Hydrothermal carbonization (HTC) represents an efficient and valuable pre-treatment technology to convert waste biomass into highly dense carbonaceous materials that could be used in a wide range of applications between energy, environment, soil improvement and nutrients recovery fields. HTC converts residual organic materials into a solid high energy dense material (hydrochar) and a liquid residue where the most volatile and oxygenated compounds (mainly furans and organic acids) concentrate during reaction. Pristine hydrochar is mainly used for direct combustion, to generate heat or electricity, but highly porous carbonaceous media for energy storage or for adsorption of pollutants applications can be also obtained through a further activation stage. HTC process can be used to enhance recovery of nutrients as nitrogen and phosphorous in particular and can be used as soil conditioner, to favor plant growth and mitigate desertification of soils. The present review proposes an outlook of the several possible applications of hydrochar produced from any sort of waste biomass sources. For each of the applications proposed, the main operative parameters that mostly affect the hydrochar properties and characteristics are highlighted, in order to match the needs for the specific application.

In light of growing concerns regarding greenhouse gas emissions and the increasingly severe impacts of climate change, the global situation demands immediate action to transition towards sustainable energy solutions. In this sense, hydrogen could play a fundamental role in the energy transition, offering a potential clean and versatile energy carrier. This paper reviews the recent results of Life Cycle Assessment studies of different hydrogen production pathways, which are trying to define the routes that can guarantee the least environmental burdens. Steam methane reforming was considered as the benchmark for Global Warming Potential, with an average emission of 11 kg_CO2eq/kg_H2. Hydrogen produced from water electrolysis powered by renewable energy (green H₂) or nuclear energy (pink H₂) showed the average lowest impacts, with mean values of 2.02 kg_CO2eq/kg_H2 and 0.41 kg_CO2eq/kg_H2, respectively. The use of grid electricity to power the electrolyzer (yellow H₂) raised the mean carbon footprint up to 17.2 kg_CO2eq/kg_H2, with a peak of 41.4 kg_CO2eq/kg_H2 in the case of countries with low renewable energy production. Waste pyrolysis and/or gasification presented average emissions three times higher than steam methane reforming, while the recourse to residual biomass and biowaste significantly lowered greenhouse gas emissions. The acidification potential presents comparable results for all the technologies studied, except for biomass gasification which showed significantly higher and more scattered values. Regarding the abiotic depletion potential (mineral), the main issue is the lack of an established recycling strategy, especially for electrolysis technologies that hamper the inclusion of the End of Life stage in LCA computation. Whenever data were available, hotspots for each hydrogen production process were identified.

Organic waste fraction disposed to landfill induce the release of greenhouse gas and leachate due to its degradation. The collection and treatment of such typology of waste is imperative in order to decrease environmental pollution and improve recycling rates. The aim of this study is to define a flexible and economically viable system to process all the RMSW and the OFMSW coming from SC, in a territory with low recycling rates. To that purpose, the survey provides a dynamic system which comply with future increases in the efficiency of SC systems. Dry anaerobic batch reactors are considered in order to treat RMSW and to operate the OFMSW, as long as SC improves. Four scenarios were considered, in particular for 10%, 25%, 50% and 75% SC rate. Biogas production has been estimated for evaluating the potentiality of each SC rate, since it can be exploited for generating electric energy and heating. Biogas generation is enhanced of the 21% by increasing from 10% to 75% SC, making the system more profitable under an energetic point of view. Moreover, the amount of electric energy which could be sold per year for each SC scenario was calculated, resulting as 631,293 kWh for the 10% SC and 442,527 kWh for 75% SC. Considerations on the exportability of the approach were also added in the paper, highlighting the affordability of the anaerobic digestion system in other countries

Bifacial photovoltaic (BPV) panels represent one of the main solar technologies that will be used in the near future for renewable energy production, with a foreseen market share in 2030 of 70% among all the photovoltaic (PV) technologies. Compared to monofacial panels, bifaciality can ensure a gain in energy production per unit panel area together with a competitive cost. However, it is of paramount importance to identify whether there is also an environmental benefit when adopting bifacial technologies as opposed to traditional monofacial ones. To obtain a proper insight into the environmental impact, this paper reviews the Life Cycle Assessment (LCA) studies of bifacial solar panels, identifying the most crucial processes and materials that raise environmental burdens. The analysis also contributes to determining whether the major aspects that influence energy production in real operation scenarios and, most of all, that can ensure the gain associated with bifaciality, are considered and how these can further affect the overall environmental impacts. In this sense, it was found that the installation parameters like the mounting structure, or the choice of ground material to raise the albedo as well as the diffuse irradiation that hits the rear surface of thepanel, are commonly not considered during LCA analysis. However, none of the analyzed studies address the issue in a comprehensive way, hampering an effective comparison between both the different works and traditional monofacial PV panels. Recommendations for future LCAs are finally proposed.