High boron Content in RO process
Published on by Andyn Munchege, AFMN limited - MD in Technology
Hello, what can be the possible cause of high Boron Content in Potable water in RO process? We are treating Sea water but having this problem of boron Content. Suggestion and help is needed. Thank you TWN team in advance.
4 Answers
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David, Nickolay and Sabin, thanks for your input and valuable suggestions.
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Boron Removal in Desalination
Hello, boron can easily be reduced using RO membrane technology to below the current WHO spec by adjusting pH with caustic soda - in my personal experience, 8.2 pH is sufficient to get Boron levels below 2 ppm. In countries like Israel, where the permeate is used for irrigation, they require much lower boron levels and then use a 3 or 4 stage configuration with increased pH up to 10.4 in the final stage. \the permeates are blended to acheive the required final spec for boron. Most membranes suppliers now supply specific membranes with high boron rejection rates. A word of warning, - when operating at the higher pH levels required, ensure that you have a quality antiscalant and good control of the dosage. -
Depending on the water salinity, boron concentration and temperature, two main processes are used to produce drinking water below 0.5 mg/L of Boron: This link is helpful, you may like to read. http://www.lenntech.com/processes/desalination/post-treatment/post-treatments/boron-removal.htm
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solution for high boron content
Seawater has naturally a high level of boron and becasue boron has a very small molecule of almost neutral charge, only a portion of it is rejected by the RO membrnaes at natural ocean water pH of 8.1 to 8.3. The WHO drinking water limit for boron is 2.4 mg/l. Seawater RO membranes would typically be able to reject boron to levels lower tha this limit. In order to achieve boron rejection to less than 1 mg/L at all times the pH of the feed water to the RO memrbanes will need to be increased to 8.9 by the addition of 30 to 40 mg/L of sodium hydroxide (casutic soda). If your target for boron is less than this level the water produced by the first pass of the RO system will need to be re-treated throuh a second pass of high-boron rejection brackish water RO membrnaes avalable by comerical supplies such as Hydranautics, Toray and Dow Filmtec.