Drum Filters for Aquaculture — Specs, Sizing & Supplier Quotes
Rotary drum filters are the primary mechanical solids removal stage in almost every RAS and partial-reuse system. This guide covers what they remove, how to size one to your flow and feed load, what separates a cheap unit from a bankable one, and what drives the price — then puts your requirement in front of qualified manufacturers.
What drum filters do
- A rotating drum covered in a fine filter screen (micro-screen) that traps suspended solids as water passes from inside the drum outward.
- Solids build on the screen, the water level rises, a level sensor starts drum rotation and a pressurised spray bar backwashes the captured sludge into a collection tray.
- It is the first treatment stage after the tank outlet: removing faeces and uneaten feed before they break down protects the biofilter, oxygen demand and water clarity.
- Standard on RAS, flow-through polishing and hatchery intake; also used on intensive shrimp and biofloc systems where solids control limits stocking density.
Typical specifications
| Parameter | Typical range | What it means for you |
|---|---|---|
| Screen micron rating | 40–100 µm (60 µm most common) | Finer screens capture more solids but need more backwash water and screen area. |
| Hydraulic capacity per unit | 50–3,000 m³/h | Depends on drum diameter, submergence and micron rating — always confirm at your micron. |
| Backwash water use | 0.2–1.0% of treated flow | Rises sharply with heavy feed loads and finer screens; budget the make-up water. |
| Backwash pressure | 4–8 bar | Dedicated booster pump; low pressure is the top cause of blinded screens. |
| Drive power | 0.25–2.2 kW motor + backwash pump | Filter power is minor next to pumping — head loss across the unit matters more. |
| Head loss | 10–40 cm | Drives the pumping energy penalty for the life of the farm. |
| Materials | GRP, HDPE or 316L stainless housing | 316L for seawater and ozone; GRP/HDPE common in freshwater. |
| Solids removal | 50–90% of TSS above the micron cut | Efficiency drops with fine and fragile particles; long pipe runs shear solids. |
Sizing guidance
Size a drum filter on the hydraulic flow it must pass and the solids load it must remove — not on the tank volume. Always specify capacity at your chosen micron rating and design feed load, and size for peak, not average.
| Project scale | Indicative drum filter duty | Design notes |
|---|---|---|
| Hatchery / nursery, up to 50 m³/h | Single compact unit, 40–60 µm | Low solids load, fine screen for larval water quality; keep a spare screen panel on site. |
| Small grow-out, 100–400 m³/h | One unit at 60 µm | Add a bypass channel so the farm keeps running during screen service. |
| Mid-scale RAS, 400–1,200 m³/h | Two units in parallel | Parallel units give redundancy and let you take one offline without stopping the loop. |
| Large RAS / multi-module, 1,200 m³/h+ | Multiple units per module | Filter per module, not per farm — a single shared filter makes every module share one failure. |
Rule of thumb: required flow (m³/h) ≈ system volume (m³) ÷ target turnover time (h). For RAS grow-out, a 45–60 minute full turnover is a common starting point; add 20–30% headroom for screen blinding, biofouling and future expansion.
How to choose
- Rated at your micron
A unit rated 500 m³/h at 200 µm may only pass 250 m³/h at 60 µm. Insist on capacity curves at the micron you will actually run.
- Screen access and spares
Panel screens replaceable without lifting the drum save days of downtime. Confirm lead time and price of replacement panels before ordering.
- Backwash pump and nozzles
Self-cleaning nozzles, adjustable spray pressure and an accessible strainer — nozzle blockage is the most common field failure.
- Controls and alarms
Level-triggered rotation, high-level alarm, run-time counters and a dry-contact or Modbus output into your farm SCADA.
- Material fit to water
Seawater, ozone or high-salinity biofloc need 316L or fully non-metallic construction; galvanic mistakes surface in year two.
- Sludge handling downstream
The filter only concentrates the problem — plan the sludge thickener, settling or discharge route before the permit review.
What drives the price
- Hydraulic capacity
Price scales roughly with screen area, so with flow and inversely with micron size.
- Housing material
316L stainless typically adds 40–80% over GRP/HDPE on the same duty.
- Micron rating
Finer screens mean more drum area for the same flow — a real cost step, not an option box.
- Controls package
Basic level switch versus full PLC, VFD, remote alarms and SCADA integration.
- Redundancy
Two half-duty units cost more than one full-duty unit but are what lenders and insurers expect.
- Freight and installation
Large drums are volumetric freight; inland transport and crane access can be material on remote sites.
Indicative class-4 budget: roughly €6k–€20k for hatchery and small grow-out units, €20k–€70k for mid-scale RAS duties, and €70k–€250k+ for large multi-unit installations including controls and installation. Confirm against at least two comparable quotations.
Common specification mistakes
- Sizing on average flow instead of peak flow, so the filter blinds at feeding time.
- Comparing quotes at different micron ratings — the cheapest unit is usually the coarsest.
- Omitting the backwash booster pump and sludge handling from the budget.
- No bypass or standby unit, so screen maintenance means stopping the whole loop.
- Long, turbulent pipe runs upstream that shear solids into unremovable fines.
Drum filters — buyer questions
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