Growth rates and photon efficiency of Chlorella vulgaris in relation to photon absorption rates under different LED-types

A general model was developed that depicts the long-term growth profiles of Chlorella vulgaris batch cultures under different light intensities of white LED light. The model equation reflects the growth with a time delay of second order at different light intensities by changing only one parameter of the entire equation. This model was applied to the data of short-term batch cultures at different incident light intensities of white, blue, green and red LEDs and growth rates were calculated. Models for the growth rates depending on the photon absorption rates for the different LED-types were developed. Photon absorption rates can be determined for other photobioreactor systems, hence the growth rates of Chlorella vulgaris in other reactor systems can be calculated using the newly developed models. At photon absorption rates up to 2.5 Einstein L−1 d−1, C. vulgaris yielded the highest growth rates under red LEDs. At higher photon absorption rates, white light led to the highest growth rates. Green and blue LEDs yielded similar growth rates which were consistently lower than the growth rates under white and red LEDs. Maximum photon efficiency of ~130 absorbed photons per fixed CO2 was reached under red LEDs.