Anaerobic membrane bioreactors (AnMBRs) have attracted much attention for mainstream domestic wastewater treatment. However, membrane fouling, operating costs, energy consumption and low filtration flux are important challenges slowing the scale-up of the technology. In this study and for the first time, granular sludge, submerged membrane, no gas sparging and low permeate flux were chosen to mitigate membrane fouling and to improve the energy and economic balance of an AnMBR. A granule-based AnMBR (G-AnMBR) was operated under four organic loading rates (between 0.5 and 1.6 kgCOD.m-3.d-1) with hydraulic retention times ranged from 13.9 to 4.9 h, and instantaneous permeate flux levels (Jp20,inst) ranged from 2.8 to 6.0 LMH to evaluate OLR impact on anaerobic digestion performance, membrane fouling extent and economic balance. Results show that COD removal rates above 83 % were achieved during the four experimental periods. Membrane fouling was directly correlated to the flux and OLR and increased from 0.03 to 2.86 kPa.d-1 as the Jp20,inst increased from 2.8 to 6.0 LMH and the OLR increased from 0.5 to 1.6 kgCOD.m-3.d-1, respectively. In all the periods, macromolecules and colloidal proteins were the major foulants deposited on the membrane. Most of the fouling was reversible and was easily removed by physical cleaning (>97.7 %). A preliminary economic assessment revealed that the permeate flux and OLR are key economic drivers for the G-AnMBR economic balance and allowed to define the satisfactory compromise between membrane purchase and chemical consumption for the long-term control of membrane fouling.