Application of Capacitive Deionisation in water desalination: A review

Nitrite desorption from activated carbon fiber during capacitive deionization (CDI) and membrane capacitive deionization (MCDI)

To enhance sustainability and resilience against climate change in infrastructure, a quantitative evaluation of both environmental impact and cost is important within a life cycle framework. Climate change effects can lead performance deterioration in bridge components during their operational phase, highlighting the necessity for a risk-based evaluation process aligned with maintenance strategies. This study employs a two-phase life cycle assessments (LCA) framework. First, risk assessments are conducted to evaluate the impact of climate change on steel plate girder bridges and prestressed concrete (PSC) girder bridges under identical structural conditions. The reduction in flexural strength of steel plate girders and PSC girders due to changes in environmental variables such as temperature and relative humidity, induced by various climate change scenarios, was evaluated analytically. Subsequently, life cycle environmental impact and cost assessments were performed, including maintenance outcomes derived from risk assessments. The findings revealed that the environmental impact and cost could increase by approximately 12.4% when climate change is considered, compared to scenarios where it is not taken into account. Sensitivity analyses were performed to identify the key factors influencing environmental impact and cost. The analysis determined that the frequency of preventive maintenance, the recycling rate, and environmental cost coefficient weight in the life cycle assessment significantly affected the results.

Hotspot analysis and improvement schemes for capacitive deionization (CDI) using life cycle assessment

As a class of environmental metrics, footprints have been poorly defined, have shared an unclear relationship to life cycle assessment (LCA), and the variety of approaches to quantification have sometimes resulted in confusing and contradictory messages in the marketplace. In response, a task force operating under the auspices of the UNEP/SETAC Life Cycle Initiative project on environmental life cycle impact assessment (LCIA) has been working to develop generic guidance for developers of footprint metrics. The purpose of this paper is to introduce a universal footprint definition and related terminology as well as to discuss modelling implications. The task force has worked from the perspective that footprints should be based on LCA methodology, underpinned by the same data systems and models as used in LCA. However, there are important differences in purpose and orientation relative to LCA impact category indicators. Footprints have a primary orientation toward society and nontechnical stakeholders. They are also typically of narrow scope, having the purpose of reporting only in relation to specific topics. In comparison, LCA has a primary orientation toward stakeholders interested in comprehensive evaluation of overall environmental performance and trade-offs among impact categories. These differences create tension between footprints, the existing LCIA framework based on the area of protection paradigm and the core LCA standards ISO14040/44. In parallel to area of protection, we introduce area of concern as the basis for a universal footprint definition. In the same way that LCA uses impact category indicators to assess impacts that follow a common cause-effect pathway toward areas of protection, footprint metrics address areas of concern. The critical difference is that areas of concern are defined by the interests of stakeholders in society rather than the LCA community. In addition, areas of concern are stand-alone and not necessarily part of a framework intended for comprehensive environmental performance assessment. The area of concern paradigm is needed to support the development of footprints in a way that fulfils their distinctly different purpose. It is also needed as a mechanism to extricate footprints from some of the provisions of ISO 14040/44 which are not considered relevant. Specific issues are identified in relation to double counting, aggregation and the selection of relevant indicators. The universal footprint definition and related terminology introduced in this paper create a foundation that will support the development of footprint metrics in parallel with LCA.

Severe nuclear accidents, including the Fukushima nuclear power plant accident, can lead to the discharge of large amounts of radionuclides into aquatic environments. Some radionuclides such as 137Cs and 90Sr have long half-lives and can remain in the environment for a long period of time. These radionuclides can be detrimental to humans and the environments because they can cause human and environmental exposure to ionizing radiation and because they can be bioaccumulated and biomagnified. Therefore, in case of a severe accident and a radioactive spill, it is important to quickly clean up and treat radioactively contaminated water to protect public health and aquatic ecosystems from unwanted radiation exposure. Ion separation technologies can play a critical role in the cleanup and treatment of radioactive water because most radionuclides in water are present as radioactive ions. Conventional ion separation technologies are typically used to decontaminate radioactive water, but many of these technologies are energy-consuming. Capacitive deionization (CDI) and membrane CDI (MCDI) are alternatives to the conventional technologies. CDI and MCDI are based on electrosorption and are less energy-intensive. However, because they have been designed and investigated for brackish water desalination, CDI and MCDI are not normally considered for the removal of radioactive ions from aqueous solutions. Toward more efficient and effective cleanup and treatment of radioactively contaminated water, this study aims at investigating the potential of CDI and MCDI for the removal of radioactive ions from aqueous solutions. Modeling and experimental investigations are performed along with techno-economic analysis to assess the applicability of CDI and MCDI for radionuclide separation. Carbon electrodes covered with carboxylic functional groups are employed to enhance their removal efficiency. This study contributes toward better protection of the public health and aquatic environments against radioactive contamination in water and the developed CDI and MCDI can be used to separate radioactive ions from aqueous environments. The results are also useful in expanding the applicability of CDI and MCDI to the treatment of various wastewater and high-salinity solutions.

Another technique for desalination, known as membrane capacitive deionization (MCDI), has been investigated as an alternative. This approach has the potential to lower the voltage that is required, in addition to improving the ability to renew the electrodes. In this study, the desalination effectiveness of capacitive deionization (CDI) was compared to that of MCDI, employing newly produced cellulose acetate ion exchange membranes (IEMs), which were utilized for the very first time in MCDI. As expected, the salt adsorption and charge efficiency of MCDI were shown to be higher than those of CDI. Despite this, the unique electrosorption behavior of the former reveals that ion transport via the IEMs is a crucial rate-controlling step in the desalination process. We monitored the concentration of salt in the CDI and MCDI effluent streams, but we also evaluated the pH of the effluent stream in each of these systems and investigated the factors that may have caused these shifts. The significant change in pH that takes place during one adsorption and desorption cycle in CDI (pH range: 2.3-11.6) may cause problems in feed water that already contains components that are prone to scaling. In the case of MCDI, the fall in pH was only slightly more noticeable. Based on these findings, it appears that CDI and MCDI are promising new desalination techniques that has the potential to be more ecologically friendly and efficient than conventional methods of desalination. MCDI has some advantages over CDI in its higher salt removal efficiency, faster regeneration, and longer lifetime, but it is also more expensive and complex. The best choice for a particular application will depend on the specific requirements.

Life Cycle Assessment in environmental impact assessments of industrial projects: towards the improvement

Various cell architectures of capacitive deionization: Recent advances and future trends

Capacitive deionization (CDI) is a class of electrochemical desalination technologies which desalinate via ion storage in electric double-layers. CDI has received renewed attention in recent years due to the ability to couple energy storage with salt separation. During galvanostatic operation, a current is applied between porous carbon electrodes until a limiting voltage is reach. The cell is then discharged by applying a reverse current, generating brine and recovering stored charge. However, CDI desalination and energy efficiency can be limited by parasitic side reactions, and selective adsorption of counter-ions (anions at the positive electrode, and cations at the negative electrode). Several material additions and electrode configurations have been proposed to overcome these limitations, with the most prominent being the addition of ion exchange membranes (IEMs) promote counter ion flux out of the desalination chamber and incorporation of carbon slurry electrodes to increase system adsorption capacity. Likewise, functionalization of carbon electrodes has been studied to improve counter-ion adsorption within EDL micropores. While the incorporation of functionalized carbon, IEMs in membrane capacitive deionization (MCDI), and the use of slurry electrodes in flow capacitive deionization (FCDI) have successfully reduced energy consumption or increased ion adsorption capacity in CDI systems, these modifications are often evaluated under limited conditions on the basis of specific performance enhancements. Additional clarity is necessary to evaluate the associated performance and cost tradeoffs across the design space. In this study, an equivalent circuit (M)CDI model, with porous electrode sub-models, was used to measure the sensitivity of CDI performance to material selection, design, and operating choices. In order to investigate the performance of FCDI, pulse-flowed electrodes of high capacity and electronic resistances were incorporated into the existing model. Similarly, fixed charge in the anodic and cathodic micropores was studied to investigate functionalized carbon. Constrained system parameters were randomly selected via latin hypercube sampling (LHS) across multiple electrode geometries and influent salt concentrations. The resultant model outputs were then correlated with input values to quantify parameter sensitivity. Our sensitivity analysis shows that operating current density, electrode specific capacitance, and contact resistance were the parameters which most significantly dictated (M)CDI performance. These parameters where then used to construct an operational space for CDI, MCDI, and FCDI. The results of our operational space were then used to develop a simplified, operational model for both capacitive and faradic materials in CDI. Using this model we conducted a techno-economic analysis (TEA) of proposed improvement to CDI. From the TEA we are able more directly set operating parameters under which CDI might favorably compete with the primary technology for desalination, reverse osmosis (RO). We are able to evaluate materials lifetimes and costs necessary to economically operate CDI. Lastly, goals for operating parameters highlighted in the sensitivity analysis (specific capacitance, voltage limits, charge efficiency, and cell resistance) were set. These benchmarks will provide target for the continued development of CDI towards and economic and viable alternative to RO for brackish water desalination.

Comparison of Faradaic reactions in capacitive deionization (CDI) and membrane capacitive deionization (MCDI) water treatment processes

Microbial desalination cell (MDC) was considered inefficient to desalinate salt water with low salt concentration, therefore, the feasibility of using capacitive deionization (CDI) and membrane capacitive deionization (MCDI) as a post-processing technologies for MDC was investigated in this study, as well as the possibility of using MDC as the power supply for CDI and MCDI. The internal resistances of MDC with different salt concentration, the desalination rate and fresh water yield during a typical desalination cycle under initial salt concentration of 35 g/L were investigated in order to find out the deadline salt concentration for the MDC to desalinate effectively. The internal resistance increased from 21.7 to 602 Ω as the concentration of salt water decreased from 35 g/L to 0.1g/L. The salt water volume increased from 42 to 48 ml when the salt concentration decreased from 35 to 15 g/L, then decreased to 38 ml at the end of one desalination cycle when the salt concentration achieved 0.05 g/L due to the salt gradient (osmotic pressure). The maximum desalination rate during one typical desalination cycle in our experiment reached 5.65 mg/h when salt concentration decreased from 27.26 to 26.32 g/L, while the minimum desalination rate was 0.534 mg/h when salt concentration decreased from 0.38 to 0.05 g/L. It was concluded that MDC was not suitable to desalinate salt water with salt concentration less than 1 g/L. When CDI and MCDI were used as the post-processing technologies for MDC, a better performance in term of electrosorption capacity was obtained from MCDI with an influent salt concentration of 1 g/L. The experimental result also showed that the electrosorption capacity of MCDI with MDC as power supply was more than that with potentiostat as power supply at 0.8V, this suggests that MDC could be an alternative power supply for MCDI.

In Korea, a greenhouse gas (GHG) environmental impact assessment (EIA) has been conducting since 2012, which sets the evaluation procedures and methods for GHG items during the EIA. However, the current EIA on GHG emissions can support wrong decision-making because the evaluation does not consider Scope 3 GHG emissions. Accordingly, this study proposed the life cycle EIA (LCEIA) method to identify changes in GHG emissions that need to be managed by considering Scope 3 GHG emissions in construction projects. The LCEIA method incorporates life cycle CO2 (LCCO2) including Scope 1, Scope, and Scope 3 GHG emissions using the concept of life cycle assessment (LCA) into the scoping step of the EIA process. The case study was conducted using existing EIA on GHG emission and LCEIA methodology for a development project in Gwangyang City. Scenario 1 is defined as an approach that calculates GHG emissions using the existing EIA method, and scenario 2 is also defined as a process using the LCEIA method. Results reveal that Scenario 2, including Scope 3 GHG emissions, had 46.4−51.2% more GHG emissions than Scenario 1. Sensitivity analysis for electricity and liquefied natural gas (LNG) density was also performed. Although the change in the carbon emission factor of electricity had a slightly sensitive effect on the research results, the LNG density was found to be less sensitive. This study believes the importance of switching to an EIA reflecting life cycle carbon dioxide (LCCO2) to calculate the exact amount of GHG emissions for construction work.

Natural gas distributed energy is recognized as a pivotal means to enhance energy efficiency and mitigate carbon dioxide emissions through localized energy cascading. Positioned as a key option for advancing the Sustainable Development Goals, this system optimizes energy utilization near end-users. While maximizing energy efficiency, it is imperative to address potential environmental challenges. A thorough, comprehensive environmental assessment, facilitated by the life cycle assessment method, proves instrumental in meeting this standard. Employing this method enables an intuitive grasp of the environmental strengths and weaknesses inherent in natural gas distributed energy within the power structure. This insight serves as a foundation for informed project decision-making, fostering the growth of the industry. We selected six environmental impact assessment categories based on the CML 2001 method, and conducted the life cycle analysis across four stages. China's inaugural natural gas distributed energy demonstration project was chosen as a model case, and an environmental impact assessment inventory was established, utilizing survey data and literature for comprehensive data collection and analysis. Results from case testing yield environmental impact assessment outcomes, with a specific sensitivity analysis for stages with notable environmental impact factors. The study underscores that the operation phase has the highest environmental impact, comprising 78.37% of the total combined environmental impact, followed by the fuel production phase. Comparative analyses with coal-fired and conventional natural gas power generation, based on dimensionless literature data, reveal that abiotic resources depletion potential is the primary contributor to the environmental impact of 1 kWh of electricity product, constituting 52.76% of the total impact value, followed by global warming potential. Concrete strategies have been outlined for decision-making in both the operational and planning phases of natural gas distributed energy projects. The strengthening of policies is pinpointed towards grid connection and scale expansion.

A comparison of multicomponent electrosorption in capacitive deionization and membrane capacitive deionization

Environmental Assessment Yearbook 2001: Editors: Liz Billing, Carys Jones, Barry Sadler, Christopher Wood. Publisher: Institute of Environmental Management and Assessment. Cost: £20 (British Pounds Sterling). ISSN 1474-9440. Order details: e.jaggs@iema.net