Dear Ghoewylah,  Factors ...

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Dear Ghoewylah, 

Factors that affect the selection of the type and dosage of the polyelectrolyte are the source, properties of solids and the type of mixing and dewatering devices to be used. Important solids properties are concentration, age, pH, alkalinity. Source of sludge to be dewatered, like primary sludge, waste activated sludge, digested sludge have various requirements. Alkalinity and pH also affect the performance of conditioning agent. Th method of dewatering is also important for selection of conditioning agent and polymers are typically used for centrifugation and belt filter presses.

As my colleagues wrote, the dosage should be determined in laboratory. The simplest is the widely used jar tests with different dosage of polyelectrolyte. Beside this Buchner funnel test for determination of specific sludge resistance could be used.

In general, the type of sludge has the greatest impact on the quantity of chemicals required.

Typical levels of chemicals (Wastewater Engineering Treatment and Reuse – Metcalf & Eddy are given hereafter

Type of sludge

Belt filter press,

kg/t dry solids

Solid bowl

Centrifuge,

kg/t dry solids

Primary

1-4

1-2.5

Primary and waste activated

2-8

2-5

Waste activated

4-10

5-8

Anaerobically digested primary

2-5

3-5

Anaerobically digested primary and air waste activated

1.5-8.5

2-5

 

However dosage could vary considerably depending on the molecular weight of polymer, ionic strength, activity level.

Therefore It is always good to consult polyelectrolyte manufacturers for more information on polymer applicability.