Deciphering microbial responses and membrane biofouling characteristics during industrial wastewater treatment with ultrafiltration

Membrane technology has been extensively utilized in industrial wastewater treatment. However, the ubiquity of microorganisms in industrial wastewaters renders membrane biofouling a principal impediment to operational efficacy and treatment performance. Notably, the unique features of industrial wastewaters including strong acidity, strong alkalinity, high heavy metal content and elevated temperature could cause remarkable variations in microbial properties, thereby influencing the development of biofouling layer. This study addressed a critical knowledge gap by systematically unveiling the microbial adaptive responses to the five prevalent industrial wastewater environments and their resulting biofouling propensities. The results demonstrated that all investigated extreme conditions provoked substantial microbial death, while simultaneously inducing significant productions of extracellular polymeric substances (EPS) and reactive oxygen species (ROS) in surviving microbes. Microorganisms seemed the most sensitive to oxidant aggression via secreting maximal EPS and forming biofilm with the highest density, but showed the minimal responses to acidic conditions. However, the most pronounced ROS generation and cellular lethality occurred at high temperature of 75 °C. Compared to the conventional aquatic environment, membrane biofouling was significantly aggravated under five extreme environments. This phenomenon was accompanied by the formation of much thinner, denser biofilms with stratified structures, potentially offering better protection to inner cells and enhancing microbial survivability. Pearson correlation analysis revealed both filtration resistance and biofilm density exhibited strong linear correlations with ROS production ( R ²>0.74) across all wastewater environments. This implied that inhibiting intracellular ROS production could be a promising and effective strategy for biofouling mitigation in actual industrial wastewater treatment.