Modelling of oxygen-evolving-complex ionization dynamics for energy-efficient production of microalgal biomass, pigment and lipid with carbon capture: an engineering vision for a biorefinery

Abstract

The success of algal biotechnology research lies in the development of economically-and-environmentally sustainable biorefineries for food, feed, fuel, and value-added products with carbon capture. The spatiotemporal availability and utilization of light for photolysis of water, mediated by the oxygen-evolving-complex (OEC), are of core importance to algal biomass production, because electrogenesis drives photosynthesis. Therefore, a comprehensive Light Harvesting Model (LHM) was formulated in the present study, using first principles, to estimate the growth of the model-microalga Chlorella vulgaris in flat panel reactors (FPRs). LHM was found to accurately estimate algal growth, photoinhibition and photoacclimation, in light-sufficient and light-limited regimes, using experimental and literature data. Other major findings are that LHM could (a) accurately predict the specific growth rate of algae as a function of the number of photons supplied per unit time per unit FPR volume, (b) successfully track the photooxidation-induced loss of quantum yield and consequent algal death at high light intensities, (c) stochastically estimate the exacerbation of quantum yield losses due to bulk mixing, light attenuation and intercellular self-shading culminating in the cessation of algal growth at high biomass densities and (d) be used for photobioreactor scale-up. Finally, the utility of LHM in energy-efficient algal biorefineries (5.82% photosynthetic efficiency) for biomass (0.83 kg m⁻³ d⁻¹), lipid (8.8 kg kg⁻¹ biomass) and chlorophyll (8.5 g kg⁻¹ biomass) production with associated carbon capture (50% biomass) was demonstrated. To the best of our knowledge, LHM is the first to successfully establish the role of OEC ionization dynamics during photoinhibition in algae.