Title: Effect of solution chemistry on organic fouling of reverse osmosis membranes in seawater desalination
 
Journal: Journal of Membrane Science
Authors: Youngbeom Yu, Sangyoup Lee, Seungkwan Hong
Corresponding author: Seungkwan Hong
Institute: Department of Civil, Environmental & Architectural Engineering, Korea University, 1?5 ga, Anam-dong, Sungbuk-gu, Seoul, 136-713, Republic of Korea 

The original and creativity of paper: The impacts of solution chemistry, on organic fouling of RO membrane at seawater-level ionic strength, were investigated. Moreover, foulants on the membrane surface were collected for further organic characterization in terms of specific UVA and fluorescence excitation and emission matrix. This study finally compared characteristic of organic fouling under different ionic strength conditions. 
 
Summary: 
The results show that organic fouling was significantly affected by the solution chemistry since permeate flux show more rapid decrease with decreasing pH and increasing calcium concentration.  However, when the ionic strength concentration was increased the effect of pH and calcium almost disappear. This statement was confirm with flux decline curves, that obtained at high ionic strength (600mM), were almost identical regardless of variation in feed water pH and calcium concentration. This is because of the significant masking of electrostatic interactions such as the change of neutralization of organic function group including organic ?calcium complexation. As shown in Fig. 1.

 
Figure 1 Influence of feed water pH on flux-decline behaviors: (a) IS = 10mM and (b) IS = 600mM.

Apart from flux decline, they also examined specific UVA for the foulants deposited on the membrane surface at the high organic strength. Specific UVA values of organic foulants at higher ionic strength were much greater than at low ionic strength. This points out that, at high ionic strength, the majority of organic compound contained hydrophobic fraction. The effect of pH and calcium respect to specific UVA was showed in Fig. 2.


Figure 2 Percent flux reduction with respect to feed water pH and calcium concentration.

In addition, based on fluorescence excitation and emission matrix (FEEM), researchers found that the major FEEM area for foulant obtained at high ionic strength which indicated the hydrophobic constituents. The results of FEEM spectra for foulant samples collected after fouling runs at different solution chemistry was showed in Fig. 3.  According to both specific UVA and FEEM results, it point toward that seawater organic fouling is governed by the enhanced hydrophobic interactions between organic matters and membrane surface as well as interactions between the organic matters.



Figure 3 FEEM spectra for foulant samples collected after fouling runs at: (a) IS = 10mM and pH 4, (b) IS = 10mM and pH 7, (c) IS = 10mM and pH 10, (d) IS = 600mM and pH 4, (e) IS = 600mM and pH 7, and (f) IS = 600mM and pH 10.

Therefore, the optional pretreatment to manipulate solution chemistry might not be effective way to control organic fouling seawater desalination



 
Application & further study: The paper point out the creative way to characterize organic fouling under the different ionic strength conditions. As our laboratory also interested by organic fouling during seawater reverse osmosis process, also we are now focusing on membrane autopsy to investigate fouling development. Thus this can be apply as additional parameter to identify fouling behavior.  

  
By Monruedee Moonkhum
Email: moon@gist.ac.kr