My interactions with Biochar go back a long way, starting with a 2010 test run with EWB members building a Iwasaki style charcoal dust maker for Coed Hills Art Space. This was for a green tech day, and it straddled the line between representing fuel production from dry waste in Nepal and carbon sequestration in UK gardens. As a demonstration unit, I had to keep opening it up mid firing to show people how it was working, and so it didn’t actually produce much charcoal that day, and I’m not sure it ever did. It is very pleasing to me that Iwasaki’s website instructions are still up, exactly as I used them nearly 15 years ago! A 2013 variation on his design is presented here.
This early experience meant that when I was living and working in Vietnam, I paid attention to the (then) street food cook stoves (see image below). They were basically built around the available 19 hole charcoal briquettes. The briquettes are made from powdered charcoal (of whatever source), pressed together with a little clay soil. Once lit, each briquette would give fierce heat for an hour or two, and the next briquette would be lit by placing it on top of the old one for a few minutes. The briquettes had enough clay/soil/ash content to remain solid after use, and metal tongs were used to lift the old one out and drop the new one in. There was relatively little dust and mess compared to loose charcoal. I thought it was brilliant, but I was living a middle class life, and all my friends and family cooked on gas stoves. The charcoal was seen as poor person’s fuel, but also, because it was hot for a long time, more suitable for full day restaurant cooking.
It next came up when I was working on the BD2050 project, and writing a thesis on bioenergy potential in Bangladesh. This introduced me to the idea of the fuel ladder (see image below). I’m not fully in agreement with this specific depiction, but it shows the essential idea that people move towards the most convenient, nicest to use fuel they can afford. At the time, some of the landless labourers in Bangladesh were paid in rice straw and leaves. These are terrible fuels to cook on, as they are so calorie-diffuse it’s very hard to crowd enough together to get a good temperature fire. Turning straw into biochar does actually use up quite a lot of the straw’s energy, but the resulting fuel is so much more efficient to cook with it can be net energy saving, delivering more energy to human use. The straw and leaves produce a lot of smoke and ash, and require a lot of poking and care to keep lit, chaining someone to the stove. Compare to turning on a gas hob, and then compare to turning on and walking away from a slow cooker, confident you will have prepared food when you get back.
This fuel ladder means that there is a relatively narrow economic band/period when biochar makes sense as cook fuel. Once an area is rich enough, on the next kitchen renovation the fuel changes to something more convenient, probably gas canisters. My Vietnamese Father-in-law now cooks on an electric induction hob, with an electric water boiler, rice cooker, air fryer and extraction fan. He is somewhat ahead of my older UK North Sea Gas dominated kitchen. At the same time, experience in Vietnam shows that while the domestic cook niche for biochar is narrow, the restaurant and street food trade will extend it by a decade or more. Which is almost a pity, as there’s other uses for biochar…
One of my last projects for Arup before I left was on the successful bid for BEIS funding for , deep breath, Integration of Biochar and Enhanced Mineral Weathering Carbon Capture Technologies into Linear Infrastructure Projects. The biochar side of this had three prongs. The first was that, unlike pumping CO2 into old gas wells, biochar is very stable and easy to handle. It can just be spread on fields, or mixed in when we’re cutting and filling a new road and a century later 90% of that biochar will still be there. The second prong is that a few infrastructure projects routinely move millions of tonnes of earth, and therefore represented a fast scale of carbon sequestration that’s really hard to achieve elsewhere. The third prong is that infrastructure projects routinely involve clearing brambles, hedges and trees before work commences. This can be about access, power cable clearances and risk, or it can be the ugly side of nesting bird protection. The theory goes that it is better to clear the site in the winter to avoid risk of nesting birds stopping work in summer, even if you pay to replant at the end. It’s stupid, but it does mean that infrastructure projects often have a lot of biomass on hand, and being able to use that for carbon sequestration on the project is damage mitigation.
Our project didn’t get selected for the Phase 2 pilot demonstration, but other biochar elements did, with Black Bull Biochar; Coal Products Limited (CPL); Lapwing Energy; Ricardo UK ltd; Severn Wye Energy Agency all receiving grants to make, use, or bury biochar. Hopefully increased supply will bring down the cost, and open up a range of ‘value added products’ where the biochar is being useful beyond simple sequestration. Adaptavate Ltd and my PhD supervisor have another project looking at the use of biochar in plasterboard. Biochar is also of interest to farmers and for soil improvement. It has much of the value of woodchip for storing water and nutrients, but being chemically stable doesn’t break down. A few years back I spent an afternoon making and digging in biochar in my Father in law’s incredibly sandy garden in Vietnam.
Where do the Black Soldier Fly come in? They’ve been of interest amongst the hippies and offgrid designers for many years, moving into startup and widescale farming a decade or so ago. Essentially, they are the latest iteration on a worm bucket. Wet food scraps and waste goes in, and their maggots wriggle around and grow while eating your waste. This particular species has a few useful quirks. The first is their maggots are very large, and will eat other grubs, so you don’t have as many infestations of fruit fly or similar to deal with. The second is their maggots will choose to move somewhere dark and cool to pupate, so setting up a nice box to one side of the compost bin means the mature larvae will separate themselves off for you. The third is that they are large (again), but this means they produce a higher ratio of prawn like protein to less digestible chitin casing. They’ve been used as fish feed and chicken feed all over the world.
Now, I have an interest in that chitin casing as a feedstock bio-polymer for 3d printing. Murhula Zigabe has come up with a neat idea for another part of the system – the frass. The frass is the residual waste left after the Black Soldier Fly Larvae(BSFL) have finished feeding on a bucket. It’s a damp powdery mixture of bits they didn’t digest, dead larvae, bacteria, fungi, and fly waste. It can be composted, but it also contains some residual calorific energy as well as various carbon compounds. This makes it quite a good candidate for drying, and making biochar with. That’s the idea behind Briquettes-de-Kivu. A rough sketch of kind of system we’re talking about is below. The frass can be composted directly, and does have more nutrients than ash, but there’s also advantages to burning out viruses and bacteria in these tight loops.
Bakuva is a city on the shores of Lake Kivu. It’s eastern DRC, and just the other side of the Ruzizi River is Rwanda. Bakuva has a population of over a million people. That’s a huge volume of waste, and huge demand for convenient cooking fuel. The conservation of energy still applies though and the biochar energy available must be smaller than the waste energy input. I knew from the BD2050 project that generally waste doesn’t have that much energy to recapture. There simply isn’t enough of it per capita to power much. I’ve done an example calculation in the image below. It uses frass energy conversion data from Figure 2 of Lalander et al, a rule of thumb guess that 10% of the available energy goes into the BSFL. I’ve used the low temperature pyrolization data of sewage sludge and veg waste from Figure 4 by Kim et al. The ratios feel about right based on my previous work, but it’s work bearing in mind that sewage and veg waste varies a lot. The first paper uses uni canteen and sewage waste from Sweden, the second one uses veg waste in Indonesia and sewage waste data from this paper using Australians. The waste stream in Bakuva will be different, but hopefully not very different.
34% of the input energy makes it to the biochar. Interactive version.
In the context of the area though, reducing water pollution into Lake Kivu, and displacing wood in the fuel ladder to reduce local deforestation and (potentially) air particulate pollution from incomplete wood burning. That’s also not looking at the increased risk of flash flooding from hillside tree cutting. It would be nice to look at the value to society provided by this waste treatment. Given the additional benefits, it has to be slightly ahead of a sewage treatment plant! How much do one of those cost in Bakuva? Heineken may know the answer.
As a side note, The clay added to the block will be coming out highly meta-formed after the charcoal block is burnt out, and possibly, along with the rest of the ash, work as making a weak concrete. There’s opportunities there for additional material system circularity. If you’re interested in that, or watching Briquettes-de-Kivu figure out how to scale and collect the waste and return the biochar, Murhula is frequently chatting on Linkedin.
Bakefoldprint 
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