Recirculating Aquaculture Systems for a Carbon Neutral Aquaculture

By Dr. Praneet Ngamsnae

Achieving sustainable food production while mitigating greenhouse gas emissions is a critical challenge for the planet. Aquaculture, as one of the fastest-growing food sectors, must evolve to align with climate-neutral goals.

Recirculating Aquaculture Systems (RASs) are emerging as a promising path to carbon neutrality in aquaculture. They offer a controlled environment for fish farming, which not only enhances production efficiency but also supports sustainable practices, minimizes environmental impacts by recirculating and reusing water, and thus significantly reduces water consumption and pollution. Furthermore, the integration of advanced technologies and innovative approaches within RAS can potentially lead to a truly carbon-neutral aquaculture industry. This article reviews the concept of carbon neutrality, describes the architecture and operation of RASs, evaluates their environmental benefits, surveys their current deployment in Southeast Asia, contemplates their social dimensions, and concludes by envisioning their future developments.

Carbon Neutrality and Major Drivers of Carbon Emissions in Aquaculture

Carbon neutrality refers to balancing emitted carbon dioxide (CO₂) with an equivalent amount sequestered or offset, resulting in a net-zero carbon footprint. In aquaculture, this entails reducing direct emissions (e.g. energy consumption, feed production, transportation), integrating renewable energy and energy recovery, and investing in offset projects to neutralize unavoidable emissions.

The carbon footprint of aquaculture systems is shaped by several interrelated factors, with feed production, energy consumption, and production techniques playing the most prominent roles. Understanding these elements is crucial for advancing sustainable aquaculture practices and reducing environmental impacts.

Feed production represents one of the largest contributors to carbon emissions, accounting for approximately 24.86% of the total carbon footprint in large yellow croaker farming (Fan 2024). This impact can be mitigated through more efficient ingredient sourcing and the incorporation of waste-derived materials into aquafeed formulations (D’Abramo 2024).

Energy consumption is another significant driver, particularly when reliant on fossil fuels. In some cases, such as for the operation of an aquaculture vessel, energy use was identified as the single largest source of carbon emissions (Fan 2024). Transitioning to renewable energy sources, such as offshore wind power, offers a viable pathway for reducing these emissions.

Production techniques also strongly influence carbon intensity. However, innovative approaches such as Recirculating Aquaculture Systems (RASs) and Integrated Multi-Trophic Aquaculture (IMTA), for example, can optimize resource utilization, enhance efficiency, and minimize waste generation, thus reducing carbon intensity (Castilla-Gavilán 2024).

Towards Carbon Neutral Aquaculture with RASs

Recirculating Aquaculture Systems (RASs) presents a viable pathway toward carbon-neutral aquaculture through integrated strategies that reduce resource consumption, optimize waste utilization, and incorporate complementary sustainable technologies.

By recirculating and reusing water, RAS can lower water consumption by up to 99% compared with conventional systems, while maintaining optimal rearing conditions (Lal 2024). Efficient waste management further contributes to sustainability; nutrient-rich effluents can be redirected to cultivating microalgae, producing biofuels and other high-value products, while sequestering CO₂ and generating oxygen (Ende 2024; Kumar 2024).

Integration with microalgae culture and aquaponics amplifies these benefits. Microalgae absorb CO₂ and nitrates from effluents, producing biomass suitable for bioenergy and bioproduct markets (Sucunthowong 2023; Kumar 2024). Aquaponics, for its part, utilizes nutrient-rich wastewater for plant production, closing nutrient loops and promoting a circular bioeconomy.

Continued technological advancements and system integration approaches remain essential to fully realize the carbon-neutral potential of RAS in global aquaculture.

Structural Design of RASs

Recirculating Aquaculture Systems (RASs) are closed-loop systems that continuously recycle water through a series of interconnected processes, which include mechanical and biological filtration, oxygenation, temperature regulation, and waste removal (Lal 2024). Their design enables the maintenance of optimal water quality while significantly reducing effluent discharge, making RASs highly suitable for high-density, controlled aquaculture.

A typical RAS consists of several integrated components working in synergy. Production tanks serve as the primary rearing space, where fish are maintained at carefully controlled stocking densities. Water from these tanks passes through mechanical filtration units, such as drum or sieve filters, to remove solid waste. It then moves to biological filtration systems often incorporating biofilters or nitrification media that convert toxic ammonia into less harmful nitrate (Bartelme 2019). The system also includes processes for controlling carbon dioxide levels and pH, ensuring a stable water chemistry conducive to fish health. Oxygenation is provided through diffusers or pure-oxygen injection systems, while heat exchangers regulate water temperature and facilitate energy recovery. To safeguard fish from microbial pathogens, ultraviolet (UV) or ozone disinfection modules are incorporated (Abdul Nazar 2013).

Overall, the architecture is designed to optimize water reuse, often exceeding 90%, and can be integrated with renewable energy sources or waste-heat capture technologies.

Advantages and Challenges of RASs

Recirculating Aquaculture Systems (RASs) offer numerous advantages that make them an attractive option for sustainable aquaculture. They significantly reduce operational costs associated with feed, predators, and parasites, while eliminating the release of parasites into natural waters. RAS also reduce reliance on antibiotics and therapeutants, providing a marketing advantage for producing high-quality, “safe” seafood. Their flexibility in location allows farms to be established near markets or on brownfield sites, provided access to clean water is available. The ability to cultivate a wide range of species, including non-endemic ones, regardless of temperature requirements, is supported by a precise environmental control that results in excellent feed conversion ratios (FCRs), faster growth, and optimal fish health through effective waste removal and stable water chemistry (Aich 2020).

From a climate change perspective, RASs have strong potential to contribute to carbon neutrality. Closed-loop water recirculation reduces freshwater extraction and wastewater discharge, lowering the carbon footprint of water treatment and pumping. The controlled nature of these systems facilitates integration with renewable energy sources such as solar, wind, and biogas, thus reducing greenhouse gas emissions. Locating production near markets decreases transportation distances and cold-chain energy demands, further cutting CO₂ emissions. Additionally, integrating carbon capture and utilization (CCU) methods, such as algal biofilters that absorb CO₂ and convert it into biomass, presents an opportunity for direct climate impact mitigation.

However, RAS also faces significant challenges. A shortage of skilled and technically proficient personnel can limit operational efficiency, particularly for large-scale systems that require 24-hour water quality monitoring. Economic feasibility often depends on market prices, waste utilization, product quality, stocking densities, energy costs, and financial considerations such as depreciation and interest rates (Aich 2020). Maintaining optimal water temperatures can be energy-intensive for certain species, and specialized expertise may be necessary for species with strict environmental needs. Selecting appropriate species is critical, especially when competing with lower-cost or imported products, requiring thorough risk assessment. Cost-reduction measures such as converting farm waste into value-added products and generating on-site renewable energy show considerable promise, but they demand both technical capacity and long-term investment planning.

In summary, beyond its environmental benefits, RAS can stimulate local economies by reducing reliance on imported seafood, creating jobs, and lowering emissions from long-distance transport (Lal 2024). However, barriers such as high capital costs, operational complexity, and need for precise biological balancing in integrated systems persist.

Contributions of RASs to Environmental Sustainability

Recirculating Aquaculture Systems (RASs) demonstrate strong potential for advancing environmental sustainability in aquaculture through their ability to optimize resource use and minimize ecological impacts. One of the most significant advantages lies in their energy efficiency and emissions management. By minimizing water exchange and integrating heat recovery systems, RASs substantially reduce the pumping and heating demands typically associated with traditional aquaculture operations. When powered by renewable energy sources such as solar, wind, or biogas, these systems can operate with a markedly reduced carbon footprint and, in some cases, approach true carbon neutrality (Castilla-Gavilán 2024).

Water conservation is another key sustainability feature of RASs. Unlike conventional flow-through systems, which require continuous large-scale freshwater input, RASs recycle more than 90% of their water (Lal 2024). This high rate of reuse not only dramatically decreases overall freshwater consumption but also limits the discharge of nutrient-rich effluents into surrounding ecosystems, thereby reducing the risk of environmental degradation.

In addition, RASs enable effective waste management by concentrating both solid and dissolved wastes within the system. This allows for nutrient recovery through methods such as anaerobic digestion, which can generate renewable biogas, or by processing the waste into nutrient-rich fertilizers for agricultural use. Such practices help close nutrient loops, reducing the reliance on synthetic fertilizers and mitigating the risks of eutrophication in natural water bodies (Asiri 2020). Through these integrated approaches, RASs offer a pathway toward aquaculture that is not only productive but also aligned with broader environmental protection goals (Aich 2020).

Social Considerations of RASs Use

The adoption of Recirculating Aquaculture Systems (RASs) presents significant social implications for livelihoods, skills development, and community perceptions. RASs can create diverse skilled employment opportunities in engineering, water quality management, and biosecurity, advancing the professionalization of aquaculture and opening new career pathways. Therefore, sustainable RAS operation hinges on capacity building through technical training and continuous knowledge transfer, equipping local operators to manage water quality, disease control, and system optimization while strengthening community resilience.

However, high capital costs may exclude smallholder farmers and reinforce sectoral inequalities unless mitigated by targeted financing, cooperative models, or public-private partnerships. Acceptance of RASs may as well be hindered by perceptions of “factory farming” and the displacement of culturally significant pond systems.

Nevertheless, proactive engagement via demonstration sites, participatory design, and transparent communication can foster trust, address cultural concerns, and promote shared ownership, ensuring smoother integration of RAS technology into local contexts.

Current Practices of RASs in Southeast Asia

In Southeast Asia, where aquaculture plays a critical role in both food security and rural livelihoods, Recirculating Aquaculture Systems (RASs) are beginning to gain traction as an innovative production method. Although their adoption remains limited primarily due to high capital requirements, technical complexity, and constraints in reliable energy supply, several promising pilot initiatives are emerging across the region.

In Thailand (Espinal 2019), Vietnam (TUEWAS 2024), and Indonesia (Hanif 2021), RAS facilities are being developed to cultivate high-value aquatic species, including tilapia, freshwater shrimp, and grouper. Many of these facilities are designed with integrated renewable energy systems, such as solar photovoltaic arrays or biogas generation, to reduce operational costs and lower carbon emissions. In addition, some RAS operations are establishing partnerships with agricultural enterprises, channeling nutrient-rich effluents into hydroponic or horticultural production.

This integration not only maximizes resource use but also exemplifies the principles of a circular economy, creating synergistic benefits for both food and energy systems while supporting broader goals of carbon neutrality.

Conclusion

Recirculating Aquaculture Systems (RASs) offer a compelling pathway toward achieving carbon-neutral aquaculture by maximizing resource efficiency, minimizing environmental impacts, and integrating renewable energy solutions alongside closed-loop nutrient cycling. These systems demonstrate that sustainable fish production can be achieved without compromising ecological integrity, particularly when designed to recover and reuse energy while optimizing water use and waste management.

Despite these advantages, the structural complexity and high upfront investment requirements of RASs remain significant challenges, particularly for smaller-scale producers. However, emerging pilot projects in Southeast Asia illustrate the technology’s potential when strategically combined with energy recovery systems and agri-aquaponic integration, creating synergistic benefits across food and energy sectors.

To unlock the full potential of RASs as a climate-neutral and sustainable food production technology, it will be essential to address social and economic barriers. This includes developing inclusive business models that enable smallholder participation, implementing targeted capacity-building programs to equip local operators with the necessary technical expertise, and fostering supportive policy frameworks that encourage adoption. Through these combined efforts, RASs can evolve from a promising innovation into a mainstream solution for sustainable aquaculture in a changing climate.