SWRO Energy Optimization

Advances in three distinct areas of SWRO system design have resulted in a significant reduction in energy consumption from lOkWh/m in the late 1970s to approximately 3.5kWh/cm by 2000. 

Large-capacity high-pressure pump/motor efficiency 

In 1978 a typical SWRO membrane/element had 15 m of membrane and produced 7.5 m of permeate per day with 98.6% salt rejection. Today a typical SWRO element contains 40 m of membrane and produces 28-34 m of permeate per day with 99.75% salt rejection. The improvement in membrane performance allows system engineers to select an optimum design point and also to plan for a wider range of operating conditions without capital cost penalties. This flexibility makes it easier for municipalilies to meet the needs of their customers and gives them the option to run at lower pressures and/or recoveries, which in turn can reduce energy consrrmption. 

2 Improved High-Pressure Pump/Motor Efficiency 

Pump manufacturers have introduced larger capacity pumps that opaute at higher efficiencies. This has given SWRO designers more options with respect to train sizes. Additionally, the energy consumption of these pump/motors designed specifically for SWRO use is lower than was available in the past. 

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Due to the low rejection of monovalent salts, osmotic pressures in NF are lower than in RO. Thus, lower pressures need to be applied, and the energy consumption is proportionally lower. RO membranes operable at ultralow pressures have been developed (Semiat, 2000 Matsuura, 2001) that allow the desalination of brackish water at pressures comparable to those applied in NF. These membranes operate at the interface of NF and RO and might be helpful in optimizing the desalination process. Hassan et al. (1998) reported the use of NF in an integrated desalination system NF-SWRO (sea water reverse osmosis) and... 

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