High pH operation in seawater reverse osmosis permeate: First results from the world's largest SWRO plant in Ashkelon

Both phases of the SWRO plant located in Ashkelon were fully commissioned in the 2nd half of 2005, and turned over commercial production of low boron desalinated water. Located in the south of Israel and representing a milestone project for desalination in terms of size and process innovation, the Ashkelon plant is designed to produce 330,000 m3/d of drinking water. An outstanding feature of the plant is the Cascade, IDE's multistage, patented process. In this process, part of the 1st stage RO permeate is treated in a combination of high and low pH stages, which remove boron and salts in subsequent steps, resulting in an overall recovery higher than 95%. The entire system is highly flexible and readily adjustable to feed water quality and temperature fluctuations. This paper focuses on both the design and the actual performance of the membranes by FILMTEC™ in the different stages of the Cascade during the first 6 months of operation. The data shows stable system performance at pH > 10 and at temperature >30°C. The final boron concentration of the total blend was consistently <0.3 mg/L. A comparison of actual membrane performance vs. prediction shows that adequate tools are available to allow the accurate and reliable design of an RO system for even such extreme conditions as pH > 10.