Oct 30, 2026Industry Solutions
RAS Drum Filter Troubleshooting: High Water Level, Frequent Backwash, Solids Carryover and Screen Fouling
Troubleshoot RAS drum-filter overflow, frequent backwash and solids carryover by checking micron size, solids load, water level, nozzles and screen fouling.
Common symptoms include rising upstream water level, nearly continuous backwash, solids after the filter, low filtered-water flow and screen blinding.
Check Actual Flow
Compare design flow, normal flow, peak flow, bypass flow and pump setting.
A filter can appear dirty when the real problem is hydraulic overload.
Check Screen Micron
A finer screen captures smaller particles but usually creates higher resistance, faster fouling and more backwash.
Check Solids Load
RAS solids load changes with feed rate, biomass, fish size, tank cleaning and uneaten feed.
A drum filter sized on flow alone may struggle when solids production rises.
Check Water-Level Control
Many drum filters trigger rotation and backwash from water-level difference.
Verify level sensor, float switch, setpoint, sensor fouling and control logic.
Check Backwash Pressure and Nozzles
Insufficient wash pressure can leave solids on the screen.
Check pump pressure, clogged strainers, valve position, nozzle blockage, spray pattern and manifold pressure.
Check Screen Fouling
Possible foulants include biofilm, grease, mineral scale, fine organic solids and algae.
Mechanical backwash may not remove every deposit.
Cleaning method should match screen material and foulant.
Check Drum Rotation
Verify motor, gearbox, drive, speed and alignment.
Intermittent or slow rotation can reduce cleaning effectiveness.
Check Inlet Distribution
Uneven flow may overload one part of the drum.
Review inlet pipe, baffles, water level and drum submergence.
Check Solids Carryover
Possible causes include screen damage, seal leak, bypass, opening larger than expected or particles smaller than the screen rating.
Inspect the screen and seals before assuming undersizing.
Practical Troubleshooting Table
Symptom | First Checks |
|---|---|
High upstream level | flow, screen fouling, micron size |
Continuous backwash | solids load, level sensor, screen area |
Poor cleaning | pressure, nozzles, fouling type |
Solids carryover | screen damage, seals, bypass, micron |
Uneven fouling | inlet distribution, nozzles |
Excess sludge water | backwash frequency, control setpoint |
Technical Basis
RAS studies commonly use drum filters as mechanical solids-removal units before biological treatment. Fine screen selection improves particle capture but also increases hydraulic resistance and cleaning demand.
The practical rule is:
troubleshoot flow, solids load, screen condition, water-level control and backwash system before changing the screen micron.
Need Help Troubleshooting an RAS Drum Filter?
Send HydroNovus the flow, screen micron, drum dimensions, fish biomass/feed, water-level behavior, backwash pressure, backwash frequency and photos of the screen/nozzles.