Fga. Fernandez et al., Airlift-driven external-loop tubular photobioreactors for outdoor production of microalgae: assessment of design and performance, CHEM ENG SC, 56(8), 2001, pp. 2721-2732
A methodology is presented for designing photobioreactors with tubular loop
solar receivers in which the fluid is circulated by an airlift device. The
design method effectively combines the relevant aspects of external irradi
ance-dependent cell growth, oxygen accumulation in the solar loop, oxygen r
emoval in the airlift device, and hydrodynamics of the airlift system that
determine the Bow velocity through the solar receiver. The design approach
developed was used to model and build a 0.2 m(3) outdoor photobioreactor. A
compact degasser in the airlift section eliminated dead zones and dark zon
es, while achieving complete separation of gas and liquid. The measured gas
-liquid hydrodynamics, mass transfer, and culture productivity were consist
ent with the model predictions. The reactor was tested with continuous cult
ure of the microalga Phaeodactylum tricornutum at various liquid velocities
through the tubular solar receiver. A biomass productivity of 1.20 gl(-1)
d(-1) (or 20 g m(-2) d(-1)) was obtained at a dilution rate of 0.050 h(-1).
Solar receiver linear liquid velocities of 0.50 and 0.35 ms(-1) gave simil
ar biomass productivities, but the culture collapsed at lower velocities. A
n adverse effect of high dissolved oxygen concentration on productivity was
observed. Oxygen accumulation could be reduced by increasing the liquid ve
locity and this enhanced the biomass yield. (C) 2001 Elsevier Science Ltd.
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