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Sludge drying
An overview of sludge drying − an introduction to sludge drying theory and technologies
Drying
In sludge drying the moisture from sludge is removed as water vapour by heating, rather than being removed as a liquid via mechanical means such as in thickening
or dewatering. The sludge is normally dried to solid concentrations above 65% to produce pellets or, at the highest solids concentrations of 90% or more, a powder. Pelleted or powdered sludge is more readily conveyed than the dewatered sludge of higher water content, which exists as large lumps.
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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
Drying related videos
Benenv sludge drying and carbonization technology
Film to demonstrate Benenv's integrated sludge drying and carbonization technology.
The technology operates as a sealed pyrolysis system in the absence of oxygen, maximising evaporation of moisture from the sludge and so reducing the sludge volume by 90%.
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 Drying topics…
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Convective dryers
Convective (or direct) dryers remove moisture from sludge by bringing the sludge particles into direct contact with hot gas
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Belt dryers
Belt dryers comprise a conveyor belt which slowly transports the sludge solids through a stream of heated air
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Flash dryers
Flash dryers use a rapid stream of rising hot air which both suspends and dries the solids.
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Fluidised bed dryers
In fluidised-bed dryers the sludge particles are gently agitated and heated by a stream of upward-flowing pre-heated gas
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Rotary drum dryers
Rotating drum dryers have a drum rotating at 4-8 RPM through which the sludge passes along with a stream of warm air
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Conductive dryers
For conduction drying, the sludge is heated indirectly by bringing it into contact with a heated surface
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Disc dryers
Disc dryers are based on vertical externally-heated discs or rings rotating in the sludge as it passes through the dryer.
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Paddle dryers
Paddle dryers are based on externally-heated paddles rotating in the mass of sludge solids held in a stationary vessel
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Solar dryers
Solar dryers comprise large greenhouses in which sludge is dried under the ambient conditions of the building.
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Pelletizers
Pelletizers
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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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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