This work focuses on using non-destructive imaging techniques to monitor in-situ the formation of algae biomass on hollow fiber membrane bioreactor treating wastewater. Optical Coherence Tomography (OCT) was employed to acquire cross-sectional scans of the algae growth in real-time under continuous operation. The proposed approach allowed evaluating in real-time the impact of the biomass on the bioreactor performance in terms of TMP increase and permeate quality.