Photobioreactor engineering for solar microalgae cultivation: methodology and applications
rX = ρφA − µs
J NADH M X K Kr r 2 X = ρφA − X Kr + G υ NADH − X Kr + G 2
GEPEA : J.Pruvost, B.Le Gouic, J.Legrand AlgoSource Technologies : F. Le Borgne, O.Lépine
Light-limited regime Limiting growth factors in microalgal cultivation systems • • • •
Light Dissolved carbon Chemical nutrients Physico-chemical condition (T, pH)
•
Physical (process) parameters
Bacterial contamination – biological drift
Biological parameters
An adequat engineering and control of the cultivation system as in PBR allows preventing from any limitation by nutrients and growth conditions (pH, T, bacterial contamination)
Productivity will then be limited by light: light-limited regime (which will guarantee by definition the maximum biomass production of the cultivation system) 2 major consequences • Except for very adverse culture conditions, light will always limit process productivity • In light-limited regime, the control of light (or its effect) will allow controlling process performances (the so-called « physical limitation » in chemical engineering) But light is a complex parameter
has to be considered with a special attention !!
Optimizing light attenuation conditions in PBR 0.8
Biomass productivity Px = Cx/τp
Fresh feeding medium (Flowrate Q)
0.7
0.6
Harvesting (Flowrate Q)
0.5
Biomass concentration Cx (kg.m-3)
0.4
Cxopt 0.3
An optimal biomass concentration exists, corresponding to an optimal dilution rate (or residence time)
0.2
0.1 0
50
100
150
Photobioreactor (Volume VR)
Residence time τpand dilution rate D
200
0.018
20
Biomass productivity Px = Cx/τp = Cx.D
0.016
VR 1 (= ) Q D
22
Residence time τp (hours)
Px max
τp =
18
Increasing biomass concentration decreases the light energy absorption rate
