Water in the city is typically exploited in a linear process, in which most of it is polluted, treated, and discharged; during this process, valuable nutrients are lost in the treatment process instead of being cycled back and used in urban agriculture or green space. The purpose of this paper is to advance a new paradigm to close water cycles in cities via the implementation of nature-based solutions units (NBS_u), with a particular focus on building greening elements, such as green roofs (GRs) and vertical greening systems (VGS). The hypothesis is that such “circular systems” can provide substantial ecosystem services and minimize environmental degradation. Our method is twofold: we first examine these systems from a life-cycle point of view, assessing not only the inputs of conventional and alternative materials, but the ongoing input of water that is required for irrigation. Secondly, the evapotranspiration performance of VGS in Copenhagen, Berlin, Lisbon, Rome, Istanbul, and Tel Aviv, cities with different climatic, architectural, and sociocultural contexts have been simulated using a verticalized ET₀ approach, assessing rainwater runoff and greywater as irrigation resources. The water cycling performance of VGS in the mentioned cities would be sufficient at recycling 44% (Lisbon) to 100% (Berlin, Istanbul) of all accruing rainwater roof–runoff, if water shortages in dry months are bridged by greywater. Then, 27–53% of the greywater accruing in a building could be managed on its greened surface. In conclusion, we address the gaps in the current knowledge and policies identified in the different stages of analyses, such as the lack of comprehensive life cycle assessment studies that quantify the complete “water footprint” of building greening systems.

The linear pattern of production-consumption-disposal of cities around the world will continue to increase the emission of pollutants and stocks of waste, as well as to impact on the irreversible deterioration of non-renewable stocks of raw materials. A transition towards a circular pattern proposed by the concept of ‘Circular Cities’ is gaining momentum. As part of this urban transition, the emergent use of Nature-based Solutions (NBS) intends to shift public opinion and utilize technology to mitigate the urban environmental impact. In this paper, an analysis of the current research and practical investments for implementing NBS under the umbrella of Circular Cities is conducted. A combined appraisal of the latest literature and a survey of ongoing and completed National-European research and development projects provides an overview of the current enabling tools, methodologies, and initiatives for public engagement. It also identifies and describes the links between facilitators and barriers with respect to existing policies and regulations, public awareness and engagement, and scientific and technological instruments. The paper concludes introducing the most promising methods, physical and digital technologies that may lead the way to Sustainable Circular Cities. The results of this research provide useful insight for citizens, scientists, practitioners, investors, policy makers, and strategists to channel efforts on switching from a linear to a circular thinking for the future of cities.

Pipelines that supply water from water resource to the reservoirs constitute an important part of water supply system construction. In this study, environmental impacts of construction of pipeline component of a water supply system in Van, Turkey are investigated using Life Cycle Assessment (LCA) methodology. Construction of pipelines is executed using conventional open cut system. Life cycle inventory (LCI) of the study is generated using primary data gathered and GaBi Professional database is used for background processes. CML 2001 was the environmental impact assessment method used. According to the results, the main contributors to AP, FAETP, GWP, HTP, MAETP are raw materials used for the production of pipelines which are high density polyethylene granules and carbon black. Most of TETP is generated because of installation of pipelines and sand used for backfilling the pipe trenches is responsible of this. Production and installation of pipelines end up with ADP due to the used materials. Transportation activities executed during the construction of pipelines have environmental impacts in every category considered; however, their contribution is not significant compared to the other activities conducted.

The Belgian Continental Shelf is a highly used part of the North Sea, where many different maritime activities thrive, such as shipping, fishing and energy production. Offshore wind energy in particular has gained importance in the region and concessions zones are allowed to be combined with aquaculture activities. It is unclear what the environmental impact of maritime multi-use is, from a life-cycle perspective, where there is potential to create synergies in the value chains, and how similar the impact compares to currently used alternatives. Therefore, this study performs a Life Cycle Assessment on a combination of a full scale existing wind energy farm and a mussel farm design. When analyzing the net environmental impact results of the multi-use offshore farm at the level of three areas of protection, i.e. human health, ecosystem quality and natural resources, it shows that the mussel farm contributes relatively the most to the net impacts, while the majority of the avoided burdens are attributed to the wind farm. Mainly the supply chain of materials required to manufacture its components followed by the operational activities of the multi-use offshore farm contribute to the environmental footprint. Moreover, taking advantage of joint activities, i.e. combined transport between the wind and mussel farm during operational activities (Scenario 1) and at decommissioning phase (Scenario 2) did not show a significant reduction in the overall net impacts of a multi-use farm. The life cycle assessment results of a multi-use offshore farm are furthermore compared with relevant terrestrial benchmarks in Belgium, i.e. nuclear energy and pork meat production. While the benchmarks have a high burden on the area of protection ecosystem quality due water and land use requirements, the multi-use farm mainly impacts the remaining areas of protection, i.e. human health and natural resources, again as a consequence of the burdens of its supply chain. This study reveals the potential of offshore multi-use farms in terms of environmental sustainability, offering valuable insights to policy-makers and value chain actors, and generally contributes to well-informed decision-making.

Circular economy (CE) approaches highlight the potential of construction materials to achieve circularity and sustainability in resource-efficient construction systems and industries. Implementing CE at the material level involves factors such as efficiency, durability, waste reduction through recirculation, and replacement, while encompassing criteria that define circularity in building materials. Understanding the inherent characteristics and behaviours of these materials is crucial for maximising their circularity potential. This chapter analyses key properties of traditional construction materials, such as concrete and steel, alongside novel sustainable materials like bamboo, timber, and biomaterials. It identifies and proposes methods to promote circularity at the material level. Additionally, the chapter explores the application of CE principles to both traditional and innovative construction materials. Furthermore, the chapter discusses indicators designed to assess circularity at the material level, serving as valuable tools for informing decision-making and implementation practices in the construction sector. Various types of indicators are presented, categorised as strategic, generic performance, performance, and water consumption indicators. Strategies aligned with waste hierarchy principles are outlined, emphasising the reduction of construction and demolition waste, lowering greenhouse gas emissions, conserving energy, and optimising costs and water resources.