Simultaneous removal of nitrate and hardness ions from groundwater using electrodeionization

Pathways and enhancement strategies for magnesium hardness removal in modified induced crystallization softening

Elevated levels of total hardness in drinking water can readily result in scaling, which poses a threat to both the safety of water quality and the convenience of its use. While there is a wealth of research on the removal of calcium hardness, there is a dearth of studies focusing on the removal of magnesium hardness. In light of this, the present study employs modified induced crystallization softening (MICS) to delineate the removal pathways and mechanisms of magnesium hardness, and to investigate viable methods for its enhancement and application. Our research has determined that magnesium hardness can be effectively removed from water through the MICS, with the dosage of softening agents (NaOH) being a significant factor that influences this removal, whereas the fixed bed height within the fluidized bed exerts minimal impact on the process. In the low-dose stage (less than 250 mg/L), when the pH is below 10.0, up to 20% of magnesium hardness can be removed, predominantly through the crystallization of (Ca0.936Mg0.064)CO3. As the dosage increases to the moderate stage (250-400 mg/L), the conversion of excess bicarbonate (HCO3-) to carbonate (CO32-) in the water hinders further removal of magnesium hardness. In the high-dose stage (exceeding 400 mg/L), when the pH rises above 10.5, the removal rate of magnesium hardness can be enhanced to over 75%, with the crystallization of Mg(OH)2 being the primary removal mechanism. Density functional theory calculations, along with molecular dynamics simulations of cohesive energy and bond energy, substantiate the feasibility of the identified magnesium removal pathways. The addition of coagulants (FeCl3) and an decrease in the up-flow velocity can further augment the removal efficiency of magnesium hardness by promoting the crystallinity of Mg(OH)2 during the high-dose stage (exceeding 400 mg/L). In practical engineering applications, the strategic control of softening agent dosages enables the achievement of varying levels of magnesium hardness removal, tailored to specific water quality requirements.

Ni-P-PTFE cathode with low surface energy for enhancing electrochemical water softening performance

Efficient cathode regeneration is a significant challenge in the electrochemical water softening process. This work explores the use of an electroless plating Ni-P-PTFE electrode with low surface energy for this purpose. The Ni-P-PTFE electrode demonstrates improved self-cleaning performance at high current densities. By combining the low surface energy of the electrode with fluid flushing shear force, the precipitation rate on the Ni-P-PTFE electrode remains stable at approximately 18 g/m2·h over extended periods of operation. Additionally, the cleaning efficiency of the Ni-P-PTFE electrode surpasses that of stainless steel by 66.34%. The Ni-P-PTFE electrode can maintain a larger active area and a longer operational lifespan is attributed to its self-cleaning performance derived from low surface energy. Furthermore, the loose scale layers on the electrode surface are easily removed during electrochemical water softening processes, presenting a novel approach to cathode surface design.

Recent breakthroughs on the development of electrodeionization systems for toxic pollutants removal from water environment

Since ecosystems are becoming inherently polluted, long-term contaminant removal methods are required. Electrodeionization, in particular, has recently been demonstrated as an effective approach for eliminating ionic compounds from contaminated water sources. Being a more environmentally friendly technology is most likely the main reason for its eminence. It uses electricity to replace toxic contaminants that are conventionally used to regenerate and hence reducing the toxins associated with resin regeneration. In wastewater treatment, continuous electrodeionization system overcomes several limitations of ion exchange resins, notably ion dumping. This prospective assessment delves into the mechanism, principle, and theory of electrodeionization system. It also focused on the design and applications, particularly in the removal of toxic compounds, as well as current advances in the electrodeionization system. Recent breakthroughs in electrodeionization were comprehensively discussed. Further developments in electrodeionization systems are also projected, with improved efficiency at the time of functioning at lower costs because of reduced energy use, proving them desirable for commercial usage with a broad array of applications across the globe.

Utilization of Electrodeionization for Lithium Removal

In this work, usage of a hybrid polymeric ion exchange resin and a polymeric ion exchange membrane in the same unit to remove Li⁺ from aqueous solutions was reported. The effects of the applied potential difference to the electrodes, the flow rate of the Li-containing solution, the presence of coexisting ions (Na⁺, K⁺, Ca²⁺, Ba²⁺, and Mg²⁺), and the influence of the electrolyte concentration in the anode and cathode chambers on Li⁺ removal were investigated. At 20 V, 99% of Li⁺ was removed from the Li-containing solution. In addition, a decrease in the flow rate of the Li-containing solution from 2 to 1 L/h resulted in a decrease in the removal rate from 99 to 94%. Similar results were obtained when the concentration of Na₂SO₄ was decreased from 0.01 to 0.005 M. The selectivity test showed that the simultaneous presence of monovalent ions such as Na⁺ and K⁺ did not change the removal rate of Li⁺. However, the presence of divalent ions, Ca²⁺, Mg²⁺, and Ba²⁺, reduced the removal rate of Li⁺. Under optimal conditions, the mass transport coefficient of Li⁺ was found as 5.39 × 10^-4 m/s, and the specific energy consumption was found as 106.2 W h/g LiCl. Electrodeionization provided stable performance in terms of the removal rate and transport of Li⁺ from the central compartment to the cathode compartment.

Electrodeionization: Principle, techniques and factors influencing its performance

Ecosystems are becoming more and more polluted, hence sustainable techniques of pollution removal are needed. In the recent times, exceedingly pure water has become ideal for several industries. Modern industry needs ultra-pure water, which is highly processed water that is devoid of colloidal particles and has a conductivity of less than 0.06 μS. A very effective method for removing ionic chemicals from polluted waters emerged recently called electrodeionization. Continuous electrodeionization (CEDI) is a technique for producing high-purity water. Besides rendering purified water, the technique has got promising wastewater treatment technologies - by facilitating the eradication of ionizable compounds, hazardous chemicals, radioactive pollutants, heavy metals and other potential contaminants. Innovative materials have been developed in order to advance and improve this technique, which would result in enormous ecological and financial benefit on a worldwide scale. In this review article, several factors that affect the performance of CEDI has been comprehended, with the impact of Ion-exchange resins and membranes as the focal point.

Selective and Chemical-Free Removal of Toxic Heavy Metal Cations from Water Using Shock Ion Extraction

Electrochemical methods are known to have attractive features and capabilities when used for ion separations and water purification. In this study, we developed a new process called shock ion extraction (shock IX) for selective and chemical-free removal of toxic heavy metals from water. Shock IX is a hybrid process that combines shock electrodialysis (shock ED) and ion exchange using an ion exchange resin wafer (IERW), and this method can be thought of functionally as an electrochemically assisted variation of traditional ion exchange. In particular, shock IX exhibits greater ion removal and selectivity for longer periods of time, compared to the use of ion exchange alone. The use of an IERW in shock ED also increases multivalent ion selectivity, reduces energy consumption, and improves the hydrodynamics and scalability of the system.

The Role of Conventional Methods and Artificial Intelligence in the Wastewater Treatment: A Comprehensive Review

Water pollution is a severe health concern. Several studies have recently demonstrated the efficacy of various approaches for treating wastewater from anthropogenic activities. Wastewater treatment is an artificial procedure that removes contaminants and impurities from wastewater or sewage before discharging the effluent back into the environment. It can also be recycled by being further treated or polished to provide safe quality water for use, such as potable water. Municipal and industrial wastewater treatment systems are designed to create effluent discharged to the surrounding environments and must comply with various authorities’ environmental discharge quality rules. An effective, low-cost, environmentally friendly, and long-term wastewater treatment system is critical to protecting our unique and finite water supplies. Moreover, this paper discusses water pollution classification and the three traditional treatment methods of precipitation/encapsulation, adsorption, and membrane technologies, such as electrodialysis, nanofiltration, reverse osmosis, and other artificial intelligence technology. The treatment performances in terms of application and variables have been fully addressed. The ultimate purpose of wastewater treatment is to protect the environment that is compatible with public health and socioeconomic considerations. Realization of the nature of wastewater is the guiding concept for designing a practical and advanced treatment technology to assure the treated wastewater’s productivity, safety, and quality.

Recent advances in the source identification and remediation techniques of nitrate contaminated groundwater: A review

Researchers have long been committed to identify nitrate sources in groundwater and to develop an advanced technique for its remediation because better apply remediation solution and management of water quality is highly dependent on the identification of the NO₃^- sources contamination in water. In this review, we systematically introduce nitrate source tracking tools used over the past ten years including dual isotope and multi isotope techniques, water chemistry profile, Bayesian mixing model, microbial tracers and land use/cover data. These techniques can be combined and exploited to track the source of NO₃^- as mineral or organic fertilizer, sewage, or atmospheric deposition. These available data have significant implications for making an appropriate measures and decisions by water managers. A continuous remediation strategy of groundwater was among the main management strategies that need to be applied in the contaminated area. Nitrate removal from groundwater can be accomplished using either separation or reduction based process. The application of these processes to nitrate removal is discussed in this review and some novel methods were presented for the first time. Moreover, the advantages and limitations of each approach are critically summarized and based on our own understanding of the subject some solutions to overcomes their drawbacks are recommended. Advanced techniques are capable to attain significantly higher nitrate and other co-contaminants removal from groundwater. However, the challenges of by-products generation and high energy consumption need to be addressed in implementing these technologies for groundwater remediation for potable use.

A review on recent advances in electrodeionization for various environmental applications

The growing contamination of ecosystems necessitates the development of long-term pollution-removal technologies. Electrodeionization, in notably, has newly proven as an efficient method for removing ionic chemicals from polluted waterways. The fact that continuous electrodeionization is a greener technique is most probably the biggest cause for its success. It replaces the toxic chemicals typically required to replenish resins with electric power, therefore eliminating the wastewater involved with resin renewal. In water treatment, electrodeionization solves some of the drawbacks of ion exchange resin beds, particularly ion dumping as beds expire. This comprehensive review explores the theory, principles, and mechanisms of ion movement and separation in an electrodeionization unit. Also, it investigated the construction and usage, notably in removing heavy metal and its current developments in electrodeionization unit. Recent advances in Electrodeionization like polarity reversal, Resin wafer Electrodeionization, membrane free Electrodeionization, and electrostatic shielding with novel materials and hybrid process along with Electrodeionization were addressed. Further advancements are expected in electrodeionization systems that exhibit better efficacy while running at lower costs due to decreased energy usage, rendering them appealing for industrial scale up across a wide range of applications across the world.

Groundwater Quality of Drinking Water Wells in the West Bank, Palestine

Groundwater, the main drinking water source in the West Bank, is highly vulnerable to pollution given the karstic nature of the aquifer. This study was aimed at screening the quality of groundwater used for water supply, in terms of physicochemical and microbiological properties, and heavy metals concentrations. Attention was given to groundwater chemistry, using piper and Durov diagrams, to assess potent impact of pollution on groundwater. Twenty-nine groundwater samples from selected wells, representing the different groundwater fields in the West Bank, were collected and analyzed. The results revealed that the concentration of the ions and parameters affecting the aesthetic and health related water quality, such as Cl−, Na+, NH4+, TDS, and NO3−, and selected (semi) metals, including Cr, Cu, Fe, Mn, Pb, Cd, and As, are within the limits recommended for drinking water. The dominant cations and anions were in the order of Ca2+ > Na+ > Mg2+ > K+ > NH4+ and HCO3− > Cl− > NO3− > SO42−, respectively. The total average groundwater hardness is approximately 2.1 mmol/L and can be attributed to calcium (approximately 60%) and magnesium. The major ground water types in the West Bank were fresh water (Ca-Mg-HCO3), fresh water mixed with another water type (Ca-Mg-Na-HCO3 or Ca-Mg-HCO3-Cl), and extreme water type (Na-Ca-Mg-HCO3-Cl or Na-Ca-HCO3-Cl) showing high TDS, Cl− and Na+. Signs of pollution, namely elevated levels of nitrate and ammonium, were, however, observed even in some deep wells (>600 m), despite the thick cover of soil, tapping the Lower Ceneomanian confined aquifer.

Nitrate, arsenic and fluoride removal by electrodialysis from brackish groundwater

Nitrate, arsenic and fluoride are some of the most hazardous elements contaminating groundwater resources. In this work, the impact of operative (flowrate, electricpotential) and water quality (salinity, contaminant feed concentration, pH) parameters on brackish water decontamination was investigated using a batch electrodialysis (ED) system. Electrodialysis at low electric potentials (5 V) was more selective toward monovalent ions, at higher potentials (>15 V) removal of all ions increased and selectivity approached one, meaning removal of all ions. Changing the flowrate from 30 to 70 L/h, increased nitrate and fluoride removal slightly, while arsenic(V) removal was maximum at 50 L/h. Rising salinity delayed removal of ions with low ionic mobility and diffusivity (i.e. fluoride, arsenic(V)). Increased feed concentration of contaminants had no impact on removal values. pH variations did not impact the nitrate, fluoride and salinity removal, yet arsenic(V) removal was greatly pH dependent. This was explained in part by lower diffusivity and higher hydration number of bi- and trivalent species of arsenic(V) at basic pH. The results of this work showed the significance of ionic characteristics (diffusivity, ionic mobility, hydration number) in ED. Nitrate concentrations satisfied guideline threshold in all experiments with concentrations below 50 mg/L. Lowest arsenic(V) concentration was 35 µg/L at the highest electric potential, 25 V. Using ionic characteristics makes separation of different ions possible, providing new opportunities for ED in environmentally friendly processes (e.g. resource recovery and zero liquid discharge).

Effects of Resin Chemistries on the Selective Removal of Industrially Relevant Metal Ions Using Wafer-Enhanced Electrodeionization

Wafer-enhanced electrodeionization (WE-EDI) is an electrically driven separations technology that occurs under the influence of an applied electric field and heavily depends on ion exchange resin chemistry. Unlike filtration processes, WE-EDI can be used to selectively remove ions even from high concentration systems. Because every excess ion transported increases the operating costs, the selective separation offered by WE-EDI can provide a more energy-efficient and cost-effective process, especially for highly concentrated salt solutions. This work reports the performance comparison of four commonly used cation exchange resins (Amberlite IR120 Na⁺, Amberlite IRP 69, Dowex MAC 3 H⁺, and Amberlite CG 50) and their influence on the current efficiency and selectivity for the removal of cations from a highly concentrated salt stream. The current efficiencies were high for all the resin types studied. Results also revealed that weak cation exchange resins favor the transport of the monovalent ion (Na⁺) while strong cation exchange resins either had no strong preference or preferred to transport the divalent ions (Ca²⁺ and Mg²⁺). Moreover, the strong cation exchange resins in powder form generally performed better in wafers than those in the bead form for the selective removal of divalent ions (selectivity > 1). To further understand the impact of particle size, resins in the bead form were ground into a powder. After grinding the strong cation resins displayed similar behavior (more consistent current efficiency and preference for transporting divalent ions) to the strong cation resins in powder form. This indicates the importance of resin size in the performance of wafers.

Dynamic characteristics of immobilized microorganisms for remediation of nitrogen-contaminated groundwater and high-throughput sequencing analysis of the microbial community

The aim of this study was to investigate the effect of adsorption by a composite active medium (nitrogen-degrading bacteria immobilized on scoria) on the removal of ammonium nitrogen (NH₄⁺-N), nitrite nitrogen (NO₂^-N) and nitrate nitrogen (NO₃^-N). Transport of these three forms of nitrogen was investigated using columns with different flow rates, initial concentrations and depths. Immobilization of the bacteria on the scoria significantly enhanced the ability of the composite active medium to remove nitrogen during the remediation process. As the flow rate increased, the shear force increased and solute diffusion decreased, thereby improving the tolerance of the bacteria for the three forms of nitrogen and reducing the penetration time. Increasing the initial nitrogen concentration resulted in a decrease in the adsorption rate constant (K_Th). The nitrogen-degrading bacteria immobilized on scoria rapidly reached saturation with regards to their nitrogen adsorption capacity. The initial nitrogen concentration of each media layer was different, and the composite active medium had a certain blocking effect, which resulted in a slow increase in the concentration of nitrogen in the deeper media layer. The transport experiments showed that the process accords with the thomas model and the Bohart-Adams model. The contents of the three forms of nitrogen were within acceptable standards for drinking water after 2 months of a column containing the composite active medium. The composite active medium can be used for in situ and ex situ remediation of groundwater containing excessive nitrogen. High-throughput sequencing analysis was used to monitor the composition of the bacterial community present within the composite active medium. During the remediation process, there were only slight changes in the structure and composition of the nitrogen-degrading bacterial community, although there were clear differences in abundance. Pseudomonas, Stenotrophomonas and Serratia were the three bacterial genera that were effective removal of all three forms of nitrogen.

Removal characteristics of a composite active medium for remediation of nitrogen-contaminated groundwater and metagenomic analysis of degrading bacteria

To investigate the removal characteristics of ammonium-nitrogen (NH₄⁺-N), nitrite-nitrogen (NO₂^--N), nitrate-nitrogen (NO₃^--N), and total nitrogen from groundwater by a degradable composite active medium, kinetics, thermodynamics, and equilibrium adsorption, experiments were performed using scoria and degrading bacteria immobilized on scoria. Removal of NH₄⁺-N, NO₂^--N, and NO₃^--N was conducted in adsorption experiments using different times, initial concentrations, pH values, and groundwater chemical compositions (Ca²⁺, Mg²⁺, HCO₃^-, CO₃^2-, Fe²⁺, Mn²⁺, and SO₄^2-). The results showed that the removal of nitrogen by the composite active medium was obviously better than that of scoria alone. The removal rates of NH₄⁺-N (C₀ = 5 mg/L), NO₂^--N (C₀ = 5 mg/L), and NO₃^--N (C₀ = 100 mg/L) by the composite active medium within 1 h were 96.05%, 82.40%, and 83.16%, respectively. The adsorption kinetics were well fitted to a pseudo-second order model, whereas the equilibrium adsorption agreed with the Freundlich model. With changes in the pH, variation in the removal could be attributed to the combined effect of hydrolysis and competitive ion adsorption, and the optimum pH was 7. Different concentration conditions, hardness, alkalinity, anions, and cations showed different promoting and inhibiting effects on the removal of nitrogen. A careful examination of ionic concentrations in adsorption batch experiments suggested that the sorption behavior of nitrogen onto the immobilized medium was mainly controlled by ion exchange. The degrading bacteria on the scoria surface were eluted and analyzed by metagenomic sequencing. There were significant differences in the number of operational taxons, relative abundances, and community diversity among degrading bacteria after adsorption of the three forms of nitrogen. The relative abundance of degrading bacteria was highest after NO₃^--N removal, and the diversity was highest after NO₂^--N removal. Pseudomonas and Serratia were the dominant genera that could efficiently remove NH₄⁺-N and NO₂^--N.

Effects of process operating conditions on the autotrophic denitrification of nitrate-contaminated groundwater using bioelectrochemical systems

Nitrates have been detected in groundwater worldwide, and their presence can lead to serious groundwater use limitations, especially because of potential health problems. Amongst different options for their removal, bioelectrochemical systems (BESs) have achieved promising results; in particular, attention has raised on BES-driven autotrophic denitrification processes. In this work, the performance of a microbial electrolysis cell (MEC) for groundwater autotrophic denitrification, is assessed in different conditions of nitrate load, hydraulic retention time (HRT) and process configuration. The system obtained almost complete nitrate removal under all conditions, while nitrite accumulation was recorded at nitrate loads higher than 100mgNO₃^-L^-1. The MEC system achieved, in different tests, a maximum nitrate removal rate of 62.15±3.04gNO₃^--Nm^-3d^-1, while the highest TN removal rate observed was 35.37±1.18gTNm^-3d^-1. Characteristic of this process is a particularly low (in comparison with other reported works) energy consumption: 3.17·10^-3±2.26·10^-3kWh/gNO₃^-N removed and 7.52·10^-2±3.58·10^-2kWhm^-3 treated. The anolyte configuration in closed loop allowed the process to use less clean water, while guaranteeing identical performances as in other conventional configurations.