Page 76 - ro membanes

3.4 MEMBRANE AUTOPSY 59
FIGURE 3.17 Damaged membrane area stained during dye testing.
FIGURE 3.18 Concentrate (A) and permeate (B) sides of damaged membrane exposed to dye test.
membrane productivity and salt rejection is due to membrane fouling and how much is caused by damage of the membrane itself. It also allows determining, in general terms, how effective membrane cleaning would be in recovering the RO-membrane performance.
Example of cell test of front- and tail SWRO elements model SWC3 from Hydranautics is presented on Table 3.3. As indicated in this table, the “Test Data (Averages)” from the cell test for rejection and flux are significantly below the membrane factory test specifications.
Salt passage decrease of 26% combined with flux decline of 14% indicates that the first (lead/front element) is biologically fouled. Since the tested elements are 2-year old, the average flux decline per year is 7%, which is on the high-end of the acceptable maximum limit. Because the biological fouling has decreased salt passage, this element will be a good candidate for rotation, i.e., installation at the tail end of the membrane vessel.