Point-of-use (POU) devices with satisfactory lead (Pb 2+ ) removal performance are urgently needed in response to recent outbreaks of lead contamination in drinking water. This study experimentally demonstrated the excellent lead removal capability of two-dimensional (2D) MoS 2 nanosheets in aqueous form and as part of a layer-stacked membrane. Among all materials ever reported in the literature, MoS 2 nanosheets exhibit the highest adsorption capacity (740 mg/g), and the strongest selectivity/affinity towards Pb 2+ with a distribution coefficient K d that is orders of magnitude higher than that of other lead adsorption materials (5.2×10 7 mL/g). Density functional theory (DFT) simulation was performed to complement experimental measurements and to help understand the adsorption mechanisms. The results confirmed that the cation selectivity of MoS 2 follows the order Pb 2+ > Cu 2+ >> Cd 2+ > Zn 2+ , Ni 2+ > Mg 2+ , K + , Ca 2+ . The membrane formed with layer-stacked MoS 2 nanosheets exhibited a high water flux (145 L/ m 2 /h/bar), while effectively decreasing Pb 2+ concentration in drinking water from a few mg/L to less than 10 μg/L. The removal capacity of the MoS 2 membrane is a few orders of magnitude higher than that of other literature-reported membrane filters. Therefore, the layer-stacked MoS 2 membrane has great potential for POU removal of lead from drinking water.

Urban stormwater, municipal wastewater effluent, and agricultural runoff contain trace amounts of organic contaminants that can compromise water quality. To provide a passive, low-cost means of oxidizing substituted phenols, aromatic amines, and other electron-rich organic compounds during infiltration of contaminated waters, we coated sand with manganese oxide using a new approach involving the room-temperature oxidation of Mn with permanganate. Manganese oxide-coated sand effectively oxidized bisphenol A under typical infiltration conditions and sustained reactivity longer than previously described geomedia. Because geomedia reactivity decreased after extended operation, chlorine was evaluated for use as an in situ geomedia regenerant. Geomedia regenerated by HOCl demonstrated similar reactivity and longevity to that of virgin geomedia. Chemical analyses indicated that the average manganese oxidation state of the coatings decreased as the geomedia passivated. X-ray absorption spectroscopy and X-ray diffraction showed that the reactive virgin and regenerated geomedia coatings had nanocrystalline manganese oxide structures, whereas the failed geomedia coating exhibited greater crystallinity and resembled cryptomelane. These results suggest that it is possible to regenerate the oxidative capacity of manganese oxide-coated sands without excavating stormwater infiltration systems. These results also suggest that manganese oxide geomedia may be a cost-effective means of treating urban stormwater and other contaminated waters.

Urea has been regarded as an important chemical compound in the food‐water‐energy nexus. However, the emission of urea from human activity, industrial manufacture, and agricultural fertilization into the environment has caused an ecological nitrogen imbalance. Besides addressing the environmental pollution, the applications of clean energy conversion from urea‐rich wastewater has strong potential for resource and energy recovery. Herein, we conducted a comprehensive overview of electrochemical urea oxidation reaction (UOR) for pollution control and energy harvesting. The present mechanisms and behaviors of UOR under different water matrices have been characterized and compared in detail. Additionally, the latest development of electrochemical UOR integrated into electrolyzers and fuel cells are presented. Finally, we discuss the prospects and challenges of UOR technologies, suggesting several directions for the electrochemical conversion of urea‐abundant wastewater in the near future.

Drinking water stagnation can lead to degradation of chlorine residual, bacterial growth (including of opportunistic pathogens and nitrifiers), and metals release from plumbing materials; however, few studies have characterized building water quality and bacterial communities during the extended stagnation periods that occurred during COVID-19 pandemic-related building closures. Additionally, despite a lack of evidence-based guidance, flushing fixtures has been recommended to restore building water quality. We aimed to evaluate the impacts of reduced building occupancy (>2 months) and weekly restorative flushing on drinking water quality, bacterial communities, and the occurrence of undesirable microorganisms in three university buildings. Reduced occupancy led to diminished chloramine and elevated intact cell counts, but values remained stable after additional weeks of limited water use. Flushing temporarily improved water quality, with chlorine and cell counts remaining stable for at least 1 day but returning to levels measured prior to flushing within 1 week. Alpha diversity was lower under more stagnant conditions, and fixture identity, not flushing, was the most influential factor on bacterial community composition, suggesting a strong influence from local biofilm. Although Mycobacterium, Legionella, Pseudomonas, Nitrosomonas, and Nitrospira were detected in samples via amplicon sequencing, concentrations measured via qPCR of M. avium complex, L. pneumophila, P. aeruginosa, and ammonia-oxidizing bacteria were very low or were undetected, supporting that stagnation alone did not lead to high occurrence of undesirable microorganisms. Findings from this study contribute to our understanding of the effects of stagnation on building water microbiomes and the efficacy of flushing to improve water quality. Under the conditions of this case study, repeated flushing on a weekly timescale during low occupancy periods was not sufficient to maintain chlorine residual and prevent bacterial growth in fixtures. Building managers need to weigh the temporary water quality benefits of flushing against the labor and water resources required considering local context.

Under the conditions employed when in situ chemical oxidation is used for contaminant remediation, high concentrations of H2O2 (e.g., up to ∼10 M) are typically present. Using 13C NMR, we show that in carbonate-rich systems, these high concentrations of H2O2 result in a reaction with HCO3 – to produce peroxymonocarbonate (HCO4 –). After formation, HCO4 – reacts with phenol to produce di- and trihydroxyl phenols. HCO4 – reacts with substituted phenols in a manner consistent with its electrophilic character. Exchanging an electron-donating substituent in the para position of a phenolic compound with an electron-withdrawing group decreased the reaction rate. Results of this study indicate that HCO4 – is a potentially important but previously unrecognized oxidative species generated during H2O2 in situ chemical oxidation that selectively reacts with electron-rich organic compounds. Under conditions in which HO· formation is inefficient (e.g., relatively high concentration of HCO3 –, low total Fe and Mn concentrations), the fraction of the phenolic compounds that is transformed by HCO4 – could be similar to or greater than the fraction transformed by HO·. It may be possible to adjust treatment conditions to enhance the formation of HCO4 – as a means of accelerating rates of contaminant removal.

Manganese oxide-coated sand can remove toxic metals from stormwater for years before regeneration with a mild acid. This geomedia could facilitate the use of stormwater as a water supply.

Highlights Pre-production of concentrated H 2 O 2 before treatment reduced the system footprint. System design was optimized based on H 2 O 2 generation, storage, and activation. Optimization reduced cost and footprint of electrochemical stormwater treatment.

Manganese oxide-coated sand can oxidize electron-rich organic contaminants, but after extended exposure to contaminated water its reactivity decreases. To assess the potential for regenerating geomedia, we measured the ability of passivated manganese-oxide coated sand to oxidize bisphenol A after treatment with oxidants, acid, or methanol. Among the regenerants studied, KMnO4, HOCl, HOBr, and pH 2 or 3 HCl solutions raised the average oxidation state of the Mn, but only HOCl and HOBr restored the reactivity of passivated geomedia to levels comparable to those of the virgin manganese-oxide coated sand. Treatment with HCl restored about one third of the reactivity of the material, likely due to dissolution of reduced Mn. Mn K-edge X-ray absorption spectroscopy data indicated that the reactive manganese oxide phases present in virgin geomedia and geomedia regenerated with HOCl or HOBr had nanocrystalline cryptomelane-like structures and diminished Mn­(III) abundance relative to the passivated geomedia. KMnO4-regenerated geomedia also had less Mn­(III), but it exhibited less reactivity with bisphenol A because regeneration produced a structure with characteristics of δ-MnO2. The results imply that manganese oxide reactivity depends on both oxidation state and crystal structure; the most effective chemical regenerants oxidize Mn­(III) to Mn­(IV) oxides exhibiting nanocrystalline, cryptomelane-like forms.