Combined Flocculation-Floatation System

Introduction

  Combined flocculation-floatation system is an effective technique for separating dispersed or emulsified particles from treated water. The technique was first applied to drinking water treatment in systems in South Africa and Scandinavia in the 1960s. Today this system is widely used in many other countries including the United Kingdom , The United States and Australia . Since it provides an efficient and economically competitive high-rate alternative to conventional clarification, as well as an effective pretreatment to granular media filtration.

Technical Information

  Flocculation applied in case of colloidal solutions, is necessary to bring solid particles into a separable form. The mixing and reaction between chemicals and contaminant particles takes place in a plug flow reactor, by means of controlled, calculated turbulence as shown in Figure 1.

Figure 1 Flocculation taking place in a plug flow reactor.

  Floatation occurs by way of attachment of floc particles to air bubbles. The flotation mechanism is more effective with smaller and lighter particles; therefore formation of large, dense floc layers is not required as it would be for a sedimentation process. The air needed for flotation is dissolved in a sub-flow of the treated water. A special inline mixer and pump are used for mixing and increasing the pressure. This makes the water to be almost saturation under the operating pressure. Upon relief of the pressure, microscopically small air bubbles are released and then mix with the wastewater. The bubbles adhere to the solid particles to form rising agglomerates, which can form a floatation layer. The layer is generally dewatered by means of the concentrator and discharge system, see Figure 2.

Figure 2 Separation of flotation layer, concentrator and discharge system

  Agglomerates with a lower floating power are separated between the sheets and reach the floatation layer later through the tops of the corrugated sheets, see Figure 3. Settling material is carried off via the through of the corrugated sheets to the sludge compartment and subsequently removed from the system.

Figure 3 Separation of particles in the corrugated sheets.

Advantages

The standard flotation systems are available as follows:

Note Other capacities are also available, please contact us for specific applications.

Applications

  The combined flocculation-floatation system can be operated with and without chemical pretreatment (flocculation). In wastewater treatment, the system is used principally with flocculation to remove suspended matter and to concentrate biological sludges in the following applications.