The biological activation of granular activated carbon (GAC) filters extends their service life until a threshold of 80% is reached for the removal of organic micropollutants (OMP). To quantify the influence of biological activity on OMP removal, the 12 indicator substances of the 2024 revised EU Urban Wastewater Treatment Directive were used. Five years of pilot testing were examined, presenting data from three GAC filters under various process settings. Hydraulic parameters (empty bed contact time (EBCT) and filtration velocity (vfiltr)) and the backwash frequency were investigated. The pilot-scale GAC filters were fed with effluent from the wastewater treatment plant Nette (86,000 p.e.), which was subsequently further treated by a pilot-scale ultrafiltration system. The suspended solids-free feed was, alongside the process settings and temperature, a further influencing factor that was investigated regarding its effects on biological activity and thus on OMP removal.The results show that biologically active GAC filters achieve consistently high removal efficiency (>90%) for highly biodegradable OMPs even after >115,000 BV (CUR <4.0 mgAC/L). However, biological activation also extends the filter service life for poorly biodegradable OMPs (e.g. carbamazepine). This could indicate a partial bioregeneration of the GAC. With appropriate process settings, biodegradation begins to compensate for the declining adsorption capacity at around 10,000–15,000 BV. The effect of backwashing diminishes as the filter service life increases and is expected to play a crucial role during the early growth phases. EBCT and vfiltr can limit the biodegradation of OMPs, thereby preventing the biological activity from being fully exploited.
Retired oil and gas well environments pose profoundly complex groundwater remediation challenges due to contaminant architectures that are characteristically deep, stratified, and severely heterogeneous. Historical remediation strategies frequently underperform because they disproportionately emphasize nominal reagent reactivity while neglecting critical dependencies on precise amendment delivery and strict treatment zone control. To resolve these systemic limitations, this comprehensive review introduces the Source architecture, Precision delivery, Verification, and Adaptive control (SPVA) framework to reassess in situ remediation of petroleum related groundwater contamination. Our analysis begins by synthesizing the mechanisms through which wellbore legacy effects, multiphase contaminant behavior, and aquifer compartmentalization inherently restrict amendment access and effective physical contact. Recognizing these physical constraints, we critically evaluate advanced delivery architectures such as discrete depth injection, and integrated chemical biological strategies. This evaluation deliberately pivots the disciplinary focus toward the structural construction of robust subsurface treatment zones. Furthermore, we investigate the persistent disconnect between localized injection achievements and overall remediation efficacy. Bridging this operational gap necessitates adopting emerging methodologies capable of verifying amendment distribution and identifying untreated zones, which seamlessly enables monitoring informed adaptive control systems. The proposed framework extensively explores the strategic opportunities provided by process modeling, machine learning algorithms, digital twins, and sustainable optimization to enhance full scale field operations. Ultimately, SPVA formalizes and extends established adaptive-remediation principles for the specific constraints of deep, stratified, legacy-infrastructure-affected aquifers. By defining remediation success around verifiable treatment-zone completeness, this structured workflow provides an evidence-based roadmap for addressing the global environmental legacy of retired wells.
Microplastics (MPs) and heavy metals (HMs) commonly co-occur in marine aquaculture systems as emerging pollutants derived from feed inputs, antifouling coatings, and industrial effluents. Their accumulation can disturb microbial homeostasis and influence the dissemination of antibiotic resistance genes (ARGs). Contrary to the widely held view that these pollutants uniformly promote ARG transfer, recent evidence indicates that they may also suppress ARG propagation under specific conditions.Although MPs and HMs are often considered synergistic drivers of ARG transfer through oxidative stress and biofilm formation, reported effects vary with particle size, polymer aging, metal type, exposure duration, salinity, pH, dissolved organic matter (DOM), and experimental realism. Recent evidence indicates that MPs may also inhibit ARG propagation under high salinity, advanced aging, or near-neutral pH, when altered surface functional groups and metal complexation reduce metal bioavailability. To reconcile these divergent findings, this review proposes a threshold-dependent "counter-selection window" as a working hypothesis. This window is defined—based on a limited number of controlled laboratory and microcosm experiments—as an environmental range in which aged MPs with elevated surface O/C ratios (>0.2) and sustained ·OH radical generation form stable surface complexes with HM ions (e.g., Cu(II), Cr(VI)), thereby reducing the bioavailable metal pool and suppressing ARG horizontal transfer. Quantitative values cited in this review (e.g., pH 6–7, salinity >30‰, MP size 75–150 nm, and 21.4–42.3% HGT reduction) are drawn from these specific experimental systems and should not be interpreted as universal boundaries applicable to all marine aquaculture environments. The duration, spatial extent, and predictability of this window under diverse field conditions remain poorly constrained, and direct validation under realistic operational settings is urgently needed. We further emphasize that this inhibitory state is unstable: acidification or increased DOM may trigger metal desorption, collapse the counter-selection window, and restore ARG proliferation. However, we acknowledge that most mechanistic evidence is derived from laboratory pure-culture, freshwater, or soil studies; direct field data from marine aquaculture systems remain scarce. Therefore, the proposed counter-selection window and inhibitory effects should be interpreted as hypothesis-generating frameworks that require validation under realistic marine aquaculture conditions, considering salinity fluctuations, feed-derived organic matter, and hydrodynamic regimes. Moving beyond the conventional unidirectional co-selection narrative, this review critically evaluates the bidirectional regulation of ARG dynamics by MP–HM interactions as reported in laboratory and microcosm studies, integrates these mechanistic findings with consideration of marine aquaculture conditions, and identifies hypothesis-driven research priorities and management strategies for assessing and mitigating ecological risks associated with complex pollutant mixtures. We emphasize that all quantitative thresholds and the proposed ‘counter-selection window’ remain theoretical constructs until validated under realistic field conditions.
Providing safe drinking water in remote karst regions requires balancing microbial protection with control of disinfection byproducts under highly heterogeneous hydrogeological conditions. Against a background of intensive agriculture, widespread livestock farming, and vulnerable karst hydrogeology in rural Southwest China, centralized supply systems have progressively replaced private wells through the implementation of Drinking Water Safety Projects. However, the behavior of N-nitrosamines in these decentralized treatment systems remains poorly constrained. Here, nine N-nitrosamines were investigated across 52 rural sites to quantify their occurrence, distribution patterns and associated carcinogenic risks. Total concentrations ranged from 3.5–16.1 ng/L in source water and 3.5–40.8 ng/L in finished drinking water. N-nitrosodimethylamine (NDMA) and N-nitrosopyrrolidine (NPYR) dominated across sites, while N-nitrosodibutylamine (NDBA) was more frequently detected after treatment. Despite detectable formation during disinfection, centralized tap water exhibited significantly lower median concentrations and reduced estimated lifetime carcinogenic risks compared to private wells. Process-level analysis suggested that N-nitrosamine occurrence was associated with both source-water characteristics and disinfectant type. Chloramine disinfection was associated with elevated concentrations, whereas free chlorine disinfection using calcium hypochlorite was not associated with a significant increase under current operational conditions. These findings clarify N-nitrosamine behavior in rural karst water systems and provide a basis for optimizing disinfection strategies to minimize chemical risks while maintaining microbial safety.
Plateau lake wetlands are important for regional hydrological regulation and biodiversity conservation and are highly sensitive to climate change and human disturbance. However, their long-term ecosystem health dynamics and driving mechanisms remain poorly understood in alpine mountainous regions. This study developed an integrated remote sensing–based framework to quantify ecosystem health dynamics and attribute their drivers in 12 representative lakes in the Yunnan section of the Hengduan Mountains (1986-2024). We constructed a Comprehensive Wetland Health Index (CWHI) by integrating vegetation, hydrological, and algal-based water quality proxy indicators using an objective-subjective ensemble weighting strategy. Long-term trends in CWHI were quantified using the Theil-Sen estimator, and the relative contributions and directionality of climatic and human drivers were assessed using an explainable machine learning approach. Results showed that all 12 lakes had positive CWHI trends, and 8 lakes (66.7%) exhibited significant increases. This improvement was consistent with improved vegetation status and reduced algal activity, which compensated for a decrease in hydrological stability. Temporal attribution indicated human activity dominated CWHI in most lakes with significant changes and exerted predominantly positive effects, whereas vapor pressure deficit (VPD) and temperature generally showed secondary negative influences. Spatial attribution further revealed a shift in dominant controls on CWHI heterogeneity from VPD to human-activity dominance, and to temperature dominance recently. These findings showed that recent improvements in plateau lake wetland health occurred under persistent climatic stress, with human activity showed positive contributions in this process. Management should prioritize lake ecosystem resilience to ongoing atmospheric drying and hydrological variability.
Anaerobic ammonium oxidation (anammox) is a promising nitrogen removal technology but remains constrained by limited operational robustness under environmental perturbations. Here, a solid-phase redox regulation strategy was proposed by coupling hydrogen peroxide (H2O2) with two distinct electron donors, inorganic ferrous sulfide (FeS) and organic lignite, to enhance system stability under continuous-flow conditions. The results show that upon the introduction of redox pairs, both systems achieved high nitrogen removal efficiency, maintaining ammonia and nitrite removal above 96.3% even under a 50% increase in nitrogen loading. Moreover, the specific anammox activity significantly increased by 3.27- (FeS-based system) and 2.87-fold (lignite-based system), respectively. Multi-omics analyses revealed that exogenous redox regulation reinforced electron transport and ATP synthesis, while reprogramming carbon metabolism toward the Wood-Ljungdahl pathway without disrupting the core anammox pathway. Notably, distinct donor-dependent effects were observed. The FeS-based system promoted direct inorganic redox cycling, leading to enhanced energy turnover and the formation of a functionally complementary multi-genus anammox consortium. In contrast, the lignite-based system facilitated co-enrichment of anammox bacteria and denitrifiers, indicating different ecological interaction modes. Both systems activated antioxidant defense mechanisms in response to controlled oxidative perturbation, indicating adaptive redox homeostasis. Overall, this study demonstrates that electron donor properties govern redox-mediated metabolic and community reorganization, providing new insights into the design of robust anammox systems.
Landfill leachate is a high-strength wastewater generated during municipal solid-waste disposal, and its composition and biodegradability vary strongly with landfill age. Dissolved organic matter (DOM) constitutes the dominant organic pool in leachate and influences treatment efficiency, toxicity, contaminant complexation, membrane fouling, concentrate management, and process sustainability. Recent ultrahigh-resolution mass spectrometry, especially Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), combined with multidimensional spectroscopy, enables molecular-level characterization of leachate DOM and tracking of its evolution during landfill aging and treatment. This review synthesizes molecular-level evidence on leachate DOM evolution, transformation, and engineering regulation within a molecular evolution–process selectivity–engineering regulation framework. Available evidence indicates that, during landfill aging, leachate DOM shifts from protein- and aliphatic-enriched mixtures toward a more oxygenated, aromatic, heteroatom- or halogen-bearing, and persistent pool, and this age-dependent evolution underlies declining biodegradability and reshapes process selectivity. We further synthesize process-selective DOM behaviors across physicochemical separation, advanced oxidation, and biological conversion, and highlight paired mass differences-based reactionomics and interpretable machine learning to link molecular fingerprints with transformation pathways and key operational metrics. Finally, we highlight the need to clarify DOM–microbial interactions, reduce method-related biases, and translate molecular descriptors into practical monitoring and operating conditions. Overall, this review argues for moving leachate treatment beyond bulk-metrics-based process stacking toward molecularly informed treatment-train design under stringent discharge limits and management strategies directed toward zero liquid discharge.
Drinking water contamination events are rare in high-income countries, yet distribution-system failures can still cause significant public health impacts. This study reconstructs a microbial contamination incident caused by wastewater intrusion into the drinking water distribution system in Kuressaare, Estonia, in May 2023, using an integrated post-event review framework for water systems that complements the after-action review approach with a technical layer combining baseline assessment, operational and infrastructure documentation, water quality and hydraulic monitoring data, and extended-period and transient hydraulic modeling. The reconstruction identified transient low-pressure conditions and flow reversals as key mechanisms enabling contamination intrusion and propagation within the distribution network. The incident was associated with 135 emergency department visits for acute gastrointestinal illness, although the total number of affected individuals remains unknown. Clinical testing detected enteropathogenic bacteria, enteric viruses, or both in 39 of 40 analyzed patient samples, and healthcare contacts from multiple districts indicated broad exposure across the distribution area. The review of response actions revealed deficiencies in preparedness and crisis management, including incomplete risk assessment and project documentation, delayed recognition of contamination, and unclear communication and operational procedures. The findings demonstrate the value of integrated post-event reconstruction for identifying contamination mechanisms, system vulnerabilities and preparedness gaps, while highlighting the importance of systemic use of routinely collected operational data. Strengthening risk-based management through improved data integration, hydraulic analysis, and preparedness planning is essential for reducing the likelihood and impact of future contamination events.
The Yangtze River Basin has experienced rapid population growth, agricultural intensification, urbanization and industrial development since the 1970s, leading to eutrophication problems. However, there is large spatial heterogeneity of development trajectories and associated changes in nutrient sources and fates within the Yangtze River basin. To capture this heterogeneity, here we applied the Integrated Model to Assess the Global Environment-Dynamic Global Nutrient Model (IMAGE-DGNM) to quantify nutrient dynamics across 12 subbasins in the Yangtze River Basin during 1970-2019. Results show that nutrient sources, delivery, retention, export, and ratios and their changes substantially differed across the subbasins. Agricultural groundwater runoff from middle-reach subbasins contributed most to the basin-wide total nitrogen (TN) delivery, while agricultural surface runoff from upstream subbasins and point sources from middle- and lower-reach subbasins had the largest contribution to the basin-wide total phosphorus (TP) delivery. The Middle Mainstream Subbasin (including Three Gorges Reservoir) accounts for less than 10% of the total basin area but contributed over one-fourth of basin-wide TN and TP retention, primarily due to its constructed dams and reservoirs. Molar N:P ratios of both nutrient delivery and export increased across all subbasins, shifting from predominantly below the Redfield ratio in 1970 to widespread P limitation in 2019. Nutrient management controlling local sources alone could only mitigate 8-32% TN loads and 10-33% TP loads in the four mainstream subbasins.
Non-toxigenic Vibrio cholerae (NTVC) are naturally thriving in various aquatic environments, including rivers, lakes, and coastal waters. Although unable to produce cholera toxin, they cause severe infections, including wound and bloodstream infections or gastrointestinal illness. Over the past three decades, a well-documented rise in NTVC infections has been reported in countries of the Northern hemisphere, linked to climate change induced rising water temperatures in coastal ecosystems. In contrast, information on the occurrence of NTVC in continental inland water-bodies is scarce, and no rise in cases has been observed. The aim of our study was thus to elucidate the biogeography and temperature response of NTVC populations in inland bathing sites in Eastern Austria, an ecoregion that has been regularly afflicted with NTVC cases in the past decades. NTVC abundance was assessed in 46 water bodies with culture-based and qPCR methods and related to geographical and environmental key-parameters. Statistical modeling identified a clear geographical gradient, with temperature, and conductivity as key-drivers of NTVC abundance. Easy-to-determine geographical and environmental thresholds were established to enable bathing-site operators and health authorities to quickly assess NTVC occurrence and potential exposure risk. The temperature response of the NTVC populations in nine selected ponds, revealed that a 1-log rise in culturable NTVC numbers and a 0.5 log rise of NTVC quantified by qPCR is obtained by a temperature increase of 6°C, a realistic and currently unfolding climate change scenario for the European continent. Improved surveillance systems linking NTVC abundance, environmental data and clinical cases would be required to protect an increasingly vulnerable population.
Debris accumulation is a primary driver of reduced hydraulic capacity and urban flooding in sewer networks, yet it remains underexamined in predictive modelling. This study develops an integrated framework to predict debris criticality (cross-sectional obstruction ≥ 25%) using a comprehensive municipal CCTV inspection database from Hong Kong’s urban drainage network, comprising 5,470 drainage folders and 30,241 inspection files collected over 14 years (2007–2021). From this network-scale database, 8,165 debris-affected pipe segments were extracted for analysis, including an isolated-debris subset for Weibull Accelerated Failure Time (WAFT) modelling and the full debris cohort for machine learning prediction. The WAFT model identified pipe diameter, age, and Vitrified Clay (Time Ratio = 0.889 vs. Concrete) as dominant physical risk determinants, compounded by traffic and industrial land use. Interpreted via SHAP, machine learning confirmed diameter and age as primary predictors. LightGBM achieved the strongest discrimination (ROC-AUC = 0.871), and threshold optimisation recovered 76% of high-criticality segments, supporting proactive intervention before hydraulic failure. This convergence of survival and ML findings provides robust cross-method validation, supporting a transition toward risk-stratified maintenance to enhance the hydrological resilience of urban catchments.
The biogeochemical dynamics of phosphorus (P) beneath ice cover, particularly at the sediment–water interface (SWI), remain poorly understood due to the lack of high-resolution in-situ characterization, limiting our ability to predict nutrient cycling in cold-region ecosystems. Despite low temperatures and limited hydrodynamic disturbance, ice cover promoted substantial accumulation of labile P and Fe(II) at the SWI, with winter diffusive P fluxes reaching 0.46–0.50 mg m−2 d−1, comparable to or exceeding those reported for many eutrophic lakes during ice-free periods. Ice cover weakened nutrient exchange and hydrological connectivity between Lake Xingkai and Lake Xiaoxingkai, whereas spring thaw restored basin-scale connectivity and promoted nutrient redistribution. Turbidity was strongly associated with labile P and Fe(II) dynamics beneath ice, suggesting that particle-related processes may be linked to winter nutrient mobilization. These results reveal strong P–Fe coupling across the SWI during ice-covered and ice-breakup periods and demonstrate that winter represents a critical, yet underappreciated, phase of internal P loading in cold-region agricultural wetland–lake systems. Management of eutrophication in the Lake Xingkai/Khanka Basin should explicitly consider winter redox processes, seasonal hydrological reconnection, and maintenance of P limitation under ice-covered conditions.
Acid Mine Drainage (AMD) poses global threats to ecosystems and has compelled the optimization of passive treatment systems via the understanding of internal hydrochemical and biological kinetics. This study systematically analyzed the performance of an integrated treatment scheme combining Anaerobic Limestone Drains (ALD) and Sulfate-Reducing Bacteria (SRB) through a multi-scale experimental and modeling approach. At the laboratory scale, the ALD reactor effectively neutralized highly acidic AMD (pH < 3.0) and favored the precipitation of Al- and Fe-hydroxides. However, the ALD exhibited lower efficiency for Zn2+ and Mn2+ removal, due to pH oscillations that altered the adsorption kinetics, as testified by reactive transport modeling in porous media. The encouraging ALD results prompted the construction of a pilot-scale ALD-SRB coupling system. Experimental results were complemented with a second numerical model to evaluate the sulfate removal performance. In the mature phase, observed and simulated results indicated a sulfate removal rate of 1.22 × 10-4 mol m-3 s-1 (R2 > 0.92), which aligned with the stabilization of the Desulfovibrio-dominated syntrophic network. This integrated strategy confirmed the tight coupling between chemical and biological reaction kinetics, providing theoretical foundations and alternative approaches for optimizing upscaled passive AMD remediation.
The ingestion of water from a drinking water distribution system (DWDS) is a potential pathway for human exposure to active antibiotic resistance genes (ARGs). DWDS biofilms are a critical reservoir of ARGs as they are continually exposed to environmental stressors, such as sub-minimum inhibitory concentrations (sub-MICs) of antibiotics, which pose a risk of ARG dissemination into bulk water. The aim of this study was to investigate associations between sulfamethoxazole exposure and ARG abundance, ARG expression, and antibiotic-resistant bacteria (ARB) in drinking water biofilms adhered to distribution pipe walls. The ARGs intI1, sul2, and sul1 were detected through qPCR and RT-qPCR in both the biofilm and the bulk water. A significant positive correlation was found between sulfamethoxazole presence and promotion of intI1, suggesting that it is associated with ARG propagation. This was further supported by the observed co-occurrence between intI1 and sul2. ARGs found in the biofilm were correlated with ARGs in the bulk water; however, this relationship was not statistically significant. Low-abundance genera in the biofilm were found to significantly correlate with intI1, which has been established to be a marker of anthropogenic pollution and horizontal gene transfer. These findings highlight the association between DWDS biofilms and ARG dynamics under antibiotic exposure and warrant further investigation into their potential role in wider resistance dissemination.
Sewage sludge generation is rising globally, straining wastewater treatment systems, land resources, and climate targets while simultaneously offering recoverable energy, nutrients, and materials within a circular economy. This review examines how the field is moving beyond disposal along three converging directions: coupling complementary processes into integrated treatment trains, widening the slate of products those trains can recover, and using data-driven tools to operate them reliably at scale. It critically assesses how coupling anaerobic digestion with hydrothermal, thermochemical, advanced-oxidation, and membrane-based processes improves resource efficiency, energy balance, and contaminant control relative to standalone units, and weighs the techno-economic and life-cycle trade-offs of integration. On the recovery side, it synthesizes integrated pathways for phosphorus, nitrogen, bioenergy, carbon materials, and solid recovered fuel, together with emerging high-value products such as medium-chain fatty acids and plant biostimulants. It further evaluates artificial intelligence and machine learning for process prediction, optimization, mechanistic interpretation, and model selection, and the barriers to their full-scale deployment. Conventional mechanical, biological, and thermal treatments, sludge properties, and policy are set out as the context that frames these advances rather than as the focus of the review. Overall, sustainable sludge management will depend on integrated, risk-aware, and data-enabled recovery systems that treat sewage sludge as a secondary resource rather than a residual waste.
Petroleum leakage in karst regions poses persistent groundwater risks because rainfall-driven recharge can rapidly remobilise residual hydrocarbons retained within heterogeneous conduit–fracture networks. Yet the event-scale mechanisms governing rapid hydrocarbon flushing, delayed release, and persistence remain poorly constrained. We investigated a crude-oil-contaminated karst spring system in southwestern China, using eight months of high-frequency monitoring of rainfall, spring discharge, and petroleum hydrocarbon concentrations, complemented by tracer tests and concentration–discharge (C–Q) hysteresis analysis. Of 139 monitored rainfall events, 59 generated hydrologically effective recharge and measurable spring responses, exporting 26.25 tonnes of petroleum hydrocarbons. Cumulative export over the monitoring period reached 44.37 tonnes when artificial water-injection responses and intervening background-flow periods were included. Tracer breakthrough and C–Q hysteresis revealed a dual-domain transport pattern. Clockwise hysteresis occurred in 67.8% of the hydrologically effective events and was consistent with rapid conduit-dominated flushing through preferential-flow pathways. The remaining 32.2% exhibited anticlockwise hysteresis, indicating delayed, storage-controlled release from secondary fracture–storage zones, prolonged concentration tailing, and persistent low-level contamination. Log-transformed event-load analyses further supported the contrasting event-scale contaminant-export patterns associated with the two recharge–transport domains. The results indicate that short-term apparent attenuation mainly reflected source removal, rainfall-driven flushing, and progressive depletion of readily mobilisable residual hydrocarbons rather than uniform intrinsic degradation or self-purification. This dual-domain framework advances mechanistic understanding of contaminant persistence and provides a basis for rainfall-event-based monitoring, risk assessment, and emergency management of petroleum leakage in karst environments.
Urban sewer networks are increasingly recognized as significant sources of greenhouse gas emissions, yet the mechanisms controlling nitrous oxide (N2O) production and consumption within sewers remain poorly resolved. In this study, we conducted a field campaign in a community sewer network in Shenzhen, South China, using a stable isotope approach to investigate the N2O emission potential and its regulatory mechanisms. Measurable N2O emissions were observed across all sites, with headspace concentrations (within the inspection wells) ranging from 0.48 to 6.25 ppm and fluxes ranging from 0.01 to 0.27 mg N2O h-1. Under lower redox potentials, the septic tanks (STs) exhibited stronger N2O emissions than the wastewater pipes (WPs). In situ measurements of N2O isotopocule signatures (δ15Nbulk, δ18O, and site preference) facilitated source/sink identification, showing that denitrification was the dominant process for N2O production. This interpretation was consistent with dual nitrate isotope measurements, which suggested a clear isotopic imprint from denitrification pathways. More importantly, the natural isotopic compositions of N2O allowed us to quantify the fraction of N2O being reduced to N2 before emission (70∼93%), providing an important benchmark in assessing the variability of net N2O fluxes from the sewer network. Metagenomic data provided complementary evidence for understanding the distribution of N2O emission hotspots and production/consumption mechanisms. These results show that urban sewer compartments can function simultaneously as N2O sources and internal sinks, and that net vent emissions reflect the balance between gross N2O production and reduction within sewer systems.
Globalization of air travel accelerates transboundary dissemination of enteric pathogens, yet conventional border screening fails to capture asymptomatic infections, creating critical surveillance blind spots. This study establishes a three-stage hierarchical early-warning framework integrating (i) mining open-source epidemic intelligence, (ii) aircraft wastewater (AW) surveillance, and (iii) community wastewater (CW) monitoring to track viral importation and subsequent local transmission. Using the Seoul–Xi'an route as a proof-of-concept during the 2024–2025 winter–spring season, we integrated quantitative PCR and high-sensitivity hybrid-capture sequencing (HybCapSeq) of AW with nanopore-based clinical genomics and structured epidemiological questionnaires to resolve viral transmission chains. Results demonstrated that viral concentrations of six diarrheal pathogens in AW exhibited high-frequency fluctuations, contrasting with smoother, sustained elevations in CW. AW surveillance detected continuous norovirus (NoV) introduction from November 2024, preceding community outbreaks by 2–3 months. Comparative genomic analysis revealed that flight-associated importation initiated 12 cryptic local transmission chains. Phylogenetically, NoV GII.17 formed a Korean-specific monophyletic lineage with Xi'an strains nested within, indicating transboundary spread. Critically, clinical isolates exhibited extreme genetic homogeneity with local CW strains and the Korean AW strain. Epidemiological investigation confirmed that 85.7% (6/7) of pediatric cases had travel history to South Korea or close contact with returnees within 14 days prior to illness onset, providing closed-loop genomic and epidemiological evidence of aviation-imported transmission. By bridging aviation surveillance with CW epidemiology through closed-loop genomic-epidemiological validation, this framework provides a scalable template for mitigating transboundary infectious disease spread and strengthening global health security.
