Screw Press Calculator
Design Philosophy
A screw press is a mechanical dewatering device used in wastewater treatment to reduce the water content of sludge by applying mechanical pressure through a rotating helical screw within a perforated or tapered cylindrical screen. It is particularly suited for biological sludges — primary, secondary, and mixed — and is widely used in decentralized and medium-scale sewage treatment plants due to its low noise, low odor, and ability to handle variable feed concentrations.
The primary design parameter for a screw press is the dry solids throughput (kg dry solids/hour), which governs the machine size selection. The hydraulic feed flow and its solids concentration together determine the dry solids loading. The machine manufacturer specifies the maximum dry solids throughput for each model, which is the binding constraint on the number of units required.
Dry Solids Calculation
The dry solids load is computed from the feed stream as follows:
where,
Q_feed : Feed flow rate to the screw press (m³/hr)
C_solids : Solids concentration in the feed (kg/m³), derived from the % w/w solids and feed density
Machine Output Moisture Content
The cake produced by a screw press typically has a total solids (TS) content of 15–25% w/w for biological sludges, depending on the sludge type, polymer conditioning, and machine operating pressure. The cake mass output is:
Number of Units
The number of screw press units required is determined by dividing the total dry solids load by the rated capacity of the selected machine model, with a minimum of one standby unit provided as per CPHEEO recommendations for continuous operation plants.
(Source: Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery, 5th Ed.; BWWT Course — TU Delft)
Calculator
(Note – all Yellow are user defined value, all white are fixed values, all green are calculated value, all orange is calculated not to be shown)
Instructions
Enter values highlighted in the Yellow
Green highlights are the results
In case of any invalid result of non-functioning of the calculator, please write to us at design@swaenviro.com. We will try and help you with your sizing and calculation
INPUT
| Parameter | Values | Units | Remarks |
|---|---|---|---|
| Flowrate | cum/hr | ||
| % w/w solids | w/w | ||
| Flowrate allowed | 0.50 | cum/hr | |
| Dry solids in water | 50.00 | kg | |
| Dry solids with moisture content | 250.00 | kg | machine output is fixed to handle certain amount of solids |