Bead filters use floating plastic beads as both mechanical filter media and biofilm surface. Water is pushed or pumped through the bed; particles are trapped between beads while nitrifying bacteria can grow on the surfaces.
The technology is common in smaller RAS, hatcheries and hobby/research systems where one compact unit should combine solids capture and some biological treatment. In large commercial RAS, separate drum filters plus dedicated biofilters (MBBR, fixed bed, trickling) are more often the standard.
Advantages
- Compact “two-in-one” function (solids + biofilm area).
- Relatively simple installation in smaller systems.
- Backwash/bed expansion releases sludge.
Limitations
- Capacity and hydraulics can bottleneck at high feed rates.
- Biofilm and solids in the same bed can cause oxygen-poor zones if aeration/expansion is inadequate.
- Backwash must be regular — otherwise headloss and TAN risk rise.
- Harder to optimise mechanics and biology separately than with dedicated stages.
Operating practice
- Track headloss and schedule washes before the bed locks up.
- Keep DO adequate in the bed if nitrification is expected.
- Expect large systems often to benefit from splitting solids and biological stages.
See also