Chemical Science International Journal

Microalgae are great users of CO₂ and can fix large amounts of this compound. In algal biomass production systems, the requirement of carbon is usually supplied by CO₂, continuously or intermittently. The relative concentrations of inorganic carbon species determine the pH and, in turn, are determined by the pH of the medium. This study aimed to establish a relation between the variation in CO₂ concentration and the pH of the medium and validate the equation proposed for the transfer of CO₂ during the supply of this gas in the liquid medium in a carbon dioxide biofixation process in an open raceway type bioreactor, provided with a carbon dioxide injection system. The experiments were performed in a 200 L open raceway type bioreactor, in which a gas injection system was used where air enriched with 12% CO_{2 (V/V)} at a specific flow rate of 0.05 min^-1. An equation was established to determine the pH variation from the variation of the CO₂ concentration in the environment. The data obtained from the proposed equation were satisfactorily explained by experimental data (r² = 0.90).