Cardboard in biochar?

I have used cardboard in biochar for years.  Lately I've been thinking about what sort of glues might be in cardboard that we should worry about. I normally just use it to get the fire started.  It's a good bridge between paper and sticks.  I only use brown cardboard, and it is usually corrugated.  I don't know if that makes a difference.  I figured that the stuff with colors might contain some nasty chemicals like cadmium or something, so I've avoided it.  I was kind of surprised to find out the negatives about using plywood to crush the biochar, and I don't do that anymore, so I wanted to check with others about using cardboard. Whaddya think?

John S
PDX OR

My knowledge is for cardboard you would find commonly in the United States/Canada.

The vast majority of cardboard is held together with starch based adhesives. It is considered eco friendly (and just so happens to be very cheap for manufacturers to use) and easy to clean up. There are additives commonly used such as borax to help increase the starch's effectiveness.

Avoid shiny or heavily printed cardboard. The waxes and inks found inside of it MIGHT be of worry. I don't know specifics outside of you might be looking at synthetic compounds so best utilize brown kraft cardboard.

Good info, Timothy.  I have used borax on purpose in my yard, as our soils here in the PNWet tend to be low in boron. It's an inexpensive source.  After I did that fertilization, one of my trees bloomed for the first time ever.  It has continued to bloom since then.

John S
PDX OR

I have made whole barrels of biochar from mostly cardboard and paper.  The beauty of it is that it crumbles/pulverizes easily in the hands, and it absorbs inoculants like urine well too.

I'm not convinced complete purity is possible, but I do try to avoid nasties in my food growing areas.

99% of my cardboard gets recycled, which is the best option where available. The remaining 1% has too much garden dirt or other stuff and it will degrade the recycling stream. I cut that into long strips and use it for firestarter in my outdoor stove. I think I would use small amounts of "pure brown" cardboard to start a char burn -- the dilution factor is enormous.

Personally, I wouldn't use char made from mostly cardboard/paper biochar in my growing areas. There are too many unknowns and too many potential chemicals that the char process cannot destroy (especially in coloured cardboard and paper).

I've been thinking a lot about using waste paper to fuel biochar creation. I would agree that you probably don't want much cardboard/paper IN your biochar, but in a retort system where fuel and char are separate, I could see it working as a  way to use a low-value material as fuel.

Some paper products can be recycled, but many cannot. I'm thinking pizza boxes, bags, etc. Even those things that are recyclable, such as cardboard, might be good to use. We have single-stream recycling here, meaning the cardboard and paper get mixed in with the glass, metal, and plastic and then sorted at a central facility.

I have to imagine an awful lot of that good paper gets wet, contaminated, or otherwise rendered unrecyclable. Even if it is recycled, it goes on a number of rides on a diesel truck to get through the process. Burning it locally to convert higher value biomass into char would likely be comfortably carbon neutral. Clean paper ash could even be used to lower the PH of soil (colored or glossy cardboard ash should likely be landfilled).

I currently make my char in a trash can in my fire pit. For burning waste paper/cardboard, I'd need a contained setup so the cinders wouldn't blow all over. But it feels like a potential way to leverage waste in a very carbon-friendly way.

Mike Farmer wrote:I've been thinking a lot about using waste paper to fuel biochar creation. I would agree that you probably don't want much cardboard/paper IN your biochar, but in a retort system where fuel and char are separate, I could see it working as a  way to use a low-value material as fuel.  

I agree -- if it's not highly recyclable, it's better to use it as fuel than bury it in a landfill.