Biofouling evolution driven by autoinducer-2 quorum sensing in reverse osmosis (RO) for water reclamation

Membrane biofouling remains a key challenge for reverse osmosis (RO) technology in water reclamation. This study investigated the biofouling development with time on RO membrane surface. During the biofouling evolution, the biofilm was examined through confocal laser scanning microscopy (CLSM) observation and foulant composition analysis. Results showed that organic/biofouling was the key contributor, and autoinducer-2 (AI-2), quorum sensing (QS) signaling molecules, were found to play an important role in coordinating community-level behaviors associated with RO membrane fouling. In the initial stage of fouling layer development, the attached cell and biopolymer contents increased with rising AI-2 activity. As development continued, the microbial community changed remarkably, exhibiting peak AI-2 activity as the membrane surface became fully covered with cells and the EPS matrix. However, in later stages, despite a decrease in AI-2 content and biological activity, the rate of increase in fouling resistance accelerated significantly due to continually accumulating foulants. As a result, the AI-2 QS was crucial during early phases of biofilm development in RO systems. This study helps to look deeply into the biological fundamentals of AI-2 mediated QS in RO fouling, enhancing the understanding of the mechanisms behind RO membrane fouling in water reclamation, and may facilitate the development of antifouling strategies.