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Separation Techniques Using Conjugated Polymers
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
Cheng-Wei Lin, Wai H. Mak, Brian T. McVerry, Richard B. Kaner
Different from removing heavy metal ions by thermodynamic adsorption and chelating of conjugated polymers, capacitive deionization (CDI) is a burgeoning technique for the removal of charged ions or salts from brackish water. Although still a relatively new desalination technology compared to other techniques such as RO, CDI is becoming more prominent with the advent of novel electrode materials and cell designs. The key premise behind CDI technology is that through an applied potential, an electric double layer (EDL) is created, thereby adsorbing ions onto the electrode surfaces. Two porous electrode plates with an applied potential separates the cations and anions from the bulk saltwater solution. Under low salinity, the energy expenditure of CDI is projected to be considerably more energy efficient compared to other desalination techniques because of the low potentials required for electrosorption.169 Unlike RO, which uses high pressure to separate fresh water from a salt solution using a semipermeable membrane, less energy is spent on separating and removing salt (the minor component) from water (the major component). Furthermore, the energy spent on separating the ion species stored on the electrode plates can be recovered upon discharge to further reduce the energy footprint.170 In other words, it is much easier to remove salt from water than water from salt.
Sustainable Development and Future Trends in Desalination Technology
Published in Andreas Sapalidis, Membrane Desalination, 2020
Mattheus Goosen, Hacene Mahmoudi
It is important to consider novel desalination processes, even if they do not currently meet the economic feasibility of conventional processes. Ramachandran et al. (2019) remarked on energy consumption in desalination by comparing capacitive deionization and reverse osmosis. Capacitive deionization (CDI) is an emerging brackish water desalination technology in which ions are removed from water by electrostatically adsorbing them onto porous electrodes (Figure 13.7). Qin et al. (2019) estimated very high values of energy consumption in CDI for brackish water desalination (e.g., ~1 to 2 g/L salt solution). These values and trends did not agree with published experiments for CDI by Wang et al. (2019). The differences were attributed to important scaling errors and incorrect values in their model resistance parameters. This was a similar observation and conclusion to that reported by Shahzad et al (2019a, 2019b), who maintained that energy and desalination system planners may make serious judgmental errors in the process selection of installations, without realizing it, if data is either flawed or inaccurate. Ramachandran et al. (2019) concluded that results from experiments and experimentally validated models suggest that brackish water desalination with reasonably high salt rejection (±70%) and water recovery (± 80%) can be achieved by capacitive deionization in an energy-efficient manner. While capacitive deionization (CDI) is a significantly less mature technology than reverse osmosis, experiments and experimentally validated models show that it has strong potential to become a competitor to other brackish water desalination technologies.
Physical similarity and parametric sensitivity analysis of the capacitive deionization process
Published in International Journal of Green Energy, 2022
Jianfei Zhang, Meng Yang, Huangyi Zhu, Qinlong Ren, Zhiguo Qu
The increasing depletion of freshwater is a serious challenge for social and economic development. Desalination of seawater or brackish water (Zhao et al. 2013) is a promising technology to overcome the shortage of freshwater. Many well-proven technologies such as reverse osmosis (Joo and Tansel 2015), multistage flash (El-Ghonemy 2018), electrodialysis (Strathmann 2010), and other methods are widely used. Among them, reverse osmosis is one of the most energy-efficient technologies for seawater desalination (Elimelech and Phillip 2011). However, the membrane module of reverse osmosis is prone to clogging and requires periodic maintenance and replacement. Due to the advantages of no demand for high pressure or a membrane structure (Suss et al. 2015), capacitive deionization (CDI), which have potentially highly energy-efficient desalination for brackish water, has attracted increasing research attention as one of the potential technologies in the future.
Remediation of water and wastewater by using engineered nanomaterials: A review
Published in Journal of Environmental Science and Health, Part A, 2018
Obadia K. Bishoge, Lingling Zhang, Shaldon L. Suntu, Hui Jin, Abraham A. Zewde, Zhongwei Qi
Capacitive deionization (CDI), which uses nanoparticles, such as silver, zinc, 3D graphene/metal oxide hybrids, is developed to enhance the desalination efficiency of different ions, including sodium, iron, calcium, and magnesium, in contaminated water.[113–115] CDI is an energy-efficient and low-cost technology for desalination because it creates high recovery property for water and uses low pressure in reverse osmosis (RO) and low temperature in multi-stage flash processes.[23,116–118] CDI uses electrophoretic driving forces to achieve desalination. During capacity deionization, ions are adsorbed onto the surface of porous electrodes that are grafted with nanoparticles by applying a low voltage ranging from 1.0 to 1.6 volt of direct current electric field. The negative electrodes attract positively charged ions, such as magnesium, sodium, and calcium, simultaneously; the positive electrodes attract negatively charged ions, including nitrate, sulfate, and chloride[119] (Fig. 5). The regeneration of the electro sorbent in this system does not require using additional chemicals. Table 4 shows the functions of nanomaterials for desalination.
Treatment options for nanofiltration and reverse osmosis concentrates from municipal wastewater treatment: A review
Published in Critical Reviews in Environmental Science and Technology, 2019
Kimmo Arola, Bart Van der Bruggen, Mika Mänttäri, Mari Kallioinen
Other technologies such as electrodialysis metathesis (EDM), membrane crystallization and capacitive deionization (CDI) have also been used to remove and recover salts from membrane concentrates and other concentrated wastewaters. Zhang et al. (2017) utilized EDM in an integrated system of NF-EDM to synthesize high solubility salts by treating NF permeate from nanofiltration of synthetic wastewater as a monovalent stream (containing most of the monovalent ions) and NF concentrate (320–730 mg/L of Ca2+ and 2026–2770 mg/L of SO42−) as a divalent stream (containing most of the divalent ions) in a EDM stack. High solubility salts CaCl2 and Na2SO4 could be synthetized and concentrated up to 7.6 and 10.5 times (compared to initial concentrations in the feeds NF permeate and concentrate for EDM) into two separate product streams with EDM. Quist-Jensen et al. (2017) recovered over 75% of Na2SO4 from industrial wastewater containing 45–55 g/L of Na2SO4 by using membrane crystallization. As discussed in the section 4.1.3, the membrane crystallization is usually more applicable for industrial wastewaters containing significant concentration of salts. Thus the utilization of membrane crystallization for membrane concentrates of municipal wastewater treatment might not be feasible in most cases due to limited concentration and value of salts present in the concentrate. Lee, Ng, Ong, Tao, et al. (2009) utilized capacitive deionization (CDI) for the removal of ions such as Na+, K+, Ca2+, Cl− and PO43− from reverse osmosis concentrates. CDI process removed over 87% of Na+, K+, Ca2+ and Cl− ions from the concentrate.