Impacts of antiscalants on the formation of calcium solids: implication on scaling potential of desalination concentrate

Both brackish water desalination and seawater desalination processes are well established and in common use around the globe to create new water supply sources. The farther the location of the source water from the ocean or seashore, the lower the salinity (TDS) of the water and the lower the osmotic pressure that needs to be overcome when desalinated water is produced. This is one of the major reasons that brackish desalination is often considered less costly than seawater desalination. A number of project considerations, however, indicate that seawater desalination can be beneficial and more cost-effective than brackish water desalination. To make a fair comparison, we need to properly compare all major aspects of both types of projects to define the best and most appropriate desalination technology. While brackish water has less feed water TDS, it is more challenging to dispose of the produced concentrate. Also, although brackish water desalination needs less energy to overcome osmotic pressure, it usually requires more energy to draw the water from the well than it takes to pump seawater from the open ocean intake. Another factor is that the temperature of the brackish well water may be lower than the temperature of ocean water, giving seawater desalination an advantage in energy demand. In comparing brackish to seawater desalination, these major aspects should be evaluated: (1) Locations of seawater and brackish water plants, relative to the major consumers of the desalinated water, (2) Transportation (pumping and disposal) costs of the feed water and produced water, (3) Potential colocation of a seawater plant with a large industrial user (e.g., power plant) of the seawater for cooling or other purposes, (4) Produced quality of brackish water and seawater desalination in terms of major minerals and emerging contaminants, (5) Sustainability of the water source: capacity and depth of the brackish water wells, as well as the type of soil. (6) Technical and economic aspects of produced concentrate disposal, (7) Permitting process costs for brackish and seawater desalination, and (8) The economics of both brackish and seawater desalination treatment processes: capital costs, operational and maintenance (O&M) costs, lifetime water cost, and total water cost (TWC). This paper discusses the major evaluation criteria and considerations involved in properly comparing the economic and technical aspects of brackish and seawater desalination to determine the more favorable desalination technology for a given desalination project.

Brackish water desalination using reverse osmosis and capacitive deionization at the water-energy nexus

Desalination and disinfection of inland brackish ground water in a capacitive deionization cell using nanoporous activated carbon cloth electrodes

The potential role of brackish water desalination within the Egyptian water supply matrix

Desalination of high salinity brackish water by an NF-RO hybrid 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.

A methodology to investigate brackish groundwater desalination coupled with aquifer recharge by treated wastewater as an alternative strategy for water supply in Mediterranean areas

Desalination of brackish water by nanofiltration and reverse osmosis

Developing cost-effective brackish water and seawater desalination technology is crucial. Capacitive deionization (CDI) and inverted capacitive deionization (i-CDI) have been recognized as a promising desalination technology with low energy consumption for brackish water.Both systems use an electric field between two porous electrodes to remove and release ions in water reversibly.Recently, CDI has started using pseudocapacitive or battery electrode materials to enhance the desalination performance.Different from the desalination principle of electric double layers, the energy storage mechanisms of pseudocapacitive and battery materials generally involve ion intercalation/adsorption or compound formation for charge balance, leading to the faradaic desalination.Low cost and high theoretical capacity make PBAs and conducting polymers be the potential materials for the faradaic desalination application.In our previous studies, two dissimilar pseudocapacitive materials show a memory effect during brackish water desalination. This allows them to retain ion capturing or releasing states without an electric field, aiding water purification and resource recovery.Based on above viewpoints, two materials with fundamentally different electrochemical properties are demonstrated to construct a high-capacity, hybrid, faradaic deionization system with CuHCF (battery type) as the positive electrode and PPy (pseudocapacitive type) as the negative electrode.The deionization performance of this CuHCF//PPy cell can be improved by reversing the appropriate cell voltage during the discharge process.The plot of specific SRC against time for the above CuHCF//PPy cell with variations in the charging cell voltage but a fixed discharging cell voltage of 0 V. In addition, Fig. 1(b) shows the plot of specific SRC against time for the same cell with variations in the discharging cell voltage but a fixed charging cell voltage of 1.2 V. From Fig. 1(a), at all charging voltages, the SRC generally decreases with the charging time, indicating the ion repelling process. The order of charging cell voltage with respect to increasing the SRC value is: 0.6 V < 0.8 V < 1.0 V < 1.2 V, revealing the impact of the charging cell voltage. From Fig. 1(b), the SRC obviously increase with prolonging the discharging time, suggesting the ion capturing process. However, the order of discharging cell voltage with respect to increasing the SRC value is: -0.4 V < 0 V < −0.1 V< −0.2 V < −0.3 V. Note that a little inverted cell voltage leads to a higher salt-removing capacity and rate in comparison with a discharge cell voltage of 0 V. However, when the inverted voltage is set at −0.4 V, the SRC profile exhibits the unstable performance, probably due to the presence of certain irreversible reactions at this cell voltage.In the stability test, Fig 2 shows the CuHCF//PPy cell still maintained more than 90% of its original SRC after 50 cycles of testing.The mean SRC values of this CuHCF//PPy system obtained from the 8, 15, and 30 mM solutions reached 35.536, 58.824, and 101.84 mg g−1, respectively.This positive correlation between SRC and solution concentration reveals the higher utilization of the electroactive materials in more concentrated solutions and the very high SRC of the hybrid faradaic CuHCF//PPy system.From Fig 3 shows the SRC values of a CuHCF//PPy cell with the charging/discharging times of 30/30 min at the charging/discharging cell voltages of 1.2/−0.2 V in the 8, 15, and 30 mM NaCl solutions.The memory effect of electrochemically active materials can further extend the application of this system to concentrating valuable ions while purifying water, showing another advantage.The results of ion-removing and salt-concentrating experiment with the discharge/charge times = 10 min/10 min for 10 cycles. In this 10-cycle test, the total amount of salts transferred is up to 152.9 mg g−1, revealing the dual function of purifying water and concentrating salts through this hybrid battery//pseudo-capacitive system.This hybrid cell showed high salt removal capacities in the media containing various monovalent and divalent cations. In this work, the suitable working potential windows of both CuHCF and PPy were systematically evaluated by CV and GCD methods with the charge balance application. Moreover, this cell provides the ability in capturing other cations such as Mg2+ and Ca2+, further broadening its future potential applications. This methodology is a promising strategy for constructing a high-performance desalination cells consisting of various active materials. Figure 1

Reverse osmosis pilot plants performance in brackish water desalination

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.

The role of desalination in bridging the water gap in Jordan

High water recovery is crucial to inland desalination but is impeded by mineral scaling of the membrane. This work presents a two-step modification approach for grafting high-density zwitterionic pseudo-bottle-brushes to polyamide reverse osmosis membranes to prevent scaling during high-recovery desalination of brackish water. Increasing brush density, induced by increasing reaction time, correlated with reduced scaling. High-density grafting eliminated gypsum scaling and almost completely prevented silica scaling during desalination of synthetic brackish water at a recovery ratio of 80%. Moreover, scaling was effectively mitigated during long-term desalination of real brackish water at a recovery ratio of 90% without pretreatment or antiscalants. Molecular dynamics simulations reveal the critical dependence of the membrane's silica antiscaling ability on the degree to which the coating screens the membrane surface from readily forming silica aggregates. This finding highlights the importance of maximizing grafting density for optimal performance and advanced antiscaling properties to allow high-recovery desalination of complex salt solutions.

California's current population of 35 million is projected to increase by about 12 million by the year 2030. In assuring supply reliability—with water management strategies shifting away from the construction of new dams, reservoirs and conveyance canals—and in addition to water conservation and water recycling, desalination is gaining considerable attention from scientists, resource planners, policy-makers, and other stakeholders. The main driving force for this renewed interest in water desalination is the remarkable technological advancement in desalination processes which has recently led to a much lower cost of desalinated water than was previously attainable. In 2003, the California Water Desalination Task Force was convened by the California Department of Water Resources pursuant to a new Legislative Law with the aim of looking into potential opportunities and impediments for using oceanwater and brackish water desalination in California, and to examine what role, if any, the State should play in furthering the use of desalination technology. After about six months of deliberations, the Task Force outlined key findings that provide context for evaluating desalination. The findings included some facts and figures about brackish and oceanwater desalination in general and highlights of several environmental issues as well as cost, energy, permitting issues, and growth-inducement related to desalination. One of the primary findings is that economically and environmentally acceptable desalination should be considered as part of a balanced water portfolio to help meet California's existing and future water supply and environmental needs. The Task Force forecasted that the potential for the increased use of desalination in California is significant and that the opportunities are great for providing water supply from oceanwater and brackish water desalination as well as recovering contaminated groundwater. Existing and envisioned desalination facilities could generate an estimated 860 million m 3 (700,000 acre-feet) per year in the next three decades. The Task Force put forward a set of 29 recommendations classified into four categories covering a broad range of issues including energy, environment, planning, permitting, funding, and equity. A detailed narrative of the Task Force findings and recommendations is presented in this paper.

Desalination of brackish water using modified natural zeolite (MNZ) that had hydrophilic character and the effect of long time of stirring has been studied. The MNZ was synthesized by destructing the natural zeolite with 6M HCl solution, followed by treating with Al(OH)3, CTAB and distilled water. The mixture was regulated to pH of 12. The mixture was then poured into a reactor for hydrothermal process at 140 oC for 24 h. The dealumination of natural zeolite was characterized using X-Ray Fuorescence spectrometry(XRF) and the MNZ was characterized using Fourier Transform Infra Red, X-Ray Diffraction, and surface area analyzer. This research was conducted in batch with variation of adsorbent weight and long time of stirring. The Absorption of brackish water using MNZ was carried out in the variation of ratio of zeolite (g) to brackish water (mL) in Batch method. The filtrate results of absorption were analyzed using Atomic Absorption Spectrophotometry (Na+ contents) and Mohr Method (Cland NaCl contents).The resulted showed that the dealumination of natural zeolite had Si content of39.28%, and Al of 3.27 %. The results of measurements with XRD produced a different form of chromatogram and type of zeolite. The dominant mineral was faujasite. The MNZ had Surface area, total pore volume and pore diameter of MNZ zeolite were 285.538m2 /g; 0.303 cm3 /g; and 7.892 nm respectively. The absorption results of Na+ and NaCl contents in brackish water were 93,7 %, and 95.9 %at ratio of 2.5 g zeolite to 50 mL of brackish water that was obtained at 2 h of long time of stirring.