Ask Lookout: When I scrape my plate into my new food scraps bin, where does it go?

Heavy machinery at the city of Santa Cruz's food waste pre-processing station
Heavy machinery linked by chutes, hoppers, pipes and tubes comprise the city of Santa Cruz’s food waste pre-processing station. Guadalupe Sanchez, the superintendent at the Dimeo Lane Resource Recovery Facility, said the apparatus cost the city about $2 million to construct.
(Kevin Painchaud / Lookout Santa Cruz)

Follow the pathway of 40 tons of meat and vegetable pieces, pits, bones and coffee grounds per week — and learn the anti-warming science behind the City of Santa Cruz’s new food scraps collection program.

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If you live in the city of Santa Cruz, you’ve probably noticed (or begun using yourself) the small brown bins that have started dotting residential sidewalks this year.

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Labeled “Food Scraps Only,” these bins are part of the City of Santa Cruz’s response to Senate Bill 1383, a state bill passed in 2016 which requires that California municipalities divert 75% of their organic waste from landfills by 2025, compared to baseline levels in 2014. The problem in the law’s sights: As organic waste decomposes in landfill conditions, it emits large amounts of methane — a greenhouse gas which, according to a 2021 report authored by the Climate and Clean Air Coalition and United Nations Environment Programme, has been “second only to carbon dioxide in driving climate change during the industrial era.”

Santa Cruz’s plan to meet SB 1383’s requirements has been a long time in the making. The citywide debut of the program — which began in August — comes on the heels of a “successful pilot program” in the Seabright neighborhood that began in late 2020. And the city has been collecting food waste from restaurants, grocery stores and breweries since 2018. Even before that, said Santa Cruz resource recovery operations manager Bob Nelson, the city has long talked about doing something with its food waste, like composting it — which is what the unincorporated areas of Santa Cruz County do. But that solution comes with its own problems, Nelson said.

“Composting facilities are really just as complicated to site as a landfill,” Nelson said. “There’s just so much regulation. So most of the options are, ‘drive it to San Jose,’ ‘drive it to Marina.’ They just weren’t great options for us.”

So if they’re not composted, what happens to your food scraps on trash day? No, they’re not turned into pig slop (at least, not in the way you might expect), nor do they become Soylent Green. The short answer is that the scraps are macerated, dehydrated and turned into a variety of useful products — including animal feed, but also biodiesel and cleaning products. But the long answer is far more interesting. Come with us as we dive into the world of food scrap recovery — one where science and engineering meet the nuts and bolts of environmental policymaking.

Movers and shakers

At the crack of dawn on any given morning except Sunday, two city truck crews rip around Santa Cruz. Their task: collect as much as four tons of food scraps, between the both of them, by hand, from houses and apartments on their designated trash day by 11 a.m.

Lookout reached out to leaders at the city of Santa Cruz, Watsonville and GreenWaste Recovery, which services the rest...

Once they complete their route, the crews begin their trek north along Highway 1 to the city’s Resource Recovery Facility at Dimeo Lane, opposite Three Mile Beach. Down a narrow road flanked by small patches of farmland, the trucks make an immediate right-hand turn after passing the facility’s gatehouse. There, out in the open, is the city’s labyrinthine food scrap pre-processing station — a cityscape of heavy machinery linked by chutes, hoppers, pipes and tubes.

A Santa Cruz resident's food scrap collection bin.
(Thomas Sawano / Lookout Santa Cruz)

The job of the pre-processing station is to break apart whole food scraps — meat and vegetable pieces, pits, coffee grounds — into a mash-like slurry, which can later be refined into usable products. First, workers back their trucks onto a sloped unloading platform with a large steel hopper at the end, into which they empty the day’s food scraps at a controlled pace. The workers take extra safety precautions while doing this: at the bottom of the hopper are a set of heavy augers (essentially big drill bits), which both move the food scraps toward the next stage of processing and break down the largest pieces. The workers operating the preprocessing station are not allowed to be on the platform while the trucks unload their food scraps, and one worker is always poised at an emergency stop button, in case anything goes wrong.

John Lippi, a senior resource recovery worker.
(Kevin Painchaud / Lookout Santa Cruz)

“There’s a whole lot of room for bad things to happen,” said senior resource recovery worker John Lippi, who is one of two workers currently assigned to the food scraps pre-processing station.

The initial set of augers carry the food scraps up a gradual slope and feed them into a shredder, which macerates the food scraps with spinning blades and empties them into another hopper. At this point, the food scraps resemble a grayish mash, punctuated by recognizable vegetable chunks, citrus rinds and the occasional piece of plastic. Another auger at the bottom of the hopper moves the shredded scraps into a large press, which further breaks down the material and releases much of the liquid and plastic contaminants in it.

The pressed material, collected into large steel dumpsters, is surprisingly inoffensive to the nose, both smelling and looking somewhat like olive tapenade.

Finally, the contents of the dumpsters are emptied into a large steel drum, which vibrates batches of mash at high speeds to release still more moisture. Pre-processing is complete. The finished slurry — and really, that’s what it is — is fed into large, 22-ton plastic containers, where it awaits pickup every 10 to 14 days by Sustainable Organic Solutions (SOS), a company which uses large centrifuges in Santa Clara to separate the slurry into a peat-like mash (turned into animal feed pellets); fat, oil and grease (turned into biodiesel); and a water and acetic acid solution.

All told, Lippi estimated that the whole system processes as much as 40 tons of food waste per week — with room for more as the program expands, said Guadalupe Sanchez, the superintendent of the Dimeo Lane facility.

Guadalupe "Lupe" Sanchez, superintendent at the Dimeo Lane Resource Recovery Facility.
(Kevin Painchaud / Lookout Santa Cruz)

“We’re still expanding,” Sanchez said. “Not all businesses have signed up. I’m gonna say we have less than 25% of businesses signed up. That’s a lot. We’ll probably have another 20 tons or so coming in per week.”

City waste reduction manager Leslie O’Malley estimates that 85% of households in Santa Cruz are complying with the food scraps program. This puts the city on track to reach the state’s goal of diverting 75% of food waste from landfills by 2025, she said.

Scrap science

But you might still be asking: How does it all really work? And how does diverting food scraps from landfills help the environment?

First, a lesson in biochemistry. Bacteria that decompose organic matter fall into two categories: aerobic and anaerobic. Aerobic (literally, “with air”) bacteria decompose organic material in environments with lots of oxygen and, like human beings, breathe out carbon dioxide — a carbon atom bonded to two oxygen atoms. Aerobic bacteria are the invisible workers behind outdoor composting: When a backyard composter turns their pile with a shovel, they are really giving the aerobic bacteria decomposing their food scraps a breath of fresh air.

Anaerobic (“without air”) bacteria, on the other hand, decompose biological material in environments without oxygen — like at the bottom of landfill trash heaps. In the absence of oxygen, anaerobic bacteria produce methane — a carbon atom bonded to four hydrogen atoms — instead of carbon dioxide.

As Elliott Campbell, a UC Santa Cruz environmental studies professor who specializes in agroecology, explains, aerobic bacteria fit into a neat, natural cycle that nets no additional carbon dioxide into the atmosphere. The amount of carbon dioxide aerobic bacteria release is commensurate with the amount of carbon dioxide plants breathe in when they photosynthesize.

“CO2 is taken out of the atmosphere — it’s used to make your peanut butter sandwich — and then the bacteria eat the peanut butter sandwich scraps and CO2 goes back into the atmosphere,” Campbell said. “So that’s a nice loop that works really well in nature and doesn’t alter the climate.”

But when anaerobic bacteria are the ones eating the proverbial peanut butter sandwich — when the peanut butter ends up in the landfill — atmospheric carbon dioxide is effectively turned into methane. And here’s the rub: pound for pound, Campbell said methane has “20 or more times the warming capability” that carbon dioxide does. When carbon enters the system as carbon dioxide but leaves as methane, it breaks nature’s delicate equilibrium — carbon dioxide in, carbon dioxide out — producing a net warming effect.

That’s the point of SB 1383: to stop the release of methane into the atmosphere. And since the warming effect of atmospheric methane is so large, that opens the door to numerous strategies — including the one the City of Santa Cruz is pursuing.

“The good news is that methane emissions from landfills are so large, that lots of different options for managing food scraps are beneficial,” Campbell said. “You can look at what Santa Cruz is doing, and then look across the state to see what other communities are doing. And there’s really a lot of variation.”

What’s next?

In the future, the city likely won’t be shipping its processed food waste to Santa Clara. Doing so is costly, said resource recovery operations manager Nelson, and defeats some of the greenhouse gas-mitigating purpose of the program — what with the need to truck the waste over the hill.

Santa Cruz waste reduction manager Leslie O'Malley.
(Thomas Sawano / Lookout Santa Cruz)

Instead, Nelson said the city plans to start feeding processed food scraps into anaerobic digesters at the city’s wastewater treatment facility. There, anaerobic bacteria break the scrap slurry down and release methane, which is in turn burned to power the facility. Since all this would take place in a sealed environment, little to no methane would be released into the atmosphere before being burned.

“The ultimate goal has always been to add [the food scraps] to the wastewater treatment digesters, because then it’s kind of a closed system,” Nelson said. “We’re actually producing stuff that the city facilities can use. So it’s fairly cost effective for the ratepayer.”

“And then, of course, if for some reason there’s a glitch in the system at wastewater, we can always take [the food scraps] to Santa Clara, at any time, and they can still use it.”

Nelson estimates that full-scale deployment of the program is about three months out, pending adjustments to the city’s existing anaerobic digester system.

But the benefits of the food scraps program extend beyond the complicated apparatus Santa Cruz has built to process food scraps. City waste reduction manager O’Malley pointed toward parts of SB 1383 that encourage municipalities to reduce food waste at the source — rather than dealing with the scraps after they’re tossed out.

“The social media post I really like are when people say, ‘You know, the best thing about this program for me, is it shows me how much food I’m wasting,’” O’Malley said. “The reality is, people overpurchase, they let food go bad, they overserve on the plate. We very purposefully called it a food scrap program, because we want people to be making the connection that their goal should be having as little in here as possible.”

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