CHAPTER 3: DEVELOPMENT OF A BIOFILM-BASED MICROAGLAE CULTURE SYSTEM FOR EFFICIENT BIOMASS HARVESTING
Abstract
Microalgae has been mainly cultivated in open ponds or closed photobioreactors in which algal cells were grown in suspension and harvested through sedimentation, flocculation, filtration and/or centrifugation. The objective of the present research is to develop an attached algal growth system to facilitate biomass harvest with improved biomass yield. In the attached system, algal cells were grown on the surface of a material rotating between nutrient-rich liquid phase and carbon dioxide rich gaseous phase. Using Chlorella vulgaris as the model algal species, 16 materials were tested for suitability as attachment materials for algal growth. Cotton duct resulted in the best cell attachment in terms of durability, attachment and economy. The algal cells from the attached growth system were harvested by simply scraping off the algal biofilm.
The operation conditions of the attached growth system were optimized for improved biomass productivity. A harvesting frequency of 7 days with a rotation speed of 4 rpm resulted in the highest cell productivity. CO2 content changing from atmospheric CO2 level (~300ppm) to 3000 ppm did not result in a significant growth performance change. The attached growth system resulted in a biomass productivity of 10.5 g m-2 day-1. The biomass harvested from the attached system had higher carbohydrate content, but lower lipid content compared to the suspension culture system.