Brackish Water Reverse Osmosis Research Articles

Techno-economic assessment of a novel algal-membrane system versus conventional wastewater treatment and advanced potable reuse processes: Part II

This study developed a comprehensive techno-economic assessment (TEA) framework to evaluate an innovative algae resource recovery and near zero-liquid discharge potable reuse system (i.e., the main system) in comparison with a conventional potable water reuse system (i.e., the benchmark system). The TEA study aims to estimate the levelized costs of water of individual units and integrated processes including secondary wastewater treatment, advanced water purification for potable reuse, and sludge treatment. This would provide decision-makers valuable information regarding the capital and operational costs of the innovative main system versus a typical potable water reuse treatment train, along with possible routes of cost optimization and improvements for the design of full-scale facilities. The main system consists of (i) a novel algal-based wastewater treatment coupled with a dual forward osmosis and seawater reverse osmosis (Algal FO-SWRO) membranes system for potable water reuse and hydrothermal liquefaction (HTL) to produce bioenergy and subsequent nutrients extraction from the harvested algal biomass. The benchmark system includes (ii) an advanced water purification facility (AWPF) that consists of a conventional activated sludge biological treatment (CAS), microfiltration (MF), brackish water reverse osmosis (BWRO), ultraviolet/advanced oxidation process (UV-AOP), and granular activated carbon (GAC), with anaerobic digestion for sludge treatment. Capital expenditures (CAPEX) and operational expenditures (OPEX) were calculated for each unit of both systems (i.e., sub-systems). Based on a 76% overall water recovery designed for the benchmark system, the water cost was estimated at $2.03/m3. The highest costs in the benchmark system were found on the CAS and the anaerobic digester, with the UV-AOP combined with GAC for hydrogen peroxide (H2O2) quenching as the driving factor in the increased costs of the system. The cost of the main system, based on an overall 88% water recovery, was estimated to be $1.97/m3, with costs mostly driven by the FO and SWRO membranes. With further cost reduction and optimization for FO membranes such as membrane cost, water recovery, and flux, the main system can provide a much more economically viable alternative in its application than a typical benchmark system.

Box–Behnken multi-response modeling and optimizing of brackish water reverse osmosis brine treatment using electrodialysis reversal with tortuous flow path

Box–Behnken multi-response modeling and optimizing of brackish water reverse osmosis brine treatment using electrodialysis reversal with tortuous flow path

Simulation and Optimisation of a Medium Scale Reverse Osmosis Brackish Water Desalination System: Energy Saving and Maintenance Opportunity

Simulation and Optimisation of a Medium Scale Reverse Osmosis Brackish Water Desalination System: Energy Saving and Maintenance Opportunity

Techno-Economic Analysis of Selected PV-BWRO Desalination Plants in the Context of the Water–Energy Nexus for Low–Medium-Income Countries

Jordan was late in adopting seawater and brackish water desalination as a source until the late 1990s and early 2000s. However, ongoing studies are still discussing the technical, economic, and socio-political aspects of brackish water reverse osmosis (BWRO) desalination plants. In this study, the water–energy nexus was considered, in order to highlight the main challenges facing BWRO desalination. We discuss the use of photovoltaic (PV) technology, together with BWRO desalination, as an approach to compensate for ecological, financial, and social challenges in Jordan. For this purpose, the performance of nine existing BWRO desalination plants in the agricultural, domestic, and industrial sectors is assessed. The water performance is assessed based on water consumption, safe yield extraction, plant recovery rate (R, %), and compliance to local and international water quality standards; the Specific Energy Consumption (SEC, kWh/m3) is taken as the main evaluation criterion to assess the energy performance of the BWRO desalination plants; and economic performance is assessed based on the overall cost of water produced per cubic meter (USD/m3). The main environmental component is the brine disposal management practice utilized by each plant. Based on this assessment, the main challenges in BWRO desalination are the unsustainable patterns of water production, mismanaged energy performance, low recovery rates, and improper brine disposal. The challenges in domestic and industrial BWRO desalination, which are completely dependent on the electricity grid, are associated with critical energy and costs losses, as reflected by the high SEC values (in the range of 2.7–5.6 kWh/m3) and high water costs per cubic meter (0.60–1.18 USD/m3). As such, the use of PV solar panels is suggested, in order to reduce the electricity consumption of the assessed BWRO plants. The installation of PV panels resulted in significantly reduced energy costs (by 69–74%) and total costs (by 50–54%), compared with energy costs from the electricity grid, over the lifetime of the assessed BWRO desalination plants.

Opportunities of Reducing the Energy Consumption of Seawater Reverse Osmosis Desalination by Exploiting Salinity Gradients.

This work presents a performance assessment of three seawater reverse osmosis-pressure-retarded osmosis (SWRO-PRO) hybrid schemes for energy consumption reduction in seawater desalination applications by using an external low salinity water source. For comparison purposes, another arrangement based on the conventional SWRO process combined with brackish water RO (BWRO) and desalination was analyzed. Reverse osmosis system analysis software environments were used to select the best SWRO configuration and operating conditions. A purposely developed model was used to evaluate the PRO system. Two different cases were assessed depending on the origin of the external low-salinity resource for the PRO process: industrial wastewater and urban treated wastewater. In the case of the industrial wastewater, due to regulations on wastewater reclamation, the best arrangement would be the first SWRO-PRO scheme which was analyzed with a specific energy consumption of 1.54 kWh/m3. If urban treated wastewater is available as an external resource, the results obtained show that this scheme, leading to the minimum specific energy consumption of 1.46 kWh/m3, is the conventional SWRO combined with BWRO. Therefore, hybrid SWRO-PRO systems are recommended to reduce the specific energy consumption of seawater desalination if an industrial wastewater source with low osmotic pressure is available.

Possibility assessment of ultrafiltration membrane pre-treatment efficiency for brackish water reverse osmosis-based wastewater reuse: Lab and demonstration.

Ultrafiltration (UF) membranes are considered a pre-treatment for brackish water reverse osmosis (BWRO) membranes because of the high rejection rate of particulates and the productivity of the final water quantity. This study presents the performance and membrane surface property analysis of UF membranes for commercial membrane manufacturers, and their structural strength and chemical resistance were evaluated. Moreover, the pilot-scale UF-BWRO process was operated for two months using real wastewater based on the results of this study. Although the overall properties were similar, the poly (ether-sulfone) UF membrane showed higher tensile strength than the polyvinylidene difluoride and polyacrylonitrile UF membranes. The UF membrane showed a high removal rate of particulates (over 90%) but low rejection rate of organic compounds, such as humic acid and sodium alginate (below 30%). After exposure to high concentrations of chemicals, the contact angle of the membranes was reduced by approximately 15% compared to that of the virgin membranes. In addition, despite the exposure to low-and high-concentration chemicals, UF membranes were relatively stable in terms of tensile strength. During the operation period of the pilot-scale UF-RO process, the UF membrane showed a high turbidity removal of over 93%, and the UF-BWRO process presented a high salt rejection of over 92%. The UF membrane showed potential for the pre-treatment of BWRO membranes.

Electro dialysis reversal (EDR) performance for reject brine treatment of reverse osmosis desalination system.

In this study, the performance of bench-scale EDR was evaluated using the samples taken from the 1st and the 2nd stage RO from the Brackish Water Reverse Osmosis (BWRO) plant in Eshtehard, Iran. The measurements indicated that original TDS of the aquifer brackish water was equal to 3,229–3,664 mg/L, whereas TDS of the 1st stage RO brine was between 5,500 and 7,700 mg/L, that TDS of the 2nd stage RO brine was in the range of 9,500–10,600 mg/L. A batch bench-scale EDR system of 12 l/h was used with a direct electric current at three different scenarios. In the first, the brine was fed at 20°C (as a reference regulated point). In the second, temperature (14, 20, 26.5°C), and in the third, voltage were changed (6, 12, 18, 24 V) to investigate their influences on performance of the EDR process, while the other operational parameters (feed flow rate, recovery ratio, quality of feed brine)were kept constant. Based on the data analysis using the ANOVA and DUNCAN tests for the second and third scenarios, it was observed that the optimum TDS removal efficiency of the EDR process can be at temperature of 26.5°C and voltage of 18 V. On the other hand, the successful performance of the bench-scale EDR in reducing the 29,000 mg/L TDS and the 45,000 μmhos/cm EC of the 2nd stage brine to 1,716 mg/L (TDS) and 2,640 μmhos/cm (EC) (at 26.5°C and 24V) could be considered as the main achievement of this research. Overall, the hybrid process RO-EDR-RO can be considered as the best technical, environmental and economical scenario for the development of Eshtehard Desalination Plant phase 2 at full scale.

Brackish water RO concentrate treatment and water recovery using cost lowering integrated technology

Membrane concentrate has to be taken into consideration when the membrane technologies are presented as a robust solution for the water reuse and reclamation. In this study, brackish water reverse osmosis concentrate stream was recovered as source water with cost lowering integrated technology and over 70 % water recovery rate. Integrated technology consists of softening, ceramic MF/UF membrane and NF/RO membrane processes. By using this process scheme, it is aimed to benefit from the advantage of not easily fouling of ceramic membranes and to reduce the fouling load that may arise from the softening process on polymeric membranes, thus completing the water cycle by making water recovery. With this method, the reverse osmosis concentrate stream with the value of 2675 ± 323 µS/cm electrical conductivity, 1299 ± 40 mg CaCO3/L total hardness and 51 ± 1.5 ppm SiO2 was recovered in quality close to the well water character that reverse osmosis feed stream. Compared with other concentrate management technologies, proposed technology seems cost competitive with 1.349 US$/m3 total cost of integrated system and final cost is 0.519 US$/m3 after excluding water cost (0.830 US$/m3). Total 72 % of concentrate flow rate may be recovered to reverse osmosis feed stream and remaining 28 % of concentrate flow rate may be turned back to softening process. Thus, it is thought that it will make an important contribution to the near zero discharge liquid concept, which is of great importance for the protection of water resources today.

Installation of the Brackish Water Reverse Osmosis System Coupled with Solar Power for Drinking Water Production in Ben Tre, Vietnam Considering Water Usage and Cost

Recently, the unbalanced water demand and supply have been occurred globally due to the climate change, industrialization, and population increase. The water shortage problem became much severe in the developing countries because the low-stage of infrastructure might result in frequent limitation of water and transportation of water. Therefore, sustainable water supplying option is the key for the boosting the local economy. The Mekong Delta area produce most of the products in agriculture and fishery in Vietnam. However, due to low income and vast area, the infrastructure for water supply has been limited in the Mekong Delta area. Moreover, due to reduced Mekong-river flow by the dam construction in upper reaches, increased seawater level by the global warming, and increased unexpected drought and flooding by the climate change, the water supply in the Mekong delta is becoming hard. Therefore, sustainable water supplying option was required. In this study, the reverse osmosis-based desalination process could use undrinkable saline water as the feed water coupled with photovoltaic panel was suggested. In order to install the decentralized and off-grid type water production plant in the proper place in the Mekong Delta, the KIST, VKIST, and central and local governments in Vietnam collaborated. The RO plant could be successfully installed by the help of the partners and the operational conditions have been monitored. If the water providing option could be separated according to the purposes such as drinking usage and other water usage, the more technical options could be applied for the water production.

Are commercial polyamide seawater and brackish water membranes effectively charged?

New developments in modeling solute transport in reverse osmosis (RO) membranes are based on the mechanistic description of solution friction and electromigration. In these models, the membrane charge significantly impacts the separation that occurs in the membrane through Donnan partitioning. One implication of membrane charge is that the salt permeability strongly depends on the ion concentration in the feedwater. In this study, we experimentally evaluate the effect of salinity, varied over almost two orders of magnitude (ca. 10–650mM), on four commercially available polyamide seawater RO and brackish water RO membranes. We found no significant effect of feed concentration on observed salt permeability, while the membrane performance closely resembled the specification by the manufacturers. We also demonstrate that a minor leak in the membrane provides a plausible alternative explanation to trend between concentration and salt permeability reported in other studies. The standard solution diffusion model provides a satisfactory description of our data for the membranes and feedwater conditions that we tested.

Optimal sizing of an integrated CHP and desalination system as a polygeneration plant for supplying rural demands

Simultaneous production of electricity, heat, and water is a global challenge for rural residential areas. In the present study, techno-economic optimization of a system including PV, wind turbine, generator, battery, and CHP system alongside brackish water reverse osmosis desalination system is investigated. The proposed polygeneration hybrid system provides the required loads of a village and health clinic in a rural area with a warm climate. This study aims to find the optimum energy cost of essential rural needs, including required electricity, heat, and water demands to improve remote areas' life quality. While previous studies often considered only one or two of these needs. Several sensitivity analyses based on the different economic and climate conditions are carried out. The grid breakeven distance, environmental aspects, and the developed hybrid energy system's technical performance are analyzed. The results demonstrate that the optimum system, including PV/WT/DG/CHP/Bat and reverse osmosis desalination unit has COE and NPC equal to 0.236 $/kWh and 428,246 $, respectively. Also, the CHP unit decreased the annual fuel consumption by about 224 m3/yr. Furthermore, the proposed hybrid system has a 58.4% lower CO2 emission than conventional natural gas-fired plants and less than 27 km of grid breakeven distance.

Reverse osmosis membrane compaction and embossing at ultra-high pressure operation

Herein, we describe the performance (i.e., flux and rejection) of commercially-available, thin film composite brackish water RO (BWRO), seawater RO (SWRO) and high-pressure RO (HPRO) membranes operating at pressures from 14 bar (200 psi) to 207 bar (3000 psi). For each membrane material, we elucidate the impacts to performance using a porous metal frit and woven tricot mesh permeate carrier materials from commercial HPRO, SWRO, BWRO and tap water RO (TWRO) membrane modules. The water permeability of all tested membranes declines with increasing pressure, whereas rejection behaves differently for different combinations of membrane type and permeate carrier. Cross-sectional SEM and FIB-SEM images confirm permanent reduction of the polysulfone support membrane thickness (38% to 60%) as well as collapse of support membrane skin layer pores – both of which may contribute to the observed performance decline. Also, at ultra-high pressures, permeate carrier materials with higher porosity cause greater embossing and, ultimately, coating film damage (defect formation) that leads to increased salt passage (loss of salt rejection). In contrast, the permeate carriers with lower porosity still lost water permeability, but maintained higher rejection. Finally, all of the observed compaction/embossing-related performance decline occurs within about 60 min after a membrane coupon was exposed to ultra-high pressure.

Dissecting the structure-compaction-performance relationship of thin-film composite polyamide membranes with different structure features

Thin film composite (TFC) polyamide (PA) membranes experience compaction at high pressure applications, resulting in the reduction in water permeability. However, the compaction mechanism is still unclear especially for different PA morphologies and substrate structures. In this work, we systematically studied the compaction of TFC PA membranes with different structures and morphologies. We first examined 2 main types of commercial reverse osmosis (RO) membranes: brackish water RO and seawater RO membranes. After that, we synthesised four types of TFC membranes with tailored PA and substrate structures to further understand the compaction behaviors. TFC membrane with a PA layer of low protuberances or nodules and dense substrate showed excellent resistance against high pressure (50 bar), with only a slight irreversible decrease of 2.1–3.5% in water permeability when retested at 5 bar. However, the PA layer of high protuberances experienced significant compaction even when it was supported by a similar dense substrate. The permeability of the TFC membrane decreased ∼10% as a result of the decrease in the effective area of the active layer. On the other hand, the TFC membrane with a PA layer of low protuberances formed atop a loose substrate showed a greater decrease (∼18.5%) in water permeability. The densified skin layer and collapsed macro-voids within the loose substrate resulted in a ∼40% decrease in the overall height of the PA layer and a 65% decline in substrate surface porosity, respectively, which are identified as the reasons for the reducing water permeability. Notably, the water-salt selectivity of this particular membrane was seriously deteriorated after compaction due to the presence of subtle defects in the PA layer caused by the drastic deformation of the loose substrate. This work deepens the understanding of the compaction behaviors of TFC PA membranes, providing a clear fundamental guidance on designing membranes applied at high operating pressures.

Assessing the potential of highly permeable reverse osmosis membranes for desalination: Specific energy and footprint analysis

The ultra-permeable membranes (UPMs) are expected to reduce the specific energy consumption (SEC) of desalination, but the potential of UPMs in hollow fiber configuration has not been well quantified. Herein, we analyse the SEC and footprints of UPM modules in three feed salinities: seawater reverse osmosis (SWRO), brackish water RO (BWRO) and low-pressure RO (LPRO). Through the modelling the fluid dynamics and mass transport of RO systems, we find that a tripling in spiral-wound SWRO membrane permeability (based on the current value of 1 L m−2 h−1 bar−1; LMH/bar) could result in 16% decrease in SEC. Contrastingly, the quadrupling of hollow fiber SWRO membrane permeability (based on the current value of 0.25 LMH/bar) could reduce the SEC by 23%. According to our analysis, hollow fiber and spiral-wound SWRO membranes with permeabilities up to 1 LMH/bar and 3 LMH/bar, respectively, can reduce the SEC of seawater desalination. On the other hand, membranes with permeabilities up to 9 LMH/bar and 12 LMH/bar can lead to SEC savings in BWRO and LPRO desalination, respectively. This study provides a general guidance to RO membrane researchers on the permeability upper-limit of which UPMs could bring about SEC and footprint savings at a system level.

Comparison of Pretreatment Methods for Salinity Gradient Power Generation Using Reverse Electrodialysis (RED) Systems.

With the increasing concern about climate change and the energy crisis, the use of reverse electrodialysis (RED) to utilize salinity gradient power (SGP) has drawn attention as one of the promising renewable energy sources. However, one of the critical issues in RED processes is membrane fouling and channel blockage, which lead to a decrease in the power density. Thus, this study aims to improve our understanding of SGP generation by using RED by investigating the effect of pretreatment on the RED performance. Experiments were conducted by using a laboratory-scale experimental setup for RED. The low-salinity and high-salinity feed solutions were brackish water reverse osmosis (BWRO) brine from a wastewater reclamation plant, and a NaCl solution simulating seawater desalination brine. Several pretreatments were applied to the RED process, such as cartridge filter (CF), microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), activated filter media (AFM), and granular activated carbon (GAC). The results indicate that the open-circuit voltage (OCV) and the power density were similar, except for in the NF pretreatment, which removed the dissolved ions to increase the net SGP. However, the pressure in the RED stack was significantly affected by the pretreatment types. The excitation–emission matrix (EEM) fluorescence spectroscopy and the parallel factor analysis (PARAFAC) quantified the organic compounds that are related to the stack pressure. These results suggest that the removal of both colloidal and organic matters by pretreatments is crucial for improving the RED performance by reducing the pressure that is increased in the RED stack.

High-Throughput Optimal Design of Spacers Using Triply Periodic Minimal Surfaces in BWRO

The development of advanced feed spacers under different working conditions can enhance the performance of the reverse osmosis (RO) desalination process. The 3D-printed experimental results on triply periodic minimal surfaces (TPMS)-based spacers in previous literature indicate that the spacers have higher permeation flux of water compared to those of the common commercial spacers. In this paper, a hybrid modeling approach is developed and applied to predict and evaluate the performance of TPMS-based spacers. The effect of feed channels’ height and porosity on the performance of spacers in brackish water RO (BWRO) process is studied by using a high-throughput approach. The predicted pressure drop by new simulations using the TPMS-based spacers (≈0.09–0.27 bar) from inlet to outlet in a typical two-stage BWRO system is reduced by more than 89% than that of using the commercial spacer (≈2.57 bar). Using the designed advanced spacers, the average permeation flux of water increases more than 8.6% compared to that of the commercial one. With the increase in feed channel height and porosity, the performance of spacers is gradually improved. TPMS-based spacers have significant industrial application prospects.

Novel dynamic and cyclic designs for ultra-high recovery waste and brackish water RO desalination

There is a drive for ultra-high recoveries in waste and brackish water RO desalination due to high brine disposal costs. In this work, two novel dynamic and cyclic designs (i.e. feed reversal and retentate recycle with a time-varying ratio in stage 3, as well as stage rotation between 1 and 3) are proposed to achieve a 90% recovery while alleviating scaling potential. The designs are conducted following FilmTec's guidelines and are simulated using validated models published previously. It is shown that retentate recycle suppresses concentration polarization, despite a higher pressure drop. Feed reversal leads to a quick drop of salt concentration due to mixing of fresh feed and brine. However, if the feed reversal is applied to the same stage, the salt concentration on the other end may be higher than brine concentration for a short period of time. Such a behavior is not observed during rotations between stages 1 and 3, whether the feed is reversed or not. Interestingly, the designs at 90% recovery demand only a few percent more energy than traditional two-stage designs operated at 80% recovery. Moreover, cycle-to-cycle salt build-up in batch-type ROs is absent in both dynamic designs presented in this work.

Thin-film nanocomposite reverse osmosis membranes incorporated with citrate-modified layered double hydroxides (LDHs) for brackish water desalination and boron removal

By intercalating citrate anions into the inter-layer of layered double hydroxides (LDHs), the inter-layer spacing of the resultant CA-Mg-LDH is enlarged from 7.5 to 11.8 Å. With the aid of this newly developed CA-Mg-LDH, novel thin-film nanocomposite (TFN) membranes have been prepared, systematically investigated, and demonstrated for brackish water reverse osmosis (BWRO) desalination. By manipulating the nanofiller concentration, a water permeance of 3.21 LMH bar−1 and a salt rejection of 98.9% are obtained for the TFN membrane at the optimal loading of 0.15 wt%. It achieves a 68% higher water permeance than the pristine TFC membrane but without notably sacrificing the selectivity, owing to the moderate enlargement of the inter-layer spacing of CA-Mg-LDH. In addition, this novel TFN membrane has a boron rejection of 75% when using a 2000 ppm NaCl solution containing 10 ppm boron as the feed at 20 bar. This work is the first attempt to use CA-Mg-LDH as nanofillers in TFN membranes for demonstration of BWRO and boron removal, offering new insights and strategies for the design of next-generation TFN membranes for water treatment.

Aquaporin launches its first series of brackish water RO membranes

Denmark's Aquaporin A/S, a water technology company dedicated to natural water treatment, with operations in Singapore and the USA, recently launched its first series of brackish water reverse osmosis (RO) membranes.

Performance and cost analyses of hybrid diesel-photovoltaic powered small brackish water reverse osmosis system in Saudi Arabia

Performance and cost analyses of hybrid diesel-photovoltaic powered small brackish water reverse osmosis system in Saudi Arabia