Control of incident irradiance on a batch operated flat-plate photobioreactor

• Nannochloropsis oculata was grown in a flat-plate photobioreactor (PBR) operated in batch mode.
• A model-free optimal search rapidly determined the optimum average fluence rate.
• Feed-forward inversion control continuously adjusted incident irradiance on the PBR.
• Controlling incident irradiance on PBRs enhanced productivity and reduced lag time.
• The procedure presented can be applied to any microorganism species or PBR design.

This study experimentally demonstrated a feed-forward inversion control scheme for maintaining an optimum incident irradiance on photobioreactors (PBRs) during batch cultivation. A data-based model-free optimization using quadratic fit was utilized to rapidly estimate the optimum average fluence rate set point value that rendered maximum microalgae growth rate. Then, the feed-forward inversion control scheme adjusted the incident irradiance with respect to the in-process measured mass concentration to maintain the optimum average fluence rate inside the PBR. Optimization of growth conditions with respect to light is of prime importance for increasing biomass and lipid productivity in microalgae cultivation. The present approach can rapidly identify the optimum average fluence rate for any given species, reduce the lag time, and increase the growth rate and productivity of microalgae. This was illustrated with Nannochloropsis oculata batch grown in a flat-plate PBR illuminated from both sides.