Life cycle assessment of a novel strategy based on hydrothermal carbonization for nutrient and energy recovery from food waste.

In this work, a novel strategy for food waste valorization was evaluated from an environmental life-cycle perspective. A system based on acid-assisted hydrothermal carbonization of food waste combined with the exploitation of hydrochar by combustion and process water through nutrient recovery stage and subsequent anaerobic digestion, was assessed and compared with stand-alone anaerobic digestion as the reference system. This combination of processes aims to recover both nutrients in a stage of struvite precipitation from process water and energy through hydrochar and biogas combustion. Both systems were modeled in Aspen Plus® to identify and quantify their most relevant input and output flows and subsequently evaluate their environmental performance through the life cycle assessment methodology. The novel combined system was found to generally involve a more favorable environmental performance than the reference stand-alone configuration, which would be closely linked to the substitution of hydrochar for fossil fuels. In addition, the impacts associated with soil application of the struvite produced in the integrated process would also be reduced compared to the use of the digestate generated in the stand-alone anaerobic digestion process. Following these results and the evolving regulatory framework for biomass waste management, mainly in the field of nutrient recovery, combined process based on acid-assisted hydrothermal treatment plus nutrient recovery stage and anaerobic digestion is concluded to be a promising circular economy concept for food waste valorization.

Novel short-term national strategies to promote the use of renewable hydrogen in road transport: A life cycle assessment of passenger car fleets partially fuelled with hydrogen.

This work presents an energy analysis combined with a comparative environmental life cycle assessment (LCA) of eight different passenger car fleets that use renewable hydrogen and a conventional fuel (natural gas or gasoline) under the same total energy input and the same hydrogen-to-mixture energy ratio. The fleets under comparison involve vehicles that use the two fuels separately or in a mixture. Using Italy as an illustrative country, this research work aims to help policy-makers implement well-supported strategies to promote the use of hydrogen in road transport in the short term. The proposed strategies achieve a carbon footprint reduction between 7 % and 35 % with respect to their conventional fleet benchmark. Within the current context, the results suggest the energy and environmental suitability of using hydrogen blends as short-term solutions, involving vehicles that require minor modifications with respect to current compressed natural gas vehicles and gasoline vehicles, while paving the way for pure hydrogen mobility.

Life cycle sustainability assessment of synthetic fuels from date palm waste.

The use of biowaste feedstock is often suggested for sustainable production of synthetic fuels through gasification followed by the Fischer-Tropsch process. While the technical performance of this type of bioenergy system has significantly been investigated, comprehensive sustainability analyses are still required. The present study evaluates the life cycle sustainability performance of synthetic diesel and gasoline from Tunisian date palm waste, and compares it with that of conventional fossil fuels. Life cycle inventories are elaborated to subsequently characterise the performance of the synthetic biofuels under a set of 12 environmental, economic and social indicators. Both environmental and economic hotspots were found to be associated with the need for electricity and oxygen. Direct emissions to the air and the investment in the plant's power section were also found to significantly affect the environmental and economic performances, respectively. Potential social impacts were found to be mainly linked to the supply chain of equipment and infrastructure, while electricity arose as the most contributing operational element. Overall, the evaluated synthetic biofuels could be considered competitive with conventional fossil fuels and contribute to the achievement of sustainable development goals only if environmentally- and socially-friendly (renewable) electricity and oxygen sources are implemented and the scale and configuration of the plant are optimised.

Revisiting the role of steam methane reforming with CO2 capture and storage for long-term hydrogen production.

Road transport is associated with high greenhouse gas emissions due to its current dependence on fossil fuels. In this regard, the implementation of alternative fuels such as hydrogen is expected to play a key role in decarbonising the transport system. Nevertheless, attention should be paid to the suitability of hydrogen production pathways as low-carbon solutions. In this work, an energy systems optimisation model for the prospective assessment of a national hydrogen production mix was upgraded in order to unveil the potential role of grey hydrogen from steam methane reforming (SMR) and blue hydrogen from SMR with CO2 capture and storage (CCS) in satisfying the hydrogen demanded by fuel cell electric vehicles in Spain from 2020 to 2050. This was done by including CCS retrofit of SMR plants in the energy systems model, as a potential strategy within the scope of the European Hydrogen Strategy. Considering three hypothetical years for banning hydrogen from fossil-based plants without CCS (2030, 2035, and 2040), it was found that SMR could satisfy the whole demand for hydrogen for road transport in the short term (2020-2030), while being substituted by water electrolysis in the medium-to-long term (2030-2050). Furthermore, this trend was found to be associated with an appropriate prospective behaviour in terms of carbon footprint.

Comparative life cycle sustainability assessment of renewable and conventional hydrogen.

Hydrogen is gaining interest as a strategic element towards a sustainable economy. In this sense, sound decision-making processes in the field of hydrogen energy require thorough analyses integrating economic, environmental and social indicators from a life-cycle perspective. For this purpose, Life Cycle Sustainability Assessment (LCSA) constitutes an appropriate methodology jointly handling indicators related to the three traditional dimensions of the sustainability concept. In this work, the sustainability performance of renewable hydrogen from both wind-powered electrolysis and biomass gasification was benchmarked against that of conventional hydrogen from steam methane reforming under a set of five life-cycle indicators: global warming, acidification, levelised cost, child labour, and health expenditure. The results led to identify the stage of driving-energy/biomass production as the main source of impact. When compared to conventional hydrogen, the life-cycle sustainability performance of renewable hydrogen was found to underperform under social and economic aspects. Nevertheless, the expected enhancement in process efficiency would significantly improve the future performance of renewable hydrogen in each of the three main sustainability dimensions.

The impact of incineration phase-out on municipal solid waste landfilling and life cycle environmental performance: Case study of Madrid, Spain.

Reducing the amount of municipal solid waste (MSW) fed to incineration while enhancing source separation and biological treatments is being considered a mean to protect the environment and human health and promote recycling. However, such a strategy can compromises the landfill reduction targets while the associated environmental benefits remain so far unexplored and, in any case, any potential benefit should be evaluated for specific situations. In this study we applied material flow analysis (MFA) and life cycle assessment (LCA) to quantitatively evaluate the potential impact of phasing-out incineration in Madrid, Spain. The current MSW management system was assessed against future scenarios that describe the elimination of incineration as well as the increase of source separation, recycling, composting, and anaerobic digestion. The results revealed that incineration phase-out jeopardizes landfill reduction. However, phasing-out incineration can reduce the impact on acidification, terrestrial and marine eutrophication, photochemical ozone formation, human toxicity cancer effects, and ecotoxicity. The climate impact ranges from irrelevant to largely beneficial depending on how the biogenic carbon is considered. The transition towards a renewable electricity mix and the increase in source separation of biodegradable waste seriously compromise the climate benefits of incineration over landfilling. Overall, actions are required in order to align incineration phase-out with the landfill reduction objective, namely upgrading material recovery facilities to reduce rejects and seeking alternative pathways for the rejects that will always exist.

Prospective carbon footprint comparison of hydrogen options.

The Life Cycle Assessment methodology is often used to evaluate the environmental performance of hydrogen energy systems. However, even though hydrogen is usually seen as a strategic energy carrier for the future energy sector, there is a lack of case studies assessing its prospective life-cycle performance. In order to contribute to filling this gap, this work addresses a carbon footprint comparison of hydrogen options from a prospective standpoint. Four relevant hydrogen production pathways (steam methane reforming, grid-powered alkaline electrolysis, wind-powered alkaline electrolysis, and biomass gasification) under three time scenarios (reference, year 2030, and year 2050) are assessed, taking into account the expected evolution of key technical parameters such as efficiencies, lifespans, and the grid electricity mix. The results show a favourable carbon footprint of renewable hydrogen from biomass gasification and wind electrolysis, with a relatively steady near-zero carbon footprint. Despite the unfavourable carbon footprint results of conventional hydrogen from steam methane reforming and hydrogen from grid electrolysis, the latter is associated with a rapid trend towards a suitable long-term carbon footprint.

Robust eco-efficiency assessment of hydrogen from biomass gasification as an alternative to conventional hydrogen: A life-cycle study with and without external costs.

Hydrogen is a key product for the decarbonisation of the energy sector. Nevertheless, because of the high number of technical options available for hydrogen production, their suitability needs to be thoroughly evaluated from a life-cycle perspective. The standardised concept of eco-efficiency is suitable for this purpose since it relates, with a life-cycle perspective, the environmental performance of a product system to its value. Hence, this work benchmarks the eco-efficiency performance of renewable hydrogen produced through biomass gasification against conventional hydrogen from the steam reforming of natural gas. For the eco-efficiency assessment, the harmonised environmental indicators of global warming, acidification and cumulative non-renewable energy demand were individually used, while the product system value was based on the levelised cost of hydrogen with/without internalisation of the external socio-environmental costs associated with climate change and human health. On the one hand, when the environmental and economic performances are separately considered, hydrogen from biomass gasification performs significantly better than hydrogen from steam methane reforming under environmental aspects (e.g., greenhouse gas emissions saving of 98%), whereas the opposite conclusion was found from an economic standpoint (levelised cost of 3.59 € and 2.17 € per kilogramme of renewable and fossil hydrogen, respectively). On the other hand, when combining life-cycle environmental and economic indicators under the umbrella of the eco-efficiency assessment, it is concluded that the renewable hydrogen option outperforms the conventional one, which is further remarked when implementing socio-environmental externalities. In this regard, a relative eco-efficiency score above 14 was estimated for the renewable hydrogen option when benchmarked against conventional hydrogen.

Environmental impact efficiency of natural gas combined cycle power plants: A combined life cycle assessment and dynamic data envelopment analysis approach.

The energy sector is still dominated by the use of fossil resources. In particular, natural gas represents the third most consumed resource, being a significant source of electricity in many countries. Since electricity production in natural gas combined cycle (NGCC) plants provides some benefits with respect to other non-renewable technologies, it is often seen as a transitional solution towards a future low­carbon power generation system. However, given the environmental profile and operational variability of NGCC power plants, their eco-efficiency assessment is required. In this respect, this article uses a novel combined Life Cycle Assessment (LCA) and dynamic Data Envelopment Analysis (DEA) approach in order to estimate -over the period 2010-2015- the environmental impact efficiencies of 20 NGCC power plants located in Spain. A three-step LCA+DEA method is applied, which involves data acquisition, calculation of environmental impacts through LCA, and the novel estimation of environmental impact efficiency (overall- and term-efficiency scores) through dynamic DEA. Although only 1 out of 20 NGCC power plants is found to be environmentally efficient, all plants show a relatively good environmental performance with overall eco-efficiency scores above 60%. Regarding individual periods, 2011 was -on average- the year with the highest environmental impact efficiency (95%), accounting for 5 efficient NGCC plants. In this respect, a link between high number of operating hours and high environmental impact efficiency is observed. Finally, preliminary environmental benchmarks are presented as an additional outcome in order to further support decision-makers in the path towards eco-efficiency in NGCC power plants.

Delving into sensible measures to enhance the environmental performance of biohydrogen: A quantitative approach based on process simulation, life cycle assessment and data envelopment analysis.

A novel approach is developed to evaluate quantitatively the influence of operational inefficiency in biomass production on the life-cycle performance of hydrogen from biomass gasification. Vine-growers and process simulation are used as key sources of inventory data. The life cycle assessment of biohydrogen according to current agricultural practices for biomass production is performed, as well as that of target biohydrogen according to agricultural practices optimised through data envelopment analysis. Only 20% of the vineyards assessed operate efficiently, and the benchmarked reduction percentages of operational inputs range from 45% to 73% in the average vineyard. The fulfilment of operational benchmarks avoiding irregular agricultural practices is concluded to improve significantly the environmental profile of biohydrogen (e.g., impact reductions above 40% for eco-toxicity and global warming). Finally, it is shown that this type of bioenergy system can be an excellent replacement for conventional hydrogen in terms of global warming and non-renewable energy demand.

Biomass pyrolysis for biochar or energy applications? A life cycle assessment.

The application of biochar as a soil amendment is a potential strategy for carbon sequestration. In this paper, a slow pyrolysis system for generating heat and biochar from lignocellulosic energy crops is simulated and its life-cycle performance compared with that of direct biomass combustion. The use of the char as biochar is also contrasted with alternative use options: cofiring in coal power plants, use as charcoal, and use as a fuel for heat generation. Additionally, the influence on the results of the long-term stability of the biochar in the soil, as well as of biochar effects on biomass yield, is evaluated. Negative greenhouse gas emissions are obtained for the biochar system, indicating a significant carbon abatement potential. However, this is achieved at the expense of lower energy efficiency and higher impacts in the other assessed categories when compared to direct biomass combustion. When comparing the different use options of the pyrolysis char, the most favorable result is obtained for char cofiring substituting fossil coal, even assuming high long-term stability of the char. Nevertheless, a high sensitivity to biomass yield increase is found for biochar systems. In this sense, biochar application to low-quality soils where high yield increases are expected would show a more favorable performance in terms of global warming.

Auto shredder residue recycling: Mechanical separation and pyrolysis.

Directive 2000/53/EC sets a goal of 85% material recycling from end-of-life vehicles (ELVs) by the end of 2015. The current ELV recycling rate is around 80%, while the remaining waste is called automotive shredder residue (ASR), or car fluff. In Europe, this is mainly landfilled because it is extremely heterogeneous and often polluted with car fluids. Despite technical difficulties, in the coming years it will be necessary to recover materials from car fluff in order to meet the ELV Directive requirement. This study deals with ASR pretreatment and pyrolysis, and aims to determine whether the ELV material recycling target may be achieved by car fluff mechanical separation followed by pyrolysis with a bench scale reactor. Results show that flotation followed by pyrolysis of the light, organic fraction may be a suitable ASR recycling technique if the oil can be further refined and used as a chemical. Moreover, metals are liberated during thermal cracking and can be easily separated from the pyrolysis char, amounting to roughly 5% in mass. Lastly, pyrolysis can be a good starting point from a "waste-to-chemicals" perspective, but further research should be done with a focus on oil and gas refining, in order both to make products suitable for the chemical industry and to render the whole recycling process economically feasible.

Hydrolysis of iron and chromium fluorides: mechanism and kinetics.

Fluoride complexes of metallic ions are one of the main problems when processing industrial effluents with high content of fluoride anion. The most important case is derived from pickling treatment of stainless steel, which is performed with HNO3/HF mixtures to remove oxides scale formed over the metal surface. Waste from this process, spent pickling liquor, must be treated for recovering metallic and acid content. Conventional treatments produce a final effluent with high quantity of fluoride complexes of iron and chromium. This work proposes a hydrolysis treatment of these solid metal fluorides by reacting them with a basic agent. Metal oxides are obtained, while fluoride is released to solution as a solved salt, which can be easily recovered as hydrofluoric acid. Solid iron and chromium fluorides, mainly K2FeF5(s) and CrF3(s), obtained in the UCM treatment process, were employed in this work. Optimal hydrolysis operating conditions were obtained by means of a factorial design: media must be basic but pH cannot be higher than 9.5, temperature from 40 to 70 degrees C and alkali concentration (potassium hydroxide) below 1.1 mol L(-1). Secondary reactions have been detected, which are probably due to fluoride adsorption onto obtained oxides surface. Mechanism of reaction consists of several stages, involving solid fluoride dissolution and complexes decomposition. Hydrolysis kinetics has been modeled with classical crystal dissolution kinetics, based on mass transfer phenomena.