Characterizing flat sheet membrane resistance fraction of chemically enhanced backflush

• The investigation of fouling control mechanism via the CEB method in FS-MBRs.
• Effect of the CEB method on the removal of the cake layer and fouling resistances.
• Evaluation of the effect of the foulant type on the efficiency of the CEB method.
• Optimization of the chemical concentration and cleaning run time for an enhanced foulant removal.

This study attempts to demonstrate the applicability of chemically enhanced backflush (CEB) to flat sheet (FS) membranes and aims at examining the membrane resistance fraction of complex organic foulants without applying hydraulic cleaning. With sodium hypochlorite (NaOCl) applied (i.e., 100–600 mg/L) as an oxidant chemical, complex soluble microbial products (SMP) foulants were effectively removed from the membrane in 60–90 min, and the membrane resistance is governed by the CEB bulk reaction and the transport, penetration and back transport of NaOCl. An in-depth study has proved that the cake resistance associated from the SMP foulants is more sensitive to CEB runtime, whereas the fouling resistance is more sensitive to the concentration of NaOCl. Nevertheless, for the foulant which mainly compose of dissolved organic matters, the cake resistance can be effectively removed in a shorter runtime and with a lower concentration of NaOCl as compared with the SMP foulant. However, high concentration of NaOCl is still needed to remove its fouling resistance. In addition, this study demonstrates that even in the absent of hydraulic backflush CEB is still highly compatible with FS membrane and the effectiveness is comparable to that of hollow fiber membrane.