Charcoal as a media

[Paul Letby]

Hey guys, I'm going to open this up for debate, as things are getting a little off topic on my personal system discussion.  There have been questions as to the safety of charcoal as a media, and I'm sure there are questions out there regarding it's environmental impact.  So let's let fly with the questions and hash this out.  I'm definitely not the expert here, and I am hoping George will weigh in on the issues. 

 

Personally I decided to use charcoal based on the fact that I have free access to wood, and needed a cheap and light media for use in a GB supported by a light stand that's not meant to support a lot of weight.  I know that activated charcoal is used in aquaria as a filter media, so I'm pretty sure it's safe.  That said we all know that many things from tropical fishkeeping don't transfer to aquaponics very well.

[Jon Parr]

Well, so far this is it. The Barrel retort lays on it's side in the larger arch, and the fire goes below in the small arch. The door will cover only the larger arch. Yet to be built is the pizza oven on top, and the exchanger above that. Soon, dammit, soon. I need to get this done, because I need copious amounts of char, and pizza...

[Vlad Jovanovic]

Very, very cool!

You know... you are going to build the micro-brewery that's supposed to go along with that...right..? Jusayin...

Nice work Jon.

[Jon Parr]

Hehe. That's what the hops planted 20' away are for...

[Bob Campbell]

That's amazing!  So much benefit from each burn.   I'm in the process of building a rocket mass stove for my greenhouse.

I'm still scrounging for materials, but came up with a cheep flue tunnel using 55 gallon barrels cut lengthwise with the end removed.  I can buy them for $5 each which is a whole lot less then 8" flue pipe. 

Jon Parr said:

I like it, Paul. A doused fire always yields some charcoal.

Bob, sorry I didn't see your question in your last comment until just now. I used a TLUD for my first few runs, then made an indirect retort. Now I am nearly finished with a retort/pizza oven/rocket stove/water heater. Sound hot? That's because it is hot! At the bottom of the contraption is a small rocket stove. The exhaust goes around a sealed barrel retort full of chips. The retort has a single pipe vent that is plumbed back to the rocket fire to burn the syngas. The heat/smoke escapes above the retort into the rear of a dome pizza oven, refracting heat to the cooking surface, and then the smoke goes thru a heat exchanger to heat my 7K gallon FT. The exhaust should be cool enough at that point to condense out the water, called wood vinegar or smoke water, which is beneficial for germinating seeds and kills pests. Hot damn, that's pretty cool. I still have to make the door for the retort area, dome the pizza oven, and plaster the whole thing to make it pretty. I plan on having it finished for my next round of workshops on the 15th

Come check it out.

[George]

Way cool.  Please post a video of the operation.  I'll say this about making charcoal - it's fun.

[Jon Parr]

Will do, George. I'm overdue to the community here to post progress on a number of projects. I'm out of town for a bit, more soon

[Jesse Hull]

Jon, is there a reason you didn't use soft refractory brick on the inside?  

You'd get better heat up times and an increased thermal shock resistance due to expansion/contraction properties.  Hard refractory (kiln) brick is not as insulating and can quickly crack due to the coefficient of thermal expansion.

Now that the thing is built, I can still suggest some things that will lengthen the life of the structure if you think it's warranted.

[Jesse Hull]

Although activated charcoal (oxidized charcoal) has more pores for adsorbing chemicals, regular charcoal will still do it to some extent.  

Eventually, it's ability to adsorb will cease, but I wonder if you'll have a longer cycle-up time due to the charcoal adsorbing ammonia, nitrate, etc.  That said, the microbes populating the charcoal might have better access to it then.

[Vlad Jovanovic]

Hi there Jesse. If I've understood the topic at hand correctly, the SSA (specific surface area) of bio-char created at "low-ish" temps (circa 400C) like Jon's apparently is, isn't really analogous to activated charcoal/carbon (while circa 900C temps would be). Process temperature seems to be the main factor governing surface area in such endevours. I bet a nice 'low' temp bio-char is much more suitable as an AP media than a 'high' temp activated carbon scenario...or as a 'control release' of fertilizer nutrients in soil...

  

[Bob Campbell]

I've watched a bunch of how to videos, and it appears the higher the temperature it is cooked at the more friable the charcoal becomes.  The higher temperature would probably increase the SSA (specific surface area), but it appears that it may also be too fragile for media where you are likely to push it around while inserting transplants.  One video made reference to only a wisp of the wood remaining in the retort.  It looked like he could crush it into dust..

Vlad Jovanovic said:

... I bet a nice 'low' temp bio-char is much more suitable as an AP media than a 'high' temp activated carbon scenario...or as a 'control release' of fertilizer nutrients in soil...

  

[Vlad Jovanovic]

Right-O Bob. While higher activated carbon type temps do increase SSA (which is after all ,what we are after in a bio-filtration media) in the case you brought up, it comes at the price of physical properties which eventually (quickly from your description, it would seem) result in low hydraulic conductivity...which certainly wouldn't seem appropriate for most biologically active systems, particularly one with as much solids to foul up percolation as AP would have (kind of why most folks don't use fine sand even though the SSA is incredible). Low-temp bio-char seems like the way to go...

Hmm...I wonder how that would play out in say a pee-ponic system with no solids to deal with...Still I suppose such a low void fraction/small particle size (due to fragility and 'crumbly-ness) would be a bummer even then (eventually), because of dead root particles and bio-slime...Certainly not as bad as it'd be in AP though...still not desirable IMO, and probably not worth the higher SSA...

[Bob Campbell]

I started my bio-char about 4 weeks ago.  The pH has continued to creep up, but nitrification has not fully settled in either.  The large chucks of charcoal that I bought at Cash and Carry were most likely made at low temperature, but I'm pleased with the durability of this charcoalt.