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 RO membrane cell on the biofouling with respect to the bacterial growth pre-adhered onmembrane surfaces and the permeate flux. Pseudomon as 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 experiments were 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.