Climate solution: Biochar

Is Biochar closer than we think?

I have found a news item about biochar titled Dead Plants are Powering Stockholm. Here’s a key passage:

Stockholm currently has five biochar production facilities working exclusively with green waste gathered within the city. Last year, they predicted that by 2020 it will produce at least 8,000 tons of char per year. That production output will be enough heat to warm 500 homes year round, which may not sound like much until you consider that in doing so they will have also sequestered the amount of carbon equivalent to removing 4,200 cars from the road.

Do read the whole news item. It is an eye-opening introduction to the potential of biochar in municipalities. Stored well in soil, the carbon would not return to air for thousands of years.

The quantities involved are way ahead of what I thought was achievable right now: most unexpected and most welcome. It calls some priorities into question. Are we looking at the best local climate actions?

Biochar is solid carbon, but most climate impacts are measured in terms of carbon dioxide gas (CO2). Stockholm’s 8,000 tonnes of biochar are equivalent to 29,300 tonnes of CO2. Reading’s population size is only 17% of Stockholm’s, so our biochar equivalent might be slightly less than 5,000 tonnes of CO2.

Compare this 5,000 with the 1,200 tonnes of emission reductions from the entire fleet of solar panels in Reading in 2018. We’d need to more than quadruple our solar panels to match biochar Stockholm-style.

Those extra panels would cost about £24 million to install (using an optimistic price of £5000 per UK average domestic solar installation; it was £6800 in Jan 2019). Stockholm invested $11 million = £8.5 million in the biochar facilities. Scaling this pessimistically down to Reading, our biochar production should need £2-3 million, which is within the reach of a community benefit business model.

  • Stockholm says it was fortunate to already have a sophisticated green waste collection infrastructure; we have one too.
  • Stockholm had to create markets for the biochar; we would too. The types of demand would be similar.
  • For the rest we can learn from Stockholm’s experience.

Demands for biochar

Making biochar for the sake of it is not enough to engage anyone except climate activists. (Imagine the reaction: “What?! You want me to BURY fuel?”). There have to be economic or social reasons too. Here are four:

Renewable bioenergy

Biochar production gives off excess heat. Stockholm uses it in a district heating system. It qualifies as bioenergy from a renewable resource. If used as such, further emissions reductions would be added to the calculations above and government subsidies may be available.

In general, any predictably large heat demand would suffice. Its location may influence where biochar production is sited.

A soil amendment

When used in plant beds and fields, biochar improves the soil structure and fertility, and retains nutrients and water, leading to better plant growth. It is fundamental to “the most fertile soil in the world” – the terra preta de índio of Amazonia.

This has positive implications for local food supply. Stockholm gives some biochar free to its citizen gardeners, and sells the rest on the open market to professional growers and to the city’s tree management team, who are reportedly enthusiastic users.

Zero food waste

Biochar is an ideal partner for another municipal waste stream: food waste. In law, human food waste fed to animals is not waste but redistribution. Whether this applies to soil creatures is untested, but stands to reason.

If one ferments food waste using lactobacilli rather than a yeast, the result is a preserve, not edible by humans or vermin but very attractive to soil creatures. None of its food energy, carbon and nutrients are lost, whereas composting loses half or more. After the finished preserve is mixed into soil it is consumed by the soil ecosystem within a very few weeks (much faster than decomposition) producing a rich worm-worked soil, a larger ecosystem, and ultimately more dead organic matter and humus which are stores of carbon.

Biochar addresses a practical problem of lacto-fermentation. This process produces a nutrient-rich liquid which normally requires (a) drainage to avoid drowning the process and (b) capture to avoid losing nutrients. Biochar used as a base layer under the fermentation absorbs the liquid. Thus simpler and cheaper undrained fermentation vessels and methods are possible.

In return, a problem of biochar is solved too. Raw biochar is so absorbent that, at first, it robs nutrients from soil. This hazard typically requires an extra stage in production to pre-charge the biochar from another nutrient source. This is unnecessary with the arrangement described above. The two components, fermented matter and biochar, can be mixed into the soil in one operation – a double boost of food and housing for the soil ecosystem.

Carbon offsets

A carbon offset is a reduction in atmospheric carbon dioxide or other greenhouse gases made in order to compensate for emissions made elsewhere. You can offset your personal emissions by contributing (normally with money) to an offsetting scheme.

Many people shy away from offsetting because some schemes have been found to be scams, with no genuine or permanent carbon reductions involved. It is not easy to judge which schemes are genuine. However, biochar is well suited to carbon offsetting – so well that it ought to be the “gold standard” – for two reasons:

  • Biochar in a properly managed store, such as soil under regenerative management, will keep its carbon out of the atmosphere permanently.
  • Independent assaying can measure soil biochar content to check the truth of claims.

Solid proof of permanently stored biochar should enable a municipality to seek offsetting status and generate an income stream. The offset price of emitting 1 tonne of CO2 was 24.36 euros per tonne on 5th Dec 2019, valuing 5,000 tonnes at about £100,000 per year (using our earlier rough estimate of Reading’s potential biochar yield). The level of proof should command a higher price. Hmmm … worth further investigation and estimation. Click here for today’s carbon price.

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