Life Cycle Environmental Impacts of Electricity from Biogas Produced by Anaerobic Digestion

Sustainability and circularity assessment of biomass-based energy supply chain

Climate change and other environmental consequences of socio-economic activities require a more sustainable and circular growth. At the same time, the limitation of the earth resource demands industries to improve resource efficiency and increase the rate of recycling of materials. There are several sustainable and circular alternatives that the industries may adopt. However, the question is that among these alternatives, which one should be selected for implementation for the highest sustainable and circular benefits. This study introduces a novel tool for assessing the sustainability and circularity of biomass-based energy supply chains, integrating multi-criteria decision-making methods with life cycle thinking approach. It evaluates five alternatives using a sustainability and circularity indicators, offering new insights into the deloyment of circular business models at companies in biomass-based energy supply chain. The tool is also applied to a specific rice straw supply chain in Italy, to assess the sustainability and circularity of five alternatives and outrank them. The results indicated that not all the alternatives are better in terms of supporting sustainable development and circular economy, compared to the baseline business model. In this supply chain, the extended lifetime for digestate from the aerobic digestion plant is the most 'sustainable and circular' alternative, while the capture of carbon dioxide from the same plant and its use for microalgae cultivation is the least 'sustainable and circular' alternative. A sensitivity analysis was conducted on different weighting sets during the assessment. It indicated that the priority of the decision makers can slightly change the outrank of the alternatives and the magnitude of the outranks.

Upscaling and environmental impact assessment of an innovative integrated multi-trophic aquaponic system

The increasing growth of the aquaculture sector has raised significant concerns regarding its environmental footprint, including nutrient discharge, substantial feed consumption, and high energy requirements. In response, innovative approaches such as aquaponics and integrated multi-trophic aquaculture (IMTA) are being developed as potentially more sustainable alternatives. This study aims to evaluate the environmental performance of an innovative Integrated Multi-Trophic Aquaponics system (IMTAcs) using the Life Cycle Assessment (LCA) approach. Given the experimental nature of the pilot plant, two distinct scaled-up scenarios were analysed: one utilizing an alternative feed (IMTAcs AF), and the other employing a commercial feed (IMTAcs CF). The functional unit was defined as 100 kcal and 1 kg of protein produced by the system, with a cradle-to-gate perspective defining system boundaries. Results revealed that IMTAcs AF has a higher global warming impact (0.234 kg CO2 eq./100 kcal) compared to IMTAcs CF (0.207 kg CO2 eq.). In both scenarios, electricity consumption was identified as the primary driver to environmental impact, exceeding 50%, in contrast to conventional systems where feed is the main hotspot. Moreover, while trends in impact categories such as net primary production use and eutrophication is opposite between the scenarios, the latter demonstrated substantial mitigation potential, attributable to the system's inherent nutrient recycling, in comparison with traditional aquaculture systems. While the findings are promising, certain limitations in the study (e.g. utilization of scaled-up data and inherent uncertainties analysed), with the scarcity of existing research, point to the opportunity for further exploration. This includes analysing real-scale implementations whenever feasible and conducting more detailed comparisons with traditional systems.

Modelling of technical, environmental, and economic evaluations of the effect of the organic loading rate in semi-continuous anaerobic digestion of pre-treated organic fraction municipal solid waste

The study concerned technical feasibility, economic profitability, and carbon footprint (CF) analysis of semi-continuous anaerobic digestion (sAD) of organic fraction of municipal solid waste (OFMSW). The research assessed the pre-treatment effect on sAD by varying organic loading rates (OLR) from 3.38 to 6.75 kgvs/m3d. Three sAD configurations were investigated: hydrodynamic-cavitated (HC-OFMSW), enzymatically pre-treated (EN-OFMSW), and non-pre-treated (AD-OFMSW). Principal Component Analysis and Supervised Kohonen's Self-Organizing Maps combined the experimental, economic, and environmental evaluations. The sAD configurations were grouped predominantly according to the OLR however, within each OLR group the configurations were clustered according to the pre-treatments. The finding highlighted that pre-treatments offset inhibition in sAD of OFMSW due to the OLR increase, being economically profitable and CF negative up to 4.50 kgvs/m3d for EN-OFMSW and to 5.40 kgvs/m3d for HC-OFMSW. Whereas sAD-OFMSW remained economically and environmentally viable only up to 3.87 kgvs/m3d. HC-OFMSW reached the highest performance. In detail, for HC-OFMSW the NPV and CF ranged from 17679.30 to 43827.12 euros and from -51.08 to -407.210 kg CO2eq/1 MWh daily produced, by decreasing the OLR from 5.40 to 3.87 kgvs/m3d. These results are fundamental since pre-treatment is usually expensive due to additional energy or chemical requirements.

Wet anaerobic digestion of organic fraction of municipal solid waste: experience with long-term pilot plant operation and industrial scale-up

This paper presents the analysis of a pilot anaerobic digestion plant that operates with organic fraction of municipal solid waste (OFMSW) from a wholesale market and can treat up to 500 kg d-1. The process was monitored for a period of 524 days during which the residue was characterized and the biogas production and methane content were recorded. The organic load rate (OLR) of volatile solids (VS) was 0.89 kg m-3 d-1 and the Hydraulic Retention Time (HRT) was 25 d during the process. The yield was 82 Nm3 tons OFMSW-1 biogas, equivalent to 586 Nm3 tons CH4 VS-1. The results obtained in the pilot plant were used to carry out a technical-economic evaluation of a plant that treats 50 tons of OFMSW from wholesale markets. A production of 3769 Nm3 d-1 of biogas and 2080 Nm3 d-1 of methane is estimated, generating 35.1 MWh d-1 when converted to electricity.

A Critical Review of Data Science Applications in Resource Recovery and Carbon Capture from Organic Waste

Municipal and agricultural organic waste can be treated to recover energy, nutrients, and carbon through resource recovery and carbon capture (RRCC) technologies such as anaerobic digestion, struvite precipitation, and pyrolysis. Data science could benefit such technologies by improving their efficiency through data-driven process modeling along with reducing environmental and economic burdens via life cycle assessment (LCA) and techno-economic analysis (TEA), respectively. We critically reviewed 616 peer-reviewed articles on the use of data science in RRCC published during 2002-2022. Although applications of machine learning (ML) methods have drastically increased over time for modeling RRCC technologies, the reviewed studies exhibited significant knowledge gaps at various model development stages. In terms of sustainability, an increasing number of studies included LCA with TEA to quantify both environmental and economic impacts of RRCC. Integration of ML methods with LCA and TEA has the potential to cost-effectively investigate the trade-off between efficiency and sustainability of RRCC, although the literature lacked such integration of techniques. Therefore, we propose an integrated data science framework to inform efficient and sustainable RRCC from organic waste based on the review. Overall, the findings from this review can inform practitioners about the effective utilization of various data science methods for real-world implementation of RRCC technologies.

A comparative life cycle assessment of anaerobic mono- and co-digestion of livestock manure in Bangladesh

Proper management of biogenic residues, particularly livestock manure and food waste, is a major challenge for Bangladesh. While mono-digestion has traditionally been used on farms for treating manure, inadequate energetic output limits its applicability. Food waste, however, is typically landfilled in current practice. Co-digestion of biowaste emerged as an alternative due to synergistic yield and capacity to handle multiple waste streams. However, its environmental performance is underreported, particularly in developing countries. This study aimed to compare the environmental implications of co-digestion and mono-digestion of livestock manure (poultry and cow manure) with food waste from a life cycle assessment perspective for the regional context of Bangladesh. Two inventory cases were considered, accounting for mechanistically calculated (case M) and experimentally reported synergistic biogas yield (case E). Co-digestion scenarios showed net benefits by reducing three of the five impact categories-considerably reducing climate change (up to 117%), eutrophication potential, and terrestrial ecotoxicity in both cases (54.5 % and 55.7 %, respectively). The highest decrease occurred for climate change by diverting food waste landfilling. However, when synergistic biogas yield was considered, acidification potential and malodor air emissions increased by co-digestion owing to a higher amount of hydrogen sulfide and ammonia in the produced gas, thus entailing significant environmental burdens. The key hotspot in most categories was open storage of digestate, necessitating appropriate post-treatment.

Current and prognostic overview on the strategic exploitation of anaerobic digestion and digestate: A review

The depletion of fossil fuels and increasing demand for energy are encountered by generating renewable biogas. Anaerobic digestion (AD) produces not only biogas, also other value-added products from the digestate using various organic, municipal and industrial wastes which have several benefits like remediating waste, reduces greenhouse gas emissions, renewable energy generation and securing socio-economic status of bio-based industries. This review work critically analyzes the biorefinery approaches on AD process for the production of biogas and digestate, and their direct and indirect utilization. The left-out residue obtained from AD is called 'digestate' which enriched with organic matter, nitrogen, heavy metals and other valuable micronutrients. However, the direct disposal of digestate to the land as fertilizer/landfills creates various environmental issues. Keeping this view, the digestate should be upgraded or transformed into high valued products such as biofertilizer, pyrochar, biodiesel, syngas and soil conditioner that can aid to enrich the soil nutrients and ensures the safe environment as well. In this context, the present review focused to illustrate the current techniques and different strategic exploitations on AD proper management of digestate products for storage and further applications. Such a technology transfer provides a proven strategic mechanism towards the enhancement of the sustainability of bio-based industries, attaining the energy demand, safest waste management, protection of environment and reduces the socio-economic issues of the industrial sector.

Assessment of the environmental sustainability of municipal solid waste valorization by anaerobic digestion and by composting in Sri Lanka

Municipal solid waste management (MSWM) remains a major concern in Sri Lanka, and various treatment methods have been deployed. Though both composting and anaerobic digestion have been effective in environmental decontamination, there are other environmental issues that should be assessed. This study aimed to evaluate the environmental impacts of a full-scale composting plant and an anaerobic digestion plant for managing the organic fraction of municipal solid waste (OFMSW) in Sri Lanka using life cycle assessment (LCA). The results show that OFMSW composting causes unfavourable environmental impacts on damage categories such as human health (6.77 × 10-4 disability-adjusted life years (DALY) tonne-1 OFMSW), ecosystem quality (1.90 × 10-6 species.year tonne-1 OFMSW), and resource scarcity (3.66 × 10-1 United States Dollar (USD) tonne-1 OFMSW). Anaerobic digestion also leads to unfavourable impacts on human health (2.13 × 10-4 DALY tonne-1 OFMSW) and ecosystem quality (6.46 × 10-7 species.year tonne-1 OFMSW). However, the impact on resource scarcity (-3.85 × 10-2 USD tonne-1 OFMSW) was avoided due to electricity production via anaerobic digestion. Specifically, the treatment of OFMSW by anaerobic digestion resulted in a reduction by 68.3% in the total environmental load as compared to composting. It can be concluded that out of the two existing systems investigated, anaerobic digestion has a more favourable environmental impact than composting.

Bioenergy from anaerobic digestion plants: Energy and environmental assessment of a wide sample of Italian plants

This study assesses the energy and environmental performances of electricity produced from Italian anaerobic digestion coupled with combined heat and power plants. The Life Cycle Assessment methodology is applied to a set of plants characterised by different power sizes (from 100 to 999 kW) and feedstock compositions (variable rates of agricultural products and by-products). Then, the average eco-profile of the produced electricity is compared with electricity produced by the national grid and photovoltaic panels. The analysis allows detection of the combinations of size and feedstock with the lowest impacts. They correspond to small and medium plants mainly fed by organic by-products. In addition, compared to electricity from the grid, the average biogas electricity is characterised by the lowest contribution in impacts categories, such as abiotic depletion potential and ozone layer depletion potential, while largest in acidification and eutrophication. Focusing on global warming potential and cumulative energy demand fossil, the impacts of average biogas electricity (155 kgCO_2eq/MWh and 172 MJ/MWh) are about 35 % and 38 % of that generated by the grid. Furthermore, it could generate 47 % less of the impact in the abiotic depletion elements category of the solar system. To enhance the farms' environmental and economic sustainability and balance the electric grid, these outcomes point out that biogas electricity produced from the agriculture and livestock sector can contribute to the decarbonisation and self-sufficiency of European countries. The results strictly depend on the operative conditions and can aid policymakers at the global level in improving the energy supply security and sustainability. Further, they provide reliable information to stakeholders to select the most sustainable solution, according to the feedstock type, power supply, and management.

Understanding the environmental impacts of biogas utilization for energy production through life cycle assessment: An action towards reducing emissions

Unlike renewable energy sources, burning fossil fuels has severe environmental impacts, such as greenhouse gas (GHG) emissions and climate change. Therefore, this study was conducted to assess and compare the environmental impacts of three biogas utilization scenarios for energy production. The life cycle assessment (LCA) method was used to compare (i) biogas combustion in combined heat and power (CHP) unit, (ii) biogas burning in a steam boiler, and (iii) biogas upgrading using pressure swing adsorption (PSA) unit to determine the most sustainable option. The results revealed that the upgrading scenario was the best option, achieving emission savings in 8 out of 10 investigated impact categories. Among them, the emission saving was the highest in the marine aquatic ecotoxicity category (-4276.97 kg 1,4-DB eq./MJ). The CHP scenario was the second-best option, followed by the boiler scenario (worst option), and both had the most beneficial performance in the ozone depletion potential category with 6.29E-08 and 9.88E-08 kg CFC-11-eq./MJ, respectively. The environmental burdens of the boiler scenario were the highest in the marine aquatic ecotoxicity category (248.92 kg 1,4-DB eq./MJ). Although the CHP and boiler scenarios contributed to environmental burdens in all impact categories, they achieved beneficial performances compared to fossil fuel-based systems.

Environmental assessment of a two-stage high pressure anaerobic digestion process and biological upgrading as alternative processes for biomethane production

Biomethane plays a key role in achieving decarbonization and sustainable development goals. According to the objectives that arise, choosing the most suitable production system allows optimization of production, thereby reducing CO₂ emissions. In this study, three biomethane production scenario life cycle assessments were compared to determine which would maintain the lowest CO₂ emissions. Conventional anaerobic digestion and an innovative process called two-stage high pressure anaerobic digestion were considered. These methods were combined with two upgrading processes: water scrubbing and biological upgrading. Cattle manure and sugar beets were used as substrates for the process. Emissions were 805.6 gCO₂eq/m³CH₄ for the traditional biogas production process combined with water scrubbing and 450.3 gCO₂eq/m³CH₄ for the two-stage anaerobic digestion process combined with biological upgrading. Furthermore, the analysis demonstrated that these values would be reduced by 29.5 % and 48.0 % if electrical energy were produced using only renewable energy sources.

Environmental Assessment of the Life Cycle of Electricity Generation from Biogas in Polish Conditions

Life cycle analysis allows for the assessment of the qualitative and quantitative relationship between selected areas of human activity and the consequences for the environment. One of the important areas is the production of electricity and heat, for which the main raw material in Poland is hard coal. An alternative may be to use biogas as a fuel for energy purposes. This article presents the assessment of environmental hazards caused by the production of energy from biogas. The analysis took into account the change of the substrate from maize silage, commonly used in Polish biogas plants, to waste from the domestic agri-food industry. The evaluation covered the acquisition of substrates, their transport to a biogas plant, generation of electricity from biogas, and management of the generated by-products. The analysis was done in terms of both the impact and sensitivity categories. It was found that the emission of pollutants related to the acquisition of the substrate plays a key role and the use of waste for the production of biogas used for energy production brings environmental benefits. The analysis has shown that replacing coal with biogas, regardless of the raw materials used in its production, results in a positive environmental effect, especially in the areas of human health and resources categories. The positive environmental effect of the production of electricity from biogas can be enhanced by switching raw materials from purpose-grown crops to waste from the agri-food industry and agriculture. An important factor influencing the environmental impact is the degree of heat utilization (the greater the percentage of heat utilization, the greater the environmental benefits) and management of all by-products.

What Are the Environmental Benefits and Costs of Reducing Food Waste? Bristol as a Case Study in the WASTE FEW Urban Living Lab Project

The city of Bristol currently generates around 48,000 tonnes of household food waste every year. This waste incurs loss of resources and environmental damage throughout the food cycle. In this paper we quantify and value the baseline socio-environmental impacts from household food waste in Bristol before examining the potential costs and benefits that may result from changes to food waste behaviour. In so doing, we look to better inform the choice of food waste reduction methods in public policy. The environmental impacts of two possible policy targets are explored: (1) a 20% increase in food waste recycling and (2) an overall decrease in food waste of 20%. Environmental impacts are estimated for 13 different hazards, including Global Warming Potential, Particulate Matter, Human Toxicity and Water Depletion. The societal consequences of these environmental changes are monetised using non-market values which allows us to directly compare the relative importance of different environmental impacts and the trade-offs between these impacts in each scenario. For example, we estimate that the Global Warming Potential of Bristol’s annual food waste equates to around 110,000 tonnes CO2, or 25,000 additional cars on the road every year. We find that a 20% improvement in recycling behaviour would lead to an annual reduction of 113 tonnes of CO2 equivalent, whilst a 20% reduction in food waste would result in an annual reduction of 15,000 tonnes CO2 equivalent. Findings suggest that the environmental impact of waste management is significantly overshadowed by the impact of resources used in food production and distribution before it becomes waste.

Recent advances in plastic degradation - From microbial consortia-based methods to data sciences and computational biology driven approaches

The conventional methods of plastic waste management such as mechanical and chemical recycling, landfill complemented by incineration and pyrosis have limited scope. Thus, microbiological-based approaches by the application of microbial consortia or cocultures are appropriate, cost-effective, and eco-friendly to manage plastic wastes. Screening of novel plastic degrading microorganisms, the formulation of microbial consortia, and utilisation of their enzymes probably play a role in plastic waste management. The by-products of microbial degradation of plastic waste can be used as bio-energy sources, that aids in the development of cost-effective bio-digesters. The recent advancements in computational biology and bioinformatics play a vital role in understanding the molecular basis of enzymatic degradation of plastic polymers by microorganisms. Understanding the three-dimensional structures of plastic degrading enzymes and their metabolic pathways play a vital role in studying the microbial degradation of plastics. The present review highlights the scope of various microorganisms and their enzymes in plastic degradation. The review emphasizes the applications of co-cultures or microbial consortia-based approaches for the enhanced degradation of plastic polymers and the production of value-added end products that can be used as the prototypes of bioenergy sources. The review also provides a comprehensive outlook on the applications of data sciences, computational biology, and bioinformatics resources, and web-based tools towards the study of microbial degradation of plastic polymers.

The Role of Anaerobic Digestion and Solar PV to Achieve GHG Neutrality in a Farm Setting

Dairy farms are challenged to increase productivity while achieving environmental sustainability, where greenhouse gas (GHG) emissions are at the center of the discussion. The U.S. dairy industry leadership has committed to a Net Zero Initiative to achieve GHG neutrality, but the specifics on how to achieve this are still uncertain. Life cycle assessment methods were used to quantify GHGs and net energy intensity (NEI) of a large (1000 cows) and a small (150 cows) farm in Wisconsin. The GHGs are 1.0 and 1.3 kg CO2-eq/kg FPCM and the NEI is 2.4 and 3.2 MJ/kg FPCM for the large and small farm, respectively. The GHG benefits from anaerobic digestion (AD, sized to process all manure on both farms) and PV (sized to match AD electricity production) are not enough to achieve GHG neutrality. Increasing the capacity of these systems showed that AD is more cost-effective for the larger farm, but the challenges and costs related to securing and disposing the extra manure needed for energy production limit its feasibility. For the smaller farm, the total annualized costs to achieve GHG neutrality are lower for PV vs. AD, even before accounting for any transportation costs related to handling the extra manure.

Biogas Production by Pilot-Scale Anaerobic Co-Digestion and Life Cycle Assessment Using a Real Scale Scenario: Independent Parameters and Co-Substrates Influence

This study evaluates the performance of different agricultural by-products to identify the potential effect of independent variables, using as the dependent variable the biogas production. A Box–Behnken experimental design was carried out in a pilot-scale plant of four stirred stainless-steel digesters under mesophilic semi-continuous digestion. The results obtained support the creation of a technical framework to scale up the process and further evaluation of the potential environmental impacts through life cycle assessment (LCA) methodology. A stable behaviour was achieved in 12 of the 13 experiments proposed. The highest value of daily biogas production was 2200.15 mL day−1 with a stabilization time of 14 days, an organic loading rate of 4 g VS feed daily, low C/N ratio and a 1:1 relation of nitrogen providers. The concentrations of CH4 remained stable after the production stabilization and an average biogas composition of 60.6% CH4, 40.1% CO2 and 0.3% O2 was obtained for the conditions mentioned above. Therefore, the real scale plant was estimated to manage 2.67 tonnes of residual biomass per day, generating 369.69 kWh day−1 of electricity. The LCA analysis confirms that the co-digestion process evaluated is a feasible and environmentally sustainable option for the diversification of the Colombian energy matrix and the development of the agro-industrial sector.

Life cycle assessment applied to waste management in Italy: A mini-review of characteristics and methodological perspectives for local assessment

Life cycle assessment (LCA) and related tools are commonly used to evaluate the potential environmental impacts of waste treatment scenarios. This manuscript presents a mini-review of studies published over the last 10 years in Italy and aims to investigate how life cycle thinking tools are applied to assess the environmental sustainability of local-level waste policies. Results reveal that different waste flows, technologies and policies have been investigated independently and in varying detail. Review suggests that boundary selection significantly affects LCA results; integration of different waste systems is therefore crucial to avoid spatial or temporal shifts of environmental impacts. Moreover, the description of methodological characteristics, limitations and transversal aspects of Italian waste management studies allows various stakeholders to assess the reliability of past and future research for waste policy planning and rebound effects prevention. This review also highlights the need to define minimum requirements of transparency and ease of reporting of the studies to private and public stakeholders. Finally, the paper investigates whether using both the organisational LCA and the life cycle sustainability approach for the overall waste management process may be useful to develop a standard method to address multi-functionalities and multiple sites.

Process modelling and life cycle assessment coupled with experimental work to shape the future sustainable production of chemicals and fuels

Meeting the sustainable development goals and carbon neutrality targets requires transitioning to cleaner products, which poses significant challenges to the future chemical industry. Identifying alternative pathways to cover the growing demand for chemicals and fuels in a more sustainable manner calls for close collaborative programs between experimental and computational groups as well as new tools to support these joint endeavours. In this broad context, we here review the role of process systems engineering tools in assessing and optimising alternative chemical production patterns based on renewable resources, including renewable carbon and energy. The focus is on the use of process modelling and optimisation combined with life cycle assessment methodologies and network analysis to underpin experiments and generate insight into how the chemical industry could optimally deliver chemicals and fuels with a lower environmental footprint. We identify the main gaps in the literature and provide directions for future work, highlighting the role of PSE concepts and tools in guiding the future transition and complementing experimental studies more effectively.

Anaerobic Degradation of Environmentally Hazardous Aquatic Plant Pistia stratiotes and Soluble Cu(II) Detoxification by Methanogenic Granular Microbial Preparation

The aquatic plant Pistia stratiotes L. is environmentally hazardous and requires effective methods for its utilization. The harmfulness of these plants is determined by their excessive growth in water bodies and degradation of local aquatic ecosystems. Mechanical removal of these plants is widespread but requires fairly resource-intensive technology. However, these aquatic plants are polymer-containing substrates and have a great potential for conversion into bioenergy. The aim of the work was to determine the main patterns of Pistia stratiotes L. degradation via granular microbial preparation (GMP) to obtain biomethane gas while simultaneously detoxifying toxic copper compounds. The composition of the gas phase was determined via gas chromatography. The pH and redox potential parameters were determined potentiometrically, and Cu(II) concentration photocolorimetrically. Applying the preparation, high efficiency of biomethane fermentation of aquatic plants and Cu(II) detoxification were achieved. Biomethane yield reached 68.0 ± 11.1 L/kg VS of Pistia stratiotes L. biomass. The plants’ weight was decreased by 9 times. The Cu(II) was completely removed after 3 and 10 days of fermentation from initial concentrations of 100 ppm and 200 ppm, respectively. The result confirms the possibility of using the GMP to obtain biomethane from environmentally hazardous substrates and detoxify copper-contaminated fluids.

Pellet Production from Miscanthus: Energy and Environmental Assessment

The production of wood pellets has grown considerably in the last decades. Besides woody biomass, other feedstocks can be used for pellet production. Among these, miscanthus presents some advantages because, even if specifically cultivated, it requires low inputs such as fertilisers and pesticides and shows high biomass yield (up to 28 tons of dry matter ha−1 in Europe). Even if in the last years some studies evaluated the environmental impact of woody pellet production, there is no information about the environmental performances of miscanthus pellet production. In this study, the environmental impact of miscanthus pellet was evaluated using the Life Cycle Assessment approach with a cradle-to plant gate perspective. Primary data were collected in a small-medium size pelletizing plant located in Northern Italy where miscanthus is cultivated to be directly processed. The results highlight how the miscanthus pellet shows lower environmental impact compared to woody pellet, mainly due to the lower energy consumption during pelletizing. The possibility to pelletize the miscanthus biomass without any drying offsets the environmental impact related to the miscanthus cultivation for all the evaluated impact categories (except for Marine eutrophication). In detail, for global warming potential, 1 ton of miscanthus pellet shows an impact of 121.6 kg CO2 eq. (about 8% lower respect to woody pellet) while for the other evaluated impact categories the impact reduction ranges from 4 to 59%. Harvesting, which unlike the other field operations is carried out every year, is by far the main contributor to the impacts of the cultivation phase while electricity is the main contributor to the pelletizing phase.

Life Cycle Assessment Analysis of Alfalfa and Corn for Biogas Production in a Farm Case Study

In the last years the greenhouse effect has been significantly intensified due to human activities, generating large additional amounts of Greenhouse gases (GHG). The fossil fuels are the main causes of that. Consequently, the attention on the composition of the national fuel mix has significantly grown, and the renewables are becoming a more significant component. In this context, biomass is one of the most important sources of renewable energy with a great potential for the production of energy. The study has evaluated, through an LCA (Life Cycle Assessment) study, the attitude of alfalfa (Medicago sativa) as “no food” biomass alternative to maize silage (corn), in the production of biogas from anaerobic digestion. Considering the same functional unit (1 m3 of biogas from anaerobic digestion) and the same time horizon, alfalfa environmental impact was found to be much comparable to that of corn because it has an impact of about 15% higher than corn considering the total score from different categories and an impact of 5% higher of corn considering only greenhouse gases. Therefore, the analysis shows a similar environmental load in the use of alfalfa biomass in energy production compared to maize. Corn in fact, despite a better yield per hectare and yield of biogas, requires a greater amount of energy inputs to produce 1m3 of biogas, while alfalfa, which requires less energy inputs in its life cycle, has a lower performance in terms of yield. The results show the possibility to alternate the two crops for energy production from an environmental perspective.

A Human Health Toxicity Assessment of Biogas Engines Regulated and Unregulated Emissions

The aim of the work is to evaluate the damage to human health arising from emissions of in-operation internal combustion engines fed by biogas. The need of including also unregulated emissions like polycyclic aromatic hydrocarbons (PAHs), aldehydes and dioxins and furans is twofold: (i) to cover the lack in biogas engine emissions measurements and (ii) to complete the picture on biogas harmfulness to human health by identifying the substances with the highest impact. To this purpose, an experimental campaign is conducted on six biogas engines and one fed by natural gas all characterised by an electric power of 999 kWel. Collected data are used to perform an impact analysis on human health combining the Health Impact Assessment and the Risk Assessment. Measurements show that PAHs, aldehydes and diossin and furans are almost always below the detection limit, in both biogas and natural gas exhausts. The carcinogenic risk analysis of PAHs for the two fuels established their substantial equivalence. The analysis of equivalent toxicity of dioxins and furans reveals that biogas is, on average, 10 times more toxic than natural gas. Among regulated emissions, NOx in the biogas engines exhausts are three times higher than those of natural gas. They are the main contributors to human health damage, with approximately 90% of the total. SOx ranks second and accounts for about 6% of the total damage. Therefore, (i) the contribution to human health damage of unregulated emissions is limited compared to the damage from unregulated emissions, (ii) the damage per unit of electricity of biogas engines exhausts is about three times higher than that of natural gas and it is directly linked to NOx, (iii) obtaining a good estimation of the human health damage from both biogas and natural gas engines emissions is enough of a reason to consider NOx and SOx.

Economic and Environmental Impact Assessment of Renewable Energy from Biomass

For a holistic evaluation of sustainability, the economic and environmental aspects should be considered jointly to avoid trade-offs between the two dimensions. In this manuscript, the themes addressed, and the approaches used in this Special Issue “Economic and Environmental Impact Assessment of Renewable Energy from Biomass” to investigate the sustainability are summarized. Different approaches such as Energy Analysis, Life Cycle Assessment, technical and economic evaluation of key processes are applied to different renewable energy pathways (biogas, wood biomass, by-product valorization, etc.). The different manuscripts accepted in this Special Issue increases our comprehension and understanding of the relation between economic and environmental performances of renewable energy from biomass.

Environmental and economic performance of an integrated municipal solid waste treatment: A Chinese case study

The application of integrated municipal solid waste (MSW) management has become increasingly common for the mitigation of the ever-growing MSW stream. However, despite their popularity across the globe, little is known about the performance of integrated MSW management (MSWM) plants. This study quantitively investigates the environmental and economic performance of an integrated MSW treatment center in the city of Horqin Left Rear Banner, Inner Mongolia Province, China, using a combined life cycle assessment (LCA) and life cycle costing (LCC) methodology. Results indicate that the integrated MSWM plant is sustainable in both environmental and economic aspects, as the life cycle environmental impacts and economic costs can be offset by substituting virgin products with recycled counterparts. Amongst the included treatments, MSW separation, brick making and plastic recycling are the greatest contributors to the total environmental burdens and economic expenses. LCC results demonstrate that the equipment cost, tax and other asset costs are the greatest contributors to the total costs of the plant. Sensitivity analysis confirms that the increasing source separation ratio results in the reduction of environmental burdens and economic expenses via the usage of biogas and photovoltaic power. Furthermore, we offer recommendations for the promotion of the environmental and economic sustainability of integrated MSW treatment facilities.

Energetic, economic and environmental assessment for the anaerobic digestion of pretreated and codigested press mud

This study investigates the feasibility of anaerobic digestion (AD) of press mud previously pretreated, using two methods: Liquid Hot Water (LHW) and Thermo-Alkaline (TA), from an economic, energetic and environmental point of view. Two scenarios, a sugar mill with and without distillery were studied, considering monodigestion and vinasse codigestion. The results have shown that the LHW and TA pretreatments are self-sufficient in terms of thermal requirements since they can recover heat from the biogas engine, but the maximum electric and thermal net energy (64 MWh d^-1 and 95 MWh d^-1, respectively) was obtained during co-digestion with vinasse. The results of the environmental Life Cycle Analysis (LCA) show that the alternatives improve the environmental profiles, in both scenarios. The endpoint impact category "Human health" had the highest contribution because of both: the burning of fossil fuel at refinery to supply the required electricity; and the production of Ca(OH)₂ when vinasse was fed. The AD of pretreated press mud by LHW in CSTR reactors was the most viable for the scenario of a sugar mill without distillery, while the alternative co-digestion with the vinasse of the press mud without pretreatment was the most viable for the scenario of a sugar mill with distillery. This research shows that both the environmental and energetic profiles and the profitability of methane production can improve when the pretreatment and co-digestion of these wastes from the sugar - alcohol production process are considered.

Environmental assessment of energy production from anaerobic digestion of pig manure at medium-scale using life cycle assessment

This study assessed the potential environmental effects of energy production from pig manure treatment by anaerobic digestion at medium-scale based on the Life Cycle Assessment of a farm in Puebla, Mexico. It also compared the results from common practices of biogas flaring and conventional management. The analysis was based on one ton of pig manure in 4 systems: two with energy production, one with biogas flaring, and the last one conventional management. The use of biogas for electricity production combined with composting techniques generated the lowest net impacts on climate change of 272 kg CO₂eq and photochemical oxidation of 0.056 kg ethylene eq, while the biogas flaring registered impacts of 344 kg CO₂eq and 0.095 kg ethylene eq. The systems with energy production had environmental benefits on fossil resources depletion by avoiding the consumption of -863 MJ and -1608 MJ, but systems that burned biogas required fossil fuel consumption of 246 MJ from the grid. The conventional management generated the greatest environmental impacts, with eutrophication being the most important negative effect due to the manure discharge into water bodies (5.97 kg PO₄eq). Sensitivity analysis shown that energy production could generate greater impacts on global warming compared to the case in which manure was used directly in crop fields, if emissions from unintentional releases and a poor digestate management are not avoided. Results are relevant for developing countries in which processes are carried out in rural and semi-industrial areas with lack of technical knowledge and economic resources.

Measurements techniques and models to assess odor annoyance: A review

Odors have received increasing attention among atmospheric pollutants. Indeed, odor emissions are a common source of complaints, affecting the quality of life of humans and animals. The odor is a property of a mixture of different volatile chemical species (sulfur, nitrogen, and volatile organic compounds) capable of stimulating the olfaction sense sufficiently to trigger a sensation of odor. The impact of odors on the surrounding areas depends on different factors, such as the amount of odors emitted from the site, the distance from the site, weather conditions, topography, other than odors sensitivity and tolerance of the neighborhood. Due to the complexity of the odor issue, the aim of this review was to give an overview of: (i) techniques (sensorial and analytical) that can be used to determine a quantitative and qualitative characterization; (ii) air dispersion models applied for the evaluation of the spatial and temporal distribution of atmospheric pollutants in terms of concentration in air and/or deposition in the studied domain; (iii) major sources of odor nuisance (waste and livestock); (iv) mitigation actions against odor impact. Among sensorial techniques dynamic olfactometry, field inspection, and recording from residents were considered; whereas, for analytical methodologies: gas chromatography-mass spectrometry, identification of specific compounds, and electronic nose. Both kinds of techniques evaluate the odor concentration. Instead, to account for the effective impact of odors on the population, air dispersion models are used. They can provide estimates of odor levels in both current and future emission scenarios. Moreover, they can be useful to estimate the efficiency of mitigation strategies. Most of the odor control strategies involve measures oriented to prevent, control dispersion, minimize the nuisance or remove the odorants from emissions, such as adequate process design, buffer zones, odor covers, and treatment technologies.

Environmental impact and economic sustainability analysis of a novel anaerobic digestion waste-to-energy pilot plant in Pakistan

A novel medium-large industrial-scale, anaerobic digestion (AD) waste-to-energy pilot plant has been investigated in terms of cost-benefit, environmental impact, and economic sustainability. This pilot plant exclusively features a multi-digester AD system induced by motorized stirring, methane purification, compression, storage and digestate-fertilizer processing systems, and subsequent electricity generation. The operational productivity and success of the pilot plant has been proven on a variety of waste feedstock substrates in the form of cow-buffalo manure and potato waste. The plant has an average energy productivity of 384 kWh/day and an annual rate of return was estimated to be 15.4%. The life cycle environmental impact analysis deliberated the significant impact potentials in terms of climate change (kg CO₂ equivalent), and fossil depletion (kg of oil equivalent) for three selected substrates: 100% cow-buffalo manure (CBM), 100% potato waste (PW), and a mixture of 75% CBM and 25% PW. The results show the climate change potential of 70 kg, 71 kg, and 149 kg and fossil depletion potential of - 2.43 kg, - 16.45 kg, and 18 kg per 2000 kg of substrate slurry, respectively. As such, the substrate of 100% CBM posed the least climate change impacts whereas 100% PW has been established most effective under the fossil depletion category.

Life cycle environmental impacts of biogas production and utilisation substituting for grid electricity, natural gas grid and transport fuels

In this study, life cycle analysis (LCA) has been applied to evaluate the environmental impacts of biogas production and utilisation substituting for grid electricity, natural gas grid and transport fuels, with a focus on Greenhouse Gas (GHG) emissions. The results demonstrate significant reductions in greenhouse gas emissions for the biogas as a fuel scenario due to the displacement of fossil petrol and diesel fuels (scenario 3), with savings of between 524 and 477 kg of CO₂ equivalent (per MWh of energy provided by the fuels). The utilisation of biogas for electricity generation saves around 300 kg of CO₂ equivalent per MWh of electricity injected into the grid (scenario 1), while Scenario 2, the upgrading of biogas to biomethane and its injection into the gas grid for heating saves 191 kg of CO₂ equivalent (per MWh of energy generated by the biomethane). The results emphasise the benefits of using life cycle analysis to provide an evidence based for bioenergy policy. The limitations of the research are identified and recommendations made for future research priorities to further the use of LCA in the evaluation of bioenergy systems.

Biogas production by means of an anaerobic-digestion plant in France: LCA of greenhouse-gas emissions and other environmental indicators

The present article assesses the environmental profile of a real-scale anaerobic-digestion plant that has been developed in France. The system utilises 13652 t of different types of feedstock related to food industry, agriculture, etc. The study is based on Life Cycle Assessment (LCA) according to Global Warming Potential (GWP), Cumulative Energy Demand (CED), ReCiPe midpoint/endpoint and USEtox. The life-cycle inventory includes real data from various sources of waste as well as the transportation distances. By considering the impact of both anaerobic digestion and transportation for the whole system, the following findings have been found: 6430 t CO_2.eq (GWP 100a); 67194 GJ_prim (CED); 231100 Pts (ReCiPe endpoint single-score: Human health), 146932 Pts (ReCiPe endpoint single-score: Ecosystems), 171568 Pts (ReCiPe endpoint single-score: Resources). Furthermore, USEtox results, for the whole system and by taking into account both anaerobic digestion and transportation, show that based on: 1) Human toxicity/cancer, anaerobic-digestion phase has around 21 times higher value comparing to transportation, 2) Ecotoxicity, anaerobic-digestion phase presents about 77 times higher value than transportation. Regarding the impact of both phases (anaerobic digestion; transportation) per t of waste or per MWh of electricity, the findings show values of 0.5-0.6 t CO_2.eq per t of feedstock (or digestate) or per MWh of electricity produced (not net). A separate subsection with comparisons of the present findings with literature studies about LCA of anaerobic-digestion plants has been included. In general, a good agreement has been observed. Moreover, comparisons of the impact of the electricity produced by means of the present biogas system with the impact of conventional electricity mixes of several countries are presented and discussed, proving the environmental benefits of the proposed anaerobic-digestion plant.

Environmental sustainability of anaerobic digestion of household food waste

Consumers are the leading producers of food waste (FW) in developed countries and the majority of household FW is still embedded in general waste where it is incinerated or landfilled. There is increasing awareness in the value of collecting FW as a separate waste stream for production of compost or recovery of energy through anaerobic digestion (AD). This study focuses on AD to evaluate the life cycle environmental sustainability of recovering energy and fertilisers from household FW in the UK. The analysis is carried out for two different functional units: i) treatment of 1 tonne of FW, which is compared to incineration and landfilling; and ii) generation of 1 MWh of electricity, which is compared to other electricity generation options. The former results in net negative greenhouse gas (GHG) emissions (-39 kg CO₂-eq./t) and primary energy demand (-2 GJ/t) due to the displacement of grid electricity and mineral fertilisers. AD has lower impacts than both incineration and landfilling across 15 of the 19 impacts. However, the application of digestate to land and the release of ammonia and nitrates lead to higher marine eutrophication (ME), terrestrial acidification (TA) and particulate matter formation (PMF). For the second functional unit, AD electricity emits 203 kg CO₂-eq./MWh, compared to 357 kg CO₂-eq./MWh for the UK grid mix. Compared to renewables, such as wind and solar, AD electricity has lower energy demand, toxicity potentials and metal depletion. However, it has higher global warming potential, ME, TA and PMF. At the UK level, treating 4.9 Mt of kerbside FW collected annually could provide 0.37% of the national electricity demand and save 190,000 t CO₂-eq./yr compared to the grid electricity. The digestate produced could displace 1% of industrial nitrogen fertilisers. Although small fractions of the national demands, they represent a valuable return from a largely unutilised waste stream and help towards implementation of a circular economy.

Environmental sustainability of integrating the organic Rankin cycle with anaerobic digestion and combined heat and power generation

Given the growing scarcity of primary energy resources, increasing the efficiency of energy conversion is one of the key challenges for optimising energy use. For this reason, low-grade or waste heat from various processes is becoming increasingly more attractive as an energy source. This study considers anaerobic digestion (AD) coupled with a combined heat and power plant (CHP) as a source of low-grade heat for electricity generation utilising an organic Rankine cycle (ORC) system. The aim is to evaluate the environmental sustainability of such a system relative to the AD-CHP system without heat recovery. Ten real AD-CHP plants using cereal silage and animal slurry as feedstocks are considered for these purposes and their impacts have been estimated through life cycle assessment. The results suggest that systems with the ORC have lower impacts than those without it, but the average reductions are relatively small (1.6-5.8%). However, for the smaller plants fed mainly with animal slurry, climate change increases significantly (up to 27 times). The reduction in impacts is greater for the bigger plants where the surplus heat available for the ORC is higher. The impacts from the ORC plant are insignificant, with its electrical efficiency and lifespan showing little effect on the results. Small slurry-fed plants without the ORC have lower environmental impacts than the bigger silage-fed plants fitted with an ORC system for nine out of 13 categories considered; climate change is up to 32 times lower. They are only slightly worse than the bigger plants with the ORC for ozone depletion and human toxicity due to the economies of scale. Therefore, while there are clear benefits of fitting an ORC system to an AD-CHP plant, greater benefits can still be achieved by utilising waste feedstocks, such as animal slurry, instead of fitting an ORC to a plant utilising cereal silage.

Use of agricultural by-products in the development of an agro-energy chain: A case study from the Umbria region

Use of agricultural and livestock by-products for anaerobic digestion (AD), in total or partial substitution of the maize silage was evaluated from an environmental and economical point of view. The evaluation process included three methodological interdependent and consequential steps: the chemical stage at laboratory and plant level, the environmental and economic steps developing the Life Cycle Assessment and Life Cycle Costing jointly. The laboratory test showed that the two mixtures prepared with by-products, in partial (MIX A) and total (MIX B) substitution of maize silage, did not show differences in bio-methane production compared to a reference mixture with the 33% of maize silage. All mixtures tested at full-scale plant, showed the same performances, resulting in a similar energy production. Environmentally, MIX B increased greenhouse gas credits derived from the avoided production of mineral fertiliser for the energetic crops, resulting also in better economic performances. The break-even transport distances follow the positive environmental pattern result, in contrast to what was found for the break-even transport distances from the economic point of view.

Assessment of Novel Routes of Biomethane Utilization in a Life Cycle Perspective

Biomethane, as a replacement for natural gas, reduces the use of fossil-based sources and supports the intended change from fossil to bio-based industry. The study assessed different biomethane utilization routes for production of methanol, dimethyl ether (DME), and ammonia, as fuel or platform chemicals and combined heat and power (CHP). Energy efficiency and environmental impacts of the different pathways was studied in a life cycle perspective covering the technical system from biomass production to the end product. Among the routes studied, CHP had the highest energy balance and least environmental impact. DME and methanol performed competently in energy balance and environmental impacts in comparison with the ammonia route. DME had the highest total energy output, as fuel, heat, and steam, among the different routes studied. Substituting the bio-based routes for fossil-based alternatives would give a considerable reduction in environmental impacts such as global warming potential and acidification potential for all routes studied, especially CHP, DME, and methanol. Eutrophication potential was mainly a result of biomass and biomethane production, with marginal differences between the different routes.