Dissolved Air Flotation (DAF) principles were applied to harvest microalgae from high rate algal pond (HRAP) effluents in a highly simplified system which consisted of an open channel and a dosing pump only. Polyelectrolyte solution is dosed into the channel through a diffuser in the vicinity of a paddle wheel, where rapid mixing occurs. Slow mixing takes place in the channel. While flocs grow, oxygen bubbles resulting from algae photosynthetic activity are entrapped. Floating flocs are removed manually at the end of the channel. Removal efficiencies of 90% were obtained at a 10 mg polyelectrolyte dose. The float had 4 to 6% solids which dewatered easily to 10% solids.

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