Cardboard to Biochar - A good idea? A bad idea?

I've been making biochar (out of wood and bones) using retorts made out of food cans, like what is shown in this video and mentioned in a few threads over in the biochar forum.

One thing that I've been pondering is whether or not it would be a good idea to make biochar out of cardboard using this method?

With the way it works I'm confident that anything that can be burned off, would be - but would it be useful as biochar afterwards?
How much toxic gick would be leftover on/in the biochar? Is there anything that would be released into the atmosphere rather than being burned off - and if so, what could those things be?

I don't know much about cardboard other than that I seem to constantly end up with good amounts of it - and I'd love to find a more eco-friendly way to use it, if one exists.
And thus, here I am - posing the question and hoping to hear from others! Maybe it's a horrible idea, maybe it's a genius idea that nobody has thought of before, but I wanted to hear other opinions before I consider giving it an attempt.

I tried turning a very small piece of cardboard from a pizza box (can't be recycled, and it's likely to be the "cleanest" source of cardboard I have) into charcoal as part of a larger batch I did.

I think it turned out well! It's just as brittle as regular charcoal, and has a nice snap to it. Now it's just a question of whether it's a good idea or not.

Because of all the news about micro plastics I am no longer a fan of using cardboard and newspaper as mulch and more.  I don't know what they use for ink or glue.  I don't know if those things go away in the process of making it into charcoal.

I personally burn un-recyclable cardboard and don't use the ashes from it in my garden.

J Hillman wrote:Because of all the news about micro plastics I am no longer a fan of using cardboard and newspaper as mulch and more.  I don't know what they use for ink or glue.  I don't know if those things go away in the process of making it into charcoal.

I personally burn un-recyclable cardboard and don't use the ashes from it in my garden.

My understanding is that the plastic and glue would burn off - that seems to be the case for my trial piece as well, as I can separate the three layers of the cardboard with minimal force. (although they're more likely to break as I try due to how thin they are)

In this case the cardboard didn't have any ink on it - I think soy-based ink would be fine, but heavy metal ink (is this still used?) would remain in the biochar.
I wouldn't want to test it, but I'm curious if whatever is printed on the cardboard would still be visible on the biochar if something used the less eco-friendly form of ink.

So, at least in the States, the vast majority of cardboard glues are 'safe' products being made up of starches. Inks are plant based as well. Unless you run into something super crazy glossy and vivid you should be okay.

Cardboard is made up up usually a high percentage of recyclables so there is a chance of contamination but at a very minute scale. I think there would be worse things in most soils at a higher level than what you might get out of it. However, that is everyone's personal risk tolerance to decide how much if any is too much.

I think my only thing that I can say as a negative (besides what is above) is that the biochar that you are producing is going to be on the more fine side than coarse. Cardboard is made up of essentially wood pump randomly laying on top of eachother dried into a sheet. If you are looking for the chunkier random sized biochar you get from a wood stock source it might not be what your looking for.

I'd love to hear results from trying to do some grows supplemented with this biochar.

I'm currently researching pfas in cardboard....about pfas
They are making me sad.
I've still got a lot of research to do, but hope to post a bit more about them in the next week.
My worry is that they have got into the paper recycling stream and hence could be in most cardboard for example. I don't think burning makes them go away.

these incinerators are actually just blowing the PFAS around the community in which the incinerator is located,"

source

The poison's in the dose as ever, and in small amounts maybe they aren't worth worrying about, but if a process ends up concentrating them onto your land, I think that would be not desirable.

Timothy Norton wrote:I think my only thing that I can say as a negative (besides what is above) is that the biochar that you are producing is going to be on the more fine side than coarse. Cardboard is made up of essentially wood pump randomly laying on top of eachother dried into a sheet. If you are looking for the chunkier random sized biochar you get from a wood stock source it might not be what your looking for.

I'll see if I can grab a picture later, but what I've been doing with my biochar is putting it through the food scrap grinder/drier I have to produce a fine mixture of food scraps and biochar. I think it will provide increased surface area as well as solving the concern of non-activated biochar absorbing nutrients, since most of it will be covering food scraps once the composting action starts.

Timothy Norton wrote:I'd love to hear results from trying to do some grows supplemented with this biochar.

I think I might give this a try - I don't have much growing space, but I could try two indoor potted plants (maybe radishes?) with weighted amounts of biochar, dried food scraps, and potting soil. One would have biochar made purely from cardboard, and one would have biochar made purely from wood grown around here.

I think weighing them would balance out the two as much as I can.

Nancy Reading wrote:I'm currently researching pfas in cardboard....about pfas
They are making me sad.
I've still got a lot of research to do, but hope to post a bit more about them in the next week.
My worry is that they have got into the paper recycling stream and hence could be in most cardboard for example. I don't think burning makes them go away.

I'm looking forward to seeing your post! I haven't heard about them before but it seems a bit alarming, although vague - I'll have to look into it more and see what happens (if anything) when they're combusted.

Logan, as long as your pyrolysis process gets up to a decent temperature you will be fine. No plastic polymers, including PFAS, can withstand heat in excess of 450-600C and thermal decomposition is the easiest and most complete method of getting that stuff gone. As a reference point, the average residential wood stove easily achieves 750C in the firebox, so if you're placing your can retorts in a good hot fire that's not starved for air, your end product will be safe and you won't be putting anything nasty into the air around you.

My understanding is that there is a worldwide cardboard shortage. Supply chains are messed up. Clean cardboard is highly recyclable; they just pulp it up and add it to the mix. And everybody demands as much post-consumer content as possible. So in my opinion, clean cardboard should always be recycled, not burned, wherever it is possible. The alternative is to cut and shred more living trees.

That said, I sometimes have cardboard that is not clean enough to recycle, or has grease stains, and doesn't belong in the recycling stream. It just causes problems. I certainly avoid sending it to the landfill. I have been known to slice it in thin strips down the channels for wood stove firestarter. If it has grease, all the better. It works well.

Or I guess you could char it in a closed retort. Problem is, it's high volume, low fibre stuff -- compared to, say, broken up sticks. So the amounts of char produced are relatively tiny. But I guess I might use charred cardboard on shelterbelts. Probably not on food growing areas though; there are just to many unknowns from my perspective.

As promised, here's a photo of my mixture of dehydrated food scraps and biochar - this is normally a light brown colour, but the biochar gives it a much darker colour as it gets ground up and mixed in.
Most of the larger pieces in this batch are eggshells, kumquat skins, and chicken bones - but the biochar seems well blended with the rest.

A bit off topic since it's not cardboard, but I think it might help show that I'm fine with a finer biochar - some of the biochar pieces I put in here were beef bone and stonefruit pits, and they all ground down well.

Douglas Alpenstock wrote:My understanding is that there is a worldwide cardboard shortage. Supply chains are messed up. Clean cardboard is highly recyclable; they just pulp it up and add it to the mix. And everybody demands as much post-consumer content as possible. So in my opinion, clean cardboard should always be recycled, not burned, wherever it is possible. The alternative is to cut and shred more living trees.

That said, I sometimes have cardboard that is not clean enough to recycle, or has grease stains, and doesn't belong in the recycling stream. It just causes problems. I certainly avoid sending it to the landfill. I have been known to slice it in thin strips down the channels for wood stove firestarter. If it has grease, all the better. It works well.

Or I guess you could char it in a closed retort. Problem is, it's high volume, low fibre stuff -- compared to, say, broken up sticks. So the amounts of char produced are relatively tiny. But I guess I might use charred cardboard on shelterbelts. Probably not on food growing areas though; there are just to many unknowns from my perspective.

Unfortunately, the only recycling service in my area seems to be one of those "take everything and dump it in a landfill for extra profit" types. They don't require any separation of materials, something like an empty jar of pasta sauce with sauce & mold still inside of it is fine, and any time I've tried to call to ask about what happens to the materials they take, I get vague answers and "let me have my boss call you back later" responses that never lead to anything.

The area I'm in, while rural, doesn't give me much freedom to go around and collect local materials - so even things like sticks are in short supply

Logan Byrd wrote:Unfortunately, the only recycling service in my area seems to be one of those "take everything and dump it in a landfill for extra profit" types.

Fair enough. It's better to use it for heating fuel /char than to send it to the landfill.

It seems the US prices for recyclable cardboard are 2-3c. /lb or $40-60 per ton. Not a lot, but if the recycling company had consumers sort out their cardboard into a separate bin it might be worthwhile.