The fouling layer development on MD membrane for water treatments: An especial focus on the biofouling progress

This study evaluated the fouling development of membrane distillation (MD) when treating different feed waters were taken from three local water bodies: Xuanwu Lake, Nan Lake and Qinhuai River. Trends of flux decline could be divided into three phases including a similar rapid decline in first phase, a slow decline in phase II, while significant difference was observed in the last phase. It could be seen that inorganic matters in feed waters had some influences on the attachment of salt crystals to membrane, mainly in the form of CaCO3. Furthermore, the biovolume exhibited little difference but the amount of extracellular polymeric substances (EPS) was distinct in the three systems. 16S rRNA revealed that although the microbial communities in feed waters had different structures, they on-membrane microbes shared the same dominant communities in the early stage due to the same growth environment including Tepidimonas, Meiothermus, OLB14_norank, Env.OPS 17_norank and Schlegelella with a relatively stable proportion of 63.5%-68.0%. However, at the later operational phase, the bacteria composition was changed with community succession, and Armatimonadetes_norank, Hydrogenophilaceae_uncultured and Methyloversatilis respectively thrived on the three scaling membrane surfaces which was correlated with the concentration of feed water, resulting the influence of inorganic substances on microbial growth was enhanced. A result obviously suggested that bacteria had great influence on the degree of flux decline due to their structure and property, especially at the later operational phase. It would be helpful to explore the structure and potential function of dominant communities on membranes and provide basic theory for the treatment of microbial pollution.