---
title: "Rotary Drum Filter Mesh Selection: Choosing the Right Micron"
description: "How rotary drum filters and micro screens work, how to choose mesh size in microns, and how to apply them in RAS aquaculture, paper mills and pretreatment."
url: https://www.waste-water-equipment-factory.com/blog/rotary-drum-filter-mesh-selection/
updated: 2026-08-05
---

# Rotary Drum Filter Mesh Selection: Choosing the Right Micron

How rotary drum filters and micro screens work, how to choose mesh size in microns, and how to apply them in RAS aquaculture, paper mills and pretreatment.

Published 2026-08-05 by the Waste Water Equipment Factory Engineering Team.

> **Key takeaway:** A rotary drum filter strains water through a fine mesh on a slowly rotating drum and washes the captured solids off with spray nozzles, so it removes particles larger than the mesh opening with very little head loss. Choose the mesh by the particle size you need to capture and the solids load: finer mesh captures more but needs more filter area and more frequent backwash.

## How do you choose the right rotary drum filter mesh?

**Key takeaway:** Pick the largest mesh opening that still captures the particles you need to remove, then size the drum's submerged screen area for your peak flow and solids load at that mesh. Finer mesh improves capture but reduces hydraulic capacity and increases backwash water, so the right choice balances capture efficiency, footprint and operating cost.

Rotary drum filters — also called drum screens, micro screens or drum micro-filters — are a compact way to remove suspended solids from large flows of water. They are used in aquaculture, pulp and paper, food processing and municipal and industrial pre-treatment. This guide explains how they work, how to select mesh size, and which details matter when you specify one.

## How does a rotary drum filter work?

A drum filter is a horizontal cylinder covered with filter panels, partly submerged in a tank.

1. **Inflow:** water enters the inside of the drum through an open end.
2. **Filtration:** water passes outward through the mesh; solids larger than the openings are retained on the inner surface.
3. **Level rise:** as solids build up, resistance increases and the water level inside the drum rises relative to the outside.
4. **Backwash trigger:** when a level sensor detects the set difference, the drum starts rotating and the spray system starts.
5. **Cleaning:** high-pressure spray nozzles outside the drum wash the screen from the clean side, pushing solids off into a collection trough inside the drum.
6. **Sludge discharge:** the trough carries the concentrated solids and backwash water out of the unit for further treatment or dewatering.
7. **Standby:** once the level difference returns to normal, rotation and spray stop until the next cycle.

Because filtration happens by gravity with a small head difference — typically a few centimeters to a couple of hundred millimeters — drum filters use little energy. Power is mainly for the drive motor and backwash pump, and only during cleaning.

### Drum filter vs. disc filter vs. bar screen

| Equipment | Typical opening | Best for |
|---|---|---|
| Mechanical bar screen | Several millimeters and up | Rags, debris and coarse solids at the plant inlet |
| Rotary drum filter / micro screen | About 10–1,000 µm | Fine suspended solids, fish feces, fibers, pre-treatment |
| Disc filter | About 10–40 µm | Tertiary polishing where footprint per flow is critical |

Coarse screening normally comes first. Our [mechanical bar screens and drum filters](/products/screening-filtration/) are often supplied together for this reason.

## How do you select mesh size in microns?

Mesh is specified by its opening (aperture) in microns (µm). The aperture sets the smallest particle reliably captured, although a cake of retained solids on the screen also captures some smaller particles.

### Step 1: Know your particle size

The most useful data is a particle size distribution of the solids in your water, or at least test results from passing samples through screens of different apertures. Without it, use experience from similar applications:

| Application | Typical mesh range | Comments |
|---|---|---|
| RAS aquaculture grow-out | 60–100 µm | Removes feces and uneaten feed before biofiltration |
| Hatchery and fine RAS polishing | 20–60 µm | Needs more screen area per unit flow |
| Paper mill white water fiber recovery | 100–250 µm | Recovers fiber and fillers for reuse |
| Municipal wastewater pre-treatment | 200–1,000 µm | Protects downstream MBR and MBBR processes |
| Surface water intake pre-filtration | 50–500 µm | Removes algae, sand and debris |
| Tertiary effluent polishing | 10–40 µm | Typically following secondary clarification |

These ranges are typical starting points; confirm with water tests where possible.

### Step 2: Balance capture against capacity

Halving the mesh opening does not simply halve the flow capacity, but finer mesh does clog faster and has a lower hydraulic loading per square meter of screen. Expect:

- larger drum diameter or length for the same flow,
- more frequent backwash and more backwash water,
- greater sensitivity to grease, biofilm and sticky solids.

### Step 3: Size for peak flow and solids load

Suppliers size drums from the flow rate, mesh size and total suspended solids (TSS). Give the peak hourly flow, not just the daily average, and the expected TSS range. An undersized drum backwashes almost continuously, which wastes water and can let unfiltered water bypass over the internal overflow.

## How are drum filters used in aquaculture and RAS?

In recirculating aquaculture systems, the drum filter is usually the first treatment step after the fish tanks. Removing solids quickly, before they break apart and dissolve, reduces the organic load on the biofilter and protein skimmer and helps keep water clear.

Key points for RAS buyers:

- **Gentle hydraulics:** the low head loss suits gravity-flow systems.
- **Backwash water:** keep it a small fraction of system flow; it carries the sludge out of the system for settling or dewatering.
- **Seawater:** specify 316L stainless steel for the frame and wetted metal parts, and a corrosion-resistant spray pump.
- **Redundancy:** for large farms, two or more drums in parallel let one be serviced without stopping circulation.

## How do drum filters recover fiber in paper mills?

Paper machines produce white water carrying fiber and fillers. A drum filter fitted with mesh of suitable aperture recovers this fiber so it can be returned to the stock preparation system, while the filtered water is reused for showers and dilution. The benefits are lower raw material losses, reduced fresh water intake and a lower solids load on the effluent treatment plant. Fiber-recovery screens often need stronger spray systems because fibers tend to staple into the mesh.

## Where do drum filters fit as pre-treatment?

Drum filters protect downstream processes from fine solids and hair:

- ahead of [package sewage treatment plants](/products/sewage-treatment-plants/), particularly MBR systems where fibers can damage membranes;
- ahead of [dissolved air flotation](/products/dissolved-air-flotation/) or [lamella clarifiers](/products/lamella-clarifiers/) to reduce their solids load;
- on industrial effluent from food, textile and slaughterhouse plants.

The separated solids are usually thickened and sent to [sludge dewatering equipment](/products/sludge-dewatering/) such as a screw press.

## What should you know about backwash design?

Backwash quality decides long-term performance. Check:

- **Spray pressure and nozzle type:** typically several bar; flat-fan nozzles positioned to cover the full panel width.
- **Water source:** filtered water from the drum's own outlet is common, with a strainer to protect nozzles.
- **Control mode:** level-triggered backwash plus a timer to clean the screen periodically even at low load.
- **Chemical cleaning:** for grease or biofouling, ask whether panels can be cleaned in place or removed easily.
- **Sludge trough:** sized for the peak solids load so it does not overflow back into the drum.

## Which materials should you specify?

| Component | Common options | Selection notes |
|---|---|---|
| Drum frame and tank | SS304, SS316L, or carbon steel with coating | SS316L for seawater and chlorides |
| Filter mesh | Polyester, polyamide, or stainless steel | Synthetic mesh for fine apertures; stainless steel for abrasive or hot duty |
| Seals | EPDM, NBR | Compatibility with oils and temperature |
| Drive | Geared motor with chain or direct drive | Variable speed helps at high solids loads |

Modular filter panels are easier to replace than a single wrapped mesh and let you change mesh size later if conditions change. Ask the supplier which spare panels, nozzles and seals to keep in stock, and how long a panel change takes, so that routine maintenance does not interrupt operation for long. For outdoor installations, also consider a cover to protect synthetic mesh from UV exposure and to limit algae growth inside the drum.

## Request a drum filter sizing

Send us your peak flow rate, TSS or solids description, target mesh or removal requirement, water type (fresh, seawater or effluent) and installation conditions. Email **inquiry@waste-water-equipment-factory.com**, WhatsApp +86 176 2154 1688, or use our [contact page](/contact/), and our engineers will recommend a drum size, mesh and material specification.

## FAQ

### What mesh size is used for a RAS drum filter?

Recirculating aquaculture systems commonly use mesh openings of about 40–100 microns, with 60–90 microns a frequent choice for grow-out systems. Hatcheries and systems with very fine solids may go finer, which requires more screen area.

### How often does a rotary drum filter backwash?

Most units backwash automatically when the water level difference across the drum reaches a set point, and some also run on a timer. Backwash frequency rises with solids load and with finer mesh.

### What material is the filter mesh made of?

Filter panels are typically polyester or polyamide woven mesh, or stainless steel woven or wedge-wire screen for coarser and more abrasive duties. The frame and drum are usually stainless steel 304 or 316L, with 316L preferred for seawater and corrosive water.

### Can a drum filter replace a clarifier?

Only when the solids to be removed are larger than the mesh opening. Fine colloidal or dissolved material passes through the screen, so coagulation with a clarifier or dissolved air flotation is needed for those.