Economic medium optimization by response surface methodology for higher biomass productivity and chlorophyll content in Chlorella vulgaris

Commercial production of microalgae is often more costly, as it requires significant quantities of various nutrients. This study aimed to utilize response surface methodology (RSM) to identify optimum levels of particular variables in a general economic culture medium, in the presence of sodium bicarbonate as an inorganic carbon source for increasing biomass productivity (BP) and total chlorophyll (CHL) content in Chlorella vulgaris microalgae. The different levels of independent variables were based on related references and studies. The predicted amount of biomass productivity and chlorophyll content in RSM was 119.37 mg/L/d and 7.61 mg/L, respectively, at optimized conditions: temperature 25°C, nitrate 716.39 mg/L, phosphate 14 mg/L, and sodium bicarbonate 259 mg/L. The results of the predicted and the actual response differed with R2: 0.75 and 0.81, and adjusted R2: 0.51 and 0.64 for BP and CHL, respectively, and were found to be in reasonable agreement with the better reliability model. This method is applied to the optimization of actual BP and CHL experiments and is found to outperform the existing methods. The optimal value found by the proposed method has a high prediction accuracy (less than 10% error), and it can be confirmed that the increased BP and CHL amount is significant (p<0.05). This information is particularly interesting for semi-industrial-scale processes, since the reduction and optimization of medium compounds might represent an improvement in the cost-effectiveness of the process and, eventually, greater profit.