ABSTRACT
The main focus of the work is to study Chlorella pyrenoidosa mediated photoautotrophic production of lipid in a bubble column photobioreactor using CO2 as carbon source under natural diurnal outdoor sunlight. The limiting and inhibiting concentrations of CO2 in sparging gas, nitrogen inhibition, reversibility of the CO2 inhibition on growth, and lipid production have been investigated under natural sunlight. A process model coupled with light distribution inside the culture has been developed considering different concentration of dissolved CO2 and urea, repression of nitrogen on lipid production under natural sunlight diurnal in nature in a bubble column reactor. The biomass titer of 4.6 g/L with 10% CO2 has been achieved within 5 days of culture under sunlight. A two stage photoautotrophic lipid production strategy in a sintered disc bubble column photobioreactor under natural sunlight has been developed. 30% (w/w-DCW) lipid within 5 days of lipid induction period has been achieved. The biomass productivity of 0.91 ± 0.01 gm/L/day in growth period with sufficient urea and lipid productivity of 410 ± 12 mg/L/day in last 2 days of urea starvation period have been achieved in outdoor photoautotrophic cultivation under natural sunlight using CO2 as carbon source.
