14th May 2022
Every time we finish a meal, and throw food scraps away in the trash, we’re contributing to a massive global problem.
Over one-third of our human food waste is trashed – and the emissions that waste produces are helping to kill our planet.
However, a new study just published in Nature has revealed a hidden hero in the fight against climate change – composting.
The researchers found that this simple act can help to significantly reduce our carbon footprint – helping to reduce the impact of our discarded food on global warming.
The scale of the food waste problem
While hunger still stalks the poorer parts of the world, globally a huge proportion of our food is wasted.
This food enters the waste stream – and over half goes to landfill, while another 12% is disposed of through controlled burning.
In the United States alone, between 73 and 152 million metric tons of emissions are released because of food waste.
To put that into perspective, that means that each person in the U.S. contributes to between 223 and 468 kilograms of these emissions every year!
Food is lost throughout its life cycle – during farming, transport and consumption. However, food waste in landfills is a particular problem.
That’s because food waste contains high levels of carbon, nutrients and moisture – making it a methane powerhouse capable of producing more emissions than any other organic source.
In fact, our landfills are the third largest source of methane emissions in the US alone, largely down to the breakdown of organic material in an airless environment – a process known as anaerobic decomposition.
The power of composting
The study set out to assess the potential of composting to help tackle the problem.
To do this, the scientists continuously monitored emissions in commercial composting facilities
They found that composting could be a game changer – producing much lower quantities of emission than food breakdown in landfills.
In total, the study found that composting organic material instead of sending it to landfills could lower methane emissions by 38–84%, depending on the efficiency of the process.
The benefit of composting isn’t just limited to emissions.
The scientists suggested that further benefits could be gained by using compost for agriculture.
This would then replace inorganic fertilizers and fertilizers which release high levels of emissions. At the same time, the use of compost could help lock carbon in the soil.
Optimizing composting for the environment
The study also find that optimizing the composting process could further increase the benefit to the environment.
Regular turning further reduced the quantity of emissions, with methane emissions dropping after the compost had been turned.
The researchers also found a link between moisture levels and emissions.
Methane emissions spiked after large amounts of water was added, which Dr Perez, one of the researchers involved in the study, told us was probably because it caused anaerobic conditions.
Reducing the amount of water added, especially during the middle and at the end of the composting process, could further reduce harm to the environment.
What can you do at home?
Dr Perez emphasized that people should minimize food waste before composting – following the U.S. EPA food recovery hierarchy.
However, he advised that when you do compost, it’s important to aim for plenty of oxygen in the compost and the correct moisture levels:
…in general a good recommendation for any type of composting process is to maximize aerobic conditions.
This can be done by regular turning to improve aeration with a frequency that does not decrease the temperature needed to reach a successful composting process.
Water additions should be made when necessary to achieve 60% ideal value, maybe continuously monitoring moisture in the pile to better assess water addition needs.
While Dr Perez noted that he didn’t have experience in the in-vessel composting technique, there are many ways to aerate the compost, and they don’t all require turning.
Moisture can be monitored either with the hand squeeze method or with easily available technology such as the Monty Monitor.
Compost, and compost well!
It’s clear that composting isn’t just good for our land and our garden – it’s also good for the environment.
We can all do our bit too, whether by advocating for composting programs in our state or country, joining a community composting program, or starting our own compost pile at home.
If you do compost at home, it’s also worth taking the time to do it right – ensuring the compost is aerated and avoiding overwatering it.
Full Q&A With The Researchers
Why do you think there was a variation in the amount of emissions produced via composting?
The variations in the magnitude of greenhouse gas emissions during the composting process were related to moisture, oxygen and temperature conditions in the compost pile.
Because these conditions differ across commonly used composting processes (e.g., in-vessel, windrow, and forced aerated static piles), we can expect that the greenhouse gas emissions will be different across them.
In our case, we worked with a typical commercial-scale aerobic composting windrow pile which was turned weekly, and water was added prior to turning when needed (total of 6 water additions). The composting process was effective as it followed the facility protocol for compost production (it was an 11-week process).
The properties of the obtained compost in this experiment were comparable to the ones produced by other commercial-scale aerobic composting windrow piles that were treated similarly.
Why do you think reducing moisture levels reduced emissions? Is it a case that current commercial composting operations use too much moisture leading to anaerobic conditions, or is there another reason?
Current commercial composting operations aim for the desired moisture content of about 60%.
What we found is that after large water addition events methane (CH4) emissions were larger. It is likely that less moisture will reduce the probability of forming anaerobic conditions for the microorganisms that make CH4, a potent greenhouse gas.
Also, when the compost is cooling down, reducing watering events could minimize the persistence of these anaerobic conditions, which would reduce nutrient losses and nitrous oxide (N2O) emission potential (which is about 300 more effective as a greenhouse gas when compared to CO2).
Can you explain further how replacing other fertilizers with compost can also help decrease emissions?
This was not assessed in our paper; however, Dr. Whendee Silver’s previous work has demonstrated that adding compost to rangeland could increase carbon storage in soils.
How important overall do you think it is that composting is implemented across the world in tackling climate change?
We estimated that changing the fate of food waste from landfilling to composting, based on this study, would reduce greenhouse gas emissions by 38 to 84%.
More research is needed to determine how this would scale globally. However, these results are promising.
What advice do you have for people who compost at home in order to minimize emissions from composting?
Although we have never worked on in-vessel composting before, in general a good recommendation for any type of composting process is to maximize aerobic conditions.
This can be done by regular turning to improve aeration with a frequency that does not decrease the temperature needed to reach a successful composting process. Water additions should be made when necessary to achieve 60% ideal value, maybe continuously monitoring moisture in the pile to better assess water addition needs.
What other steps can people take to reduce harm to the environment from food waste?
In general, we recommend that people follow the U.S. EPA food recovery hierarchy which emphasizes, in order of relevance, three main actions: prevention (source reduction), diversion (alternative management such as composting, anaerobic digestion among others), and as last resource disposal (landfilling and incineration).
Pérez, T., Vergara, S. E., & Silver, W. L. (2023). Assessing the climate change mitigation potential from food waste composting. Scientific Reports, 13, Article 7608.