Natural Attenuation of Chromium and TCE on Memphis Aquifer Sand, a Bench-Scale Study

Groundwater serves as a major source of drinking water for many people across the world. Aquifer properties have been studied extensively, as well as contaminant transport within aquifers and remediation of contaminated aquifers. A common component of alluvial aquifers is sediment deposition. ASTM-D2419-14 defines sand as particle of rock with size range of between 0.075 mm and 4.75 mm. Sand is mostly composed of silica and has physical and chemical attributes which cause its specific characteristics. Silica is considered chemically inert, unable to enter most chemical reactions in aqueous geochemistry field. However, would it be wise to disregard the potential effect that sand may have on the adsorption process of contaminants, or do researchers need to take a closer look at the sand characteristics specific to the research location or remediation site? The aim of this dissertation is to first determine if sand characteristics, physical and chemical, can influence the adsorption patterns of various contaminants. Secondly, to provide a standard method with high reliability and reproducibility by which others can also test the sand they have at their disposal to determine if and how the sand specific to their location interacts with their chosen contaminant. The third goal was to utilize such method on three different contaminants: Hexavalent Chromium as a heavy metal and oxyanion, Trichloroethylene (TCE) as a chlorinated volatile organic solvent, and Bromide as a conservative tracer which passes through the system with no interaction. These three contaminants are significantly different from each other, and not only do they represent a wide range of behaviors expected from contaminants, but they are also commonly found in urban or industrial superfund sites. During this study, six different sand samples were collected from three different core samples drilled. The six sand samples covered both geographical and depth variations. The method was developed, optimized, validated, and the reproducibility was calculated using %RSD values, which were recorded for \u3c1% for bromide, indicating a high reproducibility value. Furthermore, when the three types of chemicals were interacted with the sand samples, the results confirmed that the sand characteristics do in fact impact the adsorption behaviors. In short, it is paramount for the purposes of modeling contaminant transport as well as remediation specialists to study the effects of sand specific to their region on the contaminant they are working with. The experiments performed consist of pH studies, kinetic studies, isotherm studies, and additional experiments. These experiments differentiated the sand samples into three distinct groups behaviorally. One cluster of sand samples showed no interaction with the contaminants, one group showed minimal interaction, and the other group showed distinguishable adsorption patterns. The influential factors on the adsorption behaviors found to be the organic carbon content, the iron content, grain size, and percentage of fine material (silt and clay). Also, it is worth mentioning that a specific sand sample can exhibit different adsorption patterns when interacted with different chemicals

Electrospun nanofibers for efficient adsorption of heavy metals from water and wastewater

Heavy metals (HMs) are persistent and toxic environmental pollutants that pose critical risks toward human health and environmental safety. Their efficient elimination from water and wastewater is essential to protect public health, ensure environmental safety, and enhance sustainability. In the recent decade, nanomaterials have been developed extensively for rapid and effective removal of HMs from water and wastewater and to address the certain economical and operational challenges associated with conventional treatment practices, including chemical precipitation, ion exchange, adsorption, and membrane separation. However, the complicated and expensive manufacturing process of nanoparticles and nanotubes, their reduced adsorption capacity due to the aggregation, and challenging recovery from aqueous solutions limited their widespread applications for HM removal practices. Thus, the nanofibers have emerged as promising adsorbents due to their flexible and facile production process, large surface area, and simple recovery. A growing number of chemical modification methods have been devised to promote the nanofibers\u27 adsorption capacity and stability within the aqueous systems. This paper briefly discusses the challenges regarding the effective and economical application of conventional treatment practices for HM removal. It also identifies the practical challenges for widespread applications of nanomaterials such as nanoparticles and nanotubes as HMs adsorbents. This paper focuses on nanofibers as promising HMs adsorbents and reviews the most recent advances in terms of chemical grafting of nanofibers, using the polymers blend, and producing the composite nanofibers to create highly effective and stable HMs adsorbent materials. Furthermore, the parameters that influence the HM removal by electrospun nanofibers and the reusability of adsorbent nanofibers were discussed. Future research needs to address the gap between laboratory investigations and commercial applications of adsorbent nanofibers for water and wastewater treatment practices are also presented

Prediction of children\u27s blood lead levels from exposure to lead in schools\u27 drinkingwater-A case study in Tennessee, USA

Lead (Pb) exposure can delay children\u27s mental development and cause behavioral disorders and IQ deficits. With children spending a significant portion of their time at schools, it is critical to investigate the lead concentration in schools\u27 drinking water to prevent children\u27s exposure. The objectives of this work were to predict students\u27 geometric mean (GM) blood lead levels (BLLs), the fractions of at-risk students (those with BLLs \u3e 5 g/dL), and the total number of at-risk students in one Tennessee school district. School drinking water lead concentration data collected in 2019 were input into the Integrated Exposure Uptake Biokinetic (IEUBK) model and the Bowers\u27 model to predict BLLs for elementary school students and secondary school students, respectively. Sensitivity analyses were conducted for both models. Drinking water concentrations were qualitatively compared with data collected in 2017. Two scenarios were evaluated for each model to provide upper and median estimates. The weighted GM BLL upper and median estimates for elementary school students were 2.35 g/dL and 0.99 g/dL, respectively. This equated to an upper estimate of 1300 elementary school students (5.8%) and a median estimate of 140 elementary school students (0.6%) being at risk of elevated BLLs. Similarly, the weighted GM BLL upper and median estimates for secondary school students were 2.99 g/dL and 1.53 g/dL, respectively, and equated to an upper estimate of 6900 secondary school students (13.6%) and a median estimate of 300 secondary school students (0.6%) being at risk of elevated BLLs. Drinking water remediation efforts are recommended for schools exhibiting water lead concentrations greater than 15 g/L. Site-specific soil lead concentration data are recommended since the IEUBK was deemed sensitive to soil lead concentrations. For this reason, soil lead remediation may have a greater impact on lowering children\u27s BLLs than drinking water lead remediation. Remediation efforts are especially vital at elementary schools to reduce the population\u27s baseline BLL and thus the BLL projected by Bowers\u27 model

Advance modification of polyacrylonitrile nanofibers for enhanced removal of hexavalent chromium from water

Hexavalent chromium [Cr(VI)] is a known carcinogenic and mutagenic heavy metal. Its level in drinking water is regulated worldwide to protect public health. This study presents a novel chemical method to modify the polyacrylonitrile (PAN) nanofibers for efficient Cr(VI) removal from water. The PAN nanofibers with an average diameter of 165 nm are produced using the electrospinning technique. Through a 2-step chemical modification process, the amidine polyacrylonitrile (APAN) nanofibers are synthesized by the conversion of nitrile groups [-C=N] in PAN nanofibers into amidines [-C(N═NH)(NH2)]. The attenuated total reflectance Fourier transform (ATR-FTIR) spectroscopy revealed the successful conversion of nitrile groups into amidoximes, resulting in amidoximated polyacrylonitrile nanofibers, and subsequent conversion into amidine functional groups, forming the APAN nanofibers. Greater concentration of hydroxylamine hydrochloride, increased reaction time and temperature yielded higher conversion of nitrile groups into amidoximes to a maximum of 37%. The Cr(VI) uptake by APAN nanofibers was found as a multilayer adsorption process modeled by Freundlich isotherm. The maximum Langmuir Cr(VI) adsorption capacity for APAN nanofibers was found as 225 mg g−1 at pH = 3.0 after 4.0 h exposure duration. The regeneration study revealed the excellent reusability of APAN nanofibers after five adsorption/desorption cycles