Disinfection byproducts (DBPs) raise concerns about drinking water safety/health. This study developed a membrane-less electrochemical system with a granular activated carbon (GAC)-based cathode and a carbon cloth anode applying a facile paired electrolysis method. Trihalomethanes and haloacetonitriles at drinking water concentration levels were treated. Except for chloroform as ~ 48% removal, all other DBPs achieved > 70% and > 60% removal in batch and continuous reactors at 2.0 V cell voltage. Enhanced removal of DBPs was achieved by electrolysis compared to open circuit and hydrolysis controls, and degradation/dehalogenation was verified by the release of halide ions, with high dechlorination and debromination efficiencies in batch (82.2 and 94.3%) and continuous (79.3 and 87.6%) reactors. Degradation was mainly contributed by the electrochemical reduction in GAC-based cathode, while anode showed little oxidizing effect on DBPs and halide ions. Dehalogenated products of chloroform and dichloroacetonitrile were identified to prove toxicity reduction. The sustainable performance was demonstrated in continuous experiments through long-term tests (168 h) at 2.0, 1.8 and 1.6 V cell voltage. GAC achieved regeneration by electrochemical treatment to obtain an extended service time, and the energy consumptions were estimated to be 0.28 to 0.16 kWh m^-3. These results suggest that electrochemical technology could be a competitive strategy for DBPs control in drinking water.

Boron is ubiquitous in seawater in the form of boric acid (H₃BO₃, pKa = 9.24) at low concentrations (4-6 mg/L). Though an essential micronutrient, excess boron intake is highly toxic to humans and many crops, making effective boron removal in seawater desalination essential. Reverse osmosis (RO) membranes alone are inadequate for the removal of uncharged boric acid to acceptable levels for agricultural use, necessitating the utilization of high-pH RO processes, which increase overall energy consumption by approximately 10-15%. This non-selective removal process also results in the elimination of other beneficial minerals, requiring subsequent remineralization. An alternative method for boron removal would benefit from reduced energy consumption, lower capital costs, and the elimination of chemical dosing requirements. Herein, we developed a novel bipolar membrane (BPM) assisted electrosorption technology that can selectively remove boron over competing anionic species in the solution (e.g., chloride). The BPM was used to create a high pH environment to ionize boric acid to borate [B(OH)₄^-], while electrosorption is utilized for boron removal. Selective boron removal is achieved by modifying a carbon electrode either through the deposition of a thin, boron-selective polymeric film or through chemical functionalization of its surface with boron-chelating groups, such as 3-methylamino-1,2-propanediol or N-methyl-D-glucamine.

Coal-fired power plants (CFPPs) generate Se-laden wastewater that could release ppm-level Se(IV) and Se(VI) oxyanions into natural water bodies. Se-rich water poses ecological damages and is facing an increasingly stringent regulatory standard. This presentation showcases our study of electroplating Se(0) on the cathode surface to remove aquatic Se(IV) or selenite. To achieve continuous electroplating, the operation temperature of our treatment system is kept at 80°C to electroplate conductive Se(0). We evaluated six affordable cathode materials based on their ability to remove aqueous selenite from the synthetic wastewater. The selection is narrowed down to graphite and nickel, which exhibit outstanding 6-h linear removal kinetics of 213.3 and 186.0 mg Se(IV) m^-2 h^-1 and 24-h removal efficiencies of 91% and 70% Se(IV), respectively. Graphite also demonstrates higher Faradaic efficiency (3.8%) than nickel (2.5%), primarily due to its large reaction area from the rough surface and inner pores. We further confirm Se(0) insertion in graphite cathode is possible using XPS and XRD, as the graphene interlayer experiences significant expansion. By fine-tuning the electric driving force to prioritize Se(0) insertion, we minimize the surface-plated Se(0) that could increase the cathode resistance. With this advantage, we successfully lower the system operating temperature to the actual temperature of the power plant wastewater (50°C). The usage of affordable graphite cathode and the decrease in operating temperature significantly reduce our system’s operation and maintenance costs. Our promising results warrant further efforts to design flow-through electroplating reactors to mitigate mass transfer constraints when treating actual power plant wastewater.

Electrochemical sulfide treatment is a promising solution for managing aqueous sulfur, which poses environmental and health concerns due to its toxic, odorous, and corrosive nature. However, sulfur is crucial for agriculture and chemical manufacturing processes, and could be recovered as fertilizer and commodity chemicals. Advancing such circular approaches requires understanding of how reaction mechanisms and operating parameters translate into product-driven and efficient sulfur recovery processes, which remains a challenge for electrochemical sulfur recovery. The goals of this study were to further identify and overcome the barriers of electrochemical sulfur recovery by investigating the mechanism of electrochemical sulfide oxidation, evaluating performance metrics, and integrating process operation with nitrogen recovery. On the mechanistic level, the results from the study suggested thiosulfate oxidation as the rate-limiting step, and the impact of elemental sulfur formation during sulfide oxidation reaction. On the process level, we examined the impact of electrolyte conditions (e.g., pH, composition, buffer strength, sulfide concentration) and operating conditions (e.g., applied potential) on the performance of sulfide removal and the generation of recoverable products (e.g., elemental sulfur, sulfuric acid). In addition, simultaneous multi-nutrient recovery (i.e., sulfur and nitrogen) as ammonium sulfate, a fertilizer, in one electrochemical reactor was also explored. The study offers recommendations for operational parameters of electrochemical sulfur recovery, which enhance the sustainability of sulfur manufacturing, minimize environmental impact by improving effluent quality, and support a circular sulfur economy.

The energy sector is a key contributor to greenhouse gas emissions and climate change and at the same time one of the largest consumers of water. Efforts to decarbonize the energy sector need to be accompanied by an increase in water efficiency, either by reducing water consumption, or switching from high-quality water sources such as freshwater and groundwater to seawater and impaired waters, which cannot be immediately used for drinking or irrigation. Green hydrogen produced by water electrolysis and powered by renewable energy will play a prominent role in the decarbonization of the energy sector, but current technologies for green hydrogen production require ultrapure water feeds, which are expensive to produce and can generate hazardous effluents. Here, I will show how elucidating the mechanisms controlling ion transport in water electrolyzers can guide the design of optimized cell architecture that not only operate efficiently with saline water feeds, but produce better performance when doing so. I will show how the membrane charge and the direction of the electric field can be leveraged in proton exchange membrane electrolyzers to limit the intrusion of competing ions near the electrodes, reducing energy demand while maximizing reaction selectivity. Optimizing the cell architecture in anion exchange membrane electrolyzers can produce even better performance with saline water feeds compared to ultrapure water by minimizing the internal resistance of the cell. These findings, guided by fundamental understandings in the electrochemistry, including ion transport mechanisms, of electrochemical cells can lead to innovative water-efficient approaches to sustain our energy needs.