Relation between Transfer of CO2 and the pH of the Medium

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% CO2 (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).