Long-Term Fouling Control Strategies in Gravity-Driven Membrane Bioreactors (Gd-Mbrs): Impact on Process Performance and Membrane Fouling Properties

Abstract

This study aims to assess the effects of periodic physical cleanings operations in Gravity-Driven Membrane Bioreactor (GD-MBR) treating primary wastewater. The impact of each cleaning strategy on the reactor performance (permeate flux and water quality), biomass morphology, and fouling composition were evaluated. The application of air scouring coupled with intermittent filtration resulted in the highest permeate flux (4 LMH) compared to only intermittent filtration (i.e., relaxation) (1 LMH) and air scouring under continuous filtration (2.5 LMH). Air scouring coupled with relaxation led to a thin (~50 µm) but with more porous fouling layer and low hydraulic resistance, presenting the lowest concentration of extracellular polymeric substance (EPS) in the biomass. Air scouring under continuous filtration led to a thin (~50 µm), dense, compact, and less porous fouling layer with the highest specific hydraulic resistance. The employment of only relaxation led to the highest fouling deposition (~280 µm) on the membrane surface. The highest TN removal (~62%) was achieved in the reactor with only relaxation (no aeration) due to the anoxic condition in the filtration tank, while the highest COD removal (~ 60%) was achieved with air scouring under continuous filtration due to the longer aeration time and the denser fouling layer. The presented results highlighted the versatility of the GD-MBR, where the choice of the appropriate operation relies on the eventual discharge or reuse of the treated effluent.