• Energy Research

The citrus peels and residue of fruit juices production are rich in d-limonene, a cyclic terpene characterized by antimicrobial activity, which could hamper energy valorization bioprocess. Considering that limonene is used in nutritional, pharmaceutical and cosmetic fields, citrus by-products processing appear to be a suitable feedstock either for high value product recovery or energy bio-processes. This waste stream, more than 10MTon at 2013 in European Union (AIJN, 2014), can be considered appealing, from the view point of conducting a key study on limonene recovery, as its content of about 1%w/w of high value-added molecule. Different processes are currently being studied to recover or remove limonene from citrus peel to both prevent pollution and energy resources recovery. The present review is aimed to highlight pros and contras of different approaches suggesting an energy sustainability criterion to select the most effective one for materials and energy valorization.

This paper aims at evaluating the best allocation of potential biomethane generation for the decarbonization of the transport system, presenting a case study in Italy. The country has some peculiar features, such as several operating biogas plants, additional potential feedstock for biogas/biomethane generation, a well-developed natural gas network and established relevant natural gas uses in different final sectors, including transport. Based on current estimates for sustainable biomethane potential by 2030, ranging from 2.3 to 7.6 billion cubic meters depending on the scenario, the analysis compares technologies for the generation, distribution and final use of biomethane. The results of the analysis confirm the potential interesting contribution of biomethane in decarbonizing the Italian transport system: a billion cubic meters of biomethane can lead to 2.33–4.37 MtCO2e savings, depending on the feedstock mix and the application. On a national basis, annual climate emission savings in 2030 range from 10.0 to 26.7 MtCO2e, depending on the scenario. Additional 3.1–8.1 MtCO2e of emissions can be avoided if the CO2 captured during the biomethane upgrading can be stored or reused. The proposed methodology could be used to extend the analysis to other countries, and to the European context.

Within the framework of defining a new energy paradigm to address climate change and other global challenges, the energy community model is gaining interest in several countries, especially in Europe. This article analyses the literature and experiences of organisational forms that fall under the definition of energy communities in a broad sense, in relation to their ability to bring improvements to the social, environmental and economic dimensions, and to ensure durability and replicability. The main elements that constitute a complete, albeit simplified, model of energy community are identified and analysed. The legislative and regulatory frameworks, technologies and social innovation frameworks, identified here as enabling elements, are discussed, as well as the elements of the energy community business models and the impacts generated at the environmental and energy, economic and social levels. The transformation potential of energy communities is confirmed as more than promising. However, in order to develop as a sustainable and replicable model capable of achieving social and environmental goals, as well as economic stability, further significant research and experimentation, following a cross-sectoral and multidisciplinary approach and strong political leadership, are needed.

Catalytic decomposition of methane is today considered as a pathway to hydrogen production that - unlike the other well-known methods - can convert methane into hydrogen without generating COx emission, but rather delivering solid Carbon, a storable and useable product which, in case of biomethane cracking, generates biogenic Carbon and a Carbon Negative route (Negative Emission Technology). Although mostly metallic catalysts have been used for this purpose, due to the rapid deactivation of this type of catalyst and the challenges of their regeneration, methane decomposition over carbon materials attracted some attention during recent years. This work provides a review of the recent studies performed on hydrogen production through methane cracking over carbon-based catalyst. The impact of operating parameters such as reaction temperature, pressure, feedstock purity, space velocity as well as the catalyst characteristics including particle size, surface area, pore volume, oxygenated compounds, and ash content on methane decomposition has been widely discussed in this review. Based on the literatures, operating temperature more than 800 ◦C and space velocity less than 1 L/g.h for pure methane are required to provide methane conversion higher than 50%. Also, reducing the concentration of methane in feedstock with inert gases as well as using carbon-based catalysts with lower particle size, higher surface area, more mesopores and oxygenated compounds can reach to an enhancement in methane conversion. Also, investigation on impact of ash content shows loading metals such as Fe, Ni, Ca, and Pd metals over carbonaceous materials improve their catalytic activities.

Extra virgin olive-oil (EVO) production is an important economic activity for several countries, especially in the Mediterranean area such as Spain, Italy, Greece and Tunisia. The two major by-products from olive oil production, solid-liquid Olive Pomace (OP) and the Olive Mill Waste Waters (OMWW), are still mainly disposed on soil, in spite of the existence of legislation which already limits this practice. The present study compares the environmental impacts associated with two different scenarios for the management of waste from olive oil production through a comparative Life Cycle Assessment (LCA). The two alternative scenarios are: (I) Anaerobic Digestion and (II) Disposal on soil. The analysis was performed through SimaPro software and the assessment of the impact categories was based on International Life Cycle Data and Cumulative Energy Demand methods. Both the scenarios are mostly related to the cultivation and harvesting phase and are highly dependent on the irrigation practice and related energy demand. Results from the present study clearly show that the waste disposal on soil causes the worst environmental performance of all the impact categories considered here. Important environmental benefits have been identified when anaerobic digestion is chosen as the final treatment. It was consequently demonstrated that anaerobic digestion should be a feasible alternative for olive mills, to produce biogas from common olive oil residues, reducing the environmental burden and adding value to the olive oil production chain.

The production of biogas for energy generation through the anaerobic digestion is seen as an effective way to exploit local renewable resources as a substitute of fossil fuels. The two main applications that are currently adopted are the electricity production through biogas internal combustion engines, potentially combined with heat recovery, and the biogas upgrading to biomethane, to be supplied to the natural gas infrastructure. This research work contributes to the discussion by analyzing the performance of a real biogas plant in Italy, based on the anaerobic digestion of the organic fraction of municipal solid waste, that has shifted from power generation to biomethane generation. The performance of the two configurations is compared by means of the expected CO2 emissions savings against the current average electricity in Italy and natural gas carbon intensities, including upstream emissions. The results show that, based on the assumptions of our analysis for the current context of Italy, 1 MWh of biogas from organic fraction of municipal solid waste can lead to 152 kgCO2,eq savings if upgraded to biomethane and injected into the grid, but only to 120 kgCO2,eq when used in engines running in full-electric mode. If the engines are also producing useful heat, emission savings increase, reaching a trade-off with biomethane if 31% of the annual heat production can be recovered. However, considering the expected 2030 electricity mix in Italy, biomethane production would still be the best solution to maximize emission savings. Performance data from real plants are an important resource to develop reliable and effective energy system models, that can support policy makers in defining local energy plans and decarbonization strategies.

Given that the pressure of climate change action on companies is increasing, it is recommended to measure the improvement of mitigation activities in terms of GHG emissions. This paper aims to highlight the still-open aspects that characterise simplified GHG accounting tools, starting from the outcomes of a case study. This study was performed using a simplified Italian software for the CO2 eq accounting of composting and anaerobic digestion, two mitigation activities that contribute an important share of global GHG emissions reduction. The tool is based on the life-cycle thinking approach. It has been applied to an Italian company that treats the organic fraction of municipal solid waste. The tool analysis has made it possible to stress several issues that are currently the object of debate in the literature, for example, the trade-off between the flexibility of the software and its user friendliness or the multifunctionality issues and their different interpretations. However, focusing on just one impact category, i.e., climate change, may lead to an incomplete picture of the overall environmental performance of the process analysed. Therefore, this tool could be improved by including other impact categories, such as eutrophication and acidification, which may be affected by the studied activities.

Hydrogen is being included in several decarbonization strategies as a potential contributor in some hard-to-abate applications. Among other challenges, hydrogen storage represents a critical aspect to be addressed, either for stationary storage or for transporting hydrogen over long distances. Ammonia is being proposed as a potential solution for hydrogen storage, as it allows storing hydrogen as a liquid chemical component at mild conditions. Nevertheless, the use of ammonia instead of pure hydrogen faces some challenges, including the health and environmental issues of handling ammonia and the competition with other markets, such as the fertilizer market. In addition, the technical and economic efficiency of single steps, such as ammonia production by means of the Haber–Bosch process, ammonia distribution and storage, and possibly the ammonia cracking process to hydrogen, affects the overall supply chain. The main purpose of this review paper is to shed light on the main aspects related to the use of ammonia as a hydrogen energy carrier, discussing technical, economic and environmental perspectives, with the aim of supporting the international debate on the potential role of ammonia in supporting the development of hydrogen pathways. The analysis also compares ammonia with alternative solutions for the long-distance transport of hydrogen, including liquefied hydrogen and other liquid organic carriers such as methanol.