Belt press, centrifuge or screw press: matching the polymer
Each dewatering machine treats the floc differently. What each one asks of the polymer, and how to tune grade and dose on site.
Why the machine matters
Polymer conditioning turns sludge into flocs that release water. How strong and how large those flocs must be depends on the forces the machine puts on them.
Belt filter press
Sludge drains by gravity on the belt before it is squeezed between rollers. It needs large, open flocs that release free water quickly, and enough strength to survive pressing without squeezing through the belt. Look for clear filtrate and sludge that lifts cleanly off the belt.
Decanter centrifuge
Flocs meet high shear in the feed zone and the spinning bowl. They need to be compact and tough rather than big and fluffy, and the dose is often higher than on a belt press. Watch centrate clarity and cake dryness together; chasing one alone wastes polymer.
Screw press
A slow-turning screw with low shear. It is forgiving and suits smaller municipal and industrial plants. Good flocculation before the screw, with enough contact time in the flocculation tank, decides how dry the cake comes out.
Choosing the charge
Biological and organic sludges usually need a cationic grade such as Sunfloc Cationic HQ. Mostly inorganic sludges, such as metal hydroxide or mineral fines, often work better with an anionic grade.
Tuning on site
Change one thing at a time: dose first, then solution strength, then the dosing point. Measure in kilograms of polymer per tonne of dry solids so you can compare day to day as sludge volumes change.
More from the blog
Too much polymer? Signs of overdosing and how to fix it
More polyelectrolyte is not always better. How to spot an overdose in the clarifier and on the press, and how to bring the dose back.
Read →Manual or automatic polymer make-up?
Batch tanks, eductors and automatic three-chamber units compared, with the practices that keep solution consistent in either case.
Read →Spec sheet, SDS and COA: what each polymer document tells you
Three documents travel with every bag of polyelectrolyte. Here is what each one is for, and which one to ask for when.
Read →Not sure which grade suits your water?
Send us a one-litre sample or describe your process. We test it in our lab free of charge and recommend a grade and starting dose, and quote within 1 business hour.