Preconcentration by reverse osmosis before evaporation - possibilities IN Sweden

An inventory has been made on how much water is removed by evaporation in Sweden, and where it is technically and economically possible to save energy by preconcentration by reverse osmosis. The result is that it is possible, mainly in the pulp and paper and dairy industries. Per year, energy equivalent to 33.10³ and 11.10³ metric tons (t) oil respectively can be saved in these industries.     

Concentration polarization in a reverse osmosis test cell

The reverse osmosis cell is a parallel plate test channel with the membrane on one side and five permeate outlets in series. Mass transfer coefficients have been measured by three different techniques in both laminar and turbulent flow. These give concurrent measurements, which show that the transfer from laminar to turbulent flow occurs in the region Re = 1000–2500. The results can be represented by the equation Sh = A · Re^0.80 · Sc^0.33, where the constant A is independent of the solute mobility and membrane retention, but varies with the channel height and the distance from the inlet zone.     

Concentration polarization in a narrow reverse osmosis membrane channel

Concentration polarization in a narrow reverse osmosis channel is bounded by the channel height and under the influence of variable transverse velocity. An attempt was made in this article to quantify concentration polarization in such a narrow membrane channel. The transverse velocity in the membrane channel was first determined and its impact on concentration polarization was investigated. Based on the concept of retained salt, analytical equations were developed for the wall salt concentration at an arbitrary point in the narrow membrane channel. Finally, development of concentration polarization in typical reverse osmosis channels under various conditions was numerically simulated and discussed. Interesting results on the details of concentration polarization in the narrow reverse osmosis channel that had never been reported before were revealed with this mechanistic model. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Complete elimination of acid injection in reverse osmosis plants

Antiscalants with broad activity spectra are available today. When properly chosen, a single antiscalant can efficiently and simultaneously control calcium carbonate, calcium sulfate, strontium sulfate, barium sulfate and calcium fluoride scales as well as inorganic foulants resulting from iron, aluminum and reactive silica present in any given water or wastewater. The effectiveness of many antiscalants towards controlling calcium carbonate scaling in reverse osmosis (RO) plants has allowed us, in the past five years, to successfully help eliminate the continuous injection of acid in all RO systems operating with polyamide membranes. A minority of systems with cellulose acetate membranes however still require acidification due to hydrolytic sensitivity of cellulose acetate towards feedwater pH higher than 6. The chemistry behind the main reason for acidification — the prevention of scaling by calcium carbonate — is reviewed. The mechanisms of calcium carbonate scaling and its avoidance by acidification or with antiscalants are discussed. Major seawater and brackish water RO plants around the world are designed and operated with the continuous injection of concentrated sulfuric or hydrochloric acid for scale control, sometimes simultaneously with an antiscalant. We present a case study in southeastern USA of a 5 million gallons permeate per day plant as a typical example among many for the conversion of major municipal RO plants. By suitable selection of an antiscalant, acid elimination was successfully attained with a simultaneous reduction in the antiscalant dosage, in this case to 2-3 mg/1 in the feedwater. While process optimization continues in the plant, current chemical cost savings due to the deletion of 93% sulfuric acid and the associated caustic soda neutralizer alone amounts to 67% of the annual cost of all chemicals used. This does not include savings through benefits accrued in equipment, operation, maintenance and safety in the plant.     

利用脂肪酶控制马尾松酸性亚硫酸盐浆树脂的沉积

马尾松酸性亚硫酸盐浆是一种易产生树脂障碍的纸浆．本文利用 三种来源的脂肪酶对马尾松酸性亚硫酸盐浆进行了生物处理．Ｖｉｂｒｏｍｉｘｅｒ 沉积实验表明，马尾松酸性亚硫酸盐浆经脂肪酶处理后树脂的沉积量明 显降低．利用来自 Ｃａｍｌｉｃｌａ ｌｉｐｏｌｙｔｉｃａ的脂肪酶对纸浆生物处理的结果也 表明，脂肪酶生物处理可以降低马尾松酸性亚硫酸盐浆树脂的Ｒ_Ｎ值（树 脂中的中性组分占中性组分与弱酸性组分之和的百分比）．例如，脂肪酶 用量为 ５Ｕ／ｇ绝干浆时，纸浆中树脂的Ｒ_Ｎ值由初绍的 ２１．２％降为１６．８％，大 多数甘油三酸酯发生水解．提出的Ｒ_N值是评价脂肪酶生物控制效果的有 效方法．     

Arsenic removal by reverse osmosis

Arsenic is widely distributed in nature in air, water and soil. Acute and chronic arsenic exposure via drinking water has been reported in many countries, especially Argentina, Bangladesh, India, Mexico, Mongolia, Thailand and Taiwan, where a large proportion of ground water is contaminated with arsenic at levels from 100 to over 2,000 micrograms per liter (ppb). Public health standards of maximum of 50 ppb have been adopted by the US and World Health Organization in the 1970s and the 80s. Carcinogenicity and genotoxicity led to the WHO recommendation of 10 ppb maximum level in 1993, followed by the US adoption of the same in 2001, with the US estimate that 5% of all US community water systems will have to take corrective actions to lower the current levels of arsenic in their drinking water. In high arsenic areas of the world, the need for better water treatment and resulting economic impact would be even greater. In this article, we briefly review the geochemistry, natural distribution, regulation, anthropogenic sources and removal mechanisms of arsenic, pointing especially to the promise of reverse osmosis (RO) as a practical means of purification. We conclude that arsenic in the commonly high oxidation states of (V) is very effectively removed by RO. With further attention to the removal of the weakly acidic arsenic (III) species in waters by the operation of RO at sufficiently high pHs made possible by the newer antiscalants, practical processes can be developed with RO to remove all major species of arsenic from water. Further studies are needed in the characterization of the arsenic species being treated and in the design of the RO process to match the demands.     

Studies on desalination by reverse osmosis

The structure of cellulose acetate membranes used for desalination in the process of reverse osmosis has been examined. By means of a technique involving aqueous solutions of the stain Biebrich Scarlet, the membranes are shown to consist of two regions, one of which acts as a mechanical support for the much thinner desalinating layer. The phenomenon of asymmetric permeation across these membranes has been studied and shown to be a consequence of the two-layer structure of the membrane.     

Criterion of ion separation by reverse osmosis

The order of ion separation by the NS-100 membrane differed slightly from that of the cellulose acetate membrane. The separation of an ion by the NS-100 membrane increased with increase in the valence of the ion, but decreased with the increase in the ionic radius. The sole criterion determining this separation order for the NS-100 membrane was the enthalpy of hydration. An ion having a higher enthalpy of hydration is bulkier in the hydrated form and is, therefore, separated more effectively by the NS-100 membrane, according to the diffusional model of solute separation. The permeability of an ion through the membrane material can be related to its enthalpy of hydration. By using this relationship, the separation of individual ions in aqueous solution with a given NS-100 membrane can be predicted from a test with a sodium chloride solution.     

Continuous enzyme-catalyzed production of 6-aminopenicillanic acid and product concentration by reverse osmosis

The efficiency of 6-aminopenicillanic acid (6-APA) production by enzyme-catalyzed hydrolysis of penicillin G using penicillin G amidase (E. C. 3.5.1.11) immobilized in polyacrylamide gel can be improved by using a lower substrate concentration and an optimized low buffer concentration. In a continuous process the combination of a stirred-tank reactor and a plug-flow reactor gives optimum productivity. Since precipitation of 6-APA is the crucial step in downstream processing, the product concentration has to be as high as possible. This can be achieved by concentrating the product solution by reverse osmosis.     

强制外循环三效蒸发反渗透浓水的中试研究

利用尿素生产过程中甲胺合成时的余热处理反渗透浓水,设计并建造一套强制外循环三效蒸发结晶处理工艺中试装置,结合试验数据考察各效蒸发器操作参数及运行效果,并对其运行成本进行分析。结果表明,当一、二、三效蒸发器及终冷凝器操作压力分别为-0.01～-0.02、-0.05～-0.06、-0.07～-0.08、-0.085 MPa时,单位蒸汽消耗比约为0.43,蒸发冷凝液电导率≤200μS/cm,可作为脱盐水站或循环水装置补水利用。     

Haemodialysis water production by double reverse osmosis

A filtration unit composed of two reverse osmosis membranes in series was evaluated for haemodialysis water production. For this purpose, hard and soft water were formulated based on European drinking water directives. The study showed that the double reverse osmosis process is efficient to produce haemodialysis water with the quality defined by the pharmacopeia requirements from synthetic soft water and hard water. In both cases, nitrate and sodium ions diffuse through the membrane limiting the water treatment. This phenomenon is correlated to the electrostatic interactions, the Donnan effect and the ion diffusivity, which govern the membrane selectivity.     

Brackish groundwater treatment by reverse osmosis in Jordan

Jordan is characterised by an arid to semi-arid climate and its population is increasing at an annual rate of 3.6%. With such a high population growth rate and fast social-economical development, water demand and wastewater production are steeply increasing, and the gap between water supply and demand is getting wider. Furthermore, the constraints for water resources development are also rising due to high investment costs and water quality degradation due to over-exploitation of aquifers. Desalination of Red Sea water by reverse osmosis (RO) and/or brackish groundwater desalination by nanofiltration or RO might be technically and economically viable to cope with water scarcity and overcome the water deficit in Jordan. The technical-economical feasibility of brackish groundwater treatment by RO for potable water production was investigated in this work. Brackish groundwater samples were collected from the Zarqa basin, Jordan, and characterised in terms of pH, conductivity, total solids, total dissolved solids, total suspended solids, and volatile solids. The water samples were pre-treated through a microfiltration cartridge (5 μm pore diameter) in order to eliminate the suspended matter. A pilot plant equipped with a FilmTec RO membrane (SW30-2521) was operated at 20-30 bar, 40°C, natural pH and up to a water recovery ratio of 77.5%. The results showed that RO is actually efficient since it highly reduced the content of organic and inorganic matters present in raw waters (rejections >98.5%) at a relatively affordable price (0.26 €/m³). This study contributes to the development of efficient technologies to produce affordable potable water in Mediterranean countries where the threat of water shortages is a severe problem.     

Improving permeation flux by pulsed reverse osmosis

Pulsed and nonpulsed reverse osmosis experiments were conducted with a sucrose solution in cylindrical cellulose acetate membranes. For pulsing frequencies up to 1 Hz, permeation increases of more than 70 per cent were observed. A simple quasisteady-state theory for concentration polarization based on a film model of mass transfer describes the increase.     

Use of simulated evaporation to assess the potential for scale formation during reverse osmosis desalination

The tendency of solutes in input water to precipitate efficiency lowering scale deposits on the membranes of reverse osmosis (RO) desalination systems is an important factor in determining the suitability of input water for desalination. Simulated input water evaporation can be used as a technique to quantitatively assess the potential for scale formation in RO desalination systems. The technique was demonstrated by simulating the increase in solute concentrations required to form calcite, gypsum, and amorphous silica scales at 25°C and 40°C from 23 desalination input waters taken from the literature. Simulation results could be used to quantitatively assess the potential of a given input water to form scale or to compare the potential of a number of input waters to form scale during RO desalination. Simulated evaporation of input waters cannot accurately predict the conditions under which scale will form owing to the effects of potentially stable supersaturated solutions, solution velocity, and residence time inside RO systems. However, the simulated scale-forming potential of proposed input waters could be compared with the simulated scale-forming potentials and actual scale-forming properties of input waters having documented operational histories in RO systems. This may provide a technique to estimate the actual performance and suitability of proposed input waters during RO.     

Considerations of energy consumption in desalination by reverse osmosis

The primary factors affecting the energy consumption of a reverse osmosis plant are considered. These are the osmotic pressure of the feedwater, the feedwater temperature, the water recovery, and the relationship between the water flux and salt flux characteristics of the membrane. In addition, the required permeate quality may have several indirect effects on the energy consumption. Permeate quality standards may impose minimum operating pressures, limit the recovery, and/or require treatment with a full or partial second stage. As a general rule, the energy required increases with increasing feed salinity and increasing permeate quality.For any given recovery, a single stage system will require less energy than a partial two stage system. However, for a specified permeate quality, a partial two stage system can operate at a higher overall recovery and a lower energy consumption than a single stage systemEnergy recovery systems can recover between 50 and 90 percent of the available energy in a reverse osmosis unit, thus significantly lowering the energy consumption. Studies have shown that with an energy recovery system, the minimum energy consumption occurs at a first stage recovery of 30 to 35 percent. Currently, very few energy recovery systems are in use due to their high capital cost, but as energy recovery systems become more available and reliable, they will greatly increase the energy efficiency of reverse osmosis plants.     

Leachate treatment by the reverse osmosis system

The DT-Module system for landfill leachate treatment installed at Yachiyo Town in the Kanto District of Japan was put into service in April 1999. The system, which is equipped with a disc-tube type reverse osmosis (RO) membrane module called the DT-Module, has been operating satisfactorily for more than two and a half years, producing very-high-quality product water, after treating very-high-salinity water with high-scaling ions. On the other hand, in Japan, the dioxin problem has become increasingly severe, and development work for dioxin removal incorporated in leachate treatment has also been requested. The DT-Module system showed excellent performance in removing dioxins from leachate. For dioxins in sludge from the settling basin and dried salt from the concentrate of the RO system, successful destruction data were obtained by furnace system heating in an oxygen-deficient atmosphere. The removal rate of dioxins by the DT-Module system and the destruction rate by the furnace were both higher than 99.9%. By applying the DT-Module system together with the furnace system, an excellent leachate treatment and a complete dioxin removal and destruction system have become available for leachate from landfills depositing incineration residue-containing dioxins.     

Fractionation of aqueous organic mixtures by reverse osmosis

Modern synthetic polymer membranes for reverse osmosis, although primarily developed for seawater desalination, are remarkably selective and chemically resistant in the case of organic solvents. Accordingly, reverse osmosis is increasingly employed for the treatment of industrial effluents such as solvent-contaminated waste water. In this case flux and selectivity can no longer be calculated with the simple relationships valid for seawater desalination. Semi-empirical relationships are presented, capable of quantitatively describing the local partial fluxes of organic-aqueous solutions. The relationships are based on the solution diffusion model but contain less stringent simplifying assumptions than in the case of dilute salt solutions.

Compared to empirical relationships, very few experiments are required to determine the model parameters. In combination with the differential mass and material balances, these equations are sufficient for process design. This is illustrated by a comparison of calculated results and experiments on a pilot plant scale and is even valid for quasi-binary systems.