The impact of flux and spacers on biofilm development on reverse osmosis membranes

► Biofilm development of reverse osmosis membranes. ► Biofouling causes TMP rise that is greater in the absence of flow channel spacers. ► Rate of TMP rise increases with imposed flux, at lower cross flow velocity and higher salinity. ► Rate of TMP rise correlates with biovolumes obtained by CLSM from membrane autopsy. ► Relative contributions of membrane fouling and spacer fouling are likely to be scenario dependent.