A project developer in upper Assam wrote to us recently. He has access to tea garden prunings and bamboo processing residue, around 5,000 tonnes a year, and he wants to turn it into biochar and sell carbon credits. Sensible questions, asked plainly.
He is not the only one. Assam grows roughly half of India's tea, and every one of those gardens cuts its bushes back on a cycle and ends up with a heap of woody material. Add the bamboo offcuts from the state's processing units and there is a great deal of biomass lying around the Brahmaputra valley.
So here is an honest answer about what it is worth, what makes it hard, and where projects like this usually come unstuck.
What a tea garden actually throws away
Tea bushes are cut back to keep them productive. A light skiff takes a little off the top most years; a deeper prune every three to four years takes off far more, and leaves real woody material between the rows — stems, thin branches, a good deal of leaf.
That woody fraction is close to ideal for pyrolysis. It is lignin-rich, low in silica compared with rice straw, and it makes a hard, stable char. Bamboo processing residue is similar, and bamboo makes good biochar for the same reasons.
The catch is that it does not all arrive at once, and it does not all arrive every year. A garden on a four-year prune cycle gives you a quarter of its area annually. Plan your plant around the volume that shows up every year, not the volume in a good year.
How much biochar comes out of 5,000 tonnes?
Less than most people assume, because most of what you collect is water.
Freshly cut prunings in Assam run around 40 to 50% moisture. So 5,000 tonnes off the field is really about 2,700 tonnes of biomass and 2,300 tonnes of water. Then the reactor takes its share: a well-run continuous unit converts 20 to 25% of dry weight into biochar. Older or badly run equipment gives far less.
From there, carbon credits. Each tonne of good biochar locks away roughly 2.2 to 2.7 tonnes of CO2 once the registry's deductions are applied — for transport, drying energy, and the share of carbon that will not last. So you are looking at something like 1,200 to 2,000 credits a year.
At the indicative range durable biochar removals have been fetching, that is real money but not a fortune, and it arrives slowly. Read what biochar carbon credits are worth before you build a business plan on it, and treat every number here as an estimate to be replaced with your own measurements.
The Assam problem nobody puts in the brochure
Rain.
Much of upper Assam gets 2,000 to 3,000 mm a year, most of it between June and September. Wet biomass is the enemy of good biochar: the fire spends its energy boiling water off, the temperature never climbs high enough, and you get smoke, tar and a soft brown char that no laboratory will certify and no buyer will pay for.
This is not a small operational detail. It is the thing that decides whether your plant runs twelve months or five.
- Budget for covered storage, not a tarpaulin. You need somewhere to hold several months of dry feedstock before the monsoon arrives.
- Consider using waste heat from the reactor to dry incoming material. It costs more up front and saves the project later.
- Assume you will stockpile in the dry months and run through the wet ones, and size your shed accordingly.
Anyone who quotes you a plant cost without a drying and storage line has not built one in Assam.
The question a registry will actually ask
Here is where most first-time projects get a nasty surprise. It is not the technology. It is additionality — the requirement that the carbon removal genuinely would not have happened anyway.
Tea prunings usually have an existing use. Many gardens leave them between the rows as mulch, where they rot down and return organic matter to the soil. Others feed them into the factory boiler as fuel, displacing coal or purchased firewood. Both of those are legitimate uses, and both make your project harder to argue.
| What happens to the prunings today | How strong is your case? |
|---|---|
| Openly burned in the field | Strong — you are preventing an emission and creating a removal |
| Left to rot as waste, no agronomic purpose | Strong, if you can show it is genuinely surplus |
| Returned to rows as mulch | Weaker — you must account for the soil carbon and nutrients you are removing |
| Burned in the factory boiler as fuel | Weak — the garden will just buy coal or firewood instead, and that emission is yours |
| Sold to a mill or an industrial buyer | Weak — it is not waste if someone is already paying for it |
The same logic applies to any large industrial buyer of biomass in your district. Where a bio-refinery or paper mill is already purchasing bamboo in the same catchment, two things follow: the price of local biomass has a floor under it, and that material is plainly not waste. Neither kills a project. Both mean you should build it around the streams the big buyer does not want — processing offcuts, undersized material, the residues left after their grade has been taken.
This is why a feasibility study should start with a feedstock map: every source within your collection radius, how much, in which months, who owns it, what it is used for now, and what it costs delivered. That map is worth more than any equipment quotation, because it is the thing a registry, a lender and a buyer will each want to see.
Which registry, and why it matters early
There are several routes — Verra's VM0044, Puro.earth and Isometric compared covers them in detail — and the choice affects your plant design, not just your paperwork.
In short: Puro.earth has the most biochar projects and a well-trodden process; VM0044 sits inside the larger Verra ecosystem; Isometric is the strictest on measurement. Pick before you buy equipment, because each one specifies what you must monitor, how often you must sample, and what your char must test at. Retrofitting monitoring onto a finished plant costs more than designing it in.
One number matters more than the rest: the H:Corg ratio, which is what proves your carbon will stay put for centuries. Why that ratio decides permanence is worth reading before you commit to a reactor, because it is set by how hot and how long you pyrolyse — a machine decision, made early.
Putting the biochar back into the tea
The plan most Assam developers have — sell the credits, give the char to the gardens — is a good one. Two revenue lines from one material, and the gardens gain soil that holds water better through the dry months.
But tea is a fussy crop, and this needs saying plainly.
Tea likes acidic soil, roughly pH 4.5 to 5.5. Most biochar is alkaline, often pH 8 to 10. Spread heavily, biochar behaves a little like lime and pushes soil pH upwards — away from where tea wants it. This is not a reason to avoid it, but it is a reason not to treat biochar as something you can apply by the truckload because it is free.
- Ask for a low-ash, lower-pH char, and get every batch tested.
- Start on trial plots, at modest rates, and measure soil pH before and after.
- Charge the char first — compost it or soak it in slurry. Raw biochar pulls nitrogen out of the soil in its first season, and a tea manager who sees a dip in the first flush will never take a second delivery.
- Keep the records. The same application data feeds your MRV, so you have to collect it anyway.
Get this right and the gardens become your advocates. Get it wrong on a big block and word travels fast in a tea district.
What it costs, and how to pay for advice
A project of this size is not a kiln in a yard. You are looking at a continuous or semi-continuous reactor, a drying and storage shed, weighbridge and sampling arrangements, laboratory testing, registry fees, an independent validation, and verification every year after that. Most of that spending lands before a single credit is sold. Our guide to choosing pyrolysis technology goes through the equipment end of it.
On paying a consultant, developers usually face two models, and it is worth understanding the trade.
| Fixed milestone fee | Share of carbon revenue | |
|---|---|---|
| What you pay | A known amount at agreed stages | Nothing much up front, a slice of every credit later |
| Who carries early risk | You | Shared |
| Long-run cost | Lower if the project succeeds | Much higher if it succeeds |
| Ownership | Stays entirely with you | Often entangled for years |
| Suits | Developers with capital and conviction | Developers who cannot fund the early stage |
A fixed, milestone-based fee is the cleaner arrangement for most developers: you keep the upside, you know the cost before you commit, and nobody is arguing about equity in year six. The trade is that you carry the early risk, which is precisely why the first milestone should be a small, honest feasibility study — one that is allowed to come back and say do not proceed. A study that can only ever say yes is not a study.
If you are working through an FPO, a cooperative or a group of small growers rather than alone, how FPOs and aggregators can co-own a project covers how to write the revenue share down before the money arrives.
Five ways an Assam project goes wrong
- Planning around fresh weight. Half of it is water. Weigh a dried sample and plan around that.
- No covered storage. The monsoon stops your plant for four months and the economics collapse.
- Assuming prunings are free waste. If the garden currently burns them in the boiler or lays them as mulch, they are neither free nor waste.
- Buying the reactor first. Registry choice sets your monitoring and your char specification. Choose the registry, then the machine.
- Spreading char in tea without testing. Alkaline char on acid-loving tea, applied at scale, is an expensive way to lose your local reputation.
Where to start
Start small and start with facts. Weigh the prunings off a measured block at a real prune. Dry a sample and find the true moisture. Map every source of woody residue within 50 to 70 kilometres, and for each one write down who owns it and what happens to it today. Make a few sacks of char in a simple kiln and send them to a laboratory.
That work costs very little and answers the question that matters: is there enough genuinely surplus biomass, arriving every year, to carry the cost of a registry?
If the answer is yes, the rest is engineering and paperwork. If it is no, you have found out for the price of a soil test rather than the price of a reactor.
When you are ready to put real numbers to it, see how we assess feedstock and feasibility, or request a biochar project feasibility assessment and we will work through your own figures — your gardens, your radius, your rainfall — with you.
Figures in this article are estimates as of September 2026 and will vary with your feedstock, moisture, equipment and location. Carbon credit revenue is never guaranteed, feedstock must be genuinely surplus and sustainably sourced, and soil application rates should be trialled locally before any large-scale use.