The 15-minute city concept: The case study within a neighbourhood of Thessaloniki.

Cities, crucial cultural hubs, mould individual and group identities. The global urban expansion, with over half the population in urban areas, presents interconnected challenges such as pollution, poverty, inequality, ageing infrastructure, resource overconsumption, land use changes, biodiversity impact and climate change. Addressing these demands ambitious actions targeting political, social and economic systems for transformative change. The theoretical framework guiding city transformation centres on an interdisciplinary approach influenced by the Smart and Green Transition. The '15-minute city' concept, emphasizing human scale and urban experience, proposes that cities enable residents to meet daily needs within a short walk or bike ride. The aim of this study was the exploration of its implementation in Greek cities, particularly Thessaloniki, which reveals inherent characteristics supporting the 15-minute concept. Through an interdisciplinary approach rooted in the Smart and Green Transition framework, the research provides concrete guidance for policymakers in tailoring urban planning strategies, allocating resources effectively and crafting policies conducive to successful and sustainable urban transformations. Moreover, prioritizing public engagement highlights the significance of community involvement in shaping urban development plans, ensuring that proposed initiatives align with residents' needs and desires. In essence, this research contributes tangible insights and actionable recommendations for Greek cities, paving the way for more liveable, resilient and sustainable urban environments.

Comprehensive investigation of recycled PVC powder.

This study constitutes a comprehensive investigation centred on comprehending the behaviour and characteristics of recycled polyvinyl chloride (PVC) powders. The overarching objective is to successfully conclude the initial research phase, during which PVC-coated fabric offcuts undergo a transformation into PVC powder while achieving complete separation from polyethylene terephthalate fibres. The study entails a qualitative description of the morphology of PVC powder particles, employing an optical microscope to distinguish the diverse shapes exhibited by these particles. The optical microscope observations of PVC powder reveal a distinct array of non-spherical particles characterized by flat, elongated shapes. These high-magnification images unveil the intricate morphological features of the particles, highlighting their irregular shapes. Subsequently, a quantitative analysis of PVC particle size distribution is performed, comparing results from optical microscopy with those obtained through mechanical sieving. The qualitative and quantitative findings obtained provide robust evidence supporting the correlation and confirm that most particles are smaller than 600 µm (93.6%) using an optical microscope and the sieving process (96.39%). The greatest fraction (83.44%) is in the size range between 200 and 600 µm. Assessing flowability, another significant aspect in the evaluation of powders, provides insights into its behaviour and interparticle interactions. The flowability results indicate a Compressibility Index of approximately 26.84%, which suggests poor flowability. This means that the powder is likely to encounter difficulties in flowing freely. This finding is in line with the Hausner ratio, which measures 1.37. This investigation of recycled PVC powder will offer insights into the potential applications and processing considerations of this powder. More concretely, the use of recycled PVC powder shows promise as a viable alternative to conventional PVC resin in plastisol formulations, offering the potential to maintain the properties of the final PVC product without adverse effects.

The concept of food waste and food loss prevention and measuring tools.

Food waste (FW) has become a global concern, with an estimated 1.3 billion tonnes lost annually, costing about $1 trillion. Environmental and social consequences of FW are significant, contributing to 6% of European Unions' greenhouse gasemissions and affecting global food security. FW occurs is a complex issue occurring at various stages of the food supply chain (FSC) and is influenced by multiple factors such as infrastructure, available knowledge and socio-economic conditions. Developed countries FW is more prevalent at the consumption stage, whereas in the developing countries losses occur in agricultural production, post-harvest and distribution stage. Accurate quantification of FW across the supply chain is crucial and monitoring key performance indicators helps identify areas for improvement. The European Union mandates FW measurement, aligning with sustainable development goals, emphasizing the need for effective waste prevention measures. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses approach was utilized to conduct a systematic literature review on FW key performance indicators (KPIs) and monitoring tools. The research identified 22 KPIs, categorized into three levels of the FSC: primary, secondary and tertiary. The most common KPIs included FW per capita, FW per portion and FW percentage. The study further discusses FW prevention measures and essential monitoring tools for addressing FW throughout the supply chain.

Urbanization and solid waste production: prospects and challenges.

The increasing urban population and the restructuring of urban economies are the main aspects that determine urban development in the twenty-first century. Rapid urbanization is among the most significant anthropogenic factors that impact ecosystems and sustainability. Urbanization is a "double-edged sword." Even though it contributes to economic prosperity and social development, at the same time, it poses severe challenges to the natural environment and social system. The scientific community emphasizes the need to investigate the relationship between cities and the environment to comprehend their dynamic interactions related with problems such as climate change, consumption of natural resources, and life quality degradation. Population growth and urbanization are central considerations of the 2030 Agenda of the United Nations Sustainable Development Goals, particularly SDG 11, dealing with making cities inclusive, safe, resilient, and sustainable. Moreover, the new circular economy model is receiving increasing attention globally as a solution to the current production and consumption model, which is based on constant growth and increasing resource input. The objective of this paper was to identify the major challenges occurred due to the rapid urbanization in a coastal city though a qualitative and quantitative waste compositional analysis. The ultimate goal is to propose the waste compositional analysis as a new indicator in the literature for determination of the degree of metabolism in an island region. According to the compositional analysis, the higher the population density in a region, the greater the volume of garbage produced and, consequently, the infrastructure necessary for waste management. Also, the increased seasonal tourist activity leads to an increase in the number of tourist accommodations and services. The results provided may also be applicable in other cities with similar characteristics related with tourism habits and the challenges they may face as a result of the waste production.

Mobilisation of textile waste to recover high added value products and energy for the transition to circular economy.

The textile industry is a major contributor to global waste, with millions of tons of textiles being discarded annually. Material and energy recovery within circular economy offer sustainable solutions to this problem by extending the life cycle of textiles through repurposing, recycling, and upcycling. These initiatives not only reduce waste but also contribute to the reduction of the demand for virgin materials (i.e. cotton, wool), ultimately benefiting the environment and society. The circular economy approach, which aims to recreate environmental, economic, and societal value, is based on three key principles: waste reduction, material circulation, and ecological restoration. Given these difficulties, circularity incorporates the material recovery approach, which is focused on the conversion of waste into secondary raw resources. The goal of this notion is to extract more value from resources by prolonging final disposal as long as feasible. When a textile has outlived its functional life, material recovery is critical for returning the included materials or energy into the manufacturing cycle. The aim of this paper is to examine the material and energy recovery options of main raw materials used in the fashion industry while highlighting the need of close observation of the relation between circularity and material recovery, including the investigation of barriers to the transition towards a truly circular fashion industry. The final results refer to the main barriers of circular economy transition within the industry and a framework is proposed. These insights are useful for academia, engineers, policy makers and other key stakeholders for the clear understanding of the industry from within and highlight beyond circular economy targets, SDGs interactions with energy and material recovery of textile waste (SDG 7, SDG 11, SDG 12 etc.).

LCA of municipal wastewater treatment.

Wastewater treatment plants play a significant role in minimizing environmental pollution by treating wastewater and reducing the release of contaminants into the environment. However, their operation can still have an environmental footprint. Therefore, Life Cycle Assessment (LCA) of wastewater treatment provides a comprehensive framework to quantify the environmental impact of plants across various categories. By conducting LCA assessments, the environmental impacts of different scenarios or treatment technologies can be compared, enabling decision-makers to identify the most environmentally friendly options. This information helps in optimizing the plant's design, operation, and resource allocation to minimize their environmental burden. The current research hypothesis was to conduct an LCA of a typical activated sludge plant in Greece, considering three different scenarios in order to provide an innovative take on wastewater treatment plant foam waste and utilize them for the production of biogas through anaerobic digestion. The assessment was carried out using OpenLCA software as well as EcoInvent v3.3. database. The study focused on the impact assessment of five categories (eutrophication potential, acidification potential, global warming potential, ozone depletion, and photochemical ozone creation). The results indicated that the baseline scenario had the highest impact on these categories, followed by Scenario I, while Scenario II had the least impact. Additionally, the cumulative energy demand assessment showed that the baseline scenario required significantly more energy compared to Scenarios I and II. However, Scenario II, which involved fine screens and utilization of biogas, exhibited the highest energy production, thereby reducing the overall energy demands for the system. Based on these findings, it is crucial for wastewater treatment facilities to actively pursue energy demand mitigation strategies by implementing energy-efficient technologies and utilizing biogas. These measures not only contribute to environmental protection but also promote a greener and more sustainable future for WWTP operations.

Construction and demolition waste framework of circular economy: A mini review.

As the demand for materials continues to increase and building lifespans shorten, the construction industry faces mounting pressure to reduce its material and environmental impacts. Mismanagement of construction and demolition waste (CDW) can have severe environmental consequences. To address this, material recovery and circular economy approaches offer significant potential for reducing construction waste through the sustainable use of resources. Existing circular economy and material recovery models that prioritize recycling and reuse efforts demonstrate a sustained commitment to supporting circular practices in the construction and demolition sector. The goal is to minimize waste production, which poses environmental challenges such as raw material shortages and sustainability concerns. Using Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement for recruiting relevant literature, this mini review aims to identify the obstacles to implementing circular economy practices in the construction industry, while exploring opportunities for material recovery and circularity. The ultimate aim is to facilitate a fair and smooth transition towards sustainable development, while addressing environmental, social and economic barriers. A more sustainable and circular approach to building construction and management can be attained by considering all the aspects of the CDW cycle, resulting in significant benefits for the environment and society as a whole.

Waste metrics in the framework of circular economy.

There are several sustainability issues that the linear economy of today's society cannot adequately tackle (i.e. resource depletion, waste treatment, etc.). As a result, the scientific community and policymakers give high priority to the implementation of the circular economy concept. The sustainable development goals of the United Nations are in line with the European Union's (EU) commitment to a smooth transition to a circular economy. Circular business models require a shift in technical elements involving R strategies to replace traditional business models (i.e. reuse, reduce, recycle, etc.). Monitoring circular economy to provide quantifiable, measurable data is necessary for a successful transition. Monitoring tools (i.e. Key Performance Indicators, quality protocols) enable decision-makers to measure circular economy performance and identify circularity's advantages and disadvantages. To stimulate the adoption of a circularity model addressing critical issues of excessive waste production and resource use, this mini review aims to address the literature gap of waste metrics in the framework of circular economy and offer insights on circular economy indicators to aid for a seamless transition to a more sustainable society. For this purpose, Preferred Reporting Items for Systematic Reviews and Meta-Analysis method was chosen to assess literature. The authors collected and analysed data from 101 records, 70 articles and 31 reports related to the topic under consideration. Through the literature review, it is obvious that moving away from linear production model frequently leads to the development of new internal capabilities along the value chain and, eventually, high efficiency that reduces costs, increasing productivity, encourages brand names, minimizes threats, creates new products and fulfils regulations and green consumer expectations.

Facile synthesis of double-cross-linked alginate-based hydrogel: Characterization and use in a context of circular economy for cationic dye removal.

Hydrogels based on natural polysaccharides have received special attention in the last decade due to their interesting features, such as availability, biocompatibility, biodegradability and safety. Such characteristics may make them sustainable and eco-friendly materials for water and wastewater treatment, meeting the concept of circular economy. In this study, a novel double-cross-linked alginate-based hydrogel has been successfully synthesized using epichlorhydrin and sodium trimetaphosphate (STMP) as cross-linker agents and then used for the removal of methylene blue (MB) dye under different operating conditions. The obtained hydrogel was deeply characterized by using various analytical techniques, namely Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Experimental results showed that the synthesized double cross-linked hydrogel with relatively high STMP concentration (0.26 M) has promising structural and textural properties. This material exhibited excellent removal ability towards MB with a maximum adsorption capacity of about 992 mg/g for an initial pH of 10. The kinetic and isotherm modeling study revealed that the pseudo-second-order and Freundlich models fitted well the measured adsorption experimental data. The MB adsorption process onto the synthesized hydrogel is exothermic, feasible and spontaneous. It mainly includes electrostatic interaction and hydrogen bonds. These findings suggest that double-cross-linked alginate-based hydrogel can be considered as an attractive and potential adsorbent for an effective cationic dye removal from aqueous environments. The use of such a green adsorbent for the treatment of organic-pollutants-rich industrial wastewaters promotes sustainability and circular economy concepts.

Nitrogen management in farming systems under the use of agricultural wastes and circular economy.

Population growth leads to an increase in the demand for energy, water, and food as cities grow and urbanize. However, the Earth's limited resources are unable to meet these rising demands. Modern farming practices increase productivity, but waste resources and consume too much energy. Agricultural activities occupy 50 % of all habitable land. After a rise of 80 % in 2021, fertilizer prices have increased by nearly 30 % in 2022, representing a significant cost for farmers. Sustainable and organic farming has the potential to reduce the use of inorganic fertilizers and increase the utilization of organic residues as a nitrogen (N) source for plant nutrition. Agricultural management typically prioritizes nutrient cycling and supply for crop growth, whereas the mineralization of added biomass regulates crop nutrient supply and CO2 emissions. To reduce overconsumption of natural resources and environmental damage, the current economic model of "take-make-use-dispose" must be replaced by "prevention-reuse-remake-recycle". The circular economy model is promising for preserving natural resources and providing sustainable, restorative, and regenerative farming. Technosols and organic wastes can improve food security, ecosystem services, the availability of arable land, and human health. This study intends to investigate the nitrogen nutrition provided by organic wastes to agricultural systems, reviewing the current state of knowledge and demonstrating how common organic wastes can be utilized to promote sustainable farming management. Nine waste residues were selected to promote sustainability in farming based on circular economy and zero waste criteria. Using standard methods, their water content, organic matter, total organic carbon, Kjeldahl nitrogen, and ammonium levels were determined, along with their potential to improve soil fertility via N supply and technosol formulation. 10 % to 15 % of organic waste was mineralized and analysed during a six-month cultivation cycle. Through the results, the combination of organic and inorganic fertilization to increase crop yield is recommended, as is the search for realistic and practical methods of dealing with massive amounts of organic residues within the context of a circular economy.

Tomato waste biochar in the framework of circular economy.

Tomato pomace was slowly pyrolyzed at 350 and 550 °C (under an N2 flow of 50 L/h) at a rate of 6 °C/min and a residence time of 1:30 h to produce two biochars named B350 and B550, respectively. In addition, the two biochars were chemically activated with ΚΟΗ (at a ratio of 1:10 w/v) at 800 °C to produce two new materials named BA350 and BA550. The four biochars produced were characterized physically and chemically (pH, yield, calorific value). They were also analyzed by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (B.E.T), elemental analysis (EA), and thermogravimetric analysis (TGA). The results showed that as the pyrolysis temperature increased (350 to 550 °C), the specific surface area (SSA) increased. The latter was also significantly increased by the activation process. EA showed a variation in the mineral content of the produced biochars, resulting in a different content of the biochars after activation. The parameters studied showed that biochars from tomato waste could be used as an organic amendment to improve soil fertility in agricultural. In addition, because of their ability to absorb water, they could be used as a water reservoir in soils in arid areas.

LCA of Barley Production: A Case Study from Cyprus.

Greenhouse gas emissions (i.e., carbon dioxide, methane, nitrous oxide) produced by agriculture contribute to global warming and climate change. Various practices followed by farmers in different environmental conditions contribute to the increase in the phenomena, and there is a need for immediate measures. The current study examines the environmental impact of barley production under rain-fed conditions in Cyprus. For this, four different nutrient management scenarios were investigated in order to evaluate the environmental performance of crop production, namely: (1) Nitrogen (20%), Phosphorous (20%), Potassium (10%); (2) Nitrogen (20%), Phosphorous (20%), Potassium (10%) and manure; (3) Nitrogen (25%), Phosphorous (10%), Potassium (0%); and (4) Nitrogen (25%), Phosphorous (10%), Potassium (0%) and manure. Data were collected from two different areas of Cyprus (Nicosia and Larnaca) through on-site visits and questionnaires. Life Cycle Assessment (LCA) was used as a method to quantify environmental impacts which were categorized into six impact categories: (i) acidification potential (AP), (ii) eutrophication potential (EP), (iii) global warming potential (GWP), (iv) ozone depletion potential (ODP), (v) photochemical, ozone creation potential (POCP), and (vi) terrestrial ecotoxicity (TAETP). LCA was used with system boundaries from field to harvest and a functional unit (FU) of one bale of hay. Research results showed that the addition of manure increased values in all impact categories. Comparing scenarios without manure (1 and 3) and with manure (2 and 4), the main process which contributed to GWP was field preparation, which resulted in 3 t CO2-Eq∙FU-1 and 46.96 t CO2-Eq∙FU-1, respectively. Furthermore, the highest contribution of sub-processes to GWP (kg CO2-Eq∙FU-1) was machinery maintenance (scenarios 2 and 4). The potential to reduce environmental impacts from barley and moreover, to mitigate the footprint of the agriculture sector in Cyprus is proposed by changing existing practices such as decreasing fuel consumption by agricultural machinery, and monitoring fertilizing and seeding. Conclusively, the carbon footprint of barley can be decreased through the improvement of nutrient management and cropping practices.

The perception of circular economy in the framework of fashion industry.

Humanity's three main components are energy, food and clothing. Each of us, individually and collectively, contributes to climate change and CO2 emissions, natural resource consumption, and social attitudes and behaviour. Global fashion trends are expected to increase in value from 1.5 trillion dollars in 2020 to around 2.25 trillion dollars by 2025, indicating that the fashion demand is on the rise. Due to climate change, soil and water scarcity, and a variety of other diseases, new natural resources must be developed from plastic fibres, natural colours must replace synthetic ones, water consumption must be reduced and the 'buy-and-throw-away philosophy' must be replaced with 'buy-less-and-these-are-needed' and incorporate the 12 'R' strategies to aid the transition to a circular economy. In the context of waste management as well as on the development of new strategy approach, the fashion industry requires a new business circular model and furthermore a new mindset.

Predicting COVID-19 future trends for different European countries using Pearson correlation.

The ability to accurately forecast the number of COVID-19 cases and future case trends would certainly assist governments and various organisations in strategising and preparing for the newly infected cases well in advance. Many predictions have failed to foresee future COVID-19 cases due to the lack of reliable data; however, such data are now widely available for predicting future trends in COVID-19 after more than one and a half years of the pandemic. Also, various countries are closely monitoring other countries that are experiencing a surge in COVID-19 cases in the expectation of similar scenarios, but this does not always produce correct results, as no research has identified specific correlations between different countries in terms of COVID-19 cases. During the past 18 months, many nations have watched countries whose COVID-19 cases have risen sharply, in anticipation of handling the situation themselves. However, this did not provide accurate results, as no research was conducted that compared countries to determine if their COVID-19 case trends were correlated. As official data on COVID-19 cases has become increasingly available, using the Pearson correlation technique to pinpoint the countries that should be closely monitored will help governments plan and prepare for the number of infections that are expected in the future at an early stage. In this study, a simple and real-time prediction of COVID-19 cases incorporating existing variables of coronavirus variants was used to explore the correlation among different European countries in terms of the number of COVID-19 cases officially recorded on a daily basis. Data from selected countries over the past 76 weeks were analysed using a Pearson correlation technique to determine if there were correlations between case trends and geographical position. The correlation coefficient (r) was employed for identifying whether the different countries in Europe were interrelated, with r > 0.85 indicating they were very strongly correlated, 0.85 > r > 0.8 indicating that they were strongly correlated, 0.8 > r > 0.7 indicating that they were moderately correlated, and r < 0.7 indicating that the examined countries were either weakly correlated or that a correlation did not exist. The results showed that although some neighbouring countries are strongly correlated, other countries that are not geographically close are also correlated. In addition, some countries on opposite sides of Europe (Belgium and Armenia) are also correlated. Other countries (France, Iceland, Israel, Kosovo, San Marino, Spain, Sweden and Turkey) were either weakly correlated or had no relationship at all.

Unified waste metrics: A gamified tool in next-generation strategic planning.

A gamification approach for tackling waste management planning and urban development provide a more engaging and interactive experience with high pedagogical potential. Existing serious games involving waste management are complex in their data ingestion, use, and presentation, limiting individuals' opportunities to gain knowledge and decision-making skills transferrable to the real world. Simulations, by comparison, provide either an oversimplified and unrealistic user interface or explore in depth individual rather than aggregate key performance indicators for waste management, limiting potential knowledge retention. There is a clear opportunity in creating an informative, easy-to-use simulation-based game to help stakeholders build understanding of waste management policies, performance, and causal relationships. This gamified tool provides clear feedback through quick-visibility performance indicators (i.e., waste accumulation index, waste compositional analysis, prevention activities etc.) and offers the opportunity, through multi-criteria decision making, of simulating real-life scenarios and previewing the possible outcomes of certain in-game actions. The research question is how the process of gamification might serve as powerful tool for educating decision makers. The results are considered as a reference point to any policy maker intending to assess environmental performance, proposed activities to reach Circular Economy targets, and European Green Deal and UN Sustainable Development Goals.