A comparison of culture biomass evolution for the microalgae Scenedesmus spinosus in a tubular pilot photobioreactor of 1.6 m³ and a raceway pilot photobioreactor of 1.2 m³ was carried out, using a nutritional Z-8 medium with the injection of carbon dioxide, and using an electronic system for monitoring and control of operational variables. For three weeks of testing, each culture was exposed to three pH levels of 6.5, 7.0 or 7.5, where random samples from both bioreactors were taken three times a week, to analyze pH, turbidity, transmittance at 640 nm and temperature. At the beginning and the end of culture, total solids were analyzed, and photographs were taken with a microscope to study the cell conditions of culture. This study revealed that the highest biomass production of Scenedesmus spinosus was obtained at pH 6.5 in the raceway photobioreactor, with a productivity of 371 g m-3 day-1, 0.78 % total solids, a turbidity of 858 NTU and 5% transmittance at the end of the culture.