Optimization of Chlorella saccharophila harvesting by surfactant-aided dispersed air flotation for biodiesel production processes

Abstract

Surfactant-aided dispersed air flotation was investigated as a low cost microalgae harvesting technique for biodiesel, using the microalgae Chlorella saccharophila and the surfactant CTAB (cetyl trimethylammonium bromide). Response Surface Methodology (Box-Behnken design) was used for optimization of both recovery and concentration factor. The effects of CTAB concentration, column height, pH and air flow rate were investigated. The measured responses were initially analyzed separately to obtain models for each response variable. It was determined that only CTAB concentration and flow rate were significant for the recovery, while all tested variables were significant for the concentration factor. Next, optimization was performed to maximize both responses (recovery and concentration factor) simultaneously. The overall optimum processing parameters determined were CTAB concentration of 100 mg L−1, a column height of 795 mm, pH of 10 and flow rate of 57.9 mL min−1. The expected values for recovery and concentration factor were 91.1% ± 1.62% and 17.9 ± 6.19, respectively. Experimental testing resulted in a recovery of 94.5 ± 2.7% and a concentration factor of 13.23 ± 0.98, which indicates that the experimental values agree with the predicted by 96% and 74% for recovery and concentration factor, respectively. This study demonstrates that surfactant-aided dispersed air flotation is a promising harvesting technique for microalgae biodiesel production processes as its energy requirement is low, can achieve high recoveries and substantially decreases the working volume of microalgae culture. However, a secondary dewatering step is recommended for further concentration prior to product conversion.