Technical University of Crete

The present paper discusses the properties of biochars produced from different feedstocks, namely sewage sludge (SS), olive tree pruning (OTP) and walnut shells (WS), after slow pyrolysis at 300–400 °C. The techniques used for their characterization are Χ-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TG) and Scanning Electron Microscopy (SEM). In addition, the toxicity of the feedstocks and the produced biochars was assessed with the use of ΕΝ 12457-2 test. Furthermore, the phytotoxicity of substrates, containing test soil, 20 wt% biochar and / or 190 mg/kg Cu was evaluated for three seeds, namely Lepidium sativum (LS), Sinapis alba (SA) and Sorghum saccharatum (SC), with the use of Phytotoxkit microbiotest kit (MicroBioTests Inc., Belgium) and the determination of the germination index (GI). The experimental results clearly show that both the feedstock type and the pyrolysis temperature affect the physicochemical properties of the produced biochars. The pyrolysis yield decreases with the increase of pyrolysis temperature and may reach values as low as 10% for OTP biochar. According to the International Biochar Initiative (IBI) sewage sludge biochar is classified as Class III because its Corg content varies between 10% and 30%, while OTP and WS biochars belong to Class I as their Corg content is well above 60%. The application of EN 12457-2 test indicates that the produced biochars exhibit no toxicity. Finally, the addition of biochar in substrates has either phytostimulant or phytotoxic effect depending on the type of the seed used and the contamination with Cu ions.

An understanding of the spatiotemporal behaviour of Meteorological drought (MD) and Hydrological drought (HD) is crucial for analysing how drought propagation occurs. Here, drought events were treated as three-dimensional grid structures spanning space (latitude and longitude) and time. 31 years (1971–2001) of global MD and HD events were analysed for evidence of propagation, and the most severe 20 MD events explored in detail. From the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) data archive, precipitation data was used for identifying MD events and an ensemble of simulated runoff from several global hydrological models used for detecting HD events. A technique was developed based on overlapping of the spatial and temporal coverage of MD and HD events, to establish propagation, and to calculate several propagation features. In three dimensions, the transformation from MD to HD was characterised based on delayed instigation, elongated duration, and dampened intensity of the HD event. Additionally, pooling of MD events that resulted in one or multiple branched HD events were identified. Results indicate that minor MD events with short durations and small areas generally do not exhibit propagation. The frequency of HD events with drought duration of 6–12-months is higher than that of MD events with 6–12-month duration. Out of 1740 extreme MD events identified for the 31-year period, 272 events propagated and resulted in 395 extreme HD events. Propagation features for the 20 most severe MD events show substantial variation based on geographical location highlighting the influence of regional climatic and hydrological conditions. This study advances the understanding of global drought propagation mechanisms by addressing key methodological challenges and providing a structured framework for future large-scale drought assessments.

This study evaluates the effectiveness of CO 2 nanobubble-enhanced hydrate-based desalination (HBD) to treat industrial effluents from the mining and metals industry. Testing was conducted in a high-pressure reactor apparatus that employed CO 2 as the gas hydrate former at 274.15 K and 3.58 MPa. CO 2 nanobubbles (NBs) were used to promote hydrate formation, aiming to streamline an HBD process without separation steps for the additives/chemicals used. Due to the limited studies on hydrate formation in sulfate-containing aqueous solutions, this research focused on the kinetics of hydrate formation in varying concentrations of Na 2 SO 4 and MgSO 4 (0.1 and 0.5 M). The results showed that CO 2 NBs significantly enhanced hydrate formation in both Na 2 SO 4 and MgSO 4 solutions, with CO 2 consumption increasing by up to approximately 51% and 35%, respectively. Additionally, a kinetics study on a real effluent from the mining and metals industry showed that the presence of CO 2 NBs increased CO 2 consumption by around 20% after 180 min. This research also evaluated water recovery and desalination efficiency in a 3-stage HBD process applied to the effluent, the concentration of which exceeded the operating range of reverse osmosis. The results indicated an improvement in water recovery from 25.13 ± 2.04% to 40.16 ± 1.43% with CO 2 NBs, underscoring their effectiveness in treating highly saline water. Moreover, desalination efficiencies of 49.54 ± 2.39% and 42.03 ± 3.43% were achieved without and with CO 2 NBs, respectively. This study represents the successful demonstration of the efficient application of the CO 2 NBs-boosted HBD method to treat high-salinity effluents and recover clean water for reuse. Graphical Abstract

This work investigates the effectiveness of various state-of-the-art techniques for determining the parasitic inductance of surge protective devices across a wide frequency range. This is critical, as the intrinsic inductive characteristics of surge protective devices influence their maximum residual voltage, which directly affects their protection efficiency against fast-front transients with high current derivatives. To provide an innovative solution to the problem of parasitic inductance determination, the parasitic inductance of single-phase and three-phase DIN rail surge protective devices is estimated by replacing the voltage-limiting components with copper blocks. Three methods are employed to estimate the parasitic inductance: (i) Impedance spectroscopy measurements, (ii) impulse current tests, and (iii) finite element analysis simulations. The results are analyzed to evaluate the accuracy of the proposed methods and address key challenges encountered in determining the parasitic inductance. It is found that the parasitic inductance of the protection mode exhibiting the longer surge current path is up to 1.6 times greater than that of the shortest surge current path for the three-phase (3+1) surge protective device, and consequently the maximum residual voltage increases by ~10% when subjected to its nominal discharge current of 20 kA with an 8/20 μs waveform for the same protection modes.

Transitioning to more sustainable materials than cement is vital for reducing the carbon emissions and ecological footprint associated with cement production. Ternary cement blends, particularly Limestone Calcined Clay Cements (LC3), are gaining attention as sustainable alternatives to Ordinary Portland Cement to reduce clinker content. Three clay samples from the western area of Chania, Crete, Greece, were calcined at 700 °C and reacted with saturated lime to assess their pozzolanic activity as potential cement substitutes. Additionally, a local marl was calcined at 800 °C and then hydrated to evaluate its binding capacity for designing mortars with hydraulic binders. The silica and alumina minerals in the calcined clays and marl, after reacting with lime and undergoing hydration, produced respectively calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), which contribute to the hardening of plasters and mortars. The study includes Attenuated Total Reflection (ATR-IR) analysis, compression tests on mortar samples aged 1 to 4 months, and workability tests on fresh mortars. The results found that calcined clays, particularly metakaolin-rich samples, reacted more significantly with lime compared to those with high calcite content and low kaolinite. Mortars containing clays and lime required a similar water-to-binder ratio to achieve workability comparable to cement-based mortars. Compressive strength showed that the portlandite produced from the hydration of the marl was insufficient to fully react with calcined clay and cement to form C-S-H. This paves the way for ongoing studies to identify the minimum and optimal lime content required to effectively promote the hydrolysis reaction forming C-S-H, in accordance with LC3 principles.

Featured Application The isotopic dataset presented in this work will serve as a crucial foundation for future archaeological, ecological, and forensic studies. Abstract This study provides a comprehensive database of sulfur isotope values from Greece, including samples of C3 and C4 plants and terrestrial and aquatic animal bones. This comprehensive analytical approach examines sulfur isotopes—along with carbon and nitrogen—in modern plants, terrestrial mammals, and fish bones (fresh and marine reservoirs) from Greece. The results show a clear offset in δ³⁴S values between terrestrial and aquatic animals, influenced by their dietary sources from marine or freshwater environments. This δ³⁴S offset and the clear difference between S-C-N isotopes permits the reconstruction of the dietary habits of domesticated herbivores and demonstrates differences in husbandry practices and animal movements. Additionally, the combination of sulfur and nitrogen values allows the reconstruction of the diet of omnivores, revealing the type of protein consumed. Finally, this isotopic dataset will provide an essential backbone for future archaeological, ecological, and forensic studies.

This study investigates structural integrity and proposes retrofitting solutions for the historical two-storey school building in Thrapsano, Crete, severely impacted by the September 2021 earthquake. An extensive methodology was adopted, incorporating field surveys, material characterization, finite element modeling, and experimental analysis. The assessment is focused on identifying structural damage, such as cracking and delamination in masonry walls, and evaluating the dynamic and static performance of the load-bearing system under seismic loads. Key interventions include grouting for masonry reinforcement, replacement of mortar with compatible materials, stitching of cracks, and the addition of reinforced concrete and metallic tie elements to enhance diaphragm action. Advanced numerical simulations, validated through experimental data, were employed to model the pre- and post-retrofit behavior of the structure. The proposed retrofitting measures align with Eurocodes 6 and 8, and the Greek code for masonry structures (KADET), aiming to restore the structural stability and improve seismic resilience while respecting the building’s historical significance. The results from the finite element analysis confirm the effectiveness of the interventions in reducing tensile stresses and improving load redistribution, ensuring compliance with modern safety standards. This case study offers a framework for the seismic retrofitting of heritage structures in a similar context.

The city of Methoni (Venetian Modone), built on a small peninsula in the southwestern Peloponnese, retained a large part of its medieval fortifications after the introduction of artillery. However, it had to be further fortified on the side of the land, where attack was easier. In this area, the Venetians carried out extensive works when they captured the city for the second time (1685-1715), shortly before it fell again to the Ottomans. The work of the Venetians extended beyond the limits of the walled city and included the extensive remodeling of constructions they had begun two centuries earlier. The project included two bastions, the remodeling of the entrance to the city, the completion of the moat, and an outer work on the opposite side.New detailed architectural survey drawings carried out by the Laboratory for the Documentation and Conservation of Historic Buildings and Sites of the Technical University of Crete complement our knowledge of this fortification campaign. The new observations augment the information deriving from published Venetian documents and plans, shedding light on the fortification design, construction methods, and phases of development. The fortifications were designed by Antonio Giancix in 1708, but their construction was made possible only in 1713-14. For the so-called Loredan bastion on the east side of the city gate, it is now possible to document how it incorporated a former ravelin built shortly before the first fall of the city to the Ottomans (1500), which was only known from historical plans. The western bastion and the northwest outer work have similar construction features and were designed in an area that had never been fortified. Their construction was related to the moat extending towards the west, completely cutting off the peninsula from the land.

The recycling of cable scrap, particularly from discarded electrical wiring, is gaining significant attention due to the rising demand for copper and the need for sustainable management of electronic waste. Traditionally, mechanical and thermal processings have been used to recover copper and plastic from cables. However, these approaches are often energy-intensive, time-consuming, and costly in terms of equipment and labor. In this study, we present a simple and effective method for recovering materials from cable scrap using a domestic microwave oven. Cable pieces (2–2.5 cm long) were exposed to 700 W of microwave irradiation under rotation for 30 s, enabling the rapid and efficient separation of high-quality copper metal from the core wire, and activated carbon from the carbonized plastic sheath. Microwaves facilitate this process through Ohmic heating, which induces electrical resistance in the metal, generating heat that mechanically loosens the metal and carbonized plastic components. The process demonstrates high efficiency, achieving an 80% reduction in energy consumption compared to conventional processings. This fast and energy-efficient method shows strong potential for scaling up to industrial recycling, offering a cost-effective and environmentally friendly way to recover high-quality materials for further use or repurposing.

Hybrid renewable energy systems (HRESs) are being incorporated and evaluated within seaports to realize efficiencies, reduce dependence on grid electricity, and reduce operating costs. The paper adopts a genetic algorithm (GA)-based optimization framework to assess four energy management scenarios that embed wind turbines (WTs), photovoltaic energy (PV), an energy storage system (ESS), and an energy management system (EMS). The scenarios were developed based on different levels of renewable energy integration, energy storage utilization, and grid dependency to optimize cost and sustainability while reflecting the actual port energy scenario as the base case. Integrating HRES, ESS, and EMS reduced the port’s levelized cost of energy (LCOE) by up to 54%, with the most optimized system (Scenario 3) achieving a 53% reduction while enhancing energy stability, minimizing grid reliance, and maximizing renewable energy utilization. The findings show that the HRES configuration provides better cost, sustainability, and resiliency than the conventional grid-tied system. The unique proposed EMS takes it a step further, optimizing not just the energy flow but also the cost, making the overall system more efficient—and less costly—for the user. ESS complements energy storage and keeps it functional and reliable while EMS makes it completely functional by devising ways to reduce costs and enhance efficiency. The study presents the technical and economic viability of HRES as an economic and operational smart port infrastructure through its cost-effective integration of renewable energy sources. The results reinforce the move from conventional to sustainable autonomous port energy systems and lay the groundwork for forthcoming studies of DR-enhanced port energy management schemes. While prior studies have explored renewable energy integration within ports, many lack a unified, empirically validated framework that considers HRES, ESS, and EMS within real-world port operations. This research addresses this gap by developing an optimization-driven approach that assesses the techno-economic feasibility of port energy systems while incorporating real-time data and advanced control strategies. This study was conducted to enhance port infrastructure and evaluate the impact of HRES, ESS, and EMS on port sustainability and autonomy. By bridging the gap between theoretical modeling and practical implementation, it offers a scalable and adaptable solution for improving cost efficiency and energy resilience in port operations.

Surface quality is a major requirement in industrial level for every mechanical part, as it can define not only their ability to be appropriately used in assemblies but also their service life. Nowadays, the increased capabilities of modern measurement equipment have allowed the study of more advanced parameters such as the uniformity of texture or functional parameters of the roughness profile, which can lead to reliable conclusions about tribological and lubrication properties of machined surfaces as well. In the present case, a thorough investigation of surface topography and texture was carried out for the case of laser engraving of square pockets on a titanium alloy workpiece under diverse process conditions. Analysis of the results revealed that apart from the high correlation of laser power and laser scanning speed with amplitude parameters of surface roughness, laser engraving can have a profound effect on directionality of the produced texture, with higher speeds and moderate VED values leading to less isotropic surfaces. Moreover, although based on the analysis of Ssk and Sku values, which were found to be mostly positive and below 4 respectively, most surfaces exhibit high peaks and reduced fluid retention capability, the latter can be increased by appropriately selecting the combination of process conditions during laser engraving process.

In this study, rice husks (RH) and sewage sludge (SS) were used as feedstock to produce carbon nanotube (CNT)-doped biochar nanocomposites at two pyrolytic temperatures, 400 °C and 600 °C. The samples were produced, physicochemically and structurally evaluated, and tested as adsorbents for the extraction of six organic micro-contaminants of emerging concern (EMCs) in as-close-to-realistic concentrations, from water and wastewater. RH biochar nanocomposites were more effective than SS biochar nanocomposites on the adsorption of EMCs, requiring lower adsorption times (5 min as compared to 10 min) to sufficiently remove (> 80%) the investigated pollutants. This was in agreement with the physicochemical analysis of biochar nanocomposites which showed a more developed porous structure for RH samples. The dominant mechanisms in the adsorption process were proven to be π-π EDA interactions accompanied by pore-filling mechanisms, along with hydrophobic and electrostatic interactions, in a less dominant role. This study showed that RH and SS biochar nanocomposites have the potential to be effectively used to decontaminate water and wastewater from emerging pollutants.

Lithium, known as the energy metal of the twenty-first century, has become a fundamental element due to its recent use in rechargeable lithium-ion batteries and electronic devices. It is anticipated that the global demand for lithium will be more than quadruple, from around 700,000 metric tons in 2022 to over 3 million metric tons in 2030. Lithium resources exist in different deposits, including brines, hard-rock pegmatites, and volcanic clays. Among them, hard rock ores are found worldwide, giving them geostrategic advantages over other types of deposits. Typically, the mineral processing of hard-rock lithium ores includes comminution to achieve a high degree of mineral liberation and a combination of dense media separation (DMS), magnetic separation, and froth flotation. This review paper aims to provide a comprehensive overview of mineral processing technologies used for the beneficiation of hard rock lithium ores, focusing on recent advances and identifying areas for further research and development towards a more sustainable lithium production. Also, the need for life cycle assessment (LCA) studies to assess the environmental impacts associated with responsible mining and beneficiation of lithium ores is briefly discussed. LCA results may assist in the acquirement of social license to operate (SLO) by the mining industry and accelerate the implementation of sustainable exploration and mining projects related to energy transition minerals, most of which are located near indigenous people’s land and environmentally sensitive areas.

This letter investigates the impact of gamma radiation on the transient performance of surge protective components under high impulse currents in the range of 0.3 – 2.0 kA generated by a 6kV/3kA combination wave generator. For the first time, the immunity of spark gaps, metal-oxide varistors, and transient voltage suppression diodes to gamma radiation is demonstrated by analyzing their residual voltage before, during, and after their exposure to a Cobalt-60 source for more than 4 minutes; samples were receiving a dose rate of 450 mGy/min. These findings (i) provide insights on test methodologies for international standards on surge protection and (ii) pave the way for implementation of surge protection schemes in highly irradiated environments, such as those encountered in the emerging power and data grids in aviation, space, nuclear, and defense industries.

Various operators run meteorological stations in the region of Crete, each of which collects important climate data. However, this fragmentation leads to difficulties in integrating and analyzing the data throughout the region. The present work describes the creation of a unified, open-source SQL database for the management of hydro-meteorological data from a large number of monitoring stations in the region of Crete and the development of an infrastructure with a user interface. The characteristics of originality and innovation of the idea lie in the integration and collection of a variety of meteorological and hydrological data from a multitude of independent meteorological and hydrological stations in the region of Crete and their dissemination to the wider scientific community through a multi-user access environment. The integration of the data into a single MySQL database and the user-friendly interaction with the database through Metabase add value to the collected data compared to storage in isolated individual databases or files. The customizable visual representation of the data, the ability to create personalized queries without requiring prior knowledge of database programming, and the possibility of automatic data entry (either via the accredited bodies’ websites or via files in specific formats) are additional original features. By providing clear visual representations of this data, the platform would improve decision-making in critical areas such as flood risk management, drought mitigation and sustainable water resource planning. The introduction of such a consolidated system would simplify hydrological studies, encourage collaboration between data providers and facilitate more informed, data-driven policy making.

Outdoor performance monitoring of the emerging photovoltaic technologies, such as organic or perovskite solar modules, under real-life environmental conditions for an extended period will set the grounds for further technological maturity while revealing distinct characteristics compared to silicon or other commercial technologies. This study focuses on the long-term outdoor performance of a solar farm enabled by graphene-perovskite panels (S. Pescetelli, A. Agresti, G. Viskadouros et al., Nature Energy, 7, 597 (2022)). In this study, we investigated the solar farm's degradation mechanisms and a peculiar dark-storage recovery effect, as well as the light-soaking phenomenon that emerges after a dark-storage recovery process. The solar farm's performance was monitored over an extended period of time, and its performance was analyzed using a combination of electrical and optical characterization techniques. It was demonstrated that the key sources of solar farm degradation were exposure to high temperatures and solar irradiance while operating outdoors, as well as lamination failure due to aging that resulted in moisture and oxygen penetration. Notably, the visual defects observed in the perovskite modules during the performance monitoring period revealed severe effect of lamination failure on the graphene-perovskite solar farm performance degradation. The reported performance degradation was found to be partially restored after panels' dark storage indicating that both reversible and irreversible mechanisms are at play. A peculiar light-soaking phenomenon was also observed after the dark storage process, which led to partial performance recovery, indicating different behavioral trends after the dark storage of panels.

In various scientific fields, including climate science, earth science, and hydrology, there is great interest in methods of causal inference. Such methods aim to identify relations of cause and effect between potential drivers and responses based on the available data (typically time series). The recently proposed method of Liang–Kleeman information flow rate (LIFR) has potential advantages for large datasets and nonlinear interactions. However, performance comparisons of LIFR with established causal inference methods are lacking. This paper begins to address this gap in the literature by comparing LIFR with the standard method of Wiener–Granger causality (WGC). LIFR is formulated on the basis of entropy exchange between components of an interacting system and can be estimated by means of data-driven measures. WGC, on the other hand, models an ensemble of time series by means of vector autoregressive models. This work first studies the causal relations in a simulated, bivariate Ornstein–Uhlenbeck linear system using both LIFR and WGC. Next, it investigates the presence of a causal link between the North Atlantic Oscillation index and the monthly rainfall amount in two cases: one is based on reanalysis data for two areas of Greece and the other on ground measurements from the island of Crete (Greece). While the analysis of the linear system shows that LIFR and WGC perform similarly and accurately detect the connectivity of the system, the analysis of the interaction between the North Atlantic Oscillation index and rainfall data by both methods reveals surprises.

State-of-the-art climate models project a substantial decline in precipitation for the Mediterranean region in the future¹. Supporting this notion, several studies based on observed precipitation data spanning recent decades have suggested a decrease in Mediterranean precipitation2, 3–4, with some attributing a large fraction of this change to anthropogenic influences3,5. Conversely, certain researchers have underlined that Mediterranean precipitation exhibits considerable spatiotemporal variability driven by atmospheric circulation patterns6,7 maintaining stationarity over the long term8,9. These conflicting perspectives underscore the need for a comprehensive assessment of precipitation changes in this region, given the profound social, economic and environmental implications. Here we show that Mediterranean precipitation has largely remained stationary from 1871 to 2020, albeit with significant multi-decadal and interannual variability. This conclusion is based on the most comprehensive dataset available for the region, encompassing over 23,000 stations across 27 countries. While trends can be identified for some periods and subregions, our findings attribute these trends primarily to atmospheric dynamics, which would be mostly linked to internal variability. Furthermore, our assessment reconciles the observed precipitation trends with Coupled Model Intercomparison Project Phase 6 model simulations, neither of which indicate a prevailing past precipitation trend in the region. The implications of our results extend to environmental, agricultural and water resources planning in one of the world’s prominent climate change hotspots¹⁰.

Background: In recent years, more and more numerical tools have been utilized in medicine in or-der to assist the evaluation and decision-making processes for complex clinical cases. Towards this direction, Finite Element Models (FEMs) have emerged as a pivotal tool in medical research, particularly in simulating and understanding the complex fluid and structural behaviors of the circulatory system. Furthermore, this tool can be used for the calculation of certain risks regarding the function of the blood vessels. Methods: The current study developed a computational tool utilizing the finite element method in order to numerically evaluate stresses in aortas with abdominal aneurysms and provide the necessary data for the creation of a patient-specific digital twin of an aorta. More specifically, 12 different cases of aortas with abdominal aneurysms were examined and evaluated. Results: The first step was the 3D reconstruction of the aortas trans-forming the DICOM file into 3D surface models. Then, a finite element material model was developed simulating accurately the mechanical behavior of aortic walls. Conclusions: Through the results of these finite element analyses the values of tension, strain, and displacement were quantified and a rapid risk assessment was provided revealing that larger aneurysmatic regions elevate the risk of aortic rupture with some cases reaching an above 90% risk.