Influence of carrier media physical properties on start-up of moving attached growth systems.

•Three spherical and two cylindrical shaped carrier media were tested.•Faster biofilm formation rates were observed with the spherical carrier media.•Larger voidage of the spherical carrier media improved COD and ammonia removal.•Carrier media physical properties and hydraulic efficiency played a role on start-up.•Start-up was not a function of carrier media protected surface area.