The 10th International Conference on Water Resource and Environment (WRE 2024)

Abstract: Nitrate from agricultural runoff and industrial waste streams is one of the major impurities in water. As high level of nitrate in drinking water may cause methemoglobinemia in infants and gastrointestinal cancer in adults, previous efforts on electrochemical wastewater treatment have aimed to solve this problem by converting nitrates to environmentally benign nitrogen gas. In the present study, we adjust this approach and propose an opportunity to transform nitrates to ammonia, which can serve as a key chemical used in fertilizer and fuel. Additionally, the electrochemical reduction of nitrate to ammonia can also offer an appealing alternative to the energy- and resource-intensive Haber-Bosch process. In this work, we explore the structure- activity relationship of copper catalysts using Cu foil, Cu particle, and porous Cu in terms of their performances in electrochemical nitrate reduction toward ammonia. Under the optimal conditions, the synthesized porous Cu exhibits a nitrate conversion of 84% with an ammonia selectivity of 85% and a Faraday efficiency of 58% at an applied potential of -0.75 V. Further investigations on surface structural effects reveal that the electrochemical surface area and the fraction of Cu(100)/Cu(111) crystal facets significantly impact their catalytic activity for electrochemical ammonia production.

Abstract: Nanostructured ceria has drawn a great interest in sustainable catalysis research due to its unique oxygen release/storage capability. In this presentation, I will introduce two research topics associated with CO2 reactions with ceria nanorods in environmental and energy fields. Firstly, a facile reflux process was developed to synthesize defective mesoporous ceria nanorods in a mild environment. Particularly, it is found that the rapid reflux synthesis enriches the surface with abundant trivalent Ce ions and oxygen vacancy sites. These features significantly improve the catalytic activity of ceria nanorod in synthesizing dimethyl carbonate (DMC) from CO2 and methanol with water as the only byproduct, which can replace the conventional toxic process using phosgene. Secondly, lithium-carbon dioxide (Li-CO2) battery has been proposed as a novel and attractive strategy for next-generation energy conversion and storage devices due to its high specific energy density and utilization of CO2 as energy source. However, the research on Li-CO2 battery still faces several challenges including low energy efficiency, slow charge/discharge rates, low power density, and short cycling life because of unavoidable formation of stable byproducts like Li2CO3 during repeated cycling. In our work, we utilized the ceria nanorods as the electrocatalyst in the cathode material for Li-CO2 batteries. The unique interaction between ceria and CO2 is found to improve the reactivity on the cathode surface, thus enhancing the CO2 reduction and Li2CO3 decomposition performance. In sum, the nanostructured ceria offers a promising opportunity for designing cost-effective materials with enhanced catalytic properties to meet future demands in sustainable research.

Abstract: The global issue of eutrophication has been exacerbated by the overuse of natural and synthetic fertilizers for irrigation and the discharge of industrial nitrate-containing chemicals into natural water sources. This widespread problem underscores the urgent need for innovative methods to denitrify wastewater using heteroatomic electrocatalysts with specific geometric structures. In this study, we successfully fabricated bimetallic Pd/Cu electrodes with Pd deposition times ranging from 1 to 3 minutes for the purposes of nitrate reduction. Various physicochemical characterization techniques were used to examine the morphology, composition, and structure of the Pd/Cu electrodes. XRD analysis confirmed the formation of a Pd/Cu alloy, while transmission electron microscopy showed a reduced nano size particles with a uniform distribution of Pd on the Cu surface. XPS analysis revealed the redox states of Pd⁰ and Cu⁺², further verifying the alloy formation. Cyclic voltammetry demonstrated that the Pd/Cu bimetallic electrode had significantly better ERN activity than bare Cu, as shown by a prominent nitrate reduction peak. The Pd/Cu electrode, with a 3-minute deposition time, achieved nearly 100% nitrate removal efficiency and an N₂ selectivity of 86% at a current density of 0.68 mA/cm².These findings underscore the effectiveness of the electrocatalytic system for water denitrification, providing a promising solution to address the pressing environmental challenge of nitrate pollution.

Abstract: The microplastics (MPs) in submicron range produced by anthropogenic and natural fracturing processes are emerging contaminants. Due to the small size, the treatment of submicron MPs by membrane processes necessitates membranes with a smaller cutoff, which not only requires greater pressure gradient but suffers from clogging. This study develops an electrophoretic separation system that utilizes the intrinsic negative surface charge of MPs to produce dilute stream free from submicron plastics particles. The separation relies on electrophoresis, at which an electric field was applied to produce an electrostatic force to counterbalance the drag force of permeation stream, preventing MPs to travel into dilute stream. Thus, the critical electric field (Ec) for complete removal of MPs could be estimated based on hydraulic condition, zeta potential, and size of MPs. The electrophoretic separation of MPs was investigated under various hydraulic condition, electric field, particle size, and initial concentration, verifying that the steady-state removal of MPs could achieve 99% at E > Ec. The distribution of MPs during electrophoretic separation was analyzed by control-volume approach, enabling the description of removal efficiency by hydraulic condition, applied and critical electric field. Ultimately, the specific energy consumption of electrophoretic separation was estimated to be comparable to conventional membrane processes.

Abstract: Stream bank erosion can provide a significant percentage of the sediment that reach water bodies. In many cases it was estimated that they can contribute up to 90%. Nature-based solutions, such as riparian forest can help significantly reduce stream bank erosion rates. While worldwide there have been major research efforts to estimate stream bank erosion rates and best management practices to mitigate them, there is a finite number of studies on stream bank erosion in Greece. The objective of this study was to estimate erosion rates is a typical Greek watershed with different riparian land-uses. The specific watershed studied was the Aggitis that is located in Northern Greece. Erosion rates were estimated with traditional methods (e.g., erosion pins) along with new methods (laser scanning and unmanned air vehicles). Erosion pins are narrow metal rods installed horizontally in the bank that are commonly used to measure the retreat of the streambanks over time. The pins were placed at 1/3 and 2/3 of the total height of the stream bank. A total of 400 pins were placed in 40 plots in different riparian land uses with 5 total measurements in different season over a two year period. The different riparian land-uses were: 1) Agricultural lands, 2) Broad-leaved forests, 3) Natural grasslands and 4) Sclerophyllous vegetation. For the laser scanning we choose three stream reaches with different geomorphological characteristics. The results of the scanning allowed to monitor stream bank erosion and deposition more precisely and at a larger scale. The first scanning took place in February of 2022 while the second measurements were taken on March of 2023. These three reaches were also surveyed with an unmanned aerial vehicle, specifically the MAVIC 2 PRO. The flights were conducted on March 2021, February 2022 and August 2022. Overall, the riparian forested areas had the lowest rates. In addition, a comparison of the pros and cons the three different methodologies was done.

Abstract: In this study, hexavalent iron oxidant was prepared from iron and manganese-containing sludge from water purification plants and was applied to organic sulfur compound under mixing-assisted oxidation desulfurization (MAOD). Dibenzothiophene (DBT)was used as a model fuel oil under high shear force, phase transfer agent or PTA (tetraoctylammonium bromide or TOAB), and oxidant (Fe(VI)) in a phase-transfer reaction to produce low-sulfur oil products. The effects of various ratios in Fe(VI) preparation, FeO42-/S molar ratio, pH regulation, mixing speed, reaction time, and reaction temperature were examined under their desulfurization efficiency.
In the preparation of Fe(VI) oxidant, nitric acid dissolution tests (1M~7M) were conducted. The results indicated that using 2M HNO3 could obtain 17,700 mg/L and 12,500 mg/L of iron and mangaPnese ions, respectively. NaOCl and NaOH ratios, 100 mL/100 g, 100 mL/200 g, 200 mL/100 g, and 200 mL/200 g, were found to synthesize Fe(VI) with the following respective concentrations: 624.8 mg/L, 1476.1 mg/L, 745.98 mg/L, and 597.93 mg/L. It was found that 200 mL NaOCl with 100 g NaOH is the optimal concentration for Fe(VI) production. Moreover, two KOH concentrations (11M and 23M) were examined and confirmed that the better yield of 658.32 mg/L was obtained using 11M KOH.
In the MAOD process, the effect of pH levels (3~12) on desulfurization efficiency was also examined using acetic acid and the optimal level was found at pH 5. Using 50 mL of 500 mg/L DBT solution under the FeO42-/S molar ratio varied from 2:1 to 12:1, the highest oxidative efficiency was observed using the molar ratio of 9:1. Moreover, the test of mixing speed (3400~6000 rpm) indicated that 3,400 rpm produced the highest sulfur oxidation. For the mixing time (5~60 minutes) and temperature (40℃~70℃), the optimal conditions for high desulfurization efficiency were 30 minutes and 40℃, respectively.　Overall, these optimal conditions were applied to reach the highest DBT oxidation efficiency at 81.8%.
By establishing an economical and safe oil desulfurization technology, this study has addressed the support of a circular economy in waste management and promoted the recycling application of wasted products.

Abstract: Water is not just an important resource, but without water, human beings and other living beings cannot exist. In order to develop an approach to the distribution and conservation of water that resonates with the importance of water for life, this contribution discusses value-sensitive water management. According to an eco-services approach to water, water resources such as rivers and water reservoirs have a range of distinct values, measurable as eco-services and as elements in value systems. After lining out this diversity of values, including a range of cultural values associated with water sources, it is possible to discuss principles of water management that help to resolve conflicts over water resources by integrating a value-perspective. Overall, this presentation raises awareness for water as a valuable resource, but also for the limits of commodification of that resource and for prudent ways to manage water in order to reduce conflict (Kallhoff 2017). However, this approach is limited to water reservoirs and not applicable to the seas and to other water systems.

Abstract: Sustainable, emission-free, and eco-friendly methods for fabricating high-quality materials have gained considerable attention in recent years. Moving away from the traditional linear synthesis process, which depends on a continuous input of finite virgin resources, a circular model can be adopted, where end-of-life products are strategically recycled and reused as feedstock.
Currently, nanomaterials are predominantly synthesized from costly raw materials using complex and inefficient processes. Although these materials enhance the functionality of various products, their disposal creates increasingly complex waste streams, contributing to a growing global waste problem and low recycling rates.
This paper outlines a pathway for transforming problematic waste streams into nanoscale, value-added materials with advanced applications, such as environmental monitoring and water purification. Target products, including silicon carbide (SiC), Au-doped TiO₂ quantum dots, and activated carbon with engineered structures, morphologies, surface areas, and physicochemical properties, have been synthesized from various problematic wastes such as electronic waste, biosolids, and industrial waste through chemical and thermal processing. The feasibility of producing microstructure-engineered materials for wastewater treatment and pollutant removal was explored, demonstrating that these waste-derived products could be excellent candidates for water purification.
These findings advocate for integrating recycled materials into high-performance applications, advancing the circular and sustainable economy. This approach reduces dependence on non-renewable resources while addressing pressing environmental challenges. By converting waste into nanostructured materials, this method not only tackles critical waste management issues but also creates new economic opportunities by providing high-value materials for advanced industrial applications.