Comparison between moving bed-membrane bioreactor and conventional membrane bioreactor systems. Part I: membrane fouling

The combination of moving bed biofilm reactor and traditional membrane bioreactor (MBR) shows great potential to be widely used in Liaohe River basin for wastewater treatment. The aim of this research is to compare the bioreactor performance and membrane fouling between integrated fixed-film activated sludge membrane bioreactor (IFAS–MBR) and MBR. Two lab-scale reactors were operated in parallel to treat synthetic municipal wastewater with continuous operation. The results indicated that both systems had the same high removal efficiency of ammonium, while the IFAS–MBR showed a higher ability to remove COD. The trans-membrane pressure in the MBR was higher than that in the IFAS–MBR during the entire operation, due to a higher total modified fouling index of the mixed liquor and the resultant higher membrane fouling potential. The concentrations of extracellular polymeric substances and soluble microbial products were higher in MBR, despite the functional groups were almost similar in two reactors. The conventional MBR had more small molecular weight components (<1 kDa) and soluble microbial metabolites. This seems to cause pore blocking, which directly results in membrane flux declining and membrane resistance rising in the MBR system. In addition, the MBR was characterized by a serious membrane fouling as more dense deposits were observed by scanning electron microscopy. On the contrary, the IFAS–MBR showed a lower membrane fouling tendency during the whole operation.