Biochar
UK Biochar Research Centre

What is biochar?


Biochar is a carbonized material produced at high temperatures in a zero or low oxygen environment. This charcoal substance has a porous crystalline structure, and can be used to increase soil fertility (IBI 2010). Since the discovery of the Terra Preta soils of the Amazon, where biochar / charcoal incorporation is providing benefits of increased nutrients and soil CEC even after abandonment up to 2000 years ago (Sombroek et al. 2003, Glazer et al. 2002) there has been increased interest in biochar production and use.

Uses: carbon storage, soil improvement, fuel

First coined by Peter Read, biochar was envisioned to refer to charcoals which are prepared for soil improvement which would potent provide a potentially very large scale carbon storage mechanism (Read 2009).


1. Carbon storage

Biochar has carbon storage properties – as is purported to persist in the soil, since is resistant to microbial degradation in the soil (Baldock & Smernik 2002) for several hundred up to thousands of years (IBI 2010) with Warnock et al. (2007) identifying 5,000 years as a common estimate. Plants uptake carbon dioxide from the atmosphere during photosynthesis and a proportion of this can be fixed in biochar and stored long-term in soil (Lehmann 2007).

2. Soil improvement

The properties of biochar which can provide benefits to the soil (composition, stability) depend on the process conditions (temperature, pressure) and feedstock (Brownsort 2009, Baldock & Smernik 2002). The biochar from Anila stove has been investigated to determine suitability of the biochar it produces as an agricultural amendment with encouraging results. The biochar was found to be of a consistent nature in terms of pH and conductivity. The yield of biochar was also enough for a yearly application rate of 0.5t/ha which would be ideal for users with small areas of land – typically the poorest farmers (Iliffe 2009).

Soil structure and physical properties

Biochar can provide water retention benefits, increase the infiltration rate and also reduce the soil albedo (reflectance of the soil – which can be beneficial in cold regions) (ref). Chan et al (2007) observed improvements to hardsetting soil including reduction in tensile strength and increases in field capacity and also pH when >50t/ha biochar was added.

Chemical / nutrient input

A high pH biochar will have a liming effect. In addition there are bio-available nutrients in the biochar, including N and P and metal ions (Sombroek et al 1993).

Interaction with fertilizer and nutrient retention

Biochar retains cations better than other forms of soil organic matter, and this ability increases as the biochar ages in the soil (Lehmann 2007). It is the high CEC of biochar which increases the retention of available nutrients in the soil (available N as NH4+) as well as any added nutrients.

Chan et al (2007) showed that biochar addition with fertiliser increased radish production, although biochar amendment alone did not increase the yield of radish. Changes in soil quality were also noted. A related effect is also identified in Asai et al (2009), where the addition of biochar is dependent on the presence of nutrients or fertilizer to produce positive benefits to rice growth. Some studies also point to reduction in availability of N where fertilizer is not added in combination with biochar (Asai et al. 2009), or no benefit to crop growth (Rondon et al 2007).

Emissions reductions

Where there is organic matter in the soil, biochar can reduce not only the loss of nutrients, but also the resultant gases from the breakdown process. Enrichment of poultry manure with biochar led to reduced nitrogen losses in mature composts (Dias et al 2009).

The priming effect

The priming effect (the accelerated decomposition of organic material in the soil) may lead to increased availability of nutrients from other organic sources in the soil, however more research needs to be done on this topic (UKBRC 2010).

Interaction with legumes

Rondon et al (2007) showed that the addition of biochar led to an increased proportion of fixed nitrogen when added used to grow nitrogen fixing plants. Three related mechanisms were identified which lead to this:
  • there could be more mycorrhizal activity inside the biochar, which can bring more nutrients to plant roots which seek out biochar in the soil
  • the N ratios is lower in the soil due to low C:N in biochar
  • increased availability of micro nutrients and higher pH

Long term benefits

The effect that the biochar has on the soil and on crop growth will also depend on the interactions with the soil type and soil microbes. This will also influence the longevity of the biochar, since biochar will after a period of time will oxidize and eventually degrade in the soil (Novak et al 2010).

It is likely that as the labile carbon fraction is lost, the initial input of nutrients will only be a short term benefit. However as biochar ages and particle size decreases, CEC will increase (Novak et al 2010).

3. Fuel

Depending on the feedstock used, biochar can also be used as a fuel (particularly wood biochar). It can be burned fully in the stove in which it is produced or, it can be extinguished (i.e. quenched with water) and stored for use later in a charcoal stove. Biochars generally have better fuel qualities than dried biomass, in terms of moisture and volatiles, and also tend to have a high energy density (Abdullah 2010). The ash content can be variable depending on the feedstock - different biomass components from the Mallee tree were tested by Abdullah (2010) and were found to have large changes in ash content. The grindability was found to vary, and was highest in the wood biochar, and this is beneficial if the biochar is to be processed, for example into pellets.
Charcoal making in Bantey Srei, Cambodia. Charcoal and charcoal fines are biochar.

More info on the calorific values of biochar?

How is biochar produced?

Biochar is a product of thermal decomposition of wood, and other biomass sources (Lehmann 2007). These processes include pyrolysis and gasification and the products are syngas, solid residue (including biochar and ash) and liquid (including tars).


Pyrolysis

Industrial processes can be divided into fast and slow pyrolysis. Slow pyrolysis is a slow heating rate and a lower temperature (generally 300 – 500oC). Carbonisation occurs, where carbon is a major product (as in biochar production) together with syn-gas and liquids. Pyrolysis is chemical decompostion at high temperatures. The word comes from greek derived ‘pyro’ fire, and lysis ‘decomposition’. Unlike combustion water, oxygen or any other reagents are not required.

Gasification

A small amount of air is required for gasification but not enough to complete the burn. In gasification cooks stoves, it is the syngas which is burned to produce the heat. The gas will mainly comprise of carbon monoxide (FOE 2009, Horne 2006, IAP 2010, Sohi et al 2009). A wide spectrum of technologies using pyrolysis and gasification are available, from medium to large scale industrial continuous units, for example Ankur http://www.ankurscientific.com/ biomass gasification units to small scale batch units including cook stoves. !!Feedstock
Any biomass can potentially be used to produce biochar including wood, crop residues, paper sludge and coconut shells (Abdullah 2010, Hossain 2010, Warnock 2007)

Biochar producing cook stoves

Improved cook stoves provide benefits which typically include increasing efficiency and reducing smoke production. Gasification stoves in addition to these benefits also produce biochar which can increase food production (where biochar is used as a soil amendment) and can thus reduce hunger. Gasification stoves can therefore provide part of the solution for 7 out of the 8 Millennuim Development Goals which aim to reduce global poverty (Warwick & Doig 2004).

Pyrolysis temperatures of 450-550oC will maximize biochar production (Lehmann 2007) which is may be higher than for most stoves, although the belonio wood gasifier can operate at temperatures 400-450oC measured with a pyrometer at the top of the flame (Belonio & Atmowidjojo n.d.). Most stoves are designed specifically to produce a clean flame suitable for cooking and not necessarily to maximize biochar production, but they can produce between 25 and 30% biochar weight from the initial feedstock weight (Samuchit 2010). This is about the maximum which would be expected from slow pyrolysis conditions (Brownsort 2009).
In addition, biochar produced below 400oC, which may be the case in many cook stoves will have a lower pH and lower CEC, however since these properties are reported to increase over time as the biochar ages in the soil, the benefits will still be provided (Lehmann 2007).

In stoves which produce biochar, pyrolysis and gasification will occur resulting in biochar production, then if incineration is allowed to follow, the biochar will turn into ash.
If at this point the stove is extinguished, then as mentioned before, the biochar can be kept for other purposes (for example as a soil amendment) or as a fuel later.

List of stoves which can produce biochar

NameLocation: continentApplicationFuelAvailability Main picture
"Majiko" stoveAfricaHouseholdsBranches
Briquettes
Dung cakes
Rice husk
Saw dust
Twigs
Wood
Commercially available
Turbo wood-gas stoveGlobalCommercial
Households
Institutional
Agri residue
Branches
Briquettes
Charcoal
Coal
Dung cakes
Pellets
Twigs
Wood
Under development
CEHEEN Improved Egaga StovesAfricaHouseholds
Rural
WoodCommercially available
TLUD Gasifier StoveAsiaHouseholdsAgri residue
Wood
Commercially available
1G Toucan TLUD for Biochar ProductionAsiaHouseholdsWoodUnder development
Juntos Gasifier StovesAfricaHouseholdsTwigs
Wood
Commercially available
Anila StoveGlobalHouseholdsAgri residue
Charcoal
Under development
Lucia BBQ Grill Unit GlobalCommercial
Households
Rural
Urban
Agri residue
Briquettes
Charcoal
Pellets
Rice husk
Twigs
Wood
Commercially available
Laboratory Gasifier and Char Study UnitGlobalInstitutionalAgri residue
Branches
Briquettes
Dung cakes
Pellets
Rice husk
Saw dust
Twigs
Wood
Commercially available
PupStove (Fan-free bi-fuel stove)GlobalCommunityAgri residue
BioOil
Branches
Briquettes
Coal
Dung cakes
Ethanol
Jatropha Oil
Pellets
Rice husk
Saw dust
Twigs
Wood
Commercially available
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  • Anderson’s TLUD
  • EverythingNice stove
  • Mafiga stove

References

  • Asai, H., Samson, B.K., Haefele S.M., Songyikhangs, K., Homma, K., Kiyono, Y., Inoue, Y., Shiraiwa, T. & Horie, T. (2009) Biochar amendment techniques for upland rice production in Northern Laos. 1. Soil physical properties, leaf SPAD and grain yield. Field Crops Research 111. 81–84
  • Baldock J.A. & Smernik R.J. (2002). Chemical composition and bioavailability of thermally altered Pinus resinosa (Red pine) wood. Organic Geochemistry 33. 1093-1109.
  • Belonio, A & Atmowidjojo, D. (n.d.) Wood charcoal gasifier stove. http://www.bioenergylists.org/files/Wood%20Charcoal%20Gasifier%20Stove%20-%20atbelonio.pdf
  • Brownsort, P.A. 2009 Biomass Pyrolysis Processes: Review of Scope, Control and Variability. UKBRC Working Paper 5. http://www.geos.ed.ac.uk/sccs/biochar/documents/WP5.pdf
  • Dias, B.O., Silva, C.O., Higashikawa, F.S., Roig, A., & Sánchez-Monedero, M.A. (2010) Use of biochar as bulking agent for the composting of poultry manure: Effect on organic matter degradation and humification. Bioresource Technology 101 (2010) 1239–1246
  • FOE 2009. http://www.foe.co.uk/resource/briefings/gasification_pyrolysis.pdf
  • Glazer, B., Lehmann, J. & Zech, W. 2002. Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal - a review. Biol. Fertil. Soils. 35 pp. 219-230.
  • Horne, B. Power Plants A guide to Energy from Biomass (New Futures 16, January 2006, The Centre for Alternative Technology. Brian Horne)
  • IAP 2010. http://iapnews.wordpress.com/
  • IBI (2010) www.biochar-international.org
  • Iliffe, R. (2009) Is the biochar produced by an Anila stove likely to be a beneficial soil additive? UKBRC Working Paper 4. http://www.geos.ed.ac.uk/sccs/biochar/documents/WP4.pdf
  • Lehmann, J. 2007. Bio-energy in the black. Front Ecol Environ 5(7) 381-387
  • Novak, J.M., Busscher, W.J., Watts, D.W., Laird, D.A., Ahmedna, M.A. & Niandou, M.A.S. 2010. Short term CO2 mineralization after additions of biochar and switchgrass to a Typic Kandiudult. Geoderma 154: 281-288.
  • Read 2009. This gift of nature is the best way to save us from climate catastrophe. The Guardian. Friday 27 March 2009. http://www.guardian.co.uk/commentisfree/2009/mar/27/biochar
  • Rondon, M.A., Lehmann, J., Ramírez, J. & Hurtado, M. (2007). Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions Biol Fertil Soils. 43:699–708
  • Samuchit 2010 http://www.samuchit.com/index.php?option=com_content&view=article&id=1&Itemid=3#sampada%20stove
  • Sohi et al 2009. Biochar, an emerging technology for climate change mitigation (UKBRC Working Paper 1)
  • Sombroek, W.G., Nachtergaele, F.O. and Hebel, A. 1993. Amounts, Dynamics and Sequestering of Carbon in Tropical and Subtropical Soils. Ambio, Vol. 22, No. 7. pp. 417-426.
  • Steiner, Teixeira, W.G., Lehmann, J., Nehls, T., Vasconcelos de Macêdo, L., Blum, W.E.H, and Zech, W. 2007. Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil. Plant Soil 291: 275-290.
  • UKBRC 2010 http://www.biochar.org.uk/
  • Warwick, H. & Doig, A. (2004). Smoke – the killer in the kitchen. Indoor Air Pollution in Developing Countries. Practical Action, ITDG.

Reports & external links




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