The effects of fluidized media characteristics on membrane fouling and energy consumption in the anaerobic fluidized membrane bioreactor (AFMBR) were evaluated. Both adsorbing granular activated carbon (GAC) and non-adsorbing silica and polyethylene terephthalate (PET) beads were evaluated. For fresh GAC, the energy requirement for fluidization increased with size, but smaller sizes led to greater reduction in membrane fouling. But when the GAC adsorption capacity was first exhausted, the reverse was noted, the larger particles reduced membrane fouling best. Non-adsorbing silica particles and PET beads demonstrated similar results to pre-adsorbed GAC, lower fouling was accomplished by the larger media that had a higher energy requirement for fluidization. The media packing ratio was also of importance, the higher the packing ratio up to 50%, the greater the reduction in fouling. Fouling reduction was also somewhat better at a given energy expenditure with lower specific gravity PET beads than with denser and smaller pre-adsorbed GAC particles. (C) 2014 Elsevier B.V. All rights reserved.