Masaru Kurihara

Boron reduction performance of reverse osmosis seawater desalination process

Abstract In recent years, seawater desalination systems using reverse osmosis (RO) membranes have been constructed to settle the lack of drinking water. RO desalination membranes have high rejection for most of solutes in seawater. Japanese drinking water standards for the water quality of the permeate can be achieved except for boron. Therefore, the boron rejection needs to be considered in the design of the RO process and during the operation of the plant. Luckily, there is a simple and easy method to estimate boron concentration. In this paper, we report measured boron permeabilities and their relation to salt permeabilities using cross-linked polyamide membranes. Chemical degradation of the membranes affected these permeabilities to different degrees. Boron concentrations in the permeate were then calculated using a computer program that was based on the boron permeabilities calculated from the measured salt permeabilities. Results obtained were compared with actual data taken at a RO plant of Toray Industries, Inc., Ehime. The model data fitted the experimental result, well. It was also found that a relationship existed in the permeate between salt and boron concentrations and that the boron concentration can be obtained from measurement of the salt concentration.

High recovery/high pressure membranes for brine conversion SWRO process development and its performance data

Toray Industries and Toray Engineering have developed a new type reverse osmosis (RO) membranes and its process for seawater desalination, which brings advantages of high water recovery, low energy cost and lower plant installation cost. The new type RO membranes, “Brine Conversion Reverse Osmosis Membrane (SU-820BCM)”, shows a superb performance at a high pressure of more than 9.0 MPa and a high salt concentration more than 5.8% concentrated seawater. The newly developed “Brine Conversion Seawater Reverse Osmosis Desalination System (BCS system)” takes the fresh water from the concentrated brine water (salt concentration 5.8%, produced under 6.5 MPa) of first stage RO modules. The newly developed “Brine Conversion Seawater Reverse Osmosis Desalination System” (BCS system) can obtain 60% recovery of fresh water, taking from the concentrated brine water (salt concentration 5.8%, produced under 6.5 MPa) of first stage RO modules in addition to a conventional system desalination (40% recovery). The cost of producing fresh water can be saved approximately 15–20%. The space of plant is also reduced approximately 30% due to reducing the space of the pretreatment process. The continuous operating performance with SU-820BCM has proved to be in good conditions in the BCS pilot plant in Japan for more than 2 years. The total capacity of this plant is 210 m3/d with 60% recovery, and the quality of the produced fresh water has been maintained at the level of less than 200 ppm TDS, which satisfies their designed specifications for drinking water.

Development of crosslinked fully aromatic polyamide ultra-thin composite membranes for seawater desalination

A crosslinked fully aromatic polyamide ultra-thin composite membrane, designated UTC-80, has been developed for seawater desalination. The excellent membrane performance was derived from the combination of both design of membrane materials and membrane fabrication technology. SU-820 spiral wound membrane element using UTC-80 membrane has high salt rejection (99.75%) and high water productivity (16 m3/d) at 56 kg/cm2 for live seawater fed at 25°C. We found that the trihalomethane rejection of the UTC-80 membrane was much higher even in the case of the seawater desalination compared to cellulose acetate membrane. The affinity of trihalomethane with membrane materials is presumed to cause the difference of trihalomethane rejection.

The thin-film composite low pressure reverse osmosis membranes

Reverse osmosis systems are generally designed and utilized on the basis of reference membrane water flux and desalting performance at 28 Kg/cm2 (400 psi) net driving pressure (NDP). Low commercial stage are capable of equivalent performance at 14 Kg/cm2 (200 psi) NDP. Further, possibly, super low pressure (SLP) membranes are capable of equivalent performanec at 7 Kg/cm2 (100 psi) NDP. These LP and SLP membranes offer immediately obvious savings in energy cost for reverse osmosis desalting and water reclamation. In addition, they can make a most important contribution to reduced membrane replacement cost and improved permeate quality when operating on high salinity feeds at higher recevery levels. Two new series and four types of thin-film composite LP and/or SLP reverse osmosis membranes have been developed. These membranes, designated UTC series, give superior performance in such area as water flux, salt rejection, chemical stability and microbiological resistance. UTC-20 & 40 series membranes are designed for use at pressure of 5–15 kg/cm2 (71–213 psi). UTC-20 series membranes are available in two grades. UTC-20 HR membrane has a high water flux over 2.4 m3/m2 day (60 gfd) and NaCl rejection above 70 % at 15 kg/cm2. UTC-20 HF membrane has a very high water flux over 3.5 m3/m2 day (86 gfd) and NaCl rejection above 50 % at 15 kg/cm2, while the magnesium sulfate rejections of UTC-20 HR & 20 HF membranes are above 99.0 %, respectively. UTC-40 series membranes are also available in two grades. UTC-40 HR membrane has high NaCl rejections above 98 % and 1.0 m3/m2 day (24.5 gfd) water flux at 15 kg/cm2. UTC-40 HF membrane has very high water flux above 2.5 m3/m2 day (61.5 gfd) and over 90 % sodium chloride rejection at 15 kg/cm2. UTC-20 & 40 series membrane are directed to use in the market for ultrapure water production and brackish water desalination at low or super low operating pressure. These new composite membranes have been successfully manufactured in continuous flat sheet form and wound into the spiral elements.

Operation and reliability of very high-recovery seawater desalination technologies by brine conversion two-stage RO desalination system☆

Abstract A reverse osmosis (RO) seawater desalination system has many advantages such as saving energy and using less installation space, and has become regular technology to obtain fresh water from seawater. A significant way to lower energy and installation space is to raise system recovery, and we have developed a new RO seawater desalination system which provides 60% recovery of fresh water for 3.5% seawater. The new technology is called a brine conversion two-stage SWRO system (BCS). This system includes several new technologies such as system configuration, energy recovery, operating condition, etc.; high-performance membrane technology; anti-biofouling technology and a new analysis method. A pilot plant has been operated successfully at Torays Ehime plant site since 1997. The first commercial plant of 4500m3/d (1.2 mgd) has been operating successfully since March 1999 in Mas Palomas (Gran Canaria, Spain). The Tortola and Curacao plants in the Caribbean have been installed with the full BCS (first-+second-stage RO system), and also operated under good conditions. A new application of the BCS, installed at the Muroto plant in Japan, has been in operation to obtain bottled drinking water and high concentrated mineralized water from deep seawater. Furthermore, other plants are under construction in Spain and the Caribbean. The BCS is presumed to be the standard SWRO system for the 21st century.

Spiral-wound new thin film composite membrane for a single-stage seawater desalination by reverse osmosis

Abstract New thin film composite membrane system, designated PEC-1000, formed by the acid catalyzed polymerization on the surface of a reinforced-porous supporting membrane, make it possible to produce potable water from seawater by reverse osmosis in a single-stage with a high recovery operation. TDS rejection over 99.9% and stable water fluxes of 0.20–0.30 m3/m2-day (5.0–7.4 gal/ft2-day) have been attained with 3.5% synthetic seawater at an applied pressure of 56Kg/cm2(800psi). For brackish water, sodium chloride rejections of 99.6–99.9% and fluxes of 0.61–0.81m3/m2-day(15.0-20.0 gal/ft2-day) have been attained with 5000 ppm sodium chloride feed at an applied pressure of 40Kg/cm2 (571psi). TDS rejection of 99.8% and water flux of 0.30 m3/m2-day (7.4 gal/ft2-day) have been attained with two- or four-inch diameter PEC-1000 composite membrane elements at an applied pressure of 56Kg/cm2(800psi) in a single-stage synthetic seawater desalination test. This performance is kept for more than 1500 hours in PEC-1000 thin film composite membrane and two-inch diameter element. 280 ppm in TDS and water flux of 0.11 m3/m2 day (2.7 gal/ft2-day) are observed at an applied pressure of 56Kg/cm2-40% water recovery with one four-inch diameter spiral-wound PEC-1000 composite membrane element in a single-stage seawater desalination. This membrane shows high selectivity for low molecular weight valuable organic materials such as ϵ-caprolactam, dimethylsulfoxide, dimethylformamide. The thickness of ultrathin salt barrier of the composite membrane is found to be 300A by the Electron Microscopy with special ultrathin section techniques.

High performance RO membranes for desalination and wastewater reclamation and their operation results

Reverse osmosis (RO) membrane is one of the most powerful tools for solving the global water crisis, and is used in a variety of water treatment scenes such as drinking water purification, waste-water treatment, boiler feed water production, ultra pure water production for semiconductor industry, etc. The desired performance of RO membrane varies according to quality of feed water being treated, and Toray has been developing RO membranes with suitable characteristic for each operating condition. RO membranes for seawater desalination and wastewater reclamation are especially regarded as most promising targets. Recently, high boron removal and energy saving RO membrane for seawater desalination and low fouling RO membrane for wastewater reclamation have been developed. In this paper, the prospect of attaining these renovative RO membrane, and furthermore, job references will be discussed.

New polymeric materials for reverse osmosis membranes

Abstract The results obtained from investigations on new aromatic polyamides containing carboxylic groups suitable for reverse osmosis are reported. The polymers are fabricated into asymmetric membranes by the Loeb-Sourirajan technique. The effects of fabrication conditions were also investigated to yield the optimum membranes for brackish water and sea water desalination, respectively. Performance characteristics of the membranes are 0.30 m3/m2·day above 98% rejection at 70 kg/cm2-35000 ppm NaCl, and 1.0–1.15 m3/m2· day, 97–98% rejection at 40 kg/cm2-5000 ppm NaCl. They exhibited good resistance in the tests carried out in alkaline medium (pH 10) and acid medium (pH 4).

Reaction kinetics of sodium bisulfite and dissolved oxygen in seawater and their applications to seawater reverse osmosis

Abstract Recently, single-stage seawater reverse osmosis (SWRO) in the Middle East has been developed. In this process, removing dissolved oxygen (DO) from the feed seawater is very important for membrane life. The reaction rate of sodium bisulfite (SBS) and DO in seawater was investigated to apply DO removal system to the SWRO. The reaction in seawater was very fast because the salinity had a positive catalytic effect and the bicarbonate ion kept the pH suitable for the reaction. By applying these results, Torays PEC-1000 membrane modules have shown excellent performance and long durability.

Single-stage seawater desalination at high temperature and salinity as present in the Middle East using PEC-1000 membrane modules

Abstract Single-stage seawater desalination at high temperature and salinity as present in the Middle East has been examined by using PEC-1000 reverse osmosis (RO) membrane modules. The experiments have been practiced with the adjusted feed-seawater as present in the Middle East. From the long-term field test results, it has been proved that PEC-1000 membrane elements exhibit sufficiently enough performance and durability for the complete single-stage seawater RO (SWRO) in the Middle East and the permeate salinity is low enough for the WHO standard (500 ppm TDS) even at high water recovery rate such as 35–40 %.