Sludge

MABEEL C.Y.Chang 2009/01/17

Special Topics on Sludge and SedimentChia Nan Universityof Pharmacy and ScienceLecture code: 961106 97(2) Semester, CNU Campus

Chapter 3

Sludge Thickening

Dr.Dr. ChiaChia--Yuan ChangYuan Chang

Associate ProfessorEnvironmental Engineering and Science

Chia Nan Universityof Pharmacy and ScienceDr. Ch

ia-YuanChang

Dr.Dr. ChiaChia--Yuan

ChangYuan Chang

Special Topics on Sludge and SedimentLecture code: 961106 97(2) Semester, CNU Campus

Sludge Thickening


Chia Nan Universityof Pharmacy and Science


Dr. Chia-Yuan C

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ChangYuan Chang


Sludge Thickening

Liquid sludges pumped from a clarifier will have a solids content of 0.5%from cone bottom clarifiers to 2% - 4% from rake bottom clarifiers.The sludge thickener must have sufficient capacity to accumulate andthicken the sludges between filter press cycles. To efficiently operate afilter press, the solids concentration in the filter press feed should approach10% solids by weight. A typical filter press will produce a filter cakehaving a solids concentration of 30% by weight.



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Sludge Thickening



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Sludge Thickening

Gravity thickening is accomplished in a tank similar in design to aconventional sedimentation tank. Normally, a circular tank is used. Dilutesludge is fed to a center - feed well. The feed sludge is allowed to settle andcompact, and the thickened sludge is withdrawn from the bottom of the tank.Conventional sludge - collecting mechanisms with deep trusses or verticalpickets are used to stir the sludge gently, thereby opening up channels forwater to escape and promoting densification. The supernatant flow that resultsis returned to the primary settling tank or to the headworks of the treatmentplant.The thickened sludge that collects onthe bottom of the tank is pumped to thedigesters or dewatering equipment asrequired; thus, storage space must beprovided for the sludge. Gravitythickening is most effective on primarysludge. A photo of gravity thickener isshown below.

Gravity thickening



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Sludge Thickening

Gravity thickeners used dewatering the treatment sludge are designedon the basis of solids loading. To maintain aerobic conditions in gravitythickeners, provisions should be made for adding 24 to 30 m3/m2dayof final effluent to the thickening tank. Typical concentrations ofunthickened and thickened sludges and solids loadings forgravity thickener are shown below.

An operating variable, sludge volume ratio normally range between 0.5 and 20 day; the lowervalues are required during warm weather. For operation, alternatively, sludge - blanket depthshould be measured. Blanket depths may range from 0.6 to 2.4 m; shallower depths aremaintained in the warmer months.



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ChangYuan Chang


Sludge Thickening



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ChangYuan Chang


Sludge Thickening

Central drive thickener for circular tank


ia-YuanChang


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Sludge Thickening

Peripheral Double Drive ThickenerFor Circular Tank




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Sludge Thickening

Thickener With Torsion TrestleFor Circular Tank



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Sludge Thickening



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Sludge Thickening

There are three basic variationsof the flotation thickeningoperation ; dissolved - airflotation (DAF), vacuumflotation, and dispersed - airflotation. Dissolved - air flotationis being widely preferred forespecially waste activatedsludge.Air is introduced into a solutionthat is being held at an elevatedpressure. When the solution isdepressurized, the dissolved airis released as finely dividedbubbles carrying the sludge tothe top, where it is removed.Photos of DAF are shown below.



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Sludge Thickening


ia-YuanChang


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Sludge Thickening




Dr. Chia-Yuan C

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Sludge Thickening



Dr. Chia-Yuan C

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Sludge Thickening

Higher loadings can be used with flotation thickeners thanare permissible with gravity thickeners because of the rapidseparation of solids from the wastewater. Typical solidsloadings for DAF units are shown below.



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Sludge Thickening

Sludge Thickening

A typical dewatering system will include: a high performanceCentrisys centrifuge, feed pump, polymer make up system,cake transport system (screw conveyor or cake pump) andthe system control panel. These components can be installedon a common skid or trailer, but may also be stand alone.The only connections required are feed, power and liquiddischarge. All the inter-connective piping and electricalconnections have been assembled and pre tested at thefactory. Typical time for setup of a system is 1-4 hours fromthe arrival on-site.

Features:High Solids CapabilitiesCentrifugally Cast Duplex Stainless Steel DesignHigher Torque Capacity than Other ManufacturersAdvanced Tungsten Carbide Wear SurfacesLower Installed Horsepower than Other ManufacturersNEMA 4X Enclosed PLC ControlsTouch Screen InterfacesOne Button Start / StopVariable Speed Bowl DrivesVariable Speed Scroll DrivesAutomatic Cleaning Cycles

Centrifuge forThickening/Dewatering (>18%)

Thickening / DewateringCentrifuge - Centrisys



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Sludge Thickening

IFT Series of Internally-fed Rotary DrumSludgeThickeners have cylindrical drums withprogressive series of screen elements that aremountedhorizontally on four shaft-mounted wheels andsupported in a structural housing.

How it Works:The smallest openings are used to screen theinfluent sludge,followed by coarser elements as the sludge thickens.The screening element is either woven mesh orwedgewire. The screens are used to remove freeliquids from a variety of sludges, including those withappreciable amounts of microbial particles. Sludgecontaining 0.5%-3% solids can be thickened to 5%-15%, depending on the type of sludge

IFT (Internally FedThickener) Rotary DrumThickener (>8%)

IFT Rotary DrumThickener - IPEC



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Sludge Thickening

The Krofta Supracell is a state-of-the-art DAF waterclarification system used in thousands of applicationsworldwide. Its features a high output, very low retentiontime, and compact, space saving design (the Supracell'sfootprint is smaller than that of other systems of similarcapacity).

Operation:

As a rotating carriage at the top of the unit travelsin one direction, untreated water flows into theunit in the opposite direction. The two opposingforces equalize each other, creating 'zero-velocity'within the flotation cell. Zero velocity allowssuspended solids (that have attached tomicroscopic air bubbles created by the AirDissolving Tube (ADT) and pressure release valve)to freely rise to the surface. Effluent extractionpipes draw clarified water off of the bottom of thetank, depositing it into a common clearwell whereit is discharged, by gravity, through the base ofthe unit. Floated sludge is removed by the spiralscoop and deposited out a central sludge well. Aportion of the clarified water is recycled throughthe ADT and introduced back into the raw waterstream to facilitate the flotation.

DAF (>4%)

Dissolved Air Flotation(DAF) - Krofta

Sludge

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