Process engineering analysis of LED-driven microalgal growth and lipid lodgement dynamics through kinetic modelling and illumination energetic approach

Abstract

Photosynthetic world of microalgae has been briefly explored for possible solution(s) in nexus of energy, environmental and healthcare challenges by zeroing in on biomass build-up and lipid lodgement as responses of the conducted study. Illumination engineering was employed to measure impacts of variations in terms of photosynthetic photon flux density (PPFD) and photoperiod of low kelvin colour temperature (KCT) white, blue, and red light emitting diodes (LEDs) on Chlorella vulgaris. Cultivation was tracked through responses in terms of dry cell weight (DCW) for biomass build-up, and as %DCW for lipid lodgement. Two-way analysis of variance (ANOVA) with interaction (type III) and effect size (η²) metric helped in understanding their statistical and practical significance respectively. The best biomass build-up (1.41 ± 0.03 g/L) was observed at 100 PPFD and 24:0h photoperiod under red spectrum and highest lipid lodgement (34.36 ± 1.45 %DCW) was obtained at 150 PPFD and 8:16 h photoperiod under blue spectrum. To bridge the lacuna in growth kinetics literature, a novel reparameterization of Von Bertalanffy model was presented. Kinetic parameters for the best possible responses under each LED setting were fitted into the model with trust region reflective (TRF) algorithm. Akaike information criteria corrected (AICc) revealed the proposed “Modified Von Bertalanffy model” to be the best out of five models (Modified Von Bertalanffy, Modified Logistic, Modified Gompertz, Modified Richards and Modified Baranyi). The duration of exponential phase was determined from the rate of change of maximum specific growth rate (${\mu }_m$). The ${\mu }_m$ values and the duration of exponential phase were correlated with the responses, hinting at future directions in understanding the kinetic studies of growth induced (during exponential phase) and stress induced (post exponential phase) cultivation. Based on the lux requirements for best possible response, the projected energy savings of various models were compared using company data sheets from Broadcom, Seoul Semiconductor, and Cree.