Engineering recirculating seawater systems for research holding, broodstock and species cultivation — mass-balanced biofiltration, solids capture, gas control and disinfection that re-use seawater while holding tight, stable, fully-monitored conditions.
A recirculating aquaculture system re-uses the same seawater continuously, treating it between passes so that water quality stays within the species’ tolerance while intake, heating/cooling and discharge volumes fall by 90–99%. That makes RAS the natural choice where a clean intake is limited, a discharge consent is tight, or quarantine and biosecurity matter. The engineering challenge is a closed mass balance: every gram of feed becomes ammonia, solids and carbon dioxide that the system must remove as fast as it is produced. Reynolds & Bauhm sizes each unit operation from that balance, so the system holds steady at design load with margin for peaks.
Drum filters and swirl/settling remove faeces and uneaten feed first — solids left in the loop break down to ammonia and rob oxygen, so fast removal protects every downstream stage.
Moving-bed (MBBR) or fixed-bed biofilters convert toxic ammonia (TAN) and nitrite to nitrate. Media area is sized from the feed-derived TAN production and the design areal nitrification rate.
Biological TreatmentFoam fractionation strips dissolved organics and fine colloids that biofilters miss — clarity, lower UV load and more stable pH, especially valuable in marine RAS.
Degassers strip the carbon dioxide that biofiltration and respiration produce (protecting pH), while oxygen cones or low-head oxygenators hold DO above saturation at density.
OxygenationIn-loop UV (and optional ozone) controls pathogens and clarifies water between tanks for biosecurity and quarantine, with residual fully managed before return.
UV & OzoneA small new-seawater bleed dilutes nitrate and salts; alkalinity (bicarbonate) and salinity are dosed/made-up to hold pH and osmotic stability.
Indicative values — sized from the feed load, species and stocking density.
| Parameter | Typical basis | Driver |
|---|---|---|
| System turnover | 1–4 system volumes/hour | Solids removal & DO delivery |
| Daily make-up | 1–10% of system volume | Nitrate & salt dilution |
| TAN target | < 0.5–1.0 mg/L | Ammonia toxicity (species-dependent) |
| Biofilter sizing | from g TAN/day & areal rate | Nitrification capacity at design feed |
| Dissolved oxygen | > 90–100% saturation | Stock health at density |
| pH / alkalinity | pH ~7.8–8.2; alk dosed | Nitrification & stock stability |
| Temperature | Set-point ± 0.5–1.0 °C | Species health & repeatability |
Tell us the species, biomass and feed regime — we’ll mass-balance the system and size the biofiltration, solids, gas control and disinfection to hold it stable and monitored.
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