Investigation of the light dynamics and their impact on algal growth rate in a hydraulically integrated serial turbidostat algal reactor (HISTAR)

There is a need for greater understanding of the light dynamics in photoautotrophic microalgal reactors as commercialization efforts move forward. This paper presents results of experiments performed to determine (1) surface irradiance (Ios(PAR)) as a function of lamp elevation; (2) depth (z) and biomass (X) dependent scalar irradiance (Iz(PAR)) and attenuation k0(PAR); (3) average scalar irradiance (Ia(PAR)) in the reactor as a function of biomass; and (4) specific growth rate as a function of Ia(PAR) and impacted by photoinhibition for the hydraulically integrated serial turbidostat algal reactor (HISTAR) illuminated by metal halide lamps. Selenastrum capricornutum was used as the test organism. Lamp elevation studies resulted in a light energy dissipation coefficient (ka) of 7.46 μmol s−1 m−2 cm−1. Light attenuation studies yielded a linear partition of the attenuation coefficient between the water and biomass; k0(PAR) = 1.97 + 0.0575X and an exponential relationship between Ia(PAR) and X; Ia456 = 277 e−0.0118X. Finally, net the specific growth rate was found to follow Steele's model for determination, resulting in a μmax = 1.73 d−1 and Iopt(PAR) = 391 μmol s−1 m−2.