Expanding Knowledge of Biochar and Its Strengthening Markets

Making biochar from a standard Air Burners, Inc., FireBox. Biochar offers several opportunities to the tree care industry. Photo courtesy of Air Burners, Inc.

Biochar offers several opportunities to the tree care industry, and the development of the biochar marketplace, supported by a growing body of research, has accelerated over the last few years. Potential from emerging markets for carbon-sequestration credits is adding to the economic benefits.

Biochar market growth is due primarily to the increasing recognition of biochar’s properties as a soil amendment. However, it also is being recognized as a carbon sink and for a growing number of new end uses, such as stormwater treatment, activated-carbon substitute, toxic-remediation media and plastics component. That increased appreciation provides opportunities. However, before delving into the value-added opportunities, let’s review what biochar is and isn’t.

Harvesting biochar from an Exeter mobile retort kiln. Photo courtesy of the author.

Biochar is the product of heating organic biomass (wood) in an oxygen-limited environment. In its simplest form, it’s charcoal. The term biochar comes from a (high-temperature) charcoal used in a biological end use, i.e., in the soil, where it can last for hundreds to thousands of years. Charcoal used as a fuel is typically made at a temperature of 250 to 300 degrees Celsius, while biochar is made at temperatures of 400 Celsius and higher, with the highest levels of stable carbon coming from higher processing temperatures.

Biochar is not used as a fuel, nor is it very cost effective to do so. However, some of the same equipment used to make biochar can be used to make charcoal. This can be an advantage if the charcoal market in your area is strong, allowing another product line out of the same investment.

Formal research into biochar’s properties and potential uses has been steadily increasing over the last decade. The International Biochar Initiative (IBI), which tracks biochar-related publications, noted nearly 5,000 articles on the subject in 2020 as compared to about 500 articles in 2010. This informational flow has allowed both the industry and the marketplace to grow as more and more people understand the benefits biochar has to offer.

Considerations for biochar production and use

The most important aspect of biochar is for it to have high carbon content and low polycyclic aromatic hydrocarbons (PAHs). PAHs are chemical compounds that are damaging to plants – mainly because, in excess, they can kill off the microbiota in the soil, disrupting the nutrient cycle. That’s why the temperature of the biochar-production process is so important. You need to cook off the PAHs. A temperature over 400 Celsius usually suffices, and almost all the production technologies do a satisfactory job if operated correctly.

Ring of Fire Biochar Kiln from Wilson Biochar. Photo courtesy of Wilsonbiochar.com.

The biochar, once created, needs to be “charged” or inoculated before use. Think of the biochar in the same way you might activated carbon, which is used as a remedy for poisoning in humans and animals, or in water filters. In both examples, the char adsorbs (attracts and binds with) the toxins over its huge surface area; one gram of activated carbon may have a surface area larger than a football field! Because biochar has a similarly huge surface area, if it’s put into the soil in its raw form, it will fill its voids with whatever it can. Early tests of raw biochar in soil found it would suppress growth. With more understanding, it was found that the biochar was taking the nutrients from the soil in order to come to equilibrium, so those nutrients were not available to the plants. They would eventually release them, but the initial suppression of growth was a negative. So, to counter the deficit, the char is typically combined with something to fill its voids ahead of in-soil application.

The most common method of inoculation is to combine the biochar with compost – usually at a 5% to 15% rate of char to compost. Another method used is to soak the char in a compost tea, which has the added advantages of reducing the dust hazard of applying raw char, immediately increasing the water content of the soil for better contact and/or plant uptake, and allowing liquid injection of the char. Another method is to mix the char with an organic supplement such as bloodmeal (for nitrogen, or N), Greensand (for iron, magnesium and potassium, or Fe, Mg and K) or rock phosphate (for potassium, or P). These will all need to be watered before or immediately upon application to be effective, or the amendments will act independently. The other caution is that most biochars have a liming effect because of their high pH, so be aware of the specific characteristics of the final application.

Photomicrograph of pyrolyzed grass clippings with more than 100m2 of surface area per gram. Courtesy of UK Biochar Research Centre.

It’s advisable to get your char tested a couple of times to know what you’re producing. Characteristics will vary with different feedstocks, but if you’re using woody debris and are consistent with processing times and temperatures in making the char, the characteristics should be relatively consistent. The full suite of characterization results should be in accordance with the International Biochar Initiative’s standards, which several labs across the U.S. can perform. More basic, you can have a soils lab tell you what the pH and carbon content are.

It also would be worthwhile to check the temperature of your operation at its peak (using a thermocouple is best, but a thermal thermometer can give you an approximation). This will assure the temperature is high enough to eliminate most of the PAHs (so you don’t kill your client’s plants!).

Burn, quench and spread forest-slash application. University of Minnesota photo courtesy of the author.

Biochar opportunities for tree care

For tree care practitioners, there are two routes to benefit from biochar – as a producer and/or as an applicator. Biochar can be made using simple techniques with several co-benefits. The simplest technology – flame-capped kilns – is relatively inexpensive and highly mobile and provides significant volume reduction of woody debris. The char can be used on site, moved inexpensively to another site or aggregated and sold. There is a big jump in capital cost and operational complexity to the next level of equipment, but these units can produce heat for a secondary use (like drying feedstock, firewood or another heat-intensive process). With advanced technology, besides heat, systems can produce syngas, wood vinegar (pyroligneous acid) and biofuels. The cost ranges from about $1,000 for a flame-capped kiln to millions of dollars for a biochar plant with multiple co-benefits.

An Exeter mobile retort kiln fully loaded for a burn, and …

… .. the raw biochar, which in this state can be sold as charcoal. Prior to use as biochar (in soil or compost), its size is reduced by various methods, such as hammer mill, lawnmowers or driving over it with a car. Photos courtesy of the author.

If you want to collaborate with a municipality or have the opportunity to cooperate with other tree care professionals, you may be able to invest in a larger-capacity facility at a stationary site. This allows capture or use of the syngas and heat fairly easily. Co-location with another business that needs process heat, electrical power or distillates can provide opportunities to benefit a wider group of stakeholders – and can yield very high-quality and consistent biochar at a potentially lower unit cost. This situation will probably be rather rare, but it could have the added potential of selling carbon credits.

Carbon credits

The carbon market is rapidly developing, and, with the increasing focus on carbon sequestration as a climate-mitigation strategy worldwide, the price is expected to increase as verification systems come more widely online. Fixed biochar-production facilities that capture the heat and/or syngas currently qualify for selling carbon credits from certifying agencies like Verra and Puro. Demand for certified carbon credits is expected to grow, which may shift the economics of biochar production and the technologies used.


The most lucrative markets for biochar have historically been agriculture related. The higher-value crops (vineyards, flowers, hoop houses, nurseries, greenhouses and intensively managed food crops) present the greatest market opportunity in that sector. There are growing markets for specialty chars, but they take much more complicated pre- and post-processing, as well as sophisticated management of processing times and temperatures, so are not feasible without considerable investments in capital and scientific research.

The most profitable course is to use what you produce. You can make the char on site or back at the yard, if conditions and regulations permit.


The Oregon flame-capped kiln or the Ring of Fire kilns (https://wilsonbiochar.com/gallery ) are the lowest-cost and most-mobile technologies, will take about four hours to generate a full load and need sufficient water for quenching. They are especially good for volume reduction; you get 5% to 15% volumetrically back in biochar.

You can up the game in terms of the daily rate of feedstock conversion with a big-box kiln (https://www.youtube.com/watch?v=y1L00ETQNpw) or the Charboss, (https://wildriverscoastalliance.com/community-posts/air-curtain-burner-demonstration) currently in beta testing. A closed, retort kiln mounted on a trailer, like the Exeter or similar unit (https://www.carboncompost.co.uk/), has higher yields (50% plus) and takes about eight hours to run a load, plus another 16 to cool down.

All the above options accept larger-sized woody debris, which makes them suitable for charcoal production. The less-mobile but higher-throughput units, like the Biochar Solutions B1000 gasifier (http://www.biocharsolutions.com/biochar-production-equipment.html), can operate continuously and use chipped feedstock. There are even more sophisticated production systems available that can produce a variety of byproducts including power, but the costs escalate quickly and require extensive permitting.

With all these technologies, the biochar can be used in soil applications. With more sophisticated control systems producing higher-quality chars, you can supply higher-value end uses like stormwater and wastewater treatment, concrete and asphalt admixtures or a variety of other emerging markets. There are 55 product uses that have been identified and are discussed at length in the book, Burn: Using Fire to Cool the Earth, by Albert Bates and Kathleen Draper, many of them with ongoing research and pilot projects in progress.

For more information, visit the U.S. Biochar Initiative website (https://biochar-us.org/) and look at their resources tab. Even more information can be found at the International Biochar Initiative website (https://biochar-
), which has a global focus and tracks research publications monthly. Dovetail Partner’s library of reports at www.dovetailinc.org contains a series of science-based reports on biochar, natural-resource management and responsible consumption.

Harry Groot is an associate with Dovetail Partners, a 501(c)(3) nonprofit organization that aims to provide authoritative information about the impacts and trade-offs of environmental decisions, including consumption choices, land use and policy alternatives.

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