| Recently, the conventional wastewater treatment processes are hardly capable of catering to the increasing requirements of ecological environment quality by human beings for their obvious limitations. As a new and efficient process for water treatment, membrane bioreactor (MBR) is widely appreciated. However, membrane fouling is still a huge bottleneck limiting the MBR application by leading to the increasing consumption of power, frequent replacement of membrane and reduction of the effluent. Membrane fouling can be divided into organic pollution, inorganic and biological pollution, in which biological fouling caused by the slow formation of biofilm on the membrane is the main factor leading to the membrane flux decline. It is the key issue need to be resolved for the MBR application process and also the hot topic being concerned currently at home and abroad to understand deeply the formation mechanism of biological fouling and propose effective measures to control membrane fouling and membrane cleaning measures on this basis in order to ensure the efficient operation of the actual process and extend the life of the membrane. Studies have shown that biofilm formation and quorum sensing (QS) are closely related, and that utilizing quorum quenching to mitigate the membrane biofouling is an effective way to control membrane fouling. In this study, a MBR apparatus treating the domestic sewage was focused as the research object. This article studied the biological effect on quorum sensing pilot MBR membrane fouling by focusing on the MBR membrane fouling analysis, the correspondence between quorum sensing and biological fouling and biological community structure, etc. And formation mechanism of biological contamination in the film was explained from the perspective of biological nature in order to lay the foundation for proposing MBR membrane pollution control measures effectively.The MBR membrane biofouling characterization is the premise to explore the membrane fouling mechanism, it can provide visual presentation of the role of Quorum sensing on the membrane fouling. In this paper, EPS and SMP content of the MBR biocake and activated sludge were detected under different run-time (different trans-membrane pressure), proteins, polysaccharides, DNA content in EPS and SMP were analysed. The results show that the major pollutants of biological fouling is EPS, but SMP play a greater role in the initial stage of contamination. The most abundant pollutants is protein in EPS in the biocake and the sludge, but the changes of polysaccharides contant also play a quiet important role. The main components of SMP in mixture are proteins and polysaccharides,proteins play an important role in preliminary,polysaccharide worked throughout the operation.Signaling molecules, microbes, genes are three necessary factors requied by quorum sensing to achieve adaptation to the environment and the regulation of the formation of biocake. The AHL type signal molecules for MBR membrane and activated sludge were detected in this study using LC-MS/MS method. Signaling molecules changing trend of type and content under different trans-membrane pressure stages was got and membrane contamination law of quorum sensing was studied. The signaling molecules causing membrane fouling was identified. The results showed that the major signal molecules of the biocake are C4-HSL, C6-HSL, C8-HSL,3-o-C8-HSL in the early stage and C4-HSL, C6-HSL,3-o-C6-HSL, C12-HSL in the biological mature stage. The content of various signal molecules are little in the late membrane fouling stage, only C6-HSL and 3-o-C8-HSL can be maintained at a higher value,they can be considered as the major signale molecules in this period. When correlating signaling molecules of sludge mixture and biocake layer with their pollutants respectively, we found the C8-HSL can promote the production of polysaccharides of SMP and EPS in the mixture, proteins and DNA can also be promoted in EPS on a generation portion in the mixture.3-o-C8-HSL can promote the production of proteins, DNA of SMP in mixture,3-o-C6-HSL in EPS can exhibit a strong role in promoting the production of protein on membrane suface.Microorganism is the main body for sewage treatment, and also the major factor contributing to formating biofilm on MBR membrane suface. In this study, sludge and biofilm on the surface of membrane under different trans-membrane pressure stages were analyzed to determine the community structure in them. By associating the signaling molecules leading membrane fouling, the main pollutants and the corresponding strain, the differences of microorganisms in type and quantity in the sludge and biofilm were discussed. We found Simplicispira, Saccharibacteria norank, Comamonadaceae Unclassified are three main generas in mixed sludge and biocake,, Comamonadaceae Unclassified can promote the production of polysaccharides, proteins and DNA of SMP and EPS by C8-HSL and 3-o-C8-HSL in the early days of pollution., Simplicispira can grow and form film on the membrane suface in the mid-term of membrane fouling, Mainly promote the secretion of protein through 3-o-C6-HSL in EPS. In late stage of membrane fouling, the content of various signaling molecules are little, C6-HSL and 3-o-C8-HSL may be the primary signaling molecules facilitating the secretion of part protein. In the early and mid-term pollution, different types of main flora produce different types of signaling molecules that activate gene expression, promoting the secretion of extracellular polymer, resulting in worse membrane biofouling, In the late stage of fouling, microorganisms decline and release abundant intracellular becoming the main mechanism of pollution, the effect of signaling molecules is in the second.Many studies have shown that quorum sensing stimulates the formation of biological fouling of MBR membrane. However, the relationship between the pollution of the phase change and quorum-sensing signal molecules has no meticulous division. This study provided more comprehensive researching and analyzing results, which illustrated more clearly the pollution mechanism in different running periods. |
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