Background and problem statement
Large land-based recirculating aquaculture is expanding quickly, but many flagship facilities still combine high capex and energy use with low tolerance to process upsets. Recent high-profile projects—and failures—have largely involved salmon, yet the core lessons are architectural and transferable across freshwater and seawater farming (finfish, crustaceans, aquaponics and other multitrophic co-productions). A dominant "plant-first" logic scales biomass around a fixed, centralised treatment plant: it can lower unit costs on paper, but it also couples biological and technical risk, magnifies single-point failures (power, pumping, water chemistry), and drives operational and compliance complexity. Meanwhile, sustainability assessment is shifting from within-farm discharge metrics toward regional nutrient carrying capacity and valorisation pathways.
Key challenges in state-of-the-art RAS (salmon as reference case)
In large grow-out RAS (salmon often the reference case), four challenge clusters dominate: (i) capex concentrated in central life-support and treatment, incentivising ever larger volumes to dilute fixed costs; (ii) opex exposure from pumping head, temperature control, oxygen and CO2 management, buffering chemistry, and energy-price volatility; (iii) systemic risk from tightly coupled loops and limited buffering, where disturbances can escalate across large biomasses; and (iv) increasing assurance, monitoring, and reporting requirements that translate into more unit processes, sensors, automation, and procedures. The common response is "technology stacking" to treat symptoms; we argue for architectural simplification instead.
The RasRace concept: designing for simplicity, modularity and containment
RASRace is a "module-first" alternative to plant-first RAS. Each production module is self-contained (tank + essential treatment and control) rather than dependent on a single, central plant. The concept uses ring-shaped tanks ("raceway") to create controlled hydrodynamics and short, manageable residence times, with physical access designed for rapid inspection, cleaning, and maintenance. Decentralising critical functions compartmentalises biological risk, reduces single-point failures, and supports stepwise capacity addition. Economically, standardised modules improve repeatability and learning rates—shifting investment logic from scaling up one bespoke facility to scaling out replicable contained units.
From effluent control to regional nutrient balancing
Beyond within-farm effluent control, circular nutrient outcomes are often constrained by regional nutrient-handling capacity and logistics. High-retention systems can concentrate sludge and dissolved nutrients, but benefits depend on practical routes for stabilisation, transport, and valorisation (e.g., fertiliser, biogas, or as growth media for heterotrophic microorganisms). We therefore propose judging recirculating systems by how well they enable simple, auditable nutrient capture and routing—not only by internal water quality and unit cost. In parallel, the CircularRainbow project (Interreg Italia-Slovenija) has investigated RAS for Mediterranean contexts where summer water scarcity can restrict flow-through land-based aquaculture. Such typology comparisons enable sustainability assessments across aquaculture typologies. Overall, the presentation highlights design choices that prioritise containment, compartmentalisation, and nutrient balancing—supporting scaling out modular units (rather than scaling up single plants) and reducing reliance on add-on complexity.