•Overview of research conducted surrounding the electrochemical regeneration of GAC.•Discusses the regenerative mechanism and theory behind electrochemical regeneration.•Varying reactor configuration ...and operating conditions affect regeneration outcomes.•Specifies industrial applications for which this technology may be used.
The electrochemical treatment of exhausted granular activated carbon (GAC) has been identified as an effective alternative to traditional adsorbent regeneration methods (e.g. thermal, chemical, and microbial). However, despite its proven potential and initial investigation over two decades ago, the development of this technology has been progressing slowly, hindering its deployment in industrial applications. Thus, a review has been conducted that aims to present the fundamentals of GAC electrochemical regenerative methods, what research has been conducted to develop the technology to the present day, and lastly, identify limitations and future prospects associated with electrochemical methods. The regenerative mechanism is firstly discussed, followed by a presentation of the varying reactor configurations and operating parameters utilized during the electrochemical treatment of GAC materials exhausted with a broad range of wastewater contaminants. Finally, emerging electrochemical technologies used for the commercial treatment of exhausted adsorbent materials and contaminated soils are discussed.
This work investigates the effectiveness of the electro-Fenton reaction for the treatment of wastewaters contaminated with petroleum hydrocarbons. More specific attention was given to field ...deployment applications in remote regions, such as the sub-Antarctic, where there is a need for low-cost technologies that can aid in remediation efforts. Naphthalene, a high priority pollutant for removal within these regions, was chosen as a model contaminant and treated with inexpensive graphite electrodes to promote the electro-Fenton pathway. Results show that naphthalene can be fully removed from a near-saturated solution, 20 mg/L, in less than 3 h of treatment. The underlying removal mechanisms were identified, and a kinetic model is presented that can accurately predict treatment outcomes at varying operating conditions of applied electric currents, 0–5 mA, and iron(II) concentrations, 0–2.0 mM. Optimal operating conditions for the electro-Fenton pathway were found to be at an applied current of 5 mA and an iron(II) concentration of 0.06 mM; this resulted in a specific energy consumption of 5.6 kWhr/kg of naphthalene removed, low enough to be operated in remote regions via sustainable energy sources.
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•Fuel spills in remote regions require low-cost remediation technologies.•Contaminated lithosphere and hydrosphere negatively affect environmental receptors.•Electro-Fenton technology is a viable pathway to clean up such spills.•A kinetic model for the electro-Fenton reaction is presented.•Energy consumption is minimal and achievable for environmental remediation.
Direct removal of carbon dioxide (CO2) from the atmosphere, known as direct air capture (DAC) is attracting worldwide attention as a negative emission technology to control atmospheric CO2 ...concentrations. However, the energy‐intensive nature of CO2 absorption‐desorption processes has restricted deployment of DAC operations. Catalytic solvent regeneration is an effective solution to tackle this issue by accelerating CO2 desorption at lower regeneration temperatures. This work reports a one‐step synthesis methodology to prepare monodispersed carbon nanospheres (MCSs) using trisodium citrate as a structure‐directing agent with acidic sites. The assembly of citrate groups on the surface of MCSs enables consistent spherical growth morphology, reduces agglomeration and enhances water dispersibility. The functionalization‐assisted synthesis produces uniform, hydrophilic nanospheres of 100–600 nm range. This work also demonstrates that the prepared MCSs can be further functionalized with strong Brønsted acid sites, providing high proton donation ability. Furthermore, the materials can be effectively used in a wide range of amino acid solutions to substantially accelerate CO2 desorption (25.6% for potassium glycinate and 41.1% for potassium lysinate) in the DAC process. Considering the facile synthesis of acidic MCSs and their superior catalytic efficiency, these findings are expected to pave a new path for energy‐efficient DAC.
In this study, a conventional strategy is introduced for the preparation of monodispersed carbon spheres (MCSs). The findings shed light on the potential of amino acids as green solvents for the direct air capture of carbon dioxide (CO2) and reveal the superior performance of MCSs as a nanocatalyst to enable low‐temperature solvent regeneration and empower energy‐efficient CO2 capture.
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•Bulk electrochemical oxidation is seemingly beneficial for petroleum spill clean-up.•Active chlorine is effective for the removal of naphthalene and its derivatives.•Carbon ...electrodes are inexpensive and competent for bulk removal of organics.•A dynamic kinetic model is proposed that can accurately predict treatment outcomes.•Energy consumption is low enough for use in remote environmental remediation.
This work assesses the potential of electrochemical technologies for the treatment of groundwaters contaminated with petroleum hydrocarbons. Specific consideration was given to deployment in Antarctic regions where numerous fuel spills have occurred over the last two centuries, and resources and manual labour for remediation efforts are limited. The polycyclic aromatic hydrocarbon, naphthalene, was a used as a model contaminant and was treated with low-cost, active carbon electrodes to promote the active chlorine degradation pathway. Results showed that 20 mg/L naphthalene solutions could be treated to sufficient standards in less than 3 h of treatment, and that the formation of toxic and chlorinated by-products is not an issue of concern if the appropriate timeframes are used (4 h of treatment). The effects of the applied current (0–160 mA) and electrolyte concentration (0.01–0.1 M NaCl) were evaluated and a dynamic kinetic model proposed and found to be in good agreement with the experimental results. The energy consumption is an important limitation in remote environmental regions where resources are scarce. It was found that an energy usage of 104 kW h/kg of naphthalene removed could be achieved.
•A sustainable hybrid technology for DAC proposed.•Combination of amino acids and dense hollow fiber membrane provide stable CO2 absorption.•Vacuum low-temperature regeneration is a viable approach ...for CO2.•Potassium glycinate (GlyK) selected as the most suitable solvent for DAC.
Direct air capture (DAC) of CO2 using liquid sorbent technology is gaining attention as a promising approach in tackling the looming climate crisis. Despite technical advancements, critical aspects such as contactor selection, energy efficiency, sustainability, and environmental compatibility still pose uncertainties. In this study, various green amino acid salts performances in a DAC system were explored using non-porous hollow fiber membrane contactors (HFMCs). Two DAC absorption and desorption apparatuses were developed. For the DAC-absorption unit, the thermodynamic and kinetic behavior of five types of aqueous amino acid salt solutions were evaluated in long-term operations. High absorption stability for most of the solutions in different solvent loadings (up to 80% CO2 solvent loaded) were observed and potassium glycinate (GlyK) was selected as the most suitable candidate for DAC. To enhance the CO2 separation efficiency, parametric analysis on air and solvent flow rates, solvent temperature and concentration were conducted using GlyK. Vacuum low-temperature desorption experiments were carried out with GlyK to evaluate the CO2 removal efficiency over a range of solvent temperatures and concentrations, CO2 loadings, vacuum pressures, and vacuum/sweep gas mode. The results successfully quantified the effect of each operational parameter under various conditions on CO2 removal in a DAC system. Finally, to investigate the impact of membrane characteristics on DAC absorption–desorption performance, a developed and validated model was used. Taken all together, hybrid technology of membrane modules and green amino acid salts is shown to be a viable pathway towards a sustainable DAC process.
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•The vapor–liquid equilibria and absorption kinetics of CO2 in GlyK are evaluated.•GlyK is identified as a viable solvent for use in direct air capture applications.•A model simulates ...the performance of GlyK in commercial scale HFMCs.•GlyK can remove up to 83 % of the CO2 in ambient air.•Solvent regeneration temperatures can be kept well below 100 °C.
Current direct air capture (DAC) technology is largely cost-prohibitive for large scale implementation due to the excessive energy required to operate a combined absorption–desorption cycle. As the desorption process consumes much of the supplied energy, there is a demand to find more sustainable sorbent materials that maintain high absorptive capacities yet can be regenerated at lower working temperatures. This work evaluates potassium glycinate (GlyK) as one such alternative absorbent. Through conducting vapor–liquid equilibria and wetted wall column kinetic studies, GlyK is found to have comparable working capacities and liquid mass transfer coefficients to those reported for the industrial standard, monoethanolamine (MEA), yet outperforms it with regards to its distinctly low regeneration temperature. To further understand how GlyK would perform in an industrial scale DAC system, an Aspen Custom Modeler® (ACM) model is developed that integrates the experimentally obtained equilibria and kinetic data with the performance characteristics of a gas-solvent hollow fiber membrane contactor (HFMC). Full-scale simulations show that via implementing a 20°–90 °C absorption–desorption cycle, GlyK can capture up to 83 % of the CO2 in atmospheric air and be 55 % regenerated within a single membrane contactor pass. As these low working temperatures vastly outperform the conventional ∼ 40°–140 °C temperature swing currently implemented in industrial CO2 processing, GlyK is concluded to be a viable and sustainable option for use within energy-efficient DAC technology whereby renewable heat sources can be used.
This work demonstrates how liquid marble (LM) technology can be used to effectively encapsulate water-soluble fertilizers within a hard, biodegradable polymeric shell. Due to its high nitrogen ...content, urea is used as a model compound for encapsulation within marbles fabricated of either polycaprolactone (PCL) or polylactic acid (PLA). The tunable release properties of the marbles are examined by fabricating polymeric shells of varying compositions (PCL and PLA) and thicknesses (28–232 μm), and their associated release profiles are assessed under a range of temperatures (10–40 °C) and pH levels (4–10). It is demonstrated that LMs are beneficial for use in controlled release applications as release profiles can be easily adjusted to meet end application needs. To better understand the underlying mechanisms of the release profiles, a kinetic model is implemented that allows for accurate simulation, and prediction, of the release characteristics under all conditions studied. The controlled and tunable release profiles attained from LMs suggest that they would be appropriate for a wide range of industries and applications.
Controlled-release fertilizers (CRFs) are sustainable alternatives as they can increase crop yield and minimize environmental contamination associated with conventional fertilizers. However, there ...remains a demand for the development of CRFs with high biocompatibility, and tunable morphologies and mechanical properties. Herein, a solvent-free mechanochemical method is developed for synthesizing urea-encapsulated metal–phenolic networks (urea–MPN matrices) as CRFs. The matrices exhibit tunable mechanical resistance, crystallinity, stiffness, and wettability properties via rearranging the internal structure of the MPNs and their subsequent interaction with the encapsulated urea crystals. Sample aging (7 days) leads to a higher degree of complexation of the MPNs, resulting in a material with increased elasticity and melting point relative to the as-synthesized sample. Thermal treatment (60 °C for 6 h) instigates structural reorganization of the urea crystals within the matrix, generating a more robust material with a 51-fold increase in Young’s modulus. As CRFs, the urea–MPN matrices can be tuned to prolong the release of urea for up to 9 days depending on the treatment applied. As the mechanochemical synthesis of MPNs facilitates the tuning of physiochemical properties and has greater practicability for inclusion within large-scale processing, it has potential implementation within a broad range of industries.
