Pathways and challenges in effectively controlling membrane fouling in anaerobic membrane bioreactors

Anaerobic membrane bioreactors (AnMBRs) have emerged as an effective technology for treating domestic and industrial wastewater. However, AnMBRs typically exhibit low membrane fluxes (<10 L/m2.h), which limits their wide application. Despite the use of various techniques to control membrane fouling, the relationships among these techniques and the challenges associated with their application remain unclear. Current literature categorizes membrane fouling control approaches into four classes, namely a reduction in the concentration of soluble microbial products (SMP), an increase in shear, an increase in particle size, and membrane optimization. Biological techniques are effective in reducing the concentration of SMP but limit the flexibility of reactor operation. The remaining three methods are non-biological techniques. Shear-induced lift force, permeation drag force, and the xDLVO theory on microparticles can be used to elucidate the mechanisms of these non-biological techniques, except for dynamic membranes. This indicates that other proposed additional forces may be disregarded. Non-biological techniques are associated with high energy costs and membrane damage. Hydrophilic membranes are effective but super-hydrophilic membranes have not been used in AnMBRs. Different materials rather than the membrane should be applied to create an electronic field for membrane fouling control. The application of dynamic membrane should not result in biofouling of a downstream water treatment process. Among current techniques, dosing flocculant is the most promising method for controlling membrane fouling, but developing an auto-flocculant dosing strategy is vital. Overall, this article provides an overview of current membrane fouling strategies and reveals their inherent relationships and challenges for their applications.