Employing low dissolved oxygen strategy to simultaneously improve nutrient removal, mitigate membrane fouling, and reduce energy consumption in an AAO-MBR system: Fine bubble or coarse bubble?

The high energy consumption associated with aeration, which is a widely used hydrodynamic method to mitigate membrane fouling in membrane bioreactors (MBR), poses a significant challenge to the widespread application of aerated MBR. In this study, low dissolved oxygen was applied to optimize the overall performance and reduce energy consumption in an anaerobic-anoxic-aerobic MBR (AAO-MBR) under fine and coarse bubble aeration conditions. Coarse bubble aeration exhibited better membrane fouling control, but induced releasing more proteins and polysaccharides in mixed liquor than that in fine bubble aeration. Coarse bubble aeration resulted in a decrease in the relative abundance of function bacteria, and there was a corresponding drop in enzymes involved in the nitrogen and phosphorus pathways. Furthermore, the average total specific energy demand (0.45 ± 0.02 kW·h/d) and total carbon emissions (0.32 ± 0.01 kg/d) of coarse bubble aeration was remarkably higher than that of fine bubble aeration (0.35 ± 0.01 kW·h/d and 0.25 ± 0.02 kg/d). Our results demonstrate that the fine bubble aeration in low dissolved oxygen-based AAO-MBR can optimize the overall performance and reduce energy consumption, thereby making it a more viable option for the wastewater treatment.