Photosynthetic efficiency of Chlorella sorokiniana in a turbulently mixed short light‐path photobioreactor

Abstract

To be able to study the effect of mixing as well as any other parameter on productivity of algal cultures, we designed a lab-scale photobioreactor in which a short light path (SLP) of (12 mm) is combined with controlled mixing and aeration. Mixing is provided by rotating an inner tube in the cylindrical cultivation vessel creating Taylor vortex flow and as such mixing can be uncoupled from aeration. Gas exchange is monitored on-line to gain insight in growth and productivity. The maximal productivity, hence photosynthetic efficiency, of Chlorella sorokiniana cultures at high light intensities (1,500 micromol m(-1) s(-1)) was investigated in this Taylor vortex flow SLP photobioreactor. We performed duplicate batch experiments at three different mixing rates: 70, 110, and 140 rpm, all in the turbulent Taylor vortex flow regime. For the mixing rate of 140 rpm, we calculated a quantum requirement for oxygen evolution of 21.2 mol PAR photons per mol O(2) and a yield of biomass on light energy of 0.8 g biomass per mol PAR photons. The maximal photosynthetic efficiency was found at relatively low biomass densities (2.3 g L(-1)) at which light was just attenuated before reaching the rear of the culture. When increasing the mixing rate twofold, we only found a small increase in productivity. On the basis of these results, we conclude that the maximal productivity and photosynthetic efficiency for C. sorokiniana can be found at that biomass concentration where no significant dark zone can develop and that the influence of mixing-induced light/dark fluctuations is marginal.

Microalgae production in a biofilm photobioreactor

“…Regarding the biomass yield on light (Y x/ph ), two values are depicted: 1.5 g-DW mol-ph -1 and a lesser value of 1.0 g-DW mol-ph -1 the first is the maximum biomass yield derived from our current comprehension of photosynthesis and the second is based on a range of dedicated studies. We believe 1.0 g-DW mol-ph -1 is a realistic aim for a large-scale microalgae production plant as this value is in the higher end of commonly measured biomass yields on light (Kliphuis et al 2010;Takache et al 2010;Vejrazka et al 2011;Zijffers et al 2010;Zittelli et al 2006). is selected as the maximum value in this graph.…”

Effective mixing and aeration in a bioreactor with Taylor vortex flow

“…The experiments by Miller et al (Miller et al, 1964) regarding a bioreactor with the Taylor vortex flow indicated that the rate of photosynthesis increases with an increasing rotor speed. Also, Kliphuis et al (Kliphuis et al, 2010) investigated the effects of the density of algae in the Taylor vortex flows on productivity. Also, it has been confirmed by Kawai (Kawai, 2010) that cell death is negligible in the range below the Reynold number based on the gap, d, between cylinders of Re = 30000, where the flow field was also measured by an ultrasonic Doppler velocity profiler.…”

Antenna size reduction in microalgae mass culture

“…The theoretical maximum biomass yield on light (YCx/ph) for Chlorella sorokiniana with nitrate as nitrogen source is approximately 1.57 g molph -1 (Kliphuis et al 2010). …”