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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Centrifugal thickening increases the sludge concentration by encouraging the particles to migrate to the walls of a rapidly rotating cylindrical vessel under the influence of a centrifugal force. Thickening centrifuges employ relatively low speeds, compared to dewatering centrifuges, such that the product sludge retains the free-flowing properties of the feed and can therefore still be pumped
The theory of centrifugation relates to sedimentation theory as it acts to enhance gravity through the centrifugal force
An overview of sludge thickening − an introduction to theory and related technologies
Processes which act to remove water from the sludge to reduce its volume are called thickening and dewatering
Sludge concentration increases as particles are encouraged to migrate to the walls of a rapidly rotating cylindrical vessel
A video to demonstrate the principles of the GEA Group's solid bowl decanter centrifuge.
Dissolved air flotation thickens sludges by encouraging the solids to float to the surface where they can be skimmed off
Gravity belt thickening thickens sludge by allowing the water to drain from the sludge under gravity through a permeable belt
Gravity thickening increases the solids concentration by allowing the particles to settle to the base of a vessel
Membrane thickeners separate suspended solids from liquid by extracting the water through a selective permeable material
Rotary drum thickening increases sludge solids concentration by agitating the solids in a cylindrical drum with porous walls
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