Sand filters are classic deep-bed filtration: water passes through a bed of sand (or similar media) where particles lodge in the pores. The technology is well known in municipal and industrial water treatment; in aquaculture it is often used for polishing, effluent treatment or continuous sand filters (e.g. DynaSand class) rather than as the sole solids step in heavily loaded RAS.
Types in farming contexts
- Batch/pressure sand filters with periodic backwash.
- Continuous sand filters where sand is washed and returned during operation.
- Multimedia filters (sand + anthracite, etc.) for a wider particle range.
Strengths and limitations
- Good polishing and steady solids removal when sized correctly.
- Continuous designs can give stable operation with fewer batch spikes.
- Backwash needs water and energy; poor operation causes channelling or media loss.
- In intensive RAS, drum filters are often first — sand as polishing or on effluent.
Design and operating notes
Size on filtration rate (m/h), raw-water quality and target outlet TSS/turbidity. Monitor headloss, backwash frequency and media level. In FlowFarm-like semi-flow concepts, continuous sand filtration is often used as an integrated biostage/particle step — see flow-through.
See also