Abstract
Abstract
Production of algae as renewable resources has been pursued actively. Attention has so far been focused on phototrophic algae. Explored here is a completely different approach that harnesses the growth ability of phagotrophic algae on microorganisms such as bacteria, which are abundantly present in waste, including activated sludge generated in wastewater treatment plants. Escherichia coli, a common bacterium, was used as an example of bacterial feed for the oleaginous phagotrophic alga Ochromonas danica. Growth characteristics and lipid contents of O. danica were determined under various conditions. Algal doubling time could be as short as 7 h, but increased to >20 h at low starting E. coli-to-O. danica ratios. The alga was also sensitive to step changes of pH and darkness. Without these factors, phagotrophic growth was similar in a wide range of conditions, even under total darkness and in deionized water with washed E. coli as the only food source. O. danica grew on E. coli with an average yield of about 25% (w/w) and a lipid content of 27% ± 8%. As a food source for phagotrophic algal growth, bacterial cells provided excess nitrogen, which was released as ammonia. Glucose supplementation was studied to avoid ammonia release and produce more algae with higher lipid content (33–34%). Results supported feasibility of this new approach and identified suitable process conditions for further development and application in real wastewater systems. Besides algal production, the approach can remove harmful bacteria from wastewater.
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