Water

24 pages, 1841 KiB

Open AccessArticle

Developing Recyclable Magnetic TiO₂-Fe₃O₄ Loading on Carbon Microtube Photocatalyst for Efficient Photodegradation of Microcystin-LR Under Visible Light

by Xinyi Zhang, Tian Xia, Ying Meng, Jiaxi Zhang, Gaofeng Chen, Zhaoting Ji and Wenli Qin

Water 2025, 17(9), 1342; https://doi.org/10.3390/w17091342 (registering DOI) - 29 Apr 2025

Abstract

Microcystins (MCs) are produced by cyanobacteria blooms in eutrophic water and can cause acute and chronic toxicity and even mortality to animals and humans. Previous MC removal strategies concernedonly highly contaminated water, in which the concentration of the pollutant was considerably larger than [...] Read more.

Microcystins (MCs) are produced by cyanobacteria blooms in eutrophic water and can cause acute and chronic toxicity and even mortality to animals and humans. Previous MC removal strategies concernedonly highly contaminated water, in which the concentration of the pollutant was considerably larger than that in the natural world. In this study, we developed a composite of TiO₂-coated magnetic carbon microtube (C-TiO₂-Fe₃O₄) and used it as a photocatalyst to efficiently remove microcystin-LR (MC-LR) from water under visible light from water. And the huge surface of the carbon microtube dramatically boosted the adsorbability and charge mobility, which lowered the recombination rate of electron–hole pairs, and hence systematically enhanced photocatalytic activity. The combination of adsorption and photodegradation endowed the composite with a better performance in the removal of trace amounts of MC-LR than the C-TiO₂. It was found that increasing the contact time and catalyst dosage, acidic environment, and lower initial MC-LR concentration had positive effects on MC-LR removal. The optimum reaction conditions of C-TiO₂-Fe₃O₄ was a reaction time of 12.68 min, a catalyst dosage of 0.39 g·L⁻¹, and a pH of 7.72. The C-TiO₂-Fe₃O₄ (surface area normalized apparent reaction rate constants K/S_BET = 1.2 × 10⁻⁴) presented a higher reaction rate than C-TiO₂ (K/S_BET = 8.4 × 10⁻⁵). Moreover, the stable removal capability of C-TiO₂-Fe₃O₄ was confirmed over multiple cycles. Finally, the ecological safety performance was also evaluated after visible light illumination. This work paves the way for the development of more efficient and easily separable purifiers for the removal of pollutants and toxins from contaminated water. Full article

(This article belongs to the Section Wastewater Treatment and Reuse)

14 pages, 8981 KiB

Open AccessArticle

Embankment Project Monitoring Using the Time-Lapse Transient Electromagnetic Method: Numerical Simulation and Field Applications

by Ying Wang, Bo Wang, Lunwei Chai and Wangping Qian

Water 2025, 17(9), 1341; https://doi.org/10.3390/w17091341 (registering DOI) - 29 Apr 2025

Abstract

To preserve flood control infrastructure, it is essential to quickly detect and accurately identify concealed leakage hazards within embankment projects. In this paper, we propose a novel embankment monitoring method based on the time-lapse transient electromagnetic method and complemented by a theoretical framework [...] Read more.

To preserve flood control infrastructure, it is essential to quickly detect and accurately identify concealed leakage hazards within embankment projects. In this paper, we propose a novel embankment monitoring method based on the time-lapse transient electromagnetic method and complemented by a theoretical framework for analyzing time-lapse data through the lens of resistivity change rates. A time-lapse model that scrutinizes dynamic response patterns associated with leakage anomalies is constructed, while the efficacy of this methodology is verified through rigorous field experiments. Our research findings reveal a well-defined negative correlation between the resistivity variation rate and the development stage of anomalies. Our proposed method demonstrates enhanced sensitivity in the detection of dynamic evolutionary patterns in latent seepage defects, particularly in low-resistivity environments. Moreover, it successfully delineates both the spatial expansions and electrical property alterations of anomalies, providing a novel technical approach for latent seepage defect monitoring and risk management in embankments. Full article

(This article belongs to the Section Hydrogeology)

► Show Figures

Figure 1

24 pages, 2681 KiB

Open AccessArticle

An Experimental Study on the Behavior of Fish in Response to Turbidity Changes—A Case Study of Korean Fishes

by Joon-Gu Kang, Nam-Joo Lee, Sung-Jung Kim and Dong-Ho Nam

Water 2025, 17(9), 1340; https://doi.org/10.3390/w17091340 (registering DOI) - 29 Apr 2025

Abstract

Climate change-induced heavy rainfall during summer months can further increase suspended solid loads in rivers, elevating turbidity. Such elevated turbidity can compromise fish gill tissue integrity and impair oxygen uptake, potentially leading to fatal impacts in aquatic ecosystems. Therefore, this study aims to [...] Read more.

Climate change-induced heavy rainfall during summer months can further increase suspended solid loads in rivers, elevating turbidity. Such elevated turbidity can compromise fish gill tissue integrity and impair oxygen uptake, potentially leading to fatal impacts in aquatic ecosystems. Therefore, this study aims to examine fish migratory behaviors and physiological responses to varying turbidity levels through experimental trials to generate baseline data for assessing fish habitat suitability. The experimental design comprised two primary components: an investigation of turbidity avoidance behaviors and an analysis of habitat compatibility through extended exposure to turbid conditions. This study focused on dominant freshwater fish species native to South Korea, Zacco platypus, Pseudopungtungia nigra, and Zacco koreanus. Fish condition in response to turbidity was monitored over a 15-day period, during which locomotor activity and water quality parameters were recorded. In the control group tank with no turbidity, all species exhibited unrestricted swimming patterns without depth preference. However, in moderate and high turbidity treatments, all demonstrated preferential utilization of middle- and lower-depth strata. In addition, the highest number of fish mortality occurred in high-turbidity zones because of respiratory impediments from elevated suspended solid concentrations. These findings provide valuable insights into fish mobility and habitat utilization patterns in rivers experiencing sudden turbidity events, such as those associated with weir operations. Full article

(This article belongs to the Special Issue Environmental Behavior, Ecological Effects and Health Risks of Pollutants in Aquatic Ecosystems)

33 pages, 4942 KiB

Open AccessArticle

Improved Oil/Water Separation by Employing Packed-Bed Filtration of Modified Quartz Particles

by Nthabiseng Ramanamane and Mothibeli Pita

Water 2025, 17(9), 1339; https://doi.org/10.3390/w17091339 (registering DOI) - 29 Apr 2025

Abstract

This study explores the development and optimization of quartz-based filtration media for industrial oil–water separation, focusing on enhancing surface wettability, minimizing fouling, and improving oil rejection efficiency. High-purity quartz particles (SiO₂: 98%, Fe₂O₃: 0.18%, particle size: 0.8–1.8 [...] Read more.

This study explores the development and optimization of quartz-based filtration media for industrial oil–water separation, focusing on enhancing surface wettability, minimizing fouling, and improving oil rejection efficiency. High-purity quartz particles (SiO₂: 98%, Fe₂O₃: 0.18%, particle size: 0.8–1.8 mm) were evaluated in three configurations: raw, acid-washed, and surface-coated with hydrophilic nanoparticles (Al₂O₃ and P₂O₅). The filtration medium was constructed as a packed-bed of quartz particles rather than a continuous sintered membrane, providing a cost-effective and modular structure for separation processes. Comprehensive material characterization was performed using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS). XRD confirmed the crystalline stability of quartz across all treatments, while SEM and EDS revealed enhanced surface morphology and elemental distribution—especially phosphorus and aluminum—in coated samples. Performance testing with synthetic oily wastewater (initial oil concentration: 183,754.8 mg/L) demonstrated that the coated quartz medium achieved superior separation, reducing residual oil concentration to 29.3 mg/L, compared to 1583.7 mg/L and 1859.8 mg/L for washed and raw quartz, respectively. Contact angle analysis confirmed improved hydrophilicity in coated media, which also exhibited lower fouling propensity. Taguchi optimization (conducted via Minitab 21.3) and regression modeling identified surface coating and operational pressure (optimal at 2.5 bar) as the most significant parameters influencing oil rejection. Post-filtration SEM and XRD confirmed structural integrity and coating durability. Additionally, flux recovery above 90% after backwashing indicated strong regeneration capability. These findings validate surface-modified quartz packed beds as robust, scalable, and economically viable alternatives to conventional membranes in oily wastewater treatment. Future research will explore multilayer coatings, long term performance under aggressive conditions, and AI-based prediction models. Full article

(This article belongs to the Special Issue Driving Water Reuse by New Technologies, Land Use and Infrastructure Planning, and Legislation Policies)

► Show Figures

Figure 1

15 pages, 11665 KiB

Open AccessArticle

Groundwater Extraction Causes a Rapid Reduction in Spring Expression at Abercorn Springs in the Recharge Area of the Great Artesian Basin, Australia

by Sharon Marshall and Andrew McDougall

Water 2025, 17(9), 1338; https://doi.org/10.3390/w17091338 - 29 Apr 2025

Abstract

Groundwater levels were monitored before, during and after groundwater pumping to understand the impacts of groundwater extraction on Abercorn Spring, a recharge spring in the Great Artesian Basin (GAB) in southeast Queensland, Australia. We measured the wetted area of the spring during this [...] Read more.

Groundwater levels were monitored before, during and after groundwater pumping to understand the impacts of groundwater extraction on Abercorn Spring, a recharge spring in the Great Artesian Basin (GAB) in southeast Queensland, Australia. We measured the wetted area of the spring during this time to understand if changes in hydrology affected the water available for vegetation communities. Sustained groundwater extraction >20 km upgradient of the spring resulted in (1) rapid drawdown of the source aquifer, causing a reduction in aquifer pressure; (2) a small decline (0.35 m) in water level at the spring; and (3) a significant change (p = 0.0001) in wetted area in winter. Recovery of water levels and wetted area of the mound spring took over three years after pumping ceased. Our study demonstrated that significant changes to the wetted area occurred with only a minimal drawdown at the springs. Abercorn Springs have a natural low variability in water level (<0.2 m), implying a stable and predictable biological community. This natural range is less than half the water level change that is currently considered for impact assessment in artesian springs in the Queensland section of the GAB, highlighting the need to incorporate updated information to inform future management of both recharge and discharge springs. In the case of Abercorn Springs, long-term monitoring and research have led to refinement of license conditions for groundwater extraction, thereby mitigating further impacts to the springs and demonstrating adaptive management. Full article

(This article belongs to the Section Water Resources Management, Policy and Governance)

► Show Figures

Figure 1

22 pages, 4222 KiB

Open AccessArticle

Simulating Anomalous Migration of Radionuclides in Variably Saturation Zone Based on Fractional Derivative Model

by Mengke Zhang, Jingyu Liu, Yang Li, Hongguang Sun and Chengpeng Lu

Water 2025, 17(9), 1337; https://doi.org/10.3390/w17091337 - 29 Apr 2025

Abstract

The migration of radioactive waste in geological environments often exhibits anomalies, such as tailing and early arrival. Fractional derivative models (FADE) can provide a good description of these phenomena. However, developing models for solute transport in unsaturated media using fractional derivatives remains an [...] Read more.

The migration of radioactive waste in geological environments often exhibits anomalies, such as tailing and early arrival. Fractional derivative models (FADE) can provide a good description of these phenomena. However, developing models for solute transport in unsaturated media using fractional derivatives remains an unexplored area. This study developed a variably saturated fractional derivative model combined with different release scenarios, to capture the abnormal increase observed in monitoring wells at a field site. The model can comprehensively simulate the migration of nuclides in the unsaturated zone (impermeable layer)—saturated zone system. This study fully analyzed the penetration of pollutants through the unsaturated zone (retardation stage), and finally the rapid lateral and rapid diffusion of pollutants along the preferential flow channels in the saturated zone. Comparative simulations indicate that the spatial nonlocalities effect of fractured weathered rock affects solute transport much more than the temporal memory effect. Therefore, a spatial fractional derivative model was selected to simulate the super-diffusive behavior in the preferential flow pathways. The overall fitness of the proposed model is good (R² ≈ 1), but the modeling accuracy will be lower with the increased distance from the waste source. The spatial differences between simulated and observed concentrations reflect the model’s limitations in long-distance simulations. Although the model reproduced the overall temporal variation of solute migration, it does not explain all the variability and uncertainty of the specific sites. Based on the sensitivity analysis, the fractional derivative parameters of the unsaturated zone show higher sensitivity than those of the saturated zone. Finally, the advantages and limitations of the fractional derivative model in radionuclide contamination prediction and remediation are discussed. In conclusion, the proposed FADE model coupled with unsaturated and saturated flow conditions, has significant application prospects in simulating nuclide migration in complex geological and hydrological environments. Full article

(This article belongs to the Special Issue Recent Advances in Subsurface Flow and Solute Transport Modelling)

► Show Figures

Figure 1

25 pages, 9643 KiB

Open AccessArticle

Numerical Modeling of the Three-Dimensional Wave-Induced Current Field

by Gabriela Gic-Grusza

Water 2025, 17(9), 1336; https://doi.org/10.3390/w17091336 - 29 Apr 2025

Abstract

This paper showcases the results of three-dimensional numerical modeling of coastal zone hydrodynamics, based on a recently developed three-dimensional analytical model incorporating a three-dimensional formulation of radiation stress. The study examines the influence of cross-shore and alongshore bathymetric variability on hydrodynamic model results, [...] Read more.

This paper showcases the results of three-dimensional numerical modeling of coastal zone hydrodynamics, based on a recently developed three-dimensional analytical model incorporating a three-dimensional formulation of radiation stress. The study examines the influence of cross-shore and alongshore bathymetric variability on hydrodynamic model results, focusing on internal volumetric current transport, bottom friction, free surface elevation, and velocity distributions. Using coastal zone cases with increasing complexity and wave datasets, we analyze differences between 2D and 3D model solutions, as well as theoretical calculations based on analytical solutions. Results indicate that in idealized, homogeneous bathymetric conditions, 2D and 3D models yield similar outputs. However, increased bathymetric complexity introduces significant variations, particularly in velocity fields and transport dynamics. Alongshore variability further modifies these distributions, emphasizing the role of lateral gradients often neglected in simplified models. The study demonstrates that neglecting alongshore bathymetric heterogeneity can lead to underestimation of key hydrodynamic variables, affecting model accuracy in coastal applications. Two-dimensional current transport fields reveal circulation patterns and possible rip current formations, suggesting that the proposed model framework provides improved insights into real-world coastal hydrodynamics. These findings highlight the necessity of incorporating three-dimensional bathymetric variability in predictive models to enhance accuracy in coastal engineering and environmental management applications. Full article

(This article belongs to the Special Issue Flow Dynamics and Sediment Transport in Rivers and Coasts)

► Show Figures

Figure 1

16 pages, 5790 KiB

Open AccessArticle

Understanding the Adsorption Mechanism of Phenol and Para-Chlorophenol onto Sepiolite Clay: A Combined DFT Calculations, Molecular Dynamics Simulations, and Isotherm Analysis

by Abdelhak Khachay, Radia Yous, Razika Khalladi, Hakima Cherifi, Bouthaina Belaid, Maymounah N. Alharthi, Stefano Salvestrini and Lotfi Mouni

Water 2025, 17(9), 1335; https://doi.org/10.3390/w17091335 - 29 Apr 2025

Abstract

This study integrates molecular dynamics (MD) simulations and density functional theory (DFT) computations to elucidate the unique adsorption characteristics of phenol and para-chlorophenol onto sepiolite by examining structural deformation, electronic properties, and adsorption energetics. The hydroxyl group (-OH) of phenol mainly determines its [...] Read more.

This study integrates molecular dynamics (MD) simulations and density functional theory (DFT) computations to elucidate the unique adsorption characteristics of phenol and para-chlorophenol onto sepiolite by examining structural deformation, electronic properties, and adsorption energetics. The hydroxyl group (-OH) of phenol mainly determines its adsorption process since it has a quite negative Mulliken charge (−0.428) and significant electrophilic reactivity (fi⁺ = 0.090), therefore enabling strong hydrogen bonding with the silanol (-SiOH) groups of sepiolite. By π-π interactions with the electron-rich siloxane (-Si-O-Si-) surfaces, the aromatic carbons in phenol improve stability. The close molecular structure allows minimum deformation energy (E_def = 94.18 kcal/mol), hence optimizing alignment with the sepiolite surface. The much negative adsorption energy (E_ads = −349.26 kcal/mol) of phenol supports its further thermodynamic stability. Conversely, because of its copious chlorine (-Cl) component, para-chlorophenol runs against steric and electrical obstacles. The virtually neutral Mulliken charge (−0.020) limits electrostatic interactions even if the chlorine atom shows great electrophilicity (fi⁺ = 0.278). Chlorine’s electron-withdrawing action lowers the hydroxyl group’s (fi⁺ = 0.077) reactivity, hence lowering hydrogen bonding. Moreover, para-chlorophenol shows strong deformation energy (E_def = 102.33 kcal/mol), which causes poor alignment and less access to high-affinity sites. With less negative than phenol, the adsorption energy for para-chlorophenol (E_ads = −317.53 kcal/mol) indicates its reduced thermodynamic affinity. Although more evident in para-chlorophenol because of the polarizable chlorine atom, van der Waals interactions do not balance its steric hindrance and reduced electrostatic interactions. With a maximum Qmax = 0.78 mmol/g, isotherm models confirm the remarkable adsorption capability of phenol in contrast to Qmax = 0.66 mmol/g for para-chlorophenol. By hydrogen bonding and π-cation interactions, phenol builds a dense and structured adsorption layer, and para-chlorophenol shows a chaotic organization with reduced site use. Supported by computational approaches and experimental validation, the results provide a comprehensive knowledge of adsorption mechanisms and provide a basis for the design of adsorbents catered for particular organic pollutants. Full article

(This article belongs to the Section Wastewater Treatment and Reuse)

► Show Figures

Figure 1

20 pages, 3544 KiB

Open AccessArticle

Construction and Application of Marine Ecological Restoration Project Effect Assessment System Based on Analytic Hierarchy Process

by Yitong Yuan, Jun Song, Ming Liu, Jingwen Li, Jun Yang and Yan Zhang

Water 2025, 17(9), 1334; https://doi.org/10.3390/w17091334 - 29 Apr 2025

Abstract

This study seeks to scientifically verify the actual effect of a marine ecological restoration project; according to the problems reflected in the assessment, the ecological restoration project can be corrected in time. This study constructs an assessment index system of marine ecological restoration [...] Read more.

This study seeks to scientifically verify the actual effect of a marine ecological restoration project; according to the problems reflected in the assessment, the ecological restoration project can be corrected in time. This study constructs an assessment index system of marine ecological restoration effect from three aspects of ecological environment, social, and economic benefits, and uses the analytic hierarchy process (AHP) to determine the index weight. Taking the Pulandian Bay ecological restoration project and the Daling River estuary ecological restoration project as examples, the application analysis was carried out. The results showed that the Pulandian Bay project scored 77.18 and the restoration effect was ‘good’, while the Daling River estuary project scored 80.19 and the restoration effect was ‘excellent’. Both achieved the effects of improving the regional ecological environment, improving ecosystem service functions, improving the quality of life of residents, and driving regional economic development. The assessment method adopted not only reflects the impact of ecological restoration on the ecological environment and economic society but also visually displays the benefits of the project, reflecting the contribution of the ecosystem to human well-being, which can provide a reference for the evaluation of similar marine ecological restoration projects. Full article

(This article belongs to the Section Oceans and Coastal Zones)

► Show Figures

Figure 1

15 pages, 4746 KiB

Open AccessArticle

Multi-Decade Variations in Sediment and Nutrient Export in Cascading Developmental Rivers in Southwest China: Impacts of Land Use and Dams

by Shucong Lyu, Qibiao Yu, Liangjing Zhang, Fei Xu, Yu Wang, Zhaojun Dong and Lusan Liu

Water 2025, 17(9), 1333; https://doi.org/10.3390/w17091333 - 29 Apr 2025

Abstract

Anthropogenic activities (represented by dams and land use change) and climate change have disrupted the delicate balance between natural and anthropogenic factors affecting riverine material transport, yet their effects across different river basins remain underexplored. This study investigated multi-decade (1980–2023) variations in sediment [...] Read more.

Anthropogenic activities (represented by dams and land use change) and climate change have disrupted the delicate balance between natural and anthropogenic factors affecting riverine material transport, yet their effects across different river basins remain underexplored. This study investigated multi-decade (1980–2023) variations in sediment and particulate carbon (C), nitrogen (N), and phosphorus (P) exports from the Jinsha (JSR) and Jialing River (JLR) basins, two cascading developmental river systems in Southwestern China, and evaluated the cumulative impacts of land use change and dam construction. The results revealed significant decreases in particulate fluxes from both basins, despite stable water discharge. Particulate material fluxes declined by 90.9–99.6% in the JSR (last decade vs. 1980–1989, with an abrupt change occurring during 2002–2003) and by 54.0–79.3% in the JLR (with an abrupt change occurring in 1994). Over time, the influence of precipitation and water discharge on material transport has diminished, whereas land use change and dams have become increasingly dominant. Key drivers include forest expansion, increased impervious surfaces, reservoir construction, and reductions in grassland and farmland; however, there are spatial differences in the relative importance of these drivers. This study provides crucial insights for decision making on regional ecological conservation and cascading development. Full article

(This article belongs to the Special Issue Environmental Behavior, Ecological Effects and Health Risks of Pollutants in Aquatic Ecosystems)

► Show Figures

Graphical abstract

17 pages, 3991 KiB

Open AccessArticle

COVID-19 and Wastewater Management in Semi-Arid Regions: Observations and Global Comparisons from a GCC Country

by Abdalrahman Alsulaili, Fahad M. Al-Fadhli, Hector A. Garcia, Omar Ali and Nasser Alenezi

Water 2025, 17(9), 1332; https://doi.org/10.3390/w17091332 - 29 Apr 2025

Abstract

The COVID-19 pandemic has led to significant shifts in global water consumption, particularly affecting wastewater treatment plants (WWTPs). In Kuwait, where high residential water usage exists, the lockdowns resulting from the pandemic created a unique opportunity to evaluate the effects of altered human [...] Read more.

The COVID-19 pandemic has led to significant shifts in global water consumption, particularly affecting wastewater treatment plants (WWTPs). In Kuwait, where high residential water usage exists, the lockdowns resulting from the pandemic created a unique opportunity to evaluate the effects of altered human activity on wastewater characteristics. This study examines the effects of the lockdown on key wastewater parameters, including flow rate, COD, BOD, TSS, total Kjeldahl nitrogen (TKN), and total phosphorus (TP). Data were collected from four WWTPs in Kuwait over 4 to 8 years, with the Kabd WWTP providing continuous daily data for an 8-year period. A comparative analysis was conducted between pre-lockdown, lockdown, and post-lockdown periods using statistical methods such as paired t-tests. The study also integrates a global comparison to relate Kuwait’s findings. Results indicate a significant increase in wastewater flow (7.6%) during the lockdown, rising from 165,486 m³/d to 178,033 m³/d. COD and BOD levels increased by 27.1% and 18.9%, respectively, while TSS showed the largest rise at 29.9%. TKN increased by 20.1%, indicating higher nitrogenous waste contributions from residential sources. These findings highlight the pandemic’s impact on wastewater characteristics in Kuwait, driven primarily by increased domestic water consumption. The study underscores the necessity of adaptive wastewater management strategies, especially in semi-arid regions, where WWTPs must be equipped to handle unexpected changes in wastewater composition. This research provides essential insights for improving the flexibility of wastewater systems with future disruptions, contributing to both environmental management and public health awareness. Full article

(This article belongs to the Section Wastewater Treatment and Reuse)

► Show Figures

Figure 1

27 pages, 8610 KiB

Open AccessArticle

Comparing SWMM and HEC-RAS Hydrological Modeling Performance in Semi-Urbanized Watershed

by Michael A. Bragg, Ashmita Poudel and Jose G. Vasconcelos

Water 2025, 17(9), 1331; https://doi.org/10.3390/w17091331 - 29 Apr 2025

Abstract

One of the most common applications of hydrological models is in studying urban watersheds, with distributed and semi-distributed models being used more frequently. The choice of modeling tools and the selection of hydrological processes to represent is dependent on the modeling objectives, available [...] Read more.

One of the most common applications of hydrological models is in studying urban watersheds, with distributed and semi-distributed models being used more frequently. The choice of modeling tools and the selection of hydrological processes to represent is dependent on the modeling objectives, available resources, and the scale of the study. Certain modeling setup parameters can have important effects on model accuracy, such as the representation of aquifer components, detailed surface storage, and discretization, among others. The effects of these parameters are often unknown since most hydrological studies do not systematically alter these parameters nor consider different modeling tools. This study performs a comparative analysis between SWMM and HEC-RAS in describing the hydrological response of a semi-urbanized headwater watershed in Alabama. Within each model, different modeling parameters were varied and the effects on the model accuracy were assessed with the stream depth and velocity collected in the field. The results showed that the parameters most impactful in SWMM modeling results were the existence of an aquifer component as well as the careful representation of surface storage. Conversely, HEC-RAS results were comparable with SWMM results when an aquifer was not present, but the runoff was highly overpredicted when infiltration was not considered. These results can indicate the applications and limitations of rain-on-grid model results that neglect interactions with shallow groundwater. Full article

(This article belongs to the Section Hydrology)

► Show Figures

Figure 1

13 pages, 1425 KiB

Open AccessArticle

Effects of Boiling and Storage on Water Quality of Tap Water, Spring Water, and Bottled Water

by Yueming Zha, Bin Cao, Lei Ni and Yaoxiong Huang

Water 2025, 17(9), 1330; https://doi.org/10.3390/w17091330 - 29 Apr 2025

Abstract

This study conducted a systematic and comparative investigation on how boiling and storage affect the water quality of tap water, spring water, and bottled water, focusing on the molecular cluster size, hardness, nitrite content, and pH value. The findings revealed that boiling reduces [...] Read more.

This study conducted a systematic and comparative investigation on how boiling and storage affect the water quality of tap water, spring water, and bottled water, focusing on the molecular cluster size, hardness, nitrite content, and pH value. The findings revealed that boiling reduces water hardness and the size of molecular clusters in both tap and spring water, with these effects lasting for several days. Boiling also decreases the nitrite content, but after one day of storage, the nitrite levels in the boiled water tend to rebound to higher levels than those in un-boiled water. However, boiled spring water stored in a closed bottle maintained lower nitrite levels than un-boiled water for up to seven days. The boiling also slightly increased the pH values of tap and spring water, and its effect could last for several days. There were correlative changes in the water hardness, cluster size, nitrite content, and pH value due to boiling. These results suggest that boiling is beneficial for drinking water because it can improve the water quality for healthy drinking. Additionally, bottled water stored for less than a year remains safe to drink as its quality does not significantly decline in that period. Full article

(This article belongs to the Section Water Quality and Contamination)

► Show Figures

Figure 1

5 pages, 153 KiB

Open AccessEditorial

Emerging Contaminants in Natural and Engineered Water Environments: Environmental Behavior, Ecological Effects and Control Strategies

by Qiuheng Zhu, Xiaodong Li and Fanhao Song

Water 2025, 17(9), 1329; https://doi.org/10.3390/w17091329 - 29 Apr 2025

Abstract

The acceleration of industrialization and urbanization has rendered water pollution one of the most pressing environmental issues worldwide [...] Full article

(This article belongs to the Special Issue Emerging Contaminants in Natural and Engineered Water Environments: Environmental Behavior, Ecological Effects and Control Strategies)

14 pages, 3519 KiB

Open AccessArticle

Compression Characteristics and Damage Constitutive Model of Loess Under Dry–Wet and Freeze–Thaw Cycles

by Yuan Yuan, Hui-Mei Zhang, Hao Liu and Pan Wang

Water 2025, 17(9), 1328; https://doi.org/10.3390/w17091328 - 29 Apr 2025

Abstract

The study of the compression characteristics of loess in seasonal regions involves analyzing the mechanical properties and mesoscale damage evolution of intact loess subjected to dry–wet freeze–thaw cycles. This study meticulously examines the evolution of the stress–strain curve at the macroscale and the [...] Read more.

The study of the compression characteristics of loess in seasonal regions involves analyzing the mechanical properties and mesoscale damage evolution of intact loess subjected to dry–wet freeze–thaw cycles. This study meticulously examines the evolution of the stress–strain curve at the macroscale and the pore structure at the mesoscale of loess by consolidation and drainage triaxial shear tests, as well as nuclear magnetic resonance (NMR), under varying numbers of dry–wet freeze–thaw cycles. Then, utilizing the Duncan–Chang model (D-C), the damage model for intact loess is derived based on the principles of equivalent strain and Weibull distribution, with testing to verify its applicability. The results indicate that the stress–strain curve of undisturbed loess exhibits significant strain softening during the initial stage of the freeze–thaw dry–wet cycle. As the number of cycles increases, the degree of strain softening weakens and gradually exhibits a strain-hardening morphology; the volume strain also changes from dilatancy to shear contraction. According to the internal pore test data analysis, the undisturbed loess contributes two components to shear strength: cementation and friction during the shear process. The cementation component of the aggregate is destroyed after stress application, resulting in a gradual enlargement of the pore area, evidenced by the change from tiny pores into larger- and medium-sized pores. After 10 cycles, the internal pore area of the sample expands by nearly 35%, indicating that the localized damage caused by the dry–wet freeze–thaw cycle controls the macroscopic mechanical properties. Finally, a damage constitutive model is developed based on the experimental phenomena and mechanism analysis, and the model’s validity is verified by comparing the experimental data with theoretical predictions. Full article

(This article belongs to the Special Issue Freeze–Thaw Dynamics and Water Pathways: Vulnerability of Infrastructures and Disasters in Mines in Cold Regions)

► Show Figures

Figure 1

10 pages, 4483 KiB

Open AccessArticle

Impacts of Small Lakes and Underlying Surface Characteristics on Local Thermal Environments in Summer

by Xuejun Qi, Jingjing Wang and Fang Yao

Water 2025, 17(9), 1327; https://doi.org/10.3390/w17091327 - 29 Apr 2025

Abstract

In recent years, rapid urbanization in China has significantly altered land use patterns and surface properties, exacerbating the urban heat island (UHI) effect. This study investigates the microclimatic regulation potential of small lakes and their interaction with three distinct underlying surfaces (granite roads, [...] Read more.

In recent years, rapid urbanization in China has significantly altered land use patterns and surface properties, exacerbating the urban heat island (UHI) effect. This study investigates the microclimatic regulation potential of small lakes and their interaction with three distinct underlying surfaces (granite roads, lawns, and woodlands). Hourly measurements of air temperature and relative humidity were conducted from 15 July to 15 August 2024, at Tianlai Lake. The results demonstrate that granite roads exhibited the highest daytime air temperatures due to their low albedo and specific heat capacity. In contrast, lawns and woodlands can reduce surrounding temperatures via latent heat dissipation. The lake’s cooling influence extended approximately 30 m from its boundary, with the air temperature decreasing by up to 2 °C near the shoreline. Relative humidity showed a negative correlation with distance from the lake, declining rapidly within 30 m. These findings highlight the role of small lakes in mitigating UHI effects and provide actionable insights for optimizing lakeside underlying surface planning in urban areas. Full article

► Show Figures

Figure 1

25 pages, 2396 KiB

Open AccessArticle

Diagnosis and Assessment of a Combined Oxylag and High Rate Algal Pond (COHRAP) for Sustainable Water Reuse: Case Study of the University Campus in Tunisia

by Chéma Keffala, Ghofrane Jmii, Ameni Mokhtar, Fouad Zouhir, Nourou Dine Liady, Bernard Tychon and Hugues Jupsin

Water 2025, 17(9), 1326; https://doi.org/10.3390/w17091326 - 29 Apr 2025

Abstract

Universities and other institutes of higher education could be considered as key actors in the implementation of sustainability pillars, such as the adoption of sustainable practices in wastewater management. However, the adoption of such practices is still an emerging issue. This paper discusses [...] Read more.

Universities and other institutes of higher education could be considered as key actors in the implementation of sustainability pillars, such as the adoption of sustainable practices in wastewater management. However, the adoption of such practices is still an emerging issue. This paper discusses the design and operation of the first combined Oxylag and high rate algal pond (COHRAP) constructed at the university campus in Tunisia for irrigation. Performance was evaluated based on the removal efficiencies of nutrients, chemical oxygen demand (COD), biochemical oxygen demand (BOD), heavy metals, coliforms, and biomass productivity. The potential reuse of sludge and algal biomass is discussed based on the Tunisian national standard regulation for sludge reuse in agriculture (NT 106.20) and the European regulation (EC, 2019/1009) for fertilizer products. Effluent phytotoxicity is tested on the germination and growth on Zea mays L. The results indicate that the COHRAP performance was globally satisfactory; however, biomass productivity (1.4 g m⁻²d⁻¹) was low, indicating the need for adjustments in the operational parameters. Despite the effluent limitations for TSS and Hg, no phytotoxic effect was observed. Regarding the heavy metal content in sludge and algal biomass, the results obtained were in compliance with NT 106.20 and EC, 2019/1009), respectively. The energy consumption of COHRAP is 1.05 kWh/m³ resulting in operational costs of 0.29 euros/m³. This study revealed that COHRAP could be a sustainable option to treat wastewater from university campuses with resource recovery. Such a choice can be improved by the implementation of an algae recovery step. Full article

(This article belongs to the Special Issue Advanced Biotechnologies for Water and Wastewater Treatment, 2nd Edition)

► Show Figures

Figure 1

2 pages, 125 KiB

Open AccessCorrection

Correction: Srivatsav et al. Biochar as an Eco-Friendly and Economical Adsorbent for the Removal of Colorants (Dyes) from Aqueous Environment: A Review. Water 2020, 12, 3561

by Prithvi Srivatsav, Bhaskar Sriharsha Bhargav, Vignesh Shanmugasundaram, Jayaseelan Arun, Kannappan Panchamoorthy Gopinath and Amit Bhatnagar

Water 2025, 17(9), 1325; https://doi.org/10.3390/w17091325 - 29 Apr 2025

Abstract

There was an error in the original publication [...] Full article

27 pages, 1501 KiB

Open AccessArticle

Underwater Digital Twin Sensor Network-Based Maritime Communication and Monitoring Using Exponential Hyperbolic Crisp Adaptive Network-Based Fuzzy Inference System

by Bala Anand Muthu and Claudia Cherubini

Water 2025, 17(9), 1324; https://doi.org/10.3390/w17091324 - 28 Apr 2025

Abstract

The underwater conditions of the coastal ecosystem require careful monitoring to anticipate potential environmental hazards. Moreover, the unique characteristics of the marine underwater environment have presented numerous challenges for the advancement of underwater sensor networks. Current studies have not extensively integrated Digital Twins [...] Read more.

The underwater conditions of the coastal ecosystem require careful monitoring to anticipate potential environmental hazards. Moreover, the unique characteristics of the marine underwater environment have presented numerous challenges for the advancement of underwater sensor networks. Current studies have not extensively integrated Digital Twins with underwater sensor networks aimed at monitoring the marine ecosystem. Consequently, this study proposes a decision-making framework based on Underwater Digital Twins (UDTs) utilizing the Exponential Hyperbolic Crisp Adaptive Network-based Fuzzy Inference System (EHC-ANFIS). The process begins with the initialization and registration of an Underwater Autonomous Vehicle (UAV). Subsequently, data are collected from the sensor network and relayed to the UDT model. The optimal path is determined using Adaptive Pheromone Ant Colony Optimization (AP-ACO) to ensure efficient data transmission. Following this, data compression is achieved through the Sliding–Huffman Coding (SHC) algorithm. The Twisted Koblitz Curve Cryptography (TKCC) method is employed to enhance data security. Additionally, an Anomaly Detection System (ADS) is trained, which involves collecting and pre-processing sensor network data. A Radial Chart is then utilized for effective visualization. Anomalies are detected using the CosLU-Variational Shake-Long Short-Term Memory (CosLU-VS-LSTM) approach. For standard data, decision-making based on the UDT model is conducted using EHC-ANFIS, with a fuzzification duration of 21,045 milliseconds. Finally, alerts are dispatched to the Maritime Alert Command Centre (MACC). This approach enhances maritime communication and monitoring along coastal areas, with specific reference to the Coromandel Coast, thereby contributing to the protection of the coastal ecosystem. Full article

(This article belongs to the Section Oceans and Coastal Zones)

25 pages, 2764 KiB

Open AccessArticle

The Optimal Capacity Estimation of Nature-Based Facilities Considering Land Cover Characteristics

by Jinsun Kim and Dongwoo Kim

Water 2025, 17(9), 1323; https://doi.org/10.3390/w17091323 - 28 Apr 2025

Abstract

Non-point source (NPS) pollution in agricultural land continues to rise despite urbanization in South Korea. NPS pollution management in rural areas has been conducted using Best Management Practices (BMPs) to reduce NPS pollution in rural areas. Among them, nature-based facilities are commonly used [...] Read more.

Non-point source (NPS) pollution in agricultural land continues to rise despite urbanization in South Korea. NPS pollution management in rural areas has been conducted using Best Management Practices (BMPs) to reduce NPS pollution in rural areas. Among them, nature-based facilities are commonly used to reduce runoff NPS pollution. To design such facilities, it is necessary to determine the Water Quality Volume (WQv), which serves as a key indicator for evaluating the performance of pollution reduction facilities, as well as the estimation of the design rainfall intensity. These are critical factors for the design of the delineation of catchment areas and NPS pollution reduction. However, conventional methods for capacity estimation often rely on total area rather than considering the specific land use distribution, leading to lower pollution reduction efficiency and excessive project costs. Therefore, this study uses actual monitoring data from existing nature-based facilities, and an analysis was performed to establish a method for determining their optimal capacity while accounting for land use characteristics. A regression analysis was conducted based on the land use area ratio, and the results demonstrated that the proposed method yields similar or improved outcomes in terms of water quality improvement and economic feasibility compared to conventional capacity estimation methods. These findings highlight the importance of incorporating diverse land use distributions into capacity estimation for improving NPS pollution management efficiency by enhancing water quality and reducing project costs. Full article

(This article belongs to the Special Issue Advanced Research in Non-Point Source Pollution of Watersheds)

► Show Figures

Figure 1

15 pages, 1552 KiB

Open AccessArticle

Recovery of Effective Acid from Waste Generated in the Anodic Oxidation Polishing Process

by Haiyang Li, Kangping Cui and Wenming Wu

Water 2025, 17(9), 1322; https://doi.org/10.3390/w17091322 - 28 Apr 2025

Viewed by 29

Abstract

The high treatment costs associated with wastewater and waste solutions produced by the anodic oxidation polishing section significantly limit industry development. To address this challenge, the present study investigates the characteristics of polishing wastewater and waste solutions, employing extraction and ion exchange combined [...] Read more.

The high treatment costs associated with wastewater and waste solutions produced by the anodic oxidation polishing section significantly limit industry development. To address this challenge, the present study investigates the characteristics of polishing wastewater and waste solutions, employing extraction and ion exchange combined with diffusion dialysis to recover effective acids. For waste tank solutions, single and dual solvent extraction experiments were conducted to determine the optimal extraction system. Electrostatic potential and interaction region indicator (IRI) analyses were performed to provide theoretical justification. Regarding cleaning wastewater, resin adsorption was applied to selectively remove aluminium ions from waste acid solutions, facilitating effective acid recovery. Static and dynamic adsorption–desorption experiments were initially performed to identify suitable resins. Subsequently, optimised parameters—including adsorption and desorption concentrations, volumes, and flow rates—were systematically established through conditional experiments, and diffusion dialysis was applied to recover acids from the desorbed solutions. The experimental results indicate that tributyl phosphate (TBP) emerged as the optimal single extractant, achieving an effective acid extraction rate of 88.67% under a solvent ratio of 4:1 at a room temperature of 28 °C. A binary solvent system, composed of TBP with 20% sulfonated kerosene, demonstrated superior engineering feasibility due to its reduced viscosity and satisfactory extraction rate of 82.19%. Moreover, adsorption–desorption tests confirmed that the resin-based method effectively recovered acids from cleaning wastewater. Specifically, under optimal operational conditions—downstream adsorption at 0.3–0.5 bed volumes (BV) and 1.0 BV/h, coupled with counter-current desorption at 2 BV and 2.4 BV/h—the acid recovery rate reached ≥95% while removing ≥90% of aluminium ions. Additionally, employing 20% sulfuric acid solution for desorption in diffusion dialysis enabled cyclic desorption. Consequently, this study successfully achieved acid reuse and substantially lowered wastewater treatment costs, representing a promising advancement for anodic oxidation polishing processes. Full article

(This article belongs to the Section Wastewater Treatment and Reuse)

► Show Figures

Figure 1

28 pages, 1378 KiB

Open AccessReview

Prospect of Conductive Materials in the Anaerobic Digester Matrix for Methane Production: Electron Transfer and Microbial Communication

by Zahra Al Hasani, Jagdeep Kumar Nayak, Noor Juma Al Balushi, Abdullah Al-Mamun and Kundan Samal

Water 2025, 17(9), 1321; https://doi.org/10.3390/w17091321 - 28 Apr 2025

Viewed by 38

Abstract

Anaerobic digestion (AD) converts organic waste into methane-rich biogas but often faces performance issues due to organic acid and ammonium nitrogen accumulation. This hinders methanogen growth and reduces methane production. Recent studies show that incorporating conductive materials (CMs) into the AD matrix can [...] Read more.

Anaerobic digestion (AD) converts organic waste into methane-rich biogas but often faces performance issues due to organic acid and ammonium nitrogen accumulation. This hinders methanogen growth and reduces methane production. Recent studies show that incorporating conductive materials (CMs) into the AD matrix can mitigate these issues by facilitating electron transfer between microorganisms. This process accelerates the oxidation of organic acids and ammonium ions, enhancing methane recovery. The effectiveness of CMs depends on their type, porosity, surface morphology, and conductivity, which foster a symbiotic microbial community. This comprehensive review paper aimed to (i) describe the influence of CMs on the growth and enrichment of the AD microbial community, (ii) quantify the enhancement of biodegradation and methane generation, and (iii) observe syntrophic interactions and interspecies electron transfer. The review also summarized the impact of different conductive materials on methane generation and the effect of operational parameters, e.g., dose, size, and external voltage application, on the conductive electrodes. The study summarized that the different conductive materials have different influences, and their application in the AD matrix has to be realistic based on availability and economic benefits. Full article

(This article belongs to the Special Issue Emerging Technologies for Nutrient Recovery and Wastewater Treatment)

► Show Figures

Figure 1

15 pages, 5758 KiB

Open AccessArticle

Investigation of Natural and Human-Induced Landslides in Red Basaltic Soils

by Huu Son Nguyen, Thi Ly Khau and Trung Tin Huynh

Water 2025, 17(9), 1320; https://doi.org/10.3390/w17091320 - 28 Apr 2025

Viewed by 46

Abstract

Landslides are mass movements of rock, soil, or debris under the influence of gravity. These phenomena occur due to the loss of slope stability or imbalance of external loads. The intensity and consequences of landslides depend on various factors such as topography, geological [...] Read more.

Landslides are mass movements of rock, soil, or debris under the influence of gravity. These phenomena occur due to the loss of slope stability or imbalance of external loads. The intensity and consequences of landslides depend on various factors such as topography, geological structure, and precipitation regime. This study investigates the characteristics of rainfall-induced landslides in red basaltic soils on the basis of field investigations, geotechnical surveys, and slope stability modeling under anthropogenic triggers. The results indicate a close relationship between soil moisture and shear strength parameters, which significantly influence slope stability. A real-time observation system recorded groundwater level fluctuation in relation to surface runoff and precipitation rates. It is revealed that intense rainfall and low temperatures regulate soil moisture, resulting in a reduction of cohesion and shear strength parameters. These findings enhance the understanding of landslide mechanism in basaltic soil regions, which are highly sensitive to precipitation. The results also highlight that human activities play a significant role in triggering landslides. Therefore, a real-time monitoring system for rainfall, soil moisture, and groundwater is essential for early warning and supports the integration of smart technologies and Internet of Things (IoT) solutions in natural disaster management. Full article

(This article belongs to the Special Issue Water-Related Landslide Hazard Process and Its Triggering Events)

► Show Figures

Figure 1

22 pages, 2259 KiB

Open AccessReview

Leading Techniques for Per- and Polyfluoroalkyl Substances (PFASs) Remediating in Water and Wastewater

by Zhenzhen Chen, Yaqian Zhao, Ting Wei and Cheng Shen

Water 2025, 17(9), 1319; https://doi.org/10.3390/w17091319 - 28 Apr 2025

Viewed by 63

Abstract

Per- and polyfluoroalkyl substances (PFASs), a class of synthetic organic compounds since the 1940s, have become widespread and persistent environmental pollutants. Due to their high chemical stability, bioaccumulation potential, and extensive industrial and household applications, PFASs have drawn significant attention from researchers worldwide [...] Read more.

Per- and polyfluoroalkyl substances (PFASs), a class of synthetic organic compounds since the 1940s, have become widespread and persistent environmental pollutants. Due to their high chemical stability, bioaccumulation potential, and extensive industrial and household applications, PFASs have drawn significant attention from researchers worldwide in recent years, while PFASs have become a hot topic, and the publications are updated very quickly. Various remediation technologies, including adsorption, pyrolysis, biodegradation, and advanced oxidation, have been developed and treated as the leading techniques to mitigate PFAS contamination. Other alternative techniques are foam fractionation, constructed wetland, and piezoelectric ball milling. However, the effectiveness of these methods varies depending on their reaction mechanisms, operational conditions, and environmental factors. This review provides a comprehensive summary of the latest advancements in PFASs removal strategies, highlighting their advantages, limitations, and potential synergies. Furthermore, future research directions and technological developments are discussed to explore more efficient, sustainable, and cost-effective solutions for PFASs remediation. Full article

(This article belongs to the Special Issue Constructed Wetlands and Emerging Pollutants)

► Show Figures

Figure 1

23 pages, 4273 KiB

Open AccessArticle

Fractal Dimension as a Criterion for the Optimal Design and Operation of Water Distribution Systems

by Santiago Gómez, Camilo Salcedo, Laura González and Juan Saldarriaga

Water 2025, 17(9), 1318; https://doi.org/10.3390/w17091318 - 28 Apr 2025

Viewed by 47

Abstract

The fractal dimension is a non-Euclidean measurement of how a fractal fills space and how irregular that arrangement is. Water distribution systems are non-Euclidean fractals whose fractal dimensions have provided insight into mathematical models to achieve optimal, minimum-cost designs. These insights are inconclusive, [...] Read more.

The fractal dimension is a non-Euclidean measurement of how a fractal fills space and how irregular that arrangement is. Water distribution systems are non-Euclidean fractals whose fractal dimensions have provided insight into mathematical models to achieve optimal, minimum-cost designs. These insights are inconclusive, as they have not yet generalized the behavior of the fractal dimension of the hydraulic gradient surface of feasible designs with respect to near-optimal solutions. To approach a mathematical description for optimality in design and operation, this paper studied the fractal dimension of the energy, infrastructural, and flow distributions of mono-objective and biobjective designs. Mono-objective designs were obtained from the Optimal Power Use Surface, while biobjective designs used NSGA-II, OPUS/NSGA-II, and GALAXY. Their corresponding fractal dimensions were computed using the box-covering algorithm. Results show that the fractal dimension only depends on the topology. From this finding, fractal analysis is proposed as a tool to define topology in the design of water distribution systems to further minimize costs obtained using current design methodologies. Pipe roughness and demand sensitivity analyses revealed weak fractal behavior, suggesting the operative use of the fractal dimension as a pipe aging and demand variation indicator. Full article

(This article belongs to the Section Urban Water Management)

► Show Figures

Figure 1

22 pages, 3617 KiB

Open AccessReview

Groundwater Vulnerability in the Kou Sub-Basin, Burkina Faso: A Critical Review of Hydrogeological Knowledge

by Tani Fatimata Andréa Coulidiati, Angelbert Chabi Biaou, Moussa Diagne Faye, Roland Yonaba, Elie Serge Gaëtan Sauret, Nestor Fiacre Compaoré and Mahamadou Koïta

Water 2025, 17(9), 1317; https://doi.org/10.3390/w17091317 - 28 Apr 2025

Viewed by 66

Abstract

Groundwater resources in the Kou sub-basin of southwestern Burkina Faso play a critical role in supporting domestic water supply, agriculture, and industry in and around Bobo-Dioulasso, the second-largest city in Burkina Faso. This study synthesizes over three decades of research on groundwater vulnerability, [...] Read more.

Groundwater resources in the Kou sub-basin of southwestern Burkina Faso play a critical role in supporting domestic water supply, agriculture, and industry in and around Bobo-Dioulasso, the second-largest city in Burkina Faso. This study synthesizes over three decades of research on groundwater vulnerability, recharge mechanisms, hydrochemistry, and residence time across the region’s sedimentary aquifers. The Kou basin hosts a complex stratified system of confined and unconfined aquifers, where hydrochemical analyses reveal predominantly Ca–Mg–HCO₃ facies, alongside local nitrate (0–860 mg/L), iron (0–2 mg/L) and potassium (<6.5 mg/L–190 mg/L) contamination. Vulnerability assessments—using parametric (DRASTIC, GOD, APSU) and numerical (MODFLOW/MT3D) models—consistently indicate moderate to high vulnerability, especially in alluvial and urban/peri-urban areas. Isotopic results show a deep recharge for a residence time greater than 50 years with deep groundwater dating from 25,000 to 42,000 years. Isotopic data confirm a vertically stratified system, with deep aquifers holding fossil water and shallow units showing recent recharge. Recharge estimates vary significantly (0–354 mm/year) depending on methodology, reflecting uncertainties in climatic, geological, and anthropogenic parameters. This review highlights major methodological limitations, including inconsistent data quality, limited spatial coverage, and insufficient integration of socio-economic drivers. To ensure long-term sustainability, future work must prioritize high-resolution hydrogeological mapping, multi-method recharge modeling, dynamic vulnerability assessments, and strengthened groundwater governance. This synthesis provides a critical foundation for improving water resource management in one of Burkina Faso’s most strategic aquifer systems. Full article

(This article belongs to the Section Hydrogeology)

► Show Figures

Figure 1

20 pages, 3782 KiB

Open AccessArticle

Fe(III) Adsorption onto Microplastics in Aquatic Environments: Interaction Mechanism, Influencing Factors, and Adsorption Capacity Prediction

by Xing Gong, Suxin Luo, Yuanyuan Yang and Qianqian Zhou

Water 2025, 17(9), 1316; https://doi.org/10.3390/w17091316 - 28 Apr 2025

Viewed by 57

Abstract

The adsorption of Fe(III) onto the surface of microplastics (MPs) enhances their toxicity and mobility in aquatic environments, posing a serious threat to human health and ecosystem balance. This study investigated the adsorption mechanism and influencing factors of Fe(III) on three types of [...] Read more.

The adsorption of Fe(III) onto the surface of microplastics (MPs) enhances their toxicity and mobility in aquatic environments, posing a serious threat to human health and ecosystem balance. This study investigated the adsorption mechanism and influencing factors of Fe(III) on three types of MPs with varying particle sizes and aging degrees using batch experiments in freshwater and saltwater. Machine learning (ML) techniques were employed to predict the adsorption capacity and conduct attribution analysis. The results showed that Fe(III) adsorption in both freshwater and saltwater followed Pseudo-First-Order kinetics and Langmuir isotherms, indicating a monolayer homogeneous physical reaction driven by oxygen-containing functional groups, hydrogen bonds and aromatic rings on the MP surface. The adsorption capacity of MPs for Fe(III) was higher in freshwater than in saltwater, and was positively correlated with the aging degree and pH value, but negatively correlated with the particle size. Among the tested ML models, the Random Forest and Gaussian Process Regression models with Bayesian Optimization performed well in predicting adsorption capacity, with pH value and aging degree identified as key factors based on SHAP analysis. This study conducted a comprehensive investigation of the adsorption behavior between MPs and Fe(III) in water, providing valuable insights for the risk assessment and prevention of MP and Fe(III) pollution in aquatic environments. Full article

(This article belongs to the Special Issue Geochemistry and Removal of Heavy Metals and Other Pollutants in Water)

► Show Figures

Figure 1

13 pages, 2131 KiB

Open AccessArticle

The Impact of Tributary Mineralization on Deep-Water Renewal in Lake Baikal During the Thermal Bar

by Bair Tsydenov, Vladislava Churuksaeva, Nikita Trunov, Andrey Bart and Dmitriy Degi

Water 2025, 17(9), 1315; https://doi.org/10.3390/w17091315 - 28 Apr 2025

Viewed by 48

Abstract

Numerical modeling methods were used to study the combined effects of the autumn thermal bar and river inflow mineralization on deep-water renewal processes in Lake Baikal. A cross-section from the Boldakov River to Maloye More strait characterized by great depths was chosen for [...] Read more.

Numerical modeling methods were used to study the combined effects of the autumn thermal bar and river inflow mineralization on deep-water renewal processes in Lake Baikal. A cross-section from the Boldakov River to Maloye More strait characterized by great depths was chosen for the study. Numerical experiments showed that under low levels of river mineralization, downwelling in the thermal bar front played a key role in water mixing. Under high levels of mineralization, the crucial factor was the large-scale near-slope circulation appearing when the stable temperature stratification of deep waters was broken. The haline characteristics of river inflow influenced the time of thermal bar appearance and the speed of propagation in the open lake. Moreover, it was shown that eddy structures can form on both sides of the thermal bar only under minor differences between river and lake mineralization levels. Full article

(This article belongs to the Section Hydrology)

► Show Figures

Figure 1

17 pages, 4856 KiB

Open AccessArticle

Worldwide Research Progress and Trends in Application of Machine Learning to Wastewater Treatment: A Bibliometric Analysis

by Kun Zhou, Boran Wu and Xin Zhang

Water 2025, 17(9), 1314; https://doi.org/10.3390/w17091314 - 28 Apr 2025

Viewed by 107

Abstract

Efficient wastewater treatment with high-quality effluent and minimal operational costs and carbon emissions is vital for safeguarding the ecological environment and promoting human health. However, the wastewater treatment process is extremely complicated due to the characteristics of multiple treatment mechanisms, high disturbance variability [...] Read more.

Efficient wastewater treatment with high-quality effluent and minimal operational costs and carbon emissions is vital for safeguarding the ecological environment and promoting human health. However, the wastewater treatment process is extremely complicated due to the characteristics of multiple treatment mechanisms, high disturbance variability and nonlinear behaviors; therefore, optimizing the wastewater treatment process through intelligent control is a long-standing challenge for researchers and operators. Machine learning models are regarded as effective tools for wastewater treatment with better simulating and controlling complex nonlinear behaviors. With the aid of bibliometric analysis, this paper aimed to summarize worldwide research progress and trends in the application of machine learning to wastewater treatment among 1226 related publications. The findings indicate that China and the United States are the two leading countries, with publications of 342 and 209, respectively, while the United States is an outstanding global collaboration leader in this field. Research institutions and authors are mainly from developing countries, and China accounts for the largest proportion of these. The analysis of journal and cited journal contributions report that almost all of the top 10 journals in publications belong to the Q1 quartile (9/10). Overall, future research will likely focus on developing systematic, strong and multi-objective models for wastewater treatment. A hybrid model could take advantage of two or more machine learning models or mechanistic models, which have been verified as excellent models for tackling limited data. Thus, predicting the pollutants in the effluent rather than the influent using hybrid models is attracting increasing attention because effective prediction contributes to reducing the loading shock of influent sharp fluctuation to wastewater treatment effluent quality. Also, the development of advanced data acquirement devices and the AI model prediction with partially default data should also be another focus of future research. Full article

(This article belongs to the Special Issue Advanced Biological Wastewater Treatment and Nutrient Removal)

► Show Figures

Figure 1

11 pages, 736 KiB

Open AccessArticle

Assessment of Acute Toxicity of Acid Mine Drainage via Toxicity Identification Evaluation (TIE) Using Daphnia magna and Chlorella vulgaris

by Carol Burgos, Soledad Chamorro, Naomi Monsalves, Gloria Gómez and Gladys Vidal

Water 2025, 17(9), 1313; https://doi.org/10.3390/w17091313 - 28 Apr 2025

Viewed by 68

Abstract

Acid mine drainage (AMD) is one of the main environmental problems in mining operations. The objective of this study was to assess AMD obtained from a copper mine via toxicity identification evaluation (TIE) using Daphnia magna and Chlorella vulgaris as indicator organisms. AMD [...] Read more.

Acid mine drainage (AMD) is one of the main environmental problems in mining operations. The objective of this study was to assess AMD obtained from a copper mine via toxicity identification evaluation (TIE) using Daphnia magna and Chlorella vulgaris as indicator organisms. AMD was fractionated via filtration and aeration at pH 3 and 11, activated carbon, cation resin, anion resin, and ethylenediaminetetraacetic acid (EDTA). The results showed that unfractionated AMD has a low organic matter content (total chemical organic demand, COD_T-183.05 mg/L), low pH (3.9), and high sulfates concentrations (2900 mg/L) and metal ions in solution (0.2–418.9 mg/L), producing high toxicity to Daphnia magna (0.00016% v/v) and no observable acute toxicity to Chlorella vulgaris (72 h-RFU 64.9%). For Daphnia magna, TIE fractionations with the greatest reduction in acute toxicity (LC₅₀) were filtration/pH11 (non-toxic) and anion resin (LC₅₀ = 0.43% v/v), with toxicity reduction percentages of 100% and 99%, respectively. Because of this, Cu was determined to be the main cause of acute toxicity to Daphnia magna. For Chlorella vulgaris, the activated carbon fraction stands out, increasing the % relative fluorescence units by 4% from 48 h to 72 h, demonstrating tolerance to AMD. The TIE technique is presented as an effective strategy to identify toxic compounds in complex samples and evaluate their effect on environmentally relevant organisms. Therefore, this study allows the analysis of the ecological risk in aquatic environments affected by mining activities, which supports environmental decision-making and the design of efficient treatment strategies. Full article

(This article belongs to the Section Water Quality and Contamination)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Water, Volume 17, Issue 9 (May-1 2025) – 102 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI