Enhancing Carbon Sequestration through Innovative Aquaculture Practices

Supervisor: Dr James Rae, School of Earth and Environmental Sciences

Co-Supervisors: Dr Andrew Whiston, RAStech;

Prof Andrea Burke, School of Earth and Environmental Sciences

 

**This project is fully funded by The Fishmongers’ Company’s Fisheries Charitable Trust for three years (tuition and stipend) with expected start in Autumn 2025**

Deadline 31^st March 2025

 

Project Summary

Rising CO₂ and growing populations create conjoined challenges for a sustainable future.  This PhD will investigate a novel approach to tackle these challenges by pairing a new CO₂ capture technology with sustainable, onshore production of protein-rich seafood.

Recirculating Aquaculture Systems (RAS) allow seafood production to be moved onshore, minimising impacts on marine environments.  Given recent policies limiting the growth of offshore aquaculture in several major production regions (e.g. Scotland, British Columbia, Norway), RAS provides a solution for future growth in this sector.  The key challenge of RAS is that services previously provided passively by marine environments (e.g. waste disposal) must be actively managed.

Waste management in RAS makes use of novel strains of bacteria that convert ammonium (NH₄⁺) into nitrate (NO₃^-).  This maintains potentially harmful ammonia-based compounds at safe levels, but it also consumes alkalinity, leading to more acidic and variable pH.  Combatting this requires an alkalinity source, most commonly sodium bicarbonate. However, the production of sodium bicarbonate produces CO₂ and is extremely energy intensive, so represents a significant portion of RAS carbon footprint.

St Andrews and RAStech have developed a novel alternative to sodium bicarbonate, which will dramatically lower the carbon footprint of RAS, and opens the door to carbon negative seafood production. Our method harnesses the natural reaction between CO₂ and limestone, which produces calcium and bicarbonate ions, providing a source of alkalinity.  In nature this reaction takes place over thousands of years - and is indeed one of the long term sinks for anthropogenic CO₂.  We have worked out a way to accelerate this reaction (known as Accelerated Weathering of Limestone - or AWL), using a reactor that produces alkalinity fast enough to keep pace with demands from RAS.  This offers a flexible, lower carbon - and critically, cheaper - solution for RAS alkalinity supply.

This PhD project will further the development and deployment of this solution in the following areas:

• Optimisation of the reactor: From pilot work, different limestone types and grain sizes, along with different flow rates of water and CO₂, yield different alkalinity fluxes. Systematic work is required to explore this parameter space to find the most efficient solution for alkalinity production while at the same time ensuring that the limestone used is clean and suitable for food production. Similarly, work with different CO₂ sources (e.g. biomass, brewery gas, etc.) is required to explore possible options for this portion of the reaction and associated sites for efficient deployment.  And within the reactor itself, optimisation of flow rates and CO₂ introduction have the potential to transform process efficiency.
• Additional carbon and nutrient drawdown: The water produced by the AWL/RAS process is rich in alkalinity, but also in CO₂ and nutrients. We have been exploring the use of paired seaweed growth to draw down nutrients and CO₂, optimising the carbon footprint of the overall system, alleviating (regulated) concerns on nutrient discharge, and creating an additional commercial product, with markets in catering and agriculture. Further optimisation will boost the efficiency of this process to keep pace with nutrient and CO₂
• Carbon and nutrient budgeting: To further optimise system performance and account for carbon and nutrient budgets, we will build a digital twin of the AWL/RAS/seaweed system. This will be used to explore cost optimisation and the potential for use in carbon markets.

The successful completion of this project will reduce the carbon footprint, cost, and nutrient budget of RAS, providing a novel solution for sustainable seafood production.

 

The RAStech facility for experimental aquaculture solutions.

Training & Skills

The student will gain deep understanding of marine chemistry, carbon cycling, and novel carbon dioxide removal strategies.  The student will also receive specific training in novel recirculating onshore aquaculture techniques, including biofiltration, pH control, and waste valorisation, as well as training and expertise in environmental and marine chemistry and analytical measurements. The student will be trained and work in a geochemistry laboratory to make nutrient and carbonate system measurements. The student will also be trained in the use of Matlab/Python to process and analyse data and create a digital twin.  Furthermore, over the course of the PhD the student will gain transferable skills such as scientific writing, statistics and data analysis, and problem-solving, as well as time management and working towards a long-term goal.

Research Environment

The student will join a dynamic research team within the Climate, Ocean, and Atmosphere at St Andrews (COASt) Group who study fundamental and topical questions about our coupled ocean-atmosphere and climate system with expertise in oceanography, atmospheric dynamics, paleoclimate, and biogeochemistry. The student will also work closely working with partners at RAStech, a SME based at the University of St Andrews Eden Campus, who specialise in novel aquaculture solutions. This broad network of colleagues and collaborators within the School of Earth and Environmental Sciences and industry will provide wide exposure to both fundamental and applied research questions and techniques, providing an ideal environment for development as an independent researcher or a career in applied environmental and marine science, including aquaculture and carbon solutions.

How to apply and Deadlines

We are looking for candidates with at least a 2:1 (or overseas equivalent) BSc or MSc in a relevant field (Biology, Chemistry, Earth Science, Environmental Science, Oceanography) with experience with laboratory work (either through their degree or through independent research or employment) or marine culturing and interests in the carbon cycle and CO₂ management. For details on entry requirements and application procedures please see information on Postgraduate Research in the School of Earth and Environmental Sciences (https://www.st-andrews.ac.uk/earth-sciences/prospective/pgr/). Applications should be made via the University of St Andrews Postgraduate Research page (https://www.st-andrews.ac.uk/study/apply/postgraduate/research/). Applications are particularly welcome from people from the Black, Asian and Minority Ethnic (BAME) community, and other protected characteristics who are under-represented in research posts at the University.  

Please get in touch with James Rae jwbr@st-andrews.ac.uk if you have any questions. 

Deadline for application: 31 March, 2025

References and Further Reading

Doney, S.C., Wolfe, W.H., McKee, D.C. and Fuhrman, J.G., 2024. The science, engineering, and validation of marine carbon dioxide removal and storage. Annual Review of Marine Science, 17, pp. 55-81.

Martins, C.I.M., Eding, E.H., Verdegem, M.C., Heinsbroek, L.T., Schneider, O., Blancheton, J.P., d’Orbcastel, E.R. and Verreth, J.A.J., 2010. New developments in recirculating aquaculture systems in Europe: A perspective on environmental sustainability. Aquacultural engineering, 43(3), pp.83-93.

Oschlies, A., Bach, L.T., Fennel, K., Gattuso, J.P. and Mengis, N., 2025. Perspectives and challenges of marine carbon dioxide removal. Frontiers in Climate, 6, p.1506181.

Rau, G.H., Knauss, K.G., Langer, W.H. and Caldeira, K., 2007. Reducing energy-related CO2 emissions using accelerated weathering of limestone. Energy, 32(8), pp.1471-1477.

Renforth, P. and Henderson, G., 2017. Assessing ocean alkalinity for carbon sequestration. Reviews of Geophysics, 55(3), pp.636-674.

Van Rijn, J., 2013. Waste treatment in recirculating aquaculture systems. Aquacultural Engineering, 53, pp.49-56.