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Sludge separation − gravitation/sedimentation
Gravitation (sedimentation or settlement) is the separation of particles from water on the basis of their weight
Thickening, dewatering & drying
Sludge drying refers to processes where moisture is removed from sludge as water vapour. These processes often require pre-treatment ('conditioning'). With sludge thickening or dewatering, moisture is removed as a liquid.
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Sludge separation − centrifugation
The theory of centrifugation relates to sedimentation theory as it acts to enhance gravity through the centrifugal force
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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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Sludge conditioning
An overview of sludge conditioning − chemical and thermal
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Introduction to sludge conditioning
Thickening and dewatering processes often need pre-treatment (conditioning) to help separate the water from the solids
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Chemical sludge conditioning
The chemical pre-treatment of sludge helps remove water upstream of thickening and dewatering processes
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Thermal sludge conditioning
Thermal processes are used to condition sludges upstream of anaerobic digestion as well as pre-treating sludge for dewatering
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Sludge thickening
An overview of sludge thickening − an introduction to theory and related technologies
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Introduction to sludge thickening
Processes which act to remove water from the sludge to reduce its volume are called thickening and dewatering
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Sludge treatment − gravity thickening
Gravity thickening increases the solids concentration by allowing the particles to settle to the base of a vessel
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Sludge treatment − dissolved air flotation thickening
Dissolved air flotation thickens the sludge by encouraging solids to float to the surface by attaching to rising air bubbles
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Sludge treatment − gravity belt thickening
GBT thickens the sludge by allowing the water to drain from the sludge under gravity through a permeable moving belt
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Sludge treatment − rotary drum thickening
Rotary drum thickening thickens the sludge by agitating the solids in a slowly-rotating vessel with porous walls
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Sludge treatment − centrifugal thickening
Sludge concentration increases as particles are encouraged to migrate to the walls of a rapidly rotating cylindrical vessel
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Other sludge thickening processes
Other processes include membrane thickening − water is extracted through a membrane, increasing the solids concentration
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Sludge dewatering
An overview of sludge dewatering − an introduction to sludge dewatering theory and technologies
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Introduction to sludge dewatering
Dewatering processes provide a concentrated, consolidated product along with a diluted stream which is predominantly water
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Belt filter presses for sludge dewatering
These presses dewater sludges to produce a cake with a dry solids content of 30% or more in the case of primary sludge
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Screw presses for sludge dewatering
A screw press is a dewatering technology based on a slowly-rotating (~5 RPM) Archimedean screw within a cylindrical screen
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Filter presses for sludge dewatering
The filter press forces water from the sludge by applying high pressures to sludge layers held between rectangular plates
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Rotary presses for sludge dewatering
This technology removes water by passing the sludge through a narrow, rotating parallel-flow channel with porous walls
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Centrifugal sludge dewatering
Centrifugation is used for thickening and dewatering sewage sludge − dewatered sludge has a higher dry solids concentration
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Sludge drying beds and lagoons
Drying beds dewater sludge by allowing the liquid to drain and to evaporate. Lagoons provide dewatering through evaporation
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Other sludge dewatering processes
Electro-dewatering technology provides enhanced removal by non-mechanical means through the application of an electric field
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Sludge drying
An overview of sludge drying − an introduction to sludge drying theory and technologies
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Introduction to sludge drying
Processes where moisture is removed from sludge as water vapour are known as 'sludge drying'
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Sludge treatment − properties of drying sludge
When sludge dries, it goes through three different phases as the water evaporates
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Sludge treatment − sludge drying operation
Sludge drying processes operate at solids temperatures of 60-93 °C to encourage water to evaporate and leave a solid residue
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Sludge treatment − sludge dryer configurations
Sludge drying processes are generally configured as convective, conductive, or as solar dryers
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Sludge treatment − conductive sludge dryers
Conductive drying indirectly heats sludge by bringing the sludge particles into contact with an externally-heated surface
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Sludge treatment − convective sludge dryers
Convective sludge dryers are the most commonly used type of dryer for sewage sludge
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Sludge treatment − solar dryers
Solar dryers make use of renewable solar energy to dry sludge and need a larger footprint to allow for increased drying times
Thickening, dewatering & drying related videos
Gravity belt thickener, Alfa Laval
A video to demonstrate the workings of the Alfa Laval AS-H gravity belt thickener which can be used for municipal sludge, and industrial sludge that flocculates.
Thickening, dewatering & drying features and blogs
Feature
Co-processing of sewage digestate by hydrothermal carbonisation
Hydrothermal carbonisation (HTC) can be used to co-process anaerobic digestion (AD) digestate and lignocellulosic (or plant-based) feedstocks to improve the the hydrochar product quality. This AD waste co-processing route has been studied at bench scale. Read article
More Thickening, dewatering & drying topics…
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Conditioning
Conditioning is the pretreatment of sludge upstream of thickening and dewatering to promote solid-liquid separation
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Thickening
Thickening processes concentrate the sludge by removing part of the free water, such that the product can still be pumped
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Dewatering
Dewatering processes mechanically remove a significant proportion of the sludge water to produce a 15-45% cake product
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Drying
In sludge drying the sludge moisture is removed as water vapour by heating, generating a pelleted or powdered product
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Conditioning
Conditioning is the pretreatment of sludge upstream of thickening and dewatering to promote solid-liquid separation
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Thickening
Thickening processes concentrate the sludge by removing part of the free water, such that the product can still be pumped
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Dewatering
Dewatering processes mechanically remove a significant proportion of the sludge water to produce a 15-45% cake product
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Drying
In sludge drying the sludge moisture is removed as water vapour by heating, generating a pelleted or powdered product
More process and operation topics…
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Sludge stabilisation
Sludge stabilisation − alkaline stabilisation, lime and solids dosing, plus anaerobic and aerobic digestion
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Thermochemical processes
Thermochemical methods are used to either significantly reduce the sludge solids content or pre-treat sludge upstream of AD
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Sludge quality
Sludge is the main waste stream from the treatment of wastewater