Water Cycle and Circular Economy: Developing a Circularity Assessment Framework for Complex Water Systems

Wastewater treatment plants circular performance models evaluation: Portugal case-study

Population growth, economic growth, and changes in societal habits have led to significant changes in resource consumption. Therefore, it's crucial to accelerate the "reduce, reuse, recycle, and recover" of resources to ensure the balance of ecosystems, and water is surely one of the most fundamental resources. The acceleration of this approach in the water cycle makes sense only if we combine a circular economy (CE) transition with a sustainable perspective. In this context, more rational usage of water resources (which are under pressure) and more sustainable wastewater practices are expected to be a way towards the CE in the water and wastewater sector. This study provides a description and evaluation of existing frameworks that can be used to measure and assess the level of circularity of the wastewater treatment plant (WWTP). The treatment of urban wastewater requires new concepts of management and operation for the adaptation of existing plants, which lack robustness and flexibility, to face these new challenges and requirements because we can no longer continue to look at the WWTP only as treatment units, but as wastewater resource recovery facilities. This transformation must be transposed according to a matrix that allows the assessment to describe the current situation, analyse the problem, identify vulnerabilities and opportunities, identify, and evaluate measures, and identify and evaluate strategies. Considering that decision-makers face profound uncertainties such as climate change, population growth, population needs, innovative technologies, economic developments, ecosystem preservation and the impacts of human and natural activities.

Water-related ecosystem services interactions and their natural-human activity drivers: Implications for ecological protection and restoration

Sustainable development faces the crucial challenge of safeguarding water-related ecosystem services, particularly in arid regions. However, scale-dependent interactions and their influencing factors remain unclear. This study addresses this local gap on the regional level by focusing on ecologically vulnerable mountain areas, employing a comprehensive quantitative and spatial analysis approach, utilizing Spearman coefficient, trade-off/synergy index, and trade-off/synergy criterion, to examine water-related ecosystem services interactions across scales in arid area. Additionally, a Geographical detector was used to identify dominant natural and human activity factors. Finally, we determined ecologically optimal and worst areas and proposed spatial planning and management recommendations for ecological protection and restoration. Key results indicate that: (1) From 1995 to 2015, water yield and nutrient delivery ratio exhibited a declining trend, while soil retention showed an increasing trend, with the weakest nutrient delivery ratio function in the reserve. (2) At the grid scale, there were 2 trade-offs among water-related ecosystem services in 1995, which decreased to 1 trade-off in 2005 and 2015. The synergistic was most prominent near Qinghai Lake, while the trade-off was most obvious in the western mountainous areas. Conversely, the county scale demonstrated synergy. (3) NDVI, slope, and precipitation dominantly influence the spatial heterogeneity patterns of soil retention_water yield, soil retention_nutrient delivery ratio, and water yield_nutrient delivery ratio, respectively, with natural factors outweighing human activities in impacting water-related ecosystem services. This study contributes to the improvement and optimization of ecological environment management decisions.

Water innovation in industrial symbiosis - A global review

Motivated by the limited attention given to water management in industrial symbiosis research, this study presents the first global review of water innovation practices in the implemented industrial symbiosis cases reported in literature. We analyze the prevalence of global water innovation practices extending beyond the commonly used broad practices of water treatment and reuse to propose six categories, including utility sharing for alternative water supply, utility sharing for wastewater treatment, water recovery, energy recovery from water, material recovery from water, and material exchange to enhance water/wastewater treatment. Our findings highlight regional variations in adoption, with Asian and Europe showcasing diverse practices. Additionally, they indicate that most symbiosis cases center on the extensive role of public utilities and shared water facilities in pursuing water innovation, while 'pure' interfirm water-related symbiosis is limited. Finally, this review highlights extensive knowledge gaps and research needs in advancing sustainable water management and innovation in industrial symbiosis. Overall, our study contributes to the development of a comprehensive framework for water innovation practices in industrial symbiosis and emphasizes the need for future research in this area.

Evolution and attribution of ecological flow in the Xiangjiang River basin since 1961

Climate change and human activities have greatly altered the ecological flow of rivers, and the conflict between human water use and natural water demand is becoming more and more prominent. Using two ecological flow indicators (ecodeficit and ecosurplus), this study focuses on assessing the characteristics of ecological flow changes at multiple time scales and introduces the Long Short-Term Memory model to construct a meteorological streamflow model for the Xiangjiang River (XJR) basin, using a separation framework to quantify the effects of human disturbance and climate change on ecological flow at multiple time scales. In addition, the fluvial biodiversity Shannon Index (SI) was used to assess the response processes of riverine ecosystems under changing conditions. The results show that the increase of XJR flow is larger (11%) after 1991, the increase in precipitation and potential evapotranspiration in the basin is 5.60%, and the decrease is 3.09%, respectively, and there are obvious cycles of all three on annual and seasonal scales. The annual ecosurplus increased, and the annual ecodeficit decreased after the hydrological variation; on the seasonal scale, the ecodeficit decreased significantly in summer and autumn, and the ecosurplus increased substantially in winter. Climatic factors were the main drivers of the increased frequency and magnitude of annual, summer, and fall high flows (91%, 94%, and 65% contributions, respectively), while urbanization expansion and reservoir diversions drove the increase in spring ecodeficit. Changes in river flow maintained the ecosurplus at a low level after 2002, further causing a decrease in river biodiversity, and the annual and summer ecosurplus were highly correlated with SI indicators (0.824 and 0.711, respectively). Our study contributes to the development of effective ecological flow regulation policies for the XJR basin.

Quantifying the impacts of a proposed hydraulic dam on groundwater flow behaviors and its eco-environmental implications in the large Poyang Lake-floodplain system

Dam-induced hydrological alterations and eco-environmental impacts have significant implications, however, these concern issues in large floodplain systems are less well understood. The present study shows a first attempt to adopt a quasi-three-dimensional groundwater flow modeling FEFLOW (Finite Element subsurface FLOW system) to investigate the influences of a proposed hydraulic dam on groundwater dynamics in the largest floodplain lake of the Yangtze River basin (Poyang Lake, China). The FEFLOW model was successfully constructed and has the ability to represent the hydrodynamics of floodplain groundwater flow. Model simulations indicate that, in general, the dam is likely to increase the groundwater levels across the floodplain during different hydrological phases. The responses of floodplain groundwater levels to the dam during the dry and recession phases are stronger (∼2-3 m) than the rising and flooding phases (<2 m). Under the natural condition, the floodplain groundwater may recharge the lake during the dry and recession phases, and discharge the lake during the rising and flooding phases. However, the dam regulation may alter the natural recharge-discharge patterns, forming a generally gaining condition of the floodplain groundwater. The proposed dam is most likely to reduce the groundwater flow velocity (∼<1 m/d) relative to the natural condition (up to 2 m/d) during different hydrological phases, and it may also alter the floodplain groundwater flow direction during the dry and recession phases. Additionally, the floodplain groundwater system is mainly characterized by losing state (-4.5 × 10⁶ m³/yr) under the natural condition, while the dam-induced groundwater system exhibits an overall gaining state (9.8 × 10⁶ m³/yr). The current research findings contribute to future water resources assessment and management by providing a foundation for assessing associated eco-environmental changes of the large lake-floodplain system.

Why are decentralised urban water solutions still rare given all the claimed benefits, and how could that be changed?

Numerous innovative decentralised urban water solutions have been described over many years, yet their application in practice is still not common at all. While many proposed solutions may have some techno-economic advantages over current systems, the real reasons for the slow uptake have more to do with system-wide inertia and technology 'lock-in' where existing solutions are preferred for simplicity and familiarity. A key factor is also the inadequate assessments in project decision making processes that should consider all relevant social, environmental and economic benefits and values. This paper highlights some key barriers and how to address them in a more holistic way. It also identifies opportunities where more integrated, hybrid solutions could offer significant benefits over current technologies. It calls on all key partners in this sector to foster broad and strong collaborations, and on water service providers to be empowered to take an inclusive leadership role in creating such innovative solutions that help address our growing challenges driven by rapid urbanisation and climate change.

Novel PVDF-PEG-CaCO3 Membranes to Achieve the Objectives of the Water Circular Economy by Removing Pharmaceuticals from the Aquatic Environment

In the aquatic environment, substances of pharmacological origin are common contaminants. The difficulty of removing them from water is a problem for the implementation of a circular economy policy. When recycling water, an effort should be made to remove, or at least, minimize the presence of these substances in the water. Porous membranes with a new functionality consisting in their adsorption capacity towards pharmaceutical substances have been developed. A Polyvinylidene Fluoride (PVDF) membrane with Calcium Carbonate (CaCO₃) nanoparticles as an adsorbent was prepared. By implementing an integrated filtration-adsorption process using sulphadiazine, as a representative of pharmacological substances, 57 mg/m² of adsorption capacity has been obtained, which is an improvement in adsorption properties of more than 50 times that of a commercial membrane. At the same time the membrane permeability is 0.29 m³/(h·m²·bar), which means that the membrane's permeability was improved by 75%.

Increasing resource circularity in wastewater treatment: Environmental implications of technological upgrades

A paradigm shift is needed in wastewater treatment plants (WWTPs) to progress from traditional pollutant removal to resource recovery. However, whether this transformation produces overall environmental benefits will depend on the efficient and sustainable use of resources by emerging technologies. Given that many of these technologies are still being tested at the pilot scale, there is a lack of environmental assessments quantifying their impacts and benefits. In particular, an integrated approach to energy and nutrient recovery can elucidate the potential configurations for WWTPs. In this study, we conduct a life cycle assessment (LCA) of emergent wastewater treatment technologies aimed at increasing resource circularity in WWTPs. We focus on increasing energy self-sufficiency through biogas upgrades and a more radical circular approach aimed at nutrient recovery. Based on a case-study WWTP, we compare its current configuration with (1) implementing autotrophic nitrogen removal in the mainstream and deriving most of the organic matter for biogas production, which increases the quality and quantity of biogas available for energy production; (2) implementing struvite recovery through enhanced biological phosphorus removal (EBPR) as a radical approach to phosphorus management, offering an alternative to mineral fertilizer; and (3) a combination of both approaches. The results show that incremental changes in biogas production are insufficient for compensating for the environmental investment in infrastructure, although autotrophic nitrogen removal is beneficial for increasing the quality of the effluent. Combined phosphorus and energy recovery reduce the environmental impacts from the avoided use of fertilizers and phosphorus and the nitrogen release into water bodies. An integrated approach to resource management in WWTPs is thus desirable and creates new opportunities toward the implementation of circular strategies with low environmental impact in cities.

Assessing circularity of multi-sectoral systems under the Water-Energy-Food-Ecosystems (WEFE) nexus

The Multi-Sectoral Water Circularity Assessment (MSWCA) is a methodological framework developed for circularity assessment of the Water-Energy-Food-Ecosystems nexus. It involves five methodological steps and includes an indicators list for the selection of case-specific indicators. This study expands the MSWCA to provide a systematic approach for selecting indicators, considering system's circular actions and multi-functionality, the capture of implemented changes, the three CE principles and the sustainable development goals. Furthermore, this study differentiates between benchmark and dynamic circularity assessment and applies the expanded MSWCA in a water system of the HYDROUSA H2020 project. The benchmark assessment indicates that the HYDROUSA system achieves a 75% increase of water circularity, 76-80% increase of nutrients circularity and 14% reduction of operational `carbon footprint compared to the baseline scenario. The dynamic assessment highlights that additional measures can improve the system's circularity performance (e.g. water circularity can reach 94%) and mitigate risks occurring from uncontrollable changes.

Horizon scanning process to foresight emerging issues in Arabsphere's water vision

The Arabsphere struggles with highly complicated water challenges due to climate change, desertification, coronavirus pandemic, and Russo-Ukrainian War. This paper explores how to build a robust water vision to pave the road to achieving sustainable development goals (SDGs) in the Arabsphere. A sustainable water future (SWF) necessitates an interdisciplinary and transdisciplinary research strategy. 'Horizon scanning' process (HSP) is one of the promising foresight methodologies. A generic process for "Horizon scanning" has been developed to cope with water crises and challenges. "DEEPEST" holistic framework has been designed to suit both the "Futurology" science and water, environment, and engineering disciplines. "DEEPEST" characterizes Demographics, Ecological, Environmental, Political, Economic, Social, and Technological features. The macro-future factors (MFF) applied in the foresight process (FP) have been presented. The results showed that Water conservation (WC), Circular Water (CW), and Emerging Water Technologies (EWTs) were the main outcomes of the 'Horizon scanning' process (HSP). The paper concluded that the preparing for a sustainable water future (SWF) must be right now and the opportunities range from the deepest water drop to the highest water drop on Earth. The essence of the conclusion is hydrosphere sustainability, particularly in Arabsphere, should be given extreme concentration, effort, and support.

Methodology for Determining Sustainable Water Consumption Indicators for Buildings

The objective of this study was the definition and determination of sustainable water consumption indicators for activity categories, as well as the evolution of water consumption in commercial buildings. These indicators were determined through statistical analyses using Shewhart charts. Within a broader scope, the research proposed a methodology to automate sustainable management of water consumption in building operation using BIM–IoT–FM integration. The scientific rigor of the methodology was based on the precepts of design science research. The methods proposed for the construction of functionalities and the application of the reference indicators provided an optimized analysis of water consumption and the detection of excess consumption and leaks. The methodology, implemented in an online prototype, AquaBIM, could deliver a significant advance for building management. A conceptual test of AquaBIM evaluated the consumption indicators and validated our methodology through its application in a commercial building. The building consumption analyses showed a potential for approximately 15% savings. In addition, five requirements of the international sustainability certification AQUAHQE were met. The results of our research provide an innovative approach for the automation of sustainable building management and could be expanded to monitor and report on the consumption of other critical resources such as electricity and gas.

Circular Economy Framework for Energy Recovery in Phytoremediation of Domestic Wastewater

Circular economy (CE) strategy is crucial in developing towards sustainable growth. It was created to promote resource utilization and the elimination of waste production. This article aimed to study the possibilities of using the CE framework in wastewater bioremediation and energy recovery using hydroponic tanks. The integration of phytoremediation with bioenergy, construction and lifespan of hydroponic tanks in phytoremediation of wastewater, selection of aquatic plants and the expected challenges in the implementation of CE in phytoremediation of wastewater were discussed. The plant-based biomass harvested and the relative growth rate (RGR) of the selected plants from the phytoremediation process was evaluated. The findings obtained indicated that the selected plants tripled in weight after 14 days cultivation period at different retention times. E. crassipes recorded the highest growth with 2.5 ± 0.03 g g−1 d−1, followed by S. molesta with 1.33 ± 0.05 g g−1 d−1 and then P. stratiotes recorded 0.92 ± 0.27 g g−1 d−1 at the end of the cultivation period. Therefore, the selected plants have been identified as having the potential to be used in phytoremediation as well as a source of energy production. The outcome of our review suggested the adoption of a lifecycle assessment as the CE framework for the phytoremediation of wastewater.

Indicators for resource recovery monitoring within the circular economy model implementation in the wastewater sector

The European Union is currently in the process of transformation toward a circular economy model in which different areas of activity should be integrated for more efficient management of raw materials and waste. The wastewater sector has a great potential in this regard and therefore is an important element of the transformation process to the circular economy model. The targets of the circular economy policy framework such as resource recovery are tightly connected with the wastewater treatment processes and sewage sludge management. With this in view, the present study aims to review existing indicators on resource recovery that can enable efficient monitoring of the sustainable and circular solutions implemented in the wastewater sector. Within the reviewed indicators, most of them were focused on technological aspects of resource recovery processes such as nutrient removal efficiency, sewage sludge processing methods and environmental aspects as the pollutant share in the sewage sludge or its ashes. Moreover, other wide-scope indicators such as the wastewater service coverage or the production of bio-based fertilizers and hydrochar within the wastewater sector were analyzed. The results were used for the development of recommendations for improving the resources recovery monitoring framework in the wastewater sector and a proposal of a circularity indicator for a wastewater treatment plant highlighting new challenges for further researches and wastewater professionals.

Validating Circular Performance Indicators: The Interface between Circular Economy and Stakeholders

The development and application of appropriate Circular Economy indicators is an issue that concerns both the scientific and the business community, as well as decision makers. The existing gap between research, policy and practice could be bridged by using a dynamic indicators selection approach that combines both expert and participatory practices. This study aims to develop such a novel approach for the selection of indicators based on views and needs of practitioners, whilst considering the complex interdependencies of the indicators and determining their importance. Twenty circularity indicators for the Water-Energy-Food-Ecosystems nexus are selected and ranked by different stakeholders. The interrelationships of the indicators are identified using the Interpretive Structural Model, resulting in six levels of importance. Cross-impact matrix multiplication applied to classification (MICMAC) analysis further enabled the classification of the twenty indicators into four categories based on their driving and dependence power. The results indicate that seven indicators—one related to regeneration of natural environment principle, four related to keep resources in use, and two related to design out negative externalities—are the driving indicators to Circular Economy. The approach can be applied to other sets of indicators as well, enabling their prioritization and implementation with other systems.

Integrating Urban Agriculture and Stormwater Management in a Circular Economy to Enhance Ecosystem Services: Connecting the Dots

Due to the rapid urbanization in the context of the conventional linear economy, the vulnerability of the urban ecosystem to climate change has increased. As a result, connecting urban ecosystem services of different urban land uses is imperative for urban sustainability and resilience. In conventional land use planning, urban agriculture (UA) and urban stormwater management are treated as separate economic sectors with different-disconnected-ecosystem services. Furthermore, few studies have synthesized knowledge regarding the potential impacts of integration of UA and stormwater green infrastructures (GIs) on the quantity and quality of urban ecosystem services of both economic sectors. This study provides a detailed analysis of the imperative question—how should a city integrate the developments of both urban agriculture and stormwater green infrastructure to overcome barriers while enhancing the ecosystem services? To answer this question, we conducted an extensive literature review. The results show that integrating UA with GIs can enhance urban food production while protecting urban water quality. This paper provides an initial context and mechanisms for future researchers and city planners regarding the manner in which the synergies between UA and stormwater GIs can create greater value for the wellbeing of urban ecosystems and resilience in the circular economy.

Conceptualizing Core Aspects on Circular Economy in Cities

Currently, there are many different interpretations in the literature of what a circular economy is and how it functions. As cities are still facing challenges to become fully sustainable, the need for a comprehensive analysis of how the circular economy can be implemented in urban areas is increasing. This article aims at outlining circular cities by their key characteristics and to further explore and provide a framework for fostering circularity at the city level. In order to achieve this goal, we performed a systematic review and analyzed key papers published in the field of circular economy to determine how circular economy practices form circular cities. We discovered that cities play a focal role in facilitating the transition towards circularity through the closing of the loops, recirculation, technical innovation, policy elaboration and citizens’ support. However, city policymakers are still uncertain about how a circular city looks like and what its purpose is, as views are ranging from a strategic ambition to a niche concept of a smart city. Such uncertainty brings challenges, especially in the transition phase that many cities are in at the moment. This further implies that circular economy applied at the urban level still needs effort and innovation to successfully pass the transition phase from the linear economy. Therefore, lastly, we developed a framework model that can be adapted in other cities to facilitate their transition to circular cities.

Interrelationship among CE Adoption Obstacles of Supply Chain in the Textile Sector: Based on the DEMATEL-ISM Approach

Globally, in the innovative and distributional circular textiles, the textile sector of Taiwan has a prominent place. Within the textile industry, the circular economy (CE) obstacles adopted have been studied by several scholars. However, the interrelationships among these obstacles are easily ignored. The present study aimed to identify CE adoption obstacles from the supply chain (SC) perspective in Taiwan’s textile sector by analyzing the interrelationships among the CE adoption obstacles and establishing a hierarchical network and the causal inter relationships of the identified obstacles. Furthermore, the CE adoption obstacles and interrelationships were analyzed using interpretative structural modeling and the decision-making trial and evaluation laboratory (ISM-DEMATEL). The common results of the two methods demonstrated that two obstacles, consumers not having sufficient knowledge and awareness of reuse/recycling (B1) and a lack of successful business models and frameworks for CE implementation (B3), were the significant obstacles influencing adopting CE in the textile supply chain, while the obstacle making the most efficient way (B12) of the right decision to implement CE was minor. Thus, the government should formulate friendly laws and regulations that encourage CE adoption, while textile firms should monitor and control recycling and efficiency approaches handling the CE adoption problems. Our results could offer first-hand knowledge to textile firms or managers to effetely achieve CE implementation objectives.

Ammonium Release and Adsorption Characters of Polyurethane-Biochar Crosslinked Material as an Additive Filler in Stormwater Treatment

The additive fillers in bioretention facilities play a leading role in stormwater treatment to purify polluted runoff. At present, many traditional materials could not meet the requirements at the same time, including low ammonium leaching quantities, high water storage volume and strong ammonium adsorption. This study investigated a polymer material, polyurethane-biochar crosslinked material (PCB), to evaluate the feasibility of using it as an additive filler in stormwater treatment compared with its raw material hardwood biochar (HB), and two traditional fillers. Successive leaching and ammonium isothermal adsorption experiments were conducted in deionized water and artificial stormwater. PCB leached 4.98-5.31 μmol/g NH₄-N, less than the leaching quantities of compost, the traditional filler. After polyurethane modification, ammonium adsorption of PCB was improved: at a typical ammonium concentration of 2 mg/L in stormwater, PCB could adsorb 43.6 mg/kg ammonium versus 34.6 mg/kg for HB. With the addition of PCB in sand column, the ammonium adsorption improved from 31.34 to 84.72%. To improve the performance of bioretention facilities, PCB is recommended to be added into filter layers in stormwater treatment, taking advantage of its high cation exchange capacity and spongy internal structure to minimize overland flooding and enhance removal of ammonium from stormwater.

Study of the Potential of Water Treatment Sludges in the Removal of Emerging Pollutants

Presently, water quantity and quality problems persist both in developed and developing countries, and concerns have been raised about the presence of emerging pollutants (EPs) in water. The circular economy provides ways of achieving sustainable resource management that can be implemented in the water sector, such as the reuse of drinking water treatment sludges (WTSs). This study evaluated the potential of WTS containing a high concentration of activated carbon for the removal of two EPs: the steroid hormones 17β-estradiol (E2) and 17α-ethinylestradiol (EE2). To this end, WTSs from two Portuguese water treatment plants (WTPs) were characterised and tested for their hormone adsorbance potential. Both WTSs showed a promising adsorption potential for the two hormones studied due to their textural and chemical properties. For WTS1, the final concentration for both hormones was lower than the limit of quantification (LOQ). As for WTS2, the results for E2 removal were similar to WTS1, although for EE2, the removal efficiency was lower (around 50%). The overall results indicate that this method may lead to new ways of using this erstwhile residue as a possible adsorbent material for the removal of several EPs present in wastewaters or other matrixes, and as such contributing to the achievement of Sustainable Development Goals (SDG) targets.