Aquaculture tank selection: PP, modular or steel

Round tanks clean themselves

Water enters a round tank tangentially and rotates. The rotation carries solids to a centre bottom drain, where they leave before they break up. That is why most RAS use round tanks. How fast the water turns is set by the inlet flow, the inlet direction and the size of the inlet openings (UPC), and it is adjusted for the species.

Cornell University and the Freshwater Institute tested the dual-drain round tank with rainbow trout at 60 kg/m³ (NRAC). Bottom-drain water averaged 19.6 mg/L TSS against 1.5 mg/L at the side wall, with the bottom drain taking 5–20% of the flow. At a diameter-to-depth ratio of 12:1, solids settled around the centre drain; 3:1 and 6:1 flushed well.

المواد

What decides the choice

• Building and site: door width, ceiling height and whether the floor can be dug.
• Species: bottom-living fish, fast swimmers and fry need different depths and flows.
• Water: seawater rules out bare steel in contact with water.
• Install time: modular and steel tanks assemble on site.
• Expansion: a grid of equal tanks is easy to extend.

Drains and outlets

A centre bottom drain takes the settled solids. A side outlet can take most of the flow. Drain lines must be sized to the treatment loop, not to the tank alone.

الأحواض الموجودة

Existing tanks can often be kept. In Riyadh we kept 25 concrete tanks and rebuilt the treatment loop around them. See fish tanks أو farm upgrades.