RAS Aquaculture Design Guide: Sizing, Equipment Selection and CAPEX Benchmarks
A supplier-neutral primer on recirculating aquaculture system design for land-based salmon, tilapia and shrimp projects — how the treatment loop is sequenced, how each stage is sized, and what capital cost ranges to use for early project screening.
1. Start from feed load, not tank volume
Every RAS component is sized from peak daily feed. Feed determines TAN production, oxygen demand, CO₂ generation and solids load. Fix your target annual tonnage, biomass curve and feed conversion ratio first; only then size tanks, pumps and treatment units. Projects that begin with a tank layout almost always end up with an unbalanced loop.
2. Solids removal comes first
Dual-drain tanks capture settleable solids at the centre; drum or belt filters at 40–100 µm remove the remainder. Fine solids that pass the filter become biofilter fouling, oxygen demand and gill irritation. Specify filter capacity at peak flow with one unit out of service, and plan sludge handling and dewatering at design stage — permitting frequently hinges on it.
3. Nitrification: the core of the loop
Moving-bed (MBBR) and fixed-bed reactors both work; the decision is driven by footprint, energy, and operator skill. Size on areal TAN removal at design temperature and pH, and protect alkalinity — nitrification consumes roughly 7.05 g of alkalinity as CaCO₃ per gram of TAN oxidised. Provide a documented biofilter maturation plan for start-up; a 4–8 week ramp is normal.
4. Degassing and oxygenation
CO₂ accumulates fastest in high-reuse systems and limits stocking density long before ammonia does. Strippers should hold CO₂ below 10–15 mg/L for salmonids. Oxygen is added after degassing, using low-head oxygenators or cones with measured transfer efficiency. Redundant supply, independent DO probes and alarm-triggered emergency diffusion are standard in bankable designs.
5. Water exchange, nitrate and off-flavour
Reuse rate sets your operating cost and your risk profile. Above ~95% reuse, nitrate control usually requires denitrification, and geosmin/MIB management requires dedicated purge tanks with clean water and 3–10 days of depuration. Model heating, chilling and pumping energy with local tariffs — energy is the largest controllable OPEX line in most temperate projects.
6. CAPEX, OPEX and bankability
Split the budget into civil works, process equipment, buildings and services, and contingency (10–15% minimum). Lenders look for a mass-and-energy balance, an independent engineer's review, a commissioning schedule with biological ramp-up, and evidence of supplier capability and after-sales support. Equipment selection should be justified on process duty, not on brand preference.