Cryptands on a Solid Support for the Separation of Europium from Gadolinium.

With the great demand for europium in green-energy technologies comes the need for innovative methods to isolate the elements. We introduce a solid-liquid extraction method using a 2.2.2-cryptand-modified solid support to separate europium from gadolinium using their differences in electrochemical potential. The method overcomes challenges associated with the separation of those two ions that have similar coordination chemistry in the +3 oxidation state. A competitive adsorption study in the cryptand system between EuII/EuIII and GdIII shows greater affinity for EuII relative to GdIII. After separation from GdIII, Eu was released by oxidizing EuII to EuIII with 99.3% purity. The purity of separated Eu is unaffected by pH between pH 3.0 and 5.5. Overall, we demonstrate that by modifying a solid support with 2.2.2-cryptand, divalent europium can be separated from trivalent gadolinium based on the differences of affinities of 2.2.2-cryptand for the two ions.

Do drinking water treatment residuals underperform in the presence of compost in stormwater media filters?

Drinking water treatment residuals (WTR), a waste-derived product, are often recommended to use as an amendment in stormwater biofilters to enhance their capacity to remove phosphate and microbial pollutants. However, their efficacy has been assumed to remain high in the presence of compost, one of the most common amendments used in biofilters. This study tests the validity of that assumption by comparing the removal capacities of WTR-amended biofilters with and without the presence of compost. Our results show that amending sand with WTR increased E. coli removal by at least 1-log, but the addition of compost in the sand-WTR media lowered the removal capacity by 13 %. Similarly, the addition of WTR to sand improved phosphate removal to nearly 1177 %, but the removal decreased slightly by 8 % when adding compost to the media. The results confirmed that dissolved organic carbon (DOC) leached from the compost could compete for adsorption sites for bacteria and phosphate, thereby lowering WTR's adsorption capacity based on the amount of DOC adsorbed on WTR. Collectively, these results indicate that the stormwater treatment industry should avoid mixing compost with WTR to get the maximum benefits of WTR for bacterial removal and improve the performance lifetime of WTR-amended biofilters.

A review of compaction effect on subsurface processes in soil: Implications on stormwater treatment in roadside compacted soil.

Sustainable cities require spacious infrastructures such as roadways to serve multiple functions, including transportation and water treatment. This can be achieved by installing stormwater control measures (SCM) such as biofilters and swales on the roadside compacted soil, but compacted soil limits infiltration and other functions of SCM. Understanding the effect of compaction on subsurface processes could help design SCM that could alleviate the negative impacts of compaction. Therefore, we synthesize reported data on compaction effects on subsurface processes, including infiltration rate, plant health, root microbiome, and biochemical processes. The results show that compaction could reduce runoff infiltration rate, but adding sand to roadside soil could alleviate the negative impact of compaction. Compaction could decrease the oxygen diffusion rate in the root zone, thereby affecting plant root activities, vegetation establishment, and microbial functions in SCM. The impacts of compaction on carbon mineralization rate and root biomass vary widely based on soil type, aeration status, plant species, and inherent soil compaction level. As these processes are critical in maintaining the long-term functions of SCM, the analysis would help develop strategies to alleviate the negative impacts of compaction and turn road infrastructure into a water solution in sustainable cities.

Development of a Highly Selective Ni(II) Chelator in Aqueous Solution.

The design, synthesis, and characterization of a novel Ni(II) chelator SG-20 is reported. SG-20 is selective in binding to Ni(II) versus other metal ions including Cu(II), Fe(II), Co(II), and Zn(II). At pH = 7.1, SG-20 binds Ni(II) with a Kd = 7.0 ± 0.4 µM. Job analysis indicates that SG-20 binds to both Ni(II) and Cu(II) with a 1:1 stoichiometry. Affinity of SG-20 for Ni(II) is pH dependent and decreases upon lowering to pH 4.0. A green solid was isolated from the reaction of SG-20 with NiCl2·6H2O in MeOH and characterized by X-ray photoelectron spectroscopy (XPS), electronic absorption and infrared (IR) spectroscopies, and mass spectrometry. Collectively, XPS and IR analysis revealed Ni-N and Ni-O interactions and a shift in C-O asymmetric and symmetric stretches consistent with Ni binding. Attempts to crystalize a mononuclear complex were unsuccessful, likely due to the Ni-SG-20 complex being in equilibrium with higher order species in solution. However, reaction of SG-20 with NiCl2·6H2O in water followed by slow evaporation yielded green crystals that were characterized by electronic absorption spectroscopy (λmax = 260 nm) and X-ray crystallography. These analyses revealed that SG-20 supports formation of a complex cluster containing six SG-20 ligands, 15 Ni(II), and three Na(I) centers, with two distinct types of Ni atoms in its outer and inner core. The nine Ni atoms present in the inner core were bound by oxo and carbonate bridges, whereas the six Ni atoms present in its outer shell were bound to N, O, and S donor atoms derived from SG-20. Overall, X-ray crystallographic analysis revealed that two chelator arms of SG-20 bind to one Ni(II) ion with an axial aqua ligand, whereas the third arm is free to interact with Ni ions within the central cluster, supporting the goal of Ni capture.

Air quality monitoring and measurement in an urban airshed: Contextualizing datasets from the Detroit Michigan area from 1952 to 2020.

With urban air quality being a pressing public health concern, community members are becoming increasingly engaged in determining the links between air quality and human health. Although new measurement tools such as low-cost sensors make local data more accessible, a better understanding of gaps in regional datasets is needed to develop effective metropolitan-scale solutions. Using scoping review methodology, we compiled 214 published journal articles and grey literature reports of air quality data from the Detroit, Michigan area from 1952 through 2020. This critical scoping review focuses on air quality datasets, but related topics such as health studies and community-based participatory science studies were examined from the included articles. Most of these publications were peer-reviewed journal articles published after 2001. Particulate matter, nitrous oxides, and sulfur dioxide were the most commonly studied air pollutants, and asthma was the most frequently associated health outcome paired with air pollution datasets. Few publications reported methods for community-based participatory science. This critical scoping review establishes a foundation of historical air quality data for the Detroit metropolitan area and a set of evaluation criteria that can be replicated in other urban centers. This foundation enables future detailed analysis of air quality datasets and showcases strategies for implementing effective community science programs and monitoring efforts.

Iron amendments minimize the first-flush release of pathogens from stormwater biofilters.

First flush or the first pore volume of effluent eluted from biofilters at the start of rainfall contributes to most pollution downstream because it typically contains a high concentration of bacterial pathogens. Thus, it is critical to evaluate designs that could minimize the release of bacteria during a period of high risk. In this study, we test the hypothesis of whether an addition of iron-based media to biofilter could limit the leaching of Escherichia coli (E. coli), a pathogen indicator, during the first flush. We applied E. coli-contaminated stormwater intermittently in columns packed with a mixture of sand and compost (70:30 by volume, respectively) and iron filings at three concentrations: 0% (control), 3%, and 10% by weight. Columns packed with a mixture of sand and iron (3% or 10%) without compost were used to examine the maximum capacity of iron to remove E. coli. In columns with iron, particularly 10% by weight, the leaching of E. coli during the first flush was 32% lower than the leaching from compost columns, indicating that the addition of iron amendments could decrease first-flush leaching of E. coli. We attribute this result to the ability of iron to increase adsorption and decrease growth during antecedent drying periods. Although the addition of iron filings increased E. coli removal, the presence of compost decreased the adsorption capacity: exposure of 1 g of iron filings to 1 mg of DOC reduces E. coli removal by 8%. The result was attributed to the alteration of the surface charge of iron and blocking of adsorption sites shared by E. coli and DOC. Collectively, these results indicate that the addition of sufficient amounts of iron media could decrease pathogen leaching in the first flush effluent and increase the overall biofilter performance and protect downstream water quality.

Nitrate removal uncertainty in stormwater control measures: Is the design or climate a culprit?

Eutrophication is caused by excess nitrate and other nutrient exported via stormwater runoff to surface waters, which is projected to increase as a result of climate change. Despite recent increases in the implementation of stormwater control measures (SCM), nutrient export has not abated, indicating poor or inconsistent removal capacities of SCM for nitrate. However, the cause of the variability is unclear. We show that both design and local climate can explain nitrate removal variability by critically analyzing data reported on the international BMP database for nitrate removal by four common types of SCM: bioretention cells, grass swales, media filters, and retention ponds. The relative importance of climate or design on nitrate removal depends on the SCM type. Nitrate removal in grass swales and bioretention systems is more sensitive to local climate than design specifications, whereas nitrate removal in the retention ponds is less sensitive to climate and more sensitive to design features such as vegetation and pond volume. Media filters without amendment have the least capacity compared to other SCM types surveyed, and their removal capacity was independent of the local climate. Adding amendments made up of carbon biomass, iron-based media, or a mixture of these amendments can significantly improve nitrate removal. The type of carbon biomass is also a factor since biochar does not appear to affect nitrate removal. This analysis can help inform the selection of SCM and modification of their design based on local and projected climate to maximize nitrate removal and minimize eutrophication.

A Review of Volatile Organic Compound Contamination in Post-Industrial Urban Centers: Reproductive Health Implications Using a Detroit Lens.

Volatile organic compounds (VOCs) are a group of aromatic or chlorinated organic chemicals commonly found in manufactured products that have high vapor pressure, and thus vaporize readily at room temperature. While airshed VOCs are well studied and have provided insights into public health issues, we suggest that belowground VOCs and the related vapor intrusion process could be equally or even more relevant to public health. The persistence, movement, remediation, and human health implications of subsurface VOCs in urban landscapes remain relatively understudied despite evidence of widespread contamination. This review explores the state of the science of subsurface movement and remediation of VOCs through groundwater and soils, the linkages between these poorly understood contaminant exposure pathways and health outcomes based on research in various animal models, and describes the role of these contaminants in human health, focusing on birth outcomes, notably low birth weight and preterm birth. Finally, this review provides recommendations for future research to address knowledge gaps that are essential for not only tackling health disparities and environmental injustice in post-industrial cities, but also protecting and preserving critical freshwater resources.

Microbial quality of surface water and subsurface soil after wildfire.

Runoff from wildfire affected areas typically carries high concentrations of fine burned residues or eroded sediment and deposits them in surface water bodies or on subsurface soils. Although the role of wildfire residues in increasing the concentration of chemical contaminants in both environments is known, whether and to what degree wildfire residues may affect microbial contaminants is poorly understood. To examine the effect of wildfire residues on growth and die-off of Escherichia coli (E. coli) -a pathogen indicator, we mixed stormwater with E. coli and suspended particles from the pre- and post-wildfire area in batch reactors and monitored E. coli concentration. E. coli grew initially in the presence of all particles, but the relative E. coli concentration was 10 times lower in the presence of wildfire residues than in natural soil from unaffected areas. Wildfire residues also decreased the persistence of E. coli during a 15-day incubation period. These results indicate that the growth or persistence of E. coli in surface water in the presence of wildfire residues was less than that in the presence of unburned soil particles, potentially due to depletion of nutrient concentration and/or loss of viability of bacteria in the presence of wildfire residues. To examine the transport potential of wildfire residues and their ability to facilitate the transport of E. coli in the subsurface system, suspensions containing wildfire residues and/or E. coli were injected through unsaturated sand columns-a model subsurface system. Transport of wildfire residues in sand columns increased with decreases in the depth and increases in the concentration of particles, but increased transport of wildfire residues did not result in the increased transport of E. coli, suggesting wildfire residues do not facilitate the transport of E. coli. Overall, the results indicate that wildfire residues may not increase the risk of the microbial contamination of surface water or groundwater via subsurface infiltration.

Reactive transport of uranium in fractured crystalline rock: Upscaling in time and distance.

Batch adsorption and breakthrough column experiments were conducted to evaluate uranium transport through altered material that fills fractures in a granite rock system at the Grimsel Test Site in Switzerland at pH 6.9 and 7.9. The role of adsorption and desorption kinetics was evaluated with reactive transport modeling by comparing one-, two-, and three-site models. Emphasis was placed on describing long desorption tails that are important for upscaling in time and distance. The effect of increasing pH in injection solutions was also evaluated. For pH 6.9, a three-site model with forward rate constants between 0.07 and 0.8 ml g(-1) h(-1), reverse rate constants between 0.001 and 0.06 h(-1), and site densities of 1.3, 0.104, and 0.026 µmol g(-1) for 'weak/fast', 'strong/slow', and 'very strong/very slow' sites provided the best fits. For pH 7.9, a three-site model with forward rate constants between 0.05 and 0.8 mL g(-1) h(-1), reverse rate constants between 0.001 and 0.6 h(-1), and site densities of 1.3, 0.039, and 0.013 µmol g(-1) for a 'weak/fast', 'strong/slow', and 'very strong/very slow' sites provided the best fits. Column retardation coefficients (Rd) were 80 for pH 6.9 and 10.3 for pH 7.9. Model parameters determined from the batch and column experiments were used in 50 year large-scale simulations for continuous and pulse injections and indicated that a three-site model is necessary at pH 6.9, although a Kd-type equilibrium partition model with one-site was adequate for large scale predictions at pH 7.9. Batch experiments were useful for predicting early breakthrough times in the columns while column experiments helped differentiate the relative importance of sorption sites and desorption rate constants on transport.