Ceramic membrane fouling caused by recycling biological activated carbon filter backwash water: Effective backwash with ozone micro-nano bubbles

Abstract

The widespread use of ceramic membranes in wastewater recycling is still hampered by membrane fouling problems. Frequent chemical cleaning increases operating and maintenance costs. This work proposes ozone micro-nano-bubble (O₃-MNB) backwash as a new backwashing method to control the ceramic membrane fouling. Activated carbon filter backwash water (ACFBW) was used as feed water for the ceramic membrane and the effect of O₃-MNB backwash was compared with tap water backwash, air-micro-nano-bubble (Air-MNB) backwash and ozone water backwash. The results of the flux tests showed that the irreversible fouling resistance (R_Fi) for the O₃-MNB backwash was only 4.8 %, 10.0 % and 23.3 % of the R_Fi for the tap water backwash, Air-MNB backwash and O₃ water backwash, respectively. The results of the SEM and CLSM analyses demonstrated that the combination of ozone with MNB for backwashing was an effective method for the removal of viable cells and majority of proteins and polysaccharides from the surface of the ceramic membrane. However, the application of ozone also led to the release of microbial DNA, which increased its binding to Al₂O₃ on the ceramic membrane. Furthermore, the increased ozone concentration transported by the MNB could promote the generation of a large number of hydroxyl radicals (•OH) due to the effect of Al₂O₃, which potentially enhanced the oxidation of macromolecular contaminants in the pores. At the same time, the electrostatic repulsion and hydrophobic action provided by the MNB improved the efficacy of peeling off the filter cake layer when cleaning the membrane pores. Consequently, this study demonstrated the effectiveness of O₃-MNB backwash in the long-term operation of ceramic membranes and provided insights into the fundamental mechanism by which this process controlled the membrane fouling.