Biochar – Unlocking potential

As our planet faces a raft of pressing issues from shrinking energy resources, climate change and over-population to food and fresh water shortages, now would seem like a good time for some foresight, creativity, innovation – and a little risk-taking.

By Dr Michelle Morrison, principal environmental scientist with Wardell Armstrong

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No single solution will be the panacea to all our problems. We’re going to need to use as many good ideas as we can. Just one of these could be the production of biochar using biomass feedstocks – combining as it does a number of very distinct benefits.

First, as a very stable form of carbon, biochar can provide a reliable means of sequestration – potentially locking away carbon in the soil for hundreds or even thousands of years, rather than allowing it to be released quickly back into the atmosphere.

Secondly, it could be used to improve soil structure and nutrient retention capacity which can help plants to grow – whether in poor quality tropical or desert soils, or brownfield land closer to home. And thirdly, the pyrolysis of biomass creates a syn(thetic) gas that can be combusted to produce renewable energy in the form of electricity and heat.

Polarised debate

A lot of the recent discussion of biochar as a method of carbon capture and storage has been focused on agricultural applications, and the debate has been polarised between pro and anti camps. Some proponents may have over-hyped its benefits with unsubstantiated claims, while detractors have damned the technology as they foresee massive land grabs with untold environmental and human health impacts. The truth, of course, lies somewhere in between.

So what exactly is biochar? Like charcoal, it’s a form of black carbon. But unlike charcoal (which is produced primarily for use as a fuel) biochar is the term used for char generated as a by-product or product of biomass pyrolysis, with the potential for applications other than fuel.

Biochar is the carbon-rich by-product that’s produced when biomass (such as wood waste, agricultural crop residues, coconut husks and so on) is heated (pyrolysed) in the absence of oxygen, causing its thermal degradation into a syn(thetic) gas and a char. This is different from incineration, which involves the combustion of materials in the presence of oxygen to produce CO2, other gases and ash with little or no organic carbon content.

Like its close cousins ‘activated carbon’ and ‘carbon black’, biochar has a number of chemical and physical characteristics which could prove very beneficial across a number of applications. A large surface area, porous structure and particle size distribution are three of the properties which have a marked influence on how biochar behaves in soil.

Pyrolysis technology itself is not new. It’s been used in the chemical industry for the production of syn-oils as precursors to certain chemicals and syn-fuels, in the plastics industry for the conversion of ethylene dichloride to vinyl chloride for the production of PVC, for the conversion of coal to coke, and the cracking of heavy hydrocarbons to lighter ones. What is novel is the application of the technology specifically for the production of char.

Combining soil improvement, carbon sequestration and renewable energy

Recent studies have shown that adding biochar to soils can in certain situations improve nutrient retention, water-holding capacity and cation exchange capacity (the ability to hold on to other charged particles such as metals), as well as reducing emissions of other greenhouse gases from soils and holding the carbon in the soil for centuries.

So in addition to potentially improving crop growth, soil productivity and structure, there’s also the potential for sequestering the carbon (which was originally taken up by the plant biomass as CO2 when it was growing) by converting it into biochar and burying it.

This is because biochar is largely resistant to microbial attack – soil bacteria get their food and energy from the breakdown of soil organic matter, “eating” their way through it and releasing greenhouse gases as by-products into the atmosphere.

And there’s yet another potential benefit of biochar – the production of renewable energy. The pyrolysis of biomass creates a syn(thetic) gas, , that can be combusted to produce electricity and heat. Some can be used to maintain the pyrolysis process, while the rest is exported for external use. The amount will depend on the conditions of pyrolysis. Low-temperature pyrolysis can yield bio-oils which can be used as fuels or processed to produce chemicals. As the temperature increases, less oil and more biochar is generated.. Eventually, at high temperatures with the introduction of a limited quantity of air, gasification takes place – creating mainly syngas with some ash and little or no organic biochar carbon. So there’s a sliding scale of biochar/energy production which is controlled largely by temperature.

Interest in biochar originated from stories of lost civilizations in the Amazon. Initially, scientists didn’t believe that large and sophisticated communities could be supported by the poor quality, acidic soils of the river basin. But the discovery of the Terra Preta (Dark Earth) soils in tracts of land in the Amazon basin, a metre or so beneath the surface, showed that manmade char (biochar), derived from the slow burning of wood and other organic wastes, was a key component in improving the poor quality tropical soil’s productivity. In fact, it’s still productive today and still able to support agriculture some thousands of years later.

A no-brainer?

The argument for incorporating biochar into agronomy in certain arid/semi-arid/tropical areas looks like a “no brainer” – providing a relatively simple and cheap answer to problems of soil fertility, soil structure, water retention and hence soil productivity. There are some caveats, however. The diverse nature of biochar feedstocks, the physical and chemical conditions within the pyrolysis plant and the eventual application can result in different biochar characteristics and therefore different results.

But in theory, biochar production could be applied to many different organic feedstocks with some adjustment of the operating conditions. The versatility of the technology means that it can be applied to biomass products and/or biomass wastes. If the operation takes in waste biomass, it will be subject to the appropriate environmental permitting regulations and may fall under the Waste Incineration Directive in the UK.

Other applications could include using biochar as a soil forming material, combined with others for the restoration of brownfield land – acting as an ameliorant for contamination through its capacity to adsorb pollutants, as well as a soil improver.

What about the application of biochar technology in the waste resource management sector? Pure biomass feedstocks such as tree cuttings, forestry and crop residues, heather and even diseased plants should all be usable. Some wastes, of course, might contain contaminant levels which render the biochar unsuitable for application to land as a soil improver or pollution ameliorant. But it may yet be possible to bury this contaminated biochar deep beneath the surface in a landfill cell or disused mine void. This would still result both in reduced volumes of waste going to landfill and in the useful sequestration of carbon, preventing its release to the atmosphere for many years.

The scale of application can also be wide. Small scale family, community or farming projects – especially in developing countries – could benefit from investments in low capex equipment/plant for creating biochar for soil improvement, coupled with localised energy production. But much larger organisations could exploit the technology too – for example as an integral part of Birmingham City Council’s 2026 project to reduce the city’s energy requirements by 60%, by 2026.

Fundamental questions

A great deal of research is currently underway into risks to the environment and human health of biochar application, its longevity in the soil, its physico-chemical properties, and potential agronomical and agricultural benefits.

But there are still fundamental questions to be answered before legislation and policy can be drafted. Can biochar from different feedstocks be characterised? Can certain biochars be “matched” with application scenarios, or are there too many variables? What’s the energy and mass balance over the entire life cycle of the production of biochar, and how does it compare with other renewable technologies? If biochar is buried to sequester carbon, what is its longevity in the soil? And what’s the cost/benefit analysis?

The UK Biochar Research Centre is at the forefront of multi- and interdisciplinary research into biochar, and is seeking to create a UK hub which can feed into the work already done elsewhere and help to answer these questions. As a consultancy business with a broad and expanding portfolio of work in energy and climate change, Wardell Armstrong is working closely with the UKBRC on a number of projects, providing consultancy on policy and legislative requirements for the implementation of biochar projects.

Much of the commercial focus so far has been on energy production – not a surprise given the incentives offered to the renewable energy sector and energy users. The only current mechanism that exists to provide an incentive for carbon sequestration is the Clean Development Mechanism. Biochar projects in developing countries can apply for registration under the CDM. However, production is unlikely to reach its commercial potential in the UK and other industrialised countries unless a similar commercial incentive is in place which rewards carbon sequestration.

Biochar in the future

If the potential of biochar as one of the ways of alleviating climate change and food shortages is to be realised, there needs to be a concerted application of the technology at a number of scales.

Its great appeal is that it can be applied across a broad range of projects – everything from individuals and small businesses using small scale, low capital equipment, to large scale, high specification plants. Many different biomass feedstocks could be used – organic waste materials such as Waste Water Treatment Works biosolids, waste wood, crop residues and forestry residues or proprietary crops such as short rotation coppice. Depending on the requirements of a particular project, the technology could be optimised for biochar, bio-oil or syngas production by altering the pyrolysis conditions. The biochar could be applied to land as a soil improver, for land restoration, for long-term sequestration, or for contamination remediation.

But none of this must come at the expense of the environment or indigenous peoples. The spectre of unethical “land grabbing” and deforestation for biomass production should be fiercely guarded against to prevent the environmental and socio-economic impacts which accompanied the first wave of biofuel production from happening again.

As long as these risks can be legislated against and avoided, biochar could be an extremely useful and timely tool in combination with other measures for more sustainable living. We could do worse than support its progress.