Recirculating aquaculture systems (RAS) are attracting growing attention as a sustainable aquaculture technology that can reduce water use, control rearing conditions, and lower environmental impacts by filtering and reusing water. At the same time, RAS facilities rely on pumps, filters, aerators, and other equipment that are often operated continuously or according to conservative fixed schedules, resulting in substantial electricity consumption to maintain stable rearing conditions.
This energy burden is one of the major challenges facing the wider adoption of land-based aquaculture. Renewable energy sources such as solar and wind power offer a promising solution, but their output fluctuates significantly depending on weather conditions. At the same time, aquaculture facilities cannot simply reduce equipment operation whenever electricity is scarce, because biological and water-quality conditions limit when and how electricity use can be adjusted. In this study, dissolved oxygen (DO) was used as the process state linking aerator operation to fish safety. The key challenge is therefore to identify and use the flexibility available within those operating limits to reduce energy use and electricity-related CO₂ emissions without compromising safe production.
A joint research team from Saitama University and the University of the Ryukyus set out to develop a process-aware energy management framework for coordinating flexible equipment operation with renewable generation, battery storage, and grid electricity in RAS. The team used experimental data from Malabar grouper (Epinephelus malabaricus), a commercially important aquaculture species, to construct a species-specific DO estimation model that accounts for the effects of fish body mass and feeding. This model linked aerator operation to a biologically meaningful operating constraint. The researchers then embedded the model into an economic model predictive control strategy that schedules aerator operation and battery/grid use in coordination with available on-site solar and wind generation. Through year-long simulations, the team demonstrated that the framework could substantially reduce electricity consumption and electricity-related CO₂ emissions while maintaining DO above the prescribed safety margin and improving resilience during grid outages. The study was published online on May 25, 2026, in Sustainable Energy Technologies and Assessments.
Key findings of the study include:
- In year-long simulations, the proposed method reduced annual electricity use by 17.8% compared with continuous aeration.
- CO₂ emissions were reduced by 31.9% while dissolved oxygen levels were maintained above the safety margin.
- In simulations of grid outages, optimized aerator control helped maintain safe DO levels and reduce the risk of fish mortality.
- Sensitivity analysis showed that process operating limits can strongly affect energy-system flexibility: under the modeled conditions, adjusting the DO safety margin within the examined range provided flexibility comparable to increasing battery capacity by a factor of 5–10.
"Our results show that aerators in aquaculture facilities should not be treated simply as fixed electricity loads," says Assistant Professor Akito Nakadomari of Saitama University, the corresponding author of the study. "From a power and energy systems perspective, the key is to understand how the process behind electricity demand determines when and how equipment can be operated. By incorporating those process dynamics and operating requirements into energy management, we can identify and use flexibility that remains hidden. In this study, dissolved oxygen provided the link between aerator operation and safe fish-rearing conditions, enabling aeration to be coordinated with renewable generation, battery storage, and the grid."
The findings bring a new perspective to research at the intersection of power and energy systems, control engineering, and aquaculture. Energy systems and fish-rearing conditions have often been considered separately, but this study shows that process dynamics and biological constraints can be incorporated into the core of energy optimization. More broadly, the study illustrates how the usable flexibility of a load can be characterized from the underlying process conditions and operating requirements that govern safe and reliable operation, rather than assumed in advance. This process-aware approach could support future research on species-specific and multivariable process models, renewable-energy-integrated aquaculture, and resilient food production systems.
"System flexibility can be enhanced not only by adding batteries or other hardware, but also by understanding the processes that shape electricity demand," Nakadomari says. "This study used dissolved oxygen to demonstrate the concept, but RAS operation is governed by multiple interacting process states and operating requirements. By incorporating those interactions into energy management, we aim to identify additional flexibility without compromising safe and reliable production. The same principle could also be extended to other essential facilities governed by safety, quality, or service requirements."
The research team also notes that the study provides a foundation for a more comprehensive characterization of RAS flexibility. With further validation, the framework may be extended to different aquaculture species, larger RAS facilities, and regions with varying renewable energy availability and grid reliability. Future work will incorporate additional water-quality states, biological requirements, production objectives, and equipment constraints so that flexibility can be evaluated from the process as a whole rather than through the single DO state used here. Such a framework could help operators make better decisions about aeration, battery capacity, renewable energy installation, and emergency preparedness.
