Ceramic membrane fouling by dissolved organic matter generated during on-line chemical cleaning with ozone in MBR

Ceramic membrane bioreactor (MBR) has attracted increasing interest due to its high flux, long membrane life-span and excellent resistance to hash operation conditions. Although ozone has been used for chemical cleaning of ceramic membranes, it is still unclear about the role of dissolved organic matter (DOM) generated during on-line chemical cleaning with ozone in the development of membrane fouling in ceramic MBR. This study clearly revealed that the released DOM could considerably induce irreversible membrane fouling, and humic acid like-substances (HAL) with molecular weight (MW) of about 500 Da were mainly responsible for the observed membrane fouling. A strong positive relationship existed between the membrane fouling rate of supernatant and the rejection level of HAL, evidenced by a high correlation coefficient (R²) of 0.99. Meanwhile, the results also showed that biopolymers with MW greater than 10 kDa were easily rejected by the ceramic membranes used, leading to the development of membrane fouling. However, the high ozone concentration helped to reduce the generation of biopolymers. The organic fractions with MW less than 500 Da in the DOM (e.g. building blocks, low-MW acid and low-MW neutrals) could pass through the ceramic membranes used, i.e. their contributions to the observed membrane fouling could be considered insignificant. Consequently, it appeared from this study that membrane fouling associated with the DOM generated by ozone during on-line chemical cleaning should not be ignored in the design and operation of ceramic MBR towards long-term process sustainability.