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Composting is a key weapon against climate change

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This summer’s excessive temperatures and rampant fires in Europe and Canada have (how many reminders and examples do us humans need?) again highlighted that climate change is no longer a theory about the future. But is here. Right now. We are now living within the predicted climate emergency.

While reductions in carbon CO2 emissions are currently prioritised in the climate emergency fight, increasing attention is now focussed on methane CH4. While carbon is at the base of the CO2e emission index, methane — although remaining in the atmosphere for a relatively shorter 12 years than CO2 — has 22 times the negative impact on our climate.

What is CO2e?

Ecometrica describes CO2e, or carbon dioxide equivalents, as a measure for describing different greenhouse gases in a common unit indexed against carbon dioxide (CO2). The key greenhouse gases — methane, carbon dioxide, nitrous oxide — all have differing global warming impacts. Methane, depending on the data source used, has an impact 20-25 times greater than carbon dioxide.

Using CO2e as the measurement unit:

  • 1kg of CO2 has a CO2e of 1kg
  • 1kg of methane has a CO2e of 25kg.

Major sources of methane

Most methane emissions derive from natural sources such as wetlands, peat bogs, and swamps: basically anaerobic — without air — natural environments containing decomposing organic matter.

Man made — or anthropogenic — sources include global warming induced melting permafrost; waste and landfills; petrochemical extraction and processing; coal mining; burning of fuels (including transportation); sewage treatment and production; farming especially of cattle and dairy; and other industrial processes.

Methane emissions account for 30% of global warming.

Food waste is a major source of these emissions. If the emissions from food waste were measured as a country, it would be the third largest emitter in the world (after the USA and China). John Doerr, in his book Speed & Scale, states that 33% of the world’s food is wasted each year generating 2 gigatons of CO2e emissions.

Unlike a belching smoke stack, methane is invisible. The importance of measuring, and therefore managing methane emissions, has necessitated the development of methane sensing satellites. The Canadian company GHGSat currently has six satellites in orbit with another four set to launch in 2023.

In 2004 satellites identified a major methane leak at a natural gas storage facility in Southern California. By the time the leak was capped over 97,100 metric tonnes of methane had been leaked into the atmosphere.

Landfills are also a significant sources of methane emissions. In August 2021 a GHGSat satellite identified that a landfill near Madrid was emitting over 8 tonnes/hour of methane.

“Cutting methane is the strongest lever we have to slow climate change over the next 25 years and complements necessary efforts to reduce carbon dioxide. The benefits to society, economies, and the environment are numerous and far outweigh the cost.” Inger Andersen, Executive Director of UNEP

Methane emissions from landfills are primarily due to the anaerobic breakdown of organic matter. Organics would include garden waste, paper and board, wood, and food waste. In a landfill anaerobic micro-organisms decompose organic material producing methane in the process (over 50% of landfill gas, or LFG, is methane).

While the food and agriculture industries play a significant role in generating organic waste, a very large volume is from individuals dumping food and garden waste. A study done by the CSIR for the Ekurhuleni Municipality measured that more than 60% of household waste sent to a landfill is organic.

So how do we fix — at speed and scale — the methane problem? And, what are the conditions for a solution to be quickly implemented at scale?

For any solution to be quickly scalable it needs to be:

  1. Fast to implement and thus not require extensive refitting or the building of additional infrastructure.
  2. Easy to implement with low training and compliance requirements.
  3. Zero or relatively low cost.

Basically: “fast, easy, cheap”.

Composting Scalability

Of all the organic waste diversion technologies available, the only one that meets all these criteria is compost. Composting is a natural aerobic process — "with oxygen" and thus no methane emissions — where micro and macro-organisms decompose organic matter producing a beneficial soil amendment.

In Scotland, the legal definition of compost is:

“the autothermic [i.e. self-heating] and thermophilic [i.e. 40-80°C] biological decomposition and stabilisation of biodegradable waste under controlled aerobic conditions that result in a stable sanitised material that can be applied to land for the benefit of agriculture, horticulture or ecological improvement”.

The following table illustrates the scalability of broad categories of composting technologies and methods:

Home composting

Home composting is one of the easiest things anyone can do. At its most basic it is just an aerobic pile of garden waste which will gradually becomes compost (we can call this “klomposting”). At a more sophisticated level, compost can be made using food waste with a bokashi system and a segmented compost-bin system. Of course vermicomposting can also be used in combination, or alone, within a household composting operation.

With the right incentives and education millions of households across South Africa could be doing some form of composting where they live. Starting tomorrow!

What would the impact of this activity be?

One million households composting 10kg of organic waste per month would reduce CO2e emissions by more than 82 thousand metric tonnes each year.

Industrial Windrow Composting

Setting up an industrial windrow system has major upfront costs. These relate to obtaining and preparing a site, compliance and certification, and equipment purchase/rental. However, once these costs have been invested, composting organic waste can be very cost effective and profitable. Additional income can be earned by charging a dumping fee to businesses and individuals for disposing their green waste.

The big advantage of windrow composting is that once the site has been setup, processing of organic waste can be scaled very quickly (the only restriction being the size of the site).

In-vessel Composting

An in-vessel composter is an enclosed system which automates the processing and conversion of organic waste to compost. These are usually smaller systems which can be installed in a waste area. Similar to the scalability of home composting, in-vessel composters can be easily installed at a large number of sites very quickly and require little investment in infrastructure.

The disadvantage is that, given their sophisticated nature, an in-vessel composter can initially be expensive on a cost/tonne basis.

However as these units are designed to process food waste, this cost is easily off-set by the rising cost — and high carbon footprint — of regularly moving putrescible organic waste to a landfill.

Within these three broad categories are a variety of composting options and technologies. For instance, home composters can purchase a pre-fabricated compost bin to contain and accelerate their composting (at one time the City of Cape Town was giving away these bins to interested home-owners).

The Environmental Benefits of Compost

While recycling organic waste into compost has significant greenhouse gas emission reduction benefits, compost has other important soil, diversity and carbon sequestration benefits. Sally Brown writing in Biocyle reports that 1 tonne of compost added to soil will sequester between 100 and 1,000kg of CO2e emissions (the variation is due to application methods and existing soil conditions).

Compost also delivers other ecological benefits which include boosting soil health, encouraging plant growth (which also then absorbs more carbon than less healthy plants), reducing fertiliser use and thus positively impacting on nitrous oxide emissions, and supporting biodiversity.

Lastly, diverting organic waste from landfill has an externality benefit of R111.00 per tonne.

Recycling Is The Last Resort

Reducing waste has to be the first priority of any emission saving programme. Food production has a massive environmental impact. The following table illustrates the GHG emissions per KG of food type produced.

Objectively, vegetarians do have the lowest carbon impact!

If individuals are going to reduce their carbon footprint they have to reduce waste (and change their consumption choices). This lesson is not only applicable to food, but to every commodity. The reality is that very little is recycled; the recycling rate of plastic, as an example, is generally less than 10% (the other 90% ends up in a landfill and in one of our rivers).

The City of Cape Town, of all South African municipalities are taking steps to reduce organic waste going to landfill. First, they have significantly increased the cost of landfilling. In the period 2017/18 to 2021/22 gate fees for general waste have increased by 53%

Secondly, the City of Cape Town have issued a notice to all organic waste generators to submit an integrated waste management plan (IWM) to the City for review and consideration.

Thirdly, as mentioned they are encouraging home composting.

Earth Probiotic Scalable On-site Composting Solutions

For the last 12 years Earth Probiotic has been developing and manufacturing, in South Africa, solutions for the on-site treatment of food waste.

Why on-site?

On-site solutions reduce waste removal costs, externalities, and thus have a positive impact on reducing carbon emissions. Managing waste on-site mitigates risk and can help protect a business against labour and logistic disruptions. Moving less waste to a landfill mitigates against the rising waste management costs. Waste management inflation is driven by increasing costs of landfilling, rising fuel prices, the weakening Rand, and disruptions in global logistic chains driving up the age of the waste removal vehicle fleet (which then leads to higher emissions per KM travelled).

Earth Bokashi Food Waste Recycling

“Bokashi” is a generic Japanese word for “fermented organic matter” and is both a food waste recycling method as well as a product. Earth Probiotic sells “bokashi” under its “Earth Bokashi” brand. Earth Bokashi utilises organic waste materials including wood shavings, spent coffee grounds, and Earth Probiotic’s proprietary indigenous microbe mix.

The Earth Bokashi system utilises anaerobic bins which, with the Earth Bokashi inoculant, ferments food waste so that I doesn’t rot or smell. The fermented contents of the Earth Bokashi bin can then be safely composted with other organic material, fed to composting worms, or simply trenched under soil.

Earth Cycler In-vessel Composting Machine

First launched in 2017, the Earth Cycler is an automated IoT connected in-vessel composter. Now with three variants, the Earth Cycler can process, dending on the version, 5,000kg, 10,000kg and 15,000kg of food waste per month. Both solutions require the addition of compostable packaging, contaminated paper, egg cartons, and other low value high carbon material.

The Earth Cycler has three key advantages:

  1. minimum energy use and can be powered by solar,
  2. output is less than 1/3 of the waste input and thus reduces logistic costs if the output needs to be moved, and
  3. the Cycler weighs and reports on input and outputs and thus provides a real time view of waste volumes and the carbon impact of diverting that waste from landfill.

Life & Earth Industrial In-vessel Composting Machine

The IVC can process up to 60,000kg of food waste a month (including the carbon input). Similarly to the Earth Cycler the IVC reports on input weights and thus can be connected to online reporting dashboards.

This is the only on-site solution in South Africa which can process this volume of food waste.


Reducing greenhouse gas emissions requires quick, and significant, wins. Composting food waste can quickly scale and must be a tool within the climate change strategist’s tool box.

Not only is composting easy and cheap to do, it also drives significant other ecological and financial benefits.

But, while we trumpet the benefits of composting, we also need to drive a food waste reduction programme. Reducing food waste has major environmental and financial benefits.

Composting is there to beneficiate what’s left.

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