AWWA ACE61649

Recently, there has been improvement in membrane performance withrespect to flux and salt rejection. There are high flux versions such as BL and NE90showing 51gfd flux and 99% rejection, 76gfd flux and 97% rejection, respectively at225psi and 2000ppm NaCl. The latest version of combining high flux and highrejection is called BLR, showing 39gfd flux and 99.5% rejection at 225psi and 2000ppmNaCl. If the flux of the above three membranes are compared with the standardmembrane BE, the relative water permeability of the four membranes is increasing inthe order of BE(1), BLR(1.5), BL(1.9) and NE90(2.8) under the same conditions.Likewise, the relative salt permeability is as follows: BE(1), BLR(0.77), BL(1.5) andNE90(5.4).In a real field application, a reverse osmosis (RO) system is not designed in such a way to utilize themaximum capacity of the high flux membrane. If it were so, then the membrane wouldbe fouled very quickly. Instead, the high flux membrane is used at a pressure as lowas possible to save the operating cost(electricity). The above membranes were usedin simulation for producing 0.6MGD from a feed water having 1000ppm TDS. Theoperating pressure(psi) and permeate TDS(ppm) on each membrane used in the system design are shown as follows; BE(154psi and 17ppm), BLR(119psi and 11.2ppm),BL(100psi and 27ppm), and NE90(77psi and 157ppm). The results show that BLR isoperated at a pressure 23% less than the standard membrane BE, meaning an energyconsumption reduction of about 23% and a savings of about $60,000 per year.Moreover, BLR produced more pure(less TDS) water than BE. Likewise BL saves 35%energy and an operating cost of about $90,000 per year, but the quality of the permeatewater (27ppm) is worse than BE. In the case of NE90, it reduces energy consumptionby 50%, but this energy savings came at the expense of permeate TDS, increasing from17ppm to 157ppm.Thus it appears that BLR is the best choice among the four membranes for both energysaving and higher purity of permeate water. Furthermore, a combination of BL andBLR enables the system to be operated at a pressure (103psi) similar to BL, yieldingthe quality of permeate water (19.9ppm) similar to BE. This combination is mostpromising since it saves on operating costs without sacrificing thequality of the product water. If it is willing to sacrifice the product water quality up to100ppm, then a combination of NE90 and BLR could offer more energy saving thanthe combination of BL and BLR. Includes tables.

Product Details

Edition:

Vol. - No.

Published:

06/17/2005

Number of Pages:

7

File Size:

1 file , 490 KB