What This Wastewater Centrifuge Is Used For
In a treatment plant the decanter is a sludge and solids machine, not a substitute for a primary or secondary clarifier. Municipal lines typically use it on primary sludge, waste activated sludge (WAS), or digested biosolids. Industrial lines use it on process and wash-water solids where a continuous 2-phase split is required. Pond depth, bowl speed, differential speed (Δn) and polymer dose set whether the solids leave as a still-pumpable slurry or as cake.
Plant-Duty Features
Adjustable weir (dam) plates set pond depth: a deep pond favours hydraulic throughput and thickening; a shallow pond lengthens the dry beach for cake.
Dual VFDs set bowl speed and scroll differential speed independently, so torque and residence time can follow changing feed DS% without swapping the machine.
Polymer dosing can be integrated when floc strength is needed. Thickening often uses a lower dose than cake dewatering; WAS and industrial fines still need a jar-tested recipe.
Wetted parts can be specified in 316L or duplex stainless (e.g. UNS S32205 / SAF 2205) where chlorides or grit require it. Scroll flights and discharge ports take tungsten carbide where abrasion is expected.
Continuous enclosed operation suits 24-hour plants. Vibration, torque and bearing-temperature alarms are used to protect the gearbox on sticky or overloaded feeds.
Thickening or Dewatering
ZK sells one LW 2-phase family. Thickening and dewatering are operating modes (pond, G-force, differential speed, polymer), not two unrelated products. Many plants still run two stages—thicken first, then dewater—because that split often lowers combined polymer, power and haulage.
Sludge thickening / process-water split
Objective
Raise solids enough to cut downstream volume while keeping a pumpable underflow. Typical centrifuge thickening on municipal WAS/primary is often in the 3–8% DS band. Exact DS% depends on feed and pond setting.
Usual feed
Dilute WAS (often ~0.5–1.5% DS), primary sludge, or industrial process water with settleable solids. This is not a replacement for a gravity clarifier on raw municipal sewage.
How the bowl is set
Deeper pond, lower bowl speed / G-force than cake duty, higher hydraulic throughput, shorter dry beach. Polymer is often lower than dewatering, but not automatically zero.
What to send
Send feed type, DS% or TSS, flow, and target thickened solids. Request a wastewater-duty quote.
Sludge dewatering (stackable cake)
Objective
Remove more water so solids leave as a conveyable cake for haulage, landfill, land application or thermal treatment. Typical municipal WAS/digestate cake is commissioned around 18–25% DS when polymer and differential speed are set correctly.
Usual feed
Already concentrated sludge: digested biosolids, mixed municipal sludge, or industrial process sludge that must leave the site as cake.
How the bowl is set
Shallower pond, longer dry beach, higher G-force and scroll torque, and usually cationic PAM on municipal biosolids. Capture rate is traded against cake dryness during commissioning.
Cake duty
Cake DS%, capture, polymer and municipal model ranges: sludge dewatering centrifuge.
Model tables (bowl diameter, rpm, motor kW) are listed with the decanter centrifuge specifications.
How the Wastewater Decanter Runs
Feed and conditioning
Sludge or process water enters through a stationary feed tube. Where floc strength is needed, polymer is dosed into the feed line so flocs form before the pond. Dose is set in kg/t DS from jar tests, then trimmed on the machine. See polymer dosing for sludge.
Separation in the pond
The rotating bowl generates centrifugal force. Settleable solids compact against the wall; the inner liquid pond overflows the weir discs as centrate. Pond depth is the main lever between hydraulic capacity and beach length.
Scroll conveyance
The scroll runs at a controlled differential speed relative to the bowl and moves compacted solids along the cylinder and up the cone. Lower differential speed increases residence time; higher differential speed clears torque on a thickening or overloaded feed.
Two discharges, two possible solids
Centrate leaves over the weirs. Solids leave through the discharge ports as a pumpable thickened slurry or as cake, depending on pond, beach, G-force and polymer—not because the machine “is” only a thickener or only a dryer.
Typical Plant Duties
Municipal WWTP sludge
Primary sludge, WAS thickening ahead of digestion, and biosolids that later go to cake. The centrifuge sits on the sludge train, not in place of the plant’s clarifiers.
Municipal sludge application →
Industrial process and wash water
Continuous 2-phase split on process and wash waters. Solids can leave as a pumpable concentrate; stackable cake is the dewatering duty on the sludge dewatering centrifuge.
Industrial wastewater application →
Agricultural and food effluent
Livestock, aquaculture and food-plant streams are sized on solids type and target DS%. Fibrous or greasy feeds usually need a trial.
Agricultural effluent application →What to Send for a Sized Quote
Process engineers size on both volumetric flow (m³/h) and dry-solids loading (kg DS/h). A machine that looks comfortable at 1% DS can overload the gearbox if the same flow arrives at 5% DS. Incomplete data delays a responsible offer.
| Send this | Why it matters |
|---|---|
| Stream description | WAS, primary, digestate, industrial process water, food effluent, etc. Chemistry and grit drive polymer, wear and cake vs slurry behaviour. |
| Feed DS% or TSS | Sets mass loading (kg DS/h) and whether thickening or dewatering is the realistic duty. |
| Flow and hours/day | Hydraulic sizing. Include min/normal/max if the plant swings. |
| Target solids | Pumpable thickened DS% or stackable cake DS%. If you need cake, the quote should be raised on the sludge dewatering page. |
| Centrate limit (if any) | A TSS or capture target changes pond, polymer and throughput. There is no single “clarification rate” for all feeds. |
| Current polymer or equipment | Helps compare with an existing thickener, belt or screw press rather than quoting in isolation. |
Wastewater Decanter FAQ
No. On a municipal plant the decanter handles sludge (thickening or dewatering). Primary and secondary clarification of the liquid train remains the job of settling tanks, DAF or filtration. Industrial process-water duty is a 2-phase solids split on a defined stream, not a plant-wide clarifier substitute.
Pumpable solids, or a plant still choosing thickening vs dewatering, are wastewater duty. Stackable cake (typical municipal 18–25% DS) is sludge dewatering; see the sludge dewatering centrifuge. Bowl diameter, rpm and 2-phase vs 3-phase are on the decanter centrifuge series.
The same bowl can be commissioned either way by changing pond depth, speed, differential speed and polymer. In daily operation most plants pick one duty per machine. Two-stage lines (thicken, then dewater) are common when combined polymer, power and disposal cost matter more than running a single unit at a compromise setting.
Centrifuge thickening of municipal WAS or primary sludge is often in the 3–8% DS range as a still-pumpable product. Gravity thickeners often sit lower. The result moves with feed DS%, sludge age, polymer and pond depth.
Volumetric flow sizes the pond; dry-solids mass sizes scroll torque. Dilute WAS can look easy in m³/h and still be torque-limited once solids rise. Send both feed DS% and flow so the offer is not based on hydraulic flow alone.
About ZK SEPARATION
ZK SEPARATION manufactures LW 2-phase and LWS 3-phase decanter centrifuges for municipal sludge and industrial process streams. Wastewater machines are specified from feed data. Applicable shipments can be supplied under ISO 9001 quality management and CE marking.
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Equipment delivered annually
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Technical patents
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Application sectors
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International clients
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Need a wastewater-duty quote?
Send feed type, DS% or TSS, flow, and whether you need pumpable thickened sludge or stackable cake. If the target is stackable cake, see the sludge dewatering centrifuge for typical municipal 18–25% DS envelopes.
