Brackish Water Reverse Osmosis Research Articles

The techno-economic case for coupling advanced spacers to high-permeance RO membranes for desalination

Innovations in advanced materials in recent years have produced great improvements in the permeance of reverse osmosis (RO) membranes for desalination. This work presents a simplified techno-economic analysis for a representative advanced spacer and a high-permeance RO membrane under typical feed and operating conditions. The results agree with common trends for specific energy consumption (SEC). For high-permeance membranes, advanced spacers are more effective than conventional spacers in improving flux in the region close to the inlet, due to a fast decrease in Reynolds number along the channel. The total cost for seawater RO (SWRO) and brackish water RO (BWRO) could be reduced by 7.5% and 32%, respectively by increasing the membrane permeance to 10 L/m2.h.bar regardless of the spacer type used. However, as feed velocity has negligible effects on total cost for high-permeance membrane systems, further cost reductions with larger membrane permeances are limited due to significant concentration polarisation and lower mass transfer. Nevertheless, when operating SWRO at constant recovery, those levels of cost reduction can be achieved with an advanced spacer at half of that membrane permeance value. This highlights that more cost-effectiveness can be gained by improving the spacer efficacy than by increasing membrane permeance.

Long-term intermittent operation of a full-scale BWRO desalination plant

The use of renewable energy sources (RES) to power reverse osmosis (RO) desalination plants is a promising option for remote communities that face water scarcity. One drawback, however, is that the plants are generally obliged to operate intermittently due to the nature of the RES, which can reduce RO system performance in terms of production, salt rejection and energy consumption. This work analyses the long-term performance of a full-scale brackish water reverse osmosis (BWRO) desalination plant that has been working under intermittent operating conditions for 14 years (~9 h d−1). The plant has two stages, a 2:1 arrangement and five spiral wound membrane elements per pressure vessel (Filmtec™BW30-400). The feed water is pumped from a groundwater well. The feed flow and water flux recovery remained practically constant (416 m3 d−1 and around 65% respectively) over the 14-year period. The plant uses antiscalant dosing (5 mg L−1) and two cartridge filters in series (25 and 5 μm) as a pre-treatment. Rinses are carried out before shut-downs. Feedwater conductivity, permeate conductivity, feed pressure, pressure drop, permeate flow, and feed flow operating data were collected. The results show a decrease of about 50% in the average water permeability coefficient and an increase in specific energy consumption from 1.82 to 2.21 kWh m−3. The results provide useful information about the behavior of BWRO desalination systems under intermittent operating conditions and should be taken into account when designing RES-powered BWRO desalination plants.

A hybrid modeling approach for optimal design of non-woven membrane channels in brackish water reverse osmosis process with high-throughput computation

Optimal design of feed spacers in spiral wound membrane (SWM) modules has attracted extensive attention in industry and academia due to their widespread applications. However, it is still mathematically difficult and computationally expensive to solve many CFD models with various design parameters. In this work, a hybrid framework that couples a system-level model with a CFD model neglecting concentration polarization (CP) phenomenon is developed to analyze the performance of brackish water reverse osmosis (BWRO) processes under industrial operating conditions using non-woven SWM modules. The simulation results are in satisfactory agreement with measurement data, while computational efficiency is about ten times of that of a previous model accounting for the CP phenomenon. Furthermore, an efficient heuristic optimal design workflow that couples a high-throughput computation (HTC) strategy with the consideration of the field synergy equation is proposed to tackle the sophisticated hydraulic optimization problems within the scope of the considered design space. For this purpose, a total number of 1958 CFD models are solved with various geometries and inlet velocities at 51 nodes (1224 cores) on Tianhe-2 supercomputer by applying the proposed HTC strategy. Using the optimized spacer structure, the average permeation flux of water is enhanced by about 9%.

Performance evaluation of reverse osmosis brackish water desalination plant with different recycled ratios of retentate

Reverse Osmosis (RO) process has become one of the most widely utilised technologies for brackish water desalination for its capabilities of producing high-quality water. This paper emphasis on investigating the feasibility of implementing the retentate recycle design on the original design of an industrial medium-sized multistage and multi-pass spiral wound brackish water RO desalination plant (1200 m³/day) of Arab Potash Company (APC) located in Jordan. Specifically, this research explores the impact of recycling the high salinity stream of the 1st pass (at different recycled percentages) to the feed stream on the process performance indicators include, the fresh water salinity, overall recovery rate, and specific energy consumption. The simulation is carried out using an earlier model developed by the same authors for the specified RO plant using gPROMS suits. This confirmed the possibility of increasing the product capacity by around 3% with 100% recycle percentage of the high salinity retentate stream.

Seawater Desalination by Using Nanofiltration (NF) and Brackish Water Reverse Osmosis (BWRO) Membranes in Sequential Mode of Operation

In this study, the applicability of nanofiltration (NF) membranes as a pretreatment prior to reverse osmosis (RO) in seawater desalination was investigated. The membranes used wereNF270 and NF90 as the NF membranes, while the brackish water (BW) RO membrane BW30 was used as the RO membrane. In desalination tests, permeates of the NF membraneswere collected and used as the feed to the BW30 membrane. The calculated permeate fluxes were 6.7 L/h.m2, 11.3 L/h.m2, 24.3 L/h.m2, and 36.6 L/h.m2 for single BW30-35 bar,NF270-30 bar + BW30-35 bar, NF90-30 bar + BW30-25 bar and NF90-30 BW30-35 bar, respectively. The calculated water recovery and rejected salt values were 51.6%, 41.4%,24.8%, 15.4% and 98.2%, 98.2%, 96.0%, 91.0% for NF90-30 bar + BW30-35 bar, NF90-30 bar + BW30-25 bar, NF270-30 bar + BW30-35 bar and single BW30-35 bar, respectively.The qualities of the product waters of integrated systems (NF+BWRO) and the single BWRO system were also investigated. Boron rejection was fairly well with average boronrejections of 59.3% and 60.2% by NF90-30 bar + BW30-25 bar and NF90-30 bar + BW30-35 bar combinations, respectively while single BW30-35 bar gave an average rejection of49.6%. The results obtained showed that the quality of product water obtained using single BWRO did not comply with the irrigation standards, while the integrated systems providedtotal compliance to irrigation standards with the exception of boron.

An Air Operated Domestic Brackish Water Reverse Osmosis Plant: Economically Sustainable Solution for Safe Drinking Water Supply for Chronic Kidney Disease of Unknown Etiology Affected Areas in Sri Lanka

Chronic Kidney Disease with unknown etiology (CKDu) is one of the crucial health issues in North Central, Uva, North Western, North, Central, and Eastern Provinces of Sri Lanka and incapacitates the kidney function. The main source for the CKDu has not yet been identified, though many scientists believed that the number of certain drinking water quality parameters is changed due to the contamination of water sources by agricultural activities. Hence, the government of Sri Lanka introduces electrically driven Brackish Water Reverse Osmosis (BWRO) plants with a capacity of 10 tones/day to supply safe drinking water for the impacted community though it is an energy-intensive process. Concurrently, a smaller version of an electrically driven BWRO plant was introduced to the rural farming community for their domestic use. However, it was not practically worked out due to various reasons such as high cost, unavailability of electrical power supply for those villages. In this study, an economical air operated domestic use BWRO plant with zero-emission was designed. This anticipated system significantly reduces the government expenditures to subsidize the water purification cost by 50% of the existing expenses. Besides, simple payback time was found to be 2.5 years, and the benefit-cost ratio to be more than 1. Evaluating the performance with the conventional values, it comprehends with more sustainable and economically viable system compared to the existing method of water purification.

Changes in feed water salinity with pumping of the wellfield used to supply a brackish water RO facility at the City of Fort Myers, Florida

Changes in feed water salinity with pumping of the wellfield used to supply a brackish water RO facility at the City of Fort Myers, Florida

Evaluation and minimisation of energy consumption in a medium-scale reverse osmosis brackish water desalination plant

The Reverse Osmosis (RO) process has been expansively used in water treatment as a result of its low energy consumption compared to thermal distillation processes, leading to reduced overall water production cost. Evaluation and minimisation of energy consumption (expressed in kWh/m3 of fresh water production) in a medium-scale spiral wound brackish water RO (BWRO) desalination plant of the Arab Potash Company (APC) are the main aims of this research. The model developed earlier by the authors has been integrated to simulate the process and achieve the main aims. Energy consumption calculations of low salinity BWRO desalination plant, with and without an energy recovery device, have been carried out using the gPROMS software suite. In other words, this research evaluated the impact of adding an energy recovery device on the RO process energy consumption of the APC, which is introduced for the first time. Also, the effects of several operating conditions of BWRO process include the feed flow rate, pressure and temperature on the performance indicators, which include the energy consumption and total plant recovery at different energy recovery device efficiencies, were studied. The simulation results showed that the total energy consumption could be reduced at low values of feed flow rates and pressures and high values of temperatures. More importantly, there is an opportunity to reduce the total energy consumption between 47% and 53.8% compared to the one calculated for the original design without an energy recovery device.

A hybrid forward osmosis/reverse osmosis process for the supply of fertilizing solution from treated wastewater

This work investigates the application of a hybrid system that combines forward osmosis (FO) and reverse osmosis (RO) processes for the supply of a fertilizing solution that could be used directly for irrigation purposes. In the FO process the feed solution is treated sewage effluent (TSE) and two different types of draw solutions were investigated. The impact of the feed solution and the draw solution flowrates and the membrane orientation on the membrane flux were investigated in the forward osmosis process. RO was used for the regeneration of the draw solution. In the forward osmosis process it was found that the highest membrane flux was 13.2 LMH. The FO process had high rejection rates for total phosphorus and ammonium which were 99% and 97%, respectively. RO achieved 99% total salts rejection rate. Seawater RO (SW30HR) and brackish water RO (BW30LE) membranes were used for the regeneration of the draw solution. The specific power consumption for the regeneration of the draw solution was 2.58 kW h/m3 and 2.18 kW h/m3 for SW30HR and BW30LE membranes, respectively. The final product water had high quality in terms of total dissolved solids concentration but the concentration of phosphorus was slightly higher than recommended due to adding 0.1 M of diammonium phosphate in the draw solution.

Potable-quality water recovery from primary effluent through a coupled algal-osmosis membrane system

A coupled algal-osmosis membrane treatment system was studied for recovering potable-quality water from municipal primary effluent. The core components of the system included a mixotrophic algal process for removal of biochemical oxygen demand (BOD) and nutrients, followed by a hybrid forward osmosis (FO)-reverse osmosis (RO) system for separation of biomass from the algal effluent and production of potable-quality water. Field experiments demonstrated consistent performance of the algal system to meet surface discharge standards for BOD and nutrients within a fed-batch processing time of 2–3 days. The hybrid FO-RO system reached water productivity of 1.57 L/m2-h in FO using seawater as draw solution; and permeate flux of 3.50 L/m2-h in brackish water RO (BWRO) and 2.07 L/m2-h in seawater RO (SWRO) at 2068 KPa. The coupled algal-membrane system achieved complete removal of ammonia, fluoride, and phosphate; over 90% removal of calcium, sulfate, and organic carbon; and 86–89% removal of potassium and magnesium. Broadband characterization using high resolution mass spectrometry revealed extensive removal of organic compounds, particularly wastewater surfactants upon algal treatment. This study demonstrated long-term performance of the FO system at water recovery of 90% and with membrane cleaning by NaOH solution.

Prediction of nanofiltration rejection performance in brackish water reverse osmosis brine treatment processes

A predictive nanofiltration model was built in Python to be used in reverse osmosis brine treatment processes. The model was fitted to rejection data obtained from NF trains functioning as a brine concentrator upstream of a gypsum precipitation reactor at a full-scale mine water treatment plant in Ahafo, Ghana. Over the six month operational period considered (September 2017 – March 2018) the rejection capability of the installed elements deteriorated considerably. This was reflected by a 13% increase in membrane pore radius, 40% decrease in effective active layer thickness and an 18% decrease in absolute value of the feed-membrane Donnan potential. Performance of elements from other manufacturers was simulated by loading their respective properties into the model. Cases modelled included a tightly wound Dow NF 90, a loosely wound Desal DS-5 DL and a Koch TFC SR-2 element. Rejections obtained from the installed MDS elements most closely approximated the performance of a loose NF element. These modelling studies have shown that the NF model built is capable of modelling nanofiltration in brackish water treatment processes. The current disadvantage of the model is the number of membrane—specific input parameters which need to be verified with independent experimentation. As a start, it is recommended that electro-kinetic data be obtained for similar solutions to enable a membrane charge density sub-module to be incorporated into the model.

Design, simulation and feasibility study of a combined CO2 mineralization and brackish water desalination process

This study presents a novel process integration scheme between CO2 mineralization and brackish water reverse osmosis (BWRO). The integration is based on the reciprocal nature of these two processes: While CO2 mineralization needs metal ions such as Na+ to convert CO2 into mineral carbonates like sodium bicarbonate, BWRO is designed to reject such ions to produce fresh water. Thus, there is a potential synergy that can be gained through their integration. To examine the feasibility of such process integration, techno-economic analysis (TEA) and CO2 life cycle assessment (LCA) are conducted for various possible configurations of the integrated process. A key requirement for TEA and CO2 LCA is the availability of mass and energy balance data. Therefore, the process is simulated with the commercial simulation software tool of Aspen Plus combined MATLAB. Another requirement is the selection of appropriate evaluation scenarios. Based on a market analysis, the proposed process is assumed to be installed either in the US or in the China to replace a respective conventional benchmark process. Also, two sources of electricity (coal and wind onshore) are considered in the evaluation in order to investigate the sensitivity of the process performance on the type of electricity used. As a result of the analysis, the CO2 avoidance cost of the designed process is calculated to be 132˜245$/metric ton of CO2 with wind-based electricity. Given other advantages of the mineralization over the geological storage, the presented process integration between CO2 mineralization and BWRO deserves further investigation as a means to produce useful chemicals and fresh water while curbing CO2 emission.

Low-recovery, -energy-consumption, -emission hybrid systems of seawater desalination: Energy optimization and cost analysis

Ultraconcentrated seawater disposal is detrimental to marine biota, and carbon emissions from desalination processes are detrimental to the atmosphere. These detrimental effects are expected to increase, given the continuously growing global water demand and the associated water stress problems caused by water scarcity and population and economic growth. Along with political inclination to impose strict environmental regulations and a carbon tax on the price of freshwater, developing low-energy-consumption, low-carbon-emission desalination systems operating at low recovery is the future of SW desalination. Such desalination systems can be achieved by integrating electrodialysis, which does not have driving force limitations, with nanofiltration and brackish water reverse osmosis (RO), which provide low-energy-consumption desalination regions, to decrease energy consumption below that of current state-of-the-art RO systems. In this study, iterative optimization algorithms were developed for hybrid desalination systems. As a result, energy consumptions as low as 1.3 kWh/m3 were achieved at recoveries <30%. Despite the higher cost of freshwater production compared with that of state-of-the-art RO systems, owing to utilization of larger membrane areas, the hybrid systems reduced carbon dioxide emissions and brine concentrations from 63 to 26 and 41 to 34%, respectively.

Potential application of osmotic backwashing to brackish water desalination membranes

Brackish water Reverse Osmosis (RO) and Nanofiltration (NF) are an attractive technology for potable water production and wastewater reclamation. However, scaling and fouling remain common problems that limit the optimal use of membranes, cause flux decline, increase energy demand and require periodic cleaning by chemical means. Herein, we consider the use of osmotic backwashing, already reported in the literature for seawater RO, as a cleaning method for brackish RO and NF. Three commercial membranes were used in a bench-scale system along with three draw solutions, NaCl, Na2SO4 and MgSO4, to assess the osmotic flux induced during a backwash cycle. The backwash flux was found to be in good agreement with calculations made using a computational model, which was then used to reveal the role of solution chemistry as well as membrane support properties in controlling the backwash intensity and duration. Specifically, sulphate-based solutions showed a good ability to maintain an osmotic flux, better than NaCl, for which lower membrane selectivity restricts use as a draw agent. While preliminary experiments demonstrated the ability of an osmotic backwash to remove CaPO4 scale, achieving nearly complete flux restoration for some cases, the process requires further optimization.

Flux Optimization in Reverse Osmosis via the Solution-Diffusion Model

This paper suggests a new method of predicting flux values at reverse osmosis (RO) desalination plants. The study is initiated by using the solution-diffusion model that is applied to the groundwater source at Abqaiq plant (500 RO plant) at Saudi Aramco, Dhahran, Saudi Arabia in order to calculate the osmotic pressure of the treated water for Shedgum/Abqaiq groundwater. For modelling purposes, the same technique is used to determine the osmotic pressure drops at the same plant configuration and operating conditions when using seawater sources such that of Arabian Gulf and the Red Sea waters. High rejection brackish water RO (BWRO) element Toray TM720D-400 with 8" is the RO membrane type that is used at Abqaiq plant. The calculated osmotic pressures of the three water sources, assuming that they are all treated at Abqaiq plant, are utilized to determine the appropriate flux values as well as membrane resistances of different BWRO Toray membranes. Values of numerous parameters such as water permeability constant, applied pressure, gas constant, water temperature, water molar volume and membrane thickness, water salinity/TDS are taken into account to develop our calculations through the solution-diffusion model. A comparison between low-pressure, standard and high-pressure BWRO Toray membranes performance have been established to select the ideal membrane type for the treatment of water from various sources at Abqaiq plant. The model results confirm an inverse relationship between the membrane thickness and the water flux rate. Also, a proportional linear relation between the overall water flux and the applied pressure across the membrane is identified. Higher flux rates and lower salinity indicate lower membrane resistance which yields to the higher water production. Modelled data predict that BWRO Toray TM720D-440 with 8" membrane is the optimal BWRO membrane choice for the three water sources at Abqaiq plant.

Membrane capacitive deionization-reverse electrodialysis hybrid system for improving energy efficiency of reverse osmosis seawater desalination

The extraordinarily high salinity of seawater (e.g., Gulf seawater) requires a seawater desalination system such as two-pass reverse osmosis (RO). However, the auxiliary brackish water reverse osmosis (BWRO) treatment for satisfying the produced water quality significantly increases the energy consumption. This study first proposes a novel concept, integrating membrane capacitive deionization (MCDI) and reverse electrodialysis (RED) with RO to treat high-salinity seawater with enhanced energy efficiency. In this hybrid system, MCDI successfully substituted for BWRO and met the required water quality regulations by the World Health Organization (WHO). Moreover, RED recovered 33% of the energy from discharges. The optimum operating conditions of the RO-MCDI hybrid system were found to be 0.8 V of applied voltage on MCDI at 50% and 80% of water recovery for the first pass RO and the second pass MCDI, respectively. In particular, the great flexibility of MCDI in removal efficiency could generate notable synergistic effects with RED, which could lead to better energy efficiency. Consequently, under optimized operation conditions, the energy consumption of this novel RO-MCDI-RED hybrid system was respectively reduced by 39.0% and even 16.8% compared to that of a typical two-pass RO system without and with RED.

Treatment of woolen textile wastewater using membrane bioreactor, nanofiltration and reverse osmosis for reuse in production processes

The reuse opportunities of separate wastewater streams and end-of-pipe composite wastewater were investigated in an integrated woolen textile mill. The main purpose was to reuse either the treated composite wastewater and/or treated/untreated separate streams depending on the water quality demand of different water use points in the production processes. In this context, three separate wastewater streams (tops-fiber, bobbins thread and fabric dyeing-finishing wastewaters) and composite wastewater were analyzed in terms of quality and quantity. Moreover, raw groundwater, softened process water, cationic ion exchangers’ regeneration wastewater, and reverse osmosis (RO) concentrates were also characterized. Wastewater treatability studies were conducted in pilot-scale employing membrane bioreactor (MBR), nanofiltration (NF) and brackish water reverse osmosis (BWRO) processes at different test conditions. In the wastewater characterization studies, peaks and oscillations were found in the separate wastewater streams depending on the production schedules and applied dyeing recipes. Therefore, due to mixing effects of separate streams, it was decided to employ pilot-scale treatability tests on the composite wastewater. In the MBR process, the average chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), and color removals were 70, 74, 86, 28, 43, and 62%, respectively. In MBR + NF and MBR + RO tests, the removals of all analyzed parameters were 40–99 and 52–99%, respectively. The pH, conductivity, turbidity, color, and TN concentrations in MBR + RO effluent were 7.6–7.8, 57–65 μS/cm, 0.6–1.2 NTU, 25–44 PtCo, and 14–16 mg/L, respectively. In addition, the COD, BOD5 and total hardness values were found under 1 mg/L. The treated water was finally disinfected with ultraviolet (UV) light to ensure microbial safety before reuse in dyeing process. Treated water samples were tested in different dyeing recipes in lab-scale to determine their impacts on woolen textile product quality. Dry-wet rubbing, water fastness, dry-cleaning and alkali-acid perspiration fastness tests were performed on the fabrics dyed with MBR + UV, MBR + NF + UV and MBR + RO + UV effluents and the results were compared with those dyed with process water (softened groundwater). It was found that especially MBR + NF + UV and MBR + RO + UV effluents did not negatively affect product quality. Surprisingly, the color depth was increased in some shades with MBR + UV effluent, possibly due to the presence of already existing salts. Overall, the product quality tests with reclaimed wastewaters exhibited very promising results. Therefore, capital and operational costs were estimated for a potential full-scale wastewater treatment and reclamation plant in the textile mill.

Sustainable Groundwater Exploitation Aiming at the Reduction of Water Vulnerability in the Brazilian Semi-Arid Region

Semi-arid regions have historically suffered from low water availability. In addition, the increasing frequency and intensity of extreme weather events credited to global climate change has made it increasingly clear that among the challenges faced by society water resource management is extremely necessary. In this context, desalination based on renewable energy resources integrated with production systems that make use of the waste resulting from this process becomes a socio-environmentally indicated alternative to expand existing supply strategies and sustainable water use in isolated locations, and/or areas distant from large urban centers, thus addressing local potential and reducing environmental impacts. This study assesses the use of Photovoltaic Solar Power Plants (PSPPs), as well as of residues generated in a Brackish Water Reverse Osmosis System (BWRO), in productive units linked to fish and family farming. This is as an alternative way to reduce water vulnerability in the Brazilian semi-arid area (BS), adhering to climate change adaptation measures in the light of Brazilian public policies through the Freshwater Program (Programa Água Doce—PAD), which aims to promote access to good quality water to approximately 500 thousand people in the Brazilian semi-arid region.

In Situ Modification of Reverse Osmosis Membrane Elements for Enhanced Removal of Multiple Micropollutants

Reverse osmosis (RO) membranes are widely used for desalination and water treatment. However, they insufficiently reject some small uncharged micropollutants, such as certain endocrine-disrupting, pharmaceutically active compounds and boric acid, increasingly present in water sources and wastewater. This study examines the feasibility of improving rejection of multiple micropollutants in commercial low-pressure RO membrane elements using concentration polarization- and surfactant-enhanced surface polymerization. Low-pressure membrane elements modified by grafting poly(glycidyl methacrylate) showed enhanced rejection of all tested solutes (model organic micropollutants, boric acid, and NaCl), with permeability somewhat reduced, but comparable with commercial brackish water RO membranes. The study demonstrates the potential and up-scalability of grafting as an in situ method for improving removal of various classes of organic and inorganic micropollutants and tuning performance in RO and other dense composite membranes for water purification.

3D CFD study of the effect of multi-layer spacers on membrane performance under steady flow

Multi-layer feed channel spacers have shown superior mass transfer enhancement than conventional dual-layer spacers used in reverse osmosis (RO) spiral wound membrane modules. However, mass transfer indicators do not directly address the economic advantages of multi-layer spacers. To allow for a direct economic comparison of spacer designs, a simplified multi-scale techno-economic model is proposed which can provide useful cost trends. A total of 8 feed spacer geometries with different attack angles (α = 0–60°) and filament sizes (df/hch = 0.4–0.6) are first investigated using 3D-CFD. Multi-layer spacers typically increase both Sherwood number (~12%) and friction factor (~140%). The techno-economic model is then used to assess the impact of these changes on the total processing cost for RO. The latter analysis found that larger pressure drops associated with multi-layer spacers in long channels have little impact on total water processing cost for RO, with multi-layer spacers showing lower total processing costs (by 2–4%) than the dual-layer spacer for both seawater and brackish water RO. Novel spacer designs should therefore emphasise flux enhancement. The importance of including energy recovery for a more accurate economic analysis is highlighted, especially for systems with low recovery ratio.