Transparent exopolymer particles as bacteria shuttle to initialize the biofilm development on membrane during filtration process

Transparent exopolymer particles (TEPs) have been commonly observed to form protobiofilms with surrounding microorganisms. However, the special role of protobiofilms in the biofilm development on the membrane during filtration remains unclear. Herein, TEP-protobiofilm developed from sodium alginate and Escherichia coli was carefully prepared, and the biofilm formation on membrane surface was examined. The finding revealed that the bacteria colonization on membrane was largely determined by the protobiofilm, which was controlled by bacteria, TEPs and their contact time. The bacteria and TEPs were respectively stained by fluorescent dyes. Analysis showed that the contact time between them was significant in the formation of protobiofilm, and then regulated the biofouling development during membrane filtration. After 8 h of contact, the bacteria adhesion on membrane was 7.9–10.3 times of that without contact and the membrane surface coverage was 8.8–12.6 times. At higher bacterial concentration, the protobiofilm can carry more bacteria, and the above phenomenon was further intensified. Quartz crystal microbalance with dissipation monitoring (QCM-D) was used to demonstrate the positive effects of TEPs on bacterial adhesion and the biofilm stability. This study suggested that TEPs which provide the comfortable habitat for bacteria, protect bacterial colony, and finally act as a shuttle to promote the rapid transfer of bacteria to the membrane surface during the initial stage of filtration, providing novel insight into the serious biofouling formation mechanism in the membrane process.