Feasibility of sinking compressed blocks of crushed biochar and clay into deep ocean waters

[Jasper Sky]

CDR experts, imagine the following scenario: Biochar is produced and then crushed to powder in an oceanside mill, and then mixed with clay (used as a binder), if necessary with a small amount of biogenic epoxy resin added for additional cohesion, and shaped into blocks about one meter on a side. These blocks are structured to be denser in kg per cubic meter than seawater, so they'll sink. 

These blocks are then loaded onto barges, which are towed out to ocean locations where the seafloor is at least 500 meters deep and relatively featureless. The blocks are dumped off the barge. 

Energy inputs are derived mostly from the gases released during pyrolysis of the biochar. Perhaps the tugs towing the barges are powered by bio-oil generated from a specialized pyrolytic treatment of some of the biomass. 

Questions:

1. Would this be a stable, durable way of sequestering carbon? Would the carbon stay on the seafloor?

2. What would be appropriate large-scale sources of biomass for pyrolysis? Kelp farming? Microalgae grown in shallow seawater ponds onshore? Bana grass plantations? Something else?

Could this approach work?

[Oeste]

Hi Jasper

Proposal: Do not waste energy by biochar production: dump wood and all other undissolvable organic mass including unrecycable plastic waste directly to the 5000 m deep ocean floor. Do it by help of a big vertical oriented hose with sufficient diameter in order to waste only one distinct location and to disturb the ocean floor ecosystem not in a wide-spread manner. The sedimentation of the organic stuff will gain stability if any say 10 m or 20 m thick layer of organic stuff is covered by inorganic material like clay, grit and stones for compaction. What will then happen within the huge disposal of organic stuff? Microbes will change the edible parts of the organic materials to methane and CO2. Both gases will stay because of the high pressure in the sediment layers and becomes converted at the low ocean floor temperature to methane and CO2 hydrates. Additional some ammonia and hydrogen sulfide will be generated but by far not in amounts which could toxify large areas around the deposal. 

Nature used similar desposals as well on the continent and in the ocean: coal and lignite seams are remnants of former moors. Productive localities in the oceans are localities of upwelling fertilized deep water. In the photic zone it produces organic litter sediment from the phytoplankton blooming (Humboldt current and Benguela current upwelling systems). Oil and natural gas deposits are remnants of these ocean floor sediments. 

Franz Oeste 

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[Eelco Rohling]

A couple of observations:

A 5-10 m ooze layer to stabilize this would require a massive amount of time to accumulate by natural sedimentation at a (high for the deep sea) 1 cm per kyr. Using grit or other coarse stuff won’t work because of pore-water (and gas) exchange through that. 

Also, burying gigatonnes of carbon this way would mean that very large surface areas would need to be covered, in contrast to your regionally focussed suggestion.

All natural deposits of coal/lignite/oil/gas (precursors) that were large enough to affect CO2 levels were gargantuan in their dimensions. 

Eelco

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On 8 Feb 2024, at 11:15, Oeste <oe...@gm-ingenieurbuero.com> wrote:



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[Andrew Lockley]

Biochar can be spread on farms to improve soil, added to concrete, used as a landscaping aggregate, etc. These uses are essentially of infinite capacity compared to the biochar market today

Andrew Lockley 

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[Jelle Bijma]

Biochar is a great product to improve agricultural soil. Don't dump it in the ocean. Use it in combination with Rockflour

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[Michael Hayes]

Hi, Jasper, 

A few thoughts:

1) I suspect that Biochar will not float if physically 'aged', or ground to a fine dust, and injected directly into deep water. The physical aging does away with many of the pores that trap air and the high water pressure will likely fill the remaining micro spaces in the char with water. 

https://www.sciencedirect.com/science/article/pii/S0045653522025644

A finely ground Biochar in the deep water is much like Dissolved Black Carbon that naturally makes its way into the deep ocean. How the ocean handles deep DBC is found bellow:

https://www.nature.com/articles/s41467-022-27954-0

The DBC easily attaches to falling particles, and thus eventually gets moved into the deepest areas by very slow benthic currents. 

The most active deep sea DBC areas are likely found around geothermal vents, see below. Injecting DBC in such areas may actually help that type of biota as some chemosynthic life can actually use DBC molecules unlike photosynthetic life, yet "the poison or cure is in the dose". Also, etching the BC with sulfur 'wets' the BC, or adds more H2O binding sites:

https://phys.org/news/2023-02-evidence-deep-sea-black-carbon-hydrothermal.html

Cultivating deep-sea vent chemosynthic 'pastures' with Biochar can have a down current reach of a thousand kilometers in some locations. The benthic biota down current is likely already able to utilize the added DBC as vent flow rates change often. Vent related mCDR efforts, any high sea benthic work, would be under the policies of the International Seabed Authority: https://www.isa.org.jm/

2) The totality of the international marine policy groups may have problems with 'dumping of waste' in the ocean. Ocean Iron Fertilization is currently under a moratorium that has lasted a decade, and OIF is likely one of the best studied mCDR efforts we currently have. The London Convention/London Protocol/ISA experts need to be convinced of the environmental safety and international socioeconomic viability. However, they only deal with international areas, or the high seas. The Wood Vault group has received millions in startup funds to simply dump wood chips in coastal waters. 

https://carbonherald.com/carbon-lockdown-sells-first-1000-tons-of-wood-harvesting-carbon-removal-to-kinnevik

3) Using Biochar in salt stressed soils seems to have several benefits beyond the norm.

https://www.intechopen.com/chapters/72499

Best regards 

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[Chris Vivian]

All,

 

I agree with what Eelco said.

 

It would indeed require a very large surface area to cope with the volume of material. As an example, Strand and Benford (2009) estimated that that if 30% of the U.S. crop residues were sequestered, 0.15 Gt crop residue per year could be deposited on the ocean floor; a volume of ~1 x 10⁹ m³/year. If this was deposited in an annual layer 4 m deep, it would cover an area of 260 km². A volume of material that was more climatically relevant globally would require a vastly larger area.

 

Also, the “at least 500 m depth” suggested by Jasper is too shallow. Most proponents of sinking biomass in the ocean have  said they are looking to a minimum of 1000 m depth.

 

Chris.

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[Chris Vivian]

Michael,

 

Your comments in point 2 of your email are inaccurate:

 

1. Ocean Iron Fertilization is NOT under a total moratorium. The London Protocol 2013 marine geoengineering amendments allow legitimate scientific research  but note that those amendments are not in force as more Parties need to ratify the amendments to bring them into force. However, Parties who have ratified the 2013 amendments are obliged by Article 18 of the Vienna Convention on the Law of Treaties (1969) to refrain from acts which would defeat the object and purpose of the treaty. The CBD decision on ocean fertilization is not legally binding.
2. While OIF is likely one of the best studied mCDR efforts, it is still a long way from being able to be deployed as shown the research plan drawn up the US National Academy of Sciences, Engineering and Medicine in 2022 - https://doi.org/10.17226/26278 - and that of the Exploring Ocean Iron Solutions (ExOIS) group - https://oceaniron.org/).
3. You are quite wrong when you say that the London Convention and London Protocol “…only deal with international areas, or the high seas”. It is a widespread misconception. The LC/LP cover all waters up to the baselines that are the base from which the territorial waters and EEZ are measured. On a straight coast the baseline  is the low water mark. Also, the London Protocol has a provision that it also applies to marine internal waters i.e., behind the baselines, that includes large bays and estuaries unless a Party opts out when it then has to have effective permitting and regulatory measures to control dumping activities and marine geoengineering activities when they come into force.

 

Chris.

 

From: carbondiox...@googlegroups.com <carbondiox...@googlegroups.com> On Behalf Of Michael Hayes
Sent: Thursday, February 8, 2024 6:33 PM
To: Jasper Sky <jasp...@gmail.com>
Cc: Carbon Dioxide Removal <CarbonDiox...@googlegroups.com>
Subject: Re: [CDR] Feasibility of sinking compressed blocks of crushed biochar and clay into deep ocean waters

 

Hi, Jasper, 

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[Michael Hayes]

Chris, thank you for the clarification. 

The technical distinctions are a priority at this point in time and on many levels. 

[Jasper Sky]

Thanks for all the input so far. Although everyone's comments were interesting, none of you actually answered the questions I posed. The questions I posed were: 

1. Would the compressed-biochar-and-clay-binder blocks, dropped to the sea floor, effectively sequester the carbon they initially contain?

2. What would be the best source of biomass for that biochar?

Note in relation to the second question that energy inputs are required to collect biomass, turn it into biochar, and then transport it to a disposal location. I am skeptical that it will ever make sense to collect corn stover from the Great Plains and turn it into biochar blocks for sinking off the West Coast, for example. This is why I'm wondering if kelp farming or oceanside seawater microalgae growing ponds might be suitable.

As for the suggestion someone made that biomass simply be thrust down a pipe and released at 5,000 m depth: surely it would take a lot of energy to force material down a pipe against the water pressure at that depth? Avoiding this energy cost is why I suggested compressing biochar into blocks designed to be denser in mass per unit volume than seawater. That too will take energy, but the energy can be derived from pyrolysis. Pyrolysis also makes the biomass into biochar and hence relatively inert in biological terms.

Regarding the suggestion that the biochar is better used for soil improvement: fair enough, though that use still entails the energy costs of distributing biochar and mixing it into soils. And how much biochar could plausibly be mixed into soils? It seems to me we're going to need to achieve negative emissions on the order of 15 to 50 GtCO2 per annum by mid-century - because we're going to realize that in addition to offsetting hard-to-abate current ongoing emissions, we're going to have to return atmospheric CO2 levels back to pre-industrial era levels of ca. 275 ppm or face the medium term catastrophe of about 15 meters sea level rise as Greenland, West Antarctic, and Wilkes Basin ice sheets disappear. I'm skeptical that we're going to find use cases for such volumes of biochar, or any other CCUS. 

I'm also skeptical that we will be able to grow enough dedicated biomass to procure 15 to 50 GtCO2 per annum sequesterable carbon, and that's another topic of interest. For all the excitement about biochar as a way of sequestering carbon, what are the plausible volumes that could be attained?

Once again, given the ecological tradeoffs and constraints on growing biomass on land, this is why I'm looking to the oceans (farming kelp, or oceanside seawater ponds for growing microalgae).

[Jasper Sky]

Re: Rewind.Earth, BioSink, etc.: several interesting questions arise:

1. Does some percentage of the raw biomass sunk turn into methane via anaerobic decomposition? And if yes, how much of that methane survives the trip from the ocean floor up to the surface where it can escape into the atmosphere? 

2. How does sunk raw biomass interact with fishing trawlers? 

3. How scalable would raw biomass sinking be? What are plausible sources whose collection would be efficient and would not entail high ecological costs?

4. How much energy (per ton of carbon removed) would be involved in collecting raw land-based biomass and transporting it to the disposal point?

And here's a big question that has been troubling me as I dive into the physical chemistry of CDR:

5. When carbon is removed from the atmosphere, as distinct from dissolved carbon removed from seawater, equilibration of partial gas pressures at the ocean surface / atmosphere interface occurs, which reverses some of the atmospheric carbon removal... maybe most of it, over a sufficiently long time-scale. So perhaps we should not be looking to land-based CDR at all. Perhaps we should be looking only to marine CDR, such that the partial-pressure equilibration dynamics work *for* us rather than *against* us. 

I'm keen to hear from anyone who has studied this. 

Eelco perhaps? Do you have a view on this (point 5 above)? I've been searching online for relevant studies and come up empty so far.

On Friday, February 9, 2024 at 11:17:26 a.m. UTC-8 amalbh...@gmail.com wrote:

I am already doing this with a much simpler method - detailed here: www.biosink.org

Also see www.rewind.earth and www.carboniferous.co.  They are fully funded startups.

[Chris Vivian]

Jasper,

 

Responses to your questions:

 

1. Yes, some of the organic matter may turn into methane. I understand that the evidence is that even in relatively shall ocean areas (hundreds of metres) little or no methane will reach the surface as it is broken down by bacteria. As most biomass sinking concepts envisage putting the biomass down to at lease 1000 m, it seems very unlikely that any would reach the surface unless they formed huge bubbles.
2. While there is some fishing at water depth of >1000 m, those areas could be avoided and if put down in water depths of several thousand metres, there would be no interaction with trawlers.
3. Not something I can answer.
4. See Metzger and Benford (2001) - https://link.springer.com/article/10.1023/A:1010765013104 - and Strand and Benford (2009) - https://pubs.acs.org/doi/10.1021/es8015556 - who did such calculations for crop wastes in the US.
5. See this recent modelling paper by Couespel and Tjiputra (2024) https://dx.doi.org/10.1088/1748-9326/ad16e0.

 

Chris.

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[Venna von Lepel]

Hi Jasper, 

from a biochar perspective let me add my two cents: 

1. Permanence: According to the latest research of Hamed Sanei biochar produced at high temperatures is mostly an inertinite material and therefore will not decompose or be eaten by microbes -  if that is what's meant by decomposition. "assessing biochar permancence - an intertinite benchmark."  https://www.sciencedirect.com/science/article/pii/S0166516223002276

If you want a short and easy digestable version of the research, we tried to sum it up on our website blog. 

https://www.novocarbo.com/Insights/biochar-as-a-permanent-carbon-sink/

2. Inputmaterial: 

Thinking about the input material. It seems good advice idea to go for additional biomass and not rely on biomass that is already grown today. The run on biomass will only accelerate and  the idea to take all the residues from agriculture and use them for pyrolysis is not sustainable or feasible.

Plus a lot of the  residues are just too valuable to be put directly into a pyrolysis system and should enter a cascading utililasation.  Not to mention the transportation problem, as a lot of residues do not occur in a central spot like a mill or production site. Those use cases (collected residues, not fit for a first usage and close to oceans) exist, but are over estimated from my POV. 

To grow additional biomass like Kelp or Seeweed  is a good idea. Kelp/ algae  is dog materials to pyrolyse - with seaweed it is important that it will not contain too much sand. Sand is an abrasive material and is hurting today’s pyrolysis  technology. This is especially important if we think about seaweed or invasive species being collected at beaches. As much as the idea is intriguing you would have to find a technology fir beyond today's status quo to match your wish for  1. permanence (controlled quality of biochar with high temperatures and process control) with a collected sand contamined biomass. 

Best V