The effect of elevated levels of CO2 on selected microalga was
studied using a simple closed photo bioreactor made of low density
poly ethylene sleeves (LDPE). Cultures were grown in LDPE sleeves
of uniform size 15 cm (w) 60 cm (L) with a total volume of 5.7 L
with a working culture volume of 1.5 L constituting approximately
40% of total volume and remaining 60% void volume filled by gas
i.e., different levels of CO2 mixed with air. The schematic representation
of CO2 supplementation to microalgal cultures in photobioreactor
is shown in Fig. 1B. The LDPE sleeves were placed
horizontally and the cultures were maintained in a constant environment
of CO2 at three different concentrations viz., 5%, 10% and
15%, respectively. The CO2 (from CO2 cylinder) was mixed with air
(from air compressor) and passed through a membrane filter
(0.22 l) and the gas was allowed to mix in a glass cylinder before
passing to the photobioreactors. The initial culture density and pH
were maintained as 0.120 g/L and 7.2 ± 0.1 respectively. The control
cultures received CO2 at less than 1%. All the experiments were
performed under batch mode. The gas volume in photobioreactors
was maintained to constant levels by supplying CO2 at every 24 h.