Upcycle Burns – Carbonized Rice Husks (CRH)


When I was preparing for Peace Corps I was doing a lot of research into natural farming and one picture I came across was of a woman standing in front of a pile of coos husks on top of some type of burner. Turns out the photo was actually taken in The Gambia of all places. This made it a definite that I was going to experiment with carbonized rice husks (CRH) and carbonized coos husks (CCH).

I had just learned about the term “upcycling” from a friend – converting waste materials into something new or more valuable. I wanted to continue with some more natural farming posts and this introduced me to a new way of looking at the process and gave me a catchier title :).

A little bit about carbonized rice husks and why they are helpful for farming and gardening. Rice husks are the casing around the edible seed and it is shed as a byproduct as rice is milled. The husks are 80% organic, 20% inorganic and hard since they are 26% lignin and 50% or so cellulose. When you carbonize the husks you remove the bad stuff (Co2, methane, other volatiles) and break down the lignin which “opens up” the nutrients to plants etc. I believe the word for this is “bioavailability.” The rice husks undergo a process called pyrolysis, which is a high heat, low oxygen burning necessary so as not to totally destroy the husks and nutrients inside. Big thanks go to Josiah Hunt and Hawaii Biochar for teaching me how to make wood biochar and introducing me to many of the concepts I’ve gotten to try here in Gambia. Thank you. Check out the website, a Tedx talk and the great things going on here:


Ok, after you make CRH you are left with:
– 44% fixed Carbon
– 33% Ash (silica)
– Potassium
– Magnesium
– Phosphorous
– Calcium

All these things lead to the following benefits:
– Improved soil aeration
– CRH provide a home for beneficial microorganisms (a home for those IMO you made)
– Better soil drainage
– Increased water retention (good for these dry areas here in Gambia)
– The carbon balances the high nitrogen content of manures
– Restores silica to fields, which rice depletes

*I also think it can be used as a good deodorizer in chicken and hog pens.

Let’s get into how to make it and the steps I went through to learn and make CRH/CCH:

Here is what I found behind my house. I thought “There’s gotta be something to do with all this.” The rice machine mills rice for a couple hours each night. The edible rice falls down and the husks fly out the back into this huge hill. The owner of the building says “Take it! Take it all. I don’t want it here!” Will do.

I needed to build the machine to carbonize the material. I made friends with the welding teacher at the school, bought some sheet metal and made it one Saturday at this shop. Here I’m learning to cut metal the old fashion way with a hammer and ancient railroad spike – it’s difficult to cut straight but I pulled it off with some help. The metal is inexpensive and the carbonizer took us about 2-3 hours to build. I have to give it up to the guys at the shop – their extremely resourceful with the little tools and equipment they have. If I were to build it myself it would’ve take 6 hours or more. Point is, I just didn’t know how to work here – it’s a completely different style, amazing though. You’ll see what I mean in the pictures below.

Drilling 100+ holes (1″ between holes) in the metal. This will let the heat from inside the carbonizer go out into the rice husks. Check out the ram in the background :). See what I mean about the different workplace style? The ram bit my clothes as I drilled.

Two great guys – Alaghie and Dudu using an I-beam and turning the sheetmetal into the base of the carbonizer. Another moment where I said “wow, that’s how you can do that. Cool.”

Making the chimney piece to go ontop of the carbonizer base. The chimney should be high enough to be overhead so the smoke does not go directly into your face. The old driveshaft is used to curve the metal into a nice circle.

Almost ready. Just need the top chimney section.

How could this scene not turn into something fun!? So bizarre. Really excited at this point to try out my first burn. Again, another example of how a spontaneous idea half way around the world can manifest with impressive quickness if you get behind it and keep your vision up. The carbonizer looks so new here; like the Tinman. Start your fire and get a big pile of coals before setting the carbonizer over the coals.

Add rice husks – depending on the size of the machine you can do between 2-7 rice bags or so. After 8+ bags it may be more efficient to use 2 or 3 smaller machines evenly spaced under the rice husks.

This is about 7 rice bags worth of husks ontop of the carbonizer.

After an hour or so you should see the first signs of carbonization/pyrolysis at the chimney. *I also had the pile carbonize at the bottom of the pile after 3 hours, but most burns – I’ve done 4 now – start near the top of the pile like this.

Simply cover up the carbonized rice husks with other rice husks. You’ll continue doing this during the ‘early burn’ phase until the pile is about 70% black. By the way, this is my welding mentor and teacher Mr. Janha coming to help out. Lots of interest in this at the garden this day.

Here’s a close up of the rice – you can see the carbonized and uncarbonized husks. Amazing to think that the black pieces are a de-lignified little miracle of bioavailability.

Pile is over 70% black so now it’s time to stir. This is the “later burn” stage. Insert a shovel or large stick into the base of the pile and lift straight up, mixing the pile until evenly black. Don’t breathe in the smoke! It’s silica and hazardous to your health. Wear a bandana over your mouth and move quickly when stirring. When the pile is 90% black you can remove the carbonizer and the coals left underneath it in order to stop the carbonizing. You don’t want to turn the pile into ash as that will destroy a lot of the good things in CRH. I let this pile go on and carbonize a little longer.

Here you can see the pile is over 90% black so we’re stopping the burn. We removed the carbonizer and coals. Next, spread the CRH out and pour a lot of water on it. Here my counterpart Momodou is helping out – we thought the fire was done after putting 8 bidongs (yellow 20L containers) of water on it. But the next day, we found a couple small portions were still sizzling and had turned into ash. Add a lot of water and make sure it’s completely out.

When you’re all done, kneel down and throw your best ‘shaka’ as a way to feel grateful and say thank you for the opportunity to make something unique from something unused. The yield is about 60% – I burned 7 bags of rice husks and ended up with around 5 bags CRH. The burn time here was around 4.5 hours.

The process also works with coos husks. Here we’re getting ready to make carbonized coos husks (CCH). This husk was left over from the milling machine that came to the school and processed our coos. Note – with coos husks you may need to add a 10cm air inlet pipe to the base of the carbonizer as it’s a denser material and could block airflow and suffocate the fire. For us, the burn went just fine without the pipe – too well actually, see below.

Here’s a mistake :). The coos pile got a little out of control and caught on fire in several places. Maybe too much wind, or leaving some straw and sticks in the husks. Either way, you can see that this is an example of what you don’t want – thick white smoke and fast burning that turns husks into ash. Gotta say, I had a panic moment when the whole pile went up – was glad no one was there in the garden. I’m thinking “It’s ok folks; it’s natural farming.” :/

Everything ended up okay though. This is the late burn stage where I stirred the pile. This burn of 6 rice bags of coos husks was done in about 3.25 hours. We got about 4 bags of CCH.

As with CRH, remove the carbonizer and coals when the pile is about 90% black and put the fire out with water.

When your CRH or CCH is done add a little bit to your garden beds and enjoy the results.

Thanks for reading again – feel free to post comments or questions below.

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