Boron rejection membranes

Boron rejection membranes exhibit up to 90+% rejection of boron, while standard membranes reject about 50-70%.(20, 29) These membranes are typically used for seawater applications where boron removal is a concern. Boron is difficult to remove with membranes because boron, which exists as boric acid, is not ionized a typical seawater pH, 7.0 - 8.0, whereas the pKa of boric acid is 9.14 - 9.25.20... 

Boron rejection membranes exhibit up to 90+% rejection of boron, while standard membranes reject about 50-70%. 

There are other types of membrane and modules available. These types spring from applications where the need is different than standard membranes can handle. Two common applications are boron rejection and sanitary processing. 

Hyung H and Kim JH, A mechanistic study on boron rejection by sea water reverse osmosis membranes. Journal of Membrane Science 2006, 286, 269—278. 

The Fukuoka plant uses UF membranes for pre-treatment. The RO system consists of a high-pressure SWRO section and a low-pressure RO (LPRO) section. The LPRO system is the second-pass RO unit that treats SWRO permeate (see Figure 2.21b) when required for example, to reduce boron in RO product water. The LPRO membranes are spiral-wound. The SWRO system has five units, each with a capacity of 11,988 m /d. SWRO feed water is treated with acid to lower the LSI value and prevent carbonate scaling. The LPRO pH is raised to >9.0 with caustic soda to enhance boron rejection at pH >9.0 boron is ionised resulting in much higher rejection. 

In general, boron rejection of RO membranes decreases with decreasing membrane permeability. In addition, it is affected by pH and various parameters, such as temperature and salt concentration. For example at pH 10 the rejection of seawater and brackish water RO membranes is about 99% and 93%, respectively (Fritzmann et al, 2007). 

The conventional SWRO membrane element TM820, which is typical with Toray, has exhibited 91-93% boron rejection, which was the highest level achieved by commercialized SWRO membrane elements (Toray, 2004 Redondo et al., 2003 Him and Hirose, 2000). This membrane element series has been installed in a large number of SWRO... 

Boron Rejection Performance of Used Membrane Element... 

Recently, Toray has been investigating SWRO membranes that focus on the removal of boron by the improvement of membrane performance. The history and future prospects of the boron removal at Toray and other companies are shown in Figure 1.7. Until 2000, although the boron rejection was also improved as various membranes were developed in each company, it was 90% at best. In the next period, from 2000 to 2003, the membranes in which a little more than 90% of boron rejection was shown were released, and these serve as main items for each company now. 

From 2003 to 2005, Toray developed and released TM820A, whose performance was appreciably improved, and offered the membrane that showed around 95% boron rejection prior to other companies. However, the supportive systems are still required to meet the WHO proposal even by using TM820A as above. Thus, the next target is 97 or 99% boron rejection performance of renovative membrane. The further development of a new... 

Figure 1.7 History and prospect of boron rejection performance of SWRO membrane element in Toray and comparable companies.

Tomioka, H., Taniguchi, M., Okazaki, M., Goto, S., Uemura, T., and Kurihara, M. (2005). Milestone of high boron rejection seawater RO membrane. In Proceedings of IDA World Congress on Desalination and Water Reuse, Singapore, Sept. 11-14. 

In addition, as indicated previously, membrane manufacturers have been focusing recently on the development of SWRO membranes with improved boron rejection. 

J. Kim, M. Wilf, J.-S. Park, J. Brown, Boron Rejection by Reverse Osmosis Membranes National Reconnaissance and Mechanism Study, Denver, CO Desalination and Water Purification Research (DWPR) Department of the Interior, Bureau of Reclamation, U.S., 2009. 

Softening and raising the pH level of the RW tends to increase the rejection rate of silica, boron, and total organic carbon (TOC). It also tends to increase silica solubility, thus reducing the risk of silica deposition on the membrane. 

The boron problem still exists due to the low rejection of boric acid through the membranes, yet several other solutions exist, as described below. Final mixing of the water is advisable in some cases to increase salt concentration slightly. Small organic compounds dissolved in the feed water may also find their way into the water produced. Salt content depends on feed quality (brackish or seawater) and may vary between 50-600 ppm of TDS. A secondary stage may improve quality with only a... 

Increases the ionization of weakly ionized species such as boron, fluoride, and organics as TOC, thereby increasing their rejection by the RO membrane. 

Koseogju H, Kahay N, Yiiksel M, Sarp S, Arar O, and Kitis M, Boron removal fiom seawater using high rejection SWRO memhranes— Impact of pH, feed concentration, pressure and cross-flow velocity. Journal of Membrane Science 2008, 227, 253-263. 

Electrodialysis/electrodialysis reversal (ED/EDR) represents 3% of aU the desalination capacity in the world [48]. It is, however, used mainly for desalinating brackish water. It can achieve 95% water recovery with minimal chemical feed. However, it can only reject ionised matter. Substances such as colloids, silica and boron at pH <8.0 are not removed. A triple-membrane system using UF-EDR-RO has been very effective in producing purified water for power plants [50]. In this integrated system, UF is used for removing suspended solids and macromolecules ... 

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