Role of rotating speed on the stability of a self-sustaining algal-bacterial photo-granules process

The effects of rotating speed (120, 130, 140 and 150 rpm) of a photo-reactor on the self-sustaining algal-bacterial photo-granules sludge (ABPG) was investigated in this study. The ABPG process maintained good granular stability at 140 rpm with an integrity coefficient of 3.0% and excellent nutrient removal. The increases of the extracellular polymeric substances (EPS) content, the portions of α-helix (32.37%) in the secondary protein structure, and the relative abundance of functional bacteria (e.g. Candidatus_Competibacter), contributed to the maintenance of granular structure stability. However, the lower rotating speed (120 and 130 rpm) resulted in slow bacterial growth and reproduction while a higher rotating speed (150 rpm) caused the disintegration of photo-granules. Overall, the results reveal the influencing mechanisms of photo-reactor rotating speed on the self-sustaining ABPG process and provide an effective approach to maintain the system stability.