pyrolysis as remediation of persistent herbicides

Does anyone have experience or knowledge of biochar/pyrolysis breaking down the chemicals being used as persistent herbicides becoming more and more common in hay and grass for weed control?

I do not. However, Redhawk discusses letting potentially poisoned staw/hay age for safe weed suppression in this thread.

Jack, it's a good question.

As Redhawk notes in the thread above, short term herbicides are broken down through aging and natural biological processes.

The long term super-persistent herbicides have an extremely stable molecule, and I would be very careful about trusting a simple aging and bioremediation process.

Personally, I suspect that pyrolysis temperatures will break down most things. That's only my gut feeling, though. I'll poke around and see if there is hard data to support that.

Jack, that's a really nice idea!  Putting my chemistry hat on, no hydrocarbons will survive the 1000F temperatures of biochar making without being transformed into something else.  It makes me wonder how many cycles of charring you'd have to carry out, though.  Some of the pesticides must still be present in the roots and soil so I assume you'll have to do this over and over again in order to eliminate the vast majority of the pesticides.  

I would think a good way to experiment with this would be to take the biochar as well as compost made from a sample of the grass that grows and do growth studies with a crop that is strongly affected by the pesticides, such as beans.  The biochar sample will demonstrate if it's safe and the compost sample will demonstrate when the soil becomes safe enough to allow for crop growth.

Some follow up, as I was at work and most of my post got deleted before I hit submit.

I did not buy into the persistent herbicide issue, until a close friend shamed me into a little more research.  Eye opening to say the least.  I have access to dozen (hundreds?) of cubic yards of animal waste, essentially free.  I have an auction barn nearby.  They scrape out their pens on a regular bases and pile it out back.  I am reluctant to approach them to help them with their 'problem' because the animals making the manure could be on any diet or source of hay.

My research has made me reluctant to bring any of this onto my pasture.  I hope I can find a way to pit kiln the manure into a biochar.  Manure is not the best feed stock and will likely need a bit more heat added.  If it does break down the chains, then I will have all the char I can handle.   I agree with the sentiment that not many chemicals can stand up to 1000F or better.  

I did some searching on the webs and found a lot of scientific papers about biochar and pesticides.  Most are written with the chemical manufacturer in mind and says the results are mixed; biochar in the soil both helping and hindering the breakdown depending on a number of factors.  What I was not able to find was a scientific paper that talked about the PROCESS of pyrolysis breaking down the chains.  Experimentation is in order.  I will have to find a corner out of the way char some cow pies and make a test bed this spring.

I have observed that cow manure piles often have a lot of weed seeds mixed in (undigested) or blown in. If a manure pile sits and ages for a year, and by next fall it is covered with every variety of broad leaf weed, it may possibly be worth a closer look.

Jack Edmondson wrote:  What I was not able to find was a scientific paper that talked about the PROCESS of pyrolysis breaking down the chains.  

To get you started:  https://upload.wikimedia.org/wikipedia/commons/8/81/Processes_in_the_thermal_degredation_of_organic_matter.svg

So, when you light something on fire, there's a bunch of chemical mechanisms happening that are driven by application of HEAT and whether or not there is an OXIDIZER present.

Evaporation/Vapourization is entirely driven by heat. When matter is heated enough, the bonds between the molocules (and eventually the atoms, hello Magma) wiggle free and turn it into a liquid - and then a gas. They float away on the wind.

Oxidation is when oxygen can attach to the molecule & alter it. Oxidation is a big driver of decay, even within our body. "Antioxidants" are important in our diet because it fights off oxidation of our essential molecules and cellular structures. This is the same for any organic matter. If you apply enough oxygen & heat, then not only will the molecules/atoms become wigglier, but oxygen is able to attach to it easier.

When a house burns down, aside from the heat itself, the airborne evaporated vapours and the gaseous oxidized chemicals are the most deadly and cancerous things a firefighter can expose themselves to.

MOST organic molecules will break down or vapourize at the temperatures required to create Charcoal from organic matter.
Salts and Minerals will take a higher heat, OR will require the application of an alkelai or an acid + heat to chemically react with it & change the bonds. (Vinegar or Lye)
Acids & Alkelis are harder to apply to material in-bulk, but they can be made organically (Vinegar from fermented fruits, Lye from hardwood ash boiled with rainwater).

The long-lasting herbicides you're worried about are probably only long-lasting in normal outdoor conditions.  Applying heat, or heat + big pH change should be able to do the trick. If you give me some names, I might be able to help you track down more specific info.

I do know that glyphosate, Roundup's key ingredient, is violate when exposed to heat & would readily break down if you charred it.

Other salts, like Aminocyclopyrachlor Potassium Salt, I have to look up.
It looks like it isn't reactive enough to degrade completely in a hot-compost pile, though those generally only get up to 105-115 degrees F.  Charring temperatures greatly exceeds that.
According to the safety data sheet for Aminocyclopyrachlor, when it's on fire firefighters are advised to NOT spray it with a water jet as it will spread the fire. This tells me that, at high temperatures, the chemical becomes reactive to water.  http://cdn.chemservice.com/product/msdsnew/External/English/N-13826%20English%20SDS%20US.pdf
The 'Initial boiling point and boiling range' is set at 810 degrees F.
Charcoal is formed at around 750 degrees F, upward of 900 degrees. Past 1,000 degrees F, the char itself can ignite.

The Safety Data Sheet also shows under 'Incompatible Materials', Strong Oxidizing Agents are listed.
One example of a strong oxidizing agent is hydrogen peroxide.

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Summary:
Check the Safety Data Sheet of each of those herbicides. They should have things like boiling point (the temp where evaporation/vaporization occurs) and materials that could possibly react violently or significantly degrade the chemical's efficacy.
It also lists if it's explosive, and if the vapors or skin contact is harmful.

You'd be able to get rid of Aminocyclopyrachlor specifically using charring-levels of heat, BUT you'd have to remain VERY FAR AWAY from that fire, because the vapors are going to be toxic as hell.
You could also try dousing it with BULK amounts of hydrogen peroxide, OR dump the soil into a huge tank of water & run an electric current through it to promote rapid oxidation.
I haven't crunched the numbers to see what chemicals you'd get off those reactions, so I don't really recommend them.

In conclusion: Yes, charring the cow patties properly should create herbicide-free char.
HOWEVER!!! Do not breathe in the smoke or vapors, and thoroughly wash yourself with soap after exposure to the smoke/vapors if you have serious concerns about herbicide being present.

I've recently become curious about this as well.  I recently read a paper that investigated using different types of agricultural residues and pyrolysis temperatures to increase CEC in "weathered" brazilian soils.  As I recall, they had the largest increase in CEC using dried coffee husks pyrolyzed at 350C for 30 minutes.  I also recall another paper showing where palm fronds pyrolyzed at an estimated  320C in a cone pit showed significant improvements as well.  This was in an area where I assume palm kernels are grown for oil/fat production.

Here in SC, I would have to source different materials to use.  I've been thinking about just collecting yard waste from all the neighbors, but theres probably >98% chance that persistent herbicides will have been used in the source area.    I'm thinking about experimenting with using palmetto fronds as they're somewhat plentiful here.  Perhaps I can experiment if I can find some material from known un-poisoned land, vs. the stuff that I get from the neighbors.

The little information that I've read so far seems to indicate that certain non-woody "high ash" K? biomass sources are best for improving CEC in sandy, poor soils like what we have in the lowcountry, though it must be added gradually over the course of several years to minimize severe PH increases.

This information is really helpful for me as well as I've been considering a similar scenario.

I live in an area with a lot of Tyson production. And while I haven't exactly found *free* chicken litter yet, but I could get massive truckloads of the stuff delivered relatively inexpensively. And I've wondered about eventually doing this, but I've been curious about the cocktail of various chemicals which may have been in the chickens themselves as well as their feed. And that has led me to wonder about whether pyrolysis would break apart those chemical bonds.

It also led me to wonder whether the Tyson meat processing plant would ever be willing to let me have waste bones or even carcasses or whatever they can't use to turn into biochar as well... which again raises some similar questions.

For that matter... I wonder if there's any chance of getting eggshells from them? Or maybe they feed those back to their chickens or something? Maybe the other waste stuff gets turned into dog food (or hot dogs?)? Lol... I don't know, but if they're just hauling any of this stuff off, I might as well be the guy that figures out a productive use for it, right?

John, consider that chickens are more likely than cows to be contaminated with arsenic, which is an element, and would concentrate rather than alter in a charcoal production process. Cows are given all kinds of horrible "medicines" too but they are large animals and the concentrations are less.