New science shows CH₄ emissions of less than 5 grams per kilo of biochar

Peer-reviewed research from Ithaka Institute, supported by Planboo, has measured methane emissions below 5 g per kg of biochar, up to 6x lower than figures currently used in carbon standards. The finding overturns a key assumption about flame curtain pyrolysis and strengthens the case for artisanal and decentralised biochar production.

Does Kon-Tiki Biochar Production Really Emit High Levels of Methane?

For years, carbon standards have required biochar producers using Kon-Tiki flame curtain kilns to account for up to 30 grams of methane (CH₄) per kilogram of biochar produced. A conservative and responsible assumption — in the absence of hard data, no one wants overcrediting. But it left a question unanswered, and for some credit buyers, an uncertainty they couldn’t ignore. 

Now, we have more research that can replace this assumption with evidence.

A study by Simon Lotz et al. through the Ithaka Institute, supported by Milkywire and Planboo, found that woody biomass with less than 15% moisture content emits no more than 5 grams of CH₄ per kilogram of biochar when processed in a properly operated Kon-Tiki kiln. That’s up to six times lower than the figure currently embedded in Carbon Standards International (CSI) methodology, which was based on feedstock moisture levels exceeding 25%.

In fact, this is not the first time we’ve seen such low methane emissions associated with Kon-Tikis and dry biomass. The new research paper by Simon Lotz and colleagues confirms previous findings published by Cornelissen et al. (2023; 2024), co-authored with Planboo’s Biochar Scientist, Dr. Ruy Anaya de la Rosa.

What Is the Kon-Tiki Kiln?

To the casual observer, a Kon-Tiki kiln in action might bear a strong resemblance to an open bonfire, the sort of activity that sends plumes of smoke and greenhouse gases (GHGs) straight into the sky. But on closer inspection, you’ll see that this particular fire is surprisingly not releasing smoke into the air. That’s due to the thermodynamics of the simple, conical design and the specific technique by which the biomass is added to the fire. By carefully layering fresh feedstock into the kiln, the hottest part of the fire remains at the top, and this creates a suction that pulls smoke from the lower layers into this heat zone (or “flame curtain”), where temperatures typically exceed 600-700° C. At these temperatures, the smoke and GHGs combust, so the fire releases little other than CO₂. But keep in mind that in the absence of this biochar production, or pyrolysis, the biomass, specifically sourced from agricultural waste streams, would ordinarily decompose and release about twice as much CO₂ in the atmosphere.

At $1000-$2000 per kiln, with a capacity of up to 1600 litres, Kon-Tikis can be fabricated locally and moved from site to site with relative ease, making them far more accessible than the industrial, high-tech alternatives that are expensive and difficult to deploy in decentralised, rural settings.

Why Methane Emissions Have Been a Sticking Point

Under the current CSI methodology, the 30 g CH₄/kg assumption has meant that many Kon-Tiki projects must offset their methane emissions through additional activities, such as tree planting, before earning carbon credits. This requirement adds cost, operational complexity, and for sceptical buyers, a lingering question mark over the net climate impact.

Note that there are certain exceptions to this methane compensation requirement. The most common exception is for projects in which the baseline (or business-as-usual) scenario is that the biomass waste is being openly burned in the field, a very common practice in many agricultural value chains, with cotton stalks and rice stubble, for example. If biochar production displaces this open burning practice, then it’s eliminating far more GHG emissions than it’s creating. According to the newly published paper, Kon-Tikis actually reduce methane and carbon monoxide emissions by more than 30% compared to open burning.

What the Research Found

The Lotz et al. study measured CH₄ emissions from properly operated Kon-Tiki kilns using woody biomass, controlling for moisture content and operational conditions. The findings:

  • Methane emissions six times lower than the current standard accounts for: Current industry standards (like CSI) assume a “default” emission factor of 30g CH4 per kg of biochar produced in a Kon Tiki kiln. This study proves that with dry feedstock, we are actually under 5g CH4. That’s a 6x improvement over the standard assumption.
  • A measurable performance floor: Maintaining flue gas temperatures above 190°C is sufficient to render methane emissions negligible, giving operators a clear and practical quality threshold.
  • Superior to Open Burning: Compared to the common baseline of farmers burning agricultural waste in the field, the Kon-Tiki kiln reduces methane emissions by 36% and carbon monoxide by 35%.
  • Net climate positive confirmed: The data confirms a carbon removal of >500 kg CO2e per ton of feedstock.

What This Means for Biochar Carbon Removal Projects Using Kon Tiki Kilns

  • Stronger carbon accounting: Credits generated from decentralised projects rest on more accurate, empirically grounded emissions data.
  • Greater credibility with buyers: One of the most common objections to Kon-Tiki carbon credits – that unverified methane emissions undermine their integrity – is now addressed by peer-reviewed science.
  • Dry feedstock is key: Planboo’s dMRV requires multiple moisture readings and photo documentation of the moisture meter. Planboo also monitors seasonality and weather patterns to avoid pyrolysis during the wet season.

    A large proportion of the world’s agricultural residues are currently burning or decomposing in fields across the Global South, where financial and infrastructure constraints make industrial biochar systems unworkable. Kon-Tiki kilns represent one of the most scalable pathways to turning that waste stream into durable carbon removal, and this research strengthens the scientific foundation beneath them. Kon-Tiki kilns are a decentralised, affordable, clean, simple, effective and very democratic way of biochar production that delivers numerous core benefits, particularly to the people living in rural areas around the Tropics. This research strengthens the case to scale up biochar production and durable carbon removals. Thank you to everyone at the Ithaka Institute, STING, Milkywire and beyond who helped make it possible.

    This research was conducted by Simon Lotz and colleagues at the Ithaka Institute. Planboo supported the study by securing and managing the STING grant funding that made the research possible. We are grateful to Milkywire for their co-support, and to the biochar producers and project developers whose work in the field continues to provide the real-world foundation for science like this. 

 

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