Wastewater Treatment and Public Health Surveillance: Advances and Challenges in the One-Health Era

1. Introduction

Wastewater systems are increasingly central to One Health: they concentrate signals from human populations, reflect pressures from clinical care and community antimicrobial use, connect to agricultural and environmental pathways, and—through discharge and reuse—shape downstream exposure. In this landscape, wastewater is no longer only an endpoint of sanitation infrastructure; it is simultaneously an engineered barrier and a shared observatory where biological and chemical hazards can be tracked, interpreted, and mitigated (Fernando Molina-Ospina’s article (contribution 3), Andreas Nocker’s article (contribution 6) [1,2,3,4,5,6].

The COVID-19 era accelerated global adoption of wastewater- and environmental surveillance approaches and clarified their core value proposition: wastewater measurements can complement clinical surveillance by providing pooled, community-level signals that support trend detection and early warning, particularly when integrated with other data streams and communicated with clear uncertainty and ethical guardrails [7,8,9,10,11,12]. Yet the post-pandemic challenge is broader than any single pathogen. The One Health era requires surveillance and treatment capabilities that address complex mixtures of hazards [13,14,15,16]—including pathogens, antimicrobial-resistant bacteria and resistance determinants, pharmaceuticals and antibiotics, and other contaminants of emerging concern—and treat these hazards as linked through shared sources, selection environments, and infrastructure pathways.

A recurring limitation in this sector is the gap between “what we can detect” and “what we can reliably control.” Analytical capacity now spans molecular pathogen detection, metagenomic characterization of resistomes and mobile genetic elements, and chemical profiling of trace contaminants. Even so, programs remain heterogeneous in sampling design, normalization, QA/QC, and interpretation frameworks, undermining inter-site comparability and slowing translation from signal detection to public health action. For One Health practices, the next phase must prioritize decision-grade systems—systems that specify when and how wastewater signals trigger confirmatory testing, targeted interventions, operational changes, and risk communication and that make uncertainty explicit rather than implicit [1,12,17].

Antimicrobial resistance exemplifies why wastewater must be treated as both a surveillance target and a managed selection environment. The WHO’s Global Action Plan on AMR underscores surveillance, evidence-based action, and cross-sector coordination as core objectives. At the same time, environmental pathways are increasingly recognized as part of the resistance ecology, motivating surveillance beyond clinical isolates. Wastewater metagenomics has been proposed as an ethically acceptable and scalable complement for monitoring population-level AMR patterns across countries while also showing that wastewater microbial composition is shaped by wastewater ecology and environmental inputs as opposed to solely human fecal biomass [18]. The implication is practical: wastewater AMR surveillance should transcend “presence/absence” and move toward frameworks that consider mobility potential, persistence through treatment barriers, and co-occurring chemical pressures that may influence selection and transfer dynamics.

In parallel, the chemical dimension of One Health is becoming more operationally binding. Conventional biological treatment alone is frequently insufficient for broad-spectrum removal of hydrophilic pharmaceuticals and other persistent micropollutants, driving interest in advanced and quaternary barriers. This technical trajectory is increasingly matched by regulatory pull. The revised EU urban wastewater framework signals tighter expectations that include both enhanced treatment performance (including micropollutant-oriented stages) and the monitoring of wastewater for health parameters (José Gonçalves’s article (contribution 2) [19].

A One Health framing also requires expanding the interpretation of “treatment” beyond unit processes inside plant boundaries. Infrastructure-based risk reduction interacts with upstream service inequities and downstream environmental attenuation pathways, including nature-based processes where relevant. For surveillance and intervention to be equitable, water and wastewater governance must remain attentive to who benefits, where monitoring actually represents populations, and how infrastructure reliability shapes exposure risk and response capacity. The Quadripartite One Health Joint Plan of Action emphasizes strengthening capacities to prevent, detect, and respond across domains, an approach that aligns with positioning wastewater systems as nodes in wider health security and environmental protection architectures [20,21,22,23,24].

By collecting contributions across treatment innovation, surveillance approaches, and broader One Health determinants, this Special Issue underscores a central point: wastewater treatment and wastewater-based surveillance are converging into a single applied domain of prevention—one that must measure what matters, remove what persists, and translate signals into resilient, evidence-based public health and environmental protection.

2. The Knowledge Gaps Addressed by the Papers in This Special Issue

This Special Issue’s scope aligns with recent expansions of wastewater/environmental surveillance guidance and practices, wherein international and national public health bodies emphasize that wastewater data is complementary evidence of population-level trends and decision-making.

The first cross-cutting theme is that “what we can detect” has expanded faster than “what we can safely remove.” The study conducted by Molina-Ospina et al. (2025) illustrates this directly: even with stable conventional performance metrics, antimicrobial resistant gene (ARG) enrichment in effluent can occur, implying that treatment optimized for bulk parameters may inadvertently select for or release mobile resistance determinants and opportunistic pathogens Fernando Molina-Ospina’s article (contribution 3). Kengne et al. (2025) shows that electron-beam irradiation complements this insight on the chemical side: highly effective parent-compound degradation does not guarantee full mineralization, and transformation products and residual organic carbon remain a practical risk-management concern (especially for reuse scenarios) (Boris Tende Kengne’s article (contribution 4). Together, these contributions foreground a One Health-relevant mismatch: removal “efficiency” measured by traditional surrogates can diverge from removal of health-relevant biological hazards (viable pathogens, ARG mobility, etc.) and chemical hazards (e.g., transformation product toxicity).

The second theme is that antimicrobial resistance (AMR) is increasingly treated as both a surveillance target and a treatment design constraint. The studies published in this Special Issue identify mobile genetic elements and disinfectant/biocide-linked genes (e.g., qac-associated markers) in wastewater treatment plants (WWTPs) as part of a wider selection context, suggesting that disinfection chemistry, influent mixtures, and operational regimes may shape resistance propagation pathways as opposed to antibiotic residues alone. This notion aligns with the broader argument that wastewater-based epidemiology metagenomics can yield globally comparable resistome signals and that wastewater is not a pure proxy for fecal biomass but rather a complex matrix shaped by ecology and environmental inputs, thus complicating both inference and standard-setting. Complementing this perspective, Andreas Nocker’s article (contribution 6) evaluates the added value of membrane bioreactors (MBRs) combined with ozonation as an advanced treatment strategy, using antibiotic resistance genes and Bacteroidales as indicators of fecal contamination and genetic load. Their findings demonstrate that while conventional and advanced treatments can significantly reduce levels of microbial and genetic markers, residual signals may persist, underscoring the need for multi-barrier approaches and robust indicator frameworks. Importantly, this study reinforces the concept that treatment performance should be evaluated not only in terms of bulk removal efficiency but also in relation to health-relevant genetic markers, supporting the integration of surveillance targets directly into treatment design and validation (Andreas Nocker’s article (contribution 6)).

The third theme is that “treatment” should be interpreted more broadly than unit processes inside WWTP boundaries. Alevizos et al. (2025) demonstrate the potential of nature-based attenuation by explicitly modeling ecosystem capacity, associated co-benefits, and inherent limitations while emphasizing the critical need for long-term datasets and protocol harmonization to move from conceptual promise toward robust, design-grade evidence suitable for implementation (Vasileios Alevizos’s article (contribution 1).

Wastewater and water surveillance frameworks must also be interpreted within broader socio-environmental contexts, particularly when infrastructure limitations shape both exposure and data representativeness. The contribution by Da Mata et al. (2025) highlights household water insecurity in the Western Amazon, illustrating how limited access to safe water and sanitation services constrains both risk mitigation and the reliability of surveillance signals Mayline Menezes Da Mata’s article (contribution 5). This perspective reinforces a critical One Health insight: wastewater-based approaches cannot be decoupled from underlying service inequities, as gaps in access and infrastructure directly influence contaminant pathways, population exposure, and the interpretability of environmental data. Addressing these disparities is therefore essential for ensuring that surveillance and treatment strategies are both effective and equitable.

Together, these studies underscore the need to reconceptualize wastewater management as an integrated, system-scale intervention, one that bridges engineered infrastructure and natural processes within a coherent One Health framework to ensure resilient, evidence-based protection of public and environmental health.

The Special Issue’s stated scope directly targets this interface by emphasizing innovations that remove complex pollutant mixtures (biological and chemical) while also advancing wastewater-based epidemiology (WBE)-enabled health surveillance. The major unresolved challenges include establishing decision-grade interpretation frameworks (thresholds, uncertainty, and harmonization) for multi-target surveillance; validating how wastewater signals translate into health outcomes and intervention tiers; and creating scalable, low-carbon advanced treatment trains that manage transformation products and selection pressures while meeting reuse and discharge goals. These needs are repeatedly emphasized across official surveillance frameworks and WBE syntheses, which stress integration, comparability, and actionable interpretation rather than detection alone.

3. Future Directions and Regulatory Implications

The research priorities that are most “implementation-critical” within a One Health framework include (a) standardizing sampling design, QA/QC, normalization, and reporting across targets (pathogens, ARGs/MGEs, and chemicals); (b) developing integrated analytics that jointly model chemical pressures and biological outcomes (including gene mobility), enabling mechanistic interpretation rather than isolated indicator tracking; (c) developing treatment-by-design approaches to surveillance and reuse, where sampling nodes and barrier performance metrics are coordinated so that surveillance supports control and control supports health protection; and (d) implementing energy and life-cycle performance benchmarking for quaternary/advanced barriers in line with climate/energy expectations.

Regulatory implications are increasingly concrete in the EU context: monitoring wastewater for health parameters (including antimicrobial resistance) and strengthening treatment expectations for micropollutants are now framed as systemic requirements, not pilot-only concepts. For Guest Editors and researchers, this implies that study designs should anticipate regulatory endpoints, namely, (i) defensible indicator panels (including AMR-relevant markers), (ii) measurable performance criteria tied to health-protective outcomes, and (iii) comparability and auditing readiness (metadata completeness, reproducible pipelines, and transparent uncertainty).

The most consequential priorities for the field converge on integration. First, surveillance should mature from single-target detection into harmonized multi-target panels and transparent reporting frameworks that support comparability, modelling, and action. Second, advanced treatment for reuse and discharge protection should be evaluated based on mineralization and toxicity-informed endpoints, with explicit byproduct governance and energy/life-cycle benchmarking, especially as quaternary expectations expand. Third, AMR should be treated as a managed emission and selection context, motivating the use of indicator sets that include resistance determinants and mobility proxies and operational strategies that reduce selective pressures when feasible. Fourth, governance must connect wastewater signals to clinical and environmental decision structures, enabling timely, proportionate responses while protecting privacy and maintaining public trust. Finally, the One Health promise will be realized only if these advances are implemented with an equity lens, one recognizing that the highest marginal gains often occur where baseline service disparities are greatest and integrated monitoring can meaningfully guide protective investment.