Bioflocculation harvesting of oleaginous microalga Chlorella sp. using novel lipid-rich cellulolytic fungus Aspergillus terreus (MD1) for biodiesel production

Abstract

AbstractThe isolation of lipid-rich cellulolytic fungi was targeted to be investigated as bioflocculant agents for microalgae harvesting. The fungal isolate coded MD1 was selected based on its lipid content, cellulolytic activity, and its harvesting efficiency for the freshwater oleaginous microalga Chlorella sp. The selected fungus which was molecularly identified as Aspergillus terreus has been applied as bioflocculant after solid state cultivation on pre-treated rice straw (as abundant agro-cellulosic waste). Optimization of harvesting efficiency of Chlorella microalga using A. terreus/rice straw biomass as the “bioflocculant” was investigated. The optimization conditions included microalga/bioflocculant ratio, microalgal age, contact time between the bioflocculant and the microalga, pH of microalgal culture at harvesting time, and cell density of microalgal culture. The obtained results revealed that the harvesting efficiency could reach 97.6% due to 24 h as contact time at 30% flocculant/microalga ratio and pH 7. While after 2 h contact time, 93.3% harvesting efficiency could be obtained using the same bioflocculant:microalga ratio at pH 6. The lipid extracted from harvested Chlorella/A. terreus mixture was applied to produce biodiesel (fatty acid methyl ester) after methylation. The resulted biodiesel contains high percentage (67.2%) of C18:1,2 unsaturated fatty acids which is considered a suitable fraction for biodiesel production. Obtained results revealed the suitability of the novel A. terreus strain as sustainable bioflocculation agent to harvest microalga(e) for biofuel production.