Urban Water Pollution Control: Theory and Technology

1. Introduction

Water security and robust sanitation infrastructure are fundamental pillars supporting public health, ecological integrity, and sustainable urban development. Rapid urbanization, industrial expansion, and climate change have exacerbated longstanding challenges, including groundwater contamination, energy-intensive wastewater treatment, and the proliferation of emerging pollutants [1,2]. Addressing these complex issues effectively requires interdisciplinary approaches that integrate environmental engineering, data science, policy analysis, and sustainable resource management [3,4]. To showcase recent advances in these domains, the following Special Issue of Water, entitled “Urban Water Pollution Control: Theory and Technology,” was launched. This Special Issue brings together innovative research on pollutant behavior, monitoring technologies, treatment methods, and management frameworks aimed at enhancing the resilience and sustainability of urban water systems.

Following a rigorous peer-review process, seven high-quality articles—comprising one comprehensive review and six original research contributions—have been accepted for publication (Contributions 1–7). These studies collectively address several pressing themes: investment prioritization in sanitation infrastructure, groundwater quality assessment and prediction, energy efficiency in wastewater treatment, urban drainage modeling, advanced adsorption materials, and real-time pollutant monitoring. This Editorial provides a synthesized overview of these contributions, highlighting their theoretical insights, methodological innovations, and practical implications.

2. Overview of the Contributions to This Special Issue

2.1. Strategic Investment Prioritization in Sanitation Infrastructure

Asfor et al. (Contribution 1) developed a multicriteria decision analysis model using the Measuring Attractiveness by a Category-Based Evaluation Technique method to address the challenge of optimizing limited financial resources in Brazil’s sanitation sector. Their model integrates economic, environmental, regulatory, institutional, and socio-health criteria, including net present value, service coverage, and environmental impact. Applied in the Serra da Ibiapaba region, the approach generated a transparent investment ranking, with Guaraciaba do Norte emerging as the top priority due to its balanced performance across weighted criteria. This methodology provides municipal authorities with a defensible framework for aligning infrastructure investments with regulatory targets and local needs.

2.2. Advanced Groundwater Quality Assessment and Spatial Management

Balla et al. (Contribution 2) conducted an integrated assessment of groundwater quality in a Hungarian settlement nine years after sewerage system implementation. Combining water quality indices, geospatial analysis, and feed-forward neural networks, their findings revealed persistent contamination by inorganic nitrogen species and organic matter despite general improvement. The optimized neural network model demonstrated exceptional predictive accuracy (R² = 0.9916 for Water Quality Index), while through spatial analysis, specific areas requiring targeted intervention were identified. Complementing the above, Bousouis et al. (Contribution 3) applied multivariate statistical methods to classify groundwater bodies in France’s Bourgogne–Franche–Comté region, identifying 11 homogeneous groups with distinct hydrochemical signatures strongly correlated with geological substrate and land use patterns. This classification provides a scientific basis for designing differentiated monitoring networks and protection strategies.

2.3. Energy Efficiency and Regulatory Compliance in Wastewater Treatment

Capodaglio (Contribution 4) provided a comprehensive analysis of energy auditing requirements under the newly adopted EU Directive 2024/3019, which mandates energy neutrality for urban wastewater treatment plants. The author reviews adaptable audit frameworks and identifies common inefficiencies, including excessive aeration and outdated pumping systems. In addition, they advocate for integrated solutions encompassing process intensification, enhanced biogas recovery, and renewable energy integration, proposing the “Electrical Energy per Order” metric as a standardized performance indicator. This work highlights the imperative for technologically adaptive treatment paradigms in the evolving regulatory landscape.

2.4. Innovative Modeling and Treatment Technologies

Kheshti Azar et al. (Contribution 5) introduced a sensitivity analysis-aided calibration methodology for urban drainage models using EPA-SWMM. By combining global sensitivity analysis with genetic algorithm optimization, they efficiently identified six influential parameters from an initial set of eleven, achieving high model accuracy (R² > 0.85) with significantly reduced computational requirements. This approach enhances the practical utility of hydrodynamic models for real-time stormwater management. In the domain of contaminant removal, Wu et al. (Contribution 6) demonstrated the valorization of steel slag through high-temperature modification, achieving >95% removal efficiency for organophosphates. Mechanistic investigations revealed synergistic adsorption processes involving hydrogen bonding, surface complexation, and ligand exchange, with the material maintaining excellent regenerability over multiple cycles, offering a sustainable solution for emerging pollutant control.

2.5. Next-Generation Water Quality Monitoring Systems

La Cognata et al. (Contribution 7) presented a systematic scoping review of three prominent real-time monitoring technologies: colorimetric sensors, lab-on-a-chip (LOC) devices, and Raman spectroscopy. Their analysis, structured using the PRISMA framework, elucidates the complementary strengths and limitations of each technology in terms of sensitivity, cost, and operational complexity. The authors propose an integrated monitoring strategy whereby cost-effective colorimetric sensors provide widespread coverage, automated LOC systems enable on-site analysis, and SERS serves as a confirmatory method for ultra-trace detection. This layered approach supports the development of smart water networks capable of early contamination warning and adaptive management.

3. Conclusions

This Special Issue presents a cohesive and multidisciplinary collection of studies that significantly advance the theory and practice of urban water pollution control. Collectively, these contributions paint a clear picture of the current state of the field: a decisive shift from traditional, siloed approaches toward integrated, data-driven, and sustainable solutions. The studies underscore that effective water pollution control in the 21st century requires a synergistic combination of strategic governance (Contribution 1), advanced predictive analytics (Contributions 2 and 5), energy- and material-efficient technologies (Contributions 4 and 6), and high-resolution smart monitoring networks (Contribution 7). This body of work demonstrates that while technological innovation is crucial, its ultimate success is contingent upon its alignment with sound economic principles, adaptable regulatory frameworks, and localized management strategies.

Looking forward, this Special Issue not only showcases current progress but also raises critical new questions and charts essential pathways for future research and policy:

New Investigative Paradigms: The integration of physical models with artificial intelligence and the IoT, as hinted at in Contributions 2, 5, and 7, must be deepened. Future investigations should prioritize the development of hybrid AI–physical models that offer both high predictive accuracy and mechanistic interpretability. Furthermore, methods like multi-criteria decision analysis (Contribution 1) and systematic scoping reviews (Contribution 7) should be more widely adopted to bridge the gap between technical possibilities and socio-economic feasibility.

Evolving Pollution Challenges: Beyond the pollutants studied herein, the water sector must urgently prepare for a new generation of challenges. Research must accelerate on the fate, detection, and removal of micropollutants (e.g., pharmaceuticals and personal care products), microplastics, and antibiotic resistance genes. The concept of a “pollution cocktail”—the complex synergistic effects of multiple contaminants in water bodies—demands greater attention, requiring more sophisticated risk assessment and treatment design.

Policy and Actionable Science: The articles collectively signal a pressing need for policies that incentivize the transition to a circular water economy, which includes creating markets for recovered resources (e.g., nutrients, energy, and modified materials such as steel slag) and mandating energy neutrality in wastewater treatment. Future policies should also support the implementation of adaptive, real-time management systems based on sensor networks and models, moving away from static, compliance-driven monitoring.

By fostering continued innovation across these interconnected fronts—technological, digital, and policy-oriented—the scientific and engineering community can meaningfully contribute to the global goals of water security, ecological health, and sustainable urban development.