When orange bins marked for “compost” drop-off first began proliferating on the streets of New York in February as a part of a division of sanitation pilot, many residents celebrated. I used to be certainly one of them: whilst an environmental reporter who has visited the landfill the place my trash finally ends up and is properly conscious of the issues with meals waste, the dearth of handy composting choices close to me was typically prohibitive. Having a bin inside strolling distance I might entry at any time meant all my meals waste would lastly be transformed again into soil.
Or at the least that’s what I believed it meant, till the information broke in April that the contents of these “compost” bins largely don’t go to compost websites, however to an anaerobic digester at a wastewater remedy plant known as Newtown Creek. There, the meals waste is blended into sewage earlier than being transformed partially into methane.
I wasn’t positive what to make of this, and neither had been my neighbors, on condition that methane is a potent greenhouse gasoline enjoying a task within the local weather disaster.
Questions on anaerobic digestion – touted as a inexperienced answer to meals waste – have gotten related in increasingly more locations as this technique is more and more part of natural waste administration plans throughout the US, with crops working or being constructed all over the place from Ohio to California and embraced by manufacturers comparable to Ben & Jerry’s. It’s additionally pretty widespread in components of Europe. However how do its environmental credentials stack up in opposition to composting?
The professionals and cons of anaerobic digestion
Each composting and anaerobic digestion, or AD, use microorganisms to interrupt down meals waste. Composting does so within the presence of oxygen, and creates (you guessed it) compost; AD does so with out oxygen and produces strong and liquid natural leftover matter known as digestate – and methane.
When anaerobic digestion is at its most climate-friendly, that methane is captured and used for what Dr Stephanie Lansing, a professor of environmental science and expertise on the College of Maryland, calls renewable vitality, whereas the solids left over after the AD course of are cured and was compost. From Lansing’s perspective, these choices make AD the clear winner over composting.
“Why would you not wish to get the renewable vitality first, after which get the compost later, since you nonetheless get each assets while you do digestion?” she requested.
However whether or not or not AD truly comes with these promised environmental advantages depends upon how an anaerobic digestion facility is run, which may fluctuate significantly. Although the methane might be was vitality to energy homes or waste services themselves, many nonetheless flare (burn and launch into the ambiance) a few of the methane they generate. (The plant nearest me, Newtown Creek, was flaring half of its methane up till this April.)
And even when all of the gasoline from a digester is being captured and used for vitality, not everyone seems to be comfy describing it as “renewable vitality”. In line with Darby Hoover, a senior useful resource specialist on the Nationwide Assets Protection Council (NRDC), “‘renewable’ implies a useful resource that may be replenished. And for me, it implies that it may be replenished with little ecological value. However producing rubbish just isn’t one thing we wish to be doing in any respect, in order that’s not one thing that we needs to be considering of as renewable.”
The NRDC isn’t anti-anaerobic digestion, and it “generally helps the inclusion of anaerobic digestion biogas in renewable vitality portfolios”, however in a “restricted” approach, Hoover added. A current report printed by the non-profit as a substitute advisable prioritizing surplus meals rescue, meals waste prevention and compost over sending meals waste on to anaerobic digesters.
One other suggestion the NRDC makes – that the solids left over on the finish of anaerobic digestion be was compost and added to soil – is an efficient apply, and one which AD proponents typically spotlight. However in actuality, the apply is underutilized: greater than half of all biosolids within the US are landfilled or incinerated somewhat than composted. When anaerobic digesters course of meals waste and sewage sludge on the identical time, somewhat than processing meals waste by itself, the tip consequence can comprise toxins that render the digestate unfit for including to grime that individuals are in shut contact with, ie backyard or public park soils.
“The takeaway just isn’t ‘you need to by no means do anaerobic digestion,’” mentioned Hoover. “However it’s ‘you need to actually suppose by way of lots of totally different parts earlier than you launch into utilizing anaerobic digestion for meals waste particularly.’”
The case for composting
Many individuals are aware of the essential argument for composting: it reduces meals waste and the related greenhouse gases, and leaves behind an finish product that helps wholesome soils.
However in response to Dior St Hillaire, co-director of composting non-profit BK Rot and chair of the Bronx Stable Waste Advisory Board, the advantages go a lot deeper.
Composting can create native inexperienced jobs, construct group and generate essential buy-in, so individuals are extra motivated to separate out their meals and yard waste somewhat than throwing it within the trash.
“That connection is misplaced while you’re eager about anaerobic digestion,” she mentioned. “You already see low numbers of recycling as a result of individuals are not related to it; they don’t consider it’s taking place or consider within the viability of it. So think about what [organics separation] goes to appear to be when you have got people who find themselves not related to that finish consequence. I believe you’ll discover actually low participation charges.”
Keeping nutrients cycling locally through compost rather than trucking waste off to a digester also promotes climate resilience. According to Clare Miflin, executive director of the Center for Zero Waste Design, adding compost to soil boosts the health of the trees and greenery that help cities combat dangerous heat. Plus, healthy soils amended with compost absorb up to “six times more rainwater”, protecting the city against floods.
A side-by-side comparison
When weighing the benefits of composting and anaerobic digestion, not everyone agrees on which should come out on top. The US Environmental Protection Agency (EPA) prioritizes anaerobic digestion above composting in its food recovery hierarchy; meanwhile, the NRDC places the two options on the same tier and says the best option depends on the scenario.
In New York City, anaerobic digestion looks likely to continue expanding, and financial incentives are almost certainly playing a role. Wastewater treatment plants with digesters receive a “tipping fee” from garbage collectors for accepting food waste, according to the EPA, and facilities that scrub their methane to pipeline quality can sell it as “renewable fuel”, at which point they’re “guaranteed a nice rate by federal law”, said Lansing.
Hoover, of the NRDC, doesn’t think that AD being part of a city’s mix of waste management strategies is necessarily a bad thing. It just means cities and their citizens need to weigh the specifics of any proposed composting or anaerobic digestion system, and demand that it’s held to the highest standards.
Along the way, city agencies need to be transparent if they want citizens to actively participate in the waste sorting necessary to make any of these solutions work. Slapping “compost” on the side of a street corner bin might convince citizens to dump their banana peels there, but if people find out later that those bins don’t actually go to compost, it could break trust and lead to composting being regarded with the suspicion currently reserved for recycling.
“We don’t want to keep sending more messages that it’s OK to say we’re doing one thing, and we’re actually doing another,” said St Hillaire.
Luckily, there are a few things everyone seems to agree on. First, certain kinds of waste are better handled by one system or the other: anaerobic digestion can accept dairy, meat and grease that compost sites can’t, while compost is better able to break down paper goods. And even more important, both options offer significant climate benefits. According to a report from the National Renewable Energy Lab, anaerobic digestion and composting have comparable emissions footprints when the AD digestate is applied to soil rather than landfilled.
From the perspective of many environmental advocates, the best solution will involve some mix of the two solutions, blending the efficiency and financial incentives of AD with the community and ecosystem benefits of composting.
“It’s not that AD trumps all or compost trumps all,” said St Hillaire. “New York City is a big city with a very dense population, we need as many [solutions] as potential.”
In different phrases, each anaerobic digestion and composting are much better choices than landfilling, so hold separating out your organics somewhat than throwing them within the trash. I do know I’ll.