Advances in efficient desalination technology of capacitive deionization for water recycling

The world is suffering from chronic water shortage due to the increasing population, water pollution and industrialization. Desalinating saline water offers a rational choice to produce fresh water thus resolving the crisis. Among various kinds of desalination technologies, capacitive deionization (CDI) is of significant potential owing to the facile process, low energy consumption, mild working conditions, easy regeneration, low cost and the absence of secondary pollution. The electrode material is an essential component for desalination performance. The most used electrode material is carbon-based material, which suffers from low desalination capacity (under 15 mg·g−1). However, the desalination of saline water with the CDI method is usually the charging process of a battery or supercapacitor. The electrochemical capacity of battery electrode material is relatively high because of the larger scale of charge transfer due to the redox reaction, thus leading to a larger desalination capacity in the CDI system. A variety of battery materials have been developed due to the urgent demand for energy storage, which increases the choices of CDI electrode materials largely. Sodium-ion battery materials, lithium-ion battery materials, chloride-ion battery materials, conducting polymers, radical polymers, and flow battery electrode materials have appeared in the literature of CDI research, many of which enhanced the deionization performances of CDI, revealing a bright future of integrating battery materials with CDI technology.

With the increasing global water shortage issue, the development of water desalination and wastewater recycling technology is particularly urgent. Capacitive deionization (CDI), as an emerging approach for water desalination and ion separation, has received extensive attention due to its high ion selectivity, high water recovery, and low energy consumption. To promote the further application of CDI technology, it is necessary to understand the latest research progress and application prospects. Here, considering electric double layers (EDLs) and two typical models, we conduct an in-depth discussion on the ion adsorption mechanism of CDI technology. Furthermore, we provide a comprehensive overview of recent advances in CDI technology optimization research, including optimization of cell architecture, electrode material design, and operating mode exploration. In addition, we summarize the development of CDI in past decades in novel application fields other than seawater desalination, mainly including ionic pollutant removal, recovery of resource-based substances such as lithium and nutrients, and development of coupling systems between CDI and other technologies. We then highlight the most serious challenges faced in the process of large-scale application of CDI. In the conclusion and outlook section, we focus on summarizing the overall development prospects of CDI technology, and we discuss the points that require special attention in future development.

Capacitive deionization (CDI) technology is utilized for efficient treatment of industrial wastewater, characterized by low energy consumption and environmental protection. In order to comprehend the correlation between key experimental parameters and the electrosorption capacity (EC) of heavy metals in CDI technology, this paper employs a genetic algorithm (GA) to optimize a backpropagation artificial neural network (BPANN) for predicting the EC of CDI technology for heavy metal ions, with the characteristics of electrode materials converted into numerical characteristics for further analysis. Compared to the BPANN, the optimized GABPANN model demonstrates superior predictive accuracy. It achieves automatic adjustment of the hidden layer structure, neuron count, and transfer functions. Furthermore, the grey relational analysis indicates that the electrode material and the initial pH value of the solution are pivotal in determining the EC of heavy metal ions. This underscores the efficacy of machine learning (ML) algorithms in forecasting the nonlinear dynamics of CDI systems and elucidates the influence of individual parameters on the efficacy of heavy metal removal.

Performance optimization of integrated electrochemical capacitive deionization and reverse electrodialysis model through a series pass desorption process

Titanium disulfide decorated hollow carbon spheres towards capacitive deionization

The existing conventional technologies like Reverse Osmosis, EDI(Electro Deionization), membrane filtration and Ultra Violet filtration offer solutions for drinking water, but various factors like capital and operational cost, ease of operation, maintenance and fouling had been the considerable driving factors to judge the techno-economic paradigm while making a technology selection. Also, the increasing demand for augmenting the safe drinking water calls for novel and sustainable breakthrough technologies. The novel and sustainable technology like Capacitive deionization (CDI) could be a potential alternative which works on electrophoretic phenomenon to provide low TDS (Total Dissolved Solids) drinking water. When water passes between a pair of carbon aerogel electrodes, ionic species are held at the charged electrode surfaces and are removed from the solution during the charging the cycle. After the electrodes become saturated with salts or impurities, the electrodes are regenerated by electrical discharge or polarity reversal, allowing the captured ions to be released into a relatively small purge stream. Thus, CDI can be used to deionize or purify water. An effort is also made to study, evaluate and compare conventional RO technology with Existing CDI technology. Batch ion absorption studies on the newly developed electrodes recorded efficiency with ion removal of 140 ppt using 5 pairs of electrodes (32m 2 area) and the SEM images of the developed electrodes indicated good porosity which in turn illustrates the potential absorption capacity of the developed electrodes. The main factors to be considered while developing an ideal electrode are some of the properties like BET(, electrical conductivity, capacitance, mechanical strength. Correlation studies on the comparison with RO and evaluation of the developed electrodes of the CDI were carried out. I. Introduction The desalination of seawater and brackish groundwater to provide fresh drinking water is an established and thriving industry. Desalinisation refers to any of several processes that removes amount of salt and any other minerals present in the saline water. Salt water is desalinated in order to produce fresh water that is suitable for human consumption or irrigation. The most commonly used technologies at present for the desalination process are Thermal Distillation and Reverse Osmosis (RO) filtration. This report will mainly deal with the research conducted for the development of an ideal electrode which is non-polluting, energy efficient, cost effective and electrically conductive, suitable for an industrial sized capacitive deionisation module. Capacitive Deionisation in other terms can be defined as a powerful desalination module which utilises low-pressure non membrane desalination process. Most of the existing industrial scale desalination centres get their energy from the combustion of fossil fuels, thus in effect exchange potable water for CO2 which causes global warming and eventually contributes to the demise of fresh water. As a result, global warming will lead to increase the need for additional desalination. Therefore, it is imperious to find methods to find desalination of water that are more energy efficient. Thus, electrochemical desalination tools like capacitive deionisation have the potential to be such an energy efficient technology. The main objective of this research is to Evaluate a newly developed electrode for electro adsorption studies and its relevance for CDI technology. Capacitive Deionization technology is evaluated by taking in to consideration factors like construction, operation and maintenance costs to that of reverse osmosis and an head on head evaluation is performed. Taking into consideration brackish type feed water the cost of construction can vary accordingly depending upon various factors. Some of the major factors that influence the design development are:-  Capacity of the water to be treated.  Blending of source water with permeate.  Quality of the feed. (TDS and constituents required removal required)  Concentrate disposal.  Pre and post treatment requirements.

Recent advances in capacitive deionization: A comprehensive review on electrode materials

Capacitive\ndeionization (CDI), as an energy-efficient and promising\nbrackish water desalination technique, has certain advantages over conventional methods\nsuch as thermal distillation, ultrafiltration, and reverse osmosis.\nHowever, CDI technology is as yet not widely applied as it can only\ntreat low salinity water due to the limitation of salt adsorption\ncapacity of the electrode. The complexity and high cost of the preparation\nof such materials with excellent salt removal capability also hinder\nthe commercialization of CDI technology. To surmount these barriers\nin CDI technology, we hereby developed a hierarchical porous carbon\n(h-PC) which was prepared via a facile, economic, and green calcination\nof biomass mixed with an activator. Our prepared h-PC electrodes demonstrate\nan outstanding salt adsorption capacity (SAC) of 83.0 mg/g when the\nNaCl concentration is 1000 mg/L for batch mode CDI. This SAC is significantly\nhigher than those reported elsewhere (normally between 15–25\nmg/g), and the ultrahigh SAC may be due to the high specific surface\narea (SSA) and favorable hierarchical pore structure of h-PC. The\nas-prepared h-PC can also effectively remove heavy metals and desalinate\nbrackish water with a wide range of salinity up to 10000 mg/L. Furthermore,\nthe h-PC-800 electrode shows outstanding cycling stability with no\ndecline of salt adsorption capacity or its corresponding charge efficiency\nin the long term continuous mode CDI process (over 200 cycles). Our\nstudy of this work may be helpful in the design of practical and economical\nmaterial for high-performance CDI application of the desalination\nof brackish water with various salinity.

Since freshwater resources are limited worldwide, desalination is crucial. Due to its low energy consumption and ease of use, capacitive deionization (CDI) desalination technology has garnered a lot of attention. Traditional electrode materials have issues like poor ion selectivity, desalination capacity, and stability that need to be improved. This study examines the performance and desalination impact of novel composite electrode materials using the preparation process, characterization technology, and capacitive deionization technology as a foundation. Using a hollow carbon ball as an example, it is discovered that the hollow structure electrode material has a high degree of graphitization, a large specific surface area, and good desalination cycle stability; however, the preparation process is difficult and expensive. The study focuses on an antimicrobial multifunctional electrode material, using MXene as a case study. It demonstrates excellent electrical conductivity, hydrophilicity, and antimicrobial characteristics, along with significant potential for seawater desalination. However, its structural stability is lacking. In conclusion, further research should investigate new materials and composite technologies to enhance the study of materials in real seawater, industrial wastewater, and other complex water samples, thereby advancing the practical use of capacitive deionization technology.

Capacitive deionization (CDI) technology has attracted a great deal of attention over the past few decades due to its high energy efficiency (less than 1 kWh/m-3) compared to conventionally utilized reverse osmosis (2–4 kWh/m-3) and distillation based (50–80 kWh/m-3) desalination technologies. However, due to a couple of issues including cost and requirement for a disruptive discharging step, it has been regarded as a challenging task to perform large-scale desalination of seawater by the CDI process. Herein, we report a novel design for a 3D desalination system utilizing porous lattice scaffolds. It can desalinate water as salty as sea water (35 g/L) with desalting efficiency comparable with conventional flow-electrode-based CDI (FCDI). By coating of ion exchange membranes and a graphene layer inside each channel of the lattice structures, honeycomb-shaped desalination cells could be realized. First, the desalination performance of the new design was investigated in batch mode. It exhibited comparable desalting performance while maintaining typical advantages of FCDI systems, such as low energy consumption and no need of a discharging step. Furthermore, since the porous structures involve channels for ion transportation and act as a structural scaffold, the cell architecture is remarkably compact and it can be readily scaled-up by varying the number of unit cells and its configuration, allowing great increase in the salt removal capacity. We scaled-up the desalination system to a 3 × 3 cell, which showed desalination efficiency four times higher than that of a 1 × 3 cell. Such facile build-up of the unit cell structure and versatile design of cell configuration provide strong potential for further scalability. We also determined that this system can be operated successfully in continuous mode, indicating that neither a distinct discharging step nor substitution of inflow and effluent are required. Because there is opportunity for much more improvement of desalting performance in terms of the electrode materials, resistance at the interface, and conductivity of the current collecting layer of this system, we expect that our approach has opened a new door in the field of desalination research.

This paper offers a comprehensive techno-economic analysis of capacitive deionization (CDI) technology, examining its significance in water treatment. The analysis begins with a detailed elucidation of CDI principles,emphasizing its operational framework, and delineating both advantages and limitations. A global overviewsurveys the adoption of CDI across industries worldwide, comparing it with alternative water purification technologies to establish benchmarks in terms of cost, efficiency, and scalability. Central to this analysis is a robust techno-economic assessment framework for CDI, incorporating a multifaceted approach that considers capital investment, operational expenses, and maintenance costs. The paper expounds on methodologies for evaluating cost-effectiveness, providing insights into the economic feasibility of CDI implementation. Furthermore, the study delves into specific case studies within the context of Vietnam, a region facing distinct water quality challenges. Through meticulous examination, the case studies highlight the applicability of CDI in addressing Vietnam’s water issues while conducting a detailed techno-economic analysis of its implementation. Challenges hindering widespread adoption are outlined alongside opportunities for enhancing cost-effectiveness and scalability. Regulatory and policy considerations crucial for promoting CDI technology within Vietnam’s context are also addressed. The paper culminates in a forward-looking assessment, prognosticating the future trajectory of CDI technology in water treatment. Recommendations are provided to optimize CDI’s techno-economic feasibility globally, emphasizing avenues for further research and development. In summary, this paper substantiates the pivotal role of CDI in addressing water treatment challenges, underscoring its potential impact on water sustainability in Vietnam and across the globe within a comprehensive techno-economic framework.

Defluorination technology is crucial for ensuring the safety of accessible water. The application of capacitive deionization (CDI) technology faces challenges due to competitive adsorption of fluoride ions within complex natural fluoride-rich brackish water matrices, which often contain high levels of dissolved inorganic carbon (DIC) species (mainly HCO3– and CO32–). These DIC species are pH-dependent, playing a significant role in the selective removal of fluoride by the CDI process. Thus, there is a knowledge gap in understanding the effects of membranes in membrane capacitive deionization (MCDI) on fluoride removal. In this study, we examined the key operating parameters in CDI and MCDI, including applied constant voltages and different types of anion-exchange membranes (AEMs), on the desalination performance in F- and dissolved inorganic carbon water matrices. The application of AEMs significantly improve the salt adsorption capacity (SAC) for both F- and DIC species, and reduced energy consumption. However, it simultaneously results in a notable decrease in F- selectivity as membranes control mass transfer. Higher applied voltages enhance the SAC performance for F- and DIC species, but also induce more severe Faradaic reactions, leading to increased energy consumption and lower energy efficiency. Additionally, ion species and pH changes during CDI and MCDI processes are interrelated, indicating that stability tests of CDI electrodes in batch mode are not reliable when using the same testing solution repeatedly. The diverse valence states of ions in the solution impact pH variations under different voltages in the CDI/MCDI process. These findings provide valuable insights into the development of water purification and desalination technology, particularly for the application and further advancement of selective fluoride removal by the CDI process.

Water eutrophication driven by nitrates (NO3 -), phosphates (PO4 3-), and ammonium salts (NH4 +), along with groundwater contamination caused by fluorides (F-) and bromides (Br-), collectively poses significant threats to both ecological systems and human health. Capacitive Deionization (CDI) has demonstrated significant potential for selectively removing these pollutants due to its low energy consumption, absence of chemical byproducts, and cost-effectiveness. However, systematic mechanistic analyses and material design strategies focusing on this specific area remain insufficient. To this end, against the backdrop of water eutrophication and groundwater contamination, this paper presents a relatively comprehensive review of the research progress regarding the removal of NO3 -, PO4 3-, NH4 +, F-, and Br- using CDI technology. The review first discusses the advantages and limitations of conventional methods for removing these pollutants. It elaborates on the ion storage mechanism of CDI and addresses its fouling mechanisms and mitigation strategies. Subsequently, for different ions, the review systematically sorts out various types of electrode materials and explains in detail the intrinsic mechanisms through which they achieve ion selectivity. Finally, the review discusses current challenges in CDI technology, such as ion selectivity, electrode fouling, complexity of real water matrices, cost, and long-term stability, and proposes specific future research directions.

Synchronous removal of tetracycline and water hardness ions by capacitive deionization

Capacitive deionized hybrid systems for wastewater treatment and desalination: A review on synergistic effects, mechanisms and challenges