Pass Reverse Osmosis Research Articles

Recovery optimization of membrane processes for treatment of produced water with high silica content

Disc tube (DT) and spiral wound (SW) configurations of nanofiltration (NF) and reverse osmosis (RO) processes were tested at pilot-scale using a two-pass configuration to treat produced water obtained from natural gas wells. First pass NF membranes were used to remove divalent cations from produced water. Permeate from the first pass NF membranes were used as feed to second pass RO membranes after increasing the pH to 10.0 to enhance silica solubility. To reduce the fouling potential on NF and RO membranes dissolved air floatation (DAF), ceramic ultrafiltration (UF), MYCELX cartridges, and organoclay filters were tested as pretreatment alternatives. Pretreatment processes were effective for turbidity and oil and grease removal but were not efficient in retaining organic matter, primarily protein-like and polysaccharide-like material, which eventually fouled the first pass NF membranes. The second pass RO membranes were scaled predominantly by silica. The overall feed water recovery of the two-pass NF-RO s...

Split partial second pass design for SWRO plants

All over the world, the reverse osmosis (RO) desalination plants are providing populations and industries with high quality freshwater. There are various requirements on water quality produced by RO desalination plants depending on final purpose of water usage. In recent years, the requirement for low Boron concentrations in RO permeate was the main parameter to be considered in designing many seawater RO systems. Beside the development of new RO membranes with improved Boron rejection, there are also other design options which can help to achieve required product quality. One of such options is also Split Partial Second Pass (SPSP) RO design. The principle of a SPSP design is based on the fact, that front elements in RO pressure vessel are always producing better permeate quality than elements at the back of the pressure vessel. In order to take advantage of better permeate quality at the front of the vessel in SPSP design, permeate is collected from both sides of the pressure vessel. Low TDS front permeate is than sent directly to final product line, while higher TDS back permeate is treated by partial second pass RO plant. At the end of the process, both permeate streams are blended together to create the final product of required quality. The SPSP design allows to select the right ratio between front and back permeate in order to obtain final product of required quality in terms of Boron, TDS and other quality parameters. The SPSP design provides cost effective option by minimizing the size of the second pass RO, which allows substantial savings on capital investments aswell as in operating cost of the plant. This paper will present in more details the SPSP design option and requirements, the important parameters influencing SPSP design and different ways of the control, and finally it will discuss benefits and savings resulting from this RO design option. It will also present actual operating data from seawater RO plant using this design option.

Enhancing boron rejection in seawater reverse osmosis facilities

Linked to potential health problems and toxicity to crops, boron is present in seawater at concentrations of ranging from 4 to 7 mg/L, and not readily removed by reverse osmosis technology. Commercially available seawater reverse osmosis (SWRO) membranes possess a wide range of rejection characteristics for boron in seawater under ambient temperature and pH, ranging from approximately 50% for low-energy membranes to greater than 90% for the newest high rejection membranes. This level of rejection is typically insufficient to reduce boron concentrations in natural seawater to less than recommended levels. Current World Health Organization (WHO) drinking water concentrations for boron are limited to 0.5-mg/L. Two techniques utilized to mitigate boron concentrations are (1) increasing the dissociation of boric acid by increasing pH prior to SWRO; and, (2) utilizing a second pass reverse osmosis system, potentially coupled with pH adjustment. Utilizing these techniques, the authors tested commercially available SWRO membranes from three different manufacturers utilizing feed water alkalization, coupled with a second pass system. Utilizing feed water alkalization alone, the authors found that all three SWRO membranes were able to produce permeate complying with WHO regulations. Using second pass RO, a boron concentration of less than 0.5 mg/L was achieved for feed pH greater than 6, and less than 0.1-mg/L for pH of 10.

Discussion of silica speciation, fouling, control and maximum reduction

In the production of ultrapure water for the power and microelectronics industries, multiple pass reverse osmosis (RO) process is commonly the major step in the reduction of dissolved and suspended matter before polishing by ion exchange and other methods to attain the high purity requirements. With the diverse location of power plants and microelectronic manufacturing facilities around the world, silica concentrations in source waters can range between 1 and 60 ppm (mg/L) to even 300 ppm in some volcanic regions. High pressure steam generators and fine microelectronic structures now require water containing less than 1 ppb (ug/L) concentrations of silica. In designing purification processes, silica has presented issues not only as formidable challenges in many locations as RO membrane foulants, as well as a contaminant requiring efficient removal. Analyses of RO membrane foulants and correlation with water chemistry in the course of trouble-shooting numerous RO processes continues to offer us opportunities to understand silica chemistry, the patterns of silica fouling and methods by which we can chemically control the RO process. Such understanding is applicable to the operation of ion-exchange resin beds as well. In this paper we review the speciation of silica in feedwaters, and chemical approaches to controlling fouling and maximizing silica reduction. Silica and silicates are addressed in the three categories of reactive soluble, non-reactive soluble (colloidal, not filterable) and non-reactive insoluble (particulate, filterable) forms. A brief review of geochemistry, the chemical and biochemical dissolution and deposition of silica and silicates in nature is provided for insights and understanding of natural processes that can be applied to the task of process design and control in silica removal from water.

Application of low pressure nanofiltration membranes for the recovery and reuse of dairy industry effluents

This paper outlines the requirements for water reuse of dairy industry treatment plant effluents. Two alternative membrane processes are described. Nanofiltration (NF) membranes were applied to the existing treatment plant effluents in the first part of the study. NF membranes were used in different operating conditions. Successive batch runs had shown that serious membrane fouling appeared not to be a problem with treatment plant effluents. Excellent rejections have been achieved. It will be possible to recover approximately 90% of the treatment plant effluent for reuse. Heavy metal removal was also very high. In the second part of the study, two pass reverse osmosis (RO) membranes were applied to the raw wastewater of the dairy industry. RO experiments demonstrated that two-pass RO produce permeate of very good quality. Almost complete COD removals were achieved and flux values decreased slightly during the each RO run.

Design and operation of 800,000 gpd reverse osmosis seawater system

The paper will review the design and operation of the 800,000 gpd reverse osmosis seawater system installed at the Punta Moron Station, of the C.A. de Administration y Fomento Electrico (CADAFE) of Venezuela. The plant will produce potable and boiler feed water for the utility. The specific areas discussed will be as follows: Pretreatment The design and operation of the Permutit Seawater Pretreatment system producing an influent to the membrane system with an SDI less than 3, will be described. Membrane System The B-10 Seawater Membrane system will be reviewed as to design and operation, with particular emphasis on the process and control features necessary to provide low maintenance operation. Brackish Water System p]The secondary brackish water B-9 system treating the influent from the seawater unit will be reviewed as to design and operation with particular emphasis on its ability to produce low TDS water for the demineralizers providing boiler feed water for the utility. The paper will outline data and the general experience with the operation of a large Reverse Osmosis Seawater plant. In addition, the integration of the brackish and seawater units into a single system will be reviewed. Operating costs will be outlined and the general question of Reverse Osmosis Seawater plant operation will be discuessed. The impact of the successful operation of this first single pass Reverse Osmosis Seawater System on the future of desalting technology will be evaluated.

Design parameters and operation of small, and medium size municipal reverse osmosis North America

The design, construction and operation of 1,000 to 250,000 gallon per day reverse osmosis systems requires a different approach than larger multi-million gallon per day systems. Smaller modular units are based on actual proven installations. The units are pre-engineexed, and factory tested in their entirety. The unit concept of reverse osmosis design allows for more reliable systems, easily and quickly installed, with a minimum of operation and maintenance attention. Small and medium size reverse osmosis systems have been running for many years. A seawater single pass reverse osmosis system has been producing potable water for over 18 months with little operator attention and maintenance. Construction and operation of small and medium size municipal reverse osmosis systems present some unique areas of consideration which differentiates these units from much larger installations. By small and medium we mean from 1000 gallons to 250,000 gallons per day capacities. The ultimate objectives of any water treating system is to obtain the quality and quantity of water desired with a minimum of operating effort and maintenance. In general, where dissolved solids are to be removed from a feedwater source, reverse osmosis is presently recognized as the most efficient method available. Large reverse osmosis systems are usually engineered on an individual basis to meet the users needs and, include on-site analysis of the raw feedwater and climate conditions. In addition, engineering consultants as well as the ultimate customers preferences need to be considered. Large quantities of time are consumed in the initial engineering, preparation of drawings and design changes. Equipment housing facilities need to be designed around the type of system selected and engineered separately. Large amounts of time are used in the construction of the system components. Membrane racks are erected individually with membranes shipped separately. Large amounts of piping needs to be cut and installed on-site. High pressure pumps, membrane cleaning systems, electrical controls and pretreatment equipment are separately built, shipped individually, and assembled on location.

Institute of African research and studies, Cairo University

Recently, the rapid worldwide growth of seawater reverse osmosis (SWRO) desalination capacity has reignited the boron removal challenge in drinking water. The objective of this review is to discuss the recent advances and patents in boron mitigation strategies in SWRO systems, and to present the energy and environmental concerns of SWRO desalination system with boron rejection. First, the operating parameters of SWRO systems that affect boron removal are presented, before we discuss the reported findings and patents of boron control improvement from the standpoint of membrane materials advancement and from the development of various configurations, such as double pass reverse osmosis and hybrid SWRO processes with other separation technologies like ion exchange (IX), nanofiltration (NF), and electrodeionization (EDI). Thereafter, issues over SWRO desalination’s detrimental environmental impact are reviewed: thus, seawater intake, brine discharge, and energy consumption constitute the main weaknesses. Then, sustainable solutions are proposed to reduce the environmental burdens. As SWRO desalination is an energy intensive process, exergy analysis emerges as a key tool to assess the performance of this process. Therefore, the use of exergy analysis to SWRO desalination in general and, as an example, to a full-scale SWRO desalination plant located in Spain, are discussed. The findings indicate that the SWRO unit is responsible for over 64% of exergy destruction due to the irreversibilities associated with the large pressure drop and the high salinity of the brine.