Membrane Filtration (UF/RO in Aquaculture)

Membrane filtration in aquaculture spans microfiltration (MF, 0.1–10 µm pores), ultrafiltration (UF, 0.01–0.1 µm), and reverse osmosis (RO, rejecting ions at 98%+), each serving a distinct treatment step. MF and UF polish RAS water, removing bacteria, fine colloids, and virus-sized particles that escape drum and media filters, and are the backbone of quarantine and broodstock water where absolute pathogen exclusion matters; UF permeate is typically disinfected to 4–6 log bacterial reduction. RO produces make-up water of defined quality from seawater or brackish sources, controlling salinity, hardness, and dissolved contaminants in hatcheries for sensitive larvae, and enabling land-based systems to be sited far from suitable water sources. Operating pressures run near 1–3 bar for UF and 50–70 bar for seawater RO, with energy costs of 2–4 kWh per m³ for RO; flux decline from fouling is the dominant operational issue, so pretreatment with media filtration and 5 µm cartridge filters is standard, and membranes require weekly clean-in-place with alkaline and acid solutions. Recovery ratios of 50–75% mean a significant concentrate stream must be disposed of. Capital and operating costs keep full membrane treatment largely confined to hatcheries, broodstock, and high-value RAS, but falling membrane prices are steadily extending its reach into grow-out water reuse.