Performance Of Reverse Osmosis Plants Research Articles

Detailed analysis of reverse osmosis systems in hot climate conditions

Hot climate countries require large amounts of desalinated water. The Reverse osmosis (RO) technique is currently considered the most reliable technique for brackish water and seawater desalination. However, its power consumption is considerably higher than all other techniques. Therefore, the present study investigates the performance of reverse osmosis plants in hot climate conditions. A typical Reverse osmosis system was designed, constructed and investigated. The ROSA software was also used for the analysis of seven different membrane elements. The experimental data were utilized in order to validate the simulation results of the ROSA software. A variance-based sensitivity analysis was performed in order to define the most effective design and operating parameters. The present investigation shows that the tap and brackish water membrane elements are more sensitive to the feed water temperature rather than the feed water pressure and concentration. Meanwhile, seawater membrane elements are more affected by the feed concentration. The detailed investigation of the different membrane elements shows that wastewater reclamation using reverse osmosis technology could be a significant source of low-cost fresh water for hot climate countries.

Optimization of membrane elements’ array in industrial reverse osmosis units

It is stated that membrane elements, due to axial concentration and flow exhaustion during filtration, work in different operation conditions that differ according to various characteristics. Designing of multistage units is based on technical characteristics' identity of all membrane elements. It is explored that the difference in individual characteristics of membrane elements can take place. This can essentially affect the operation characteristics of a whole industrial unit. Particularly, it could lead to degradation of the permeate quality and the unit performance. Research on packaging the membrane elements in reverse osmosis units has shown that a simple replacement of membrane elements without the consideration of the individual characteristics can degrade the performance characteristics and affect the constancy of the unit operation. An optimization system of membrane elements’ array was suggested to solve these problems and to upgrade the performance of reverse osmosis plants. The first step of the system is determination of individual characteristics of membrane elements. For the calculations using the individualized data, it is suggested to use the method of approximate calculation and the balance equations for water flows (source water, permeate, and retentate), and for the concentrations of the dissolved solids. The suggested optimization system of a membrane elements’ array allowed the configuration of the membrane elements in the housings of one stage in such a way that the symmetry of the flows and of the pressure difference was achieved. The optimum value of the performance and the selectivity was achieved considering the hydraulic characteristics in one stage.

Control of severe membrane silica scaling: investigation and trouble shooting

Reverse osmosis (RO) continues to develop into an important means for water purification. The increase in RO applications has forced many projects to contend with water sources containing higher levels of sparingly soluble minerals. In many parts of the world, membrane silica scaling is becoming a limiting parameter for the design and operation of RO systems using brackish feed water. Located in the northeast of China and established since 2009, the LiaoNing Panjing power company is the only energy supplier of the Panjing Lioabin economic zone (400 km2). The power generation requires demineralized water coming from the power plant water treatment facility, which consists of a primary filtration step followed by RO trains and ion exchange resins. At the end of 2011, the RO plant performance severely dropped—normalized flux declined by 50%—indicating an occurrence of fouling or scaling on the membranes. Membrane autopsies have shown evidence of silica scales resulting from high levels of silica (50 ppm) in the feed water. This paper describes the investigation and troubleshooting processes used to restore membrane performance. The process utilized thorough scientific analysis, deposit removal via very efficient proprietary membrane cleaners, and dosing a novel antiscalant developed specifically to reduce silica deposition on RO membranes. To date, the chemical-based solution used to curb scaling has been effective in ensuring smooth operation of the membranes in the power plant water treatment facility.

Experience with integrated ultrafiltration/reverse osmosis systems in industrial applications in Spain

Abstract While fresh water resources are increasingly limited, efforts are taken aiming at a more efficient use of those resources and the value of water reuse, not only due to environmental but also due to economic aspects. This is especially true for the industrial sector, with a high potential to save water by reuse. This is expected to be even more critical in the coming future as the price of the water increases and the access to good quality water sources near the industries decreases. Reverse osmosis (RO) technology has been used in the industrial sector for decades for various purposes such as softening, ultra pure water production, or water reuse. But like in other applications such as desalination, in industrial applications, membrane fouling remains as one of the main causes for poor RO plant performance. This implies frequent downtime for cleaning and maintenance and shorter membrane life time, leading to significant operational costs. Therefore, the selection of a proper pretreatment is essential to produce a high quality feed water for the RO system in order to ensure a more sustainable and reliable operation. In the past decades, ultrafiltration (UF) has become more popular for RO pretreatment in the municipal and lately in the industrial sector too. Ultrafiltrate water is virtually free of particles, colloids, and suspended solids. Therefore, plugging of RO feed channels is minimized and the RO cleaning frequency can be noticeably reduced. In comparison with conventional filtration (e.g. sand filtration), UF requires significantly lower footprint, produces a higher and more consistent water quality regardless of variations in the feed quality, and usually needs less power and chemicals. This paper will review the design and operational data of a number of successful full-scale integrated membrane systems (UF followed by RO) installed in different types of industries and treating diverse water sources.

Enhancing permeate flux in a RO plant by controlling membrane fouling

Concentration polarization near the membrane surface increases local trans-membrane osmotic pressure and solute passage. It is governed by solute properties, membrane properties and hydrodynamics. Increasing the feed velocity confines the affected area to a thinner layer and usually results in reducing membrane fouling and scaling phenomena. Higher feed velocity reduces scaling and fouling. The results of fouling control by changing softening process from lime to caustic regime have been outlined in this work in the reverse osmosis (RO) units that treat brackish water for producing 400 m 3/h industrial water. Performances of these RO units were not satisfactory for many months due to high tendency in membrane fouling even following the recommendations of membrane supplier. Therefore, a new softening method has been applied successfully for enhancing the RO plant performance. This improvement in performance of RO units clearly justifies the importance of softening regime as a key parameter in fouling control.

Early discovery of RO membrane fouling and real-time monitoring of plant performance for optimizing cost of water

RO plant operators, end-users, membrane manufacturers and system suppliers have been facing two major problems since the advent of commercial membrane technology applications for water desalination utilizing reverse osmosis (RO) and other membrane processes: how to reliably monitor their membrane system performance and how to detect membrane fouling and scaling development in real time and before significant or irreversible loss of performance efficiency occurs, resulting in lower plant availability and significantly higher OM costs. The current industry-standard performance analysis and evaluation technique is based on trending RO flux decline characteristics of membranes via normalizing system operating data in accordance with ASTM D-4516 standard method. This paper discusses the shortfalls of this technique, and introduces a practical new technology for measuring and monitoring membrane fouling and flux performance in real-time. The new Silent Alarm™ technology, designed as an early-warning system, allows the discovery of any fouling or scaling development on the RO membranes in the very early stages, thus providing a valuable tool for the plant operator to take immediate corrective measures before it is too late. Two major brackish and seawater Arabian Gulf RO plant case studies with and without a fouling history are discussed. This proven capability to monitor RO plant performance in real-time and measure the actual development of any membrane fouling or scaling very early on has a direct and dramatic positive impact on optimizing the total cost of desalinated water.

Early discovery of RO membrane fouling and real-time monitoring of plant performance for optimizing cost of water

RO plant operators, end-users, membrane manufacturers and system suppliers have been facing two major problems since the advent of commercial membrane technology applications for water desalination utilizing reverse osmosis (RO) and other membrane processes: how to reliably monitor their membrane system performance and how to detect membrane fouling and scaling development in real time and before significant or irreversible loss of performance efficiency occurs, resulting in lower plant availability and significantly higher OM costs. The current industry-standard performance analysis and evaluation technique is based on trending RO flux decline characteristics of membranes via normalizing system operating data in accordance with ASTM D-4516 standard method. This paper discusses the shortfalls of this technique, and introduces a practical new technology for measuring and monitoring membrane fouling and flux performance in real-time. The new Silent Alarm™ technology, designed as an early-warning system, allows the discovery of any fouling or scaling development on the RO membranes in the very early stages, thus providing a valuable tool for the plant operator to take immediate corrective measures before it is too late. Two major brackish and seawater Arabian Gulf RO plant case studies with and without a fouling history are discussed. This proven capability to monitor RO plant performance in real-time and measure the actual development of any membrane fouling or scaling very early on has a direct and dramatic positive impact on optimizing the total cost of desalinated water.

Effect of different operation pressures for various membranes on the performance of RO plants

The aim was to study the effect of different operation pressures on the performance of reverse osmosis (RO) plants for various types of membranes. The study was conducted in a pilot plant at the University of Basrah, College of Engineering, which has a capacity of 9 m 3/h. The plant is comprised of two parallel vessels containing five elements for each vessel, 8″ in diameter and 40″ in length. The first vessel has Saehane membranes, type RE8040BE-400 ft 2 manufactured in South Korea. Koch membranes, type 8822-XR-365 ft 2 made in the US, were used in the second vessel. The pilot plant uses brackish water from the Tigris River with TDS <600 ppm. The new type of RO membranes (Saehane) were used for the first trial for production of desalted water from brackish water less than 600 ppm and the results were compared with performance of the Koch membranes. It was found that over 180 days of continuous operation, the amount of permeate for Saehane membranes is larger than Koch membranes by about 26%. It was also observed that the quality of permeate water stream for Koch membranes is less than for the Saehane membranes by about 11%.

Improve RO system performance and reduce operating cost with FILMTEC fouling-resistant (FR) elements

A new generation of chemically modified, FILMTEC thin-film composite, aromatic polyamide membrane elements has been introduced that exhibits reduced rates for bacterial adhesion, longer induction periods before biofilm start developing, and extended operating times between chemical cleanings. When these biofouling-resistant (FR) elements are coupled with the optimized use of selected biocides to prevent biofilm growth, a significant reduction in chemical cleaning frequency is achieved. This paper reviews biofouling in membrane systems and describes the development of the FR elements through full-scale field trials over about 3 years, focusing in the improvement achieved in mitigating the negative effects of biofouling on the performance of reverse osmosis plants. Some economic guidelines are given to estimate the potential value of FR technology.

The application of a novel chemical treatment program to mitigate scaling and fouling in reverse osmosis units

The principal cause of reverse osmosis (RO) system failures is membrane fouling, which results from the accumulation of water-formed or water-borne deposits that impede the flow of fluid and increase the pressure differential across a membrane. Anti-scalant chemicals have been used for many years in RO units to minimize fouling, prevent scaling, and improve RO plant performance. The conventional method for controlling scale formation on membranes involves addition of sulfuric acid and a scale inhibitor to the feed water. However, the desire for improved chemical treatment programs to prevent scaling and fouling in RO units brought Saudi Aramco and Specialty Chemical Suppliers together. The challenge to produce a chemical treatment program that was simpler, safer, and more economical than the traditional sulfuric acid treatment and a scale inhibitor was identified as a mutual goal. This paper presents the results of intensive trials conducted by Saudi Aramco and the chemical suppliers to evaluate commercially available chemical formulations.

An approximate analytical solution for the performance of reverse osmosis plants

Recent developments in membrane technology and appropriate construction material made reverse osmosis plant attractive for large desalting capacity. Reserve osmosis showed a growing demand specially in sea water desalting. It can be considered the optimum process in areas where sufficient electric power is available at low cost. Due to these reasons, mathematical modeling of reverse osmosis plants became an important task in the design procedure. In this paper, the partial differential equations representing the material and momentum balances inside a hollow fine fiber reverse osmosis model are discretized by the method of orthogonal collocation. The approximate analytical solution is obtained by applying the one point collocation method in the radial and axial direction. This leads to simple expressions for the recovery and product concentration. The obtained expressions are compared by the more exact results obtained by using higher order collocation method. The applicability of these results to the design and operation of reserve osmosis plants will be disucssed.

Calculation of the expected performance of reverse osmosis plants

The designer of a reverse osmosis plant must forecast the brine and product stream concentrations from the membrane salt rejection and the ratio of product to feed flows (product recovery). this paper reviews the derivation of equations which predict these concentrations, and furthermore, yield an average feed stream concentration between feed and brine which allows the forecasting of plant productivity at high recoveries. The derived equations are contrasted with other less accurate equations which have been used in the industry.