Cristina Sousa Coutinho Calheiros

Introduction: Constructed wetlands (CWs) are widely applied as low energy, nature-based wastewater treatment systems, particularly in decentralized contexts, while microbial fuel cells (MFCs) are increasingly being investigated to recover energy through bioelectrochemical processes that are favored by the redox gradients present within CWs. The integration of these two sustainable solutions is gaining increasing attention due to its potential to generate synergistic benefits. However, despite the growing number of studies on CWMFC systems, there still remains a lack of consolidated synthesis regarding system design, performance outcomes, and intensification strategies (approaches that enhance process efficiency by accelerating reaction rates, improving electron transport, and maintaining redox stratification for stable system operation). Consequently, several critical knowledge gaps persist, including limited reporting on long-term stability and durability, insufficient economic assessments, lack of standardized design and performance metrics, and underrepresentation of microbial community structure and function. Methodology: This review covers CW-MFC studies published between 2010 and 2026 across several regions of the world and includes laboratory, mesocosm, pilot, and full-scale systems, focusing on system design, operational strategies, microbial processes, treatment, and energy recovery performance. Results: Most CW-MFC studies are at laboratory and pilot scale, with limited full-scale applications, and their performance depends primarily on reactor and flow regime configurations, electrode materials and their positioning, substrate type, and redox gradient profile. Many studies have reported encouraging Chemical Oxygen Demand (COD) and nutrient removal efficiencies, with values reaching up to 99% COD removal, 95% Total Phosphorus (TP) removal, and 100% ammonium-nitrogen (NH4 +-N) removal. CW-MFC systems generally improve organic matter and nutrient removal compared to conventional CWs; however, the electrical energy recovered is typically low and tends to decrease with increasing system scale. Discussion: Overall, CW-MFC systems are best regarded as sustainable, multifunctional wastewater treatment technologies rather than primary energy recovery systems, as their practical feasibility is more constrained by long-term stability, material durability, and insufficient economic reporting rather than by treatment performance.

This study provides a preliminary baseline characterization of macroinvertebrate assemblages colonizing floating islands installed in two NE Portuguese river reaches with contrasting anthropogenic and hydromorphological conditions: the urban, weir-influenced Fervença River and the more rural, reservoir-like Côa reach within a former dam-work area. A single campaign in February 2025 combined water characterization and macroinvertebrate sampling on islands and adjacent margins. Fervença showed higher mineralization and microbiological contamination, but a more varied assemblage dominated by tolerant taxa. Côa showed better water quality but strong Astacidae dominance. Results indicate colonization only; robust replicated monitoring is needed before inferring ecological improvement.

Floating wetland islands (FWIs), traditionally applied for ecological restoration and water purification, are increasingly recognized for their multifunctional potential. Their ability to combine environmental remediation with food production positions FWIs as a promising nature-based solution (NbS) for advancing sustainable development. To identify research trends and knowledge gaps in this emerging field, a bibliometric analysis and systematic review of FWIs for crop production were performed using the Scopus database. A total of 83 publications were identified between 2000 and 2024, the majority being research articles (78.3%), with “Environmental Sciences” as the predominant subject area (35.8%). China emerged as the leading contributor, accounting for 71 publications (16.9%). Keyword co-occurrence analysis revealed three main thematic clusters: “agriculture,” “hydroponics,” and “wetlands,” reflecting the interdisciplinary nature of FWIs, which combine elements of hydroponic cultivation, ecological engineering, and water quality management. The review emphasizes the importance of plant selection and system design, not only to enhance nutrient retention but also to maximize biomass productivity, particularly when the goal is to obtain harvestable crops. From an economic perspective, FWIs show favorable viability: revenues from crop sales often surpass operational costs, though construction remains the most significant investment. Social acceptance tends to be high when commercial value is demonstrated; however, barriers such as limited technical training and concerns over food safety remain. Despite varied terminology, FWIs systems consistently demonstrate multifunctionality, offering solutions for both ecosystem restoration and sustainable crop production. Graphical Abstract

Sustainable resource management in the face of climate change is a pressing challenge for our society. This paper delves into the water-energy-food-ecosystems (WEFE) nexus, a scientific framework that supports the integrated assessment and management of the interconnected resources. Shifting from sectoral to cross-sectoral and transdisciplinary perspectives, the WEFE nexus addresses interdependencies and interactions among water, energy, food, ecosystems, and climate. This paper focuses on the extended nexus, incorporating ecosystems as a fourth pillar, underscoring the importance of considering ecosystems on an equal footing with water, energy, and food sectors. In addition, the paper emphasizes the significance of monitoring and modelling techniques, laying the foundations for understanding the nexus complexities and assessing uncertainty. The paper offers an overview of integrated nexus modelling, system analysis and socio-economic modelling, bridging the gap between nexus science and practice. It highlights the role of multifaceted stakeholder engagement methods, policy assessment, and institutional analysis in nexus models. Quantifying the nexus through indicators, and its alignment with the Sustainable Development Goals, EU Green Deal, and EU Blue Deal are also key focal points. Finally, the last part of the paper addresses challenges in existing nexus modelling attempts, advocates for the integration of transdisciplinary information, and presents lessons learned. The paper concludes with recommendations for the future of the WEFE nexus, emphasizing its potential in fostering transformative change toward sustainable resource management and inclusive policymaking.

The concepts of “modularity” and “prefabrication” require a deeper understanding being crucial to investigate their relation with the circular economy. Prefabrication involves pre-manufacturing building elements off-site and their transport to the construction site and assembly. Prefabrication can be divided into different categories: Component, Non-volumetric, Volumetric, Modular construction, Hybrid structures, or Whole building prefabrication; and can be based on linear (e.g., columns or pillars), bidimensional (e.g., walls or floor panels), or tri-dimensional elements (e.g., modules or whole prefabricated houses). The most commonly used materials are steel, wood, and concrete, although plastic, composite, and nature-based materials are increasingly being explored. While comparing the prefabricated materials, steel has high embodied impacts but recycle and reuse potential, timber has biogenic content and high reuse potential, and concrete poses transport and assembly challenges. The refurbishment of prefabricated buildings and the use of prefabricated elements in refurbishment are also discussed. The main benefits of adopting prefabrication are impact, cost, material, waste, and time reduction, with quality increase; and the challenges are cultural, technical, and market aspects with some investment required. A bibliometric analysis explores the relationship between modularity, prefabrication, and circular construction and concludes that the link between the three concepts seems fragile and unclear.

Nature-based solutions (NBS) are frequently implemented without taking the system’s perspective into account and with the main focus on technical and economic issues of implementation. This study was conducted to test the hypothesis on the potential synergistic effects between circularity and NBS to holistically tackle urban challenges. The main objective is to establish preliminary insights on the obstacles and perspectives of NBS integration and implementation, through a questionnaire set up by the network of experts gathered within the COST Action CA17133 Circular City. The following research questions arise: (i) what differences exist in the level of NBS application according to the variance of engaged countries; and (ii) what are the main obstacles and perspectives for the NBS implementation in order to holistically tackle urban challenges, enhancing the sustainable connection among urban environment, nature, and human well-being. To go beyond the current state-of-the-art and reflect on the research conducted within the Circular City Action, this study aims to open a multi-geographical academic dialogue across Europe and beyond and to move towards a holistic approach to circular cities. Accordingly, this study is: (1) multi-geographical and context-based, providing input for thirty-three EU countries and four non-EU countries to give an overview of the main obstacles and perspectives of NBS implementation, and (2) approach-directed, aiming to formulate a holistic approach to deal with societal challenges. This document intends to provide qualitative and quantitative insight into the potentials and obstacles of NBS implementation in Europe, as well as to motivate further discussion and research to achieve holistic and sustainable cities.

Water quality assessment stands as a fundamental step in water resource management. In addition to substances and organisms present in the water, land use and land cover are two factors also affecting water quality. This study analyzed the correlation and influence between water quality and land use and land cover in the Miranda River Basin (MRB) and the natural wetlands in the Pantanal Biome. Using a watershed-wide approach, results suggested that water quality management policies can be considered in terms of sub-basins (smaller planning units). The Water Quality Index (WQI) was considered GOOD or EXCELLENT throughout the MRB. It was observed that the natural wetlands have the capacity to contribute to improving the WQI, with reductions in thermotolerant coliforms and turbidity; however, high values were found for thermotolerant coliforms, a temporal increasing trend of biochemical oxygen demand (BOD), and a reduction in dissolved oxygen and total phosphorus. Conversely, in these flooded areas, trends of a decrease in dissolved oxygen and an increase in BOD levels were found. Natural wetlands play important hydrological and ecological roles in water quality, storing, removing, and cycling nutrients. They are highly relevant areas for defining watershed management and conservation strategies, environmental protection, and providing ecosystem services.