The inadequate management of wastewater in rural areas poses a significant sanitary and environmental risk. Constructed wetlands, although effective in reducing organic matter and suspended solids, often show limitations in the complete removal of pathogens, thereby hindering compliance with reuse or discharge standards. To address this the current study introduces a novel approach by evaluating the efficiency of copper sulfate (CuSO₄) as a dual-purpose germicidal and complementary coagulanting agent in a domestic wastewater treatment system using a horizontal subsurface flow constructed wetland (HSSF-CW). The novelty lies in utilizing CuSO₄'s synergistic properties to enhance both physical clarification and biological safety, offering a robust alternative for decentralized sanitation. The field-scale experiment comprised a septic tank, a coagulation stage with CuSO₄, and a horizontal subsurface flow constructed wetland (HSSF-CW) planted with Canna indica (total hydraulic retention time: 4.92 days). Prior to field-scale validation, a laboratory experimental design based on jar tests was conducted using CuSO₄ concentrations between 1–5% and doses ranging from 150–400mg/L, which identified an optimal dose of 250mg/L (3%). This optimal dose was subsequently applied and validated under field conditions. Physicochemical parameters (pH, turbidity, BOD, COD, nitrates, and phosphates) and microbiological indicators (fecal and total coliforms) were monitored weekly over a three-month period. The application of CuSO₄ significantly improved effluent quality (p < 0.05), reducing turbidity by ≈90%, BOD by >88%, COD by >89%, nitrates by ≈98%, and fecal coliforms by >90%, with residual copper concentrations averaging 0.05mg/L which is well below national and international regulatory limits, thereby minimizing concerns regarding effluent toxicity. Dissolved oxygen increased by approximately 73% (from 2.68 to 4.64mg/L) thus highlighting a substantial improvement in wetland system health and treatment performance. Although chlorine achieved complete coliform removal, it presented risks of forming halogenated disinfection by-products (THMs). In contrast, CuSO₄ does not generate such compounds, provides an additional coagulating effect, and maintains residual safety levels below regulatory toxicity limits. These findings demonstrate that CuSO₄ is a highly relevant, low-cost, and sustainable alternative for improving effluent quality in rural areas thereby effectively facilitating the safe reuse of treated water in agriculture or environmental discharge.
This study evaluated the hydrochemistry, groundwater recharge mechanisms, and nitrate pollution sources in the Upper East Region of Ghana using an integrated approach of ion chromatography, laser spectroscopy, and stable isotope analyses (δ¹⁸O–H₂O, δ²H–H₂O, δ¹⁵N–NO₃⁻, and δ¹⁸O–NO₃⁻). A total of 90 water samples (60 boreholes, 20 hand-dug wells, and 10 surface water samples from dams) were collected and analysed. The results indicate that most groundwater and surface water samples were classified as fresh, although one borehole exceeded the 1000mg/L TDS guideline. Approximately 46.7% of boreholes and 80% of hand-dug wells exhibited nitrate concentrations above the natural background value of 3mg/L. The δ¹⁸O and δ²H compositions of borehole and hand-dug well samples cluster along the Global Meteoric Water Line, confirming meteoric origin, while surface water samples plot away from the line, indicating significant evaporative isotopic fractionation. Dual‑isotope (δ¹⁵N–NO₃⁻ and δ¹⁸O–NO₃⁻) and hydrochemical analyses (NO₃⁻/Cl⁻, NO₃⁻/Na⁺, Cl⁻/Na⁺ ratios) evidence indicates that nitrate in groundwater is predominantly associated with organic waste sources (manure, sewage and septic effluents), although these sources could not be unequivocally differentiated because of overlapping isotopic signatures. No clear isotopic evidence of extensive denitrification was observed; however, the absence of complementary redox indicators precludes definitive assessment of denitrification processes. The findings suggest that groundwater nitrate contamination is predominantly associated with mixed organic sources, including manure, sewage, and septic effluents, although overlapping isotopic signatures preclude definitive source attribution. Consequently, poor sanitation infrastructure is considered a likely contributing factor rather than the sole dominant driver of nitrate contamination. This study integration of hydrochemical and isotopic tracers provides robust evidence for groundwater recharge processes and nitrate source characterization in the Upper East Region of Ghana. The findings support improved sanitation management, routine groundwater quality monitoring, and targeted nutrient management to reduce nitrate contamination in vulnerable rural aquifers.
Rapid urbanisation and largely untreated discharge have degraded surface water across the districts bordering Delhi, yet assessments there remain fragmented, with microbiological contamination less well characterised than chemical loading and geospatial mapping seldom applied to an integrated index. This study addresses that gap by consolidating physical, chemical, and microbiological measurements into a single Water Quality Index (WQI) and predicting it across the peri-urban National Capital Region of India, in support of Sustainable Development Goal 6. Surface water was sampled at 118 sites across seven industrially active districts, Ghaziabad, Gautam Buddha Nagar, Faridabad, Gurugram, Jhajjar, Sonipat, and Baghpat, that hydrologically influence the National Capital Territory of Delhi. Ten parameters were measured, including total and faecal coliforms as microbiological indicators. Four decision tree-based regressors, RT, REP Tree, AR_REP Tree, and BG_RT, were benchmarked, and BG_RT was the most accurate, returning CC of 0.9903, NSE of 0.9705, RMSE of 25.5894, MAE of 17.9543, and rRMSE of 8.59% on the testing data. Sensitivity analysis by the Cosine Amplitude Method ranked total suspended solids (Rij = 0.9735) and total solids (Rij = 0.9384) as the dominant controls on WQI, with total and faecal coliforms contributing moderately (Rij = 0.7232 and 0.6743). Geospatial interpolation of the predicted index located severe degradation in the western and eastern zones (WQI > 563.66) and better quality in the less urbanised south (WQI ≤ 86.72). The framework offers a low-cost, scalable tool for prioritising source control, decentralised wastewater treatment, and safe water reuse.
Ensuring safe and reliable drinking water in healthcare facilities is essential for protecting vulnerable patients; however, maintaining acceptable water quality remains a major challenge in developing countries. This study evaluated heavy metal(loid) contamination in hospital drinking water in Khulna, Bangladesh, identified potential contamination sources, and assessed associated human health risks. Sixty drinking water samples were collected from randomly selected healthcare centers and analyzed for Fe, Cr, As, Pb, Cd, Zn, and Cu using AAS and hydride generation AAS (HG-AAS). Mean concentrations (mg/L) of Fe, Cr, As, Pb, Cd, Zn, and Cu were 0.0174, 0.0139, 0.0013, 0.0243, 0.0038, 0.0009, and 0.0112, respectively, with a substantial proportion of samples exceeding WHO guideline values. Principal Component Analysis and Cluster Analysis indicated that Fe, Zn, Cr, and Cu mainly originated from geogenic processes and pipe corrosion, whereas Pb and As were linked to aging distribution systems and groundwater, while Cd reflected localized anthropogenic contamination. The Heavy Metal Pollution Index classified approximately 83.34% of samples as highly polluted, whereas the Heavy Metal Evaluation Index identified about 28.33% as suitable for use, highlighting contrasting assessments of water quality. The Nemerow Index indicated contamination levels ranging from unpolluted to moderately polluted. Monte Carlo simulation showed that the mean non-carcinogenic hazard indices (HI) for adults (2.1) and children (1.7) exceeded the acceptable threshold of 1, with substantial portions of the simulated distributions also exceeding this benchmark. Total carcinogenic risks likewise exceeded conventional acceptable-risk ranges. These findings highlight the urgent need for effective water treatment, routine monitoring, and improved management of hospital drinking water systems to minimize carcinogenic health risks.
This research examines the influence of access to clean water and sanitation in Latin America from 2000 to 2024 on PM2.5 air pollution. The study employs quantile regression and robust panel estimation methods (PCSE, DKSE, and FGLS) to analyze the impact of infrastructure inclusivity on air pollution, while controlling for income, industrial structure, renewable electricity output, energy productivity, and CO2 emissions. Results demonstrate that improved access to basic water services (LBWS) and sanitation services (LBSS) consistently and significantly reduces PM2.5 concentrations, hence confirming their efficacy in mitigating air pollution. An inverted U relationship exists between economic growth, industrialization, and pollution, alongside the impact of renewable electricity output on pollution reduction and rebound effects in less efficient economies through energy productivity. The Dumitrescu-Hurlin tests of causation illustrate a bidirectional relationship between infrastructure and air quality, indicating that they mutually reinforce one another. This study affirms that water and sanitation are not merely social necessities, but essential instruments of environmental governance crucial for fostering egalitarian, low-carbon, and sustainable development across Latin America.
Bangladesh’s river systems carry microplastics (MPs) and potentially toxic elements (PTEs). The underexplored Rupsha River, near the Sundarbans, was studied for MPs and PTEs. Surface water and sediment samples from four urban sites were analyzed: MPs via stereomicroscopy and ImageJ, PTEs (As, Cd, Cr, Pb) by atomic absorption spectrophotometry. Relative pollution risks were evaluated using the Pollution Load Index, Ecological Risk Index, and Principal Component Analysis to understand potential contamination patterns. Significant spatial variation was observed, with Site 3 identified as a pollution hotspot featuring 283.33±23.33 particles/L in water and 11.47±0.66 particles/g in sediment. MPs were predominantly black, smaller than 0.5mm, and consisted mostly of fragments and fibers. Cd and Pb were the primary drivers of degradation; Cd reached “very high” ecological risk levels at two sites, and the Heavy Metal Pollution Index exceeded the critical threshold of 100 at all stations. Multivariate analysis revealed a spatial occurrence of MP abundance and PTE concentrations (i.e., As, Cr, and Cd), potentially indicating shared sources in industrial effluents and urban runoff. Therefore, the Rupsha River is significantly contaminated with MPs and PTEs, threatening the local aquatic environment. This study highlights the urgent need for targeted pollution control and stricter industrial effluent regulations.
Maintaining an optimum and stable anaerobic digestion (AD) process has been a major challenge for biogas plants processing soluble feedstock with high carbon content. In this study, we investigate the impact of solids-retentive digestate recirculation and activated carbon (AC) supplementation on the AD process of whey permeate in a semi-continuous stirred tank reactor system. The optimal AD performance was observed in reactor R4 (treated with one-time AC supplementation combined with solids-retentive digestate recirculation), which produced an average CH4 yield of 60.53 NLCH4·kgVS−1. While this represents a modest 6.6% increase over the baseline control (R1: 56.77 NLCH4·kgVS−1), it allows for process stabilization of whey permeate AD. Attempting solids-retentive digestate recirculation without AC (R3) resulted in severe VFA accumulation and a ∼20% drop in CH4 yield (45.02 NLCH4·kgVS−1). The integration of AC successfully rescued the closed-loop system from thermodynamic failure, demonstrating that AC-assisted AD is a highly viable strategy for minimizing liquid effluent discharge without sacrificing methanogenic energy recovery. Our study further demonstrated that solids-retentive digestate recirculation and AC supplementation influence chemical oxygen demand removal, trace mineral profiles and microbial community dynamics of the digestate. Microbial community profiling via 16S rRNA gene amplicon sequencing indicated that solids-retentive digestate recirculation enriched the Methanosarcina population, while AC supplementation was linked to an increase in Methanoculleus abundance. In addition, it is demonstrated that AC-assisted AD could improve solid-liquid separation of the digestate following centrifugation. This study provides new insights into the distinct impact of AC supplementation and solids-retentive digestate recirculation on the AD process, both for renewable energy production and wastewater treatment systems.
This study emphasizes the development and application of citric acid-functionalized Luffa cylindrica (CALC) as an innovative, sustainable, and low-cost biosorbent for the targeted removal of ether amine (EDA), a widely used quartz collector in iron and phosphate ore flotation. Spectroscopic and electrokinetic characterizations confirmed successful esterification and a significant increase in surface negativity following functionalization, which boosted electrostatic affinity toward the cationic surfactant. Batch EDA adsorption studies revealed a strong pH dependency, achieving a maximum removal efficiency 88.5% (11.35 mg/g) at pH 10. Kinetic data followed the pseudo-second-order model (R2 > 0.99), whereas equilibrium data were best fitted by the Freundlich isotherm (R2 > 0.99), indicating multilayer adsorption on the heterogeneous luffa surface. Thermodynamic parameters indicated spontaneous and exothermic adsorption process (ΔG° ≈ −15 kJ/mol; ΔH° = −22.66 kJ/mol; ΔS° = −24.96 J/mol.K). Ultimately, this work highlights the practical significance of upgrading agricultural material into high-performance materials, offering an eco-friendly pathway to enhance water reuse and minimize chemical contaminants in mining effluents, caused by flotation reagents.
Fluoride contamination of rural groundwater poses a significant public health risk in South Africa, where seasonal monitoring recorded concentrations of 5.8–7.1 mg/L, exceeding the WHO guideline of 1.5 mg/L. This study valorised raw sugarcane bagasse (Saccharum officinarum) as a low-cost biosorbent for defluoridation, optimised using Response Surface Methodology with a Box-Behnken Design (RSM-BBD). FTIR spectroscopy confirmed –OH and –COOH surface groups as primary fluoride binding sites, SEM-EDX revealed a porous morphology with a BET surface area of 4.1 m²/g and pore volume of 0.01 cm³ /g. The point of zero charge (pHPZC = 6.78) confirmed a net negatively charged surface at the operating pH of 7.2–7.8, indicating ligand exchange as the dominant uptake mechanism. A 17-run BBD varying initial fluoride concentration (4–8 mg/L), adsorbent dosage (5–15 g), and temperature (20–30 °C) yielded a significant quadratic model (F = 4.06, R² = 0.92, lack-of-fit p = 0.1710). Optimal conditions of 5.767 mg/L, 10.577 g, and 24.863 °C produced a predicted removal of 89.28%, confirmed experimentally at 88.61% (error = 0.75%), yielding a treated fluoride concentration of 0.76 mg/L from a worst-case inlet of 7.1 mg/L. The Langmuir isotherm provided the best equilibrium fit (R² = 0.993; qm = 6.31 mg/g; RL = 0.050–0.347) over Freundlich (R² = 0.943). Thermodynamic analysis confirmed spontaneous, endothermic adsorption across 15–35 °C. The Weber–Morris intraparticle diffusion model best described the rate data (R² = 0.979), indicating a two-stage boundary-layer and pore-diffusion process; between the reaction-order models, PFO (R² = 0.967) outperformed PSO (R² = 0.877) on R² and RMSE. Desorption screening identified 0.5 M NaOH as the optimal eluent (85% recovery), with performance confirmed over five regeneration cycles. Raw sugarcane bagasse is a viable, low-cost biosorbent for community-scale defluoridation under ambient conditions, supporting SDGs 3, 6, and 12.
Integrating water quality outcomes with energy consumption remains a key challenge in assessing the sustainability of drinking water treatment plants (DWTPs). Traditional water Quality Indices typically focus on treated-water performance, while energy assessments rarely account for associated quality outcomes. To address this gap, this study develops and applies an integrated Energy–Quality Efficiency Index (EQEI) that jointly evaluates water quality improvement and energy use within a single framework.Results show that Treated-water quality remained consistently high over the study period, while variations in the integrated efficiency indicators were primarily associated with changes in energy consumption. These patterns become more apparent when water quality and energy metrics are evaluated jointly through the EQEI framework. The proposed approach supports long-term integrated performance assessment of DWTP under varying raw-water conditions, without implying operational optimisation or inter-plant benchmarking.
Freshwater reservoirs in semi-arid regions are increasingly threatened by anthropogenic pressures and climate variability, yet systematic long-term assessments of their water quality remain scarce – particularly in the Bundelkhand region of central India, where water scarcity is chronic and monitoring infrastructure is limited. This study addresses this gap by conducting a 24-month integrated physico-chemical assessment of four reservoirs (Sujara Dam, Vrindavan Pond, Barighat Dam, and Mahendra Sagar Pond) in Tikamgarh district, Madhya Pradesh. Guided by established methodologies and multivariate statistical frameworks validated in comparable semi-arid systems, we quantified seasonal and spatial variations in 18 parameters including nutrients, oxygen demand indices, major ions, and trace metals. Key limitations acknowledged in this study are the absence of microbial (fecal coliform) analysis and sediment nutrient fraction data, which constrain a full understanding of pathogen risks and internal loading dynamics – areas identified for future research. Despite these limitations, the study provides a robust baseline for water quality degradation drivers in data-scarce semi-arid regions, demonstrating that multivariate analysis (PCA, WQI) can effectively apportion pollution sources even with constrained resources. The findings underscore the urgency of targeted management interventions and continuous monitoring to safeguard water security in Bundelkhand, in alignment with Sustainable Development Goal 6.
Groundwater's suitability for irrigation is influenced by the long-term consequences of human activity, especially the interaction of urbanization, industrialization, agriculture, and seasonal aspects like precipitation and water-table variations. Despite growing irrigation reliance in urbanizing agricultural zones like Gazipur, Bangladesh, comprehensive assessments integrating hydrochemistry, water quality indices, and trace metal contamination remain limited. This study addresses this critical gap by systematically evaluating the combined influences of natural hydrogeochemical processes and anthropogenic activities to ensure sustainable irrigation management. This study analyzed 144 groundwater samples across the Gazipur district during the dry season to assess irrigation water quality based on 19 physicochemical parameters, including 8 trace elements. Hydrochemical analyses revealed that HCO⁻ (74.0%) and Cl⁻ (17.01%) were the dominant anions, while Ca²⁺ (43.0%), Na⁺ (32.0%), and Mg²⁺ (23.0%) constituted the primary cations. Piper and Gibbs diagrams classified the majority of the groundwater samples under the Ca–Mg–HCO₃ facies, identifying rock–water interaction as the predominant natural mechanism governing water chemistry, with minor anthropogenic influences. Based on the water quality index (WQI), 73.6%, 20.8%, and 5.6% of the samples were categorized as excellent, good, and poor quality, respectively. Furthermore, the trace metal pollution index (TMPI) indicated 68.1%, 9.7%, and 22.2% of groundwater as low, medium, and high pollution categories, respectively. Hierarchical cluster analysis (HCA) revealed that Pb and Cd in groundwater contribute to the overall pollution burden captured by the composite indices (WQI and TMPI). Finally, the study demonstrated that comprehensive irrigation suitability assessments overwhelmingly classify the groundwater as suitable for irrigation; however, elevated trace metal levels—particularly Pb exceeding national limits in certain locations—result in localized occurrences of poor water quality (5.6%) and elevated trace metal pollution (22.2%), emphasizing the urgent need for targeted monitoring and strict industrial discharge regulations in Gazipur to protect long-term soil health and food security.
Water scarcity in arid and semi-arid regions relies on energy-intensive water treatment technologies, leading to increased greenhouse gas emissions. However, consistent cross-technology comparisons are limited. This study analyzed the carbon footprint of major water treatment systems and identified the key drivers of environmental performance. The authors reviewed 40 studies using a PRISMA-based approach and normalized the results to 1 m³ of treated water. The analysis includes seawater desalination, brackish water treatment, wastewater reuse, and conventional treatments. The carbon footprint varied from 0.07 to 24 kg CO₂-eq/m³ . Thermal desalination exhibited the highest emissions (up to 24 kg CO₂-eq/m³). Reverse osmosis has lower values (approximately 1–4 kg CO₂-eq/m³). Wastewater reuse had the lowest impact, with emissions up to 79% lower than those of traditional thermal seawater desalination. Renewable energy reduces emissions by over 90%. Energy sources, salinity, plant scale, and chemical use drive these differences. These results highlight the need to integrate the water–energy–carbon nexus into water-supply planning. Wastewater reuse and renewable-powered desalination offer clear pathways for reducing environmental impacts in water-scarce regions. These findings directly support Sustainable Development Goal 6 (Clean Water and Sanitation) and Sustainable Development Goal 13 (Climate Action) by identifying low-carbon pathways for water supply in arid regions.
In fast-growing cities, urban ponds are significant sources of potable and/or community water, but their water quality is seldom evaluated at the extensive spatial level. To the best of our knowledge, this study is among the first integrated assessments of urban pond water quality at the ward scale across all 41 administrative wards of Chittagong City Corporation (CCC) in Bangladesh. During post monsoon (November-December 2025), 492 water samples were collected from the ponds and tested for physicochemical parameters and heavy metals, while 410 samples were separately processed for microplastic analysis. A Water Quality Index (WQI), Heavy Metal Pollution Index (HPI), human health risk assessment, Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), and ten supervised machine learning models were combined to characterize water quality and determine dominant water quality drivers. The ward average WQI ranged from 78.33 to 166.11 (mean: 115.63), with 85.4% of wards being classified as Poor, signifying that the overall quality of water is deteriorating with the major problem being turbidity, nutrient enrichment and fecal contamination. All the wards had HPI value above the critical threshold (HPI>100), the highest heavy metal contamination was near the industrial and port adjacent area. Although the measured arsenic concentrations remained below the ECR 2023 permissible limit, the conservative lifetime oral-exposure assessment indicated elevated non-carcinogenic and carcinogenic risks, particularly due to arsenic. Microplastics were found in all wards and the most common polymers found were PET, PP, HDPE and LDPE. A significant amount of spatial heterogeneity in the city was identified by PCA and HCA which showed distinct environmental gradients and four clusters of pollution. ElasticNet performed best in predicting the WQI (R² = 0.8425, RMSE = 31.87, MAPE = 18.87%), and among the evaluated machine learning models, turbidity was the most significant factor influencing the variability of WQI was identified by the SHAP analysis. The integrated framework developed in this study could serve as a solid foundation for the monitoring, cluster-based remediation and risk-based implementation of the Environment Conservation Rules (ECR 2023), and can be transferred to other rapidly urbanizing areas for the assessment of urban freshwater systems.
The rapid growth of solar panel manufacturing industry has significantly increased the need for sustainable management of fluoride-containing wastewater generated during production processes. This study develops a superstructure-based optimisation model to synthesise an optimal treatment pathway that simultaneously considers economic, environmental, occupational health (IOHI), and inherent safety (NuDIST) objectives. A fuzzy multi-objective optimisation approach was employed to balance these conflicting objectives, enabling systematic decision-making for technology selection. The proposed model successfully identified treatment configurations that complied with regulatory fluoride discharge limits while optimising performance across multiple sustainability criteria. The results showed that precipitation using CaCl2 combined with ion exchange provided the most balanced solution for the case study, achieving the highest fuzzy satisfaction degree (λ = 0.44), a low NuDIST score of 2.67, an annual operating cost of USD 7701,251/year, an IOHI of 12, and carbon emissions of 67,680 kg CO2e/year, while fully complying with regulatory fluoride discharge limits. Sensitivity analyses on influent fluoride concentration and chemical prices further demonstrated the robustness of the proposed optimisation model under varying operating conditions and economic uncertainties. Overall, this research advances the application of superstructure-based modelling for wastewater treatment design by integrating safety and occupational health with economic and environmental objectives, providing a comprehensive decision-making tool for industries managing fluoride-containing wastewater, particularly in the solar manufacturing sector.
This study employed two hybrid electroactive constructed wetland systems to treat recalcitrant landfill leachate. Each hybrid system included a media-based vertical flow (VF) stage, followed by a horizontal flow (HF) stage, and a water-column-based floating treatment (FT) unit as a post-polishing stage. The VF and HF stages between the two systems differed in the media used (stone dust vs. brick chips). The electroactive systems operated with (closed-circuit operation) and without (open-circuit operation) external resistor loads. Mean removals of 57%-89%, 42%-67%, 70%-87%, and 90%-93% for organic matter, nitrogen, phosphorus, and coliforms, respectively, were achieved by the two hybrid systems. The brick chips-based hybrid system achieved better pollutant removal than the stone dust-based system. Electrochemically unoxidized organic matter altered the redox gradient, which negatively influenced organic, nitrogen, and coliform removal of the upflow-based VF units. The HF and FT stages improved the removal performances of both systems. Filler material-induced adsorption controlled phosphorus removal. The closed-circuit operation enabled more intensive electrochemical oxidation of organic matter. Supplementary electron production via this electrochemical route supported NO3-N reduction, as the leachate wastewater was largely nonbiodegradable. Nutrient removal via plant uptake ranged from 0.1% to 2%, indicating their minor impact on overall removal. Power density production (across the two systems) ranged from 40 mW/m3 to 1294 mW/m3 during the closed-circuit operation. Internal resistance reduced bioelectricity production in the stone dust media-based system. This study identifies the pollutant removal mechanisms and the interacting factors (i.e., media, biodegradation ratio, redox potential, and external resistor load) in hybrid electroactive constructed wetland systems dosed with hardly degradable landfill leachate.
Ibuprofen (IBU), a widely detected emerging contaminant, is poorly removed by conventional constructed wetland (CW) substrates. Iron-sulfide minerals have shown promise as functional alternatives, yet their comparative performance for long-term IBU removal remains poorly understood. Here, we systematically compared pyrite (FeS2) and ferrous sulfide (FeS) as CW substrates through 177-day experiments under varying operating conditions, integrating effluent ecological risk assessment with surface chemistry, biofilm, and microbial community analyses. The FeS system achieved significantly higher and more stable long-term IBU removal (69.8%) than the FeS2 (60.4%) and gravel (38.9%) systems. Ecological risk assessment revealed that effluents from all systems elicited qualitatively similar hormetic response patterns in Chlorella pyrenoidosa, and the iron-sulfide systems did not elevate the effluent biological impact relative to the gravel control. Mechanistically, FeS sustained an active iron-sulfur cycle that promoted a polysaccharide-rich biofilm matrix and selectively enriched genera positively correlated with IBU removal (e.g., Thiobacillus, Geobacter). These findings demonstrate that FeS is a promising CW substrate for enhanced removal of emerging contaminants, while highlighting the need for transformation product analysis to fully assess environmental safety.
This study investigates concurrent water–oil flow through a pipeline configuration consisting of a return bend and a sudden contraction. The Eulerian–Eulerian Volume of Fluid (VOF) model implemented in ANSYS Fluent is used to analyze flow patterns and pressure drop for various combinations of kerosene and lubricating oil with water. The results indicate that the return bend section exhibits minimum pressure drop for both viscous oils, whereas the sudden contraction and downstream sections experience higher pressure losses, particularly at higher superficial velocities. The study highlights the influence of viscosity and pipeline geometry on flow behavior and provides useful insights for the design of efficient two-phase flow systems.
Groundwater contamination by trace metal poses significant environmental and public health risks, particularly in developing countries where groundwater is a major drinking water source. This study evaluates seasonal variation of trace metals (Al, Cu, Fe, Mn, Cr and As) and associated risks in southeastern Bangladesh. The concentration of As and Mn exceeded tolerable limits during dry period and Fe exceeded permissible limits in both seasons. Drinking water potability was assessed through the Heavy Metal Evaluation Index (HEI), Heavy Metal Pollution Index (HMPI), and Nemerow’s Pollution Index (NI) resulting poorer water quality during the dry season. Chronic non-carcinogenic health risk evaluated using Hazard Quotient (HQ) and Hazard Index (HI) was highest for As and Mn, with 82% in the wet season and 68% in the dry season, and falling into the medium-to-high HI risk categories. In both seasons, the highest HI values were associated to oral intake, exhibiting maximum HI values of 37.726 (adults) and 48.659 (children) in the wet season. Carcinogenic risk or Lifetime Cancer Risk (LTCR) was slightly higher during the wet season, especially in Lakshmipur and Noakhali, with children being the most vulnerable group. During wet season, 99% children and 89% adults crossed the high risk threshold, barely one adult fell below low category and nearly none of the children did. The wet season child mean LTCR was 3.63 × 10⁻³ , indicating 3 times higher cancer risk than dry season. Continuous monitoring and mitigation measures are recommended, particularly in Chittagong and Lakshmipur, to reduce pollution exposure and protect public health.
Eutrophication caused by persistent nutrient enrichment remains a major threat to the ecological stability and sustainable management of river systems exposed to anthropogenic pressure. This study investigated the spatial and seasonal variability of trophic conditions in the Styr River (Western Ukraine) under continuous discharge influence using an integrated framework combining nutrient-based trophic indices, Positive Matrix Factorisation (PMF), Random Forest (RF) modelling, and Bayesian source apportionment analysis. Total nitrogen (TN) and total phosphorus (TP) concentrations were analysed at monitoring sites representing background, impacted, and discharge-affected conditions. Trophic conditions were evaluated using the phosphorus-based trophic state index (TSIP) and the trophic level index (TLI). The results demonstrated pronounced spatial heterogeneity of trophic conditions within the investigated river system. Riverine sections were predominantly characterised by eutrophic conditions with clear seasonal variability, whereas the discharge-affected site exhibited persistently elevated hypertrophic conditions with comparatively weak seasonal fluctuations. PMF modelling resolved five principal nutrient-source factors associated with hydrological runoff, background hydrochemical conditions, biological activity, agricultural influence, and point-source discharge. Bayesian analysis was additionally used to evaluate uncertainty in source contributions. The obtained results indicate that trophic-state formation in the studied river system depends not only on nutrient concentrations, but also on the persistence, structure, and probabilistic dominance of nutrient sources. The proposed framework provides a process-oriented approach for identifying dominant nutrient-loading pathways and assessing eutrophication risk in regulated river systems under continuous anthropogenic pressure. The findings highlight the importance of source-oriented nutrient mitigation, adaptive monitoring strategies, and long-term discharge control for sustainable river-water management and water-quality protection consistent with SDG 6 objectives.
