Influence of bioflocculation parameters on harvesting Chlorella salina and its optimization using response surface methodology

The present investigation deals with a cost effective harvesting of microalga, Chlorella salina, for biodiesel production with microbial flocculant, an exopolysaccharide (EPS) from marine Bacillus subtilis. The process with five independent variables namely temperature, pH, flocculation time, bioflocculant size and cationic inducer (ZnCl2) concentration, were evaluated using one factor at a time and were statistically optimized by response surface methodology (RSM). Bioflocculation was enhanced by adding ZnCl2 as the cationic inducer, which worked under the principle of “divalent cation bridging (DCB)” theory. Additionally ZnCl2 did not distort the cell's structural integrity. Using RSM, a maximum efficiency was found to be more than 98.66% with flocculation parameters as temperature (30.63 °C), pH (10.4), flocculation time (6.2 h), bioflocculant size (0.34 ml) and cationic inducer size (0.031 mM). This flocculation study concluded that chemical flocculation could be disadvantageous due to cell disintegration, toxicity and cost consumption, whereas a bioflocculation is environmental friendly as well as cost prohibitive process.