Crab shells in biochar?

For years, I thought it was a waste to throw away bones after eating meat, and then drive to the store and buy bone meal.  The bone meal probably came from a CAFO.  So nice to know that you're supporting animal cruelty and environmental destruction :).  I was hesitant at first because I didn't want cats, dogs, and rats to be digging up my garden.   Then I started putting my bones into the biochar. It works great and there is even research to show that it improves the biochar.

Yesterday I went crabbing.  I ate quite a bit and was left with crab shells. Aren't they made from similar stuff as bones? Calcium something? Can you tell I have zero college credits in chemistry? I was thinking that if I dried them out, they would do well to be burned in the biochar like the bones.  Has anyone tried this? Anyone with more than zero credits in chemistry have any informed opinions?  Whaddya think? A good idea or a bad idea?

Thanks,

John S
PDX OR

Not to derail from your question, but I use crab meal in my garden for it's chitin content. Chitin works well to suppress nematodes and acts as a slow release fertilizer. I did it for the first time this growing season and feel like it benefited the beds.

It's a related idea. It sounds like you just dry it out and then spread it.  Do you crunch it beforehand? Or does it come that way?

John S
PDX OR

John Suavecito wrote:Yesterday I went crabbing.  I ate quite a bit and was left with crab shells. Aren't they made from similar stuff as bones? Calcium something? I was thinking that if I dried them out, they would do well to be burned in the biochar like the bones.

I have added animal bones to my biochar pan at times, but we make our biochar in a warming pan inside our wood-stove, so more often, I just put the bones in the wood stove itself, and sift them out when we empty the ashes. Bone seems to take more oxygen and a higher temperature to burn than wood. (I recall reading that somewhere, but I'm not totally sure it was a reliable source...)

It's been a while since I've gone crabbing. I think we mostly burn them in the wood stove - same as the bones. However, in the summer, I tend to put both just in one of my more secure composts. I make sure to wrap the bones/shells in a brown paper bag, usually adding some sawdust and some finished biochar to the bag to help control smells that might attract attention. That said, I'm generally dealing with rats, racoon, feral cats and loose dogs; not coyote,  cougars, wild boar or bears.

I see no reason not to give it a try. At the very least, I believe it won't do any harm. It may just "sterilize" the shells, rather than turn them to biochar. Readings on tera preta mentions fish bones, and one source mentions tortoise bones, but I haven't specifically seen mention of shells, either bivalve or crab. Tera preta would have been fresh water areas, I think, and I don't know what creatures like crayfish etc are both fresh water and that near the equator.

I'm feeling like I may do an experiment.  I might burn half of the shells in the biochar and merely dry out and crush the other half, with the burned char. I didn't realize that people were selling crab shells commercially.  

JohN S
PDX OR

John Suavecito wrote:Do you crunch it beforehand? Or does it come that way?

It comes pre-ground. I actually sourced mine on Etsy and was pleased with the quality.

I’d probably lean towards mixing the shells in with my biochar (in a secure container) for charging purposes.  Given how bad they smell after a few days, I’d wager there is quite a bit of residual nitrogen in the shells.

Gray Henon wrote:I’d probably lean towards mixing the shells in with my biochar (in a secure container) for charging purposes.  Given how bad they smell after a few days, I’d wager there is quite a bit of residual nitrogen in the shells.

Good point!

I found some research that said this in the abstract:

Based on the TGA/DTG results, two temperatures, 350 and 500 °C, were selected to obtain pyrolytic samples in macroscopic quantities in order to characterize the morphology and surface chemistry of the solid fraction. More than 50% of the nitrogen atoms were still in the carbonaceous matrix after the 500 °C pyrolysis in the C–N=C, C–NH and 3C–N-type bonds. The ash content < 1% included hydroxylapatite-type crystalline matter. Based on these results, we may conclude that crab shells have a high potential as precursor of nitrogen-containing biochar.

https://www.researchgate.net/publication/339634058_Thermal_degradation_of_crab_shell_biomass_a_nitrogen-containing_carbon_precursor  Authors: Zoltán Sebestyén, Emma Jakab, Andrea Domán, Peter Bokrossy

The article appears to be a bit beyond my decoding abilities at the moment, but the bit I read suggested that they're considering that a lot of crab/shrimp etc shells from existing food processing plants is landing in landfill, and they're looking at up-cycling it.

I do have to confirm Gray's comments. They do smell really bad.  I'm putting them into a shed until they dry out and they will hopefully not smell as bad anymore.

John S
PDX OR

So I started the experiment.  I threw half of them in the biochar as it was burning. Guess what? Those don't smell bad anymore.  

I threw the other half under the plywood without burning them and will be running over them for a week or two.  I bet they don't smell that bad afterwards either, because charcoal absorbs smells.

We'll see.

John S
PDX OR

I'm curious, did they turn to charcoal as easily as wood or bone?  I've found that bone turns to charcoal much more readily than wood does, for whatever reason.  I'm curious how well the shells charred?  As an aside to that, with no actual evidence, I think using them either in their natural form or as charcoal is a great idea.  I'm pretty much from the school of thought that all organic matter added to the soil is probably beneficial.

I use crustacean shells from the beach in my compost, and my dogs do not seem to dig for it in my hardware clothed BEAM compost piles. Crustacean meal from the farm store is labeled as a source of calcium as well as nitrogen, and it has highly beneficial chitin too. Kelpie Wilson and other researchers have said that Nitrogen is the main nutrient lost in making anything into biochar, so this and the burning of microbes on the shells would be downsides in my view. I also doubt crabshells contribute very much to wildfire risk, and reducing fuel load is the main reason I convert woody debris into biochar;). I am confident the charred shells would not hurt anything in the garden, but I would just crush and compost them or feed them to worms without charring.

As a data point, one of the places where they make biochar in a kontiki kiln that I designed is near the coast. Look up Parihaka if you're curious about the history and significance of this community. Spending a weekend there to do a burn was such a huge privilege and a bucket list experience for our family.

Anyway, as we did the burn we talked about what they might use to inoculate the biochar, and Urs the head gardener pointed to a large bucket at the far end of the grassy space. "What's in there?" says me.

"Kina shells from new year's," was his answer. This was late February and sea urchin exoskeletons had been quietly marinating in their rotten juice all that time. "Go on, take a whiff."

Nothing prepares you for the smell of kina gone bad. On a scale of 1 to 10 (rotten eggs), this was about 80.

"That'll do," I said.

When it came time to quench everybody shifted to upwind positions and we bucketed the effluvium over the coals. I checked in with Urs about a week later and he said there was no smell at all. I imagine that the material is not very different from crab shells, so there's some prior art to go from.

Ben Zumeta said, " I would just crush and compost them or feed them to worms without charring."

This is a great idea! I bet the worms would love them, leaving the shells intact.  They are in containers so I don't think that an animal would try to break into them.  I bet they wouldn't smell bad afterwards.

John S
PDX OR

Trace Oswald said, "I'm curious, did they turn to charcoal as easily as wood or bone?  I've found that bone turns to charcoal much more readily than wood does, for whatever reason.  I'm curious how well the shells charred? "

The ones I burned were indistinguishable from the rest of the biochar, as I also had bone in there.  I couldn't smell anything from them afterwards.

The ones that I'm crushing still smell bad, but not quite as bad.  We'll see in a few days when I check again.

John S
PDX OR

One week later, the charred crab shells still don't smell, of course.

The non-charred crab shells have much less of an odor.  Charcoal is used sometimes to absorb odors, so that makes sense.  After crushing for a week or two, I drench it in my special inoculation sauce, which itself is rather "fragrant".  I'm feeling like two weeks of that and the animals won't recognize it as former meat shells.   I mainly don't want them to dig it up, looking for the hidden meat, that they think they smell.

John S
PDX OR

Isn't diatomaceous earth just crushed shells and coral?

Diatoms live in the oceans, but they are extremely numerous and extremely tiny. The biggest ones are about 1/50 of a centimeter. You might not be able to see them without a microscope.  Maybe if you isolated it on a white piece of paper.  They create most of the oxygen that we breathe.  They multiply fast in the right conditions. The ocean floor is filled with literally tons of dead diatom shells = diatomaceous earth.  They might be useful as a small part of an inoculation drench, but they wouldn't work as the only thing that you put into biochar to nutrify it.  

John S
PDX OR

Phil Stevens wrote:"Kina shells from new year's," was his answer. This was late February and sea urchin exoskeletons had been quietly marinating in their rotten juice all that time. "Go on, take a whiff."

Nothing prepares you for the smell of kina gone bad. On a scale of 1 to 10 (rotten eggs), this was about 80.

"That'll do," I said.

LOL, that's simply awesome. And yes, the worse the stinky liquid, the happier the char is to aborb it. Works every time.

John Suavecito wrote: Anyone with more than zero credits in chemistry have any informed opinions?  Whaddya think? A good idea or a bad idea?

Chemistry time!!!
Chitin, the main structural material of crab shells is very similar to cellulose...see the polymer structural differences in these chem stick figures:

One of cellulose's hydroxyls gets replaced with a simple amide.  Chitin is the same polymer that insects and fungi use.  I haven't charred crab or lobster (I am in Maine so shame on me!) shells yet, but I have charred dried mushrooms before and they do make biochar as well.  One of these days I'm going to char some mycoinsulation to see how it alters its thermal and mechanical properties.

On another chemistry note, diatom shells consist of mainly silica.

Thanks Greg,
That's exactly what I was hoping for.  My junior elementary science mind gets me thinking that the crab shells may be more like a energy boost than a chemical catalyst then. Cellulose is pretty similar to carbohydrate I think, so my sense is that it is more like food to the microbes than vitamins.  Both are useful.  The remnants of crab body would surely provide stinky vitamins.  

John S
PDX OR

Timothy Norton wrote:Not to derail from your question, but I use crab meal in my garden for it's chitin content. Chitin works well to suppress nematodes and acts as a slow release fertilizer. I did it for the first time this growing season and feel like it benefited the beds.

Yes...it additionally encourages re-population of the treated soil with chitin-degrading microbes, many of which will be suppressive to plant pathogenic fungi and possibly nematodes as you noted.  The following appears open-access at this point:    https://journals.asm.org/doi/10.1128/aem.01361-13

Yup, cellulose is a carbohydrate.  The repeating rings you see are sugar molecules that were polymerized into the cellulose and which fungi take apart to eat the sugar.  So a great powerhouse of stored energy.  The chitin is also an energy source, but then also has those amides that are a source of nitrogen that microbes can use to build proteins, RNA, DNA, etc.  But when you char cellulose or chitin they will lose those uses and will take on new superpowers that biochar has been providing in the soil for 100s of millions of years.  So much goodness that biosynthesis generates.  I'm always very sad when I see this being burned to ashes.  It feels like undoing all life's efforts to me.

John Suavecito wrote:Thanks Greg,
That's exactly what I was hoping for.  My junior elementary science mind gets me thinking that the crab shells may be more like a energy boost than a chemical catalyst then. Cellulose is pretty similar to carbohydrate I think, .....

Just to add for orientation sake, carbohydrates, like proteins and fats/lipids, are broad classifications.    Starch, chitin, cellulose, ..... even DNA and RNA....are all broadly speaking grouped as 'carbohydrates'.....and this nomenclature makes sense when you look at the structures posted above by Greg Martin.  From simple sugars to long chain polymers, carbs are fundamental to our lives---Carbon and hydrogen.....think "C&H....pure cane sugar....grown in Hawaii.....under the sun.."  (if I'm recalling the advertising jingle correctly).  Proteins run the gamut from small neurotransmitter peptides to large chains of amino acids and within organisms can have roles that are structural, enzymatic, and probably more that I'm not thinking of.  In the same way, protein-rich amendments to soil may encourage organisms with high protease activity to degrade the protein and make use of the amino acid building blocks that make up those proteins.  Fats/lipids also are comprised mostly of carbon and hydrogen, but deviate from the carbohydrate group in having little relative oxygen content, typically no ring structure to the monomer building blocks, and not generally being as long-chained as carbohydrates.  Their properties of being resistant to solubilization in water (oil droplets in your pasta water) are what allow them to congeal and 'self-organize' and form spherical shapes....like the membranes of the cells constituting all known organisms.  Once again there are specific enzymes...'lipases'....to break these down by microbes in the soil so that the basic building blocks can be re-used.

The microbial world is pretty key to all of this as noted in many prior posts and articles....

(Due to my long and 'windy' answer, Greg beat me to it! :-)  )

Greg Martin wrote:..... I'm always very sad when I see this being burned to ashes.  It feels like undoing all life's efforts to me.

But wouldn't this be a necessary part of the diversity of earth's cycles?  I've been trying to justify, in discussions with others, that if I have not been able to use all of my garden produce, it's not sad and wasteful to toss it back into the garden if it feeds the very organisms that aided in the soil fertility of the garden in the first place.  Would the biochar produced in this regard not qualify as this type of 're-birth'?

So it sounds like there could be a justification to charring half and either putting the other half in the worm compost or just directly in the other char to be crushed without burning.  Great info!

John S
PDX OR

Thanks to both of you. I just don't have the chemistry background to get all of that, and I'm sure lots of our other readers don't have that background either.

John S
PDX OR

John Weiland wrote:

Greg Martin wrote:..... I'm always very sad when I see this being burned to ashes.  It feels like undoing all life's efforts to me.

But wouldn't this be a necessary part of the diversity of earth's cycles?  I've been trying to justify, in discussions with others, that if I have not been able to use all of my garden produce, it's not sad and wasteful to toss it back into the garden if it feeds the very organisms that aided in the soil fertility of the garden in the first place.  Would the biochar produced in this regard not qualify as this type of 're-birth'?

Totally with you on re-birth via nutrient recycling.  For me, I just see burning to ash as destroying all that energy captured in the original photosynthesis in a one step drop back to the abiotic, versus in as many drop steps (or re-births) as can be squeezed into the entropy downcycle.

Tossing back into the garden is perfect, John!  The many someones who eat it there are at least equivalent to us eating it, in my opinion.