HarvestingFrom Phyco.orgGathering algae consists of separating algae from the growing medium, drying, and delivering it, either for end use or chemical processing. In addition, if delivery is to a distant location, the algae may need to be packaged for transport. Separating algae from its medium is also called harvesting algae. Scientists have considered at least three methods for separating algae from the medium wherein it grows, which are detailed below.
[edit] FlotationFroth Flotation is a method of separating algae from the medium by adjusting PH and bubbling air through a column to create a froth of algae that accumulates above liquid level. Froth flotation and drying are currently considered too expensive for commercial use. [edit] Harvesting Algae by Froth FlotationRef: http://www.pubmedcentral.nih.gov/ Harvesting Algae by Froth Flotation, 1961, Gilbert V. Levin, John R. Clendenning, Ahron Gibor, and Fredrick D. Bagor, Resource Research Inc., Washington D. C. Summary This paper describes how to harvest algae using froth flotation, which separates algae from its medium by adjusting pH and bubbling air thorugh a column of medium. The algae collects in a froth above the liquid level, and may be removed by suction. The pH required depends on algal species. The discussion section of the paper briefly evaluates froth flotation and two other separation methods, centrifugation and floccaltion. For this evaluation, the value of dried algae is considered to be between $80 and $100 (US) per ton. Centrifugation uses a centrifuge to separate algae from liquid. The cost of centrifugation and subsequent drying was estimated to be between $65 and $200, which is too much to be commercially viable. Floccaltion uses chemicals to cause the algae to form lumps. The chemicals used during floccaltion are difficult to remove from the algae after sepation. The cost to remove these chemicals may be too expensive to be commercially viable. The cost of froth flotation was estimated to be too high for commercial use. Although, the cost may be reduced with further research. [edit] Dissolved Air FlotationRef: http://www.ajol.info/viewarticle.php?id=18344&jid=186&layout=abstract Dissolved Air Flotation Process for Algae Removal in Surface Water Treatment in Kenya, 2004, W. O. Mulaku and Nyangeri Nyanchaga, Journal of Civil Engineering Research and Practice, Vol 1 No 2, October 2004, pp 27-38. Summary Dissolved Air Flotation (DAF) separates algae from its culture (Kenyan lakes and ponds) using features of both froth flotation and flocculation. It uses alum to flocculate an algae/air mixture, with fine bubbles supplied by an air compressor. Alum is a common name for several trivalent sulfates of metal such as aluminum, chromium, or iron and a univalent metal such as potassium or sodium, for example AlK(SO4)2. The purpose of this study was to determine how much algae can be removed from lake water using DAF. The process can remove from 70% to 90% of algae in a culture. Lesser amounts of removal can be easily achieved. [edit] CentrifugationA centrifuge is a useful device for both biolipid extraction from algae and chemical separation in biodiesel. Coupled with a homogenizer, one may be able to separate biolipids and other useful materials from algae. Centrifugation is a method of separating algae from the medium by using a centrifuge to cause the algae to settle to the bottom of a flask or tank. Centrifugation and drying are currently considered too expensive for personal use, though may prove useful on a commercial and industrial scale. See: Centrifugation [edit] FlocculationFlocculation is a method of separating algae from the medium by using chemicals to force the algae to form lumps. The main disadvantage of this separation method is the additional chemicals are difficult to remove from the separated algae, probably making it inefficient uneconomic for commercial use, though it may be practical for personal use. [edit] See also |
