Small batch composters are digging deep to find big waste solutions

At Bishop O’Dowd High School in the Oakland hills, gardener Ned Lange is making small-batch vermicompost from the school’s food scraps. He takes scraps like leafy greens, peels, and stems that won’t make it into the cooked lunch, and blends them into a smoothie that he feeds into an 8-by-4-foot corrugated steel bin that is home to 100 pounds of worms.

He lifts the roof off and carefully peels back pages of damp newspaper that are beginning to disintegrate. Underneath, he digs a small trench to feed the worms, scooping up a handful of shredded coconut husk and food scrap smoothie. A cluster of worms writhes through the dirt. These reddish-pink hermaphrodites poop out a nutrient-rich compost many gardeners lovingly call “black gold.”

This artisanal waste is a favorite among small-scale community gardeners, who are part of a “community composting” network. The worm poop makes excellent “craft compost” that, much like other niche artisanal foodstuffs, is high-quality and made in small batches. The vermicompost is just one kind of the craft compost made in backyards, at schools and food banks, offering an ideal soil amendment for edible gardens. Like the compost made from scraps thrown into the green bins outside of residential units and businesses, craft compost is vital to diverting food waste from landfills, where it would otherwise produce potent greenhouse gases. “So you start to remediate soil over time, by using this compost in a garden, which is a really powerful and wonderful thing,” Lange said.

Because craft composters like Lange control what goes in the compost pile or worm bin, the resulting soil has very high levels of nutrients and organic matter. This helps restore the soil’s structure, meaning the soil can better feed the microbes living in it, which in turn improves the nutrient uptake for the plants growing in the soil. The restored soil structure also helps it sequester carbon from the atmosphere. “We can be using our soils as a battery for that storage—if we go back to compost as a way of taking care of our fertilizer needs,” said Lange.

At O’Dowd, where the vermicompost project has been running since August, the bulk of the compost stays on site, where it gets dispersed into planter beds that grow some of the food used in the school’s kitchen. Although the four-acre garden doesn’t grow enough to feed the nearly 1,400 students, it serves as a living lab where they can get hands-on experience growing food, watching the process from start to finish. As for the worms, they eat their bodyweight in food and double their population every three months. Lange says he gives them to other gardens within the Oakland Unified School District, calling them “expensive inputs for small community gardens who don’t have that kind of funding.”

“So we’re at full population right now and it allows us to pretty much grab a scoop, just give it to other people all the time,” he said.

Keeping the worms happy takes little effort on his part. Most days, he takes the food scraps and blends them using an industrial grade garbage disposal installed in an outdoor sink that sits next to the bin. He gives the worms an occasional shower, keeping the soil moist and fluffy at about 70 to 80 percent moisture content. “I joke that my worms must be the healthiest worms on the planet because they eat nothing but micro greens,” said Lange.

The black gold gradually sinks to the bottom of the container as the worms make their way through more food. Once a week, Lange moves a bar across the underside of the bin to harvest the vermicompost, which crumbles through a steel grid. Lange harvests between three and five gallons a week—the end product of putting in 500 pounds of scraps.

Although the worms digest the food quickly, they aren’t able to digest everything. Lange says he has to be cautious of acidic foods like pineapple, papaya, and other citrus fruits, which can eat the worms’ skin. He sorts those scraps out, usually tossing them into the conventional green waste bin that will be picked up by Waste Management of Alameda County, a private company that is the exclusive provider of commercial compost collection services for Oakland. Other un-compostable scraps from students’ unfinished lunch—like dairy products and meat—head out to Waste Management’s Altamont facility in Livermore.

And that’s the catch: Not all compost is created equal.

The Bay Area is actually home to two composting communities, which are intertwined but sometimes also at odds. While craft compost is made in small batches by a decentralized community that includes people like Ned Lange, almost everything else ends up at Altamont. This is the kind of composting most Oakland residents are familiar with: municipal composting. Residents put food scraps in green bins outside their homes, and the Waste Management crew collects them on trash day.

Craft composting is focused on quality, but municipal composting deals with the scale of city-wide waste. Waste Management’s site is less selective about its waste stream; here, green waste includes things like pizza boxes, chicken bones, compostable service ware, and post-consumer food lathered in oils and dressings. It creates a different kind of compost, one that is not carefully calibrated with a certain nutrient ratio, but is especially effective in diverting masses of material from the landfill.

With its industrial equipment and larger space, Waste Management is far better suited to handle the scale of the East Bay’s green waste. Its scale has a disadvantage, though: It’s much harder to control for contaminants like glass, plastics, and chemicals. Lange knows exactly what’s moving through his piles, but Waste Management has to process everything their drivers collect.

“Everything that goes in our bins winds up in their piles, and that often includes plastics. We call it ‘aspirational composting,’” says Lange—aspirational, because, using standard composting methods, it won’t really break down.

*****

The Bay Area already leads California in its sheer volume of composting, thanks, in large part, to the mandatory curbside collection of green waste that began in 2009 in San Francisco. Oakland began requiring separate compost collection in July, 2016.

In 2014, former Governor (and previously Oakland mayor) Jerry Brown signed into law Assembly Bill 1826, which implemented gradual organic waste recycling throughout California. It required businesses that generate eight cubic yards of organic waste a week to pay for the service.  That level was reduced to four cubic yards of organic waste a week in 2017, and then to four cubic yards of solid waste of any sort in 2019. The idea behind the 2019 mandate was to encourage people to sort their waste more accurately, disposing of compostable materials in green waste bins instead of just putting it all in the trash.

Municipal collection accounts for the vast majority of waste collected in the Bay Area. “Oakland residents on average divert 3,900 tons of green waste mixed with food a month, or approximately 145 tons per day,” wrote Karen Stern, director of communications for Waste Management’s Northern California chapter, by email. That green waste is sent to Altamont, where it is processed in a covered aerated static pile (CASP) composting facility, she wrote. The facility can process 500 tons per day.

This is crucial in helping California achieve the legislature’s ambitious goal of a 75 percent green waste reduction of 2014 levels by 2022. This goal was outlined in Senate Bill 1383, also signed by Brown in 2016.  Nick Lapis, the director of advocacy for the non-profit Californians Against Waste, says the idea behind this bill was to maximize the amount of compostable waste that can be removed from the landfill waste stream.

Composting methods can be a point of ideological contention, but Lapis is a pragmatist who doesn’t see municipal and community composting as an either/or decision. “I think that community composting and the urban agriculture side of things is really important to make that connection. And just as much, we need big garbage companies to do the bulk of the work,” says Lapis.

Kourtnii Brown, the founder of Common Compost, an organization that seeks to expand vermicomposting in urban settings, says that the two kinds of systems can be symbiotic. “How we’re doing it at the small scale provides a lot of lessons for municipal programs,” says Brown.

For example, she says, vermicomposting demonstrates how quickly composted food scraps can recycle nutrients to the soil and the food that grows in it. And, she continues, “We’re able to create synergies where it makes their programs more efficient and more cost effective.”

But the craft composters say that making small batches has some advantages. One of them is that you don’t have to truck the waste to a central facility—and that alone reduces greenhouse gasses. Lange thinks there’s good potential to connect high-volume food scrap producers—like restaurants—with local composters. “So you’re not shipping it as far and creating that secondary carbon,” he says.

“I think, ultimately, compost is an agricultural product,” says Lapis. “So it really makes sense for it to be produced near where the markets are. I think we need more smaller facilities, in addition to the big ones.”

Brown, who designed the worm bin at O’Dowd, stresses that creating compost in a community setting also shows people that uneaten food is a valuable resource that can be used to grow more food. For example, she says, the vermicompost bin that she built for the Sunnydale Boys and Girls Club completely transformed the facility’s community garden. Before they had the bin, Brown says, the club didn’t have a good way to dispose of food donations that were not edible, like watermelons that appeared fine on the outside, but turned out to be rotten. The club had to shoulder costly green waste fees to dispose of bad food. But once the garden had a vermicompost bin, the members were able to create a nutrient-rich fertilizer from inedible donations and other scraps. The soil “started getting much stronger,” according to Brown, and yielded better crops.

“So by just simply managing materials in a different way, we’ve been able to ignite some food security in underserved communities,” Brown says. “That was a really wonderful outcome with that program.”

Both Brown and Lange point out that it’s easier to control what goes into the compost when you’re making small batches. Even though Waste Management has strict guidelines for what is acceptable compostable waste, stray glass and plastic are often mixed in. Reducing this contamination relies, to some degree, on educating people about what can and can’t go in a green bin. But it also requires an upgrade in municipal compost facility technology. The current technology uses lasers to detect particle size, but it can’t distinguish between the fine-grain soil and crushed glass that might have also ended up in the composting. Density-measuring technology can filter out things like glass particles, but it’s a costly upgrade.

The Altamont facility is tested by the US Composting Council, which inspects the composted soil for contaminants, including E. coli and salmonella, as well as heavy metals. A report from the US Composting Council from October 10 of this year indicates that the soil was also tested for physical contaminants like film plastic, glass, metal, and sharps, and passed inspection for each. 

Still, Brown thinks inspection should be even more rigorous. “We’re really concerned about toxicity of microplastics and PFAs (per- and polyfluoroalkyl substances), which are not required to be tested at this point,” she said.

But municipal composting has its own strengths. For example, restaurants and schools, which produce a lot of food waste and rely on take-out containers, need these giant facilities with their industrial equipment to break down compostable utensils, cups and plates. That’s essential in mitigating the huge amounts of plastic that would otherwise likely end up in a landfill. Yet, even some of those materials will be screened out, because they don’t break down in the CASP facility.

And diverting waste from the landfill is essential to reducing greenhouse gases. In a landfill, waste gets piled up, creating an anaerobic environment. Without oxygen, it will break down into methane, a potent greenhouse gas. Composting significantly reduces this methane. When a compost pile is periodically turned, it introduces oxygen, creating an aerobic environment that helps the food break down into heat and carbon dioxide. Carbon dioxide is also a greenhouse gas, but it contributes less to global warming because it absorbs far less heat than methane.

This transformation takes a lot of effort and a lot of space—the kind most small organizations simply can’t afford. The piles have to be monitored for temperature, and the ones at Waste Management take about 30 days to degrade. (Lange’s piles at O’Dowd take up to seven weeks, probably because he adds sawdust to enrich the carbon ratio.) As green waste constantly rolls in, there has to be space for piles at the different stages of decomposition.

“Location is an issue, especially in places like the Bay Area,” said Lapis, where space is expensive and competitive. Moreover, composting facilities can’t set up shop in high-density urban areas, where smells and loud machinery can be a disturbance.

*****

At O2 Artisans Aggregate, Brown attends to a vermicomposting bin that’s been parked in a shaded corner between several towering open-door, warehouse-like spaces. The hum of generators and other industrial equipment punctuates the otherwise still ambience of this quiet West Oakland neighborhood. This is her “office” and demo site, where she gives the run-down on her worm bin to groups of interested composters and school-age children and teenagers. The bin at O2 is a smaller version of O’Dowd’s bin, and Brown feeds these worms, which she jokingly calls her “livestock,” with food scraps from neighbors and her own home. She’s laid out the base frame for another bin that she’s assembling for the Edible Schoolyard Project, a nonprofit that focuses on food education at schools.

“All these bins are meant to manage waste that is produced on the site. So everything that’s out in our community—it manages the waste that’s there,” says Brown.

The bin also saves gardens money. Two gallons of vermicompost goes for $80, according to Brown, and the money saved from buying fertilizer can now be used to employ students to manage the worm bin, for example. Brown said the students log how much food is funneled through the bins, monitoring what goes in and what comes out, after harvesting once a week. Students learn how food scraps are “recycled” into new produce and benefit from meaningful employment, says Brown.

Common Compost is still in its piloting phase, and has bins scattered throughout the Bay Area, mostly at schools, food banks, and community gardens. Brown hopes to scale up in the next few years, maximizing the bins indoors and outdoors that can turn food into this black gold.

For now though, it’s time to give the worms a shower. She unwinds a hose hanging nearby and fans the water stream across the bin. She next turns the water off, and gently lays down sheets of newspaper on top. Then she closes the bin, and lets the worms get to work.

This story was updated on December 8, 2019 to correct the year AB 1826 was signed.