Stefano Capello and Sara Groppelli on Limenet’s approach to limestone-based OAE

In this episode of Plan Sea, hosts Anna Madlener and Wil Burns sit down with Stefano Capello, CEO and founder of Limenet — an Italian startup focused on limestone-based ocean alkalinity enhancement (OAE) and net-zero lime production — and Sara Groppelli, a PhD researcher at the University of Milano-Bicocca studying the impact of Limenet’s approach on phytoplankton communities. Stefano discusses Limenet's journey from theoretical experiments in his grandmother’s garage to a pilot plant in Italy that is navigating key, real-world questions around cost efficiency and scale, environmental safety, permits and regulatory pathways, and community engagement.

Stefano recounts Limenet’s unconventional beginnings, which started as a prototype research project in his grandmother’s garage, and now operates a pilot facility in southern Italy. Since 2023, Limenet has focused on developing an OAE approach that pre-dissolves limestone alkalinity in reactors and pre-equilibrates seawater with atmospheric CO2 before releasing it back into the ocean. This closed-system approach is designed to reduce scientific uncertainty in alkalinity additions and to minimize risks such as particle sedimentation or unwanted precipitation.

Now, Limenet is focused on addressing key questions about how its OAE approach could be scaled. Stefano shares updates on the company’s journey to reduce the energy intensity of its lime production and the associated costs, and how the team is engaging communities and policymakers as they navigate Italy’s regulatory landscape. 

The ecological safety of Limenet’s OAE approach are also important to thoroughly evaluate, and Sara shares updates from her research on potential impacts on phytoplankton communities. Sara highlights how controlled alkalinity enhancement appears to have limited ecological disruption when carefully designed. However, long-term and site-specific studies are important to thoroughly understand potential impacts and also co-benefits, such as potential buffering against ocean acidification. 

Listen to the full episode to learn more about Limenet’s growth and how the team is approaching important questions around environmental safety, cost and scale, monitoring and evaluation, community engagement, permitting pathways, and more.

Plan Sea is a semi-weekly podcast exploring ocean-based climate solutions, brought to you by the Carbon to Sea Initiative and the American University Institute for Responsible Carbon Removal. Subscribe on your preferred podcast platform and find the entire series here.

ACRONYMS/CONCEPTS:

• CDR: carbon dioxide removal
• ISO: International Organization for Standardization
• MRV: monitoring, reporting, and verification
• OAE: ocean alkalinity enhancement

Plan Sea is a semi-weekly podcast exploring ocean-based climate solutions, brought to you by the Carbon to Sea Initiative & the American University Institute for Responsible Carbon Removal.

Transcript

0:00 - Introduction & Meet Limenet

Anna (0:13):  Welcome to a new episode of Plan Sea: Ocean Interventions to Address Climate Change. I'm your host Anna Madlener, Senior Manager for MRV at the Carbon to Sea Initiative, and with me is my co-host Wil Burns, Co-Executive Director of the Institute for Responsible Carbon Removal at American University. 

Good morning, Wil. 

Wil (0:30): Hi, Anna. 

Anna (00:31): In today's episode, we are picking up a format that we did a lot of in earlier seasons, which is introducing an ocean-based carbon dioxide removal startup. More precisely, we are welcoming Stefano Capello, CEO and founder of Limenet, and Sara Groppelli, a PhD student at the University of Milano-Bicocca, who's been working on Limenet’s biological studies. Limenet is an Italian startup that was founded in 2023 and is exploring limestone-based ocean alkalinity enhancement and net zero lime production. They're implementing a hybrid open and closed system approach, which means that they're currently pre-dissolving the alkalinity in a reactor and pre-equilibrating the alkaline enhanced seawater with atmospheric carbon dioxide before releasing it back to the ocean. Over time, they intend to develop instead, or move towards, a pre-dissolved but non-equilibrated approach, which would allow for larger scale. And we'll dive deeper into this in the episode. Wil, what are you excited about in today’s episode?

Wil (1:31): A couple of things. I mean, in general, it's an interesting extension of some of the earlier work that we've seen in terms of reactor-based liming. But I think most specifically I'm interested, of course, in how this is being regulated and what the regulatory journey has been to date for this company. And I'm also interested in the ecological implications of an intervention of this sort. 

Anna (2:01): Yeah, I think in addition to that, I am, as usual, interested in the implications of this pre-dissolution and sometimes pre-equilibration of the carbon dioxide and its implications for the monitoring of these approaches. I’m curious to decipher that a bit and share more about those advantages and disadvantages. I think a key but often complicated part of all those many different OAE or ocean alkaline enhancement pathway combinations. And so with that, shall we bring them in? 

Wil (02:37): Sounds good. 

Anna (2:41): Hi Stefano, hi Sara, how are you? Thanks for joining us today. Do you both want to quickly introduce yourselves and tell us who you are? 

Stefano (2:53): Absolutely. Thank you, first of all, Anna, for this kind introduction. I'm Stefano Cappello. I am the CEO and founder of Limenet, an Italian startup that is working in the ocean alkalinity enhancement ecosystem, and I have a background in mechanical engineering. I'm a mechanical engineer. I am 30 years old, and I am living in North Italy, so happy to be here with also Sara. 

Sara (3:19): Yes, hi everyone and thanks for the invite. My name is Sara Groppelli and I'm a PhD student at the University of Milan-Bicocca. My doctoral research focuses on evaluating the impact of Limenet, in particular on phytoplankton communities. And I also live in the North of Italy and I am 28. 

Anna (03:41): Great, shall we all say our ages Wil? I’m 30 as well.

Wil (03:49): That’s not happening. Yeah, so am I. 

Anna (3:52): Exactly. Well, that was great. Thank you for sharing that. We've never had that on the pod before. Well, to ease us into the introduction, Stefano, would you mind sharing a bit of Limenet's history and its inception? 

Stefano (4:08): Yeah, absolutely. So actually, Limenet started as a research project in which we basically were trying to understand how to counteract  ocean acidification. And we are living in Italy, so Italy is really surrounded by the Mediterranean Sea. So seawater and sea in general is something that we have in our heart, in our blood. And so, actually, that's why maybe we came out with this idea. To understand deeply how it was possible to counteract ocean acidification, and this was in 2018. Actually, I was not yet thinking about Limenet, actually I didn't know anything about ocean alkalinity enhancement. 

But then in 2020, we had the opportunity with some professor of Politecnico of Milano, that's an Italian, really famous Italian engineering university in North Italy, to deeply study this new concept of buffered accelerated weathering of limestone that was potentially on paper a process able to remove carbon and meanwhile increasing the buffering capability of the sea. Of course it was working on paper but the reality is something different. So in the garage of my grandmother, since I was really skeptical that it was working, I started a small project, really in the garage, with an Arduino, so it's a small computer, and then a small circuit with a pump, and really easy, a bottle of CO2 and some lime, to understand how to produce alkalinity in a controlled way, and how to simulate the, it's not really the weathering, but the solution of CO2 and the buffering of CO2 with some alkaline. And that was in late 2020, early 2021. Then, it was working actually, I was really surprised, but it was working the first time. And we then decided to make a bigger prototype, but in the garage of the other grandmother that I have, because the first one I was really pissed off of, you know, water everywhere, limestone everywhere. So really she helped me for a summer, but then she told me no, no, no way. So, fortunately, I had another grandmother with a bigger garage, and so I put another pilot there with bigger pumps, bigger pipes, and we did a lot of tests. We also studied the dissolution not just of lime but also limestone with different dimensions, but we understood that basically limestone, of course, we knew, but it was really, really slow in the dissolution, and then we did another pilot, but not more the garage because it was maybe too complex. 

Anna (7:13): The second grandmother was also pissed? 

Stefano (7:15): No, actually no, because she has a bigger garage, but she was more friendly. But however, the prototype we did in a city in Italy, North Italy, but close by the sea, that's called La Spezia, it's really close by Cinque Terre, that's a nice location for holiday. And we did a lot of experiments there through 2022. Meanwhile, I was working in a big corporation that's called Leonardo. And as soon as I saw that it was stable, more or less, the alkalinity, I quit the job the next day. I saw the data from Politecnico of Milano and I say, okay, if I don't quit the job, I'm stupid. And so I found, fortunately, an entrepreneur in Milano. And so after six months, I started this company with him as a co-founder and also with other two people that helped me to do that. And also Giovanni Capello, that's the inventor of this technology and this approach. And then we began to raise money and to understand how also not just making working the process, but also the company because it's quite different. And we then started to raise money, to hire people and to do a fourth prototype. That's what we did basically last year in another city in Augusta in South Italy, since unfortunately La Spezia didn't have a lot of space in the port, since it's more touristic. And we found by really random a port in South Italy that was really, really open to these new approaches, so we went there. We co-financed privately this pilot plant that is able basically to transform 100 kilograms per hour of CO2, so CO2 lime, into an equilibrium solution of bicarbonate, so we basically reached the TRL 7 more or less of this technology and also we did a showcase in a control system to remove the first batch of CO2 as a showcase. 

9:23 - Limestone, Lime, and Net-Zero Feedstocks for Ocean Alkalinity Enhancement

Anna (9:23): We went from the garage to the TRL 7. Thank you so much. I just wanted to quickly intercept with a question. Thank you so much for the outline. We also haven't had the garage story yet on the podcast, I think. Well done. But before we dive deeper into the exciting progress that you've made in Sicily, can you lay out which combination of an ocean alkalinity enhancement method you are working on? You of course mentioned already limestone as the feedstock, but in sort of a general terms and big picture, what does your process look like? And what are you doing? 

Stefano (10:02): Let's say that the process can be divided into parts. The final goal of all of us, our company, is try to remove CO2 with the ocean. So try to increase alkalinity, non-equilibrated into the sea with some alkaline feedstock, and then to remove carbon. But here is the big question. How are you able to source a low-carbon or zero-carbon, alkaline, feedstock? So we found out that limestone can be a feedstock, however limestone dissolution is quite slow, it's really really very slow, and something that is faster is lime, however how can you produce lime that is net zero? The process, the simplest process that came out is you take limestone, you calcine the limestone with electricity in an electric calciner. So basically you heat up the limestone up to 900 degrees. You basically split the limestone into two things. One is lime and one is CO2. Then you need to remove the CO2 coming from this calcination. And based on stoichiometry, you need just 50% of the lime you have just produced. Then the other 50% can be used as a raw material feedstock for ocean alkalinity enhancement. And that is the easiest approach, so easiest, most straightforward, to prove that it's possible to produce zero carbon, at least if, let's say, the life cycle assessment that have of course some percentage of inefficiency. But theoretically, this 50% of lime can be a feedstock for ocean alkalinity enhancement applications, so non-equilibrated applications. And basically, this is what we are trying to achieve, commercially speaking, and then there will be new innovation. How to source... let's say not using 50% of the lime, maybe use some parts of limestone, with a high pressure vessel in order to dissolve it, maybe use also some other minerals to do the alkalinity, zero alkalinity. So this is basically where we are based on the technology of the climate of what we are developing. In fact, Anna, maybe that is something that we are different. I mean, our approach is a little bit peculiar with other competitors is that Limenet is structured as an engineering company more than a project developer company. So the goal of Limenit is to provide technology to users that could be project developers. And to develop innovation of the technology. So this is our first go-to-market technology, but then our goal is to try to improve, make a lot of progress in improvement, try to understand all the scientific knowledge gap of the chemical side, the biological side, to understand also which part of the world is better to use, I don't know, calcium, in which part is better for sodium, in which is better, I do not know, whatever it is. And so this is our approach. So with a scientific-based approach and then engineering a challenge, how to put on the ground what on paper seems to work.

13:37 - Pre-Dissolved vs. Pre-Equilibrated OAE: Reducing Uncertainty and Scaling Impact

Anna (13:37): And before we dive into the next specific questions around Aurora and the sequestration potential, etc. I'm curious if you want to share briefly how you are using the terms pre-dissolved or pre-equilibrated or non-equilibrated. I actually might have it wrong in my head. I thought that you are pre-dissolving and pre- equilibrating before you release the water back into the ocean. So I'm wondering if you want to briefly share the approach that you're currently implementing. 

Stefano (14:07): So basically I understand your question because sometimes it seems quite difficult to understand the differences. So the goal of Limenet is to try to decrease all the scientific uncertainty. So when you throw something or you inject something into the ocean you should understand exactly the alkalinity you inject. That could be equilibriated or non-equilibriated. The alkalinity you want to inject is not…the goal is try not to have a solid with particles, but it's better to have pre-dissolution of the alkalinity. That means that you want something that is dissolved, not in a slurry, so not with particles, but with ions, so it's something dissolved. So this is what we do in reactors. Measuring before the flow of water and after the injection of alkalinity in a controlled way. So that is the first thing, pre-dissolution. The second thing is are you injecting something that is already equilibrated with the partial pressure of CO2 or not? And that is the difference between a pre-equilibrated or non-equilibrated. In our process, the goal to produce net-zero lime is doing it with a pre-dissolution and pre-equilibration with the atmosphere. Then, in order to do the removal, you need to inject the alkalinity that is pre-dissolved but non-equilibrated. So it means that it's not equilibrated with the partial pressure of CO2 in the atmosphere so it can of course capture CO2. However, the goal is to do that in a pre-dissolved way, basically you put something in the ocean that's already measured and not in particles that can sediment, can go down with gravity, but maybe can also have some particular secondary precipitation because I have too high pH in the surroundings of the particles. So this is basically what we believe that it's better to do, and also other companies are doing like that. So we believe this is the best approach. 

Anna (16:42): Okay, thank you. So you're sort of eliminating this difficulty of ensuring that your feedstock dissolves in the ocean water rather than you doing that in a reactor. However, afterwards you are still facing that joint challenge that is air sea gas exchange. So you still require the equilibration with the atmosphere to occur in the open ocean like any other approach [sic]. 

Stefano (17:05): If you do net-zero lime when you want to capture CO2 in the ocean, you need to do it in a non-equilibrated way. However, it's impossible to say eliminating uncertainties, you are trying to reduce the uncertainty as much as possible. Of course, today the uncertainty is also because we also still [sic] understanding the biogeochemistry of these new approaches. So part of the uncertainty is also because we are really in the first phase of these new technologies. Maybe next years, these uncertainties will diminish because more science will be produced. 

Wil (17:52): Yeah, so that's a good transition to my next question. You've said your TRL is already at seven, right, which is pretty impressive, but what additional research do you think you need to reach the level of actual large scale utilization at this point? 

Stefano (18:11): So maybe just to be 100% transparent, TRL7 is the storage part of our pH-equilibrated approach. Then about the calciner, we are more at TRL 5. We should reach TRL 6, TRL 7 by 2026. For the non-equilibrated approach, we're lower, we don't know TRL 3, TRL 4, because it's not the first priority of Limenet, we don't equilibrate it now. Because as I was saying before to Anna,  Limenet is more now focused on being an engineering company, trying to solve engineering challenges for the electric calcination and for the machine that produces alkalinity. And we are trying to also, with the help of the PhDs that we are working with, like Sara, but also there are others. There is Sara that is working on biology, then there is another colleague of Sara, David, is working in biology, there is a PhD working on chemistry, then there is PhD working on fluid dynamics simulation. So we are going to understand, you know, like a puzzle, different parts of this complex science of the ocean. 

Wil (19:39): And so what kind of additional research then do you think you need in that context? 

Stefano (19:44): So we will need different research. So one research is the scientific research that should be done for the non-equilibrated, working together the fluid dynamics part, the chemistry part, in order to understand when you inject non-equilibrated alkalinity, how it goes, and how it sinks eventually. And this is one part. The second part is regarding the environmental impact and so we need to do scientifically this research, not on specific species but on the environment and the ecosystem we have there. So if we want to do a project in South Italy, we want a project in New York, in Boston, we need to do an environmental impact assessment on that area specifically on habitat biodiversity. So that is something that we are trying to do not just for the science but for environmental permit. Because it's really important to decrease the uncertainties on, I don't know, coccolithophores or another species or bacteria, but I believe based on the industrial plan that we need to do that for this technology to scale up. But we are looking at our fieldYou know, we don't have this vision. So I believe that we really need to focus on how it has been done for other industries such as salmon, desalinization plant, steel-making industry, basically we need to do the same. So we need to understand what's the impact there in the place where we do that based on what it has already been done, so following environmental impact permitting, habitat biodiversity. So that is what's missing because nobody yet has been done. So this is what we are trying to do in Italy with the Minister of Environment, try to frame a framework of activities that must be done to decrease the uncertainties on the environment where you do the plant. So this is what I believe are the two most priorities we need to do. 

22:10 - Energy, Costs, and the Path to Gigaton-Scale Carbon Removal

Wil (22:04): Ultimately, how much sequestration do you think could be effectuated at scale with the Limenet process? 

Stefano (22:12): That's really tricky. So of course, as much as we can. So we need to remove 10 gigatons of CO2. So we really need to, like if we double the energy production of renewable, we would do like 1 gigaton of negative emission. If we want to do 10 gigaton, we need to double and double and double, and then there is also another industry that needs to be decarbonized. So energy will be a constrain and then of course industrial permitting, biodiversity impact for places where we will implement it. So potentially not lime, but ocean alkalinity enhancement can solve part of the issue. Then we will see. 

Wil (22:59): Let's talk a bit about cost. What do you think, ultimately, at an nth-of-a-kind stage of development, the cost per ton of sequestration could be with this process? 

Stefano (23:11): So the cost is not limited, it's really OPEX driven, so it really depends on the energy and the energy price basically. So for instance our first of a kind plant that we aim to do, not, let's say not this one that is smaller, but the first commercial that will be able to remove more or less 16 or 15,000 tons of sodium per year. It should cost 260, 300 euros per ton of negative emission with a cost per megawatt hour of 40 dollars. Is it low, is it high, I don't know. This is basically what we have. If we have the same cost of energy with big plants, we could reach 170, 180 euro [sic], more or less. Of course, it's not 30 euros, unfortunately. So this is basically what we believe this technology may cost, because the real challenge is really how to source net-zero alkaline feedstock to make ocean alkalinity enhancement. So that's the biggest challenge. 

Wil (24:26): You know, you've referred a number of times, obviously, to one of the 10,000 pound elephants in the room, which is energy, right? Which is what we talk about with a lot of these processes. And so I thought I wanted to circle back on that. But did I understand you correctly that if you wanted to get to a gigaton [sic], you'd have to double the total amount of renewable energy? 

Stefano (24:52): Eh, more or less. 

Wil (24:5): Globally. 

Stefano (24:54): Yeah, globally, so it's a crazy amount of energy. 

Wil (24:58): Right, right. 

Stefano (24:59):  But it's not just Limenet, it's direct capture approaches, any approaches. Because, you know, maybe there are approaches that can maybe cost 100 kilowatt, 200 kilowatt per hour of the energy for one ton of CO2. But maybe they're not scalable. So that's the issue. So that says something that we find out if, for instance: If you use some materials that are secondary products, maybe you can do 1 million tons in the world, 2 million, 10 million. But if you really want to do giga-tons, I believe we need to think a little bit outside the box and try to think, okay, let's try to use maybe existing infrastructure, but not depending on the industry we have now. 

Anna (25:58): I mean, this is also really the crux of the different CDR, carbon dioxide removal, approaches at large, right? Like what you're describing is a result of the desire for certainty. I always kind of think about this from a perspective of the more certain your, or more measurable, your CDR impact is that often comes along with more energy requirements because in your case, energy, if I understand it correctly, is required for this pre-dissolution and for the sourcing of the low carbon alkaline feedstock. If you go for a sort of more open system approach where you were adding the raw feedstock, for example, close by to where it's from, you're releasing or you're relying on nature to do the dissolution of your feedstock ultimately reducing your overall energy requirement, but it comes at a higher uncertainty because you will never be able to fully prove that your feedstock dissolved, you will have to rely on studies and models, etc., etc. So you have a higher uncertainty in your measurability, but a larger potential for scale because you're relying on nature to do this and you don't need the sort of human renewable energy. So I think this is a really important balance that we're striking in the CDR world in general. But these hybrid approaches, like the ones that you're developing, Stefano, they're really impactful because they're teaching us a lot about this interim place, so to say, where you're studying, like you said, a lot of the processes in the water and the ocean with respect to air-sea gas exchange and environmental impacts, and you're delivering certainty on the dissolution piece. 

Stefano (27:48): I completely understand your point, Wil, and also what Anna said. I believe that in that case, right now in 2026, we really need to decrease those uncertainties and so it's better to spend a little bit more energy now to show that it's working, to show it's safe, and then try to decrease the energy with some...

Anna (28:15): Non-equilibration, yeah. 

Stefano (28:16): Yeah, non-equilibrating, decreasing an MRV naive approach. 

28:22 - Environmental & Ecological Impacts of OAE

Anna (28:22): Well, naive is maybe the wrong term, I would argue. Like it's just a more uncertain approach right now. We have more questions around it, more scientific uncertainties or things we need to answer. But I want to sort of segue that question into the next one. Regardless of the OAE approach, there is always this risk of precipitation. So if you add too much alkalinity too fast, this of course is primarily a risk when you do a non-equilibrated approach. Vice versa, if you do an equilibrated approach, you have risk of CO2 outgassing again. So I'm curious how Limenet is thinking about sort of navigating those challenges. 

Stefano (29:01): So as I was saying before, Anna, it's incredibly important to think of this process with 360 overview. So not just chemistry, but also fluid dynamics. It's incredibly important. So what we are obsessed with [sic] also with our studies in biogeochemistry is the pH and Omega, so the saturation index of aragonite. 

Anna (29:32): For those non-scientists, quickly illuminate what the aragonite saturation is. 

Stefano (29:40): So basically, it's how much bicarbonates are inside a sample of water. So it's the saturation, let's say, of the carbonates between precipitation and non-precipitation. So for us, it is incredibly important that the fluid dynamics and eventually the real measurements in the sea that should be speaking with the model go hand in hand. So you cannot do ocean alkalinity enhancement without this data and without this model set. It's impossible because you need to know that the alkalinity you inject, it dilutes below the threshold of this omega-ragonite that could be 6, 7, 8, it depends where you are and the temperature in particular. So if you, if let's say the volume of water, let's assume this volume of water with higher omega, because you just inject it, doesn't dilute in just a few minutes, it will precipitate immediately. So that's why it's incredibly important that when you do this application of ocean alkalinity enhancement, you are really, really taking care about this control volume that must be diluted in a specific amount of time. And you are able to do that,you are able to measure it, and also to model it and measure it in a real life, real open environment, you need to do the specific dilution before and then you need to understand in the sea that the omega goes below the threshold in a specific amount of time. But it also depends on the temperature change [sic]. 

Anna (31:24): And summarizing also a bit of the MRV questions into this, what does your process currently look like to test and prepare yourselves for that monitoring? So when you refer to the fluid dynamics, we often also hear this term near field modeling, right? So you really want to model and understand exactly how your water disperses away from the addition site. That you have to do by collecting lots of measurements. What does that currently look like in your field trial that you've set up in Sicily? 

Stefano (31:58): So the field trial we did so far was with this closed system. So the MRV was quite easy, because you measure the water before and the water later, and then you have a simulation of the plume. We have a measurement system, so a multi-parametric measurement system close by the injection, and so we measure that the pH and variables are below the threshold. So that is easy. Instead, for the non-equilibrated approach, we are working with Isometric to understand how our biogeochemical model can be used to claim in the future the removal, but we are not yet there. So we are structuring this with a hybrid approach between model, biogeochemical model, and real measurement with these different sensors that we will place in the sea. We don't know yet at which depth of the sea, how many, you know, because it's a high cost, high CAPEX cost at the beginning. We believe to place four or five of these multi-parametric probes in the area and to understand. 

Anna (33:17): And if I'm not mistaken, part of the challenge with using lime as a feedstock is that the risk for precipitation is quite high. Do you have any intuition already for this sort of scale, I suppose, or addition rate at which you can safely do it? 

Stefano (33:36): The goal is to use a ship like a barge in the future, so to understand in the area how much alkalinity you can inject in order to be below this omega threshold and then eventually also to use like a platform that makes a circle to increase this dispersion. 

Anna (34:00): But always close to shore in order to reduce your transport emissions. 

Stefano (34:05): Yes, absolutely, but also for permits because right now it would be hard even to get permits in national water, in international waters now it's impossible. 

Anna (34:20): Some of the studies around your approach and ocean alkalinity enhancement, in general, sort of tout the potential co-benefit of increasing the buffering capacity against acidification. Do you envision that these effects would largely be localized around your addition site in Sicily, or could they have larger impacts? 

Stefano (34:40): Maybe it's Sara, do you want to reply? 

Sara (34:43): Yes, I can answer this. I think that the increase in alkalinity primarily will strengthen the buffering capacity locally, of course, and then in the specific area where Limenet is applied. Of course, over time, the treated water will be gradually mixed with the surrounding water, so there is the potential for a wider scale effect. Although this will develop more slowly and is harder to quantify in the short term. Of course, as Stefano was mentioning, the fluid dynamic studies and models are really important and I think that the integrated approach of modeling and field experiment will allow to track the immediate benefits in the treated water, but also the potential broader implication of the treatment. 

Wil (35:46): Okay, let's circle back a bit. Stefano, you've already talked a bit about additional needs for research in terms of ecological implications. So I want to drill down a little bit on some of the ecological aspects of this process. One thing I've seen in some of the literature, and either one of you can address this, is there's been speculation we might see changes in the ratio of diatoms to dinoflagellates if we deploy liming processes. And this could obviously have impacts on the transfers of energy in these ecosystems and could have cascading impacts on higher trophic levels ultimately, if you fundamentally restructure the architecture of these assemblages. Could you explain what the research to date has told us may occur?

Sara (36:43): Actually, the research to date indicates that moderate and balanced ocean alkalinity enhancement generally has limited impact on the diatom-denoflagellate ratio. For example, in our first experiment that we made in Italy, in La Spezia, in the Mediterranean Sea, the ratio remained more stable across treatments with increased alkalinity than in the controls. So this suggests that controlled ocean alkalinity enhancement does not drastically alter the phytoplanktonic community. Actually, from the literature we know that some species may respond differently under high or unbalanced ocean alkaline enhancement, with diatoms potentially decreasing and then the denoflagellate increasing. But of course, I think that the type of ocean alkalinity enhancement and the nutrient availability also play a key role. We know that silicate-based treatments can favor diatoms because they need silica to produce the frustules, while calcium-based or alkalinity treatments may benefit coccolithophores or dinoflagellates. So it really depends on a lot of factors. The strength of the treatment, the type of the technique that we use, the environmental condition and all the parameters that are involved, such as pH, temperature. 

Wil (38:20): So some of the research today also says that this approach might favor silicifying organisms, right? You've talked a bit about that already. And it's been suggested this might actually be beneficial from a perspective of carbon dioxide sequestration. Could you expand on that a bit? 

Sara (38:41): Of course, we can start saying that promoting silicifying organisms like diatoms can enhance both the ecosystem productivity and the carbon sequestration. When diatoms dominate, energy is transferred more efficiently to zooplankton and to the higher trophic levels, so the food web is more, let's say, linear and the carbon is exported faster to the seafloor via their silica-based frustules. Diatoms, as I was mentioning, require the silica acid to build their frustules. So the benefits depend also here on the environmental conditions, including nutrients availability, pH, and temperatures. When conditions are favorable, diatoms grow, sink efficiently, and transfer the carbon from the surface ocean to the deep ocean. It is important to say that the goal, in my opinion, of ocean alkalinity enhancement is not to artificially alter the planktonic communities, but rather to enhance natural processes where silicifying organisms are already present and the conditions are supporting their growth. So, to be clear and to answer your question, favoring diatoms with ocean alkalinity enhancement increases carbon export because diatoms have heavy silica shells, as I was mentioning, that make them sink faster when they die or they aggregate. And this sinking transports carbon from the surface to the deep ocean, effectively removing CO2 from the water through the photosynthesis. So boosting diatoms' growth enhances the biological carbon pump and increases carbon export to the deep ocean. So always keeping in mind that we don't have to alter anthropogenically the phytoplankton community, but to operate where these communities are already present and the conditions are good for them. 

Wil (40:59): So we've touched on this a bit already, but maybe to tie the bow, what additional research do we need now to conduct to be confident that this process won't have substantial adverse ecosystem impacts? It sounds like one of the things we need to do is obviously look at it in different environments, right, where there's impacts such as temperature and nutrient availability and so forth, but what else needs to be done to to do this assessment and at what scale do we need to be doing this at to be reasonably confident in terms of the impacts?

Sara (41:37): Yes, there's definitely a lot of research to do. One important area, in my opinion, is understanding the potential effects on the food web. We know that we inject some material, but we need to understand whether the trace elements could accumulate or magnify in the trophic levels and eventually affect higher organisms or seafood safety. So the research now is going also to understand how trace materials and trace metals remain in the food web. Yeah, these kinds of effects often emerge only over longer timescales, so long term studies are essential and also field trial studies. 

Wil (42:44): And how long-term do you think those studies need to be, right? Because that's one of the questions I always have with a lot of these shorter studies, right, is not looking at concentration over time, right, which is going to be a critical consideration, I think, for a lot of these. How long do we need to assess this to be able to draw those kinds of conclusions? 

Sara (43:06): Actually, I think that we need to understand the life cycles of what organism we are testing on and actually we can concentrate our we can focus, our work, on I don't know species with economic value or something that people can understand and rely on. I mean, it's important that common people can understand that it's not a problem also for them. So study the high impact species. I don't know if Stefano wants to add something on the next steps. 

Stefano (44:04): No, I agree that we need to study with a time that some species live, so with the specific life of this species. What species? I don't know, it's more a science, but I’m not a scientist. 

44:19 - MRV, Carbon Credits, Regulation & Community Engagement

Anna (44:19): Well, we've had a number of recent episodes actually on environmental impact studies and research, but certainly I think you hit an important point that there's a difference between some of the organisms that are impacted potentially or that need to be studied on a long term. And then there are species that are culturally or economically important that need to be studied. We briefly touched upon this earlier, in Augusta, Sicily, of course in the south of Italy, Limenet is operating its first pilot plant and you've shared a few months ago that you will start working with the registry Isometric to receive carbon credits from this operation. I’m wondering if you want to share a little bit more about what we can expect in this regard in 2026.

Stefano (45:08): So actually we are awaiting formal permits from the Ministry of Environment that we hope should arrive by, let's say before summer, that can make us operate this plant in order to make OAE. So then we are fortunately finishing this calciner integration that we hoped to be done say more at the end of 2026, but maybe 2027. So, operationally speaking, it will be more at the beginning of 2027, when we will be really able to make not batch tests, but running 24-7. Right now, in 2026 and early 2027 we will do more batch tests, more for scientific purposes than for industrial production. 

Anna (46:11): And one additional question on that, if you already know, I'm conscious that of course, this takes time and you're looking at 2027 to deliver these credits, but you claim on your website that you've been already Iso-certified or that your MRV approach has been Iso-certified by Rina. Is your MRV approach changing, or how has it changed working with a registry like Isometric that I may assume has potentially more sort of specified CDR and OAE guidelines,or do you anticipate it changing considerably? 

Stefano (46:45): Actually, the MRV we did, it's MRV for the production of net zero lime, so for the equilibrated. So it's not for the non-equilibrated. It's also on our website, so you can also download it and see it. And so there are no biogeochemical models on it, it's more regarding the chemistry, regarding the uncertainties that we believe based on the measurement you do it, and so you discount some CO2 that would leak on the area. 

Anna (47:19): Mm. 

Stefano (47:22): But it's more on the storage of the feedstock production of the alkalinity.

Anna (47:30): Feedstock production, yeah, right. And then you anticipate sort of using a combination of isometrics protocols. 

Stefano (47:38): Yeah, absolutely. Basically, it's really similar to the oceanic enhancement protocol from coastal outfall, but in an equilibrated way. So, we assess the feedstock material as we take it, the energy cycle, feedstock cycle, the life cycle assessment of it. And then the non-equilibrated part. 

Anna (48:10): Yeah, so you would be modeling out the air-sea gas exchange. Okay.

Wil (48:16): So, let's just talk briefly about some of the governance considerations. You inverted a bit already about the regulatory requirements in Italy, and you also mentioned London, the London Convention. What's the regulatory environment look like for this approach right now, and what do you contemplate will be the next step? And then let's talk a little bit about London's role, if any. But let's start with the domestic. How does this get regulated and what's going to happen in the next step? 

Stefano (48:53): That's really, I believe that after funding is the toughest question and toughest topic because... There are let's say two levels. One level is a legal framework, so is it legal to make ocean alkalinity enhancement, is it legal to inject something into the sea? So we found out that there are no rules anywhere, but that governments are open [sic], based on what I see, to include this technology in legislative framework of law. And that is basically what we are trying to do in Italy, to include the ocean alkalinity enhancement inside the Italian environmental code, code law, actually I don't know how to translate in English, but it's basically where it's written everything that is legal to be done, industrially speaking. How can we do that? Basically, we need to pass through the Parliament in Italy to approve this law. But in order to do that, we need this environmental impact framework that should be done before making an industrial plant and that the Minister of the Environment at least in Italy should assess. As soon as it's legal, then there are administrative permits that are based on this legal framework. And the administrative framework permits are based on industrial waste treatment, injection stuff. So it's tricky because when you find the persons that understand what you're doing, they try to help you. Not give you permits because you know them etc, but because it's something that is really similar to a desalination plant, to something that's already in the industry. So I believe that as soon as we are able to prove to politics and to include this new technology inside this will be more straightforward for everybody, not just for Limenet but for all the world. And this is for a coastal outfall of ocean alkalinity enhancement. For open ocean ocean alkalinity enhancement will be harder, so we need to pass through the London Convention, etc. But I believe it should be done in a second step. So, first of all, we need to make it legal in a country from a coast and then to say why is not legal the same stuff outside?

Wil (51:50): But Italy is a party to the London Convention and its regulations also apply to coastal waters, right? So London must be having a role in this currently also, correct? 

Stefano (52:06) No. That's the paradox. So if you do that, if you do the injection through the land, it's national but this is really a paradox. If you the injection from the land with a pipe it's national administration even though you inject at two kilometers far into the sea. But if you just have a barge, small palafloor, and you are two meters, not on the land, but on the sea, no more the country. This is really a paradox. And you inject it in two meters. But it's not connected to the land. 

Wil (52:53): Yeah, it's an ongoing question in London too. So it'll be interesting to see how that gets resolved. So I have one other question, which is Sara before mentioned a bit talking about what kind of concerns are going to be important for the community, largely in terms of ecosystem impacts, things of that nature. Those are obviously questions that will be front and center if you're talking about doing this at any kind of scale, probably even at the experimental scale. And you've got a lot of potential stakeholders that would be involved in looking at what happens in coastal areas or in open ocean areas, you know tourism, fisheries and so forth. What procedures are contemplated for community engagement if you reach the field experiment level or potential deployment of these approaches?

Stefano (53:53) So Limenet, we are basically using the Frontier Community Benefit Plan guidelines that are basically aligned to the US Department of Energy requirements for community benefit plans. So this is the framework we are using. In Europe it's quite different, so we are, at least in Italy, we are not so concerned about community engagement with respect to what it is in the US. But since we want to work with Frontier, we decided to have it started. So how we do that and how we did it is we first of all try to engage with the community. So with labor, with all the stakeholders, what we find in the region where we want do that. So we did in La Spezia, we did also in Augusta, and we do a community assessment. So basically what we did is to study with books, with articles, what was the history of the region, what was the history of the city. So we found out that the region of Augusta from after the war, it was really heavily industrialized by petrochemicals that basically made a really big mess and so also the people were really, really against petrochemicals. They had so many cancers, many illnesses, etc. So then we do basically a stakeholder analysis in which we try to map the stakeholders and try to understand who they are and the taxonomy of the stakeholders that could be impacted by this project. And then we try to understand in the local context. And to ensure that everything and everybody are included and also try to categorize with different categories such as NGOs, such as local teenagers, community, schools, industrial players, local authorities, etc. So we really try matrix of these different stakeholders. And then we try to engage them in basically, meetings, in-person meetings. So this is what we did with local authorities, with the potential industrial players there, and also with schools and with the community. How we did that, we basically, with networks and with papers around the city, we try to engage people and try to say, OK, on this day, we are doing this meeting because we are in the...  I don't know how to say that, comune in Italian, so where is the center of the city? 

Anna (57:57): Municipality. 

Stefano (57:59): Municipality, yeah, correct. And basically, we did this for two times. One year before we wanted to be there, so basically we did late 2023 in Augusta, and we did the end of 2024. So we did this community engagement and we tried to understand and to show them why did we do that, what's the advantages, what the science behind it, why we decided to do this test there, and try really to be as much as transparent as possible with them and we really got really good feedback. And finally, we basically tried to understand, when we will be operating, the workforce and community agreements that we have with them. This is basically what we did and of course there are also these guidelines, also how you are able to increase the quality of job creation, also the workforce, how to use it, ensure the worker rights, the diversity, inclusion, the environmental justice of it. So this is the approach that we are trying to follow and so then we improve based on [sic] the feedback of the population. So after each meeting we give them a survey, how they feel, what's the question, and are they happy, not happy, are they worried? 

Wil (58:38): And do you have, I guess, two brief follow-up questions on that. One, do you have formal contractual community benefit agreements in place or will prior to doing this, or is it more informal? 

Stefano (58:57): It's more informal right now. 

Wil (58:59): So, the last thing I'd ask is just a hypothetical. Let's say you went to these communities and, you know, the local municipalities are telling you,you don't essentially need to do this, it doesn't sound like the federal government's necessarily requiring it. Let’s say that you get the permits that you require, but it's clear that the communities don't want you to do this. What would you do? 

Stefano (59:28): I will do that, so I will try to find an agreement. 

Wil (59:34): But if you couldn’t get one, I'm just saying, let's say you get the permits, but the community says, we don't want you to do this. What do you do? 

Stefano (59:45): No, actually, I don't have to arrive to that situation. It's important that if you have a no, it's a no before you make the final investment decision, you get the administrative permit. So you really need to work in advance to get at least an informal yes with the communities because they're entrepreneurs, investors, I mean. Then you need to do the project, because if not, you will need to cut the jobs of your company. That's also something that we experienced in Augusta, not for the community, but for the Ministry of Environment. So we got a note from the Ministry of Environment, because they said, no, we are doing another restoration analysis in that city, so it cost a lot of millions of euros, and we need to wait, etc. Before having that no, we were hiring people from Augusta for running the plant. And then we had to tell these people, guys, the Ministry of Environment said no, we need to wait one year. That’s no good. So, based on this experience, you need to have this information really, really far before. So that's why it's really, very important that you are 100% transparent, you try to engage them in a deeply and really humble way and also because, I mean, at the end of the day, we are here to try to save the environment, not to make it worse. 

Anna (1:01:28): I think it's a a really important learning from the OAE community in the past two, three years to very much prioritize community engagement. And every project is learning this in their own ways, but I'm very glad to hear that you're prioritizing it despite not being, I suppose, legally obligated to do. So I think that's very much the right way. With that, perhaps we have to wrap it up. Thank you so much, Stefan and Sara, for joining us. I'm looking forward to catching up, having you, hopefully, back in a year or so with more updates and news. 

Stefano (1:02:08): Thank you, Anna. 

Sara (1:02:09): Thank you.

Anna (1:02:11):  And as always, of course, thank you to our listeners. If you have any feedback, recommendations for episodes or so, feel free to email us at plansea@carbontosea.org. If you liked the episode, please comment, please share it widely. And with that, wishing you a wonderful weekend.