Closed Circuit Desalination Research Articles

Energy, exergy and exergoeconomic (3E) analysis and multi-objective optimization of a closed-circuit desalination system with side-conduit

Membrane desalination technologies such as reverse osmosis (RO) are being widely used around the world to deal with the growing freshwater shortage. In addition, the use of new reverse osmosis technologies that improve the performance of traditional ones, has received more attention. The main problem in desalination plants is the high total specific energy consumption as well as high capital investment, maintenance and repair costs. In this study, the performance of a new closed-circuit reverse osmosis (CCRO) desalination system with side-conduit as a replacement for energy recovery device, is investigated based on energy, exergy and exergoeconomic (3E) analysis. 3E analysis is performed based on four important factors including 1) concentration of inlet feed water 2) number of cycles 3) osmotic pressure 4) mass flow rate of feed water. Then, using the output data obtained from 3E analysis, the optimal points for six key parameters of exergy efficiency, net driving pressure (NDP), total unit cost product (SUCP), mass flow rate of permeate, recovery ratio and specific energy are determined through multi-objective optimization. The simulation results show that in the proposed system, by increasing the number of cycles, the recovery ratio increases while the system costs also increase due to increase in pressure and concentration of inlet feed. It is found that the optimal recovery ratio of 64.29% is obtained for 9th cycle and inlet feed concentration of 6.95% and the optimal specific energy consumption of 2.5 kWh/m3 is obtained for 7th cycle and inlet feed concentration of 6.07%.

Closed circuit desalination of O&G produced water: An evaluation of NF/RO performance and integrity

Reclamation and reuse of oil and gas (O&G) waste streams is being considered as an option to alleviate stress on freshwater supplies. While limited treatment is necessary to reuse O&G wastewater (e.g., produced water (PW)) for subsequent hydraulic fracturing, high removal of organic matter and total dissolved solids (TDS) is needed to enable broader reuse (e.g., irrigation, stream flow augmentation). This study focused on the use of closed circuit desalination with nanofiltration (NF) and reverse osmosis (RO) to remove TDS and organic matter from pretreated PW. The performance and fouling propensity of three commercial NF and RO membranes was compared during the concentration of ~900 feed batches (440 h). Up to 99.6% TDS and 89% dissolved organic carbon (DOC) was removed, producing high quality permeate. Membrane characterization revealed minimal scaling and organic fouling of the three membranes, suggesting that closed circuit desalination (CCD) might be a promising method to facilitate reuse of PW.

CCD Series no-24: closed circuit desalination compared with plug flow desalination processes of partial concentrate recycling in identical four-element modules

AbstractIn light of the growing emphasis of the desalination industry on high recovery low energy processes to save water and energy with reduced needs for handling of brine effluents, the present study evaluates the prospects of reaching such objectives with plug flow desalination (PFD) techniques of internal/external partial concentrate recycling (PCR) and closed circuit desalination (CCD) of complete concentrate recycling. Comparison between the cited RO techniques is demonstrated by means of a versatile theoretical model database which addresses the unit configuration, module design, elements’ specifications, module recovery, degree of PCR, flow rates, and other pertinent parameters which contribute to trustworthy model results. A comprehensive comparative model analysis of CCD and PFD–PCR with identical four-element modules under the same module recovery, concentration polarization, and initial flow rate conditions revealed that CCD is by far the best process to achieve high recovery with exceptional...

A desalination system with efficiency approaching the theoretical limits

The objective of this project is to design a new desalination system with energy efficiency approaching the theoretical thermodynamic limit—even at high recovery ratio. The system uses reverse osmosis (RO) and a batch principle of operation to overcome the problem of concentration factor which prevents continuous-flow RO systems from ever reaching this limit and thus achieving the minimum possible specific energy consumption, SEC. Batch operation comprises a cycle in three phases: pressurisation, purge, and refill. Energy recovery is inherent to the design. Unlike in closed-circuit desalination (CCD), no feedwater is added to the pressure circuit during the pressurisation phase. The batch configuration is compared to standard configurations such as continuous single-stage RO (with energy recovery) and CCD. Theoretical analysis has shown that the new system is able to use 33% less energy than CCD at a recovery ratio of 80%. A prototype has been constructed using readily available parts and tested with feedwater salinities and recovery ratios ranging from 2,000 to 5,000 ppm and 17.2–70.6%, respectively. Results compare very well against the standard configurations. For example, with feedwater containing 5,000 ppm NaCl and recovery ratio of 69%, a hydraulic SEC of 0.31 kWh/m3 was obtained—better than the minimum theoretically possible with a single-stage continuous flow system with energy recovery device.

CCD series no-22: Recent advances in RO, FO and PRO and their hybrid applications for high recovery desalination of treated sewage effluents

The performance of the osmotic-pressure RO, FO and PRO processes is analyzed on the basis of a uniformed model with water flux derived from the modified conventional expression Jw=β∗A∗(Δπ−Δp) where β (<1.0) stands for the FO actual/ideal flux ratio of a given membrane in a defined salinity gradient and also applies to PRO; whereas β=1.0 applies to RO membranes. The β parameter takes account of the detrimental effects on flux in FO and PRO membranes and becomes unity for RO membranes. The uniformed model is explored to evaluate the various aspects of RO, FO and PRO and some of their FO–RO and PRO–RO hybrids, with emphasis on advanced closed circuit desalination RO (CCD) and PRO (CC-PRO) techniques and widespread feed sources such as treated sewage effluent (TSE) and seawater (SW) or seawater brine (SWB) from SWRO desalination plants. The results of this comparative study reveal that the desalination of SW and TSE with CCD proceeds with low energy of near absolute energy conversion efficiency at the ultimate state-of-the-art, unattainable by the conventional techniques practiced today. With regard to FO and PRO, this comparative study reveals that the effectiveness of both processes depends on the actual/ideal flux ratio (β) which manifests membranes' detrimental effects. Moreover, this study also shows that PRO power generation is also a function of the permeation/draw flow ratio (δ) apart from β and the salinity gradient and that operating at high δ (e.g., 40) of high power density (PD) yields low net electric power density (NEPD) which takes into account the power consumption of the auxiliary components in the PRO system. The distinction between PD and NEPD considered in the context of the SW–SE and SWB–TSE salinity gradients suggests that such applications are unlikely to become economically effective for energy generation and the same conclusion is also true for the application of the FO–RO and PRO–RO hybrids for the desalination of TSE which proceeds most effectively by direct CCD with exceptionally high recovery and low energy.

CCD series no-19: The lowest energy prospects for SWRO through single-element modules under plug-flow and closed-circuit desalination conditions

The future targets of the SWRO desalination industry to reduce significantly energy consumption are realized already today by the newly emerging closed-circuit desalination (CCD) technology with demonstrated energy consumption of 2.12 kWh/m3 for Mediterranean water (4.0%) and 1.72 kWh/m3 for ocean (3.5%) water without the need for energy recovery with energy saving greater than 35%. The fundamental differences between CCD and the conventional plug flow desalination (PFD) techniques are evaluated in the present study by rigorous theoretical model simulations of CCD compared with multi-stage PFD of the same single-element modules under the same conditions in the flux range of 13.0–0.1 lmh. The results of this study reveal that CCD under fixed flow and variable pressure conditions behaves as near-perfect multi-stage PFD with energy dependence on recovery also manifesting increased frequency of CCD cycles and residence time. The origin of energy savings by CCD and multi-stage PFD compared with conventional single-pass through multi-element module is revealed and explained. While multi-stage SWRO designs are economically prohibited by high fabrication costs, CCD designs are simple and inexpensive and should play a major role in future design of SWRO desalination plants of low energy consumption and high energy conversion efficiency without the need of ERD.

CCD series no-20: high-flux low-energy upgrade of municipal water supplies with 96% recovery for boiler-feed and related applications

This study describes the application of closed circuit desalination (CCD) as a first pass for boiler-feed supplies with high recovery (96%) and low energy (0.34 kWh/m3) from a municipal source (553 μS/cm) comprising the scaling constituents Ca (65 ppm), SO4 (180 ppm), SiO2 (32 ppm), F (1.2 ppm), Ba (0.022 ppm), and Sr (0.295 ppm) in addition to modest amounts of Na (65 ppm) and Cl (18.8 ppm). The 96% recovery trials were performed using a pilot comprised of a single module (8″) with three elements (ESPA2-MAX) under fixed flow and variable pressure consecutive sequential CCD conditions at flux of 27.5 lmh and feed temperature of 20.7°C. Under the specified trial conditions, average permeates of 13 μS/cm electric conductivity (~6.5 ppm) are produced with energy consumption of 0.59 kWh/m3 which translates 0.34 kWh/m3 at 25°C and pressurizing means efficiency of 75%. The process proceeds at pH 5.0 in the presence of an antiscalant (Hydrex-4192 and 4102) with recycled concentrates of high super-saturated silica (max. 800 ppm) without any signs of scaling and/or fouling. The module performance results of this study are scalable to larger CCD systems of similar process design.

CCD series no-21: illustration of high recovery (93.8%) of a silica containing (57 ppm) source by a powerful technology of volume reduction prospects

The Fabbri farm well-water source (TDS: 1,304 ppm; SiO2: 57 ppm) in the California Central Valley was desalinated with up to 93.8% recovery under extreme silica supersaturation (930 ppm) conditions using a closed-circuit desalination (CCD) pilot with a single module (8″) of three elements at pH 5.5 in the presence of an antiscalant (FLOCON-260). Experimental trials of the Fabbri source at 17.2 and at 19.6 lmh 7.2 are described in this study with complete online data provided for an extended 8-h trial at 17.2 lmh of 92.8% recovery with consecutive sequential pressure variation of 6–14 bar and electric conductivity (EC) of average permeates (230 μS/cm) and of brine (23,450 μS/cm) cited in parentheses and specific energy consumption of 0.918 kWh/m3 with high-pressure pump efficiency of 55%. Analysis of the consecutive sequential online data during the extended and all other trials revealed unchanged module pressure difference and minor variations of maximum and minimum applied pressures, EC of permeates and recycled concentrates, and a sequential period which ruled out any scaling and/or fouling effects. The findings of this study clearly suggest the viability of the CCD as a powerful technology of considerable prospects for volume reduction applications on route to zero liquid discharge.

CCD series no-16: opened vs. closed circuit SWRO batch desalination for volume reduction of Silica containing effluents under super-saturation conditions

Opened-circuit desalination (OCD) of a high salinity source (>10,000 ppm) also containing large amounts of Silica (>124 ppm) by the application of a single-element module batch apparatus under the conditions of fixed applied pressure of declined flux at low pH was reported to proceed with 80–85% recovery by a high-energy process of low permeate productivity through high super-saturation conditions of silica. The present study describes theoretical model simulations of OCD and closed-circuit desalination (CCD) processes of same feed source (10,000 ppm NaCl–125 ppm SiO2) with different apparatus of identical single-element (SWC6-MAX) modules which execute either closed- or opened-circuit desalination under fixed pressure (47 bar) of variable flow conditions. The results of this theoretical study reveal milder batch process conditions for CCD compared with OCD manifested by longer sequence duration (23.35 instead of 15.95 min), much lower energy consumption (1.57 instead of 7.93 kWh/m3) with average TDS of permeates about the same for both processes up to ~75% batch recovery, and higher for the former process (531 instead of 316 ppm TDS) at the ultimate batch recovery of both (~83%) with same pattern also repeated for the average Silica content in permeates (6.76 instead of 3.65 ppm silica). Silica in the recycled concentrates of both CCD and OCD processes is found in the range of 125–728 ± 6 ppm) and reveals desalination under high super-saturation conditions with Silica maximum of ~5.8-fold (~580%) excess over its ordinary saturation level.

CCD Series No-15: simple design batch SWRO-CCD units of high recovery and low energy without ERD for wide range flux operation of high cost-effectiveness

Closed-circuit desalination (CCD) is a batch process of low energy without need for an energy recovery device (ERD), high recovery irrespective of the number of elements per module, and wide range flux independent of cross-flow and/or recovery, which can be made continuous by the engagement of a side conduit for brine replacement with fresh feed. Batch units for seawater desalination (SWRO-CCD) of the general NMEn (n = 1–3) design, where N stands for the number of modules and n for the number of elements per module, are low-cost systems since avoid the need for ERD and the valves means for the making such a process continuous. Such SWRO-CCD batch units, which pose for recharge between desalination steps, can supply 10 → 1,200 m3/d low-cost seawater permeates sufficient for communities of 100 → 12,000 resident on the basis of 100 L/d/person and for much larger communities if supplied permeates used primarily for drinking and cooking applications. Batch SWRO-CCD units are ideal for small seashore communities with access to shallow beach wells in light of their low-energy consumption and great operational flexibility such as of low flux energy saving mode during night time of low demand with increased production as function of demand at higher flux and greater energy expense during daytime. The wide range flux performance capability of the referred batch units make them ideal for integration with renewable energy sources through solar panels and/or small wind turbines. The energy consumption and permeates quality (parenthesis) as function of flux for the referred units with ME3 (E = SWC6-MAX) modules’ designs for ocean seawater (35,000 ppm) operation of 50% recovery using pressurizing means of 85% efficiency are as follows: 1.79 kWh/m3 (595 ppm) at 13 Lmh; 1.97 kWh/m3 (388 ppm) at 20 Lmh; 2.12 kWh/m3 (309 ppm) at 25 Lmh; and 2.25 kWh/m3 (259 ppm) at 30 Lmh. The experimentally confirmed cited energy figures, even at high flux, manifest high-energy conversion efficiency unattainable by conventional SWRO techniques.

CCD series no-13: illustrating low-energy SWRO-CCD of 60% recovery and BWRO-CCD of 92% recovery with single element modules without energy recovery means—a theoretical extreme case study

In contrast with the conventional SWRO and BWRO plug flow desalination (PFD) techniques where recovery depends on the number of lined membrane elements and energy consumption on the efficiency of energy recovery device (ERD), the newly conceived closed-circuit desalination (CCD) technologies enable the attainment of high recovery, irrespective of the number of elements per module with low energy consumption without need for ERD. The present theoretical model analysis describes the extreme performance prospects of CCD illustrated by a single-element SWRO–CCD unit performing up to 60% recovery with near absolute energy efficiency without need for ERD (e.g. 50% recovery; 13 lmh; 1.573 kWh/m3 for 32,000 ppm NaCl feed equivalent to ocean seawater of 35,000 ppm) as well as by a single-element BWRO–CCD unit performing up to 92% recovery with low energy (e.g. 90% recovery; 25 lmh; 0.472 kWh/m3 for 1,500 ppm NaCl feed equivalent to common brackish water sources of 1,700–2,000 ppm). Another illustration pertains to the performance of a single-element BWRO–CCD–PFD unit, wherein replacement of brine by fresh feed takes place at the end of each CCD sequence by a brief PFD step with results showing only a minor increase in energy consumption compared with that of BWRO–CCD (e.g. 90% recovery; 25 lmh; 0.488 kWh/m3 for 1,500 ppm NaCl feed). The illustrated theoretical model’s results show good agreement with experimental data and manifest the conceptual differences between CCD and conventional RO techniques at their extreme.

CCD series no. 18: record low energy in closed-circuit desalination of Ocean seawater with nanoH2O elements without ERD

Experimental trials of seawater desalination under closed-circuit desalination conditions are described with a unit comprising four modules, each of four Qfx-SW-400-ES nanoH2O elements, with seawater feed in the cited (parentheses) ranges of salinity (33,801–37,197 ppm), flux (9.2–13.4 lmh), recovery (42–53%), and temperature (15.0–18.4°C). The normalized results of this study revealed specific energies in the range of 1.453–1.775 kWh/m3 and permeates in the range of 379–682 ppm. The lowest energy trial in the series of 1.453 kWh/m3 with permeates of 682 ppm is observed with feed of 35,329 ppm at flux of 9.2 lmh flux and 47% recovery, and this energy is the lowest ever recorded for Ocean seawater desalination. The highest energy trial in the series of 1.775 kWh/m3 with permeates of 548 ppm is observed with feed of 33,913 ppm at flux of 12.3 lmh and 53% recovery. In comparison with SWC6 elements in the same unit, the experimental data with the Qfx-SW-400-ES nanoH20 elements reveals 8–12% lower energy consumption and permeates of 2–3-fold higher TDS.

Closed Circuit PRO Series No 5: clean energy generation from seawater and its concentrates by CC-PRO without need of energy recovery

This study explores the prospects for clean energy generation in coastal regions from salinity gradient made of seawater (SW) and its concentrates (SWC) by the CC-PRO technology of near absolute energy efficiency without energy recovery device and semi-permeable membranes such as HTI-TFC (A = 2.49 lmh/bar, B = 0.39 lmh, and S = 564 μm) of 48.3 bar maximum applied pressure and alike. This power generation process is fueled by SW as low salinity feed and SWC as high salinity feed (HSF) and the regeneration of HSF from the produced high salinity diluted feed achieved through evaporation ponds of the types extensively used by the sea salt manufacturing industry. Large-scale harvesting of clean energy from the sea could be found particularly attractive along coastlines of arid zones where climate conditions (e.g. solar radiation, temperature, wind, humidity, etc.) favor effective evaporation from reservoirs of SWC. The simulated CC-PRO process of the SW (4.2%)–SWC (25%) salinity gradient with the HTI-TFC membrane revealed maximum membrane power density of 55.6 W/m2 and net electric power density after accounting for the auxiliary pumps of 39.3 W/m2 at the hydraulic pressure difference of 48.3 bar under draw/permeation flow ratio of 5.0 and membrane actual/ideal flux ratio of 0.2 estimated from available forward osmosis data of the same membrane in the 1.0–3.0 NaCl salinity gradients range. HTI-TFC membrane surface area of 1,000 m2 should provide 943 kWh electric energy per day enough to desalinate 377 m3/d of SW (4.2%) with 50% recovery by means of the closed circuit desalination (CCD) technology (RO: 2.5 kWh/m3). The results of this study reveal that the CC-PRO technology opens the door for large-scale commercial clean power generation from SW–SWC salinity gradients already with existing PRO membranes and improved economic feasibility when PRO membrane of higher actual/ideal flux ratio and burst pressure shall become available in the near future.

CCD Series No-14: SWRO-CCD under fixed-pressure and variable flow compared with fixed-flow and variable pressure conditions

A theoretical model on the basis of the conceptual principles of closed circuit desalination (CCD) is explored in the present study for the performance assessment of the single-element seawater desalination reverse osmosis (SWRO) unit ME (E = SWC6-MAX) of near absolute energy efficiency without an energy recovery device (ERD) under fixed-pressure (FP) of variable flow compared with fixed-flow (FF) of variable pressure conditions. Performance simulations of same feed source (3.2% NaCl), sequence duration (9.01 min), recovery (60.3%), average flux (14.9 lmh), concentrate recycling flow (4.0 m3/h), number of CCD cycles (10), and cycle period (0.90 min/cycle) under FP (65 bar) compared with FF (37.1–71.3 bar) conditions revealed the respective specific energy values (SE) of 2.177 and 1.792 kWh/m3 with average permeate Total Dissolved Salts (TDS) of 574 and 464 ppm. The average SE sequential progression under FF conditions (1.234–1.792 kWh/m3) compared with that under FP conditions (2.140–2.177 kWh/m3) reveals the declined percent energy-saving mode of the former as function of increased recovery (R) in the order: 32.2% (R = 40%); 30.1% (R = 45%); 26.4% (R = 50%), 21.9% (R = 55%); and 17.7% (R = 60,3%). Since conventional SWRO desalination of Ocean seawater (~35,000 ppm TDS equivalent to ~3.2 NaCl) is normally being carried out with ~45% recovery, average flux near 15 lmh and an applied pressure around 65 bar using ERD, the findings of the current study suggest RO energy saving of 30.1% before accounting for ERD energy losses if the desalination is performed with SWRO-CCD under FF conditions. This conclusion is supported by the reported SE (2.46 kWh/m3) for the conventional SWRO desalination plant in Australia compared with the extrapolated SE value for Ocean water (~1.70 kWh/m3) from normalized experimental SWRO-CCD data with Mediterranean seawater. The average TDS of permeate projections during the batch sequence progression under FP (110–574 ppm) compared with FF (291–454 ppm) conditions reveals higher quality permeates by the former up to 54% recovery and thereafter, the preference of the latter mode. The observed inversion takes place due to rapidly declined flux under the FP conditions towards the end of the batch sequence which creates a fast rise in TDS per cycle manifested also by the average TDS.

Closed circuit desalination series no-12: the use of 4, 5 and 6 element modules with the BWRO-CCD technology for high recovery, low energy and reduced fouling applications

The newly emerging closed circuit desalination (CCD) technologies of high recovery and low energy for seawater (SWRO-CCD) and brackish water (BWRO-CCD) have been demonstrated thus far with short modules comprising one to four elements (MEn; n = 1–4). The present study explores the plausible application of longer modules of five to six elements each (ME5 and ME6) in the context of the BWRO-CCD technology on the basis of theoretical model simulations with emphasis on recovery, energy consumption, permeates quality and membrane fouling aspects. The plausibility of the ME4 (MR = 40–50%), ME5 (MR = 40–60%) and ME6 (MR = 40–65%) modules in the cited Module Recovery (MR) ranges (in parentheses) for BWRO-CCD application has been confirmed by IMS Design results on such modules with ESPA2-MAX elements using 2,500 ppm NaCl feed at flux of 24.5 lmh. In order to establish the relationships between conventional BWRO and BWRO-CCD which operates on the basis of different principles, a comprehensive theoretical model analysis was performed on the 4ME6 + 2ME5 + ME6 conventional system compared with the 7ME6 BWRO-CCD unit design of the same number of modules and elements (ESPA2-MAX) under similar and different flux conditions for recovery of ~90% using the same feed source (2,500 ppm NaCl) and identical theoretical equations to generate the compared data. The noteworthy conclusions reached from the results of the comparative theoretical study are as follows: (1) BWRO-CCD may reach any desired high recovery made possible by the composition and quality of the source without need of staged pressure vessels and booster pumps and with greater facility and flexibility compared with conventional techniques. (2) The energy consumption of BWRO-CCD is considerably lower compared with that of conventional techniques under same flux conditions, especially in the 80–90% recovery range, without any need for energy recovery. (3) The quality of BWRO-CCD permeates in the 80–90% recovery range is somewhat inferior to that of conventional techniques under the same flux conditions. (4) BWRO-CCD flux increase of ~25% compared with that of conventional techniques will lead to similar quality permeates in the 80–90% recovery range with lower energy consumption by the former despite the flux increase. (5) Convention multi-stage BWRO techniques require high MR in the first stage (up to ~65%) in order to reach ultimate high process recovery and this implies increased probability of fouling and scaling of tail elements due to decreased average cross-flow; whereas, MR in BWRO-CCD is independent of sequence recovery and this implies the ability to select MR of desired cross-flow to minimize fouling and scaling effects.

CCD Series No-10: small compact BWRO closed-circuit desalination (CCD) units of high-recovery, low-energy and reduced fouling for supplied water upgrade to industry, irrigation, domestic, and medical applications

The recently emerging new closed circuit desalination (CCD) technology enables performing high-recovery and low-energy BWRO desalination of reduced fouling irrespective of the number of elements per module and thus opened the door to a new class of small compact units for diverse applications. The design aspects and performance prospects of such small compact BWRO-CCD units (<5.4 m3/h; <130 m3/d) are illustrated with modules comprising either two or three elements each (MEn with n = 2–3). Since small compact BWRO units are extensively used for supplied water upgrade to industry, irrigation, domestic and medical applications, the unique performance characteristics of said small compact CCD units of high recovery and low energy is exemplified with feed of 200–750 ppm NaCl which cover the range of 230–900 ppm of ordinary supplied water sources worldwide. The supplied water upgrade by said compact CCD units are illustrated at the level of a single-pass quality permeates as well as at the level of double-pass quality permeates of exceptionally low salinity in the range 0.13–1.54 ppm depending on the feed salinity and the membrane salt rejection characteristics. The double-pass process in these compact CCD units implicate the use of first pass permeates as feed to the second pass, thereby enabling the same unit execute either a single or a double-pass process depending on the desired quality of permeate.

Closed circuit desalination series no-9: theoretical model assessment of the flexible BWRO-CCD technology for high recovery, low energy and reduced fouling applications

Compared with conventional BWRO techniques, the conceptually different closed circuit desalination technology for brackish water desalination (BWRO-CCD), has been analyzed with respect to its modular design and performance characteristics on the basis of theoretical model simulations of a typical four elements module (ME4; M = ESPA2-MAX) in the feed salinity range of 500–6,000 ppm NaCl, which corresponds to that of common brackish water sources with up to 7,000 ppm TDS. The model analysis results of the BWRO-CCD technology demonstrate a unique consecutive sequential desalination process with staged flow and pressure boosting without the use of staged pressure vessels and booster pumps. The theoretical model simulations of the BWRO-CCD technology over a wide range of feed salinity (500–6,000 ppm NaCl) have consistently revealed flexible and versatile performance under fixed flow and variable pressure conditions characterized by low energy consumption, high recovery, and reduced fouling characteristics achieved by means of simple designed systems of high modularity. The superb performance characteristics of the BWRO-CCD technology makes it ideal for a wide spectrum of noteworthy applications, such as treatment surface and groundwater for domestic use, desalination of clean domestic and industrial effluents, desalination of brackish water, production of high-quality permeates for industry, decontamination of drinking water including nitrate removal, boron removal from first-pass SWRO permeate, as well as many others. The theoretical model analysis results reveal that BWRO-CCD is an advanced technology which meets the criteria of high recovery and low energy consumption with reduced fouling in the simple apparatus of modular designs.

Closed circuit desalination series no. 8: record saving of RO energy by SWRO-CCD without need of energy recovery

A theoretical model is developed for comparing reverse osmosis (RO) energy and permeates quality of closed of circuit desalination (CCD) and conventional plug flew desalination (PFD) under the same conditions. The application of the theoretical model is illustrated by a comparison between a CCD unit with two modules each of four elements and a single module conventional PFD unit with eight elements in the context of ocean water (3.5%) desalination with 50% recovery at 25°C under average flux of 13 LMH and 85% efficiency of feed pressurizing pumps using the same membrane elements (SWC6). This model analysis reveals savings of RO energy by CCD compared with conventional PFD as function of its absolute energy conversion (AEC) efficiency (in bracket) as followed: 9.8% (95%), 13.4% (90%), 17.2% (85%), 20.6% (80%), 23.8% (75%), and 28.7% (70%). Most large and modern conventional seawater RO plants operate with AEC efficiency in the range of 70–80% and therefore, the actual RO energy saved by CCD compared with such conventional techniques is found in the respective range of 28.7–20.6%. Despite the large difference in RO energy revealed by the model analysis between the compared techniques, both produce about the same quality permeates. CCD is a continuously staged and pressure-boosted consecutive sequential technology which operates with near AEC efficiency without need for energy recovery (ER) from brine, and the low RO energy requirements by this technique manifest the average diagonal sequential pressure rise as function of increased sequential recovery under conditions of fixed flow rates of pressurized feed and permeate. According to the model analysis, CCD of ocean water (3.5%) at 13 LMH with 50% recovery proceeds with 1.625 kWh/m3 compared with 1.962 kWh/m3 by conventional techniques with AEC efficiency of 85%. The model analysis energy of 1.625 kWh/m3 for ocean water (3.5%) CCD at 13 LMH with 50% recovery agrees with extrapolated energy for ocean water (1.60–1.70 kWh/m3) from experimental results (2.0–2.1 kWh/m3) received for the Mediterranean water (4.1%) under the same conditions. A pressure-volume work model for high pressure pump (HP) (85% eff.) in CCD revealed under infinitesimally small permeation of near zero flux conditions the theoretical minimum energies 1.40 and 1.25 kWh/m3 for the Mediterranean (4.1%) and ocean (3.5%) water, respectively. Extrapolation of experimental CCD energies (HP + CP) to near zero flux revealed 1.44 and 1.29 kWh/m3 for the Mediterranean and ocean water, respectively. The difference between the extrapolated (HP + CP) and theoretical minimum (HP) revealed the minor circulation pump (CP) energy contributions 0.04 and 0.05 kWh/m3 in CCD of the Mediterranean (2.78%) and ocean (3.87%) water sources, respectively.

Industrial and brackish water treatment with closed circuit reverse osmosis

Closed Circuit Desalination (CCD™) technology is an emerging platform for reverse osmosis (RO) water treatment and desalination. It lowers the feed pressure requirement, improves the membrane performance, increases the operational flexibility, and eliminates the need for energy recovery devices using only standard RO equipment. For industrial water treatment and brackish water desalination applications, CCD technology achieves maximum recovery in single-stage units while saving energy. Alternately, a CCD unit can be added to a conventional RO process to concentrate brine and raise recovery. Over 97% recovery has been demonstrated in a single-stage operation. The recovery rate of a CCD unit can be adjusted at the control panel without modification of system hardware, limited only by the scaling characteristics of the feedwater. Maximum recovery operation and high flexibility have significant cost-cutting implications for industrial water treatment and inland brackish desalination, where both feedwater supply costs and brine disposal fees can be significant. CCD systems also demonstrate excellent resistance to fouling and scaling. Cross-flow supplied by a circulation pump washes the membranes, and salinity cycling disrupts and greatly reduces the scaling and fouling. Short membrane arrays and high cross-flow allow the CCD process to operate at higher average fluxes than conventional RO processes, without exceeding the membrane manufacturer’s flow or recovery specifications. This paper describes the design and modeling of high-recovery CCD processes and compares the measured and calculated specific energy consumption levels to validate modeling methods and tools. Two brackish water RO cases are considered: one using Desalitech’s seawater reverse osmosis–CCD (SWRO-CCD) process and the other using its hybrid plug flow desalination–SWRO–CCD (PFD-SWRO-CCD) process. CCD systems are compared favorably to conventional RO trains modeled with the same feedwater, high-pressure pumps, and membranes operating at the same average flux and overall recovery percentage.

Closed circuit desalination series no-5: high recovery, reduced fouling and low energy nitrate decontamination by a cost-effective BWRO-CCD method

The newly conceived and recently reported closed circuit desalination (CCD) Technology has been successfully demonstrated for nitrate decontamination. The application of the brackish water reverse osmosis- CCD (BWRO-CCD) Technology to feed sources of 98, 144 and 197 ppm NO3 gave the respective amounts of 19, 27 and 45 ppm NO3 in permeates from said sources obtained with 90% recovery at 20°C. The illustrated NO3 rejection finding of the BWRO-CCD Technology, considered in the context of high flux, high recovery, low energy demand and reduced fouling factors may suggest the plausibility of this cost-effective approach for nitrate decontamination of drinking water worldwide.