Desalination Of Brackish Groundwater Research Articles

Desalination of brackish water using cascade Rankine cycle based reverse osmosis system

The desalination of brackish ground water using cascade Rankine cycle is proposed. A pair of a Rankine cycle like steam Rankine cycle (SRC) and organic Rankine cycle (ORC) as a waste heat recovery. The single stage steam turbine for the SRC unit while the scroll expander for ORC unit is selected. Simulation of cascade RO system performance is considered using R245fa as a working fluid for ORC unit. The saturated steam from solar Scheffler disc will expand into steam turbine, where the reject heat from steam turbine will utilize for evaporation of ORC working fluid. The high-pressure RO pumps integrated with SRC and ORC turbines to provide net driving pressure to the RO module. This type of system is well suitable for desalination of brackish water due to moderate working temperature & pressure. Result shows that the pair of Rankine cycle will increase the overall (cascade) efficiency of the system. The basic input parameters are optimised with Taguchi approach. The performance of the system shows a good agreement with variation of mass flow rate of the steam in which the permeate flow rate from RO will increase along with the cycle efficiencies.

Site specific assessment of the viability of membrane Capacitive Deionization (mCDI) in desalination of brackish groundwaters for selected crop watering

Membrane Capacitive Deionization (mCDI) desalination is an emerging technology that can, potentially, be scaled to an appropriate capacity and powered by photovoltaics for farm applications where costs of electrical power provision are prohibitive. In order to assess the critical influences of location and mCDI configuration on profitability, a farm scale economic model was developed to calculate annualized profits, internal rate of return, return period and bore salinity thresholds for farm profitability with mCDI desalination for a 10-year investment period for various crops at selected locations in south eastern Australia with known groundwater quality issues. Results show that the cost of water supply including bore drilling and pumping, mCDI desalination, photovoltaics, brine disposal and water storage is less than AU$1/m3 for typical field applications with salinity removals <2.3 dS/m. We show that application of mCDI improves profitability over irrigation with brackish water of between AU$2500/ha/yr and AU$44,200/ha/yr depending on the crop. By providing a system level cost analysis, the results highlight areas where there is scope for cost improvements in both mCDI desalination and agricultural processes. The operational scale mCDI performance and sizing model presented here can be modified for use in other desalination applications.

Irrigation with RO concentrate and brackish groundwater impacts pecan tree growth and physiology

Water scarcity has become a salient problem in southern New Mexico. A combination of drought and a decrease in surface water for irrigation encouraged to search for other sources of water. Desalination of brackish groundwater (BGW) using reverse osmosis (RO) results in a highly salty water or RO concentrate. In this study, impacts of using BGW and RO concentrate for irrigating pecan trees inside a greenhouse were evaluated. The objective was to determine if pecan trees are suitable for irrigation with BGW and RO concentrate, and evaluate the possible effects on pecan growth and physiological parameters. For each of two growing seasons (2017 and 2018), three irrigation treatments of 0.8, 4.0 (BGW), and 8.0 ds/m (RO) were applied every 14 days for 8 months. Four-year-old pecan trees were planted in pots filled with sandy-loam soil. Response variables included plant height and diameter, as well as physiological data including photosynthetic rate, chlorophyll content, transpiration rate, stomatal conductance, stem water potential, and leaf ions concentrations. Net pecan growth was 2.75 cm less in RO concentrate irrigated pots than control by the end of the second season. Plants irrigated with RO had the lowest chlorophyll content (30.75) and the lowest stem water potential (-17.22 bar). Na+ and Cl− concentrations reached 0.056 and 0.027 meq/l in the leaf samples in RO irrigated pecans. All trees survived the first season but only 75 % of the pecan trees irrigated with BGW and 50 % of those irrigated with RO survived the two seasons of the experiment. This suggested that continuous long-term irrigation with BGW and RO concentrate is not suitable in arid areas and new irrigation scheduling protocols are needed for safe reuse of BGW and RO concentrate.

Exploratory ranking analysis of brackish groundwater desalination for sustainable agricultural production: A case study of the Arava Valley in Israel

Management of environmental resources presents challenges across agricultural production. In the case of the semi-arid region of Arava Valley in Israel irrigation with groundwater brackish water is a widespread practice that has severe limitations. In this research studies are taking place for brackish groundwater upgrading for unrestricted use for irrigation and sustainable agricultural production. The treatment system applies two main treatment stages: nanofiltration and reverse osmosis membrane process and, the pilot system with the capacity of around 1 m3/h. Different mixtures of nanofiltration and reverse osmosis, Brackish and potable permeates are then applied for irrigation of pepper crops.The field results together with the graphical visualization approach using Hasse diagram technique show that the conventional brackish feed water produces good revenue about fruit weight, fruit diameter, and fruit length. A membrane treatment using nanofiltration and reverse osmosis yields an increase in production (more fruit number). Extension of the research at the field level may aid to optimize irrigation use strategy to increase the food production.

Commissioning a High‐Recovery Brackish Groundwater Desalination Plant in San Antonio

Optimizing San Antonio Water System's new desalination plant yielded operational strategies and lessons learned for engineers and operators.

A Pilot Study of an Electromagnetic Field for Control of Reverse Osmosis Membrane Fouling and Scaling During Brackish Groundwater Desalination

This study investigated the effects of an electromagnetic field (EMF) on control of membrane fouling and scaling during desalination of brackish groundwater using a pilot reverse osmosis (RO) skid. The groundwater was primarily CaSO4 type with a total dissolved solids concentration of 5850 mg/L and hardness of 2500 mg/L as CaCO3. Two EMF devices were installed in the pipeline before a cartridge filter and in the RO feed inlet to induce an electric signal of ±150 kHz to the groundwater. The effects of EMF on membrane scaling were evaluated under accelerated conditions, i.e., without pH adjustment and addition of antiscalant. Two-phase experiments were conducted: Phase 1 (376 h) with the EMF devices turned on after 150 h baseline operation; and Phase 2 (753 h) with the EMF devices turned on from the beginning of testing. The EMF significantly reduced membrane scaling and improved RO performance by 38.3% and 14.3% in terms of normalized water permeability decline rate after 150 h and 370 h operation, respectively. Membrane autopsy results indicated that the fouling layer formed under the influence of EMF was loose with a low density and was easily removed by hydraulic flushing.

Impact of intermittent operation on reverse osmosis membrane fouling for brackish groundwater desalination systems

Solar powered reverse osmosis systems are a promising technology for remote communities facing water insecurity. These systems are often operated intermittently with extended shutdown periods to reduce energy storage requirements and system cost. This article experimentally evaluates the effect of intermittent operation on membrane fouling with brackish groundwater. Lab-scale results show that the use of anti-scalant during operation and a rinse with clean water before shutting down the system results in high membrane permeability, above 70% of the initial membrane permeability after seven days of operation. Without rinsing, the lab-scale results showed the membrane permeability dropped to less than 50% of the initial permeability. Membrane autopsy using scanning electron microscopy for mineral deposits and adenosine triphosphate for quantifying biofouling revealed the fewest deposits when anti-scalant and a rinse were performed. To show scalability, pilot-scale studies were conducted and showed similar permeability declines and fouling structures in membrane autopsy. These results will help inform the advancement of reliable solar powered reverse osmosis systems for remote areas.

A Spatially Resolved Thermodynamic Assessment of Geothermal Powered Multi-Effect Brackish Water Distillation in Texas

Brackish groundwater desalination is increasingly being considered as a means to supplement drinking water in regions facing scarce freshwater supplies. Desalination is more energy intensive and expensive than traditional freshwater sources. One method of offsetting carbon emissions is to pair desalination technology with renewable energy sources. This research assesses the geographical feasibility of using a geothermal multi-effect distillation (MED) plant to produce freshwater from brackish aquifers in Texas. The system is analyzed using a thermodynamic model of a binary cycle MED plant. The thermodynamic model is integrated with spatially resolved information of Texas’ geothermal gradient and existing brackish well data (such as depth, salinity, and temperature) to quantify production potential. The results from this study allow for a comparison of potential geothermal desalination plant implementation across all of Texas, rather than a single site assessment. Although this water treatment approach is technologically viable across much of Texas, the system proves to be very energy intensive in all areas except for two hot geopressured fairways in Southeast Texas, the Frio and the Wilcox. In both locations, our research concludes the binary cycle-MED plant can operate self-sufficiently, producing both freshwater and electricity. One well in the fairways can produce 121–1132 m3 of water per day, enough for 232–2133 people. The framework outlined in this paper can be useful to policymakers and water planners considering where to build desalination facilities.

Surface-Induced Silica Scaling during Brackish Water Desalination: The Role of Surface Charge and Specific Chemical Groups.

Silica scaling of membranes used in reverse osmosis desalination processes is a severe problem, especially during the desalination of brackish groundwater due to high silica concentrations. This problem limits the water supply in inland arid and semiarid regions. Here, we investigated the influence of surface-exposed organic functional groups on silica precipitation and scaling. A test solution simulating the mineral content of brackish groundwater desalination brine at 75% recovery was used. The mass and chemical composition of the precipitated silica was monitored using a quartz crystal microbalance, X-ray photoelectron spectroscopy, and infrared spectroscopy, showing that surfaces with positively charged groups induced rapid silica precipitation, and the rate of silica precipitation followed the order -NH2 ∼ -N+(CH3)3 > -NH2/-COOH > -H2PO3 ∼ -OH > -COOH > -CH3. Force vs distance AFM measurements showed that the adhesion energy between a silica colloid glued to AFM cantilever and the studied surfaces increased as the surface charge changed from negative to positive. Thus, for the first time direct measurements of molecular forces and specific chemical groups that govern silica scaling during brackish water desalination is reported here. The influence of the different functional groups and the effect of the surface charge on silica precipitation that were found here can be used to design membranes that resist silica scaling in membrane-based desalination processes.

An overview on the state of art on IAH coastal aquifer dynamics and coastal zone website

The website of the IAH Coastal Aquifer Dynamics and Coastal Zone Management (CAD-CZM) Network, linkable at the web address www.iah-cad-czm.net, aims at improving the knowledge about coastal aquifer for supporting worldwide the assessment, development and management of water resources endangered by saltwater intrusion. The overall target of this project is promoting the development of web-GIS that gathers coastal aquifer data from different sources to assist, by the support of researchers, professionals, stakeholders and water managers to make the correct choices for the sustainable use of these precious resources. The CAD-CZM network tries to satisfy the interest expressed in the recommendations issued on different occasions by UNESCO and IAEA for studying coastal areas in the frame of joint programs in cooperation with other international agencies. The CADCZM website structure aims to collect information coming from any kind of source, as technical as scientific, and its target is to make them available in the aim of taking under control the rate of exploitation and the management of these vulnerable groundwater resources. The website organization is like that anyone could find the specific coastal zone, he is interested in gaining information, only looking for it on the google earth link, present inside the website. Once identified the area of interest, it is possible to download, if present, the specific sheet including all the information collected, checked and uploaded, by the scientific committee of the website. Starting from the analysis of a database of more than 70 coastal aquifer, reporting information about lithology, hydrogeological and geochemical characteristics, salinity sources, applied monitoring methods, management strategies, and seawater and brackish groundwater desalination technologies adopted, an updated overview of the state of the knowledge about seawater intrusion all over the world is presented.

Desalination of brackish groundwater and reuse of wastewater by forward osmosis coupled with nanofiltration for draw solution recovery

This study evaluates a treatment system centered on forward osmosis (FO) to extract high-quality water from real brackish groundwater and wastewater. The groundwater had salinity of 4 g/L, while the wastewater sample consisted of a secondary effluent. These feed solutions were treated first in a FO step, achieving a recovery of >60%. Subsequently, the diluted draw solutions were subject to a nanofiltration (NF) step to regenerate their original osmotic pressure and to simultaneously collect a final permeate product. Magnesium chloride and sodium sulfate were both suitable draw solutes for this application. MgCl2 had a larger specific reverse salt flux and induced a more pronounced fouling-related flux decline with groundwater samples. Na2SO4 was re-concentrated with a higher permeability NF membrane but may require the use of anti-scalants. The average fluxes obtained in high-recovery batch FO were between 5 and 11 L m−2h−1 with an initial bulk draw osmotic pressure in the range of 12–15 bar. Relatively low flux decline was observed in fouling experiments with both samples, while physical cleaning proved promising to recover the related loss in productivity. The final product waters were all of very high quality, suggesting the potential of this coupled system for water reuse and desalination. Some challenges related to the relatively low water flux in the FO step, as well as the loss of draw solutes and the gradual change in composition of the draw solution, need further analysis to establish the technical and economic feasibility of the system.

Low cost desalination of brackish groundwaters by Capacitive Deionization (CDI) – Implications for irrigated agriculture

Research into desalination of groundwaters for agricultural application in Australia has previously focused on the viability of large scale reverse osmosis plants. Capacitive Deionization (CDI) is an alternative method of desalination that has been demonstrated to be effective for desalting moderately saline (brackish) waters in pilot studies and can be powered using photovoltaics. Using a farm scale economic model coupled to a CDI performance model, potentially viable agricultural applications for CDI have been identified with variation in crop type and CDI configuration enabling optimisation. Scenarios for grapes, oranges, almonds, apples and tomatoes were modelled with maximum internal rates of return (IRR) and annualised profits (AUD$/ha/yr) determined. Groundwater bore salinity thresholds above which the regime is not feasible were found to be 4.2 dS/m for grapes, 5.5 dS/m for oranges, 4.4 dS/m for almonds, 14 dS/m for apples and 8.5 dS/m for tomatoes for a 60 ha crop with an investment period of 10 years. Costing of CDI desalinated water was scenario dependent with a large portion falling below AUD$1/kL. CDI desalination was found to be economically feasible for a range of scenarios and should be explored further as an option to assist with global water and food security concerns.

Multi-layered spatial methodology for assessing the technical and economic viability of using renewable energy to power brackish groundwater desalination

Wind and solar energy can potentially be used to power desalination facilities to sustainably meet growing water demands with a smaller carbon footprint than conventional approaches. This work presents a detailed method for assessing the technical and economic viability of using these renewable forms of energy to power desalination facilities. The method relies on a multi-layered, spatial model that incorporated multiple variables such as depth of water resource, salinity levels, magnitude of local renewable energy resources, distance to water infrastructure, and, for comparative purposes, the local price of water. To illustrate this method, it was applied to 1445 site locations on state of Texas lands owned by the General Land Office that overlay brackish aquifer resources. Using this method, 193 potentially economically viable sites were identified that have estimated renewable desalination water production costs lower than local municipal water prices. The results of this analysis showed that using wind to power a desalination facility is economically preferable at 145 of the 193 sites; solar was preferable at the remaining 48 sites. Solar and wind resources are both abundant in Texas; however, the particularly high capacity factors for wind across much of the state helps wind deliver the lowest cost electricity.

Study of polyethyleneimine coating on membrane permselectivity and desalination performance during pilot-scale electrodialysis of reverse osmosis concentrate

Abstract A two-electrical stage and four-hydraulic stage pilot-scale electrodialysis system was used to investigate desalination performance and ion permselectivity of Ionics monovalent permselective membranes (CR671/AR112B) and normal grade membranes (CR67/AR204) (Suez Water Technologies & Solutions) to treat reverse osmosis (RO) concentrate in a brackish groundwater desalination plant. Monovalent permselective cation-exchange membrane CR671 was manufactured by surface modification of standard normal grade membrane CR67 with highly-branched polyethyleneimine coating. The covalently bonded polyethyleneimine layer on membrane surface was characterized by methylene blue dye test, Fourier transform infrared spectroscopy with attenuated total reflection (ATR-FTIR), and electrochemical impedance spectroscopy (EIS). The pilot-scale testing demonstrated the monovalent permselective membranes achieved the same desalting efficiency as the normal grade membranes under the same current density. The energy efficiency in terms of normalized salt removal decreased with the increasing current density (i.e., desalination level) but increased with feed water salt concentration. Polyethyleneimine coating on the CR671 membrane enhanced the selective transport of monovalent cations over divalent cations while having negligible impact on the membrane electrical resistance. The total stack resistance of electrodialysis was insensitive to concentration changes in the diluate and concentrate chambers during desalination of RO concentrate. The electrodialysis system achieved additional 55% of water recovery by treating RO concentrate, enhancing the overall water recovery from 82.5% of the primary RO to 92.1%. Scaling on the ion-exchange membranes and electrodes was effectively mitigated by addition of antiscalant and pH adjustment in concentrate and electrode rinsing streams. Electrodialysis was demonstrated a viable technology to modify product water quality and improve water recovery for desalination concentrate treatment.

Cost-optimal design of a batch electrodialysis system for domestic desalination of brackish groundwater

This study presents the pareto-optimal design of a domestic point-of-use batch electrodialysis (ED) system. Specifically, the optimal geometry, flow-rates, and applied voltage for total cost minimization were explored for varying production rate (9–15 L/h) and product concentration (100–300 mg/L) requirements, while feed concentration and recovery ratio were maintained at 2000 mg/L and 90%, respectively. Capital cost dominated over energetic cost; hence, optimal designs maximized current density. Capital cost was significantly higher for 100 mg/L systems, than 200 and 300 mg/L: $141 vs. $93 and $79, at 12±0.5 L/h of production. Pumps were an important consideration, contributing up to 46% of the total cost. Large membrane length-to-width aspect ratios (3.5:1 to 6:1) and thin channels (0.30–0.33 mm) promoted high current densities, and 11–21 cm/s velocities optimized mass transfer against pressure drop. Optimal voltages were 0.9–1.3 V/cell-pair at 9 L/h, and decreased at higher rates. Lastly, higher production was obtained primarily by increasing cell-pair area rather than number of cell-pairs (36–46). It was additionally observed that active area increased linearly with feed concentration (1500–2500 mg/L), while recovery (60–90%) minimally affected design. This work also suggests that voltage control during the batch process, and less expensive pumps, can further reduce cost.

Minimum energy requirements for desalination of brackish groundwater in the United States with comparison to international datasets

This paper uses chemical and physical data from a large 2017 U.S. Geological Survey groundwater dataset with wells in the U.S. and three smaller international groundwater datasets with wells primarily in Australia and Spain to carry out a comprehensive investigation of brackish groundwater composition in relation to minimum desalination energy costs. First, we compute the site-specific least work required for groundwater desalination. Least work of separation represents a baseline for specific energy consumption of desalination systems. We develop simplified equations based on the U.S. data for least work as a function of water recovery ratio and a proxy variable for composition, either total dissolved solids, specific conductance, molality or ionic strength. We show that the U.S. correlations for total dissolved solids and molality may be applied to the international datasets. We find that total molality can be used to calculate the least work of dilute solutions with very high accuracy. Then, we examine the effects of groundwater solute composition on minimum energy requirements, showing that separation requirements increase from calcium to sodium for cations and from sulfate to bicarbonate to chloride for anions, for any given TDS concentration. We study the geographic distribution of least work, total dissolved solids, and major ions concentration across the U.S. We determine areas with both low least work and high water stress in order to highlight regions holding potential for desalination to decrease the disparity between high water demand and low water supply. Finally, we discuss the implications of the USGS results on water resource planning, by comparing least work to the specific energy consumption of brackish water reverse osmosis plants and showing the scaling propensity of major electrolytes and silica in the U.S. groundwater samples.

Prevention and management of silica scaling in membrane distillation using pH adjustment

Membrane scaling by silica is a major challenge in desalination, particularly for inland desalination of brackish groundwater or geothermal water, which often contain high concentrations of silica and dissolved solids. Adjustment of feed pH may reduce silica scaling risk, which is important for inland facilities that operate at high water recoveries to reduce brine disposal costs. However, water recovery of reverse osmosis is also limited due to increased osmotic pressure with feed water concentration. Membrane distillation (MD) is a thermally driven membrane desalination technique that is not limited by increased osmotic pressure of the feed. In this investigation, pH adjustment was tested as a strategy to reduce silica scaling risk in the MD process. With feed water pH less than 5 or higher than 10, scaling impacts were negligible at silica concentrations up to 600 mg/L. Scaling rates were highest at neutral pH between 6 and 8. Cleaning strategies were also explored to remove silica scale from membranes. Cleaning using NaOH solutions at pH higher than 11 to induce dissolution of silica scale was effective at temporarily restoring performance; however, some silica remained on membrane surfaces and scaling upon re-exposure to supersaturated silica concentrations occurred faster than with new membranes.

Selective separation of mono- and di-valent cations in electrodialysis during brackish water desalination: Bench and pilot-scale studies

Selective separation of mono- and multi-valent ions has important applications in water reuse, desalination, and salt production. Innovative monovalent permselective cation-exchange membrane CR671 was developed by modifying the normal grade membrane CR67 with polyethyleneimine coating. Bench- and pilot-scale electrodialysis experiments were conducted at a brackish groundwater desalination facility to investigate desalination performance and ion selectivity using the CR671 and CR67 under different operating conditions. Both normal grade (CR67 and AR204) and selective (CR671 and AR112B) membranes achieved same desalting efficiency. Na-selectivity in terms of relative transport number using sodium as the standard ion was affected significantly by current density and linear velocity for the normal grade membranes while the selective membranes exhibited stable good Na-selectivity. The Na-selectivity of the CR671 was demonstrated up to 9 and 5 times better than the CR67 during pilot- and bench-scale electrodialysis, respectively. Hydraulic retention time and electrodialysis stack staging had minor impact on Na-selectivity at high current density. With the same hydraulic conditions, overall desalination behavior and ion selectivity were highly comparable between bench- and pilot-scale electrodialysis. It infers that bench-scale testing results can be used to simulate and project desalination performance and ion selectivity of pilot- and potentially full-scale electrodialysis applications.

Enhanced Flux and Electrochemical Cleaning of Silicate Scaling on Carbon Nanotube-Coated Membrane Distillation Membranes Treating Geothermal Brines.

The desalination of inland brackish groundwater offers the opportunity to provide potable drinking water to residents and industrial cooling water to industries located in arid regions. Geothermal brines are used to generate electricity, but often contain high concentrations of dissolved salt. Here, we demonstrate how the residual heat left in spent geothermal brines can be used to drive a membrane distillation (MD) process and recover desalinated water. Porous polypropylene membranes were coated with a carbon nanotube (CNT)/poly(vinyl alcohol) layer, resulting in composite membranes having a binary structure that combines the hydrophobic properties critical for MD with the hydrophilic and conductive properties of the CNTs. We demonstrate that the addition of the CNT layer increases membrane flux due to enhanced heat transport from the bulk feed to the membrane surface, a result of CNT's high thermal transport properties. Furthermore, we show how hydroxide ion generation, driven by water electrolysis on the electrically conducting membrane surface, can be used to efficiently dissolve silicate scaling that developed during the process of desalinating the geothermal brine, negating the need for chemical cleaning.

Fouling mitigation in submerged VMD for the treatment of brackish groundwater concentrates with transverse vibration and crystallizer

The management of brackish groundwater concentrates remains as a problem from the desalination of brackish groundwater. This study accessed the feasibility of various fouling mitigation techniques during the treatment of brackish groundwater concentrates at a 4-fold concentration factor for the purpose further volume reduction of wastewater. The study has demonstrated the importance of proper selection for fouling control techniques to the corresponding foulants. While vigorous agitations such as stirring could trigger earlier membrane deterioration in the brackish groundwater concentrates with inorganic foulants, a thermal crystallizer unit was able to effectively prolong membrane performance and promote the harvesting of calcium carbonates. On the other hand, vigorous transverse vibration of membrane module at 500rpm showed significant improvement of the membrane performance in terms of anti-fouling, anti-wetting and water production for the treatment of brackish groundwater concentrates with the presence of humic substances. With the aid of transverse vibration, 8.7-fold concentration factor was achieved in brackish groundwater concentrates with humic substance at 70°C.