Volute Dewatering Screw Press
Volute Screw Press for Industrial Sludge Dewatering
Volute screw press for continuous sludge thickening and dewatering. Learn how sludge source, solids concentration, dry solids load and cake requirements affect equipment selection.
Volute Screw Press for Sludge Dewatering
A volute screw press is a continuous sludge thickening and dewatering system used to reduce the water content and volume of conditioned sludge before transport, disposal or further treatment.
The equipment combines a slow-speed screw with fixed and moving rings. As sludge moves through the dewatering section, water is released through the filtration gaps while increasing pressure gradually forms a sludge cake at the discharge end.
However, screw press selection should not be based on wet sludge flow alone.
Two sludge streams with the same flow rate can place very different loads on the machine if their solids concentrations are different.
For this reason, preliminary selection should consider:
- sludge source
- wet sludge flow
- feed solids concentration
- dry solids load
- operating hours
- polymer conditioning
- required cake condition
- final disposal method
The objective is not simply to choose a machine with a larger nominal capacity. The objective is to match the dewatering system to the actual sludge load and operating conditions.
How a Volute Screw Press Works
A typical volute screw press combines three functions in one continuous process:
flocculation → thickening → dewatering
Conditioned sludge first enters the flocculation or feed section, where polymer helps form larger and more stable flocs.
The sludge then enters the screw section.
As the screw rotates slowly, water passes through the gaps between the fixed and moving rings. The moving-ring structure continuously shifts relative to the fixed rings, helping reduce solids accumulation on the filtration surface.
As the sludge moves toward the discharge end, the available volume gradually decreases and internal pressure increases.
The final result is separated into:
- filtrate, which leaves through the ring gaps
- dewatered sludge cake, which exits from the discharge end
The actual cake condition and filtrate quality depend on the sludge characteristics, polymer selection, operating settings and equipment sizing.
For unfamiliar or difficult sludge, bench testing or pilot testing is preferable before final equipment selection.
Sludge Types and Applications
Volute screw presses can be considered for many municipal and industrial sludge-dewatering applications, particularly where continuous operation, compact installation and relatively simple operation are required.
Typical sludge sources include:
- municipal biological sludge
- industrial biological sludge
- food and beverage wastewater sludge
- DAF floated sludge
- textile wastewater sludge
- mixed primary and biological sludge
- chemically conditioned sludge, subject to suitability review
- sludge from packaged wastewater treatment systems
The same machine should not automatically be applied to every sludge type.
Oil content, inorganic solids, fiber, polymer response, feed concentration and sludge age can all affect dewatering performance.
For this reason, the sludge source should always be identified before selecting a model.
Sludge Thickening vs Sludge Dewatering
Sludge thickening and sludge dewatering are related but they are not the same treatment objective.
Sludge thickening mainly increases the solids concentration and reduces liquid volume before another treatment step.
Sludge dewatering aims to remove significantly more water and produce a sludge cake that is easier to transport, dispose of or treat further.
This distinction is important during equipment selection.
For example, a project may receive a very dilute sludge stream and ask for a screw press simply because the client wants to “reduce sludge volume”.
Before recommending a dewatering machine, the project should first confirm:
- current sludge concentration
- required final condition
- whether intermediate thickening is needed
- the actual dry-solids load
- the final handling method
A screw press should not be recommended simply because a wet sludge flow rate is available.
Why Dry Solids Load Matters
Wet sludge flow alone can be misleading.
Consider two sludge streams:
- both have the same flow rate
- one has a relatively low solids concentration
- the other has a much higher solids concentration
The hydraulic flow is the same, but the amount of dry solids entering the dewatering equipment can be very different.
That difference directly affects the required machine capacity.
A simplified dry-solids calculation is:
Dry Solids Load = Sludge Flow × Solids Concentration
In practice, unit conversion and sludge density must also be handled correctly.
For preliminary equipment selection, HydroNovus therefore asks for both:
- wet sludge flow, m³/h
- feed solids concentration, %
Where possible, dry solids load in kg DS/h should also be provided.
This gives a much more useful basis for model selection than flow rate alone.
Where the Screw Press Fits in the Sludge Line
A screw press should be considered as part of the sludge-handling line, not as an isolated machine.
A typical arrangement may be:
DAF / clarifier / biological sludge → sludge storage → polymer conditioning → volute screw press → sludge cake
The filtrate normally returns to an appropriate point in the wastewater treatment process, depending on its quality and the overall plant mass balance.
For industrial ETP projects, sludge handling should therefore be reviewed together with the water-treatment process.
For example, a DAF system may successfully remove suspended solids and oil from the wastewater, but those contaminants are then transferred into the floated sludge.
That sludge still requires:
- storage
- pumping
- conditioning
- dewatering
- cake handling
This is why the DAF process and the sludge-dewatering system should be evaluated together during project design.
Polymer Preparation and Conditioning
Polymer conditioning is an important part of sludge dewatering.
The polymer helps fine particles and biological solids form larger flocs that can release water more effectively during the dewatering process.
Poor polymer selection or preparation may result in:
- weak floc formation
- poor filtrate quality
- unstable cake discharge
- excessive polymer consumption
- reduced equipment capacity
Polymer type and dosage therefore should not be treated as fixed values for every sludge.
Where sludge characteristics are uncertain, jar testing, bench testing or pilot testing can help establish a more suitable conditioning program.
For projects requiring automatic polymer preparation, HydroNovus can also integrate polymer preparation and dosing equipment into the sludge-dewatering system.
Information Required for Screw Press Selection
A useful screw press quotation requires more than a sludge flow rate.
For preliminary model selection, please provide as much of the following information as possible.
Sludge Data
- sludge source
- wet sludge flow, m³/h
- feed solids concentration, %
- estimated dry solids load, kg DS/h
- sludge temperature, if relevant
- pH, if relevant
- oil or grease content, if significant
- inorganic or fibrous solids, if significant
Operating Data
- operating hours per day
- continuous or batch operation
- existing polymer type, if known
- existing polymer dosage, if known
- wash-water availability
- electrical supply
- indoor or outdoor installation
Project Requirement
- required cake condition
- sludge disposal method
- available installation space
- existing sludge storage tank
- existing sludge pump
- downstream conveying requirement
- filtrate return arrangement
If the exact dry-solids load is not available, send the sludge flow and solids concentration and HydroNovus can use them as the basis for preliminary evaluation.
Screw Press vs Belt Press vs Chamber Filter Press
No single sludge-dewatering technology is the best choice for every project.
The correct equipment depends on sludge characteristics, operating philosophy, capacity and cake requirements.
Volute Screw Press
A volute screw press is typically considered where the project requires:
- continuous operation
- compact installation
- relatively low-speed operation
- automatic sludge dewatering
- biological or conditioned sludge treatment
Final suitability still depends on sludge characteristics and polymer response.
Belt Filter Press
A belt filter press is also a continuous dewatering system and may be suitable for projects requiring higher throughput.
It generally requires:
- effective polymer conditioning
- belt washing
- wash-water supply
- sufficient installation space
Chamber Filter Press
A chamber filter press operates in batches rather than continuously.
It is often considered where relatively high filtration pressure or a comparatively dry cake is required.
The final selection should consider:
- sludge type
- filtration behavior
- operating cycle
- labor requirements
- cake dryness requirement
- available footprint
The purpose of comparing these technologies is not to make the screw press look suitable for every project.
It is to identify which dewatering method best matches the actual sludge and operating requirement.
System Configuration Options
Depending on the project scope, a sludge-dewatering package may include:
- sludge feed pump
- polymer preparation system
- polymer dosing pump
- flocculation tank
- volute screw press
- automatic control panel
- wash-water system
- filtrate collection
- sludge cake discharge arrangement
- screw conveyor or other cake transfer equipment
The final configuration should be confirmed according to the site layout and the equipment already available at the treatment plant.
Frequently Asked Questions
Can a screw press be selected from sludge flow alone?
No. Wet sludge flow is only one part of the selection basis.
Feed solids concentration and dry-solids load are also important because two sludge streams with the same flow can contain very different amounts of solids.
What feed solids concentration is required?
There is no single concentration that applies to every sludge.
The acceptable range depends on sludge characteristics, polymer response, equipment configuration and the required dewatering result.
For low-concentration sludge, it is especially important to confirm whether the actual requirement is sludge thickening or sludge dewatering.
Does the screw press require polymer?
Many sludge-dewatering applications use polymer conditioning to improve floc formation and water release.
The polymer type and dosage depend on the sludge and should be evaluated rather than assumed.
Can a screw press handle DAF sludge?
It can be considered for DAF sludge, but suitability depends on the actual sludge characteristics.
Oil content, chemical precipitates, solids concentration and polymer response should be reviewed before final selection.
Can the filtrate return to the wastewater treatment plant?
In many installations, filtrate is returned to an appropriate upstream treatment stage.
However, its pollutant load should be included in the overall plant mass balance rather than ignored.
What information should I send for model selection?
The most useful information is:
- sludge source
- sludge flow
- feed solids concentration
- operating hours
- polymer information, if available
- required cake condition
A recent sludge analysis or sample test can improve the reliability of the preliminary selection.
Request a Preliminary Screw Press Selection
Choosing a sludge-dewatering machine from wet sludge flow alone can lead to an incorrect model selection.
For a preliminary engineering review, send HydroNovus:
- sludge source
- wet sludge flow
- feed solids concentration
- operating hours
- polymer information, if available
- required cake condition
- final sludge disposal method
If you have a recent sludge analysis, please include it.
Based on this information, we can review the dry-solids load, preliminary equipment configuration and any additional data required before final selection.
Request Screw Press Selection
