Small municipal plants that haul liquid sludge or rely on drying beds can cut sludge volume sharply by adding a mechanical dewatering line with automatic polymer dosing. This reference configuration uses a screw press or belt filter press, selected on sludge type, operating hours and staffing.
The challenge
Many small municipal wastewater treatment plants were built with minimal sludge handling. Waste activated sludge is stored in a tank and hauled away as liquid, or spread on drying beds that are slow, weather-dependent and land-hungry. As connected populations grow and disposal costs rise, hauling liquid sludge at around 1% solids means paying to transport mostly water.
Operators need a dewatering line that fits into an existing building or a small new shed, works with the sludge the plant already produces, runs with little supervision and integrates with existing pumps and controls.
Our solution
The reference solution is a mechanical dewatering line with automatic polymer preparation and dosing, built around either a multi-disc screw press or a belt filter press. Both are proven technologies for municipal sludge; the selection depends on sludge characteristics, required throughput, operating hours and available staff.
For plants with limited operators and moderate solids loads, the screw press is usually preferred: it is enclosed, slow-turning, quiet and largely self-cleaning, and it can process thin waste activated sludge without a separate thickener. For plants with larger loads or primary sludge in the mix, a belt filter press with gravity thickening zone can offer higher throughput per machine.
In both cases, sludge is fed at a controlled rate, conditioned with a correctly prepared polymer solution, and dewatered to a cake that can be conveyed directly into a skip or truck. Filtrate returns to the plant inlet.
Process flow
- Sludge holding – waste sludge is collected in a mixed holding tank to keep the feed homogeneous.
- Feed pumping – a progressive cavity pump with variable-speed drive and flow meter delivers sludge at a steady rate.
- Polymer preparation – an automatic unit makes down powder or emulsion polymer to a dilute solution and allows maturing time.
- Flocculation – polymer is dosed in proportion to sludge flow and mixed in a flocculation tank or in-line mixer.
- Dewatering – the conditioned sludge is thickened and pressed in the screw press or belt filter press.
- Cake handling – a screw or belt conveyor transfers cake into a skip, hopper or truck.
- Filtrate return – filtrate and wash water drain back to the headworks for treatment.
Scope of supply
- Multi-disc screw press or belt filter press, sized for the design solids load with operating hours confirmed in design
- Automatic polymer preparation and dosing unit with dosing pumps
- Sludge feed pump with variable-speed drive and electromagnetic flow meter
- Flocculation tank or in-line mixer
- Cake conveyor and, for belt presses, wash-water booster pump
- PLC control panel with interlocks to existing sludge pumps and signals to the plant SCADA
- Installation supervision, commissioning with polymer optimization, and operator training
Other options from our sludge dewatering range, including plate and frame filter presses and decanter centrifuges, can be considered where higher dryness or larger capacities are required.
Why this configuration works
Polymer conditioning drives performance. The dewatering machine can only separate water from sludge that has been properly flocculated. Automatic make-down, adequate maturing time and flow-paced dosing keep floc formation consistent and avoid the overdosing that wastes chemical.
The machine matches the plant. Selecting between screw press and belt press on sludge type and staffing, rather than defaulting to one technology, gives a line that operators can actually run day to day.
Integration is straightforward. The line takes sludge from an existing holding tank and returns filtrate to the existing inlet, so the upgrade usually needs only a modest building, power supply and drainage.
Hauling costs fall. Moving from liquid sludge to a cake of typically 15–22% DS reduces the hauled volume dramatically, which is often the main economic justification.
Commissioning settles the numbers. Polymer type, dose and machine settings are optimized on site with the real sludge, since results vary with sludge age, primary/secondary ratio and temperature.
To size a dewatering line for your plant, send the plant flow, sludge production or solids load, current sludge concentration and preferred operating hours to [email protected] or via our contact page.
Reference configuration — final design depends on site data.
Design basis
| Design solids load | 50–300 kg DS/h |
|---|---|
| Feed sludge | Waste activated or mixed sludge, typically 0.5–4% DS |
| Polymer dose | Typically 3–8 kg active polymer per t DS (by jar test) |
| Expected cake dryness | Typically 15–22% DS for activated sludge |
| Polymer solution | Typically 0.1–0.3%, prepared automatically |
| Filtrate | Returned to plant headworks |
