Water. desalination + reuse

RESEARCH November-December 2014 | Desalination & Water Reuse | 33 | a ring filter to a feed water tank. From there and after addition of antiscalants and reducing agents, the feed water passed through parallel ultrafiltration modules, cartridge filters and 4-inch diameter RO elements (see table 1). The feed pressure in the Filmtec Seamaxx element was four bar lower than in the Filmtec throughout the trial (figure 3). This, the researchers said, demonstrated Filmtec Seamaxx's lower energy requirement – and therefore cost – to meet the same permeate production capacity as the Filmtec product. Salgado and her colleagues found, from the long-term trial, that energy saving from the use of Filmtec Seamaxx over the Filmtec product was about 7%. And they saw no significant difference in evidence of fouling which was, however, negligible for both products over the eight months of the trial. Permeate flow in both modules was steady at about 0.65 m 3 /h (figure 4). ACCElERAtEd fouling A shorter-term study that focused on fouling compared Filmtec Seamaxx with Filmtec SW30 ULE. Again the parallel systems were operated at the same flux and recovery (figure 5) but this time flux was significantly higher than in the longer trial at 18 l/m 2 /h with recovery at 35% (see table 2). The flux was greater than recommended for the feed water used and the recovery was challenging given that only three elements – this time eight-inch diameter – were in play for each pressure vessel. These aggressive conditions were chosen, Salgado explains, to highlight any difference between the test membranes in their resistance to fouling. A 3.5 bar feed pressure difference between the Filmtec and Filmtec Seamaxx elements again was consistent throughout the trial (figure 6) with Filmtec Seamaxx showing the lower energy requirement. Permeate flow loss in the Filmtec and Filmtec Seamaxx membranes reflected increased fouling as anticipated from the test conditions (figure 7). But the greatest loss was in the Filmtec vessel and the difference between the two systems grew as the trial progressed. Salgado says the results are "very promising" as a demonstration of fouling resistance in the Filmtec Seamaxx element. The promising verdict was made on the grounds that the first membranes in the Filmtec Seamaxx vessel encountered still greater flux than their counterparts in the Filmtec vessel owing to the greater permeability of the Filmtec Seamaxx membranes. Dow evaluated the performance of the Figure 1. Dow's progress in reverse osmosis membrane development. Figure 2. Elements running in parallel in the pilot unit arrangement. Table 1. Conditions for eight-month trial. Table 2. Conditions for short-term fouling study. Table 3. Commercial-scale test conditions and outcomes.

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