Technical Glossary
Definitions of key terms and parameters used in screw press sludge dewatering engineering.
B
Biosolids
Treated sewage sludge that meets regulatory criteria for beneficial reuse, such as land application or composting.
C
Cake Dryness
The percentage of dry solids in the dewatered sludge cake, typically expressed as % DS. Higher values indicate more effective dewatering.
Capture Rate
The percentage of total solids retained in the dewatered cake. A capture rate of 95% means only 5% of solids pass into the filtrate. Also called solids recovery.
Conditioning
The addition of chemicals (typically polymer flocculants) to sludge before dewatering to improve water release and cake formation.
D
DAF Sludge
Sludge produced by Dissolved Air Flotation units, commonly used in food processing and industrial wastewater treatment. Typically high in organic content.
Dewatering
The process of removing water from sludge to reduce its volume and weight. Mechanical dewatering uses physical force (pressure, centrifugal, gravity) rather than thermal energy.
Dry Solids (DS)
The mass of solid matter remaining after complete drying of a sludge sample. Feed sludge is often expressed in % DS or g/L.
F
Feed Concentration
The dry solids content of the sludge entering the dewatering device, typically between 0.5% and 5% for screw press applications.
Filtrate
The liquid (water) separated from sludge during dewatering. Also called centrate (in centrifuges) or pressate. Should be low in suspended solids for good capture rate.
Floc Zone
The initial section of a screw press where conditioned sludge enters and flocs form. Designed for gentle handling to preserve floc structure.
Flocculation
The process of using polymers or chemicals to aggregate fine particles into larger flocs that can be more easily separated from water.
G
Gravity Zone
The section of a screw press where free water drains by gravity through the screen. No mechanical pressure is applied in this zone.
M
MBR Sludge
Excess sludge from Membrane Bioreactor systems. Often finer particle size and higher SVI than conventional activated sludge, requiring adapted conditioning.
P
Polymer
A long-chain organic molecule used as a flocculant to condition sludge before dewatering. Can be cationic, anionic, or nonionic depending on sludge charge characteristics.
Pressure Zone
The final section of a screw press where mechanical pressure is applied via the narrowing screw geometry to maximize water extraction from the sludge.
S
Screw Press
A continuous mechanical dewatering device that uses a slowly rotating screw inside a cylindrical screen to separate water from sludge through progressive compression.
Sludge Thickening
The process of increasing the solids concentration of sludge, typically from <1% to 3–6% DS, as a pre-treatment step before dewatering.
Solids Loading Rate
The mass of dry solids fed to the dewatering device per unit time, expressed as kg DS/h. This is the primary capacity parameter for screw press sizing.
W
WAS (Waste Activated Sludge)
Excess biological sludge produced in the activated sludge process. One of the most common sludge types requiring dewatering at municipal wastewater treatment plants.
Wash Water
Water used to clean the screen of a screw press during operation. Prevents blinding and maintains filtration efficiency. Consumption is typically 24–160 L/h depending on model size.
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