Seawater desalination and reverse osmosis plant design

Plant site, water intake, pretreatment, choice of materials of construction, design alternatives and energy recovery are important variables to be considered in the design of seawater desalination plants employing “permasep” B-10 reverse osmosis modules. Techniques are outlined to permit custom design of seawater desalination plants which offer reliable long term performance as well as competitive economics.     

Seawater reverse osmosis—Statement of the art assessment

Considerable time and effort has been spent in developing new membranes and system configurations for Seawater Reverse Osmosis. This has led to reverse osmosis being accepted as a viable method for seawater desalination.     

Influence of temperature and permeate recovery on energy consumption of a reverse osmosis system

A model permits analysis of the influence of temperature on permeate recovery and energy consumption. The proposed model is based on the following assumptions: (1) membrane morphology is temperature-independent; (2) membrane rejection and other transport characteristics of membranes are position-independent; (3) specific water permeability of membranes was based on exponential dependence of viscosity vs. temperature; (4) temperature-dependence depembrane rejection is assumed to be linear. This allows for analyzing the influence of channel geometry, feed concentration, flow rate and temperature on permeate recovery and energy consumption. Calculated data are included. The solutionpresented can be segmented andbuilt into systems for comprehensive techno-economic evaluation of the RO-based process where temperature-dependence of process characteristics has to be considered.     

High recovery system in seawater reverse osmosis plants

Seawater desalination by the reverse osmosis (RO) method is an energy-saving system compared with the evaporating method, and can perform seawater desalination efficiently. Seawater RO desalination technology has been established and become a reliable system. Seawater desalination plants using RO technology have spread and the scale of the plants has increased significantly. More economical and efficient RO method seawater desalination systems have come to be required. A high recovery system, which offers reduction of plant construction cost and running cost was devised. Towards realization of this high recovery system, simulation and the field tests were done to confirm the practicality. Furthermore, a high recovery system was adopted for the biggest desalination plant in Japan, and it is performing favorably. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Distillation and reverse osmosis energy consumption and costs

The paper compares the energy requirements of single and dual purpose MSF distillation with seawater reverse osmosis plant. Energy consumptions are given both as heat and power consumptions for distillation and as power consumption for R.O. To enable a true comparison to be made these inputs are referred back to the heat inputs from fuel needed at the boiler plant or appropriate thermal power plant.Energy recovery is also considered for reverse osmosis and it is shown that the energy input can be expected to decrease by some 35% for a typical example.Although the prime energy input needed for reverse osmosis is shown to be substantially lower than for dual purpose distillation, the overall costs taking account Of capital charges, energy, replacements and other operating costs, are found to be in a band width of about 5% for plants in the range of 5000 to 15000 m³/day. Reverse osmosis plant water costs are significantly less than distillation if membrane life increases from 3 years to 5 years, particularly with small plant capacities.     

Seawater reverse osmosis system projects,a manufacturer's viewpoint

A reverse osmosis desalination system will provide excellent service if care is taken in the design, selection, installation and operation of the system. Precautions should be taken not to overly complicate the design and operation. The environment dictates that the highest quality components should be used. Satisfactory operation is highly dependent upon the experience of the manufacturer and the preparations taken prior to installation and commissioning of the system.     

海水反渗透淡化用带流体切换器的能量回收设备

Energy recovery device （ERD） is an important part of the seawater reverse osmosis （SWRO） desalination system. There are principally two kinds of ERDs, the centrifugal type and the positive displacement （PD） type. The PD type is of extensive concern and is preferred in large-scale plants. In this article, an innovative fluid switcher was presented and a two-cylinder hydraulic energy recovery unit with a lab-scale fluid switcher was set up. Tap water was used as the working medium instead of the actual seawater and brine in SWRO desalination plants. Under steady state operating conditions, the experimental results were obtained on the variations of the pressure and flow rate to and from the energy recovery unit. The hydraulic recovery efficiency （En） of the energy recovery unit with the fluid switcher reached up to 76.83%.     

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.     

Pilot experiences on the recovery of polluted reverse osmosis membranes

The recovery of Reverse Osmosis membranes, polluted by fouling, precipitations … etc., presents a triple interest: economical, strategical and of feasibility of the procedure in certain applications.The present work describes and analyzes the results obtained in a research project on the possibility of recovering polluted R.O. membranes. To carry out the research, a pilot plant and “industrial” membranes, i.e. of the dimensions and configurations in the market were used.     

Integration of reverse osmosis and membrane crystallization for sodium sulphate recovery

Reverse osmosis and membrane crystallization are evaluated in this work as stand-alone and integrated technologies for the recovery of Na₂SO₄ from aqueous solutions. When SO₂ is removed from flue gases by absorption in an aqueous solution and reacts with NaOH, a reusable product (i.e., Na₂SO₄) of industrial interest can be obtained.For stand-alone reverse osmosis, the effect of the concentration of the feed solution and pressure is studied. For membrane crystallization, the influence of the concentration and flow rate of the feed and osmotic solutions on the process performance has been determined. The characterization of the obtained crystals shows that Na₂SO₄·10H₂O is obtained. From the experimental results, the potential for integration of reverse osmosis and membrane crystallization is simulated. It was concluded that using a reverse osmosis unit prior to the membrane crystallization unit minimizes the total membrane area in comparison with the stand-alone processes.     

Seawater pretreatment by continuous sand filter for seawater RO (reverse osmosis) desalination plant

Sand filtration is conventionally applied to the preteatment of raw seawater in the RO desalination plant to maintain the seawater quality within the low SDI (Silt Density Index) level. However, the conventional fixed bed type has some difficulties of unstability of the filtrate quality in the backwash period and complicated operation sequence. In solving these difficulties, the applicability of the continuous sand filter has been studied with four years operation at Kure, Japan.The operational result shows that the filtrate is kept in the SDI level of four (4) which is applicable to the seawater RO desalination plant.This continuous sand filter has the advantage of stability, operation and energy saving as compared with the conventional batch type so that our developed continuous sand filter will improve plant economics for the seawater RO desalination plant.     

Effect of recovery on desalination of the black sea water by reverse osmosis

The effect of fresh water recovery was studied during Black Sea water RO desalination with cellulose acetate tubular membranes. Two different schemes of brine pretreatment before RO were investigated.It was shown that ultrafiltration can be applied as an effective alternative method for Black Sea water pretreatment. Up to 30% recovery, the product flux as well as the salt and the specific ionic rejection are all fairly stable. Special experiments showed that in a stable turbulent regime Ca ions removal from Black Sea water before RO with tubular membranes hold out no technological advantages.     

Techniques for achieving high recovery from saturated water sources using reverse osmosis membranes

In water-short areas of the world there is a premium for extracting the largest fraction possible of usable water from limited water supplies. Likewise in the elimination of wastewater through recycling, there is also a premium for maximizing the recovery of good water from the waste stream.Reverse osmosis membranes are being utilized to accomplish both of these functions. This paper will discuss several approaches for maximizing the fresh water recovery from saturated water sources using reverse osmosis membranes.     

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.     

反渗透浓缩液的再利用

介绍了反渗透浓缩液再利用的方法,综述了这些方法的原理、特点及应用,重点讨论了脱除反渗透浓缩液过饱和度进行回用以提高系统回收率的方法,以及膜蒸馏技术对浓缩液的回用处理、废水浓缩液处理及海水淡化浓缩液制盐,指出了反渗透浓缩液再利用在经济和环境上的必要性。     

Industrial wastewater treatment for reuse with reverse osmosis

This paper discusses the use of RO for industrial wastewater reclamation for its reuse. The performance of RO pilot plants processing several industrial wastewaters is outlined. The operating problems and pretreatment requirements are described. The potential benefits resulting from reusing wastewaters from selected industrial processes are shown.