Waste as a balance-sheet item
Biochar has two buyers for the same tonne: one for the material, one for the carbon inside it. Appraised as a by-product, it often decides the financing.
In most economies waste is an accounting footnote. In a small island state it is a landfill within sight of the road, a leachate risk to the aquifer beneath it, and a shipping cost paid in both directions. What follows concerns the least glamorous of the things that can be made from it, and possibly the most useful.
What biochar is, for present purposes
Biochar is the carbon-rich solid that remains when biomass is broken down under heat in the near-absence of oxygen. The processes that produce it are various, and are not the subject here. What matters commercially is the character of the output: a stable, porous solid, on the order of nine parts carbon in ten, which does not readily decay. Carbon that would otherwise have returned to the atmosphere within a season or two, by decomposition, open burning or a landfill vent, instead stays where it is put for a period measured in centuries.
That single property is what gives the material two independent markets.
The soil case
Applied to land, biochar improves water retention and holds on to the nutrients applied alongside it. The benefit is largest precisely where soils are poorest: over-cultivated ground, thin tropical soils, land that has carried one crop for a century. In small island agriculture that describes rather a lot of it.
There is a secondary effect worth noting. Where the feedstock is itself nutrient-rich, sargassum being the obvious Caribbean case, a portion of the nitrogen and phosphorus is retained in the char rather than returned to the coastal water it came from. The same tonne of weed that would have rotted on a beach and fed the next bloom goes onto a field instead.
The carbon case
A tonne of high-carbon biochar, taken at nine parts carbon in ten, embodies about 3.3 tonnes of carbon dioxide that is consequently not in the air. The figure is worth deriving rather than quoting: the mass ratio of carbon dioxide to carbon is 3.66, so a tonne of pure carbon is the ceiling at 3.66 tonnes, and anything above it in a prospectus is an error.
Because the permanence is long and the material is countable, biochar is among the few carbon removals for which the verification bodies have been willing to write proper methodologies; Puro.earth and Verra both issue credits against it. That places it in the removal category rather than the avoidance category, which is the half of the voluntary market with genuine scarcity and genuine corporate buyers. A facility taking in on the order of a hundred thousand tonnes of mixed waste a year will sequester tens of thousands of tonnes of carbon dioxide annually, the range being wide because char yields are wide.
Two buyers for the same tonne
General-purpose biochar carries a market price in the region of $300 a tonne, varying considerably with quality, certification and packaging. The same tonne can instead be retired as carbon: at a conservative $30 per tonne of CO₂ against 3.3 tonnes embodied, that is about $100 a tonne of char.
| Route, per tonne of biochar | Realised |
|---|---|
| Material sale, general purpose at ~$300/t | $300 |
| Carbon removal, 3.3 tCO₂ at $30/tCO₂ | $99 |
| Carbon removal, 3.3 tCO₂ at $100/tCO₂ | $330 |
At conservative carbon prices the physical sale is worth appreciably more. At the prices high-quality removals have lately commanded, it is not. The point is not which of them wins in a given year, but that a producer with both routes open has a floor beneath the material rather than a single counterparty and a single price.
Neither market is deep. Local agricultural demand on any one island will absorb a fraction of what a serious facility produces, so the greater part of the output is exported or credited. Both routes carry costs that are easily left out of a model: monitoring and verification for the carbon, freight and certification for the material.
The bankable end of the project
A waste-to-value project asks a lender to underwrite four things at once: a feedstock supply, a process, an offtake and a price. The biochar stream is the one where three of the four are least contentious. The feedstock is a liability somebody is already paying to dispose of. The measurement methodologies exist and are audited by third parties. And removal credits can be pre-sold, which means a portion of the revenue may be contracted before the plant is built, which is not true of a great deal else in the project.
This is why biochar is habitually underweighted in these appraisals. It is treated as a by-product because it is physically the smaller stream. Financially it is often the part that makes the rest legible to an infrastructure lender.
What it does not settle
Char yields vary severalfold with feedstock and operating conditions, and outputs quoted for a single plant can differ by a factor of four according to which assumption is carried through the model. Underwrite the low end. Permanence has to be managed rather than assumed, since char that is later burned sequesters nothing, so the end use must be contracted and monitored. Verification is neither free nor quick, and is routinely omitted from operating cost. And the soil benefit, though real, is site-specific enough that a result from one island’s fields should not be transferred to another’s without trial plots.
None of these are reasons to leave it alone. They are reasons for the appraisal to be done properly.
The full study
The work behind this note is a feasibility study prepared for a Caribbean government in 2025: some forty pages covering feedstock availability, plant configuration, capital and operating cost, sensitivity analysis, environmental assessment and the socio-economic case. It goes a good deal further into the engineering than is useful here.
It is available for a fee to counterparties with a serious interest in the subject. Enquiries to office@vindician.com.