Influence of different biofilm carriers on the operation and membrane fouling of submerged membrane bioreactors

• Different biofilm carriers were combined and examined with MBRs in parallel.
• Using granular or sponge carriers effectively mitigated membrane fouling in MBRs.
• Fixed rope carriers accelerated fouling in an MBR.
• Types of carriers altered the sludge filterability of MBRs.
• Types of carriers affected the production of SMP.

It has been reported that the combination process of biofilm and submerged membrane bioreactors (MBRs) can mitigate membrane fouling. In this study, the influence of using three different biofilm carriers (fixed rope carrier, moving granular carrier and moving sponge carrier) on the operation and membrane fouling of MBRs was investigated. Using rope or sponge carriers with MBR processes improved the removal efficiency of nitrogen via the creation of an anoxic part inside the carriers. However, membrane fouling became very severe when rope carriers were used. Using granular or sponge carriers effectively mitigated membrane fouling because they mechanically cleaned the membrane surface. The cake/gel layer on the membrane surface was perfectly removed by granular or sponge carriers. However, the deterioration of the filterability of the mixed liquor suspensions was significant with granular carriers, leading to the evolution of physically irreversible fouling, whereas such deterioration was insignificant with the sponge carrier. The characteristics of the soluble microbial products (SMP) significantly varied depending on the types of carriers used, which could influence the filterability of mixed liquor suspensions and the development of irreversible membrane fouling.