A Breakdown of the Breakdown: What’s happening in your compost?

Compost is usually considered the smelly mound of waste scraps at the end of your garden, but there is much more occurring within that mound of scraps than meets the naked eye. This article will explore what the fundamental processes of compost are, why it is increasingly sought after in the horticultural and agricultural world, and how it could help heal our environment from the growing damage caused by climate change.

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Compost is the result of the process ‘composting’, which is essentially a way to rapidly decrease the time taken for organic materials to decay into a nutrient-rich substance that increases the productivity of soil. This makes compost very beneficial to gardeners and farmers for a variety of reasons. The way in which compost is made requires:

• Organic material, which consists of pretty much everything except meat/fish/eggs (though egg shells are fine), large quantities of fats/oils, coal/charcoal ash, and non-herbivorous excrement);
• Warmth;
• Moisture;
• Well-oxygenated environments;
• The mesophilic (grows best at 20^oC-45 ^oC) and thermophilic (grows best at 41^oC-122 ^oC) microorganisms that drive the composting process.

When all of these variables are available, the composting process can begin. 80-90% of the organisms involved in the composting process are aerobic bacteria, and are the most important as they consume the organic waste and excrete fertilising elements such as nitrogen, phosphorus, magnesium. The other 10-20% of microorganisms involved are anaerobic bacteria. The anaerobes can produce toxic waste which emits a foul odour, due to them releasing hydrogen sulphides. Invertebrates are also involved in the composting process. The biological processes that cause the rapid breakdown of organic materials can be divided into three stages:

1. The first stage of composting is usually only a couple of days long. This is where mesophilic microorganisms begin to physically breakdown the organic matter. This results in the compost reaching approx. 40^oC.
2. The second stage of composting can last between a few days and several months. The mesophilic microorganisms are replaced by thermophilic microorganisms, which further breakdown organic matter into smaller pieces due to the increase of temperature (65^oC), thus being able to break down more complex compounds like proteins, fats and complex carbohydrates.
3. The third and final stage of composting lasts for several months. The thermophilic microorganisms use up all of the available compounds, so the temperature drops and the mesophilic microorganisms can once again recolonise the compost and finish the degradation process, leaving behind a nutrient rich ‘humus’.

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Despite the vast knowledge surrounding composting and its benefits, there are still 6.7 tonnes of household food waste going to landfill each year in Britain alone. The issue with this is healthy compost requires a well-oxygenated environment to prevent the build-up of toxic waste from anaerobic bacteria, but landfill is not well oxygenated. This means that lots of anaerobic breakdown occurs, releasing a large amount of greenhouse gases into the atmosphere. One of those major gases is methane, which is 25-30x more potent than CO₂. This is a major issue, as 1-4% of the total greenhouse gas emissions can be attributed to organic waste in landfills. This is an easily preventable addition to the source of climate change.

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Learning to compost saves organic waste from being exported to landfill sites. If everybody composted their food scraps, this could drastically reduce the associated emissions contributing to global warming by encouraging aerobic breakdown of waste. As well as reducing emissions the production and application of compost can also increase soil health. Soil carbon depletion due to climate change is an issue of growing concern; the growth in extreme weather conditions (such as floods, storms and droughts) tends to cause rapid soil erosion, leading to intense depletion of soil nutrients. Consistent composting can restore the lost nutrients, and increase soil health. This is particularly important for farmers, who need healthy soil for successful crop yields.

Hyperlink list:

• What materials can be composted: https://www.gardenorganic.org.uk/what-can-i-compost
• The stages of compost breakdown: https://www.livescience.com/63559-composting.html
• Landfill and organic food waste: https://innovate-eco.com/what-happens-to-food-waste-in-landfills-the-full-environmental-impact/
• Soil health in agriculture: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2610104/