Can charcoal save the world?


Terra preta means "black earth". More importantly, if less literally, it means fertile soil—created 1000s of years ago out of nutrient-starved rainforest dirt by the strange alchemy of charcoal.

No one knows exactly how Amazonian natives made terra preta, but that isn't stopping modern agriculture scientists from attempting to recreate, and build on, the successes of this ancient farming technique. Using biochar—charcoal created in an oxygen-free environment—they're hoping to improve soil quality and sequester carbon. But first, they have to deal with that pesky little thing called evidence.

Biochar really is a promising product, but we're only beginning to understand how promising it might be, where it would be most useful and, even, how it works.

The best biochar is made by pyrolysis, according to Kurt Spokas, Ph.D., a USDA-ARS soil scientist and adjunct professor at the University of Minnesota. Pyrolysis takes plants, animal manure or any other kind of organic biomass, traps it in an oxygen-free environment and heats it to around 550°C. At the end, you're left with biochar, and a mixture of hot gases and some liquids. Condense the vapors and collect the liquids and you get liquid fuel and enough combustible gas to fire up the next batch of biomass.

Advocates have long hoped that biochar—spread over farm fields—would improve soil quality and crop yields, while simultaneously trapping carbon in the soil.

The science on the second goal is a little more clear-cut than the first.

Biochar definitely does imprison carbon, and does it better than normal charcoal, said John Bonitz, a farm outreach and policy advocate with the Southern Alliance for Clean Energy. The charcoal left behind by a campfire, for instance, is chemically made up of carbon joined to lots and lots of oxygen molecules, but is primarily ash and has lost most of its carbon to burning. Like sorority girls in a slasher film, the oxygen is easily picked off by bacteria, which speeds up the process of decomposition, breaking the chemical bonds and leaving the carbon that does remain to drift back into the atmosphere.

Subtract the oxygen, however, and the carbon molecules get tough—forming ring structures that don't easily shatter and are more resistant to microbial attack, Spokas said. Lab research, done by him and others, suggests that these bonds have the potential to hold fast for anywhere between hundreds to hundreds of thousands of years. That means less carbon in the atmosphere. It's also good news for anyone who'd like to see carbon neutral, or even carbon negative, biofuel production. Of course, that's in a test tube.

"There's a whole suite of caveats that come along with those estimates because we can't mimic the natural environment in the laboratory," Spokas said.

In fact, most of what we know about biochar comes from the lab. Spokas' team is one of the first in the United States to start running tests in the (literal) field, as part of the USDA-ARS multi-location biochar and pyrolysis research initiative. However, they've only been at that for two years. Not long enough, he says, to make definitive statements, particularly when it comes to biochar's impact on soil quality. The key question—"Does biochar-infused soil lead to more crops and better soil fertility?"—is still wide open.

But there is some tantalizing data coming out of those lab tests. It seems that, by putting microbial life on slow-mo, biochar also works to trap nitrogen in the soil. Not only does that mean less nitrous oxide—another greenhouse gas&mash;in the atmosphere, it could also mean less nitrogen fertilizer applied to the ground, and less excess nitrogen leaching away into the water supply.

Spokas says field trials will make it clear what types of soil benefit the most from biochar—right now, it looks like the Midwest might not get that much of a boost, compared to, say, the sandy soils of the Southeast. Researchers also want to find out whether biochar alone will do the trick, or if a successful soil stew needs more ingredients.

"Terra preta research indicates that there was kitchen garbage discarded with the charcoal," said Bonitz. "And that would increase the bacteria and fungi activities in the final product."

Ultimately, the lack of information centers around the fact that terra preta is old and biochar, well, isn't.

"Currently all ongoing biochar research is on short time periods, maybe 10 years at most. Whereas, with terra preta, we're looking at the residual effects of 1000s of years," Spokas said. "It's a good inference that we could see some positive benefits from biochar, but we're still trying to figure it out. And if there are any short-term negative effects, we wouldn't see those in the terra preta research."

Image courtesy Flickr user Doug Beckers, via CC.


  1. I thought Black Earth was a bacterial cocktail that lived in the soil. I read in the Atlantic about 9 years ago that natives in areas with Black Earth are able to dig it up and then mix it in other areas of soil, and that it would replenish itself in the original areas. If Black Earth can be propagated this way, it could be very useful in Africa where the soil is poor in many areas.

    1. @somnambulance, according to Wikipedia it renews itself at 1cm/year. Propagation in this way is going to require patience…

      As far as Africa is concerned, you really don’t want to be importing soil biota from another continent. Importing the techniques is a much better idea, but for that we have to reconstruct them, at least, and perhaps figure out how and why they work (so that we can say whether and how well they’ll work somewhere else).

  2. “biochar – charcoal created in an oxygen-free environment”

    Isn’t this all charcoal? The remnants of a campfire aren’t charcoal, they’re burnt embers.

  3. Carbon carbon bonds via biochar is a solid idea and I expect both science and engineering will continue to evolve. But I think a more commercially viable strategy is to focus on carbon-hydrogen bonds (which are the basis of most things in our world from simple sugars, textiles, plastics, coal, oil, natgas, et al)

    Carbon is a sticky and loves to bind with other elements– but via human intervention (and help via catalysts!) it has a choice- oxygen or hydrogen.

    We all know the implications of CO2 as a waste byproduct released into the air. But why not treat CO2 as a feedstock for bioreactors (algae/bacteria) or chemical reactors that release oxygen and bind carbon to hydrogen to create a biohydrocarbon for valuable biomaterials or less profitable biofuels? Neither is an option today, but given our progress around nanostructured catalysts and engineering prowess in bio industrial and chemical manufacturing systems – both remain doable options for the future. But first, we need to get the public to understand that the world is made of (and powered by) carbon and hydrogen bonds. This is where we need to master molecules…

    Garry G
    Brooklyn, NY

    1. There’s a couple people on this, one company (at least) is Carbon Sciences.

      Maggie, describing the bioavailable oxygen molecules as sorority girls in a slasher film made my morning. Very cool topic too. Tanks.

  4. Subtract the oxygen, however, and the carbon molecules get tough—forming ring structures that don’t easily shatter and are more resistant to microbial attack

    Those are the Polycyclic Aromatic Hydrocarbons (PAHs). They are ‘resistant’ to bacteria, for similar reasons that they are ‘carcinogenic’ to humans. PAHs (Benzopyrenes specifically) were the first scientifically identified carcinogen.

    Whether the source of PAH is coal ash, or pyrolized wood, I wouldn’t eat root vegetables from PAH laden soil, and probably not leafy greens either, nor anything with edible seeds.

    So, what was the life expectancy of these people who ate food from the terra preta soils?

    1. People have been burning crop stubble for probably thousands of years yet here we all are alive and hopefully well.

  5. The guys at the Shipyard in Berkley have been messing with gassification for a while, and it generates biochar as a side effect. They sell experimentation kits through Allpower Labs that allow you to build your own gassifier to power a generator, car, etc. They even have a race where the vehicles are powered by gassifiers and other non-petroleum means called Escape From Berkeley.

    In case you can’t tell, I’m jealous that they’re on the west coast and I’m most of the way across the country in Ohio. Otherwise I’d be involved in that mess.

  6. The question is not whether biochar production is scientifically feasible or not. We have to take into account its social and environmental consequences. For the production of charcoal to be profitable in the way it is being conceived, it would need to be done at a massive scale. Such large-scale production of charcoal would require many hundreds of millions of hectares of land for biomass production (primarily tree plantations). As the unfolding disaster of agrofuels clearly demonstrates, such major land-conversion poses a major threat to biodiversity and ecosystems that play an essential role in stabilising and regulating the climate and are necessary to ensure food and water security. It threatens the livelihoods of many communities, including indigenous peoples. ‘Biochar’ and agrofuels are closely linked: charcoal is a byproduct from a type of bioenergy production which can also be used to make second-generation agrofuels, i.e. liquid agrofuels from wood, straw, bagasse, palm kernel residues and other types of solid biomass.

    1. Planting new forests. Sounds like a nightmare. Yes there’s a lot of science to be done in social/environmental issues, but not sure it sounds scarier than the existing systems. New forests wouldn’t have to be done as a monoculture.

    2. You’ve never heard of Hemp?
      Soooooo much better than trees, soooo much less destructive to the environment.

      Education. That’s the key.

    3. It is true that there is a strong need to obtain your source biomass from the wastestream!

      You can run your car off of wood chips from the fallen limbs on your land, and the byproduct is this wonderful soil enhancer. I use it in the garden and it’s pretty amazing. The bugs love it but you have to leave them some volatiles to eat, you can’t burn it until it’s pure carbon.

      You can make a biochar reactor yourself:

    4. I’m puzzled, Quilombo. In your last sentence you list a slew of waste materials that could be used sustainably to make biochar, biofuels, and/or biopower. These are the types of biomass that even biofuels critic Tim Searchinger has endorsed as being carbon neutral:

      Yet earlier in your comment you claim it can’t be done without widespread land conversion.

      I agree with your final point and I question your first point. I don’t know that land-use changes are so inevitable.

      Farmers I know are skeptical of bioenergy. Why should they convert their crop land (where they grow two or three food/feed crops per year in rotation) to produce a single crop of something (biomass) for which there is no current market? Even tree farmers are unlikely to give up the opportunity to grow higher-value dimensional lumber, pulpwood, or hardwood veneers – versus low value biomass for energy.

      These opportunity costs must be weighed and modeled carefully before we alarmingly conclude that massive land-use-changes are inevitable.

      That’s not to say we should not be aware of this possibility and work to prevent it! We certainly should develop strong policies to avoid unintended consequences. But as Snig points out, all climate mitigation experts agree, we need to plant new forests wherever we can. The question arises, what will people do with those forests?

      And as one who spent his boyhood on the farm, let’s be clear that the global is different from the local. Scope and scale are critical and often overlooked factors in these discussions.

      Sure, European biodiesel consumption once played a role in tropical deforestation. Yes, that was a bad mistake.

      However, here in the Southeastern United States, we grow 38% more trees than we’re harvesting. And blessed by climate, the trees here re-seed and grow back when you cut them. We’ve got a long way to go before bioenergy creates deforestation in GA, FL, SC, or NC.

      And speaking of social impacts, I know some forestland owners who are angry about how the pulp industry has systematically depressed prices to the breaking point. They sure would like to have another market for their wood. And in places where the mills are closing-up and off-shoring, they have no other market than bioenergy (including pellets, biopower, and maybe biofuels).

      ‘Round here, folks say that prohibiting bioenergy is the thing that would threaten livelihoods.

      In a world where all politics are local, but all carbon is global, we must proceed with care and caution. Incendiary statements don’t usually help in that process.

  7. “Like sorority girls in a slasher film, the oxygen is easily picked off by bacteria,”

    Best random simile ever.

  8. Cornell University has been studying Terra Preta and biochar for some time. Google ‘Terra Preta Cornell’ for their relevant web pages, published papers, etc.

  9. I can’t say I ever bought biochar as a viable form of carbon sequestration. In fact, I don’t really buy viable sequestration at all (except possibly leaving the oil where it is now). But as a method of improving soil fertility, it is very exciting. Relatively easy to manufacture, and unlike fertilizers and such, the nonconsumability of it as a soil additive would make it especially valuable. Improving the viability of poor croplands would slow deforestation considerably.

    Indirectly, I can see it leading to CO2 level benefits. Primarily, the mature trees that are preserved would consume more carbon dioxide than the crops in the same plot would if “repurposed.”

    The point about harmful compounds working their way into the food chain does need investigation though.

  10. Garry .
    That was beautifully put & succinct, it’s not a war on carbon, it’s a war for proper carbon accountancy. Given that, carbon can be used to the highest benefit; In the Soil.

    PAHs are not an issue, biochar’s are created at 300 -600C below the temperatures for formation of PAHs.

    The Biochar Fund deserves your attention and support.
    Exceptional results from biochar experiment in Cameroon

    Sustainability Standards are essential, the same as Soil Carbon Sequestration Standards. That said this is the only biofuel system that builds SOC with every energy cycle, for the increase of net primary biomass and food production.

    The Economics;
    Cornell Biochar Project Offset Opportunity, 09 update;
    A feasibility study is underway to assess a 1 to 2-ton/hour continuous capacity slow pyrolysis plant as part of the Cornell University Renewable Bioenergy Initiative (CURBI).

    To me, in the long run, the final arbiter / accountancy / measure of sustainability will be
    soil carbon content. Once this royal road is constructed, traffic cops ( Carbon Board ) in place, the truth of land-management and Biochar systems will be self-evident.

    A dream I’ve had for years is to base the coming carbon economy firmly on the foundation of top soils. My read of the agronomic history of civilization shows that the Kayopo Amazon Indians and the Egyptians were the only ones to maintain fertility for the long haul, millennium scales. Egypt has now forsaken their geologic advantage by building the Aswan dam, and are stuck, with the rest of us, in the soil C mining, NPK rat race to the bottom.
    see recent meta analysis;

    The Ag Soil Carbon standard is in final review by the AMS branch at USDA.
    After initial review, approval is expected this month. Contact Gary Delong . 515-334-7305 office
    Read over the work so far;

    In my efforts to have Biochar’s potential included, I have recruited several to join the list, briefed the entire committee about char when issues concerning N2O & CH4 soil GHG emissions were raised, fully briefed a couple of the 120 members when they replied individually to my “Reply all” briefs. The members cover the full spectrum of Ag interest.

    With the Obama administration funding an inter-departmental climate effort of NASA, NOAA, USDA, & EPA, and now even the CIA is opening the data coffers, then soil carbon sensors may be less than 5 years away. I’m told by the Jet Propulsion Lab mission specialists responsible for the suite of earth sensing satellites, that they will be reading soil carbon using multiple proxy measurements in 5 years. Reading soil moisture to 3 foot dept in two year with SMAP, Reading GHG emissions and biomass from the tree tops down next year when the Orbital Carbon Observer (OCO, get it:) is rebooted, to 1 Ha resolution and don’t even ask about the various spectrometric, lasers, UV, IR, lidars , ground-penetrating- radars, interferometry etc.

    Then, any farmer can click “Google Carbon maps” to see the soil carbon accounted to his good work, a level playing field to be a soil sink banker.
    The Moon Pie in the sky funding should be served to JPL

    Since we have filled the air , filling the seas to full, Soil is the Only Beneficial place left.
    Carbon to the Soil, the only ubiquitous and economic place to put it.

    Hope to see you at ISU for the 2010 US Biochar Conference

    Dr. Robert Brown , and the team in Ames Iowa are planing the next national biochar conference. The Conference will be June 27-30 in Ames Iowa Hosted by Iowa State University.

  11. To reduce a bit of the confusion here let me emphasize that the basic biochar model calls for NOTHING to be grown specifically to produce it. The intended feedstocks are waste products. Any organic waste can be converted to biochar by pyrolosis — for example, corn stover, sugarcane bagasse, wood slash left after logging or even municipal waste.

    Instead of fouling the air (through burning) or releasing methane through natural decay or leaching into the water, these “wastes” become a biochar resource that, when mixed with fertilizer (synthetic or organic), become a powerful soil amendment that enriches fertility and increases productivity.

    Crop productivity increases — drawing down more atmospheric carbon giving more food and/or fuel grown on less (not more) land. The byproduct gases of pyrolysis are captured to generate energy. The carbon returned to the soil increases long term sequestration and filters pollutants that would otherwise leach into the soil. And all this is accomplished while feeding more people.

    This is a agricultural paradigm shift from the present extracting, depleting and polluting model to one the puts waste into the right place and in the right form to restore the soil. The more and longer you do it the better it gets. Thus, it promises to achieve the dream of moving from productivity-and-depletion to productivity-and-restoration. Such a reciprocity with the earth system is the path to true sustainability for the 21st Century.

    PLEASE read more at the very thorough and informative website of the International Biochar Initiative — — and find out why Al Gore, James Hansen, Bill McKibben, Tim Flannery and James Lovelock are all pointing to its promise.

  12. Good article. The debate on biochar seems to be polarised between high enthusiasm and apocalyptic warnings (this is a comment on the wider debate, not contributions in this thread). Proponents of biochar need to recognise that, even if large-scale land use is not inevitable, it is a danger: some biochar advocates and companies are calling for the dedication of hundreds of millions of hectares of land to biochar production. Biochar may be intended for waste-stream feedstocks, but the market will follow its own logic: if fast-growing plantations are a profitable source of biochar, they may be used at a large scale. Also, waste feedstocks may be obtained from biofuel plantations, boosting their profitability and exacerbating existing problems (e.g. deforestation for palm oil plantations.)

    None of this is inevitable, and it does seem that in some areas (using biochar stoves for cooking and soil fertility on small farms in developing countries and adding biochar processes to existing large-scale farms) biochar has great potential. But including it in carbon offset schemes may give it momentum similar to the ill-considered move to corn ethanol. Sustainability standards – both social and environmental – are crucial but, especially in the voluntary (non UN/EU) carbon markets, often lacking or ignored.

    As a UNEP presentation put it: ““Biochar is new and poorly understood technology and it is likely that its effectiveness as a carbon storing strategy will depend heavily upon economic and environmental factors. Research is still at a preliminary stage and large-scale biochar is inadvisable until these uncertainties are resolved.”

    1. hey there self-propelled,

      can you give a link or specific citation for your statement that, “some biochar advocates and companies are calling for the dedication of hundreds of millions of hectares of land to biochar production”?



      1. Anon #23:

        “There is a global production potential of 594 million tons of carbon dioxide equivalent in biochar per year, simply by using waste materials such as forest and milling residues, rice husks, groundnut shells, and urban waste. Far more could be generated by planting and converting trees. Initial analyses suggest that it could be quite economical to plant vegetation for biochar on idle and degraded lands, though not on more highly productive lands.”

        Carbonscape quotes an estimate that there 930 million hectares of “degraded” land which “have a chance of being profitably reclaimed” ie planted with biochar feedstock:

        Peter Read proposes new biomass plantations of trees and sugar covering 1.4 billion hectares:
        Peter Read, 2008. Biosphere carbon stock management: addressing the threat of abrupt climate change in the next few decades: an editorial essay. Climatic Change.
DOI 10.1007/s10584-007-9356-y

        I don’t think that the adoption of biochar as a climate change/soil-treatment strategy will inevitably lead to large-scale, destructive land use. Nearly all of its current advocates are focused on waste-stream feedstocks. However, with interested parties pushing for biochar’s adoption as an offset mechanism both at the UN and elsewhere, the potential exists for abuse by other, less scrupulous players who may be attracted by offset prices.

        The quotes above refer to converting “idle” or “degraded” land for biochar feedstock use, which is both questionable and worrying, as land used by indigenous or poor communities have historically been similarly classified as a pretext to land appropriation. I have heard similar arguments from individuals involved in oil-palm production arguing that because the forest is “degraded”, conversion to plantation is justified.

        Adoption of biochar seems premature as its potential for sequestration is uncertain:

        “”Biochar certainly has potential,” says David Wardle, a soil scientist at the Swedish University of Agricultural Sciences in Uppsala. “But it’s premature to be already including it in carbon accounting. Maybe it really is an answer. But we don’t know that yet.””

        “much remains unknown about how charcoal influences the dynamics of native soil organic C and its loss as CO2. As long as this remains the case, strong advocacy for the addition of charcoal or biochar to soil to offset human-induced CO2 emissions remains premature.”

  13. This something that I’ve been interested in for a very long time.
    I imagine a wastewater treatment system that generates methane gas. Add to that a system that burns the methane and pipes the exhaust gas into a fluidized bed pyrolysis chamber (continuous feed biochar reactor), feed the sludge from the wastewater treatment process into the fluidized bed pyrolysis system to create a biologically inert biochar.
    This kind of system could provide soil amendment in developing countries and solve waste management problems at the same time. The carbon sequestration is only the icing on the cake, developing countries can be carbon negative pretty easily.
    Why am I the only one who ever thinks of these things?

  14. The Research is over a decade deep:

    This is the finest explanation I have read on the process of biochar testing. Hugh lays it out like medical triage to extract the data most needed for soil carbon sequestration. A triage for all levels of competence, the Para-Medic Gardener to the Surgeon Chem-Engineer.

    The Ozzie’s for 5 years now in field studies
    The future of biochar – Project Rainbow Bee Eater

    The Japanese have been at it decades:
    Japan Biochar Association ;

    UK Biochar Research Centre

    Virginia Tech is in their 4 th year with the Carbon Char Group’s “CharGrow” formulated bagged product. An idea whose time has come | Carbon Char Group
    The 2008 trials at Virginia Tech showed a 46% increase in yield of tomato transplants grown with just 2 – 5 cups (2 – 5%) “CharGrow” per cubic foot of growing medium.

    USDA in their 2 nd year; “Novak, Jeff” , & “david laird” ,
    There are dozens soil researchers on the subject now at USDA-ARS.
    and many studies at The ASA-CSSA-SSSA joint meeting;

    Nikolaus has been at it 4 years. Nikolaus Foidl,
    His current work with aspirin is Amazing in Maize, 250% yield gains, 15 cobs per plant;

    My 09 field trials with the Rodale Institute & JMU ;
    Alterna Biocarbon and Cowboy Charcoal Virginia field trials ’09

    Most recent studies out;
    Imperial College test,
    This work in temperate soils gives data from which one can calculate savings on fertilizer use, which is expected to be ongoing with no additional soil amending.

    The BlueLeaf Inc./ Dynamotive study are exciting results given how far north the site is at 45 degrees, and the low application rates. I suspect, as we saw with the Imperial College test, the yield benefits seem to decrease the cooler the climate. In 2008, a 20% increase in grain yield was shown and for a forage mixture in 2009 a 100% increase in fresh biomass was obtained. Other parameters showing increases with CQuest Biochar included earthworm, nematode and mycorrhizal root colonization, supporting the hypothesis that biochar may serve as a refuge for soil microbes. Surface soil water infiltration was also greater in biochar amended soil.


    This PNAS report (by a Nobel lariat) should cause the Royal Society to rethink their report that criticized Biochar systems sequestration potential;
    Proceedings of the National Academy of Sciences
    Reducing abrupt climate change risk using
    the Montreal Protocol and other regulatory
    actions to complement cuts in CO2 emissions

    Congressional Research Service report (by analyst Kelsi Bracmort) is the best short summary I have seen so far – both technical and policy oriented. .
    Recent Up Date;

    Every 1 ton of Biomass yields 1/3 ton Charcoal for soil Sequestration (= to 1 Ton CO2e) + Bio-Gas & Bio-oil fuels = to 1MWh exported electricity, so is a totally virtuous, carbon negative energy cycle.

    Biochar viewed as soil Infrastructure; The old saw;
    “Feed the Soil Not the Plants” becomes;
    “Feed, Cloth and House the Soil, utilities included !”.
    Free Carbon Condominiums with carboxyl group fats in the pantry and hydroxyl alcohol in the mini bar.
    Build it and the Wee-Beasties will come.
    Microbes like to sit down when they eat.
    By setting this table we expand husbandry to whole new orders & Kingdoms of life.

    This is what I try to get across to Farmers, as to how I feel about the act of returning carbon to the soil. An act of penitence and thankfulness for the civilization we have created. Farmers are the Soil Sink Bankers, once carbon has a price, they will be laughing all the way to it.
    Unlike CCS which only reduces emissions, biochar systems draw down CO2 every energy cycle, closing a circle back to support the soil food web. The photosynthetic “capture” collectors are up and running, the “storage” sink is in operation just under our feet. Pyrolysis conversion plants are the only infrastructure we need to build out.

    Given the current “Crisis” atmosphere concerning energy, soil sustainability, food vs. Biofuels, and Climate Change what other subject addresses them all?

    This is a Nano technology for the soil, a fractal vision of Life’s relation to surface area that represents the most comprehensive, low cost, and productive approach to long term stewardship and sustainability.

    Carbon to the Soil, the only ubiquitous and economic place to put it.

  15. The wonderful thing about this process is that it is not difficult or expensive to do, in fact there are many relatively easy ways of implementing this tech. There are several woodstove manufacturers ( and the Lucia stove) that are making biochar capable stoves, that also burn less fuel and make less smoke particulates (a huge health problem with traditional stoves and firepits).

    The one downside of gasification is the fuel burning required. There are several groups working on using solar power to provide the heat for the process, making it as carbon negative a method for creating fuel and sequestering carbon as there is.

  16. I have always used charcoal in water to grow my plants and cuttings in. I will have to take time to read this more fully but I am so glad that wonderful ANCIENT charcoal is being used and still loved.

  17. So can I just grind up some charcoal briquettes and throw them into my soil, instead of burning them in my barbecue?

  18. Pehaps some clarity on the topic could be found by testing in reality by oneself with some old barrels and veggie grilling feast guests ? And later testing whether the charcoal powder mixed with compost slurry does make new permanent soil out of sands ? I mean, testing without buying any instructions or devies… and if worried about trees being cut, why not use sun dried water weeds from overnutrified over grown freah waters ?

    Here is Do It Yourself instructions, by using scavenged materials:

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