Comparison of Centrifugation, Dissolved Air Flotation and Drum Filtration Techniques for Harvesting Sewage-grown Algae

Three different techniques of harvesting microalgae from four pilot scale (125 m 2) and two demonstration ponds (1200 m 2) have been investigated. The processes included centrifugation, chemical flocculation followed by flotation and continuous filtration with a fine-weave belt filter. None of these processes was completely satisfactory. Centrifugation gave good recovery and a thickened slurry, but required high capital investment and energy inputs. Dissolved air flotation was more economical, but, if the recovered algae were to be incorporated into animal feed, the use of flocculants such as alum could have undesirable effects on the growth rate of the animals. This problem could be overcome by the use of non-toxic flocculants. The continuous filtration process had significant advantages in energy efficiency, economics and chemical-free operation. The only drawback of this process was that the efficiency depended on the size and morphology of the algae. * To whom all correspondence should be addressed. 51 Biomass 0144-4565/88/S03.50 © 1988 Elsevier Applied Science Publishers Ltd, England. Printed in Great Britain 52 T.-S. Sim, A. Goh, E. W. Becker