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Author      Title/Abstract      

Algae Harvesting Using Flotation
Author: John Bratby
Date: 11/12
Preprint, IWA’s 6thInternational Conference on Flotation in Water and Wastewater Systems, New York, NY, October 29-31, 2012

This paper discusses dissolved-air flotation (DAF) applied to algae harvesting for the algae-to-biofuels industry. The DAF process is the most effective means of separating a relatively low concentration of algae from a large body of water. Some of the important design features of DAF that promote effective algae separation and harvesting, as well as thickening of the separated algae, are discussed. The efficiency of recovery is a significant issue because it relates to the economics of the separation technique. However, it is not necessarily of overriding importance since the water from the separation unit can be recycled back to the algae growth units. The efficiency of recovery and operation of the separation technique depends to a large extent on the means by which the algae is conditioned. The paper discusses various inorganic and organic chemicals for algae coagulation, to facilitate algae separation by DAF. Inorganic coagulants tend to be the most effective, although some natural and synthetic polymers are effective. Ideally the coagulant used should not detract from the animal feed option for the co-product from algae biofuel processing. Chitosan is discussed as one option, but other organic polymers that are GRAS certified should be used preferentially to those products that are not certified.