Fouling control in a gravity-driven membrane (GDM) bioreactor treating primary wastewater by using relaxation and/or air scouring

Gravity-driven membrane bioreactors (GD-MBR) have been proposed as a sustainable water treatment due to the low energy requirements in terms of operation. The objective of this study is to investigate the effect of different physical cleaning strategies on the membrane performance in a gravity-driven membrane bioreactor treating primary wastewater. The Optical Coherence Tomography (OCT) allowed evaluating the impact of the physical cleaning on the biomass developed on the membrane surface. Applying relaxation did not enhance the membrane performance, however, it led to an increase in thickness and a decrease in the biomass specific hydraulic resistance. Using air scouring under continuous filtration increased the biomass specific hydraulic resistance by compressing the biomass (~50% decrease in thickness). When air scouring was applied at the end of a relaxation cycle, a higher biomass removal and a significant increase in flux (250%) were observed. Biopolymers were found to constitute 55% of the fouling layer. This study highlighted the suitability of an in-situ monitoring approach as a key tool to evaluate the impact of different physical cleaning strategies on the biomass removal in membrane filtration process.