd be a much more efficient way to do it."

Back at A1's Rattler Ridge compound, the biggest issue is what's going into in the compost bins. "It's commingled material," says Yost. "It's supposed to be food scraps and green waste."

"The biggest challenge is the quality of the material we get," he continues. "People throw glass in there -- glass is just killing us. If I could do one thing, I'd go door to door and get people to quit throwing trash in their compost."

Editor's note: I'm an avid backyard composter. I haven't participated in the city's master composter training, but I did win the blue ribbon for best compost at the 2015 Denver County Fair, after a second-place finish the year before. My latest challenge: keeping puppy Aoife out of the compost. The ravenous lurcher is dead set on eating rotten vegetables.

Read more articles by Eric Peterson.

Eric is a Denver-based tech writer and guidebook wiz. Contact him here.
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