Two-stage Reverse Osmosis Research Articles

Groundwater treatment by reverse osmosis

An experimental study was undertaking over 12 months in a two-stage reverse osmosis module in the beverage industry. The groundwater was treated by reverse osmosis to eliminate the water solutes. The obtained results showed that the reverse osmosis process is well adapted for this treatment; the retention is more than 95% for the totality of solutes (the total conductivity decreased from 1070 μs/cm to 33 μs/cm). However, we observed fouling phenomena expressed in a decrease in the permeate flow. In addition, the mass balance carried out showed that the fouling principal factor is limestone scale on the membrane surface. The fouling evolution with time was modelled and presented by the R f / R m ratio variation.

Application of high flux brackish water thin film composite membranes in the desalination of highly saline ground water

The improvements in flux and membrane designs have enabled us to install smaller and economical two-stage reverse osmosis systems suitable for small village communities situated near coastal areas to provide safe drinking water. In addition, the advent of higher productivity and better salt rejection membranes has allowed us to operate the systems at low pressure in both stages. Our two-stage sequential reverse osmosis system has been field tested, and proved economically feasible. The product water quality obtained from this system is 500 ppm to 700 ppm from highly saline (equivalent to seawater, 35,000 ppm) water. The two-stage reverse osmosis design permits the system to operate for much longer periods using the same membrane modules and to produce better-quality product water. Reported herein are the results of the application of the high-flux thin-film composite membrane in a two-stage desalination plant to treat highly saline groundwater at village Nelmadur in Ramnathpuram district in Tamil Nadu.

Technical Evaluation of a Reverse Osmosis Desalination Plant in the Caribbean: A Case Study

The aim of this paper is to determine the recovery rate and other performance parameters using a numerical model. The results are presented for a two-stage seawater reverse osmosis desalination unit with spiral-wound modules. The model, which is based on the mass and momentum transport equations, takes into consideration the longitudinal variation of the velocity, the pressure and the salt concentration in the membrane modules. Data given by plant authorities reveal that the plant is currently operating at a recovery rate of 67.53%. This project has shown that for the Desalination Company of Trinidad and Tobago, the recovery rate currently achieved by the plant (67.53%) might not be the most economical. Slightly reducing the recovery rate drastically reduces the energy cost, resulting in an overall reduced cost per cubic meter of desalinated drinking water.

Feasibility study of treatment of amoxillin wastewater with a combination of extraction, Fenton oxidation and reverse osmosis

Wastewater from the synthesizing of amoxillin is characterized by its very high TOC and low biodegradability and the presence of organic solvents and dissolved salts. These hamper direct biological or membrane-based treatments. A combined process of extraction (EX), Fenton oxidation (FO) and a two-stage reverse osmosis (RO) was proposed to treat such wastewater. EX and FO were performed in a serial approach to function as the pretreatments to remove the solvents and other organics before RO treatment. It was noted the appropriate phase ratio (A/O) was 1:1 and the contact time was 3 h. Appropriate dosages of FeSO 4 and H 2O 2 were 10 g/l and 2 g/l, respectively. Under the appropriate conditions, TOC can be reduced by 50.6% and 37.8% in the EX and FO units, respectively. TOC can be further reduced 10.1% and 1.2% in the first and second RO processes, respectively. There was consequently an overall TOC removal efficiency of 99.7% after the whole process of EX–FO–RO–RO. Dissolved salts were also greatly removed during the two-stage RO process. The observations by using SEM showed that the RO membrane can be protected well by the pretreatments of EX and FO.

Production of process water using integrated membrane processes

AbstractApplication of ultrafiltration, nanofiltration, reverse osmosis, membrane distillation, and integrated membrane processes for the preparation of process water from natural water or industrial effluents was investigated. A two-stage reverse osmosis plant enabled almost complete removal of solutes from the feed water. High-purity water was prepared using the membrane distillation. However, during this process a rapid membrane fouling and permeate flux decline was observed when the tap water was used as a feed. The precipitation of deposit in the modules was limited by the separation of sparingly soluble salts from the feed water in the nanofiltration. The combined reverse osmosis—membrane distillation process prevented the formation of salt deposits on the membranes employed for the membrane distillation. Ultrafiltration was found to be very effective removing trace amounts of oil from the feed water. Then the ultrafiltration permeate was used for feeding of the remaining membrane modules resulting in the total removal of oil residue contamination. The ultrafiltration allowed producing process water directly from the industrial effluents containing petroleum derivatives.

Energy saving in two-stage reverse osmosis systems coupled with ultrafiltration processes

In this paper the optimization of the main design parameters is performed for a double-stage seawater reverse osmosis (SWRO) system coupled with an ultrafiltration process; the minimal energy consumption is the goal of the optimization process. The energetic benefits for the membrane process are calculated, deriving from the use of a hybrid two-stage/two-pass lay-out with ultrafiltration pre-treatment, which is a typically a low energy consumption process. Also the benefits on membranes’ efficiency and duration are assessed by examining the very low Silt Density Index (SDI) of the water exiting the ultrafiltration section. The analysed system includes a SWRO membrane in the high pressure stage and a BWRO membrane in the low pressure one, according to a well-known practice for small and medium size plants. Such plant lay-outs allow to threat high TDS feedwater (up to 40 g/l), usually adopting very cheap membranes and operating them with a very low recovery factor. A comparison with a single stage RO section is performed, assuming a typical TDS of the seawater for Mediterranean regions and a fixed TDS level for the final product (<500 mg/l). The investigation mainly concerns technical and energetic aspects, but a brief cost analysis is finally presented in order to assess the economic viability of the proposed solution.

Nanofiltration and reverse osmosis of model process waters fromthe dairy industry to produce water for reuse

In dairy plants the process waters generated during the starting, equilibrating, interrupting and rinsing steps contribute to the production of effluents. They correspond to milk products (milk, whey, cream) diluted with water without chemicals. The treatment of these dairy process waters by nanofiltration (NF) or reverse osmosis (RO) operations was proposed to concentrate dairy matter and to produce purified water for reuse in the dairy plant. The study reports one-stage and two-stage (NF + RO and RO + RO) spiral-wound membrane treatments with five model process waters representative of the main composition variations observed in dairies. Performances (permeate flux, milk components rejection, purified water characteristics) of the different operations were compared. Discussion was focused on the comparison between quality of produced waters and vapour condensates (from product drying and evaporation processes) reused in dairy plants. Accordingly, both total organic carbon (TOC) and conductivity of water treated by a single RO or NF + RO operations were convenient for reuse as heating, cooling, cleaning and boiler feed water. With the two-stage RO + RO process, a more purified water complying with the TOC drinking water limit was achieved.

Ultrapure Water Production by Continuous Electrodeionization Method: Technology and Economy

Electrodeionization (EDI) and mixed bed deionization (MBDI) processes usually occupy the same position in the technological scheme of ultrapure water production, being used for the additional purification (conditioning) of reverse osmosis (RO) permeate (see, [1, 2]). A comparative analysis of the main differences of EDI and MBDI allows these methods to be more expediently used in water conditioning technology. The MBDI process has been used on a commercial scale for more than three decades, mostly in combination with a two-stage RO process. For this method, the content of active chlorine in the initial water flow is maintained within 0.05 – 0.08 mg liter in order to provide for a 3 – 4 month cellulose acetate regeneration cycle in the RO membranes. The ion exchanger is regenerated by treatment with strong acid and alkali solutions, which yields considerable volumes of highly mineralized waste waters implying the need for thoroughly monitoring the pH level. The EDI technology does not involve chemicals and does not require scrubbers for the flow neutralization after acid and alkali regeneration, reservoirs for the storage of concentrated acids and alkalis, the corresponding pumping equipment and valves, and double pipelines of corrosion-resistant steel, which significantly reduces both capital equipment and operating costs.

Treatment of agricultural drainage water via lagoon/reverse osmosis system

Treatment and reuse of agricultural drainage water (ADW) is complicated by the presence of soluble organic and inorganic pollutants in addition to hazardous chemicals. Large-scale desalination systems for agricultural drainage water require the development of affordable pretreatment for removal of soluble organic matters, which include residuals of agrochemicals and industrial pollutants. Current reports pertinent to the assessment of the typical characteristics of agricultural drainage water indicate that chemical oxygen demand (COD) concentration ranges from 50–250 mg/l. This paper presents process design features of an integrated scheme for the treatment of agricultural drainage water for reuse in non-agricultural purposes. The system essentially comprises aerated lagoon and two-stage reverse osmosis (RO) or electrodialysis for a plant capacity of 30,000 m 3/d. Results reveal the preliminary technical and economic feasibility of the proposed treatment/desalination system. The capital, operating and unit costs have been estimated. Recommendations for management of brine have been developed.

日本膜学会膜学研究奨励賞（２００２年）受賞論文 濃縮水昇圧２段法海水淡水化逆浸透プロセス・解析技術の確立

Many large seawater desalination plants, using reverse osmosis (RO) membranes, are now running in the world, and large efforts have been conducted in order to reduce the production cost.As one of the solutions for cost reduction, a new scheme called a brine conversion two-stage RO process was developed. In this process, pre-treated seawater is fed to the first stage and approximately 40 % of permeate is obtained from seawater, and concentrate of the first stage is boosted up its pressure again and more permeate is obtained at the second stage RO, in which 60 % can be totally recovered. In this two-stage process, high pressure is applied in order to obtain the effective pressure for the concentrated seawater at the second stage.This process became possible through the development of a new composite membrane and a new element, which can be operated at high pressure and high concentration.In this study, we developed a method to analyze and design the brine conversion two-stage RO process, and it was verified for each stage by comparing simulated result with the actual plant data. Then, we found the relationship between the permeability of TDS (total dissolved salt) and that of boron, and established the technique to estimate the concentration of boron in the permeate.

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

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 Toray's Ehime plant site since 1997. The first commercial plant of 4500m 3/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.

Design of a 1.4 mgd desalination plant based on MSF and RO processes for an arid area in India

Although India receives an average rainfall of 100 cm, some parts of the country get only scanty rains and are subject to chronic water shortages. Due to the occasional failure of the monsoons, a drinking water problem in these areas becomes quite acute. Water has to be brought in tankers and railway wagons to meet the drinking water needs of the people. With the advent of desalination technology based on both thermal and membrane processes, it is being considered as an alternate source to provide/augment the drinking water sources in the coastal water scarce areas. R & D work carried out at the Bhabha Atomic Research Centre (BARC) on desalination in the last 10–15 y has resulted in the development of technology for brackish water and seawater desalination in the country. Operation of pilot plants based on both membrane and thermal desalination has provided useful data for the design of large-scale desalination plants. This paper gives the details of a 1.4 mgd (6300 m 3/d) desalination plant to be installed in a coastal area for augmenting the drinking water supply. This consists of a 1.0 mgd multi-stage flash (MSF) and a 0.4 mgd two-stage reverse osmosis (RO) plant based on an indigenously available cellulosic membrane. A two-stage RO process is required in view of moderate salt rejection of cellulose acetate membranes for seawater feed. These membranes, however, possess better chlorine tolerance and fouling resistance compared to TFC membranes. As such this system is more appropriate under Indian conditions. The steam for the MSF plant will be available from a thermal power station where the plant is to be set up. Part of the product water obtained from the MSF plant will be used for entire boiler feed make up of the power station (in lieu of obtaining steam and power for the desalination plant). The remaining product water from the MSF plant (around 0.6 mgd) and RO plant (0.4 mgd) will be blended to get potable water of 250 ppm TDS. The MSF and RO plants are based on indigenous technology using most of the materials and equipment made locally. The detail design aspects and the cost estimates are presented in the paper.

Design of a 1.4 mgd desalination plant based on MSF and RO processes for an arid area in India

Although India receives an average rainfall of 100 cm, some parts of the country get only scanty rains and are subject to chronic water shortages. Due to the occasional failure of the monsoons, a drinking water problem in these areas becomes quite acute. Water has to be brought in tankers and railway wagons to meet the drinking water needs of the people. With the advent of desalination technology based on both thermal and membrane processes, it is being considered as an alternate source to provide/augment the drinking water sources in the coastal water scarce areas. R & D work carried out at the Bhabha Atomic Research Centre (BARC) on desalination in the last 10–15 y has resulted in the development of technology for brackish water and seawater desalination in the country. Operation of pilot plants based on both membrane and thermal desalination has provided useful data for the design of large-scale desalination plants. This paper gives the details of a 1.4 mgd (6300 m 3 /d) desalination plant to be installed in a coastal area for augmenting the drinking water supply. This consists of a 1.0 mgd multi-stage flash (MSF) and a 0.4 mgd two-stage reverse osmosis (RO) plant based on an indigenously available cellulosic membrane. A two-stage RO process is required in view of moderate salt rejection of cellulose acetate membranes for seawater feed. These membranes, however, possess better chlorine tolerance and fouling resistance compared to TFC membranes. As such this system is more appropriate under Indian conditions. The steam for the MSF plant will be available from a thermal power station where the plant is to be set up. Part of the product water obtained from the MSF plant will be used for entire boiler feed make up of the power station (in lieu of obtaining steam and power for the desalination plant). The remaining product water from the MSF plant (around 0.6 mgd) and RO plant (0.4 mgd) will be blended to get potable water of 250 ppm TDS. The MSF and RO plants are based on indigenous technology using most of the materials and equipment made locally. The detail design aspects and the cost estimates are presented in the paper.

Economics of seawater desalination by reverse osmosis

The ultimate goal in the scientific study of desalting and water purification is to design a process that produces potable water at the lowest possible cost. Presently two major techniques are commercially used in different parts of the world: distillation and membrane processes. The dominant distillation process is multi-stage flash (MSF), and the main membrane process is reverse osmosis (RO). Although cost factors vary by site, the total cost of producing potable water from seawater with the RO process is usually less than thermal desalting processes. In this paper results of a study carried out in Kuwait to compare the unit cost of water produced from one-stage and two-stage hollow fiber (HF) and spiral wound (SW) seawater RO systems are presented. Results indicate that an average reduction in product water cost of about 22% could be achieved when one-stage RO is used instead of two-stage RO to produce drinking water from seawater in Kuwait. Moreover, an average of 11.84% of the capital investment cost can be saved by using a one-stage instead of a two-stage RO system. A greater reduction in product water cost is expected in the future as there is more room for improvement in the design, operation and maintenance of seawater desalination by RO technology.

Design and performance of two-stage reverse osmosis plant

Simple explicit equations are derived for the design of permeate-staged and reject-staged reverse osmosis plants. Their accuracy has been tested against iterative numerical procedures. Errors in the membrane area of both stages are below 10% under normal operating conditions. Therefore, the method can be usefully applied for quick initial estimates and for discriminating between competing processes. Two design examples are presented: sea-water desalination and sugar solution concentration. Recoveries of up to 40% can be expected even for highly concentrated sea-water (50 000 ppm). Concentrations of more than 35 wt.% can also be obtained with relatively low energy. In both cases reverse osmosis proves to be competitive with evaporative processes.

Verification of design criteria, experience and results obtained with the plate module line at DROP, Kuwait

The essental objective of the Plate Module Line at DROP is to test the PG plate module system (identical with GKSS licence G 4.2) with various types of membrane (A, B and C) in desalination stage I of a two-stage reverse osmosis seawater desalination plant, designed for a nominal potable water capacity of 1000 m 3/day at 40 % recovery. After a general description of the plate module line, the design criteria of desalination stage I in particular are compared with the results of the first two years' operation converted to standard conditions. In view of the substantial differences in performance between the membrane type C, a thin film composite membrane, and types A and B, which both belong to the class of integrally asymmetric phase inversion membranes on a cellulose acetate basis, the operating results for a 1000 m 3/day plate module plant are extrapolated solely on the basis of a type C membrane in desalination stage I. Experience with other plant components will also be reported on, e.g. desalination stage II with spirally wound module elements, the energy recovery system, materials employed and the fully-automatic control system.

Treatment of Tar Sand Wastewaters with Activated Carbon, Ozone and Reverse Osmosis

Tar sand deposits offer long-term potential for satisfying future energy needs. Two large field-scale extraction experiments near Vernal, Utah, employed either a sequenced reverse-forward combustion technique (TS-2C) or a steam flooding procedure (TS-1 S) to recover in-place bitumen. This report documents the evaluation of activated carbon, ozone and reverse osmosis in treating the two types of tar sand wastewaters. Substrates included untreated and pretreated (filtration, foam fractionation, chemical treatment with ferric chloride) TS-1S and TS-2C wastewaters. Activated carbon, at a dose of 1,000 mg/L, reduced the Total Organic Carbon (TOC) of TS-1 S wastewater after treatment by 350 mg/L of ferric chloride to 2.3 mg/L TOC, a reduction of 91.6%. At the same adsorbent dos, activated carbon reduced the TOC in TS-2C wastewater from 678 mg/L to 546 mg/L. A study of the six commercially available adsorbents yielded little difference in adsorption capability for either wastewater. Ozonation of TS-lS wastewater after pretreatment by either foam fractionation or chemical treatment with ferric chloride then activated carbon yielded residual TOC levels of less than 1.2 mg/L. Reverse osmosis (RO) studies included investigation of four membrane types (cellulose acetate, poly-ether amide, poly-ether urea and a noncellulosic on a poly-sulfone base), three applied pressure levels (250, 400 and 550 psig) and two solution pH levels (5.5 and 7.8) with 5.0 µ (micron) filtered TS-2C wastewater as the substrate. A two-stage RO process achieved maximum organic and inorganic rejections of 98% and 97%, respectively.

Factors influencing optimum seawater reverse osmosis system designs

Potential seawater desalination applications require an evaluation of both single-stage and two-stage reverse osmosis system configurations when selecting the most cost effective process design for a specific application. The preferred reverse osmosis staging should be derived from cost factors, membrane performance parameters, feedwater characteristics and other application site-specific considerations. This paper presents a comparative analysis of single-stage and two-stage seawater reverse osmosis systems, illustrating how the optimum design is influenced by the choice of operating parameters and related cost factors. Computer aided design techniques used by Fluid Systems in evaluating reverse osmosis array options are discussed. Performance characteristics of Fluid Systems' single-stage and high-flux seawater elements are used in the analyses to arrive at the optimum system designs for a range of feedwater salinities. The approach of using pilot plant test results for long-term performance predictions is described.

Two-stage reverse osmosis seawater desalination

The product water recovery is introduced as a figure of merit in assessing the economic viability of two-stage reverse osmosis desalination at high feed salinities. Design calculations on a two-stage seawater desalination plant in Kuwait using the GKSS plate system are included.

Field experience of seawater desalination by reverse osmosis system, operating in Saudi Arabia

The reverse osmosis system has been broadening its application capability for these several years. Especially in recent years, there have been substantial approaches to seawater desalination, proving technical and economical viabilities to generate fresh water from the sea. A seawater reverse osmosis plant has been operating successfully since January 1977 at Ras Al Khafji, Saudi Arabia, producing the product water of 200 to 300 ppm TDS from the seawater with a high salinity of about 45,000 ppm TDS. The pretreatment process consists of coagulation/clarification, dual media filtration and polishing sand filtration along with the appropriate chemical dosages. The seawater desalination employes a two-stage reverse osmosis plant of 40 M 3/D in capacity, using ROGA 6085 CTA modules and ROGA 4160HR modules respectively for the first-stage and for the second-stage. The brine concentrate from the second-stage is recycled back to the feedwater inlet of the first-stage. The two-stage RO seawater desalination system is proving greater reliability and better performance: the product water quality is maintained safely within the recommended limitation of the WHO drinking water standard.