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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
Thickening processes are those which concentrate the sludge by removing part of the free water, i.e. the water not associated with the sludge particles or flocs. In doing so, the finished product retains the liquid, free-flowing characteristics of the feed sludge, so that it can still be conveyed by pumping. Thickening normally increases the dry solids (DS) content to between 4 and 6%.
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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 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
Thickening 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 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 topics…
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Centrifuges
Centrifugal thickening increases sludge concentration by encouraging particles to migrate to the walls of a rapidly rotating
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Flotation thickeners
Dissolved air flotation thickens sludges by encouraging the solids to float to the surface where they can be skimmed off
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Gravity belt thickeners
Gravity belt thickening thickens sludge by allowing the water to drain from the sludge under gravity through a permeable belt
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Gravity thickeners
Gravity thickening increases the solids concentration by allowing the particles to settle to the base of a vessel
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Membrane thickeners
Membrane thickeners separate suspended solids from liquid by extracting the water through a selective permeable material
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Rotary drum thickeners
Rotary drum thickening increases sludge solids concentration by agitating the solids in a cylindrical drum with porous walls
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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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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