SWRO System Research Articles

Impact of SWMM Fouling and Position on the Performance of SWRO Systems in Operating Conditions of Minimum SEC.

Due to water stress in the world in general desalination technologies are becoming increasingly important. Among the available technologies, reverse osmosis (RO) is the most widespread due to its reliability and efficiency compared to other technologies. The main weakness of RO is the loss of performance due to membrane fouling, which usually affects the water permeability coefficient (A), causing it to decrease. In RO desalination plants, fouling does not affect all spiral wound membrane modules (SWMMs) in the pressure vessels (PVs) in the same way. This will depend on the type of fouling and the position of the SWMM inside the PV. In this study, the impact of A and the position of the SWMM on the performance of the RO system is analyzed. For this purpose, decrements of up to 50% have been assumed for the seven SWMMs in series considering nine commercial SWMM models. The operating point analyzed is that which minimizes the specific energy consumption (SEC), a point obtained in a previous work carried out by the authors. The results show how the impact of A on the SWMM in the first position is more significant than the impact on modules that are in another position for the nine SWRO models studied. A drop of 50% in the coefficient A of the first element produces a permeate loss in the pressure pipe between 0.67 and 1.35 m3 d-1. Furthermore, it was observed that the models with the lowest coefficient A exhibited the highest performance losses in terms of permeate production when A was decreased.

Coupling of electromembrane processes with reverse osmosis for seawater desalination: Pilot plant demonstration and testing

Reverse osmosis (RO) is the most widespread technology to produce drinking water from seawater (SW). However, the integration of different membrane processes offers interesting alternatives. In this work, electromembrane processes were integrated with RO to desalinate real seawater in a pilot plant with 25 m3/day capacity. Electrodialysis (ED, either two-stage or single stage), shortcut reverse electrodialysis (scRED) and assisted reverse electrodialysis (ARED) pre-desalinated seawater before RO with the ED-ED-RO, ED-RO, and scRED-ARED-RO process schemes. Treated wastewater was used as salt sink in the scRED-ARED tests. The performance of the pilot plant can be summarized as follows: water recovery of ~27–51%, productivity of ~7–14 L/(m2 h) in the electromembrane processes and of ⁓19–31 L/(m2 h) in the RO process, energy consumption of 3.5–8.4 kWh/m3. The ED-RO configuration yielded the maximum productivity of the electromembrane step, while the scRED-ARED-RO integration reached the minimum energy consumption. Overall, the energy performance of the pilot plant (especially in the ED-RO and scRED-ARED-RO schemes) was comparable to that of a standalone SWRO system. The field tests demonstrated that the coupling of electromembrane processes with RO is feasible and suggest the possibility to develop alternative and competitive industrial pants for seawater desalination.

Development and experimental evaluation of an innovative self-boosting energy recovery device for small-scale SWRO system

Development and experimental evaluation of an innovative self-boosting energy recovery device for small-scale SWRO system

Aquatech designs SWRO system for detergent manufacturer in India

Aquatech designs SWRO system for detergent manufacturer in India

Study of energy recovery efficiency in a sliding vane pressure exchanger for a SWRO system

Study of energy recovery efficiency in a sliding vane pressure exchanger for a SWRO system

SWRO system performance optimization: part I – energy recovery devices Aly

SWRO system performance optimization: part I – energy recovery devices Aly

Seabed gallery intakes: Investigation of the water pretreatment effectiveness of the active layer using a long-term column experiment

Seabed gallery intake systems used for seawater reverse osmosis facilities employ the same principle of water treatment as slow sand filtration in freshwater systems. An investigation concerning the effectiveness of the active layer (top layer) in improving raw water quality was conducted by using a long-term bench-scale columns experiment. Two different media types, silica and carbonate sand, were tested in 1 m columns to evaluate the effectiveness of media type in terms of algae, bacteria, Natural Organic Matter (NOM) and Transparent Exopolymer Particles (TEP) removal over a period of 620 days. Nearly all algae in the silica sand column, 87% (σ = 0.04) of the bacteria, 59% (σ = 0.11) of the biopolymer fraction of NOM, 59% (σ = 0.16) of particulate and 32% (σ = 0.25) of colloidal TEP were removed during the last 330 days of the experiment. Total removal was observed in the carbonate sand column for algal concentration, while the bacterial removal was lower at 74% (σ = 0.08). Removal of biopolymers, particulate and colloidal TEP were higher in the carbonate column during the last 330 days with 72% (σ = 0.15), 66% (σ = 0.08) and 36% (σ = 0.12) removed for these organics respectively. Removal of these key organics through the 1 m thick column, representing the active layer, will likely reduce the rate of biofouling, reduce chemical usage and minimize operating cost in SWRO systems. The data show that the media will require several months at the beginning of operation to reach equilibrium so that high organic removal rates can be achieved. No development of a “schmutzdecke” layer occurred. The experimental results suggest that unlike freshwater slow sand filtration wherein most water treatment occurs in the upper 10 cm, in seawater systems treatment occurs throughout the full active layer depth of 1 m. The results of this study will help in designing and operating seabed gallery intake systems in varied geological conditions.

Performance Analysis of 20 Micron Self-cleaning Disc Filter Versus Cartridge Filters for RO Membrane Protection After Media Filtration in a SWRO System

Performance Analysis of 20 Micron Self-cleaning Disc Filter Versus Cartridge Filters for RO Membrane Protection After Media Filtration in a SWRO System

Pre-treatment with nanofiltration (NF) in seawater desalination—Preliminary integrated membrane tests in Urla, Turkey

In this study, the applicability of nanofiltration (NF) was investigated as a pre-treatment stage of reverse osmosis (RO) process for seawater desalination. The desalination performance of such integrated system was checked. Previously, NF (NF90 and NF270) and SWRO (SW30) membranes were used individually in the close-loop operation. Next, the NF permeate was collected using NF membrane by a continuous operation and then this permeate was used as a feed for a closed-loop SWRO system. The performances of single SWRO, NF and NF+RO integrated systems were compared in terms of permeate qualities and quantities. The results showed that permeate recovery of NF270 membrane was higher than that of NF90 membrane. However, the salt rejection of NF90 membrane was better than that of NF270. The single SW30–RO membrane showed an average rejection of 98.2% for salinity, while the permeate recovery value was only 28% at 55bar. Also the average permeate flux of single SW30–RO membrane was 30.1L/hm2. For the integrated system experiments, the highest permeate flux was found with NF90 (30bar)+SW30–RO (40bar) combination. Similar permeate flux values were obtained with single SW30–RO and NF90 (30bar)+SW30–RO (30) bar combination. The lowest permeate flux was found with NF270 (30bar)+SW30–RO (40bar) combination. Salinity was also highly rejected by all integrated system combinations. Permeate recovery values of integrated system combinations showed similar trend with permeate flux. Regarding permeate quality, it was seen that all integrated system combinations were better than single SW30–RO membrane. It was obtained that the permeate quality with NF90+SW30–RO combination was better than that with NF270+SW30–RO combination.

Realistic power and desalted water production costs in Qatar

Water security in Qatar is of main concern. Low water pricing in Qatar does reflect the real value of water. The high cost of desalted seawater (DW) calculated in this paper calls for the use of more energy efficient desalting system such as the SWRO system in place of the multistage flash (MSF) and multieffect thermal vapor compression (METVC) methods presently used. Both MSF and METVC use thermal energy of about 270 kJ/m3 and pumping energy of 2–4 kWh/m3. In this paper, the mechanical energy equivalent to the thermal energy supplied to the MSF (or METVC) systems is calculated. When added to the pumping energy, it gives the specific consumed energy of more than 20 kWh/m3, compared to 4–5 kWh/m3 for SWRO system. Qatar’s ground water (GW) is overexploited, depleted, and quality deteriorated, and thus the demand for DW is on the rise, with the more financial burden. Moreover, DW productions mean more air and marine environment deterioration. The water subsidization by the government should be reviewed, and water demand management should be applied. Wastewater should be treated for reuse to decrease the demand on both GW and DW. The calculated costs of DW at different natural gas price are calculated, and compared with the underestimated cost reported by the government.

Formation and speciation of haloacetic acids in seawater desalination using chlorine dioxide as disinfectant

To evaluate the formation potential of disinfection byproducts (DBPs) in a SWRO system when chlorine dioxide (ClO2) is used as a chemical disinfectant, the impact of principle precursors such as natural organic matter (NOM) and bromide ion on haloacetic acids (HAAs) formation and its speciation was investigated. In the presence of high bromide levels found in seawater, the active oxidizing agents formed by the action of ClO2 can react with NOM, resulting in halogenation reactions, and the production of brominated DBPs as the predominant byproducts. Elevating the initial levels of organic substances and bromide ions not only enhanced the total content of HAA5 formed, but also shifted the speciation of HAAs from the chlorinated to fully brominated forms at higher disinfectant doses and longer contact times of ClO2 disinfection. In addition, HAA5 formation potential increased in the order of transphilic>hydrophobic>hydrophilic NOM, suggesting HAA5 yield formed during ClO2 disinfection significantly depends on the characteristics of NOM that can lead to different speciation distribution of DBPs. However, at high doses of ClO2, it was observed that the disinfectant dose plays a more important role in speciation distribution of HAA5 than the characteristics of organic precursors.

A Dynamic Optimization Strategy for the Operation of Large Scale Seawater Reverses Osmosis System

In this work, an efficient strategy was proposed for efficient solution of the dynamic model of SWRO system. Since the dynamic model is formulated by a set of differential-algebraic equations, simultaneous strategies based on collocations on finite element were used to transform the DAOP into large scale nonlinear programming problem named Opt2. Then, simulation of RO process and storage tanks was carried element by element and step by step with fixed control variables. All the obtained values of these variables then were used as the initial value for the optimal solution of SWRO system. Finally, in order to accelerate the computing efficiency and at the same time to keep enough accuracy for the solution of Opt2, a simple but efficient finite element refinement rule was used to reduce the scale of Opt2. The proposed strategy was applied to a large scale SWRO system with 8 RO plants and 4 storage tanks as case study. Computing result shows that the proposed strategy is quite effective for optimal operation of the large scale SWRO system; the optimal problem can be successfully solved within decades of iterations and several minutes when load and other operating parameters fluctuate.

Demonstration of an energy recovery device well suited for modular community-based seawater desalination systems: Result of Danfoss iSAVE 21 testing

The option of building smaller, decentralized plants is more feasible now that HP pumps and energy recovery devices (ERD) are available for use in small-scale seawater desalination plants with efficiencies comparable to those typically associated with larger plants. A demonstration SWRO system producing 125 cubic meters of product water per day was designed and commissioned utilizing the Danfoss iSave 21 energy recovery device. The desalination subsystem utilizes an inter-staged membrane configuration, low flux, and low recovery design to reduce specific energy consumption, fouling potential, and membrane cleaning requirements. Test results show that a specific energy consumption lower than 2 kWh/m3 is easily achievable utilizing standard components, and that the improved second-generation iSave 21 unit has significantly lower lubrication flows than the previous model.

Power generation with salinity gradient by pressure retarded osmosis using concentrated brine from SWRO system and treated sewage as pure water

Salinity power generation using hollow fiber modules was examined using the pressure-retarded osmosis (PRO) system between pure water and concentrated brine. Pure water and concentrated brine were supplied from a regional sewage treatment facility and sea water desalination (sea water reverse osmosis [SWRO]) plant. To minimize the effect of the concentration polarization near the membrane surface on the pure water side, the number of open ports in the module was increased from 3 to 4 and that modification was found to be effective because non-permeating pure water, which left the module through fourth port, flushed leaked salt from the brine side through the membrane. Our prototype PRO plant got the maximum output power density, 7.7 W/m2 at a 2.5 MPa hydraulic pressure difference and a 38% permeation of pure water into the brine. To remove the organic foulant in the pure water, a low pressure Reverse Osmosis (RO) membrane and coagulation–sedimentation method with ozonation showed good results. However, the pressure drop across the RO membrane itself and cost concerns have not yet been solved. Based on the pure water’s flow simulation, the hollow fiber element was found not to effectively work if the module and element for the SWRO were used without modification because the flow pattern of pure water and brine inside the module and element during the PRO operation was different from that during the RO operation.

The Unexpected Performance of Highly Permeable SWRO Membranes at High Temperatures

In recent years, the development of new seawater reverse osmosis elements has focused on maximizing membrane area and membrane permeability. Such developments led to a new generation of SWRO elements with significantly increased permeate flows and lower pressures. When tested at the same pressures and temperatures, today’s membranes produce nearly twice as much permeate compared to SWRO membranes from ten years ago and compared to today’s tighter, higher rejecting SWRO membranes. Utilizing the highly permeable membranes leads to lower energy consumption and lower operating cost for the SWRO plants. Membrane permeability is further increased with increasing feed water temperature. As temperature increases, the membrane structure is affected and seawater viscosity decreases. This leads to a further reduction in energy consumption and operating cost. While permeability of the membrane increases with increasing temperature, the seawater osmotic pressure is also increasing. At temperatures above 25 C, osmotic pressure is more sensitive to temperature changes than membrane permeability. This leads to the diminishing influence of permeability and the increasing influence of osmotic pressure on the system feed pressure. In some situations, the net effect leads to very little change in feed pressure as temperature increases above 25C. This paper will review the theory behind the competing influences of membrane permeability and osmotic pressure on overall feed pressure. The paper will demonstrate how the evolution of the SWRO permeability has resulted in the increasing influence of osmotic pressure on the membrane performance. The theoretical results will be supported with actual membrane tests performed in the laboratory and on a pilot unit. The paper will identify the temperature ranges and the membrane permeabilities that have the least and greatest influence on the operating cost of an SWRO system.

Integrated pressure and flow control in SWRO with a HEMI turbo booster

The high pressure hydraulic energy management integration (HP-HEMI) energy recovery device (ERD) centralizes brine hydraulic energy recovery, feed pressure and flow control and brine pressure and flow control into one compact and fully integrated unit. The objective is to dispense with feed pressure control valves (i.e. elimination of throttling losses) as well as a variable frequency drive (VFD) on the high pressure feed pump (HPP) resulting in the twin benefits of a substantial reduction in energy consumption and capital costs. This paper reports on test results of a production HP-HEMI coping with recoveries and pressures that accurately simulate an SWRO system dealing with typical feed temperature and membrane fouling variations. The paper further reports on development of a PLC control scheme that regulates feed flow and brine flow via adjustment of the HP-HEMI control features to meet a wide variety of membrane operating conditions. The paper also outlines future research concerning mitigation of equipment failure and further enhancements of system control.

Technical and Economic Analysis for a Med System and Hybrid Med-ro Desalination in Chp Plant

Effective integration of membrane/thermal desalination and power technology can improve the performance of thermal desalination and reduce the cost of desalted water. In this paper two study cases with different configuration desalination processes are considered and compared. This comparison is performed using THERMOFLEX software. The first case is a 25 MW gas turbine engine that is coupled with a MED_TVC thermal desalination plant and for the second one a hybrid desalination system is coupled with the mentioned gas turbine. For the hybrid process proposed to feed the MED unit with brine discharge of SWRO system. The operation of the hybrid configuration was simulated, the technical and economical results calculated and compared with those that could be achieved by an equivalent MED-TVC system. The main target of this analysis is to improve performance of MED-TVC desalination process by changing its feed water flow pressure, as well as to determine the changes in unit product cost of the desalinated water compared with MED-TVC product cost.

The effects of feed water de-gassing on the permeate flux of a small scale SWRO pilot plant

The effects of pressure release on feed water cavitation have been studied using a small pilot scale SWRO system. The presence of dissolved atmospheric gases in seawater leads to a potential for cavitation within the porous membranes used in high pressure processes. The rapid application and release of applied pressures in the range of 10–60 atm was found to cause visible cavitation throughout the bulk solution phase. This phenomenon was not related to increased gas solubility under the applied pressure, since no additional gases were allowed into the system. It was found that almost complete removal of the initial dissolved atmospheric gases prevented this cavitation. Earlier laboratory scale studies had reported that removal of cavitation by feed water de-gassing enhanced permeate flow rates by 3–5% but this level of improvement was not observed in the pilot scale study operating at an applied pressure of 38 atm with seawater feed. It is possible that larger effects may be observed with the use of more ...

A comparative study for boron removal from seawater by two types of polyamide thin film composite SWRO membranes

In this paper, field performance of a small-scale seawater reverse osmosis unit installed in Urla Bay-Izmir, Turkey was analyzed and presented. The design of SWRO system in Urla consists of two types of FilmTec polyamide thin film composite spiral wound seawater reverse osmosis membranes (high rejection FILMTEC XUS SW30XHR-2540 RO membrane and FILMTEC SW30-2540 RO membrane) which could be operated in parallel. To make a comparative study between two types of membranes regarding their desalination performances and boron rejections, each membrane was operated individually for each set of experiments. This comparison was made via investigation of the effects of feed seawater temperature (10–16 °C), operating pressure (55, 60 and 62 bar), and pH adjustment on the feed side (pH 7.0–7.5).

Effect of chlorine and acid injection on hollow fiber RO for SWRO

Bio-fouling results in deterioration of permeate quality and flux in reverse osmosis (RO) process. Cellulose triacetate hollow fiber membrane used for RO in SWRO has anti-chlorine property that makes technical sense compared to polyamide spiral-wound RO for overcoming bio-fouling. Mode of chlorine injection is the controlling factor of sterilization in SWRO system. This work evaluated the effects of five different modes of chlorine injecting system as well as HCl injection on the performance of HF RO system. In addition, effects of HCl and anti-scalants on anti-scale performance of HF RO system were also investigated, respectively. A brief list of chemical costs under different abovementioned operating conditions was covered in a cost analysis. The results indicated that the injecting mode that employed continuous chlorine with a relatively low concentration of 0.3–0.4 mg/L at pH 5.8–6.2 was preferable in the aspects of total bacterial count (TBC) removal, permeate flow rate, differential pressure, permeability ( P p ), performance factor (η) and chemical costs. HCl injection could improve the sterilization and prevent scaling on the membrane surface efficiently. The expense of anti-scalant (MDC220) was higher than HCl.