Bicarbonate alkalinity and carbon can be provided by the addition of sodium bicarbonate to the cultivation medium.
In synthetic cultivation media for the cultivation of Spirulina sp. the most frequently used medium is Zarrouk medium,which provides carbon as sodium bicarbonate in the amount of 16.8 g L1 . In the earlier studies, sodium bicarbonate was added to media containing anaerobically digested wastes
in amounts in the range of 9–17 g L1 , but 2–4 g L1 is now considered as sufficient . Furthermore, suggested that supplementation of sodium bicarbonate need not exceed 0.5% of the culture medium to be adequate for Spirulina growth in effluents of anaerobically digested pig and cattle manure. It has been suggested that many factors, including
bicarbonate (HCO3) furnishes the carbon skeleton needed
for algal biomass particularly, proteins. It may be essential
for protein synthesis in the organism, probably because
sodium is necessary for the activity of certain enzymes involved
in protein synthesis, formation of coenzymes and adenosine
phosphates and biosynthesis of sulfur-containing proteins,
respectively . Moreover, algae put up different metabolic
products during photosynthesis, using only light and nutrients.
The relative amounts of these products are tightly linked to
environmental and nutrient conditions, including CO2 levels.
Carbon is required as non-mineral nutrient for algal growth
as as reported by Walker. Similar to the results reported from
this study, the OD680 and biochemical constituents of the
tested alga had greatly affected when grown under different
concentrations of sodium bicarbonate as compared by control
culture after 12 days. The statistical analyses have already
revealed that sodium bicarbonate exerted a significant positive
effect on the algal constituents of proteins and chlorophyll
(p > 0.01). In accordance with the study results, previous studies
have shown sodium bicarbonate can be added as a form of
inorganic carbon to increase cell dry weight, FAME, and pigment
production . Even though, reported that
inorganic carbon of alkalinity in the form of bicarbonate
was consumed rapidly, in turn causing the attenuation of cell
growth of Scenedesmus sp. Moreover, it has been reported that
the elevated CO2 concentrations decrease the relative concentrations
of proteins and pigments in the cells but increase carbohydrate
content of the A. platensis which was accompanied
by reduction in the maximum biomass yield as reported by
Gordillo et al.