Effect of Soluble Microbial Products(SMP) and its Transformation on Membrane Fouling in a Submerged Membrane Bioreactor(SMBR)

Membrane fouling is the main bottleneck of the membrane bioreactor(MBR) and its widespread application. In this paper, a lab-scale submerged MBR treating synthesis wastewater was operated to examine the affecting mechanisms and correlation of soluble microbial products(SMP) with membrane fouling. A single-fiber microfiltration set-up was fabricated and applied to evaluate the importance of sludge properties of different sludges, including MLSS, EPS, SMP and their organic components, to the fouling evolution rate. It was revealed that MLSS, EPS and SMP all show positive correlation with the fouling rate(ΔTMP/Δm). However, the importance of SMP separated from MBR activated sludge(AS) to fouling rate(rp = 0.126) is rather lower than that of SMP in MBR cake sludge(CS)(rp =0.871). The protein and polysaccharide in CS-SMP, other than humic-like substances, were proved to be the major substances affecting fouling layer formation. Both the examination by fluorescence excitation emission matrix(EEM) and the observation under confocal laser scanning microscopy(CLSM) display that the SMP have to transform in the term of surface properties and size distribution with the development of membrane filtration. The AS-SMP has obvious protein-peak compared with MBR effluent, which implies that the protein is preferentially intercepted by membrane compared with other organic components. Whilst, after the membrane interception, the SMP in CS has a size as large as 100 μm, which would facilitate the cake layer formation and hence is determinative for the fouling evolution. A comprehensive observation of fouled membrane surface with CLSM also demonstrates that there are two types of fouling layer on the membrane surface, i.e. cake-dominant and gel-dominant fouling layer, both of which are highly depend on the content of AS-SMP in SMBR. It was noted that the SMP in SMBR and cake sludge is the major foulant. The present work is valuable for understanding of the membrane fouling mechanisms and also for proposing the strategies for membrane fouling control in SMBR.