Bicarbonate induced enhanced production of microalgal extracellular polymeric substance and its characterization

Chlorella vulgaris, a green microalga, produces extracellular polymeric substances (EPSs) that aid in microalgal self-settling and offer protection against physicochemical stresses. To develop an efficient bioprocess for EPS production, C. vulgaris was cultivated in modified Bold's Basal Medium with varying initial concentrations of sodium bicarbonate in photobioreactors. At 130 mM bicarbonate, higher biomass concentration of 1.60 ± 0.04 g/L and productivity of 0.19 ± 0.02 g/L/d were achieved after 8 days. A relatively higher EPS yield of 183 ± 2 mg/g biomass was obtained at 190 mM bicarbonate resulting in 5-fold increase over control. EPS promoted maximum microalgal auto-flocculation within 8 h in 190 mM bicarbonate and was identified as a glycoprotein with molecular weight of 1400 kDa. This innovative strategy of utilizing bicarbonate as a source of dissolved inorganic carbon not only enhances EPS production but also demonstrates a potentially scalable method for carbon dioxide capture from flue gases.