PosiDAF is an innovative process that enhances the performance of conventional dissolved air flotation (DAF) processes for algae removal, eliminating the need for coagulation. Bubble modification is achieved by the addition of polymers prior to the air saturator making the surface of the bubbles produced positively charged.

Efficient flotation relies on effective collision and attachment of bubbles and particles. This is achieved by coagulation to make the cells (e.g. algae) less negative thus minimising repulsive effects between the cells and the strongly negatively charged bubbles. In DAF processes the bubbles are produced using an air saturator; recycled water is saturated with air at high pressure and subsequently released at atmospheric pressure.

Work has been performed to demonstrate the efficiency of this process in terms of algae removal. It was determined that with no chemical addition to the recycle flow, approximately 10% cell removal could be achieved. Highly hydrophobic, cationic surfactants removed cells efficiently, reaching 63% removal for a recycle ratio of 20%. Use of specific polymers results in a removal efficiency of 95 %, much greater than that predicted theoretically.

Water Innovate is currently developing the PosiDAF process for the treatment of algae laden waters.

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