Food waste is a major issue in the context of pollution, climate change, and the future circular economy. Composting kitchen waste is a promising method to recycle elements, yet the efficiency of composting is limited, calling for new processes that degrade rapidly and thoroughly organic matter. Here, we built a rapid laboratory-scale aerobic composting system, equipped with a water bath fueled with either solar energy, or electricity under low sunlight. We tested compositing with and without energy. Results show that only three days are needed to raise the temperature to over 45 °C by energy composting in winter, leading to notable increases in pH, total nitrogen, and cation exchange capacity after 7 days. Composting materials were thoroughly decomposed and mature in 10 days, displaying pH of 7.5, ratio of total organic carbon to total nitrogen of 9.9, cation exchange capacity of 65.61 cmol kg⁻¹, and germination index of 80.4%. Overall, energy composting starts biodegradation quickly in 2 days, reduces effectively the inhibition from some waste compounds, decomposes organic substances well, and yields mature compost.

The European Green Deal has set climate and energy targets for 2030 and the goal of achieving net zero greenhouse gas emissions by 2050, while supporting energy independence and economic growth. Following these goals, and as expected, the transition to “green” renewable energy is growing and will be intensified, in the near future. One of the main pillars of this transition, particularly for Mediterranean countries, is solar photovoltaic (PV) power. However, this is the least land-efficient energy source, while it is also highly competitive in food production, since solar parks are often developed in former agricultural areas, thus resulting in the systematic reduction in arable lands. Therefore, in the context of PV energy planning, the protection and preservation of arable lands should be considered a key issue. The emerging technology of agrovoltaics offers a balanced solution for both agricultural and renewable energy development. The sustainable “symbiosis” of food and energy under common lands also supports the specific objective of the post-2020 Common Agricultural Policy, regarding the mitigation of and adaptation to the changing climate, as well as the highly uncertain socio-economic and geopolitical environment. The purpose of this study is twofold, i.e., (a) to identify the state of play of the technologies and energy efficiency measures of agrovoltaics, and (b) to present a comprehensive analysis of their interactions with the water–energy–food–land nexus. As a proof of concept, we consider the plain of Arta, which is a typical agricultural area of Greece, where we employ a parametric analysis to assess key features of agrovoltaic development with respect to energy vs. food production, as well as water saving, as result of reduced evapotranspiration.

Curcumin was extracted from Curcuma Longa employing a green, bio-based, and food-agreed surfactant-free microemulsion (SFME) consisting of water, ethanol, and triacetin. Concerning the high solubility of curcumin in the examined ternary mixtures, it was attempted to produce highly concentrated tinctures of up to a total of ~130 mg/mL curcuminoids in the solvent by repeatedly extracting fresh rhizomes in the same extraction mixture. The amount of water had a significant influence on the number of cycles that could be performed as well as on the extraction of the different curcuminoids. In addition, the purity of single extracts was enhanced to 94% by investigating several purification steps, e.g. vacuum distillation and lyophilization. Through purification before extraction, the water insoluble curcumin extract could be solubilized indefinitely in an aqueous environment. Additional stability tests showed that solutions of curcumin can be stable up to five months when concealed from natural light.

This research develops a bottom-up procedure to assess the potential of food-energy-water (FEW) systems on the rooftops of buildings in an urban district in Spain considering the urban morphology of the built environment and obtains accurate assessments of production and developmental patterns. A multicriteria decision-making technique implemented in a geographical information system (GIS) environment was used to extract suitable rooftop areas. To implement this method, the slope (tilt), aspect (azimuth), shading, and solar radiation of the rooftops were calculated using LiDAR (Light Detection and Ranging) data and building footprints. The potential of FEW system implementation was analysed at the building and morphology levels. The results showed several differences between residential and non-residential urban morphologies. Industrial areas contained the highest productivity for FEW systems. The production was 2.51 kg of tomatoes/m², 48 kWh of photovoltaic energy/m², and 0.16 l of rainwater/m². Regarding the residential urban morphologies, the more compact tents resulted in better performance. Among the FEW systems, although water could best benefit from the features of the entire roof surface, the best production results were achieved by energy. The food system is less efficient in the built environment since it requires flat roofs. The methodology presented can be applied in any city, and it is considered optimal in the European context for the development of self-production strategies for urban environments.