CLSM images of proteins
EPS is the major structural component of biofilm and may
affect membrane permeability (Chen et al., 2006). Considering
the fact that proteins are one of the major components of EPS,
their temporal variations in the biofouling layer of the OMBR
were investigated by CLSM observation using FITC as the
staining dye. It could be seen from Fig. 5 that proteins in the
biofouling layer were distributed in dispersed form and had
aggregated into some clusters on the 3rd day. Similar to the
variations of b-D-glucopyranose polysaccharides, more proteins
deposited and formed a continuous layer on the 8th day,
and the thickness of the biofouling layer formed by proteins
further increased on the 25th day. Although there are no CLSM
studies on the distribution and abundance of proteins on FO
membrane surface in OMBRs until now, prior FT-IR investigations
have revealed that protein was one of the major
FO foulants in OMBR systems (Zhang et al., 2012b; Wang et al.,
2014b). In Table 3, the mean thickness and corresponding
vertical spreading of proteins in the biofouling layer increased
with the operation time. However, their biovolume significantly
increased by 530% from the 3rd to 8th day and then
became stable, indicating that proteins had reached the
maximum distribution and abundance on the FO membrane
surface when the OMBR was operated about 8 days. Similar to
the polysaccharides located in the biofouling layer, the proteins
had also spread uniformly enough in the initial stage of
the biofouling layer obtained from the variations of their
horizontal spreading in Table 3. Furthermore, the biovolume
of proteins had the similar value to that of polysaccharides on
the 3rd day, but became much bigger on days 8 and 25. While
the exact mechanism is not known, this result suggests that
proteins might have played a more significant role in the
development of biofouling layer on the FO membrane surface.