One of the controlling factors to cultivate microalgae is the pH
of the culture medium [34]. Generally, pH of 7–8 is plausible for
microalgae to grow [34]. Nevertheless, it is worth to mention that
suitable microalgae strains for biodiesel production should not
only contain high lipid yield, but should be able to withstand pH
changes during cultivation cycle. For example, high pH value
(9.0–9.5) was observed in photobioreactor due to shortage of inorganic
carbon after rapid consumption by microalgae [35]. Sometimes,
pH can also drop drastically if high concentration of CO2 is
continuously supplied to the culture medium and caused adverse
effect towards the growth of microalgae