Sludge separation − filtration
Filtration theory defines the way in which water flows through the bed, which is formed of the sludge solids (cake)
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A belt filter press (BFP) combines drainage and mechanical pressure sequentially, ultimately providing sludge dewatering by pressing the sludge between two revolving permeable belts to squeeze out the water from the sludge. This produces a cake (the dewatered product) having a dry solids (DS) content of 30% or more in the case of primary sludge. This is to be distinguished from the lower-energy gravity belt thickener process which achieves a maximum DS content of ~10%.
Filtration theory defines the way in which water flows through the bed, which is formed of the sludge solids (cake)
An overview of sludge dewatering − an introduction to sludge dewatering theory and technologies
Dewatering processes provide a concentrated, consolidated product along with a diluted stream which is predominantly water
These presses dewater sludges to produce a cake with a dry solids content of 30% or more in the case of primary sludge
Sludge solids separation theory − a brief introduction to the theories around sludge sedimentation, cake filtration and cake compression.
Centrifugal dewatering consolidates sludge by encouraging particles to migrate to the walls of a rapidly rotating cyclinder
Drying beds dewater sludge by allowing the liquid to both drain from the sludge under gravity and evaporate from its surface
A filter press dewaters sludge by pressing it between a series of porous plates at high pressure to squeeze out the water
A lagoon is a large shallow reservoir filled with sludge, which settles and stabilises over an extended time period
A rotary press dewaters sludge by passing it along a channel formed between two slowly-rotating circular permeable screens
A screw press dewaters sludge by passing it along the inside of an inclined permeable cylinder using an Archimedean screw
Conditioning is the pretreatment of sludge upstream of thickening and dewatering to promote solid-liquid separation
Thickening processes concentrate the sludge by removing part of the free water, such that the product can still be pumped
Dewatering processes mechanically remove a significant proportion of the sludge water to produce a 15-45% cake product
In sludge drying the sludge moisture is removed as water vapour by heating, generating a pelleted or powdered product
Sludge stabilisation − alkaline stabilisation, lime and solids dosing, plus anaerobic and aerobic digestion
Thermochemical methods are used to either significantly reduce the sludge solids content or pre-treat sludge upstream of AD
Sludge is the main waste stream from the treatment of wastewater