Effects of online chemical cleaning on removing biofouling and resilient microbes in a pilot membrane bioreactor

• Membrane biofouling was controlled by online chemical cleaning in a pilot MBR.
• Microbial compositions on the membrane are different from those in mixed liquor.
• Online chemical cleaning changed the dominant microbial groups on the membrane module.
• Resilient bacteria repeatedly caused membrane fouling.

Membrane biofouling in membrane bioreactor (MBR), resulted from microbes and their associated extracellular polymeric substances (EPS), is a primary challenge for wide application of MBR. However, the dynamic change of microbes attached on membrane remains little understood. In the study, a pilot MBR was constructed to estimate the effects of online chemical cleaning on membrane biofouling and meanwhile to study the microbial compositions and dynamic change before and after online chemical cleaning. Results showed that the trans-membrane pressure (TMP) increased with running time and online chemical cleaning temporarily eased TMP. Using the scanning electron microscopy, it was clearly observed that the microbes adhered into the EPS and formed biofilm before online chemical cleaning, and the biofilm was disrupted and most microbes on the membrane surface were removed after online chemical cleaning. EPS assay results showed that online chemical cleaning removed most protein and humic substances, but only a little part of polysaccharide. Microbial phylogenetic cluster displayed that some microbes attached on the membrane were clustered together and obviously separated from those in the mixed liquor sludge, indicating the special property of the microbes on the membrane. The microbial community dynamic analysis demonstrated that the dominant group on the membrane was changed from Burkholderiaceae to Flavobacteriaceae and Saprospiraceae after online chemical cleaning. Furthermore, some microbes such as Acinetobacter, Xanthomonas, Cloacibacterium and Flavobacterium were found to repeatedly cause the membrane fouling. The results might be helpful for developing biological-based cleaning method and antifouling strategies in the future.