Microalgae are currently being considered a promising feedstock for biofuel production in view of its ever increasing worldwide demand. With the development of new bioprocesses and plant configurations, industrial-scale microalgae production is on the route to become an interesting technological alternative for the global biomass supply chain. In this context, this work aims to evaluate the profiles of CO2 consumption and O2 production, as well as the related pH modification, in photosynthetic cultivations of the Chlorophyceae microalgae Chlorella vulgaris under various conditions in a flat-plate photobioreactor. A central composite design was outlined in order to assess the influence of three process variables on microalgae growth and associated parameters: light intensity (60-120 μE s-1 m-2), CO2 supplementation in the gas feed (0-12%) and nitrogen concentration in the culture medium (156-2300 mg L-1). The injection of CO2 in the cultures led to an immediate drop in medium pH, from the initial 7.5 of a standard BG-11 medium to an average 4.8 in cultivations with 12% CO2 bubbling. Within seven days of cultivation, a pH rise in the batches was observed due to microalgal photosynthetic activity. Dissolved O2 profiles also displayed a peculiar behavior in response to the employed 12 h photoperiod, being higher in the light phase of the cycle than in the dark one. The availability of such data in the scientific literature may aid in scale up of microalgae processes and their integration to other industrial facilities, such as in the use of CO2 from fermentation in sugarcane mills.