Conventional RO Research Articles

Novel 16-inch spiral-wound RO systems for water reclamation — a quantum leap in water reclamation technology

Two 16-inch pilot RO systems (designated as 2EPV and Super-Flux) that incorporated 16-inch RO membrane elements, innovative patented flow distributors for even distribution of feed water into and out of each RO membrane element and electromagnetic field (EMF) coils in the pressure vessels for fouling mitigation were tested at a local water reclamation plant. Their performance was compared with the existing full-scale conventional 8-inch RO system. All RO systems used ultra-filtrated secondary effluent from a nearby wastewater treatment plant as the feedwater. The average permeate fluxes of the 16-inch 2EPV (2 elements per vessel) and Super-Flux (4 elements per vessel) RO systems were found to be about 2 and 2.6 times, respectively, higher than that of the full-scale 8-inch RO system. The feed pressure and salt rejection of both 16-inch pilot RO systems were better maintained than the full-scale 8-inch RO system, suggesting that both 16-inch pilot RO systems were more capable of inhibiting membrane fouling. The effectiveness of EMF in reducing RO membrane fouling in the 16-inch pilot RO system had also been demonstrated in this study. The energy consumed by the 16-inch pilot RO system was about 12–16% lesser than that of the 8-inch full-scale RO system. Projections based on the average operating permeate fluxes obtained showed significant savings in the number of RO elements and pressure vessels when the 16-inch Super-Flux RO system is adopted instead of the 8-inch RO system.

Beneficial use of co-produced water through membrane treatment: technical-economic assessment

Large amounts of co-produced water are generated during natural gas production. This study investigated the viability and cost effectiveness of ultra-low pressure reverse osmosis (ULPRO) and nanofiltration (NF) membranes as potential techniques for beneficial use of produced water by meeting potable and irrigation water quality standards and concentrating iodide in the brine. A 2-stage laboratory-scale membrane testing unit was employed to examine rejection of various constituents of concern at a low and high recovery using produced water generated from sandstone aquifers. The performance of two ULPRO membranes TFC-ULP (Koch) and TMG10 (Toray America) and one NF membrane NF-90 (Dow/Filmtec) was compared to a conventional RO membrane (TFC-HR, Koch). These membranes were pre-selected during previous bench-scale experiments with regard to specific flux, fouling propensity, salts and organics rejection, and iodide recovery efficiency. Of the membranes tested, the NF-90 achieved the highest specific flux. The salt rejection and iodide recovery by the NF-90, however, were much lower than the RO and ULPRO membranes tested. The permeate quality of the NF-90 met USEPA National Primary Drinking Water Standards, but exceeded the Secondary Standards regarding chloride and total dissolved salts. The two ULPRO membranes TMG10 and TFC-ULP, exhibited a higher specific flux as compared to the TFC-HR while displaying a similar rejection, notably the TMG10 which showed a very stable rejection at low and high recoveries. Cost analysis showed that the ULPRO membrane system provided marginally lower overall O&M costs than RO for meeting drinking water standards. The ULPRO membrane operation resulted in even lower treatment cost than RO and NF for meeting irrigation water standards, especially at high energy cost. Findings from these studies indicated that ULPRO membranes can provide a viable and cost-effective solution to beneficial use of produced water from sandstone aquifers.

Boron removal by adsorption onto activated alumina and by reverse osmosis

The presence of boron compounds in waters increases in a continuous and parallel way to industrial development. Therefore, their harmful effects on living organisms also increase, especially on plants, since this element manifests an important micronutrient-toxic boron duality. The aim of this study is to investigate the boron removal by the adsorption process onto activated alumina and by membrane processes. Boron removal from aqueous solutions was investigated using activated alumina. Experiments were conducted to delineate the effect of stirring time, pH, adsorbent dose and boron concentration. Effects of foreign ions such as sulfate, fluoride, nitrate, hydrogenocarbonate and silica on boron removal by adsorption onto activated alumina were studied. The content of boron in water can be also reduced by means of various membrane processes. The reverse osmosis tests were carried out with the use of Osmonics spiral module equipped with AG 2514 TF membrane. Using conventional RO, significant removal of boron has been observed only in its ionic form. Experiments were conducted to present membrane retention as a function of pH and to delineate membrane performance.

食品産業における膜技術の新たな展開 野菜・果実加工プロセスにおける膜分離技術の展開

Membrane technology in the vegetable and fruit processing has been applied for concentration using RO membrane and for clarification using UF or MF membrane.Recent technological advances related to the development of new membrane system, advanced separation and recovery of valuable components, improvement quality, saving energy consumption and reduction of environmental negative impact, have expanded the range of membrane separation.We have developed two new membrane systems. One is RO concentration system for material including the solid. Conventional RO system has been used for only juice concentration including the solid below 0.5mm particle size, by this new RO system, it is possible to concentrate liquid including 0.5mm-10mm particle size solid.Another is electrodialysis system for reduction of nitrate in a green vegetable, the characteristic of this system is to be operated under high concentration (Brix20), low velocity and low temperature condition.

Field evaluation of capillary UF technology as a pretreatment for large seawater RO systems

RO seawater systems operating on a surface feed water, originating from an open intake source, require an extensive pretreatment process in order to control membrane fouling. Considerations of long-term membrane performance stability have lead to an initial design concept of operation of seawater RO systems at a low permeate flux rate and low permeate recovery. In recent years the nominal performance of composite seawater membrane elements has improved significantly, and in parallel new backwashable microfiltration and ultrafiltration capillary technologies have been introduced commercially. This new membrane technology can be utilized to treat seawater from a surface sources. Use of membrane capillary technology as a pretreatment step can improve quality of the surface feed water to a level comparable or better than the water quality from the well water sources. A better feed water quality enables more effective optimization of operating parameters in the RO systems. Both permeate flux and system recovery rate can be increased considerably without creating membrane fouling conditions. Operation of seawater systems at higher permeate flux and recovery rate results in improved economics of RO seawater desalting. Field evaluation of hybrid membrane systems consisting of UF membrane pretreatment unit and a RO seawater unit was conducted subsequently at two test sites. The first test site was at the Red Sea (Eilat site) and the second test site was on the Mediterranean (Ashdod site). The RO membranes were commercial seawater elements in spiral wound configuration. The UF equipment utilized capillary backwashable elements operated in dead end flow mode. For comparison, a second pilot system consisting of conventional pretreatment and an RO unit was operated in parallel at the above sites. The conventional pretreatment unit included in line flocculation followed by media filtration. The tests were conducted over a period of two years. Raw water quality reflected seasonal changes of composition and weather conditions. The performances of UF and RO equipment were evaluated over a wide range of operating parameters such as recovery and flux rate. Field results were used to project and compare the economics of the seawater RO desalting process using conventional and membrane pretreatment. This paper will describe the experimental procedure and results of parallel operation of an integrated membrane unit and a conventional RO sweater system. The economic analysis of both designs based on local site conditions, will be provided as well.

Deployment of a submarine reverse osmosis desalination prototype plant (RODSS): field tests and preliminary technical evaluations

The innovative RODSS approach (Reverse Osmosis Deep Sea System — EU-DG XIII innovation project 1998–2001) exploits seawater hydrostatic pressure at a depth of about 450m below sea level. This presentation concerns the deployment and field tests of a small-production-capacity (10m 3/d) prototype desalination unit immersed 1 mile offshore the southwest coast of Pantelleria Island, Sicily. The desalinated water produced in the sea depth at about atmospheric pressure is continuously pumped up through a buoyancy controlled reinforced conduit to a storage tank ashore via a high-pressure pump sited in the sea depth. The RODSS prototype has required a dedicated design work for all its components: it consists of a 5m long fiber glass pressure vessel, which contains all working apparatuses (osmotic modules, desalinated water storage tank, sea water circulation pump, desalinated water delivery pump, flow meters, temperature and pressure transducers, etc.) and a sea-line (desalinated water delivery conduit and electric power cable joined together) connecting it to the plant site ashore. The deployment of the RODSS prototype is described with the help of short texts and field pictures. The field tests of the RODSS prototype concern its working characteristics and are presented with the help of dedicated tables which detail the numerical values of basic parameters such as: working pressure, water salinity and temperature, and conversion coefficient. The presentation ends with preliminary conclusions on the RODSS technology potential for seawater desalination vis-a-vis conventional RO technology.

Behavior of a reverse osmosis plant adopting a brine conversion two-stage process and its computer simulation

A new scheme of reverse osmosis seawater desalination, which is called a brine conversion two-stage process, has been proposed by Toray Industries. In this process, a second-stage is added to a conventional RO unit, and the concentrated brine from the unit is further desalinated at the second-stage to increase the water recovery ratio over 40 up to 60%. The recovered energy from the first-stage brine is used to pump the feed to the second-stage up to approximately 10 MPa. For this purpose, a new membrane, UTC-80BCM, has been developed besides a conventional UTC-80. A test plant based on this scheme (210 m 3/day) was built at Ehime factory, Toray, Inc. and was run under a wide range of operation conditions. In this paper, the results of these membrane properties and the mass transfer coefficients of each spiral-type element are reported. Using these data, we found that a computer program, which was developed previously, could simulate the behavior of the new scheme, when appropriate temperature and pressure corrections were adopted.

Desalination of brackish fish pond effluents — pilot testing and comparative economic evaluation of integrated UF-RO systems vs. conventional systems

Following the recent market penetration of back-washable capillary micro- and ultra-filtration membranes, their application for treating polluted fresh water and for pre-treatment of wastewater as well as polluted brackish and seawater is now widely considered. In 1998 Mekorot initiated a field testing program to investigate the operation of integrated UF-RO systems to desalt polluted brackish surface water in comparison with a system using conventional pre-treatment. The results show that UF pre-treatment yields a performance superior to that obtained by the conventional pre-treatment regarding quality and overall system availability. However, at times of very high turbidities, a high load on the UF requires reduction of the filtration rate, effecting significant water losses. Therefore, a clarifier is needed to reduce loads of the UF and to improve substantially its performance regarding filtration rate and water losses. A preliminary economic evaluation made for a case study of an integrated UF-RO 20,000m 3/d desalination plant, indicates a projected cost of about 40–45 US cent/m 3. This cost is significantly lower than the projected seawater desalination cost. Therefore, a priority should be given to this source desalination in the new water sources development plan, especially in inland locations where neither potable nor brackish groundwater sources are available. The paper presents the results of the ongoing optimization study to improve the performance of the UF and conventional RO systems, and provides a detailed economics case study.

食品用耐熱性逆浸透膜モジュール「サーモプラス」

Conventional RO element of spiral-wound type has no heat resistance. so application of this RO element is limited such as for food processing which does not require hot water sterilization.New RO element can be poerated under the hot water sterilization (90°C) or high temperature and pressure opetation (60°C, 5 MPa) by modifing heat resistance.

耐塩素性に優れる芳香族系コポリアミド中空糸型ＲＯ膜

A new copolyamide hollow fiber RO membrane was designed and developed for the increase of chlorine resistance.The asymmetric hollow fiber RO membrane showed sufficient RO performance and higher chlorine resistance than conventional composite flat sheet RO membranes made of fully aromatic polyamide.The new HOLLOSEP (HS-series) module, loaded with the RO membrane is being operated in more than 20 places and these applications are being proved for this module where RO performance and chlorine resistance are beneficial.

Desalting water costs using waste heat from power systems combined with the VTFE and vapor compression

An updated desalted water cost comparison will be presented for the Reverse Osmosis, Multistage Flash Evaporator and the high efficiency performance Vapor Compression Vertical Tube Foaming Flow Evaporator (VTFE). The capital cost of the VCVTFE plant is based on a realistic conceptual design for a 2.5 mgd single purpose plant. There are several interesting desalting design concepts that will be presented which can only be realized through the use of the low ΔT vertical tube foaming flow evaporator. Together with the vapor compression cycle, high performance ratios of about 35 lbs. product per 1000 Btus can be readily achieved. These high efficiency concepts and use of waste heat are economical with current day high fuel costs. Conceptual designs will also be discussed of several distillation options using waste heat from a 20 MWe gas turbine. A design of a plant using the waste heat from the bottom end of a power plant for fresh water production from seawater will be presented. Cost comparisons of these low energy consuming concepts will be made with conventional MSF and RO systems. The turbine exhaust steam (waste heat) normally rejected through the seawater cooled condensers can be used to produce distilled water with an efficient vertical tube foaming flow single effect evaporator using enhanced flutted tubes. A discussion will be presented on the VCVTFE process design including the options and selection of the critical hardware for the efficient vapor compression plant design. A summary table will be presented which will include plant capital costs and water costs for several values of energy costs.

Hybrid reverse osmosis — ultrafiltration membranes

A new group of asymmetric non-cellulosic membranes having a performance intermediate between that of a conventional RO membrane and an ultrafilter has been developed. Its main characteristics are high fluxes (4–10 m3/m2 day) at low pressures (6–10 at) and moderate rejections for various salts. From 200 mg/l solutions of NaNO3, Na2SO4 and KH2PO4 rejections up to 40%, 70% and 90%, respectively, were obtained. The new membranes can withstand large variations in pH (1 to 13) and have excellent chemical and biological stability. The membranes have been tested in a mobile SUF pilot plant operating on oxidation pond effluent. High rejections for BOD, COD, bacteria and suspended solids as well as a 20% reduction in salinity have been obtained.