Journal of Groundwater Science and Engineering

Remediation technologies for heavy metal-contaminated water resources

Samar A El-Mekkawi, Sh K Amin

, Available online , doi: 10.26599/JGSE.2026.9280089

Abstract(51) FullText HTML (24) PDF(1)

Abstract:
Heavy metals, including arsenic, lead, cadmium, chromium, mercury, copper, nickel, and zinc, are common contaminants in global water resources. Their occurrence stems from both natural geogenic and anthropogenic sources, such as industrial, mining, or urban activities. Heavy metals can be found in groundwater due to geogenic mobilization and leaching from ore deposits. They can also be found in streams and lakes impacted by mine drainage, industrial effluents, agricultural runoff, and urban stormwater. Elevated concentrations pose risks to human health and ecosystems, necessitating monitoring, remediation, and the safe management of generated residuals. A variety of technologies exist for heavy-metal removal. The selection and use of these technologies depend on contaminant concentration, speciation, and available resources. In this review article, the latest technologies for heavy-metal removal are presented and discussed. The availability and maturity of each technique, energy demand, management of generated residual, environmental impact, and recommended applications are discussed. Algal bioremediation and constructed wetlands are the most sustainable techniques due to their ecosystem benefits, carbon capture, and lowest energy consumption, while the most efficient industrial techniques are membrane technologies and ion-exchange systems due to their high metal selectivity and purity; however, the main restrictions are high cost and an energy-intensive nature. The most distinctive approach involves hybrid systems, which offer a more resilient and sustainable alternative by integrating complementary mechanisms that enhance flux stability, improve selectivity, and reduce energy consumption, such as the combination of Reverse Osmosis with Membrane Distillation (RO-MD) and Reverse Osmosis with Pressure Retarded Osmosis (RO-PRO). The hybrid approach, in various sequences, enhances efficiency, scalability, and ecological restoration.

Distribution and controlling mechanisms of rare earth elements in geothermal waters of Xiamen, Southeastern China

Shuai-chao Wei, Wei Zhang, Ruo-xi Yuan, Feng Liu, Long Li, Xiao-xue Yan

, Available online , doi: 10.26599/JGSE.2026.9280104

Abstract(69) FullText HTML (27) PDF(2)

Abstract:
Rare Earth Elements (REEs) are effective tracers of fluid–rock interaction and fluid mixing in geothermal systems, but their behavior in coastal geothermal waters remains poorly constrained owing to the combined effects of seawater intrusion, high ionic strength, and complex ligand competition. In this study, five geothermal water samples from the Xiamen coastal geothermal system, southeastern China, were characterized by hydrochemical analysis, Post-Archean Australian Shale (PAAS)-normalized REE patterns, anomaly indices, and PHREEQC speciation modeling to constrain the distribution and controls of dissolved REEs. Total dissolved REE concentrations (∑REE) range from 0.044 μg/L to 1.651 μg/L, with higher values in coastal waters than in the inland geothermal end-member. All samples show the fractionation pattern light rare earth elements (LREEs) > Middle Rare Earth Elements (MREEs) > Heavy Rare Earth Elements (HREEs), whereas PAAS-normalized patterns indicate relative HREE enrichment and generally negative Ce anomalies. Eu anomalies vary systematically from positive in the inland geothermal water to weak or absent in coastal waters. Regional comparison suggests that deep water–rock interaction controls the overall REE source and abundance levels, whereas seawater mixing primarily modifies REE fractionation, anomaly signatures, and aqueous speciation. Speciation modeling further shows that REEs in coastal geothermal waters are mainly associated with fluoride-, sulfate-, and carbonate-bearing complexes, whereas carbonate complexes dominate in the inland sample. Overall, REE behavior in the Xiamen system is governed by the coupled effects of water–rock interaction and seawater mixing, providing new insight into REE migration and fractionation in fault-controlled coastal geothermal environments.

Heat transfer performance and dynamic effects of middle-shallow U-tube ground heat exchangers under geological stratification

Chang-zhe Wang, Feng Liu, Li-juan Yuan, Hua-jun Wang

, Available online , doi: 10.26599/JGSE.2026.9280101

Abstract(1698) FullText HTML (541) PDF(3)

Abstract:
Previous research has lacked sufficient attention to the heat exchange performance of middle-shallow U-tube ground heat exchangers (GHEs), particularly regarding the impact of vertical lithology heterogeneity. In this study, a heat transfer model of GHEs coupling vertical lithological variations and ground temperature distribution is established, based on field test data of middle-shallow boreholes in Langfang, Hebei Province. The heat transfer characteristics of GHEs within the depth of 200–300 m and their influencing factors are analyzed. Results show that the flow velocity and wall thickness strongly affect the heat transfer of middle-shallow GHEs. Increasing the flow rate helps to enhance heat transfer, but is not conducive to improving energy efficiency of the system due to higher power consumption of circulating pumps. There is an optimal flow rate range of 2–3 m³/h for PE-RT GHEs. Furthermore, reducing the wall thickness from 8 mm to 3 mm can significantly improve the heat transfer per unit depth by 10–12% for PE-RT GHEs. The thermal influence distance (TID) of GHEs exhibits significant lithological differences and seasonal variations along the depth. As the depth increases, the TID in winter and summer exhibits increasing and decreasing trends, respectively. Especially, the TID of sandy layers due to a high thermal conductivity is greater than that of clay layers under the same conditions. For 250–300 m deep GHEs, the maximum TID reaches 5.8 m in winter and 7.3 m in summer, respectively, after running for five years. The heat transfer performance of middle-shallow GHEs has an attenuation risk of up to 33–35% during long-term operation, which can be alleviated using an intermittent operation strategy. The present findings can offer a useful reference for the design and optimization of middle-shallow GHEs in similar geological conditions.

New Insights into Soda Water in Shallow Groundwater of the North China Plain

Bo Gao, Jiang-tao He, Bao-nan He, Yan-jia Chu, Zhen Chen, Ji-chao Sun

, Available online , doi: 10.26599/JGSE.2026.9280103

Abstract(2001) FullText HTML (660) PDF(5)

Abstract:
Soda water in shallow aquifers represents a unique hydrochemical type, often enriched in arsenic (As), fluorine (F), iodine (I), and other components, while also acting as a critical driver of soil salinization. However, existing studies have failed to effectively distinguish between salinization (characterized by soluble salt accumulation) and alkalization (characterized by soda-alkali enrichment). The "New Insights" of this study do not rely on new data but derive from an in-depth excavation and interpretation of the 2006–2009 National Groundwater Pollution Survey dataset—the only authoritative background dataset covering the entire North China Plain. Focusing on shallow groundwater in the North China Plain, this study refines the identification criteria for soda water based on existing concepts, analyzes its spatial distribution characteristics, delineates typical zones, and conducts a preliminary investigation into the genetic differences across regions. Results show that when using the criterion—"HCO₃⁻ + CO₃²⁻ as dominant anions with [(HCO₃⁻ + CO₃²⁻) - (Ca²⁺ + Mg²⁺)] > 0 meq%"—combined with hydrochemical cluster analysis, soda water is primarily concentrated in two zones: The mountain-front discharge zone (Area A) and the runoff-ancient Yellow River channel zone (Area B). These two zones account for 88.48% of all soda water samples and exhibit distinct hydrochemical features. In Area A, groundwater has a simple anion composition dominated by HCO₃⁻, a median total dissolved solids (TDS) content of 501.15 mg/L, and elevated concentrations of F⁻ and NO₃⁻. In contrast, Area B is characterized by diverse anions (HCO₃⁻, SO₄²⁻, and Cl⁻), a higher median TDS (863.56 mg/L), and enrichment of reductive components including As, F⁻, I⁻, Fe, and Mn. Genetic analysis reveals that soda water in Area A forms through the combined effects of mineral weathering, dissolution, and calcite-dolomite precipitation. In contrast, groundwater in Area B evolves under calcite-dolomite precipitation controlled by evaporative concentration, with further modifications by microbial geochemical processes and agricultural activities. This study clarifies the spatial distribution patterns and genetic mechanisms of soda water in the North China Plain, laying a foundation for further research on its formation processes.

Identification of the effects of shallow-buried mining on the hydrochemical evolution of phreatic groundwater in arid and semi-arid regions: A case study of the Ten Tributaries Basin

Zhuang Wang, Jun-nan Li, Ge-su Tao, Chao-zhu Li

, Available online , doi: 10.26599/JGSE.2026.9280095

Abstract(1707) FullText HTML (579) PDF(11)

Abstract:
Revealing the evolution of phreatic water hydrochemistry under natural processes and mining activities in shallowly buried mining areas of arid and semi-arid regions is key to identifying the impacts of mining on groundwater. Taking the Ten Tributaries Basin in the upper Yellow River as the study area, this study combined ion ratios, stable isotope tracing, and the Chemical Mass Balance (CMB) model to reveal and quantify the effects of coal mining (recharge area) and mirabilite mining (discharge area) on phreatic water chemistry. Results show that mining activities are the key anthropogenic factor driving the spatial differentiation of phreatic water chemistry, with influence intensity exhibiting significant spatial heterogeneity. In undisturbed areas, natural dissolution processes contribute more than 80% of the hydrochemical composition, dominated by carbonate dissolution. However, in mining-affected areas, groundwater chemistry deviates from natural evolutionary pathways, characterized by enhanced dissolved-ion input and more complex ionic compositions. In recharge areas, coal mining mainly promotes carbonate dissolution and vadose-zone disturbance, increasing TDS by factors of 1.96 and 1.88, respectively, relative to natural conditions. In discharge areas, mirabilite mining is dominated by evaporite dissolution and deep saline-water mixing, leading to TDS increases by the factors of 4.41 and 3.24, respectively. These mining effects are superimposed on the pathway-controlled groundwater flow system, resulting in distinct spatial differentiation of groundwater hydrochemistry. The improved CMB model effectively quantifies the impacts of mining disturbances on groundwater chemistry. The results provide scientific support for groundwater resource management and ecological protection in shallowly buried mining areas of arid and semi-arid regions.

Online First

NewsMORE+

DownloadMORE+

Top ViewedMORE+

Top DownloadedMORE+

LinksMORE+

Share Article