Anyone making biochar from seaweed?

Seaweed Is Growing Out of Control. We Can Turn It Into Biochar and Jobs.

At Waste Free ’23, we focus on upcycling waste fast and reducing poverty while doing it.

Across many coastlines, invasive seaweed is piling up. It blocks fishing, damages tourism, smells when it rots, and releases methane. Scientists are warning that seaweed blooms are expanding worldwide and may represent a major ecological shift: https://ethicalmarkets.com/scientists-warn-of-regime-shift-as-seaweed-blooms-expand-worldwide/

Removing it costs money. But it is also a resource.

We reviewed the research. Seaweed can be turned into biochar. Studies show:
- Good char yield
- High nutrients like potassium, calcium, and magnesium
- Alkaline properties that help improve acidic soils
- Strong potential as a soil amendment

This is not just carbon storage. It is nutrient recovery and soil improvement.

At Waste Free ’23, we use a fan assisted TLUD that:
☸ Reduces smoke
☸ Improves airflow
☸ Increases efficiency
☸ Produces better quality biochar
☸ Is low cost and locally buildable

See here: Building Design https://wastefree23.org/biochar/how-to-build-a-solar-fan-assisted-cone-tlud/
                Guidelines to use it https://wastefree23.org/biochar/use-a-fan-assisted-cone-tlud-to-make-high-quality-biochar/

We have completed and ongoing projects showing strong results. More updates soon.

If you live near a coastline with seaweed problems, this is an opportunity. We have practical, low cost tools and can collaborate on pilots and grants.

What do you think?

If you want to explore this, email us at wastefree23@gmail.com

I know that I read about some sort of outside the box use for seaweed in the Caribbean which the locals came up with exactly due to the problems you're talking about. I think they were making building blocks out of it!

We love to say in Permaculture "the problem is the solution" and biochar is certainly one option.

One concern I have is getting the seaweed dry enough that the charring is as efficient as possible. Do you do anything special to manage that?

A second concern is that I've heard locally that burning salty wood in a wood stove damages the metal. It sounds from your description that you're burning it in a cone, so that may be less of an issue than a wood stove. How many cycles have you tested your system with, and has there been any sign of damage?

I definitely agree in principle. This is a good option for areas where pollution is an issue.

Some of the other good uses are composting, animal feed, human feed, and some of the suggestions in these links:
https://www.greenislandcreative.com.au/blog/5-uses-for-seaweed
https://earthbound.report/2021/04/15/10-different-uses-for-seaweed/

I find it interesting that the Caribbean and some other places are struggling with an excess of seaweed, and in my region, we're trying to encourage the recovery of our kelp forests. Kelp is a key link to keeping the entire northwest coast ecosystem healthy.

I did a little research and found this article: https://www.epa.gov/habs/sargassum-inundation-events-sies-impacts-human-health

They are very concerned about exposure to it:

Exposure to hydrogen sulfide and ammonia, produced during the decay of Sargassum, may also cause mild to serious health effects, including respiratory, cardiovascular, and neurological impacts. Additionally, Sargassum accumulates and leaches pollutants, including pesticides and heavy metals like arsenic, which could harm human health and the environment.

A local said that burning it could be very dangerous if you breath in any of the smoke. Some of the dangers from the chemistry between sulfur, chlorine and fire.

I suppose the real solution is for humans to quit polluting our oceans!

Locally they make sea soil.  Put the ethically harvested seaweed in a big pile.  A few months later it's ready to add to the garden.  Nothing quite as amazing as sea soil for healthy veg.

The biochar I've tried is good, but nothing as good as composted seaweed...and no fuel needed to heat the compost either.

I am not a fan of biochar so I feel a better use would be to use seaweed to add organic matter to soil.

Next best use would be to eat it as there are lots of vitamins and minerals.

As others have said, the high moisture content of seaweed would suggest that composting may be better than char.

I've also read about potential heavy metal and other contaminants...so batches would need to be tested first, especially if it was to be used on food crops.

I suspect a controlled pyrolizing of dry material will be safer for human health than uncontrolled decomposition.
I think the compost would have the same problems of being contaminated with heavy metals, but at least some of the other pollutants will be destroyed during the charcoal making process

The Tlud design and burning instructions seem very well done, but I can't find the details on how to use seaweed as feedstock

To prep the seaweed,I would get a 55 gallon drum, perforate the bottom and sides, elevate it for air flow, stick a sheet metal cylinder down the middle,and fill it with seaweed.
After it dried a little, I would pull out middle cylinder
After it dried completely, I would break it up into bits, and use it the same way as coffee husks.

If I had this problem / resource, I think I would add biochar to the composting seaweed, and maybe a layer on top too, to capture all that lovely ammonia and sulfur. Free fertilizer and inoculated char. Bingo!

The sea soil is tested from time to time as it's a commercial operation. Apparently, the invisible beasties that like to compost the seaweed also break down the things that would become toxic if burnt.  

I read a paper on the chemistry about 25 years ago. The temperature the seaweed is broken down has a big influence.   It either needs to be fairly cool like a hot compost pile or extremely hot, and then it's gassified and the gas needs to be captured and somethingsomething it was an extremely boring paper even if the topic was interesting.   Perhaps science has discovered new things now.

All i know for certain
1. Sea soil is the only soil amendment that I found worth the cost of importing to the farm.  It works.  I've used it in the garden since the 1990s without any problems. Family has used variations of it since the late 1950s without issue.  Composted seaweed is a common historical soil amendment.

2. Biochar is lovely, but in my tests, doesn't show enough benifits for me to spend money on again. I might make some at home, but there is plently of dry material to collect that doesn't risk offing toxic gas when heated.  I also feel a bit uncomfortable with the fuel used to heat the char in an industrial setting.

r ransom wrote:

2. Biochar is lovely, but in my tests, doesn't show enough benifits for me to spend money on again. I might make some at home, but there is plently of dry material to collect that doesn't risk offing toxic gas when heated.  I also feel a bit uncomfortable with the fuel used to heat the char in an industrial setting.

I'm not aware of any commercial biochar manufacturing nowadays that uses fuel other than the biomass itself to drive the process. Pyrolysis releases more heat than it requires, so most of the time we are looking for good ways to use that heat, e.g. displacing fossil energy. Or if the feedstock is wet and the kiln needs it to be dry, then that might be where it goes.

The business case for making lots of biochar disappears if you're paying for energy instead of making it. And one of the reasons it's great to make it in a home fire is that you get the benefit of that energy. Plus, sometimes (like today) you get lucky and get colours besides black.

William Bronson wrote:
I suspect a controlled pyrolizing of dry material will be safer for human health than uncontrolled decomposition.
I think the compost would have the same problems of being contaminated with heavy metals, but at least some of the other pollutants will be destroyed during the charcoal making process

I'd worry about two main things if I was trying to make biochar from seaweed. I've done small amounts and these are the problems:

1. You have to dry it first. If there's heaps of it washed up on a beach, good luck with that (I've seen lots of photos of Caribbean islands where this problem has been pronounced in recent years). It's going to start rotting first unless you've got a place to put it and machinery to take it there and spread it out, or an actual drying oven of some sort. And all of that will take fuel, and therefore money.

2. You have to get rid of the salt, usually by rinsing. If it rains a lot and you've spread it somewhere that water can drain away, this will take care of some salt. But I've tacked up some thick and leathery pieces of kelp to the fence and left them out in the weather for an entire year and they still tasted salty (good, though, aside from almost cracking a tooth). Salt is bad because in the temperature range at the lower end of pyrolysis, the chlorine contributes to the formation of dioxins and we really don't want those around. Salt in the biochar itself isn't a dealbreaker because it can be rinsed out.

Phil Stevens wrote:... It's going to start rotting first unless you've got a place to put it and machinery to take it there and spread it out, or an actual drying oven of some sort. And all of that will take fuel, and therefore money.

Is it just my imagination, or do things which are salt contaminated take a lot longer to dry? This may be because I grew up with fresh water, and am now by the ocean, so the humidity is much higher in my new location, and that, rather than the salt, could be at the root of the observation?

I'm not sure this would work in my ecosystem, but this is the concept I read about some time ago:
https://mexiconewsdaily.com/news/mr-sargassum-built-13-houses-with-seaweed-blocks/

Essentially, the fellow is making bricks:

made from ground sargassum, limestone and other organic material. The sargassum content of each sargablock is about 40%.

He's using these blocks to make low-income housing.

I think brick making might be a better use even if the sargassum content is only 40%

I make a lot of biochar, but I would just mulch with seaweed or kelp. That is if it hadn’t disappeared locally in oceanic heat waves last decade.

There are a lot of great questions and comments here. I use seaweed in biochar, as I have posted many times here in this forum.  I have also used freshwater algae that was overgrown in a lake. They are both highly nutritious.  As many of you mentioned, I don't use it to burn.  I make the biochar out of wood, mostly because we have a ton of extra wood here in the PNW USA.  I use the seaweed to inoculate the biochar after it has been burned and crushed.  I am able to lay it out flat and dry it.  Then I put it in 5 gallon buckets when it's dry. I just add some when I start the inoculation process, along with many other low cost/free nutritious amendments.  Remember, even if there are small amounts of toxins, charcoal and biochar are used as filters to clean, remove and store those chemicals where they won't get into the food.  This is even done commercially.  When I tested my soil, it was low in sodium, so I don't worry about the salt.  If I lived in a highly alkaline desert location I might.  

John S
PDX OR

What happens to all the salt when the seaweed is composted?

I think that it just makes a chemical reaction with the other nutrients in the biochar.

John S
PDX OR

John Suavecito wrote:There are a lot of great questions and comments here. I use seaweed in biochar, as I have posted many times here in this forum.  I have also used freshwater algae that was overgrown in a lake. They are both highly nutritious.  As many of you mentioned, I don't use it to burn.  I make the biochar out of wood, mostly because we have a ton of extra wood here in the PNW USA.  I use the seaweed to inoculate the biochar after it has been burned and crushed.  I am able to lay it out flat and dry it.  Then I put it in 5 gallon buckets when it's dry. I just add some when I start the inoculation process, along with many other low cost/free nutritious amendments.  Remember, even if there are small amounts of toxins, charcoal and biochar are used as filters to clean, remove and store those chemicals where they won't get into the food.  This is even done commercially.  When I tested my soil, it was low in sodium, so I don't worry about the salt.  If I lived in a highly alkaline desert location I might.  

John S
PDX OR

Great point John, I do use kelp to inoculate biochar as well. Good to hear algae works as well.

using seaweed to inoculate biochar rather than trying to burn it directly makes way more sense to me, the salt and moisture issues alone would be a nightmare. I just compost mine with wood chips and let it break down naturally, the soil loves it.

William Bronson wrote: What happens to all the salt when the seaweed is composted?

I don't think it goes away. However, it's the soil type and natural pH along with annual rainfall that determine whether it's a potential problem or not.

In my area, dry prairies where the soil is naturally basic, I would use it more sparingly and monitor closely. In the Pacific Northwest, with naturally acidic soils and heavy rainfall, I would use as much as I could get my hands on.

The founder of Black Lake Organic nursery once gave a talk at Evergreen State College for their food program that I sat in on, and he asserted [“everything in sea salt is good for plants, or even necessary, except for the chlorine in NaCL.”] (paraphrased from memory) Most tap water has chlorine as well, and little of the other 70+ oceanic elements beneficial to most life in most contexts.

Ben Zumeta wrote:The founder of Black Lake Organic nursery once gave a talk at Evergreen State College for their food program that I sat in on, and he asserted [“everything in sea salt is good for plants, or even necessary, except for the chlorine in NaCL.”] (paraphrased from memory) Most tap water has chlorine as well, and little of the other 70+ oceanic elements beneficial to most life in most contexts.

Perhaps -- I don't think one rule fits all. It's worth remembering that salt was historically used as a weapon of war to systematically destroy fertile lands.

If the sea salts are naturally washed or leached away, no problem. If they build up (especially sodium), as it certainly would in low rainfall areas like mine, it's potentially a poison you can never get rid of. From my perspective, it's all in the dose, and how long it remains in the soil. The micronutrient / trace element aspect is quite interesting though.

I have on the Eastern Shore of Nova Scotia in an area where farmers have been using seaweed as fertilizer for centuries. When I moved here, I soon learned that all of the experienced organic gardeners used seaweed in their compost. I was surprised to learn that they all agreed that you did not have to worry about washing the salt out of the seaweed if you gathered it after it had been up on the beach or in the marsh for a few days. I've been using unwashed seaweed in my compost for 10 years now, and have never seen any sign of damage from salt.

Have made biochar from water hyacinths. Express the juice of the water hyacinths first. That is the value part. A liquid fertilizer high in potassium.  Then mixed Bach with biochar from the hyacinths and false banana leaves. Made 200
Pounds of the stuff. Testing now on veggies in a garden

D Fujito wrote:Have made biochar from water hyacinths.  

Am I right that water hyacinths are a fresh water plant? Do they ever grow in brackish water?

How much salt does sea weed bring with it?  Would be my primary concern.

That said how are you going to dry it at scale?  Before you can char it you have to boil/extract all the water out of it.  And that takes a lot of energy.  Know that even a layer just 3 or 4 inches thick will remain wet in the middle for a long time if being sun dried.  Maybe some sort of centrifuge instead?  Some sort of reverse flow multi stage dryer?  Done correctly it might be a fresh water source.  If you are hauling in millions of tons of it most of that will be water.(quick google would suggest roughly 95% based on land based plants like lettuce)

Leaving that aside though is there a better use for it?  From here on I am talking fresh water pond moss, algea, etc.  Experience suggests it is one of the best possible mulches.  The top 1/2" to 1" dries and is very fragile but under that it creates a mulch moisture trap that is incredible for moisture holding.  And it lasts about 2X to 3X as long as grass clippings or straw.  And its weed suppression is very good too.  It is heavy, lots of work to harvest and other problems but it is my #1 choice for mulching around small trees etc where it can remain undisturbed longer term.

As I stated earlier, on a home scale for a suburban sized yard, I can lay it out flat in the summer and it dries quickly. I use it for adding nutrients to the biochar. It is not the main source of carbon.  Large farm/industrial scale is another matter.

John S
PDX OR