A socio-economic analysis of biomethane in the transport sector: The case of Italy

Hydrochar and synthetic natural gas co-production for a full circular economy implementation via hydrothermal carbonization and methanation: An economic approach

Herein we study the economic performance of hydrochar and synthetic natural gas co-production from olive tree pruning. The process entails a combination of hydrothermal carbonization and methanation. In a previous work, we evidenced that standalone hydrochar production via HTC results unprofitable. Hence, we propose a step forward on the process design by implementing a methanation, adding value to the gas effluent in an attempt to boost the overall process techno-economic aspects. Three different plant capacities were analyzed (312.5, 625 and 1250 kg/hr). The baseline scenarios showed that, under the current circumstances, our circular economy strategy in unprofitable. An analysis of the revenues shows that hydrochar selling price have a high impact on NPV and subsidies for renewable coal production could help to boost the profitability of the process. On the contrary, the analysis for natural gas prices reveals that prices 8 times higher than the current ones in Spain must be achieved to reach profitability. This seems unlikely even under the presence of a strong subsidy scheme. The costs analysis suggests that a remarkable electricity cost reduction or electricity consumption of the HTC stage could be a potential strategy to reach profitability scenarios. Furthermore, significant reduction of green hydrogen production costs is deemed instrumental to improve the economic performance of the process. These results show the formidable techno-economic challenge that our society faces in the path towards circular economy societies.

Assessment of the incubating environment for investment in biogas technology in Syria by using AHP and SWOT

In light of the massive energy supply shortage due to the Syrian war since 2011, renewable energy adoption has a high potential to cover the actual energy demand. Hence, this study aims to shed light on the factors that affect investment in biogas technology. With the scarcity of research on alternative energies in Syria, this paper focused on the characteristics of the Syrian environment toward biogas technology adoption. The results show that Syrian society accepts and desires to adopt new technologies, representing an optimal strategy to stimulate biogas technology use and the need to spread awareness about its benefits. The SWOT model was applied to identify strengths, weaknesses, opportunities, and threats facing biogas technology adoption. The analytical hierarchy process model was applied to set priorities and make better decisions related to the knowledge of biogas, acceptance of biogas technology, desire for and common approach for its use, the resulting organic fertilizer, and administrative and financial aspects. The work concludes that the southern region was at the forefront in the areas studied in terms of weights of biogas technology investment criteria, subsequently, the central and later the coastal regions. By presenting a systematic and comprehensive approach, this study represents a roadmap to assist decision-makers in inking decisions related to adopting and deploying biogas technology on a larger scale and contributes to developing a criterion for selecting biogas sites in Syria.

Integration of photovoltaic panels and solar collectors into a plant producing biomethane for the transport sector: Dynamic simulation and case study

In the current energy and environmental framework, the environmental impact of the road transport sector and the urban waste management and disposal are extremely important for highly crowded cities. This work assesses the energy, economic and environmental performance of an innovative paradigm for the full decarbonisation of the road transport sector. This problem is integrated with the management of the organic fraction of municipal solid waste. In particular, the proposed technology is based on an anaerobic digestion plant coupled with a biogas upgrading unit, for the production of biomethane. In addition, photovoltaic panels and solar thermal collectors are also considered for matching electrical and thermal demands, in order to achieve a fully-renewable system. To this scope, the system also includes suitable thermal and electric storages. The economic analysis also considers specific public funding policies, currently available for this technology. This system aims to be a novel paradigm in the energy scenario of waste disposal and road transport sector refurbishment. TRNSYS software was adopted to perform an accurate dynamic simulation for a one-year operation of the system. The anaerobic digestion model is developed by the authors in MatLab and integrated in TRNSYS, for dynamic simulation purpose. Results show that the plant is almost self-sufficient due to the integration of storage systems for both the thermal and electric energy. The photovoltaic system is able to reduce by 45% the energy dependence from the grid. Energy and environmental analyses show a Primary Energy Saving of 126% and a reduction of CO₂ equivalent emissions by 112%. The economic feasibility analysis shows a promising Simple Payback period of 6 years.

Economic assessment for vegetable waste valorization through the biogas-biomethane chain in Italy with a circular economy approach

The current geo-political framework and the environmental concern about pollution and global warming are leading Europe to rethink its energy production, moving forward to the incentivization the renewable energy market. In this scenario, the use of waste from the agri-food sector shows a huge potentiality to enhance the transition in line with the circular economy principles. Biogas production represents an environmental friendly strategy to successfully recover large amounts of waste and by-products to produce renewable energy. Furthermore, in light of the rising need of green biofuels, biogas can be converted into biomethane, allowing the implementation of a full circular model. The objective of this paper is to perform an economic assessment to evaluate whether the upgrading of an existing biogas plant, in which the diet includes also vegetable waste from a plant producing frozen vegetables, could be profitable considering different scenarios, to reach a sustainable circular model. The analysis will be conducted through the Discounted Cash Flow method, considering four main indexes: NPV, DPBT, IRR, and PI. The results highlight the unprofitability of the biogas-biomethane chain if the upgrading system is performed maintaining the same characteristics of the starting plant. On the other hand, if changes in the digester's diet occur, the investment becomes immediately profitable in the considered time-span. The circular economy model is not completely accomplished, as profitability can only be reached if silage maize is partially kept as feedstock. Moreover, the conversion of the plant is not economically feasible if an adequate subsidy is not provided. The economic assessment of the upgrading system for biogas to biomethane is an essential element to be provided to the agribusiness entrepreneurs, as they need all the relevant economic aspects to decide to invest and adopt this solution to establish an innovative circular business model in agriculture.

How to use biogas?: A systematic review of biogas utilization pathways and business models

There are many options for the utilization of biogas in different energy sectors (power, heat, mobility). The technical possibilities of using biogas are more diverse than the actual business models applied in the biogas industry. This paper shows the possible utilization pathways of biogas, divided into coupled power and heat generation, direct utilization and upgrading to a gas of a higher value. Subsequently, an overview of the business models discussed is given by a systematic literature review. The latter shows that the investigation of biogas business models is focused mainly on the last decade and has increased slightly over time. The regions of investigation can be found worldwide, with a clear focus on Europe. Direct use is studied mainly in the Asian and African regions. In the European context, a shift from investigating combined heat and power use to upgrading the biogas produced is evident.

Designing the biomethane production chain from urban wastes at the regional level: An application to the Rome Metropolitan Area

This paper proposes a methodology to design the biomethane production chain from MSW at the regional level and to assess the environmental and economic performance of the chain. In the design phase, the following parameters are considered: number and production capacity of biomethane plants, localization of plants, waste flows among municipalities and plants. The model is adopted to design the biomethane chain in the Rome Metropolitan Area (Italy). Several structures of production chain are designed and their performances are assessed. The economic factors mostly able to affect the performance of the chain are waste disposal tariff, biomethane selling price, and the economic incentive provided to biomethane producers. Their impacts are discussed through sensitivity analyses. Results show that the structure maximizing the economic performance has the worst environmental performance and vice versa. Hence, a new structure of the economic incentive is proposed, aimed at re-aligning economic and environmental performance.

Mathematical Analysis and Update of ADM1 Model for Biomethane Production by Anaerobic Digestion

Biomethane is a renewable product that can directly substitute its fossil counterpart, although its synthesis from residual biomasses has some hurdles. Because of the complex nature of both biomasses and the microbial consortia involved, innovative approaches such as mathematical modeling can be deployed to support possible improvements. The goal of this study is two-fold, as we aimed to modify a part of the Anaerobic Digestion Model No. 1 (ADM1), describing biomethane production from activated sludge, matching with its actual microbial nature, and to use the model for identifying relevant parameters to improve biomethane production. Firstly, thermodynamic analysis was performed, highlighting the direct route from glucose to biomethane as the most favorable. Then, by using MATLAB® and Simulink Toolbox, we discovered that the model fails to predict the microbiological behavior of the system. The structure of the ADM1 model was then modified by adding substrate consumption yields in equations describing microbial growth, to better reflect the consortium behavior. The updated model was tested by modifying several parameters: the coefficient of decomposition was identified to increase biomethane production. Approaching mathematical models from a microbiological point of view can lead to further improvement of the models themselves. Furthermore, this work represents additional evidence of the importance of informatics tools, such as bioprocess simulations to foster biomethane role in bioeconomy.

The Knowledge Based Agricultural Bioeconomy: A Bibliometric Network Analysis

The last ten years have witnessed an increase in publications focusing on bioeconomy as a proposal to confront the global challenges of climate change, depletion of non-renewable resources and ecosystem degradation. This paper investigates the scientific literature on issues related agricultural bioeconomy by applying a bibliometric network analysis. Bibliometric analysis is applied to the publications of the Scopus database during the period 2010–2020 in order to provide an overview of the main aspects that characterize agricultural bioeconomy. The results showed that out of a total of 1100 scientific papers, only 2.45% were published in 2010, while the corresponding share in 2020 was 20.81%. In the five years of 2016–2020, cumulatively, 70.63% of the publications were made, showing the dynamic evolution of bioeconomy. In addition, out of 85 countries in total, Germany and Italy are the two countries with most publications, while the fragmentation of research is evident with the creation of two main nodes, the European and the American. Moreover, keyword analysis showed that biomass and sustainability are two main recurring concepts, confirming that, currently, bioeconomy operates at three different levels: energy demand, land demand, and governance. It is apparent that to boost the development of agricultural bioeconomy, the following aspects should be assessed: the effective use of resources, an understanding of the key drivers of agricultural bioeconomy, and a clear perception of their associations. There is still no consensus as to which are the key factors that will accelerate its sustainable development. Our pursuit is to use the tools of bibliometric analysis to reach more critical conclusions regarding the agricultural bioeconomy, rather than approach it in a static way.

Optimizing hydrothermal carbonization of olive tree pruning: A techno-economic analysis based on experimental results

In this study the optimization of the hydrothermal carbonization process for the conversion of olive tree pruning into biofuel is presented. To this end, a combined experimental-economic assessment is performed. Experimental data obtained at laboratory scale were used to estimate the economic performance of a hypothetical industrial scale plant. To evaluate the viability of the project, three different plant sizes according to their capacity were selected (1250-625-312.5 kg/h). The discounted cash flow method was applied for the profitability analysis. Different scenarios were analyzed considering the reduction of associate costs or the improvement of the revenues compared to the baseline case. Results indicate that with the sizes studied, none of the alternatives are profitable. Despite that, the larger capacity shows the best outcomes. In this case, minimum selling price of 0.39 €/kg for hydrochar is required to reach profitability. Lower plant sizes would require higher selling prices (i.e., 0.46 €/kg for 625 kg/h capacity and 0.59 €/kg for 312.5 kg/h capacity). Similarly, a reduction of 33% in the electrical energy consumption can make the plan be profitable for the larger capacity. Likewise, a reduction until 0.053 €/kWh in the electricity price must be reached for achieving profitability. Thus, importance of government incentives is revealed in this work given that the reduction of costs along with the improvement in the revenues for the selling of the product can make the project economically viable. Other parameters like the number of workers are also interesting to consider as for example the reduction by two units improves the NPV value in almost 600 k€ for all the plant sizes.

Promoting Sustainability: Wastewater Treatment Plants as a Source of Biomethane in Regions Far from a High-Pressure Grid. A Real Portuguese Case Study

Wastewater treatment plants (WWTP) located in regions far from a high-pressure grid can produce renewable biomethane, which can partially substitute the natural gas locally consumed. However, the economic viability of implementing biomethane plants in WWTP has to be guaranteed. This paper uses the discount cash flow method to analyze the economic viability of producing biomethane in a WWTP located in Évora (Portugal). The results show that, under the current conditions, it is unprofitable to produce biomethane in this WWTP. Since selling the CO2 separated from biogas may result in an additional income, this option was also considered. In this case, a price of 46 EUR/t CO2 has to be paid to make the project viable. Finally, the impact of potential government incentives in the form of feed-in premia was investigated. Without selling CO2, the project would only be profitable for feed-in premia above 55.5 EUR/MWh. If all the CO2 produced was sold at 30 EUR/t CO2, a premium price of 20 EUR/MWh would make the project profitable. This study shows that the economic attractiveness of producing biomethane in small WWTP is only secured through sufficient financial incentives, which are vital for developing the biomethane market with all its associated advantages.

A review of circularity and sustainability in anaerobic digestion processes

The debate on the relationship between the long-established concept of sustainability, and the relatively novel one of circularity in constantly increasing biogas production remains. In this study, additional discussion elements to such an open debate are provided. With its role in the bioeconomy and ongoing ambiguity, a bibliographic review of anaerobic digestion is provided. In particular, this study aims to i) verify whether sustainability assessments and circularity measurements are performed in different ways in anaerobic digestion projects and ii) understand which indicators have been utilized for each pillar of sustainability. Initially, 152 scientific documents from the Scopus and Web of Science scholarly journal databases were selected. Specific eligibility criteria that were any type of measurement of circularity and/or assessment of sustainability, were used for screening. Fifty-eight articles met these criteria and were analyzed in depth. The results show that the terms circularity and sustainability are not always univocal concepts in the reviewed scientific contributions. Consequently, the relative criteria or measurements for their analysis are not the same. As a result, a different interpretation of the two concepts is suggested. Circularity should be considered as one of the ways to achieve the broadest objective of sustainability.

Academic Activities Recommendation System for Sustainable Education in the Age of COVID-19

Currently, universities are going through a critical moment due to the coronavirus disease in 2019. To prevent its spread, countries have declared quarantines and isolation in all sectors of society. This has caused many problems in the learning of students, since, when moving from a face-to-face educational model to a remote model, several academic factors such as psychological, financial, and methodological have been overlooked. To exactly identify the variables and causes that affect learning, in this work a data analysis model using a Hadoop framework is proposed. By processing the data, it is possible to identify and classify students to determine the problems they present in different learning activities. The results are used by an artificial intelligence system that takes student information and converts it into knowledge, evaluates the academic performance problems they present, and determines what type of activity aligns with the students. The artificial intelligence system processes the information and recommends activities that focus on each student’s abilities and needs. The integration of these systems to universities creates an adaptive educational model that responds to the new challenges of society.

Waste generation, wealth and GHG emissions from the waste sector: Is Denmark on the path towards circular economy?

Municipal solid waste (MSW) is one of the most urgent issues associated with economic growth and urban population. When untreated, it generates harmful and toxic substances spreading out into the soils. When treated, they produce an important amount of Greenhouse Gas (GHG) emissions directly contributing to global warming. With its promising path to sustainability, the Danish case is of high interest since estimated results are thought to bring useful information for policy purposes. Here, we exploit the most recent and available data period (1994-2017) and investigate the causal relationship between MSW generation per capita, income level, urbanization, and GHG emissions from the waste sector in Denmark. We use an experiment based on Artificial Neural Networks and the Breitung-Candelon Spectral Granger-causality test to understand how the variables, object of the study, manage to interact within a complex ecosystem such as the environment and waste. Through numerous tests in Machine Learning, we arrive at results that imply how economic growth, identifiable by changes in per capita GDP, affects the acceleration and the velocity of the neural signal with waste emissions. We observe a periodical shift from the traditional linear economy to a circular economy that has important policy implications.

A Local Ecosystem Assessment of the Potential for Net Negative Heavy-Duty Truck Greenhouse Gas Emissions through Biomethane Upcycling

Decarbonising heavy-duty trucks is challenging due to high journey power and energy requirements. With a growing fleet of commercial vehicles in the UK, biomethane can provide significant reductions in greenhouse gas (GHG) emissions compared to fossil diesel. Methane is a potent GHG with a global warming potential (GWP) of 23–36, therefore reducing levels in the atmosphere can have a significant impact on climate change. There are a range of anthropogenic sources of methane that could be collected and processed to provide sustainable energy (upcycled), e.g., agricultural waste and the waste water system. This paper explores the impact of using upcycled methane in transport in South East England, evaluating local sources of anthropogenic methane and the environmental and economic impact of its use for a heavy-duty truck compared to fossil and battery electric alternatives. Analysis concludes that the use of upcycled methane in transport can provide significant reductions in lifecycle GHG emissions compared to diesel, fossil natural gas or battery electric trucks, and give net negative GHG emissions where avoided environmental methane emissions are considered. Furthermore, upcycling solutions can offer a lower cost route to GHG reduction compared to electrification.

Improvement of an Online Education Model with the Integration of Machine Learning and Data Analysis in an LMS

The events that took place in the year 2020 have shown us that society is still fragile and that it is exposed to events that rapidly change the paradigms that govern it. This has been shown by a pandemic like Coronavirus disease 2019; this global emergency has changed the way people interact, communicate, study, or work. In short, the way in which society carries out all activities has changed. This includes education, which has bet on the use of information and communication technologies to reach students. An example of the aforementioned is the use of learning management systems, which have become ideal environments for resource management and the development of activities. This work proposes the integration of technologies, such as artificial intelligence and data analysis, with learning management systems in order to improve learning. This objective is outlined in a new normality that seeks robust educational models, where certain activities are carried out in an online mode, surrounded by technologies that allow students to have virtual assistants to guide them in their learning.

Drivers of CO2-Emissions in Fossil Fuel Abundant Settings: (Pooled) Mean Group and Nonparametric Panel Analyses

The present inquiry addresses the income-environment relationship in oil-producing countries and scrutinizes the further drivers of atmospheric pollution in the respective settings. The existing literature that tests the environmental Kuznets curve hypothesis within the framework of the black-box approaches provides only a bird’s-eye perspective on the long-run income-environment relationship. The aspiration behind this study is making the first step toward the disentanglement of the sources of carbon dioxide emissions, which could be employed in the pollution mitigation policies of this group of countries. Based on the combination of two strands of literature, the environmental Kuznets curve conjecture and the resource curse, the paper at hand proposes an augmented theoretical framework of this inquiry. To approach the research questions empirically, the study employs advanced panel cointegration techniques. To avoid econometric misspecification, the study also employs for the first time a nonparametric time-varying coefficient panel data estimator with fixed effects (NPFE) for the dataset of 37 oil-producing countries in the time interval spanning between 1989 and 2019. The empirical analysis identifies the level of per capita income, the magnitude of oil rents, the share of fossil fuel-based electricity generation in the energy mix, and the share of the manufacturing sector in GDP as essential drivers of carbon dioxide emissions in the oil-rich countries. Tertiarization, on the contrary, leads to a substantial reduction of emissions. Another striking result of this study is that level of political rights and civil liberties are negatively associated with per capita carbon emissions in this group of countries. Furthermore, the study decisively rejects an inverted U-shaped income-emission relationship and validates the monotonically or exponentially increasing impact of average income on carbon dioxide emissions.

The relationship between municipal solid waste and greenhouse gas emissions: Evidence from Switzerland

Municipal solid waste generation is becoming a prominent issue in the environmental arena. The aim of this paper is to investigate the relationship among municipal waste generation, greenhouse gas emissions, and GDP in Switzerland over the period 1990-2017. We apply both time series procedures (stationarity and causality tests) and a Machine Learning approach. Empirical findings underline a bidirectional causal relationship between municipal solid waste generation and GDP, indicating that the Environmental Kuznets Curve hypothesis holds for Switzerland. Moreover, we found that waste recovery (recycling and composting) is a key driver in mitigating greenhouse gas emissions. In fact, in the Tree Model, the probability that a change in the waste recovery variable could lead to a reduction in the greenhouse gas emissions registered a value of 87%.

Waste generation in Spain. Do Spanish regions exhibit a similar behavior?

We analyze waste generation differences across Spanish regions by studying the evolution of two complementary indicators: municipal solid waste per unit of GDP as well as in per capita terms. To that end, we apply the recent statistic developed by Phillips and Sul (2007) which allows us to test for the null hypothesis of convergence. In the present case, this hypothesis is equivalent to admitting that the waste generation follows a similar path across the Spanish regions. Our results lead us to reject this hypothesis, which implies that Spanish regional waste generation is quite heterogenous and exhibits several patterns of behavior. We observe that the northern regions exhibit the lowest waste ratios while the insular and Mediterranean coast regions have the highest waste generation. This different behavior is also explained by some socioeconomic factors. Per capita income, environmental spending and education level are helpful in this regard. The population dispersion and the number of years that a region has been governed by a left-wing party are also associated with lower levels of waste generation. Finally, we can also observe that the regions with the highest levels of waste generation are greatly dependent on the tourism industry. Then, strategies targeting the transit towards a more sustainable economy in Spain should take into account this fact. In particular, the adoption of methods for the reduction of the waste levels generated by tourism activities in these areas can be very useful.

Integration of IoT and Blockchain to in the Processes of a University Campus

Currently, universities, as centers of research and innovation, integrate in their processes various technologies that allow improving services and processes for their members. Among the innovative technologies are the Internet of Things that, through a variety of devices, allows obtaining data from the environment and people. This information is processed in cloud computing models and Big Data architectures that obtain knowledge through data analysis. These results lead to improving processes and making better decisions that improve the services available at the university. The integration of technologies allows for the generation of a sustainable environment that seeks the cohesion of the population with the environment, in such a way that economic growth is guaranteed in balance with the environment. However, all technology needs to guarantee the security of processes and data, and for this purpose, a new technology such as blockchain is integrated, which seeks to respond to two needs, the security and agility of processes. Integrating this technology in a university requires the analysis of the blockchain components to generate a new layer that adapts to the architecture of a university campus. This ensures that the data are kept cryptographically private to avoid exposure and that the entire process is verified by multiple blocks.

Impact of Industry 4.0 on Environmental Sustainability

Industry 4.0 is a concept that originated from the German industry, and whose essence is the use of technology for efficient production. In business today, the emergence of Industry 4.0 for production, and its related technologies, such as the Internet of Things (IoT) and cyber-physical systems, amongst others, have, however, a negative impact on environmental sustainability as a result of air pollution, the poor discharge of waste, and the intensive use of raw materials, information, and energy. The method used in this study is an analysis of a literature review of manuscripts discussing topics related to Industry 4.0 and environmental sustainability published between 2000 and 2020. There is currently a gap existing between the actual and the desired situation, in that production occurs in a weak sustainability model, and, therefore, this research debates the effects on environmental sustainability and the challenges facing Industry 4.0. Four scenarios are discussed: a deployment scenario, an operation scenario, integration and compliance with sustainable development goals, and a long-run scenario. The results indicate that there is a negative relationship related to the flow of the production process from the inputs to the final product, including raw materials, energy requirements, information, and waste disposal, and their impacts on the environment. However, the integration of Industry 4.0 and the sustainable development goals enhance environmental sustainability to create ecological support that guarantees high environmental performance with a more positive impact than before. This paper will help stakeholders and companies to provide solutions to the existing environmental challenges that can be mediated through adopting new technologies. The novelty of this study is its depiction of Industry 4.0 and its technologies integrated with sustainable development goals to create a sustainable Industry 4.0 combining environmental protection and sustainability.

Environmental Policy Stringency, Technical Progress and Pollution Haven Hypothesis

The present inquiry provides a common ground for the analysis of two strands of literature, the environmental Kuznets curve (EKC) and the pollution haven hypothesis (PHH). To this end, the study sets out a simple variational model, which identifies the structural composition of the economy and the level of economic development as the primary determinants of the magnitude of the domestic environmental degradation. The juxtaposition of the mentioned literature strands undermines the optimistic view that economic growth, in the long run, leads to the reduction of atmospheric pollution. To assess the empirical validity of the pollution haven conjecture, the study employs the OECD Environmental Policy Stringency Index and the refined data on carbon emissions embodied in imports for the dataset of 26 OECD countries in the time interval between 1995 and 2011. By employing pooled mean group (PMG) estimators, the study, for the first time, accounts for a number of issues mentioned in the literature as factors that confine the inferential power of existing empirical studies on the EKC. The strong and robust confirmation of the pollution haven conjecture indicates that at least in the context of global common pool resources, a purely national perspective of the EKC is not satisfactory.

Main Dimensions in the Building of the Circular Supply Chain: A Literature Review

Circular economy is an alternative to the traditional production model and has therefore attracted a great deal of attention from researchers. The change in the production system is accompanied by new logistical needs related both to resources and waste and to the distribution and recovery of products. The circular supply chain involves return processes and the manufacturer intends to capture additional value in the supply chain. In this paper, value chains have been mapped to visualize the links and interactions between the different stages and actors to understand the complexities of these systems and to make informed decisions. For this reason, and based on thorough literature review, the final objective of this work is to achieve a conceptual framework to study circular supply chain, which uses the main theoretical perspectives in strategic management literature. Four dimensions have been identified to support the development of these new supply chains—greater intensity in the relationships established in the supply chain, adaptation of logistics and organizational, disruptive and smart technologies, and a functioning environment. It can be concluded that to develop a new relationship capacity will allow for reaching more frequent, closer relationships with more actors. These relationships will be developed within an adapted organizational and logistical framework that is framed in new business model archetypes. However, dimensions related to the business environment such as sectoral, legislative, and fiscal frameworks must be incorporated.

Biogas from Anaerobic Digestion: Power Generation or Biomethane Production?

Biogas is a fuel obtained from organic waste fermentation and can be an interesting solution for producing electric energy, heat and fuel. Recently, many European countries have incentivized the production of biomethane to be injected into natural gas grids or compressed and used as biofuel in vehicles. The introduction of an upgrading unit into an existing anaerobic digestion plant to convert biogas to biomethane may have a strong impact on the overall energy balance of the systems. The amount of biomethane produced may be optimized from several points of view (i.e., energy, environmental and economic). In this paper, the mass and energy fluxes of an anaerobic digestion plant were analyzed as a function of the biogas percentage sent to the upgrading system and the amount of biomethane produced. A numerical model of an anaerobic digestion plant was developed by considering an existing case study. The mass and energy balance of the digesters, cogeneration unit, upgrading system and auxiliary boiler were estimated when the amount of produced biomethane was varied. An internal combustion engine was adopted as the cogeneration unit and a CO2 absorption system was assumed for biogas upgrading. Results demonstrated that the energy balance of the plant is strictly dependent on the biomethane production and that an excess of biomethane production makes the plant totally dependent on external energy sources. As for the environmental impact, an optimal level of biomethane production exists that minimizes the emissions of equivalent CO2. However, high biomethane subsides can encourage plant managers to increase biomethane production and thus reduce CO2 savings.

Bioenergy Yields from Sequential Bioethanol and Biomethane Production: An Optimized Process Flow

This study investigates the potential of different stages of the bioethanol production process (pretreatment, hydrolysis, and distillation) for bioethanol and biomethane production, and studies the critical steps for the liquid and the solid fractions to be separated and discarded to improve the efficiency of the production chain. For this, Napier grass (a fast-growing grass) from Effurun town of Delta State in Nigeria was used and the novel pretreatment method, nitrogen explosive decompression (NED), was applied at different temperatures. The results show that the lowest glucose (13.7 g/L) and ethanol titers (8.4 g/L) were gained at 150 °C. The highest glucose recovery (31.3 g/L) was obtained at 200 °C and the maximum ethanol production (10.3 g/L) at 170 °C. Methane yields are higher in samples pretreated at lower temperatures. The maximum methane yields were reported in samples from the solid fraction of post-pretreatment (pretreated at 150 °C, 1.13 mol CH4/100 g) and solid fraction of the post-hydrolysis stage (pretreated at 150 °C, 1.00 mol CH4/100 g). The lowest biomethane production was noted in samples from the liquid fraction of post-pretreatment broth (between 0.14 mol CH4/100 g and 0.24 mol CH4/100 g). From the process point of view, samples from liquid fraction of post-pretreatment broth should be separated and discarded from the bioethanol production process, since they do not add value to the production chain. The results suggest that bioethanol and biomethane concentrations are influenced by the pretreatment temperature. Napier grass has potential for bioethanol and further biomethane production and it can be used as an alternative source of energy for the transportation sector in Nigeria and other countries rich in grasses and provide energy security to their population.

Adopting a Circular Economy: Current Practices and Future Perspectives

All scientists, researchers, and citizens are involved in achieving sustainable goals. Their current actions contribute to writing a story for future generations, and interesting perspectives can be narrated based only on a great sense of social responsibility. The literature gives a great deal of attention to the models of a Circular Economy (CE). This topic is multidisciplinary and different sectors are involved in its development. This Special Issue aims to underline the relevance of the CE models in the scientific field and its applications in real contexts in order to achieve sustainability goals.

A Structured Literature Review on Obsolete Electric Vehicles Management Practices

The use of electricity for transportation needs offers the chance to replace fossil fuels with greener energy sources. Potentially, coupling sustainable transports with Renewable Energies (RE) could reduce significantly both Greenhouse Gas (GHG) emissions and the dependency on oil imports. However, the expected growth rate of Electric Vehicles (EVs) could become also a potential risk for the environment if recycling processes will continue to function in the current way. To this aim, the paper reviews the international literature on obsolete EV management practices, by considering scientific works published from 2000 up to 2019. Results show that the experts have paid great attention to this topic, given both the critical and valuable materials embedded in EVs and their main components (especially traction batteries), by offering interesting potential profits, and identifying the most promising End-of-Life (EoL) strategy for recycling both in technological and environmental terms. However, the economics of EV recycling systems have not yet been well quantified. The intent of this work is to enhance the current literature gaps and to propose future research streams.

Tourism-Based Circular Economy in Salento (South Italy): A SWOT-ANP Analysis

This paper is aimed at eliciting, by means of a multi-level perspective, potential drivers and barriers of the tourism industry in order to generate valuable information for policy makers to improve policy strategies for an effective transition towards sustainability. A Strengths, Weaknesses, Opportunities and Threats–Analytic Network Process (SWOT-ANP) framework was employed to explore the potential development of a second-generation biorefinery in Salento (a touristic area located in the southeast of Italy in Apulia Region) able to integrate waste management, renewable energy and bio-products production based on resource circularity in the tourism industry. Results indicate that survey participants recognized a higher level of priority for the pressures coming from the overall external setting involving values, dominant practices, rules and technologies (landscape and regime) over the internal tourism industry dynamics (niche). Results also show that the top five ranked factors are mainly pertaining to weaknesses (excessive bureaucracy and lack of technology and infrastructure) and threats (social acceptability and lack of long-term planning by governments), which can concretely jeopardize the transition towards a greater sustainability in the investigated area. The analysis presented constitutes a valuable model for agenda setting in order to find adequate policy actions to promote the transition.