Inorganic Contaminants In Groundwater Research Articles

Presence and Dispersion of Organic and Inorganic Contaminants in Groundwater

This paper offers an extensive examination of studies published in the recent past and highlights the documented issues surrounding groundwater pollution, its sources, and distribution worldwide. The depletion of groundwater resources and the deteriorating overall quality present a significant cause for concern, particularly as a large human population relies on groundwater as a drinking water source. The review focuses on various factors contributing to groundwater pollution, including anthropogenic activities, hydro climatological influences, and natural processes. Special attention is given to organic contaminants such as pesticides, herbicides, and emerging pollutants, which have been found to have a substantial impact on groundwater quality. Additionally, the review covers pollution caused by inorganic pollutants like arsenic and other heavy metals, with a particular emphasis on regions experiencing a higher incidence of these contaminants in groundwater. Furthermore, the paper includes a compilation of studies that highlight the increased occurrence of waterborne illnesses resulting from fecal and microbial contamination, often caused by inadequate sanitary practices. To provide a comprehensive understanding of the global groundwater pollution problem, the review also encompasses an examination of contaminants like fluoride and nitrate.

Comprehensive characterization of aerobic groundwater biotreatment media

Aerobic biotreatment systems can treat multiple reduced inorganic contaminants in groundwater, including ammonia (NH3), arsenic (As), iron (Fe), and manganese (Mn). While individual systems treating multiple contaminants simultaneously have been characterized and several systems treating one contaminant have been compared, a comparison of systems treating co-occurring contaminants is lacking. This study assessed the treatment performance and microbial communities within 7 pilot- and full-scale groundwater biotreatment systems in the United States that treated waters with pH 5.6–7.8, 0.1–2.0 mg/L dissolved oxygen, 75–376 mg CaCO3/L alkalinity, < 0.03–3.79 mg NH3-N/L, < 4–31 µg As/L, < 0.01–9.37 mg Fe/L, 2–1220 µg Mn/L, and 0.1–5.6 mg/L total organic carbon (TOC). Different reactor configurations and media types were represented, allowing for a broad assessment of linkages between water quality and microbial communities via microscopy, biofilm quantification, and molecular methods. Influent NH3, TOC, and pH contributed to differences in the microbial communities. Mn oxidase gene copy numbers were slightly negatively correlated with the influent Mn concentration, but no significant relationships between gene copy number and influent concentration were observed for the other contaminants. Extracellular enzyme activities, community composition, and carbon transformation pathways suggested heterotrophic bacteria may be important in nitrifying biofilters. Aerobic groundwater biofilters are complex, and improved understanding could lead to engineering enhancements.

Household and community systems for groundwater remediation in Bihar, India: Arsenic and inorganic contaminant removal, controls and implications for remediation selection

The presence of arsenic (As) and other inorganic contaminants in groundwater is a key public health issue in India and many other parts of the world. Whilst a broad range of remediation technologies exist, performance can be highly variable, and appropriate selection and management of remediation approaches remains challenging. Here, we have identified and tested the performance of a range of small-scale remediation technologies (e.g. sand filters, multi-stage filtration and reverse osmosis (RO)-based systems; n = 38) which have been implemented in Bihar, India. We have undertaken spot-assessments of system performance under typical operating conditions in household and non-household (e.g. community, hospital, hostel/hotel) settings. The removal of As and other inorganic contaminants varied widely (ranging from ~0–100%), with some solutes generally more challenging to remove than others. We have evaluated the relative importance of technology type (e.g. RO-based versus non-RO systems), implementation setting (e.g. household versus non-household) and source water geochemistry (particularly concentrations and ratios of As, Fe, P, Si and Ca), as potential controls on remediation effectiveness. Source water composition, particularly the ratio ([Fe] – 1.8[P])/[As], is a statistically significant control on As removal (p < 0.01), with higher ratios associated with higher removal, regardless of technology type (under the site-specific conditions observed). This ratio provides a theoretical input which could be used to identify the extent to which natural groundwater composition may be geochemically compatible with higher levels of As removal. In Bihar, we illustrate how this ratio could be used to identify spatial patterns in theoretical geochemical compatibility for As removal, and to identify where additional Fe may theoretically facilitate improved remediation. This geochemical approach could be used to inform optimal selection of groundwater remediation approaches, when considered alongside other important considerations (e.g. technical, managerial and socio-economic) known to impact the effective implementation and sustainability of successful groundwater remediation approaches.

Applicability of weathered coal waste as a reactive material to prevent the spread of inorganic contaminants in groundwater.

It is necessary to determine an environmentally friendly method of reusing the vast amount of coal waste that is generated during coal preparation. This study evaluates the applicability of using weathered coal waste in a permeable reactive barrier to prevent groundwater contamination. Coal waste, with different weathering degrees, was obtained from two coal mining sites in South Jeolla Province, Korea. The reactivities of the coal waste with inorganic contaminants, such as copper, cadmium, and arsenic, were examined in batch and column experiments. The batch experiment results indicate that the coal waste removal efficiencies of copper (99.8%) and cadmium (95.4%) were higher than those of arsenic (71.0%). The maximum adsorption capacities of coal waste for copper, cadmium, and arsenic calculated from the Langmuir isotherm model were 4.440 mg/g, 3.660 mg/g, and 0.718 mg/g, respectively. The equilibrium of adsorption was attained within 8 h. The column experiment results reveal that the coal waste effectively removed inorganic contaminants under flow-through conditions. Faster breakthrough times were observed in single solute system (As(V) = 19.3 PV, Cu(II) = 47.6 PV) compared with binary solute system (As(V) = 27.8 PV, Cu(II) = 65.4 PV). To confirm the applicability of using coal waste in a groundwater environment, its decontamination ability was analyzed at low concentrations and under various pH conditions. To examine the potential ecological risks in the subsurface environment, a test to determine acute toxicity to Daphnia magna and a toxic characteristic leaching procedure (TCLP) test were conducted. The coal waste was found to satisfy appropriate standards. The acute toxicity test also confirmed the ecological safety of using coal waste in a groundwater environment. The acceptably high capacity and fast kinetics of inorganic contaminant sorption by the coal waste indicate it could potentially be employed as a reactive material. The recycling and application of this abundant waste material will contribute to solving both coal waste disposal and water pollution problems.

Functional iron chitosan microspheres synthesized by ionotropic gelation for the removal of arsenic (V) from water

Arsenic (As) is considered one of the most serious inorganic contaminants in groundwater. The maximum limit of As in drinking water is 0.010mgAs L−1 according to the World Health Organization. Functional Iron Chitosan Microspheres (F-ICM) were synthesized by ionotropic gelation of chitosan and ferric nitrate for removal of As (V) from water. The effects of iron concentration (0.7, 5.5 and 11.2gFe+3/100g chitosan), pH range (4–9), sorbent dosage, possibility of reuse and presence of interfering anions were analyzed. F-ICM were effective for As (V) adsorption in a wide range of pH with removals higher than 88.9%, reaching concentrations < 0.010mgAs L−1. A higher proportion of iron in the matrix favored the removal of As(V) in a pH range 6 to 9. Kinetic data of As(V) adsorption onto 0.7 F-ICM under all tested initial concentrations fitted well with the pseudo second-order kinetic model. Sorption isotherm experimental data were satisfactorily fitted with the Langmuir equation; the maximum sorption capacity for As(V) was 120.77mgAs(V) (gF-ICM1) and the Langmuir constant was 0.331 L mg1. A good performance of the adsorption capacity was obtained in four successive adsorption cycles of reuse and in the presence of interfering anions, indicating the high adsorption capacity of the synthesized microspheres.

Ground-penetrating radar (GPR) responses for sub-surface salt contamination and solid waste: modeling and controlled lysimeter studies.

The assessment of polluted areas and municipal solid waste (MSW) sites using non-destructive geophysical methods is timely and much needed in the field of environmental monitoring and management. The objectives of this study are (i) to evaluate the ground-penetrating radar (GPR) wave responses as a result of different electrical conductivity (EC) in groundwater and (ii) to conduct MSW stratification using a controlled lysimeter and modeling approach. A GPR wave simulation was carried out using GprMax2D software, and the field test was done on two lysimeters that were filled with sand (Lysimeter-1) and MSW (Lysimeter-2). A Pulse EKKO-Pro GPR system with 200- and 500-MHz center frequency antennae was used to collect GPR field data. Amplitudes of GPR-reflected waves (sub-surface reflectors and water table) were studied under different EC levels injected to the water table. Modeling results revealed that the signal strength of the reflected wave decreases with increasing EC levels and the disappearance of the subsurface reflection and wave amplitude reaching zero at higher EC levels (when EC >0.28S/m). Further, when the EC level was high, the plume thickness did not have a significant effect on the amplitude of the reflected wave. However, it was also found that reflected signal strength decreases with increasing plume thickness at a given EC level. 2D GPR profile images under wet conditions showed stratification of the waste layers and relative thickness, but it was difficult to resolve the waste layers under dry conditions. These results show that the GPR as a non-destructive method with a relatively larger sample volume can be used to identify highly polluted areas with inorganic contaminants in groundwater and waste stratification. The current methods of MSW dumpsite investigation are tedious, destructive, time consuming, costly, and provide only point-scale measurements. However, further research is needed to verify the results under heterogeneous aquifer conditions and complex dumpsite conditions.

Nickel sulfide formation at low temperature: initial precipitates, solubility and transformation products

Environmental context Remediation technologies often rely on manipulation of redox conditions or natural redox processes to favour microbial sulfate-reduction and mineral sulfide formation for treatment of inorganic contaminants in groundwater, including nickel. However, few data are available on the structural properties, solubility and mineral transformation processes involving nickel sulfides. These data are needed in order to constrain the long term performance of groundwater remediation efforts. Abstract The formation of nickel sulfides has been examined experimentally over the temperature range from 25 to 60°C. At all conditions studied, hexagonal (α-NiS) was the initial precipitate from solution containing Ni2+ and dissolved sulfide. Freshly precipitated nickel sulfide possesses significant residual Ni–O coordination as revealed by X-ray absorption spectroscopy. With progressive aging, residual Ni–O coordination is replaced by Ni–S coordination. The formation of millerite (β-NiS, rhombohedral) was not detected in any of the synthesis experiments. In the presence of elemental sulfur, hexagonal NiS converted to polydymite (Ni3S4) and vaesite (NiS2). Thus, conversion of nickel monosulfide to thiospinel and disulfide structures appears to be redox dependent, analogous to aging and transformation processes of iron sulfides. In the absence of elemental sulfur or with only hydrogen sulfide or bisulfide present, transformation of hexagonal NiS was not observed after 1680 h at 60°C. Low-pH solubility experiments yielded a solubility product for hexagonal NiS of log Ks0 = –2.69 ± 0.26. Solubility data at pH &gt; 3 suggest that Ni–bisulfide complexation is important in controlling the solubility of Ni in sulfidic solutions.

Deep subsurface microbial processes

Information on the microbiology of the deep subsurface is necessary in order to understand the factors controlling the rate and extent of the microbially catalyzed redox reactions that influence the geophysical properties of these environments. Furthermore, there is an increasing threat that deep aquifers, an important drinking water resource, may be contaminated by man's activities, and there is a need to predict the extent to which microbial activity may remediate such contamination. Metabolically active microorganisms can be recovered from a diversity of deep subsurface environments. The available evidence suggests that these microorganisms are responsible for catalyzing the oxidation of organic matter coupled to a variety of electron acceptors just as microorganisms do in surface sediments, but at much slower rates. The technical difficulties in aseptically sampling deep subsurface sediments and the fact that microbial processes in laboratory incubations of deep subsurface material often do not mimic in situ processes frequently necessitate that microbial activity in the deep subsurface be inferred through nonmicrobiological analyses of ground water. These approaches include measurements of dissolved H2, which can predict the predominant microbially catalyzed redox reactions in aquifers, as well as geochemical and groundwater flow modeling, which can be used to estimate the rates of microbial processes. Microorganisms recovered from the deep subsurface have the potential to affect the fate of toxic organics and inorganic contaminants in groundwater. Microbial activity also greatly influences the chemistry of many pristine groundwaters and contributes to such phenomena as porosity development in carbonate aquifers, accumulation of undesirably high concentrations of dissolved iron, and production of methane and hydrogen sulfide. Although the last decade has seen a dramatic increase in interest in deep subsurface microbiology, in comparison with the study of other habitats, the study of deep subsurface microbiology is still in its infancy.

The role of sorbed humic substances on the distribution of organic and inorganic contaminants in groundwater

Mineral-bound humic substances modify inorganic surfaces in subsurface sediments, changing the nature and number of complexation sites for contaminants. Because of adsorptive enrichment, the reactive surface area or site concentration contributed by mineral-bound humic substances can exceed that of dissolved or colloidal humic substances by two orders of magnitude. Mineral-bound humic materials may, therefore, provide a major sink for the removal of contaminants in groundwater. The reactivity of the humic substance is primarily determined by the structural and bulk chemical properties of the humic substance and the aqueous solution chemistry. Organic and inorganic contaminants sorb readily to mineral-bound humic substances. The sorption of hydrophobic organic compounds increases as ionic strength decreases, is enhanced by divalent cations, and displays non-linear isotherms and competitive adsorption behavior. Collectively, these results suggest that hydrophobic adsorption, rather than phase partitioning, is the primary sorption mechanism for neutral organic molecules on these particle coatings. Mineral-bound humic substances augment, rather than change, the intrinsic complexation properties of mineral surfaces for metal cations. The degree of sorption enhancement promoted by mineral-bound organic material varies strongly with pH and depends on the magnitude of the stability constants between the metal cation and the humic substance, the strength and magnitude of adsorption of the humic substance by the mineral surface, and the extent of aqueous complex formation between the non-sorbed humic substance and metal. The simplest sorption model for humate-modified surfaces is the linear additivity model (LAM). Sorption data for certain hydrophobic organic compounds and metal cations appear to conform to this model.

Interacting precipitation/dissolution waves: The movement of inorganic contaminants in groundwater

Chemical reactions with minerals occur in groundwater flow in permeable media to produce zones of constant solid and aqueous phase compositions. These zones are separated by “waves” or step changes in composition. The occurrence of wave‐wave interactions resulting from nonuniform boundary conditions has important implications in inorganic pollutant transport through permeable formations. Three physical flow situations produce these conditions : injection of a finite volume of fluid followed in time by a compositionally different fluid, the flow of a reactive fluid through a compositionally layered media, and reversal in the direction of flow of a chemically reactive fluid. The theory we present when applied to contaminant transport indicates that a significant amount of contaminant initially precipitated can be redissolved during subsequent flow, and the patterns thus evolved can indicate the nature of the contaminating source.