Questions regarding pH and quench water

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sinthome

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Sep 4, 2019, 3:19:07 PM9/4/19
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Hi, I'm just getting started making biochar in a KonTiki cone kiln. I am wondering if there are known uses for the highly alkaline quench water or do most people just dump it out? Also is it necessary to add pH lowering agents to the biochar or if I just let it "charge" in urine, compost or similar fertilizer for a few weeks will the pH approach 6-7 on its own? Thanks.

Nando Breiter

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Sep 4, 2019, 4:44:16 PM9/4/19
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I would suggest to reduce the particle size as much as you practically can, and then either co-compost it aerobically, or perhaps ideally, add it to a vermicompost setup.

Composting worms have a gullet like digestive tract, like a chicken, and will consume biochar the size of sand particles or smaller to grind any decomposing biomass they consume into smaller particles. In the process of passing through a worm's digestive tract, the char becomes deeply embedded in the evolving humic matter, is further ground down in size so that it easily aggregates with other evolving soil elements, and becomes coated and embedded with organic matter. It's pH will be neutralized, as worm castings tend toward being slightly acidic. 

A few commercial vermicomposters add biochar to their worm feed, and there have been some research showing that biochar significantly increases composting worm populations and particularly worm cocoon production. There is also research indicating that worms in the Amazon consume char and ash from forest fires, which speculates that worms might have played an essential role in the formation of Terra preta. One of the unique aspects of Terra preta is how deeply integrated the char particles are in the soil matrix, and how small they are, visible only under a microscope, largely bound to clay particles via a calcium cation bridge.

Reducing the particle size increases the available surface area of the char. Fertility effects largely depend on exposed surface area. Reducing the particle size by half will double the exposed surface area. Imagine a cube of char 2 cm in each dimension. 6 faces of with an area of 4 cm2 each totals 24 cm2 of surface area. Break that cube down to precisely half its size, and you get 8 cubes 1 cm in each dimension. Each of the smaller cubes has a surface area of 6 cm2. 8 cubes x 6 cm2 = 48 cm2. 

Crushing biochar to the size of sand particles is as effective as adding significantly more biochar of a larger particle size to a plot, so it is well worth the time. Starting with one 2 cm cube, reducing the size to 1 cm provides 48 cm2 surface area, 5 mm / 98 cm2, 2.5 mm / 196 cm2, 1.25 mm = 392 cm2, 0.6 mm = 800 cm2 surface area. 0.6 mm char particles will have 16 times more exposed surface area compared to the same amount, by weight of 1 cm char particles. Once they pass through a worm a few times, they will be even smaller. 

All this crushing and vermicomposting takes time, but given that however you obtain it, biochar is expensive, I'd rather take the time to multiply the value of the biochar I can make or buy, than rush ahead to get it in the soil as soon as possible. 
Pongeetal.2006.pdf
BiocharAmendmentForVermicomposting.pdf
Hagemann2017OrganicCoatingonBiochar.pdf

sinthome

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Sep 4, 2019, 7:26:25 PM9/4/19
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Excellent reply, thank you. I do have about 200 sq ft of worm beds currently, so this is great news. I had read some anecdotal report on the reddit biochar forum by someone who arguef confidently that adding biochar in any sizable quantity had a detrimental effect on their worm populations, so I wasn't planning on doing this. But perhaps the particle size is key?

My plan for crushing the char was to run over it repeatedly with a tractor, but maybe this will not create small enough grains? What would be the best way of reducing the particle size without generating a lot of dust and extra labor? I am doing batches of around 2-3 cu yds at a time, so it is a lot but doesn't justify a large expensive grinder for me.

I'm still interested in using the highly alkaline quench water in some way, if anyone has experience with this please lmk!

Nando Breiter

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Sep 4, 2019, 8:08:58 PM9/4/19
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To crush the biochar, you could use a PTO driven hammer mill, if that would work for you, of the type that is often used to crush grains for feed. Look for a used hammer mill in your area. 

To keep the dust down, wet the char, and definitely wear a good mask.

In regards to the proportion of char to worm feed, check for published research, experiment with small section of your worm bed first, give your worms a choice. It may be that the char will need to compost for a bit before the worms will ingest it. 


CarbonZero Sagl
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sinthome

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Sep 4, 2019, 10:08:31 PM9/4/19
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Hmm, yeah I have been casually looking for a feed grinder, but there isn't much grain production in this area, so I haven't seen any around. I will experiment with a small pto driven chipper/shredder and see how well it performs.

Nando Breiter

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Sep 5, 2019, 5:47:42 AM9/5/19
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Please give us an update once you've had a chance to experiment. I've seen a video where someone used a small scale compost shredder to pulverize char, and it seemed to work rather well, but the video didn't go into any detail on this aspect. It was just a short clip of a few seconds within a longer video about making "terra preta".


CarbonZero Sagl
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