Optimization of Chlamydomonas reinhardtii cultivation with simultaneous CO2 sequestration and biofuels production in a biorefinery framework.

Algal biomass is regarded as a sustainable energy feedstock for the future. Enhancement of the biomass and metabolite production of microalgae increases the economic feasibility of the biofuel production process. The present study encompasses on bioethanol production from Chlamydomonas reinhardtii through a biorefinery approach. The biomass and carbohydrate productivity of C. reinhardtii UTEX 90 and CC 2656 were enhanced by optimizing the physico-chemical parameters. The following conditions were found suitable for the improvement of biomass and metabolite content of C. reinhardtii: pH 6.5-7.0, incubation temperature 30 °C, initial acetate and ammonium chloride concentration of 1.56 g L-1 and 100-200 mg L-1, respectively. Under the optimized operational condition biomass and carbohydrate productivity of C. reinhardtii UTEX 90 and CC 2656 were 512 mg L-1 d-1 & 266.24 mg L-1 d-1 and 364 mg L-1 d -1 & 163.80 mg L-1 d-1, respectively. The amount of CO2 sequestered during the cultivation process by UTEX 90 and CC 2656 were 113 mg L-1 d-1 and 74.95 mg L-1 d-1, respectively. The depigmented and defatted carbohydrate rich biomass was considered as raw material for bioethanol production. The bioethanol yield range was 90-94% of the theoretical yield using Saccharomyces cerevisiae INVSC-1 in a double jacket reactor. To improve the viability of the process, the spent media after ethanol fermentation was subsequently used for methane production using mixed microbial consortium. The energy recovery from the process was 40.39% and 39.7% for UTEX 90 and CC 2656, respectively when C. reinhardtii biomass was used as substrate for biofuel production. The present investigation concedes with the potentiality of algae as a favourable 3rd generation feedstock to address the existing challenges of clean energy production with concomitant CO2 sequestration.