role in the control of biofouling progress through effects on cell proliferation
and biofilmmaturation [14]. The effects of the applied TMP on the
organic fouling [15,16] and biofouling [14,17] have been investigated.
Higher TMP results in an increased deposition rate of foulants and formation
of compact fouling layers.Moreover, the permeate flux generated
by applying TMP affects concentration polarization (CP) which
concentrates solutes on the membrane surface [18], resulting in bacterial
growth and biofilm formation [17]. Cross-flow velocity on the membrane
surface is a significant parameter which affects the shear force
and CP on the membrane surface [19]. It has been reported that high
cross-flow velocity is effective in controlling membrane biofouling
[14]. Since these studies evaluated the effect of operating conditions
on biofouling of RO membranes through filtration of bacterial suspensions,
they did not consider the hydrodynamic accumulation and bacterial
adhesion on the membrane surface separately.
In this study,we investigated the effect of operating conditions such
as TMP and stirring rates in the cylindrical ROmembrane cell on the biofouling
with respect to the bacterial growth pre-adhered onmembrane
surfaces and the permeate flux. Pseudomonas putida (P. putida), used as
model bacterial species, was adhered on the surface of a circular polyamide
RO membrane set on a cylindrical stainless steel membrane
cell. The cell was then fed continuously with feed water containing
only nutrients for the bacteria, and biofouling experimentswere carried
out by controlling the TMP and stirring rate on the membrane surface.
The stirring rate in the cell corresponded to cross-flow velocity on the
membrane surface in commercial operations. The biofouling experiments
evaluated changes in the permeate flux and the bacterial volume
adhered on the membrane surface. The osmolarity on the membrane
surface was calculated as a function of the nutrient concentration to estimate
the degree of CP. In addition, the influence of drag force caused
by the permeate flux and hydrodynamic shear force caused by the stirring
rate was evaluated.