Urbanization has exacerbated urban heat island (UHI) effects, posing challenges to thermal comfort, energy efficiency, and urban resilience. Urban green and blue infrastructure (UGBI) offers effective cooling solutions; however, their performance varies significantly across urban morphology, climate zones, and local contexts. This review synthesized 203 empirical studies conducted in 102 cities across 43 countries and 23 Köppen climate zones, offering a comprehensive evaluation of UGBI cooling intensity, spatial reach, and influencing factors. We provide three key recommendations to enhance climate adaptation: (1)establish a standardized evaluation framework for UGBI cooling effects, integrating data collection, modeling approaches, and indicator systems to enhance cross-study comparability; (2)analyze variability in UGBI performance across diverse climatic and urban contexts, highlighting how factors such as vegetation density, urban geometry, and socioeconomic constraints influence cooling intensity and attenuation; (3) explore synergistic interactions between UGBI, urban morphology, and innovative materials, proposing integrated strategies for sustainable urban planning. By bridging critical gaps in cross-climatic comparisons and offering actionable insights, this review provided practical guidance for enhancing urban resilience to climate change.

How to cite: Yang, M., He, J., and Lu, T.: Urban green and blue infrastructure and microclimate regulation: a systematic review of urban heat island and urban planning strategies , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1902, https://doi.org/10.5194/egusphere-egu25-1902, 2025.

Climate change impacts increasingly affect human wellbeing worldwide, particularly through consequences of extreme weather events such as heavy precipitation, flooding and heat. Densely populated areas face greater exposure to these hazards than rural areas. The Urban Heat Island (UHI) effect exacerbates the impacts of heat in cities. Nature-based solutions (NbS) such as green and blue infrastructure can be used to adapt to climate change effects and mitigate urban heat stress as well as extreme precipitation impacts. Adaptation measures like urban green spaces (parks, gardens), street trees, vegetation on buildings (facade, roof greenings), water bodies or grass grid paver unsealings have significant cooling effects, enhance water retention and thus can increase thermal comfort and flood resilience of urban dwellers. While Cologne is recognized for its abundance of green spaces like the inner and outer `green belt´, there is still potential to improve and expand existing NbS to more effectively mitigate the challenges of climate change and the UHI effect. The successful implementation of additional NbS to address these challenges is dependent on public acceptance as the establishment and maintenance often rely on public participation. As part of the AKT@HoMe Project aiming to analyse the climate change adaptation potential through citizen participation by assessing the willingness to act and operational empowerment of residents in two socioeconomically contrary districts in the city of Cologne, this research is dedicated to analyze the acceptance of and the activation potential for the implementation of NbS.  

To understand residents’ perception of heat stress and the acceptance of NbS in the two districts, we conducted an anonymous survey, achieving over 150 responses. The survey utilized a quantitative, self-administered questionnaire, available in online and paper-based formats. Distribution took place via community events, mailbox inserts, and online platforms between summer 2024 and winter 2024/25. Results show that residents of both districts experienced a high level of heat stress in the past and expect a further increase in future. Preferences for mitigation measures include urban parks and forests, water-permeable pavers, and street trees among other, but also technical, solutions. NbS and hybrid measures are preferred over solely grey measures. Despite a high willingness to act, such as creating and maintaining NbS at home and in the city district, only few of the surveyed residents currently already engage in such activities.  

This gap was further examined through workshops with residents from both districts. Throughout three independent sessions citizen were participating in a three hour `future workshop´, working out future scenarios and options to adapt to UHI in their districts. The findings show that residents see the city government as primarily responsible for implementing NbS but also desire a more active role in the process to foster greater engagement, for example through neighbor groups. This highlights the need for a co-creation process between civil society and the public sector, ensuring that residents can actively contribute to the successful implementation and upkeep of NbS. 

How to cite: Ehresmann, S., Moraw, L., Eingrüber, N., Dlugoß, V., and Nehren, U.: Citizen perception of and activation for implementing Nature-based Solutions (NbS) against heat stress in the city of Cologne, Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4850, https://doi.org/10.5194/egusphere-egu25-4850, 2025.

Nature-based solutions (NbS) are gaining recognition as increasingly effective strategies to confront the escalating challenges posed by climate change and urbanization. By utilizing natural processes and ecosystems, NbS offers sustainable approaches to enhancing urban resilience, mitigating climate extremes, and improving environmental quality. These solutions, which are a form of blue-green infrastructure include green roofs and bioretention cells. They address critical issues such as flooding, heatwaves, and biodiversity loss while providing additional benefits like improved air quality and recreational spaces.

Within the Horizon Europe project NBSINFRA, the potential of NbS is investigated through City Labs experimental hubs established to implement, monitor, and refine NbS in diverse urban settings. Prague is one of the five City Labs, showcasing innovative NbS projects in collaboration with local stakeholders and institutions. A key site within the Prague City Lab is the University Centre for Energy Efficient Buildings (UCEEB), where advanced NbS technologies, such as green roofs and bioretention cells, are implemented and observed to assess their effectiveness in enhancing urban resilience. The presented study primarily focuses on the hydrological behavior and long-term performance of a small experimental bioretention cell at UCEEB, which serves as a critical component of the Prague City Lab.

This study outlines a five-year experiment conducted on the bioretention cell at UCEEB, designed as a multilayered system with a biofilter composed of 50% sand, 30% compost, and 20% topsoil, sand layer and a drainage layer, planted by perennial vegetation. Bioretention cell is isolated from the surrounding soil by a waterproof membrane and is instrumented by a system of sensors. Four time-domain reflectometry probes monitor soil water contents of biofilter and five tensiometers record the water potential in a biofilter. The amount of a discharge from bioretention cell is recorded by a tipping bucket flowmeter and inflow is measured by rain gauge. Over the course of five years, the study focused on parameters such as water balance, retention capacity, soil water potential, and plant growth to evaluate the cell's hydrological performance and its evolving efficiency.

Results of experimental study and modeling using HYDRUS 2D revealed significant temporal changes in the performance of the bioretention cell. The runoff coefficient decreased over time due to increased evapotranspiration. Peak flow reductions ranged from 30% to 100% for individual rainfall epizodes. Median runoff delays were approximately 50 minutes, and peak flow delays varied from 0 to 100 minutes, indicating increasing variability over time. Inverse modeling in Hydrus 2D demonstrated a fivefold increase in the saturated hydraulic conductivity of the biofilter, alongside with a decrease in the saturated hydraulic conductivity of the sand layer. These findings offer valuable insights into the long-term performance of bioretention cells and their contributory role in advancing sustainable urban stormwater management through NbS.

How to cite: Maresova, P. and Snehota, M.: Evaluating the Long-Term Performance of Bioretention Cell: A Five-Year Study from the Prague City Lab, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9804, https://doi.org/10.5194/egusphere-egu25-9804, 2025.

In recent decades, mountain villages have experienced significant depopulation, that, coupled with the devastating effects of climate change, has led to conditions of decay and neglect. Therefore, it is essential to implement measures aimed at promoting repopulation, enhancing tourism, and ensuring hydrogeological safety in these areas. In this context, Nature-based Solutions (NBS) represent a promising approach for the restoration of such locations, offering a range of services to address emerging societal and development challenges especially climate change, water security, human health, disaster risk and socio-economic development.

To address these needs, a greywater recovery and management systems has been developed within the framework of the NBS4MOV project ^[1]. The project is developing a stand-alone green wall technology to treat and reuse greywater (i.e. the wastewater generated from domestic activities excluding toilet flush) in buildings. This technology is made up of 3 levels of greenery and a collecting tank as a base. Each level is composed by 4 pots containing a mixture of perlite and coconut fibre and different plant species: Carex morrowii, Hedera helix and Lonicera nitida.

The pots are arranged to form 4 columns, each one representing an independent vertical flow intermittently supplied by greywater. The entire structure has been constructed primarily using durable and recyclable materials, assembled without adhesives to allow for disassembly and reuse of components at the end of their lifecycle, complying with circular economy principles.

The preliminary experimental phase included laboratory tests to assess the performance of the technology before field installation. Initially, tests were conducted on the substrate at varying moisture levels to evaluate its drainage capacity. This information is crucial for sizing the system based on the volume of greywater to be treated. Subsequently, as the prototype is intended for installation in a mountainous environment, tests were conducted in a cold chamber to evaluate the effects of external temperatures on system performance.

Results highlight that the limited thermal insulation of the structure and the small size of the pots led to rapid freezing. However, the presence of water in the substrate (with a moisture content of 50%) was found to delay freezing times. Possible solutions to address these challenges are currently under investigation.

Despite these challenges, the technology, designed as a living wall with a high level of customization, can be integrated with buildings, enhancing their architectural value, and adapting to the specific characteristics of the installation site. For these reasons, the system holds significant potential for the regeneration and development of resilient areas, not only in isolated rural villages but also in more urbanized contexts, with direct implications at urban and social levels.

[1] NBS4MOV is the acronym for Nature-based Solutions for Mountain Villages, and it is part of the project NODES which has received funding from the MUR – M4C2 1.5 of PNRR with grant agreement no. ECS00000036

How to cite: Fasano, C., Bosio, R., Cagninei, A., Boano, F., and Costamagna, E.: Prototyping NBS: a living wall system to enhance the built environment resilience in mountain areas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16856, https://doi.org/10.5194/egusphere-egu25-16856, 2025.

Wastewater treatment in lagoons: a systematic review and a meta-analysis

Demetrio Antonio Zema^1,*, Paolo S. Calabrò², Domenica Pangallo¹

²    Mediterranean University of Reggio Calabria, AGRARIA Department, Loc. Feo di Vito, I-89122 Reggio Calabria, Italy

¹ Mediterranean University of Reggio Calabria, DICEAM Department, Via Graziella, loc. Feo di Vito, I-89122 Reggio Calabria, Italy

Corresponding author: Demetrio Antonio Zema (dzema@unirc.it).

Abstract

This study has carried out a systematic review of 36 scientific papers (reporting 63 case studies) published in the last 15 years about the treatment of industrial, agri-food and municipal wastewater in lagoons. A concentration of studies from a few countries (Italy, Algeria and Iran) and about municipal wastewater (70% of papers) was revealed by the bibliographic analysis. Aeration was supplied in more than 50% of case studies; the storage capacity of lagoons (adopted as a measure of size) was extremely variable (over seven orders of magnitude), while their depth was generally lower than a few metres. The efficiency of lagoon treatments at removing COD was in a wide range (25-98%). Very few studies analysed the energy intensity of treatments in lagoons. The meta-analysis applied to a further selection of 10 papers with 29 case studies revealed significant differences in pH and dissolved oxygen concentration, due to aeration or type of treated wastewater. Treatment efficiency was higher in aerated lagoons compared to non-aerated systems, and did not depend on the type of treated wastewater. Based on the analysis of the reviewed papers, an urgent research need on this topic arises, mainly due to the oldness of most analysed studies. Practical suggestions are given to optimise the depuration performances of lagoons: (i) application of intermittent and night aeration; (ii) reduced air flow rates; (iii) adaptation of microbial biomass to high contents of inhibiting compounds in wastewater; (iv) construction of baffles to keep the planned hydraulic retention time avoiding short-circuit; (v) integration of lagoons with other treatments (e.g., constructed wetlands); (vi) ferti-irrigation of crops with lagoon effluents rather than disposal into water bodies.

Keywords: Chemical Oxygen Demand; aeration; dissolved oxygen; agri-food wastewater; municipal wastewater; COD removal rate.

How to cite: Pangallo, D.: Wastewater treatment in lagoons: a systematic review and a meta-analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5639, https://doi.org/10.5194/egusphere-egu25-5639, 2025.

The bioelectrochemical systems are sustainable solutions to face energy, water, and wastewater-related challenges. A three-chambered bioelectrochemical system, known as a microbial desalination cell (MDC), operates on the combined principles of a microbial fuel cell and electrodialysis. This self-powered system is capable of simultaneously treating wastewater and desalinating seawater. In the anodic compartment, microbial digestion of organic substrate treats wastewater. At the same time, the potential generation across the anode and cathode, resulting from electron production during the degradation process, leads to seawater desalination. Additionally, the oxygen reduction reaction (ORR) in the cathodic chamber significantly contributes to the overall performance of the system. Enhancing the ORR of the cell through catalyst incorporation has been shown to improve the system’s performance. The addition of a Sr-Mn-based perovskite, an abundant transition metal oxide compound, was synthesized using a facile method to be used as a cathode catalyst. The performance of the catalyzed reactor was compared to a non-catalyzed system with carbon electrodes. The addition of a catalyst resulted in a COD removal of 81.1 ± 0.5%, which was 35.5% higher than that recorded in the scenario without a catalyst. Similarly, in terms of desalination, the MDC with catalyzed cathode exhibited an 83.3 ± 1.2% desalination efficiency compared to the control MDC (45.76 ± 1.4%). This improved electrocatalytic performance of the system due to the catalyst was explained through the electrochemical analysis of the synthesized perovskite. The non-reliance of the MDC system on any external power source makes it a self-sustained and green technology for performing wastewater treatment and saltwater desalination, contributing to the Sustainable Development Goal 6 of clean water and sanitation.

How to cite: Mishra, S., Dubey, B. K., and Ghangrekar, M. M.: Perovskite-based catalyst for sustainable wastewater treatment and seawater desalination through microbial desalination cell, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1039, https://doi.org/10.5194/egusphere-egu25-1039, 2025.