ABSTRACT

Microalgae have been identied as a potential alternative resource for biofuel production. Signicant drawbacks to algaculture include dilute culture density and the small size of microalgae, which translates into the need to handle large volumes of culture during harvesting. This energy-intensive process is therefore considered a major challenge for the commercial-scale production of algal biofuels. Most of the currently used harvesting techniques have several drawbacks, such as high cost, occulant toxicity, or nonfeasibility of scale-up, which impact the cost and quality of products. As harvesting cost may itself contribute up to one-third of the biomass production cost, substantial amounts of research and development initiatives are needed to develop a cost-and energy-effective process for the dewatering of algae. Several factors, such as algae species, ionic strength of culture media, recycling of ltrate, and nal products, should be considered when selecting a suitable harvesting technique. Harvesting cost and energy requirements must be reduced by a factor of at least 2 if algal biomass production is to be viable for very low-cost products such as biofuels. There could be considerable cost and energy savings in custom-designed,

6.1 Introduction ....................................................................................................77 6.2 Harvesting Processes ...................................................................................... 79 6.3 Gravity Sedimentation .................................................................................... 79 6.4 Centrifugation .................................................................................................80 6.5 Filtration .........................................................................................................80 6.6 Flotation .......................................................................................................... 81 6.7 Flocculation .................................................................................................... 81 6.8 Electrolytic Coagulation ................................................................................. 82 6.9 Energy Efciencies of Harvesting Processes ................................................. 83 6.10 Conclusion ......................................................................................................85 References ................................................................................................................86