After forming small flocs in the coagulation step (see coagulation), flocculant is dosed in order to create bigger and more stable flocs. The flocculant is often called polymer or poly-electrolyte.
Flocculant / poly-electrolyte must be prepared from a powder polymer or a fluid concentrated polymer.
Polymer is a product that must be well mixed with water to prevent clot formation. After mixing with water a certain maturation time is necessary to "unfold" the polymer chain.
Flocculant needs to "mature" (30 to 45 minutes) before it can be dosed.
Matured polymer is a sticky liquid.
In smaller plants the production is matured in a "manual polymer mixing unit". Usually the powder or liquid is mixed in a reaction tank 1 x per day.
For larger installations we strongly recommend automatic polymer make up stations for both powder and liquid polymer applications.
An automatic polymer make-up station consists mostly of three compartments with a dosing screw and a powder storage.
The dosing screw (8) at the bottom of the powder storage (9) is provided with a heating element (10) to prevent condensation.
In a polymer make up station of liquid polymer, the entire powderbuffer and dosing screw is replaced by a polymer dosing pump
The stirred flocculator is an open tank with an agitator that delivers the necessary mixing energy. In a classical physico-chemical treatment, there are 2 or 3 mixing chambers.
The flocculator is used for pH correction, coagulation and flocculation. Depending on the application, the rotation speed and the type of agitator are determined. The volume of the flocculator detemines the residence time and a visual inspection gives an immediate idea of the floc forming.
The mixing energy in a pipe flocculator is provided with the feeding pump and through the many bends and strictures.
The contact time is very short and visual inspection is difficult.
This type of flocculator is mainly chosen where easy physical-chemical reaction is suspected.
The manual polymer make-up station is composed of a polypropylene or polyethylene tank with a mixer and a powder dispersion system.
A low-level alarm is also present in order to avoid dry-running of the polymer dosing pump.
Aaqua also provides a timer so the mixing continues 45 minutes after polymer dosing, in order to achieve a good maturation of the polymer.
Those manual polymer make-up stations are available in volumes from 500 to 3000 liters.
A water flow meter and a water solenoid valve are provided (optionally). This way you become a half-automatic unit. Only the powder dosing has to be done manually once a day.
The flow meter is an important tool in the control of the dosing and ensures that a correct dosage of chemicals takes place.
The electromagnetic flowmeter is the most common as the flow meter measurement takes place in an open tube without "obstacles" and is thus almost insensitive to pollution.
