Environmental balance of the UK biogas sector: An evaluation by consequential life cycle assessment

Cover crop cultivation strategies in a Scandinavian context for climate change mitigation and biogas production - Insights from a life cycle perspective

Cover crop cultivation can be a vital strategy for mitigating climate change in agriculture, by increasing soil carbon stocks and resource efficiency within the cropping system. Another mitigation option is to harvest the cover crop and use the biomass to replace greenhouse gas-intensive products, such as fossil fuels. Harvesting cover crop biomass could also reduce the risk of elevated N2O emissions associated with cover crop cultivation under certain conditions, which would offset much of the mitigation potential. However, harvesting cover crops also reduces soil carbon sequestration potential, as biomass is removed from the field, and cultivation of cover crops requires additional field operations that generate greenhouse gas emissions. To explore these synergies and trade-offs, this study investigated the life cycle climate effect of cultivating an oilseed radish cover crop under different management strategies in southern Scandinavia. Three alternative scenarios (Incorporation of biomass into soil; Mowing and harvesting aboveground biomass; Uprooting and harvesting above- and belowground biomass) were compared with a reference scenario with no cover crop. Harvested biomass in the Mowing and Uprooting scenarios was assumed to be transported to a biogas plant for conversion to upgraded biogas, with the digestate returned to the field as an organic fertiliser for the subsequent crop. The climate change mitigation potential of cover crop cultivation was found to be 0.056, 0.58 and 0.93 Mg CO2-eq ha-1 in the Incorporation, Mowing and Uprooting scenario, respectively. The Incorporation scenario resulted in the highest soil carbon sequestration, but also the greatest soil N2O emissions. Substitution of fossil diesel showed considerable mitigation potential, especially in the Uprooting scenario, where biogas production was highest. Sensitivity analysis revealed a strong impact of time of cover crop establishment, with earlier establishment leading to greater biomass production and thus greater mitigation potential.

A critical review on phycoremediation of pollutants from wastewater-a novel algae-based secondary treatment with the opportunities of production of value-added products

Though the biological treatment employing bacterial strains has wide application in effluent treatment plant, it has got several limitations. Researches hence while looking for alternative biological organisms that can be used for secondary treatment came up with the idea of using microalgae. Since then, a large number of microalgal/cyanobacterial strains have been identified that can efficiently remove pollutants from wastewater. Some researchers also found out that the algal biomass not only acts as a carbon sink by taking up carbon dioxide from the atmosphere and giving oxygen but also is a renewable source of several value-added products that can be extracted from it for the commercial use. In this work, the cleaning effect of different species of microalgae/cyanobacteria on wastewater from varied sources along with the value-added products obtained from the algal biomass as observed by researchers during the past few years are reviewed. While a number of review works in the field of phycoremediation technology was reported in literature, a comprehensive study on phycoremediation of wastewater from different industries and household individually is limited. In the present review work, the efficiency of diverse microalgal/cyanobacterial strains in treatment of wide range of industrial effluents along with municipal wastewater having multi-pollutants has been critically reviewed.

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.

Life-cycle assessment as a prospection stage for the biochemical methane potential of pretreated lignocellulosic biomass

The goal of neutrality in greenhouse gas emissions has intensified the search for renewable fuels. However, it is crucial to ensure sustainability of new technologies before proposing their implementation. This study proposes the use of life-cycle assessment (LCA) as an intermediary tool to identify critical hotspots in the exploration of hydrothermal pretreatment of lignocellulosic biomass, followed by biochemical methane potential assessment. Brewer s spent grain (BSG) was investigated, and laboratory-scale results were applied in an attributional assessment model with business-as-usual serving as the baseline. The LCA revealed that assumptions made in the lab could pose limitations. In Brazil, the two-stage co-digestion of pretreated hydrothermal BSG showed promising prospects, with a reduction to a new value of -54 kg CO2-eq Ton-1 BSG compared to 90 kg CO2-eq Ton-1 BSG in the business-as-usual scenario. Within the top ten global beer producing countries, only Brazil and Spain demonstrated potential for exploring this proposal.

Anaerobic digestion as a sustainable technology for efficiently utilizing biomass in the context of carbon neutrality and circular economy

Carbon emissions and associated global warming have become a threat to the world, the major contributor being the extensive use of fossil fuels and uncontrolled generation of solid wastes. Energy generation from renewable energy sources is considered an alternative to achieving carbon neutrality. Anaerobic digestion (AD) is a sustainable technology that has been endorsed as a low-carbon technology complimenting both waste management and renewable energy sectors. The AD technology recovers the volatile matter from waste biomass as much as possible to produce biogas, thus reducing carbon emission as compared to open dumping or burning. However, there is a need of compilation of information on how each subsystem in AD contributes to the overall carbon neutrality of the entire system and chances of achieving a circular economy along with it. Therefore, this article aims to clarify the associated internal and external factors that determine the low carbon characteristic of anaerobic digestion technology. From this review, the potential of AD system for energy-atmosphere-agriculture nexus has been explored. Carbon emission mapping of the potential entities involved in AD were identified and perspective to life cycle assessment and future research direction has been pointed out. Climate change impact and acidification potential are the two entities that can influence the overall environmental sustainability of an AD system. It was recognized that each stage of AD system starting from substrate supply chain, biogas production, upgradation, utilization, and digestate application had a remarkable effect on the overall carbon emission potential based on its design, operation, and maintenance. Selection of suitable substrates and co-digesting them together for improved biogas production rate with high methane content and proper digestate post-processing and storage can vastly reduce the carbon emission potential of the AD technology. Further, a case scenario of India was assessed considering the utilization of major surplus biomass available through AD. Re-routing the three major substrates such as agricultural crop residues, animal wastes and organic fraction of municipal solid wastes through AD can reduce at least 3.5-3.8 kg CO2-eq per capita of annual carbon emission load in India. Furthermore, the pathways in which the policy and legislations over establishment of AD technology and how to explore linkages between achieving circular economy and low carbon economy for Indian scenario has been highlighted.

Life cycle environmental impacts of using food waste liquid fodder as an alternative for pig feeding in a conventional Cuban farm

This work aimed to compare cleaner production alternatives for pig production in the Cuban context through the Life Cycle Assessment (LCA) approach emphasizing the utilization of food waste (FW) as a substitute for traditional grain-based pig feeding. A conventional waste management method (lagooning) was assessed, including more environmentally friendly approaches (use of anaerobic digestion (AD) process); including the substitution of a fraction of solid fodder with food waste liquid fodder (LF), obtained from food waste. The analysis was based on one porcine equivalent livestock unit. The environmental impact categories assessed were global warming, terrestrial ecotoxicity, human carcinogenic toxicity, freshwater ecotoxicity, terrestrial acidification, and freshwater eutrophication. The major environmental benefits for pig production were observed when the maximum capacity of pigs was considered. In addition, favorable environmental performance was achieved by considering the substitution of solid fodder by LF, the AD as a waste management process, and the valorization of the solid and liquid effluents. The avoided products-related activities were the main contributor to freshwater ecotoxicity, human carcinogenic toxicity, and terrestrial ecotoxicity impact categories (up to 71 %). The sensitivity analysis showed that the variation in LF composition (protein concentration) could have a remarkable impact in all impact categories. Climate change performed as the more sensible impact category, suggesting that greenhouse gas (GHG) emissions, such as CO₂ and N₂O, are important drivers to change the environmental impact and need more attention. This research demonstrates that the environmental profile of the process can be improved by applying a cleaner production approach (AD as a waste management alternative and LF substituting solid fodder).

Environmental Impact Evaluation of University Integrated Waste Management System in India Using Life Cycle Analysis

Decarbonization of university campuses by integrating scientific waste approaches and circular economy principles is the need-of-the-hour. Universities, the maximum energetic corporations and places for clinical studies and social activities, have a duty to assemble low-carbon campuses and play a vital function in lowering CO2 emissions. An environmental life cycle assessment was conducted to compare proposed municipal solid waste (MSW) treatment systems with the existing system in the residential university campus (RUC) in Kharagpur, West Bengal (India). The results show the existing MSW disposal practice in RUC (baseline scenario has the highest GWP (1388 kg CO2 eq), which can potentially be reduced by adopting integrated waste management system with source segregation as represented in futuristic scenarios (S2—50% sorting) and (S3—90% sorting)). Compared to S1, GHG emission was reduced by 50.9% in S2 and by 86.5% in S3. Adopting anaerobic digestion and engineered landfill without energy recovery offsets the environmental emissions and contributes to significant environmental benefits in terms of ecological footprints. Capital goods play a pivotal role in mitigation the environmental emissions. The shift towards S2 and S3 requires infrastructure for waste collection and sorting will contribute to reduction of associated environmental costs in the long-term.

Life cycle management in bakeries: a proposed roadmap towards sustainability

PURPOSE

Some commercial/industrial sectors have increased their interest in sustainability, in some cases changing their business focus, from a profit-centered approach to a more balanced view, including environmental and social factors. It means that the interest in sustainability is increasing. Life cycle management (LCM) is a methodology/concept that can contribute to this paradigm shift. In this research, the potential application of LCM in the bakery segment was investigated, considering the entire value chain related to the sector (inputs, packaging, suppliers, customers, waste management).

METHODS

Bakeries were visited, in Teresina, Piauí, Brazil, to learn about the products, services, production processes, and the socio-environmental and economic sustainability practices, aiming at identifying bottlenecks and to propose alternatives based on LCM. Besides the field approach, the study was structured based on the literature that brings the concepts and potentialities of applying LCM in various economic/industrial sectors. The PDCA cycle and the SWOT Matrix were also used to assist the implementation of LCM. A roadmap was proposed aiming at the LCM implementation in bakeries.

RESULTS

The results show that although the sector has some environmentally sustainable practices (waste separation, energy savings, reuse of products, inputs purchased locally), the primary intention is to reduce costs and not to mitigate environmental impacts. Regarding social responsibility, they donate bread to institutions. This is an important attitude, but not the only one for fulfilling the social role within the value chain. They do not consider suppliers that show concern for the environment (certified companies), and both marketing and product labels do not evoke these issues too.

CONCLUSIONS AND RECOMMENDATIONS

Thus, there is the possibility of implementing LCM in bakeries if there is a concern with sustainable production and consumption. A roadmap for implementing LCM in bakeries was proposed including some steps: mapping the life cycle of products/processes/services associated with the sector; analyzing factors that can influence the actions towards sustainability; disseminating life cycle information to the entire value chain; efficient waste management, including the partnership with recycling companies; and treatment of the collected data and improvement proposal, using management tools such as the PDCA Cycle, the SWOT Matrix, and Environmental, Social and Governance (ESG) aiming at the search for environmental and economic sustainability and social fair alternatives.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11367-021-02008-7.

Anaerobic digestion of poultry litter - A consequential life cycle assessment

Concentrated land spreading of poultry litter has the potential to cause nutrient build-up in soils, eutrophication of water bodies, air pollution and the spread of pathogens. As a result, alternative routes for the disposal of poultry litter are being sought. A consequential life cycle assessment was conducted to examine several scenarios where biogas produced from poultry litter is used to generate heat and electricity or is upgraded to biomethane which can substitute natural gas. For all of the scenarios considered in this study, diverting poultry litter to anaerobic digestion leads to reduced environmental impacts for global warming, fine particulate matter formation and terrestrial acidification. However, the extent to which environmental impacts are reduced varies significantly across the scenarios. Displaced processes including electricity or natural gas, peat moss production and avoided land spreading of litter contribute the most to reducing environmental impacts. Consequential life cycle assessment is a suitable tool to inform decision-makers about the impact of introducing a new multifunctional technology like anaerobic digestion when considering the systems which are displaced. The results show the range of potential environmental outcomes, rather than predicting a single most-likely outcome. The results of this study indicate that anaerobic digestion is a suitable disposal route for poultry litter which may lead to reduced environmental impacts. This type of analysis is recommended when considering alternative feedstocks and valorisation pathways in the circular economy.

A Conceptual Review on Using Consequential Life Cycle Assessment Methodology for the Energy Sector

Energy is engaged in the supply chain of many economic sectors; therefore, the environmental impacts of the energy sector are indirectly linked to those of other sectors. Consequential life cycle assessment (CLCA) is an appropriate methodology to examine the direct and indirect environmental impacts of a product due to technological, economic or social changes. To date, different methodological approaches are proposed, combining economic and environmental models. This paper reviews the basic concept of CLCA and the coupling of economic and environmental models for performing CLCA in the energy sector during the period 2006–2020, with the aim to provide a description of the different tools, highlighting their strengths and limitations. From the review, it emerges that economic modelling tools are frequently used in combination with environmental data for CLCA in the energy sector, including equilibrium, input-output, and dynamic models. Out of these, the equilibrium model is the most widely used, showing some strengths in availability of data and energy system modelling tools. The input-output model allows for describing both direct and indirect effects due to changes in the energy sector, by using publicly available data. The dynamic model is less frequently applied due to its limitation in availability of data and modelling tools, but has recently attracted more attention due to the ability in modelling quantitative and qualitative indicators of sustainability.

Bioenergy for a Cleaner Future: A Case Study of Sustainable Biogas Supply Chain in the Malaysian Energy Sector

A life cycle assessment (LCA)-based environmental sustainability evaluation conceptual framework of biogas production has been proposed to improve the sustainability of biogas supply chains. The conceptual framework developed in this study can be used as a guideline for the related stakeholders and decision makers to improve the quality and enhance the sustainability of biogas production in Malaysia as well as promoting biogas as a clean, reliable and secure energy. A case study on an LCA analysis of a zero waste discharge treatment process has been conducted. In the zero discharge treatment system, biogas can be produced with a maximum water recycle and reuse. It was indicated that the biogas production and zero discharge treatment of a palm oil mill effluent were environmentally sustainable as the system utilized organic waste to produce bioenergy and achieved zero discharge. However, there were other aspects that should be taken into consideration, particularly regarding the sources of electricity and upstream activity, to ensure the sustainability of the system holistically.

Life cycle assessment of anaerobic digestion of pig manure coupled with different digestate treatment technologies

The direct use of digestate on farmlands as soil amendment is becoming an uneconomic option for farmers. Moreover, there are serious environmental concerns about its oversupply in regions with intensive biogas plants. Downstream technologies, offering innovative upcycling methods to handle huge amounts of digestate, have absorbed great interest in this context. In this study, three digestate treatment technologies were compared from a life cycle assessment perspective to combine the environmental impacts from pig manure transportation to biogas plants, biogas production, different digestate treatment technologies, and the use of final products. The results showed that scenario including digestate fractionation into solid and liquid, and their use for compost production and microalgae cultivation, respectively, would be a suitable downstream strategy with lower impacts on human health, ecosystem quality, and climate change damage categories, however future improvements still required. The results showed that sealed storage system or fast-continuous downstream processes as well as shorter distances between biogas plants and farms can significantly enhance the environmental performance of coupled anaerobic digestion and microalgae production. The high energy payback also signified that co-digestion of pig manure and microalgae would be energetically favorable in this context. However, having compared the results with a baseline scenario demonstrated that the direct use of digestate on farmlands, under controlled conditions to avoid its over application, is still the most environmentally favorable option, despite being a costly option for farmers. The results achieved in the present study suffered some uncertainties because technologies under consideration are at their infancy stage, thus further research still is required to find the most sustainable solutions.

LCA analysis of food waste co-digestion

The i-REXFO LIFE project designs an innovative business model with the objective of reducing significantly the amount of landfilled food waste. Given the availability of supermarket food waste in the Umbria region (Italy), the logistics is optimized using a Vehicle Routing Problem Solver, mass and energy balances of the biogas plant are partly calculated and partly measured from a real biogas plant. The data obtained from food waste transport and anaerobic co-digestion process are used as input for LCA analysis. The aim of the methodology is to assess the environmental and economic benefit of the substitution of energy crops (like corn silage) with food waste in anaerobic digestion. Two approaches are adopted: consequential LCA and attributional LCA. Only one impact category is taken into account: climate change. This decision has been taken to focus on two decision making criteria (economic feasibility and GHG emissions reduction). The results show that a reduction of 42% in the carbon footprint of the electricity produced from the biogas plant can be obtained by substituting about 9900 t of corn silage with 6600 t of food waste. Through the combined use of economic analysis and consequential LCA it has been possible to identify an optimized scenario in which: food waste produced from food industries is collected and used to produce energy in Expired Food Energy chains (EFE), while the food obtained from supermarkets is used to promote charity initiatives in actions aiming at the Reduction of Expired Food waste (REF).

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.

Environmental assessments of biological treatments of biowaste in life cycle perspective: A critical review

Municipal biowaste is a major environmental issue. Life-cycle assessment is a valuable tool to assess recycling options, and anaerobic digestion and composting have performed adequately. However, reviews indicate several discrepancies between studies. Thus, we critically review 25 life-cycle assessments of the composting and anaerobic digestion of municipal biowaste. Our objective is to identify decisive factors, methodological gaps and processes that affect environmental performance. We generally identified methodological gaps in expanding systems borders. In energy systems, the replaced energy source did not consider power generation or dynamic regulation. All studies adopted mixed energy sources or marginal approaches. Agroecosystems included the carbon sequestration potential and compensation for the production of synthetic fertilizers only. A limited range of scientifically proven benefits of compost use has been reported. In general, studies provided a limited account of the effects of use on land emissions, but contradictory assumptions emerged, mainly in modelling synthetic fertilizer compensation. Only three studies compensated direct emissions from the use of synthetic fertilizers, and none included indirect emissions. Further studies should include an analysis of the additional benefits of compost use, compensate for the effects of emissions from synthetic fertilizer use on land and mix attributional and consequential approaches in energy system expansion.

Understanding the effect of Ca and Mg ions from wastes in the solvent regeneration stage of a biogas upgrading unit

This paper reveals the effect of calcium and magnesium ions in carbonation experiments carried out to regenerate sodium hydroxide from a biogas upgrading unit. This novel study arises as an alternative to standard physical process whose elevated energy consumption imposes economic restrictions. Previous works employed alkaline waste to turn them into value added product. Nevertheless, no attractive economical results were obtained due to the low regeneration efficiencies. Our hypothesis is that both calcium and magnesium waste composition percentages have an impact in the result, hence this work propose an isolated study aiming to determine the of each one in the global performance. To this end, the operational parameters (reaction time, reaction temperature and molar ratio) were tuned as well as physicochemical properties of the final solid samples were analyzed by several techniques. The results indicate that calcium is much more prone than magnesium to reach high efficiencies in aqueous carbonation experiments. Additionally, higher quality products were achieved with calcium. The results of this study suppose an important step for understanding the aqueous carbonation through waste in the path to achieve a more sustainable city and society.

Development of a pragmatic framework to help food and drink manufacturers select the most sustainable food waste valorisation strategy

Food waste is a significant contemporary issue in the UK, with substantial environmental, social and economic costs to the nation. Whilst efforts to reduce food waste are laudable, a significant proportion of food and drink manufacturer waste is unavoidable. On the one hand, there is a drive from industry to reclaim as much value from this waste as possible, for example, by conversion to valuable products in what is known as "valorisation". At the same time, growing social and legislative pressures mean that any attempts to valorise food waste must be performed in a sustainable manner. However, for every company and its specific food wastes, there will be multiple valorisation possibilities and few tools exist that allow food and drink manufacturers to identify which is most profitable and sustainable for them. Such a decision would need to not only consider environmental, social and economic performance, but also how ready the technology is and how well it aligns with that company's strategy. In response, this paper develops and presents a hybrid framework that guides a company in modelling the volumes/seasonality of its wastes, identifying potential valorisation options and selecting appropriate indicators for environmental, social and economic performance as well as technological maturity and alignment with company goals. The framework guides users in analyzing economic and environmental performance using Cost-Benefit Analysis and Life Cycle Assessment respectively. The results can then be ranked alongside those for social performance, technological maturity and alignment with company goals using a weighted sum model variant of Multi-Criteria Decision Analysis to facilitate easy visual comparison. This framework is demonstrated in the form of a case study with a major UK fruit consolidator to identify the optimal strategy for managing their citrus waste. Possibilities identified included sale of imperfect but still edible waste via wholesale at a significantly reduced profit and the investment in facilities to extract higher value pectin from the same waste stream using a microwave assisted pectin extraction process. Results suggest that continued sale of waste to wholesale markets is currently the most beneficial in terms of economic viability and environmental performance, but that in the medium to long term, the projected growth in the market for pectin suggests this could become the most viable strategy.

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.

Environmental Assessment of a Hybrid Solar-Biomass Energy Supplying System: A Case Study

Local energy supply by renewable energy, such as solar energy and biomass, using distributed energy systems plays an important role in global energy structure. This study investigated the environmental performance of a hybrid solar-biomass energy supplying system by life-cycle assessment method. The results showed that in terms of environmental and energy impacts, the construction stage and the disassembly and recycling stage of the system contribute little to the whole life-cycle environmental impacts. According to the results of most of the selected impact categories, the solar subsystem contributed the most environmental emissions during construction stage, followed by the two anaerobic reactors; therefore, the excessive pursuit of high solar energy proportion can correspondingly lead to even more serious environmental problems. The integrated energy supplying system significantly reduces non-renewable energy consumption, climate change impacts, acidification as well as eutrophication effects due to the replacement of alternatives such as lignite coal, and from fertilizer production. The present hybrid solar-biomass energy supplying system not only produces clean thermal energy but also reduces the disposal of organic wastes and produces valuable agricultural products.

Synergizing carbon capture storage and utilization in a biogas upgrading lab-scale plant based on calcium chloride: Influence of precipitation parameters

Herein a strategy for biogas upgrading in a continuous flow absorption unit using CaCl₂ as capturing agent is reported. This process is presented as an alternative to the standard physical regeneration processes to capture carbon dioxide (CO₂) from biogas effluents with inherent high energy penalties. This work showcases a systematic study of the main parameters (reaction time, reaction temperature, and molar ratio reactant/precipitator) affecting calcium carbonate (CaCO₃) precipitation efficiency in a reaction between sodium carbonate (Na₂CO₃) and CaCl₂. In addition, the purity and main characteristics of the obtained product were carefully analysed via in a combined characterization study using Raman, XRD, and SEM. Our results indicate that acceptable precipitation efficiencies between 62 and 93% can be reached by fine tuning the studied parameters. The characterization techniques evidence pure CaCO₃ in a calcite structure. These results confirmed the technical feasibility of this alternative biogas upgrading process through CaCO₃ production.

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.

Using microalgae in the circular economy to valorise anaerobic digestate: challenges and opportunities

Managing organic waste streams is a major challenge for the agricultural industry. Anaerobic digestion (AD) of organicwastes is a preferred option in the waste management hierarchy, as this processcangenerate renewableenergy, reduce emissions from wastestorage, andproduce fertiliser material.However, Nitrate Vulnerable Zone legislation and seasonal restrictions can limit the use of digestate on agricultural land. In this paper we demonstrate the potential of cultivating microalgae on digestate as a feedstock, either directlyafter dilution, or indirectlyfromeffluent remaining after biofertiliser extraction. Resultant microalgal biomass can then be used to produce livestock feed, biofuel or for higher value bio-products. The approach could mitigate for possible regional excesses, and substitute conventional high-impactproducts with bio-resources, enhancing sustainability withinacircular economy. Recycling nutrients from digestate with algal technology is at an early stage. We present and discuss challenges and opportunities associated with developing this new technology.

Life Cycle Assessment of Biofertilizer Production and Use Compared with Conventional Liquid Digestate Management

Handling of digestate produced by anaerobic digestion impacts the environment through emission of greenhouse gases, reactive nitrogen, and phosphorus. Previous life cycle assessments (LCA) evaluating the extraction of nutrients from digestate using struvite precipitation and ammonia stripping did not relate synthetic fertilizer substitution (SFS) to nutrient use efficiency consequences. We applied an expanded LCA to compare the conventional management of 1 m³ of liquid digestate (LD) from food waste against the production and use of digestate biofertilizer (DBF) extracted from LD, accounting for SFS efficacy. Avoidance of CH₄, N₂O, and NH₃ emissions from LD handling and enhanced SFS via more targeted use of nutrients in the versatile DBF product could generate environmental savings of up to 0.129 kg Sb eq, 4.16 kg SO₂ eq, 1.22 kg PO₄ eq, 33 kg CO₂ eq, and 20.6 MJ eq per m³ LD, for abiotic resource depletion, acidification, eutrophication, global warming, and cumulative energy demand burdens, respectively. However, under worst-case assumptions, DBF extraction could increase global warming and cumulative energy demand by 7.5 kg CO₂e and 251 MJ eq per m³ LD owing to processing inputs. Normalizing these results against per capita environmental loadings, we conclude that DBF extraction is environmentally beneficial.

Environmental impacts of food waste: Learnings and challenges from a case study on UK

Food waste, particularly when avoidable, incurs loss of resources and considerable environmental impacts due to the multiple processes involved in the life cycle. This study applies a bottom-up life cycle assessment method to quantify the environmental impacts of the avoidable food waste generated by four sectors of the food supply chain in United Kingdom, namely processing, wholesale and retail, food service, and households. The impacts were quantified for ten environmental impact categories, from Global Warming to Water Depletion, including indirect land use change impacts due to demand for land. The Global Warming impact of the avoidable food waste was quantified between 2000 and 3600 kg CO₂-eq. t^-1. The range reflected the different compositions of the waste in each sector. Prominent contributors to the impact, across all the environmental categories assessed, were land use changes and food production. Food preparation, for households and food service sectors, also provided an important contribution to the Global Warming impacts, while waste management partly mitigated the overall impacts by incurring significant savings when landfilling was replaced with anaerobic digestion and incineration. To further improve these results, it is recommended to focus future efforts on providing improved data regarding the breakdown of specific food products within the mixed waste, indirect land use change effects, and the share of food waste undergoing cooking. Learning from this and previous studies, we highlight the challenges related to modelling and methodological choices. Particularly, food production datasets should be chosen and used carefully, to avoid double counting and overestimation of the final impacts.

Life cycle environmental impacts of substituting food wastes for traditional anaerobic digestion feedstocks

In this study, life cycle assessment has been used to evaluate life cycle environmental impacts of substituting traditional anaerobic digestion (AD) feedstocks with food wastes. The results have demonstrated the avoided GHG emissions from substituting traditional AD feedstocks with food waste (avoided GHG-eq emissions of 163.33 CO₂-eq). Additionally, the analysis has included environmental benefits of avoided landfilling of food wastes and digestate use as a substitute for synthetic fertilisers. The analysis of the GHG mitigation benefits of resource management/circular economy policies, namely, the mandating of a ban on the landfilling of food wastes, has demonstrated the very substantial GHG emission reduction that can be achieved by these policy options - 2151.04 kg CO₂ eq per MWh relative to UK Grid. In addition to the reduction in GHG emission, the utilization of food waste for AD instead of landfilling can manage the leakage of nutrients to water resources and eliminate eutrophication impacts which occur, typically as the result of field application. The results emphasise the benefits of using life-cycle thinking to underpin policy development and the implications for this are discussed with a particular focus on the analysis of policy development across the climate, renewable energy, resource management and bioeconomy nexus and recommendations made for future research priorities.

Nitrogen losses to the environment following food-based digestate and compost applications to agricultural land

The anaerobic digestion of food waste for energy recovery produces a nutrient-rich digestate which is a valuable source of crop available nitrogen (N). As with any 'new' material being recycled to agricultural land it is important to develop best management practices that maximise crop available N supply, whilst minimising emissions to the environment. In this study, ammonia (NH₃) and nitrous oxide (N₂O) emissions to air and nitrate (NO₃^-) leaching losses to water following digestate, compost and livestock manure applications to agricultural land were measured at 3 sites in England and Wales. Ammonia emissions were greater from applications of food-based digestate (c.40% of total N applied) than from livestock slurry (c.30% of total N applied) due to its higher ammonium-N content (mean 5.6 kg/t compared with 1-2 kg/t for slurry) and elevated pH (mean 8.3 compared with 7.7 for slurry). Whilst bandspreading was effective at reducing NH₃ emissions from slurry compared with surface broadcasting it was not found to be an effective mitigation option for food-based digestate in this study. The majority of the NH₃ losses occurred within 6 h of spreading highlighting the importance of rapid soil incorporation as a method for reducing NH₃ emissions. Nitrous oxide losses from food-based digestates were low, with emission factors all less than the IPCC default value of 1% (mean 0.45 ± 0.15%). Overwinter NO₃^- leaching losses from food-based digestate were similar to those from pig slurry, but much greater than from pig farmyard manure or compost. Both gaseous N losses and NO₃^- leaching from green and green/food composts were low, indicating that, in these terms, compost can be considered as an 'environmentally benign' material. These findings have been used in the development of best practice guidelines which provide a framework for the responsible use of digestates and composts in agriculture.

Product vs corporate carbon footprint: Some methodological issues. A case study and review on the wine sector

Carbon footprint (CF) is nowadays one of the most widely used environmental indicators. The scope of the CF assessment could be corporate (when all production processes of a company are evaluated, together with upstream and downstream processes following a life cycle approach) or product (when one of the products is evaluated throughout its life cycle). Our hypothesis was that usually product CF studies (PCF) collect corporate data, because it is easier for companies to obtain them than product data. Six main methodological issues to take into account when collecting corporate data to be used for PCF studies were postulated and discussed in the present paper: fugitive emissions, credits from waste recycling, use of "equivalent factors", reference flow definition, accumulation and allocation of corporate values to minor products. A big project with 18 wineries, being wine one of the most important agri-food products assessed through CF methodologies, was used to study and to exemplify these 6 methodological issues. One of the main conclusions was that indeed, it is possible to collect corporate inventory data in a per year basis to perform a PCF, but having in mind the 6 methodological issues described here. In the literature, most of the papers are presenting their results as a PCF, while they collected company data and obtained, in fact, a "key performance indicator" (ie., CO₂eq emissions per unit of product produced), which is then used as a product environmental impact figure. The methodology discussed in this paper for the wine case study is widely applicable to any other product or industrial activity.

SIMSWASTE-AD - A modelling framework for the environmental assessment of agricultural waste management strategies: Anaerobic digestion

On-farm anaerobic digestion (AD) has been promoted due to its improved environmental performance, which is based on a number of life cycle assessments (LCA). However, the influence of site-specific conditions and practices on AD performance is rarely captured in LCA studies and the effects on C and N cycles are often overlooked. In this paper, a new model for AD (SIMS_WASTE-AD) is described in full and tested against a selection of available measured data. Good agreement between modelled and measured values was obtained, reflecting the model capability to predict biogas production (r²=0.84) and N mineralization (r²=0.85) under a range of substrate mixtures and operational conditions. SIMS_WASTE-AD was also used to simulate C and N flows and GHG emissions for a set of scenarios exploring different AD technology levels, feedstock mixtures and climate conditions. The importance of post-digestion emissions and its relationship with the AD performance have been stressed as crucial factors to reduce the net GHG emissions (-75%) but also to enhance digestate fertilizer potential (15%). Gas tight digestate storage with residual biogas collection is highly recommended (especially in temperate to warm climates), as well as those operational conditions that can improve the process efficiency on degrading VS (e.g. thermophilic range, longer hydraulic retention time). Beyond the effects on the manure management stage, SIMS_WASTE-AD also aims to help account for potential effects of AD on other stages by providing the C and nutrient flows. While primarily designed to be applied within the SIMS_DAIRY modelling framework, it can also interact with other models implemented in integrated approaches. Such system scope assessments are essential for stakeholders and policy makers in order to develop effective strategies for reducing GHG emissions and environmental issues in the agriculture sector.

Climate regulation, energy provisioning and water purification: Quantifying ecosystem service delivery of bioenergy willow grown on riparian buffer zones using life cycle assessment

Whilst life cycle assessment (LCA) boundaries are expanded to account for negative indirect consequences of bioenergy such as indirect land use change (ILUC), ecosystem services such as water purification sometimes delivered by perennial bioenergy crops are typically neglected in LCA studies. Consequential LCA was applied to evaluate the significance of nutrient interception and retention on the environmental balance of unfertilised energy willow planted on 50-m riparian buffer strips and drainage filtration zones in the Skåne region of Sweden. Excluding possible ILUC effects and considering oil heat substitution, strategically planted filter willow can achieve net global warming potential (GWP) and eutrophication potential (EP) savings of up to 11.9 Mg CO₂e and 47 kg PO₄e ha^-1 year^-1, respectively, compared with a GWP saving of 14.8 Mg CO₂e ha^-1 year^-1 and an EP increase of 7 kg PO₄e ha^-1 year^-1 for fertilised willow. Planting willow on appropriate buffer and filter zones throughout Skåne could avoid 626 Mg year^-1 PO₄e nutrient loading to waters.