Composting and climate

I like to tell people that composting, but more specifically community composting is the best climate action you can take. How can that be when composting is only listed at no. 67 on Project Drawdown’s list of most impactful solutions that we have to mitigating climate change? There are two main reasons: 

• Project Drawdown has assessed industrial composting, not community composting 
• Project Drawdown necessarily measures direct impacts, not harder to quantify indirect impacts 

But how is community composting more efficient than industrial composting? There’s a LOT to be said on this topic but I’ll try to get it down to a few pertinent points. First off, we need to acknowledge that backyard composting is known to be ineffective at best and sometimes downright climate damaging. This is a sensitive point as many gardeners are very fond of their compost heaps and feel like they’re ‘doing the right thing’ for the environment. But just as ‘oils aint oils’ not all composting is equal. Depending on how closely you manage the dynamic, ever changing status of your compost heap will determine how good of an end product you achieve, how quickly, and how much of the carbon is lost to the atmosphere as climate damaging gases. 

Then there’s that word ‘industrial’. Industrial (composting) implies high efficiency, a situation where engineers have carefully measured and designed and set up machines to manage the composting process for the best outcomes while minimising issues. And here’s where I’m going to step on some more toes but engineers may not be the best equipped to manage a biological process. Don’t get me wrong, the fact that we have some wonderful machines that have been developed to compost or process different types of organic wastes on large scales by seasoned practitioners and very clever people is great. But to the engineers I would say two words: APPROPRIATE SCALING 

I get this a lot actually, and yes it does occur in instances of mansplaining but people who are otherwise favourable of our operation like to advise me that we should ‘get a machine to do the turning’. We turn all of our compost by hand. In 2020 we composted over 12 tonnes of food waste, with greater volumes of autumn leaves and other feedstock materials mixed in. That’s a lot of heavy lifting. I think I’m getting away from the main point of this article (climate benefits of community composting) and I could write a whole other article about the health and social benefits of active jobs for uni students to break up their screen time… 

But manual labour vs. machinery is also a climate issue. When a process is appropriately scaled and costed to involve manual labour (with fair pay) it ends up being far superior in climate benefit via the avoidance of steel and other materials and all of the embodied emissions that they carry with them. 

What the heck do I mean by appropriately scaled? Composting is a funny thing, and it pays to think of not just the biological processes but also the chemical and physical. I’ve previously mentioned that our composting is more efficient than backyard, single household composting because we consolidate the food scraps. If you manage it correctly you can make your own backyard heap a little more efficient by consolidating scraps over the course of a week instead of adding them slowly each day. When it comes to industrial/commercial composting this consolidation of scraps occurs with LARGE volumes of food waste. But that brings its own problems. It’s the reason that the township of Tarago has previously had problems with the nearby facility that ships in food waste from all over Western Sydney. Understanding the source of these problems (notably odour) also highlights that composting is anything but ‘simply putting food waste in a pile’. Over the past two years of running Capital Scraps I’ve come across a worrying number of people who think that this is what composting is!! 

If you put food waste into a pile the high water and nitrogen content leads to a process of putrefaction, not composting. Putrefaction is defined by the Oxford Dictionary as ‘the process of decay or rotting in a body or other organic matter.’ Composting is different. Again, I could write a whole separate article on this but suffice to say, if you leave food waste in a pile, of any size, for long enough (depends on the size of the pile) it will create its own anerobic situation leading to the generation of methane, ammonia and other volatile chemicals (including many stinky ones). If your compost smells, it is guaranteed to be emitting methane also. Methane is a greenhouse gas that is 25-32 times more potent at warming our atmosphere than carbon dioxide. ‘Landfill gas’ is mostly methane. The mission of Capital Scraps is to eliminate the production of landfill gas from Canberra’s food waste and we manage our composters accordingly.  

THIS is what we mean by appropriate scale: we collect up small amounts (1-7 kg per household) of kitchen scraps from the local area (ideally low to medium density housing) for efficient composting (hot composting with injections of 40-80 kg of scraps per instance) that is well managed (scheduled feeding and turning of heaps to maximise the healthy community of aerobic organisms that transform the scraps into plant feeding humic acids and other useful molecules). And we do it all on an electric bike! This is how we are able to process scraps from around 80 households or more in a 3m long wooden composter that can live directly in the suburb where the waste is generated. We don’t have to stick it in a container on a train to process it outside of town and we don’t have to build a stainless steel drum to keep odours trapped within either. We just need to tend our heaps with a little manual labour to keep them healthy and productive and climate beneficial to boot. 

It’s about shifting the populations of microbes within the composter back to aerobic conditions while also keeping them well fed. This ever-changing situation within the composter happens on the micro scale, and it’s not homogenous. Consider that our composters produce more odours in summer. This is a problem caused by the heap drying out. How does that make sense? If you know composting you’ll know that too much water in the compost heap leads to an anaerobic state that (depending on C:N ratio) can lead to odour. But a dry heap is more heterogenous and has the issue of impeded water movement which leads to wet little anerobic pockets surrounded by dry matter. This is just one of the problems that can be solved by getting stuck in with a pitchfork, at the same time shifting the overall population back to the climate friendly aerobic state. 

Developing a machine that could do the fine-grained work of a pair of human hands and pitchfork to achieve a similar quality of outcomes would be impressive but a financial folly. 

In summary: composting with careful management on the community scale is the best option to directly eliminate methane emissions from household kitchen scraps as it is timely (no big piles of food waste waiting to be processed) and appropriately scaled. 

And as far as the indirect benefits go:  

• Raising awareness around food waste as a climate issue (no. 1 on Project Drawdown! avoidance is key) 
• Green jobs for youth 
• Getting carbon back into our soils (literally drawing down carbon) 
• Healthier community gardens or compost supplied to other local greening projects 
• Low bar of entry to climate conversations, absolutely anyone can get involved: contribute (scraps/service fees/donations), volunteer, gainful employment, attend fun and social working bees 
• Educational benefits; carbon cycle, soil health, microbiology, biochemistry, circular economy 

All of these benefits are worth pursuing, and the direct benefits are fantastic but can they be quantified? At Capital Scraps we’ve been lucky enough to have a few other people (besides myself as founder) want to support our aims as a way of ‘offsetting’ their climate footprint. Currently, the National Emissions Reduction Fund can pay you for the climate benefits of using compost as long as you can prove that the carbon % of your soil (on acreage) is stably increased over a long period (many years). That’s clearly not something that many people can get involved with (you need a farm as a first step) but is there a way to at least quantify the DIRECT reductions in emissions that we are affecting by diverting scraps from landfill? 

As outlined above, compost isn’t simply compost when it comes to which gases are being emitted. It all comes down to how you manage it. So, I was thrilled today to have a conversation with a random stranger who said he might be able to help measure methane emissions from our heaps. We have a solid hypothesis and can predict which parts of our process are emitting some methane and associated gases (including smelly ones, so it’s easy to tell when you get it wrong!). We are also assured that our process is extremely well managed to minimise these emissions. But in order to translate this activity into a real price on carbon it would be great to get some data. So, to the lovely couple who stopped to chat at our public composter in Ainslie today, thank you! And if you happen to read this on our website soon, know that I am very enthusiastic to get some data if you are able to borrow the right meter for the job.