Adsorption is a promising under-the-sink selenate remediation technique for distributed water systems. Recently it was shown that adsorption induced water network rearrangement control adsorption energetics on the α-Al₂O₃ (012) surface. Here, we aim to elucidate the relative importance of the water network effects and surface cation identity on controlling selenate and sulfate adsorption energy using density functional theory calculations. Density functional theory (DFT) calculations predicted the adsorption energies of selenate and sulfate on nine transition metal cations (Sc–Cu) and two alkali metal cations (Ga and In) in the α-Al₂O₃ (012) surface under simulated acidic and neutral pH conditions. We find that the water network effects had a larger impact on the adsorption energy than the cationic identity. However, cation identity secondarily controlled adsorption. Most cations decreased the adsorption energy, weakening the overall performance, the larger Sc and In cations enabled inner-sphere adsorption in acidic conditions because they relaxed outward from the surface, providing more space for adsorption. Additionally, only Ti induced Se selectivity over S by reducing the adsorbing selenate to selenite but not reducing the sulfate. Overall, this study indicates that tuning water network structure will likely have a larger impact than tuning cation–selenate interactions for increasing adsorbate effectiveness.

Heterogeneous catalysis holds great promise for oxidizing or reducing a range of pollutants in water. A well-recognized, but understudied, barrier to implement catalytic treatment centers around fouling or aging over time of the catalyst surfaces. To better understand how to study catalyst fouling or aging, we selected a representative bimetallic catalyst (Pd-In supported on AlO), which holds promise to reduce nitrate to innocuous nitrogen gas byproducts upon hydrogen addition, and six model solutions (deionized water, sodium hypochlorite, sodium borohydride, acetic acid, sodium sulfide, and tap water). Our novel aging experimental apparatus permitted single passage of each model solution, separately, through a small packed-bed reactor containing replicate bimetallic catalyst "beds" that could be sacrificed weekly for off-line characterization to quantify impacts of fouling or aging. The composition of the model solutions led to the following gradual changes in surface composition, morphology, or catalytic reactivity: (i) formation of passivating species, (ii) decreased catalytic sites due to metal leaching under acid conditions or sulfide poisoning, (iii) dissolution and/or transformation of indium, (iv) formation of new catalytic sites by the introduction of an additional metallic element, and (v) oxidative etching. The model solution water chemistry captured a wide range of conditions likely to be encountered in potable or industrial water treatment. Aging-induced changes altered catalytic activity and provided insights into potential strategies to improve long-term catalyst operations for water treatment.

Lithium (Li) is listed in the fifth Unregulated Contaminant Monitoring Rule (UCMR 5) because insufficient exposure data exists for lithium in drinking water. To help fill this data gap, lithium occurrence in source waters across the United States was assessed in 21 drinking water utilities. From the 369 samples collected from drinking water treatment plants (DWTPs), lithium ranged from 0.9 to 161 μg/L (median = 13.9 μg/L) in groundwater, and from <0.5 to 130 μg/L (median = 3.9 μg/L) in surface water. Lithium in 56% of the groundwater and 13% of the surface water samples were above non-regulatory Health-Based Screening Level (HBSL) of 10 μg/L. Sodium and lithium concentrations were strongly correlated: Kendall's τ > 0.6 (p < 0.001). As sodium is regularly monitored, this result shows that sodium can serve as an indicator to identify water sources at higher risk for elevated lithium. Lithium concentrations in the paired samples collected in source water and treated drinking water were almost identical showing lithium was not removed by conventional drinking water treatment processes. Additional sampling in wastewater effluents detected lithium at 0.8-98.2 μg/L (median = 9.9 μg/L), which suggests more research on impacts of lithium in direct and indirect potable reuse may be warranted, as the median was close to the HBSL. For comparison with the study samples collected from DWTPs, lithium concentrations from the national water quality portal (WQP) database were also investigated. Over 35,000 measurements were collected from waters that could potentially be used as drinking water sources (Cl < 250 mg/L). Data from WQP had comparable median lithium concentrations: 18 and 20 μg/L for surface water and groundwater, respectively. Overall, this study provides a comprehensive occurrence potential for lithium in US drinking water sources and can inform the data collection effort in UCMR 5.