Environmental impacts of producing bioethanol and biobased lactic acid from standalone and integrated biorefineries using a consequential and an attributional life cycle assessment approach

Review of methodological decisions in life cycle assessment (LCA) of biorefinery systems across feedstock categories

The application of life cycle assessment (LCA) to biorefineries is a necessary step to estimate their environmental sustainability. This review explores contemporary LCA biorefinery studies, across different feedstock categories, to understand approaches in dealing with key methodological decisions which arise, including system boundaries, consequential or attributional approach, allocation, inventory data, land use changes, product end-of-life (EOL), biogenic carbon storage, impact assessment and use of uncertainty analysis. From an initial collection of 81 studies, 59 were included within the final analysis, comprising 22 studies which involved dedicated feedstocks, 34 which involved residue feedstocks (including by-products and wastes), and a further 3 studies which involved multiple feedstocks derived from both dedicated and secondary sources. Many studies do not provide a comprehensive LCA assessment, often lacking detail on decisions taken, omitting key parts of the value chain, using generic data without uncertainty analyses, or omitting important impact categories. Only 28% of studies included some level of primary data, while 39% of studies did not undertake an uncertainty or sensitivity analysis. Just 8% of studies included data related to dLUC with a further 8% including iLUC, and only 14% of studies considering product end of life within their scope. The authors recommend more transparency in biorefinery LCA, with justification of key methodological decisions. A full value-chain approach should be adopted, to fully assess burdens and opportunities for biogenic carbon storage. We also propose a more prospective approach, taking into account future use of renewable energy sources, and opportunities for increasing circularity within bio-based value chains.

Integrated lactic acid production from lignocellulosic agricultural wastes under thermal conditions

The production of lactic acid (LA) from agricultural wastes attracts great attention because of the sustainability and abundance of lignocellulosic feedstocks, as well as the increasing demand for biodegradable polylactic acid. In this study, we isolated a thermophilic strain Geobacillus stearothermophilus 2H-3 for use in robust production of L-(+)LA under the optimal conditions of 60 °C, pH 6.5, which were consistent with the whole-cell-based consolidated bio-saccharification (CBS) process. Sugar-rich CBS hydrolysates derived from various agricultural wastes, including corn stover, corncob residue, and wheat straw, were used as the carbon sources for 2H-3 fermentation by directly inoculating 2H-3 cells into the CBS system, without intermediate sterilization, nutrient supplementation, or adjustment of fermentation conditions. Thus, we successfully combined two whole-cell-based steps into a one-pot successive fermentation process to efficiently produce LA with high optical purity (99.5%), titer (51.36 g/L), and yield (0.74 g/g_biomass). This study provides a promising strategy for LA production from lignocellulose through CBS and 2H-3 fermentation integration.

The limitations of bioeconomy LCA studies for understanding the transition to sustainable bioeconomy

PURPOSE

Transition to bioeconomy requires all actors and stakeholders to measure the impact of systems that use bioresources and technologies to provision society. There are however some challenges with integrating LCA into business development and management, which have important implications for bioeconomy. There have been many LCA studies published in the twenty-first century, but the question must be answered: how useful are these LCA studies to help understand and manage transition to sustainable bioeconomy?

METHOD

This research used a structured literature review to identify 83 bioeconomy LCA studies published from January 2006 to June 2021 (excluding bioenergy). The studies were analysed for compliance with the ISO 14044 standard, with specific reference to the goal, commissioning perspective, system boundary, function and functional unit, impact methods and categories.

RESULTS AND DISCUSSIONS

It was found that more than 85% of the studies reviewed failed to present the required goal statement and a description of the function of the system. Nearly 13% of the studies did not define the system boundary, and only 17% included a full life cycle including raw material extraction, production, use and end-of-life stages. The majority of the LCA studies surveyed from 2006 to 2021 were either (i) not in compliance with the ISO standards or (ii) space and style limitations of the publication process prevented competent practitioners from properly conveying their work. This suggests that the value and integrity of the literature are undermined by not rigorously addressing the first and most important stage of an LCA study.

CONCLUSION

When interpreting the results, a major shortcoming noted was that most studies did not consider the industrial symbiosis needed between feedstock, technology, primary products, side streams, downstream valorisation and long-term circularity in order to properly understand the transition pathways required. Bioeconomy technologies were imagined as displacers for feedstocks and processes to adapt business as usual, rather than as transformers of the system to a sustainable footing.

RECOMMENDATION

If LCA studies are going to provide meaningful information for actors and stakeholders to assess whether a system will be able to operate sustainably, studies should include a full, integrated system, standards should be adhered to and approaches should perhaps go beyond mere eco-efficiency, or doing less harm, as these are not necessarily indicative of sustainability. Historical bioeconomy LCA studies do not provide great insight into the transition to sustainable bioeconomy.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11367-022-02053-w.

Inventory review and environmental evaluation of first- and second-generation sugars through life cycle assessment

In recent years, there has been a great movement towards the generation of knowledge related to the biorefinery concept. First-generation biorefineries bear the stigma of using arable land and edible crops for fuel instead of as sources of food and feed. However, second-generation biorefineries have not reached the level of full technical feasibility. Bearing in mind the objective of sugar production from sugar, starch, or lignocellulosic raw materials, the purpose of this study is to assess the environmental impact of first- and second-generation biorefineries, considering as an example for the comparative evaluation, the production of sugar fractions from crops (starch and sugar crops), and lignocellulosic biomass (hardwood and softwood). The characterization results were obtained using the ReCiPe 1.1 model, implemented through the SimaPro 9.0 software. Both production systems are inherently different and have strengths and weaknesses that must be carefully analyzed. The resulting environmental profile shows that the silviculture of wood contributes less to the environmental impact than cropping activities in most impact categories. In general, this study suggests that first-generation systems are burdened environmentally by the use of fertilizers, which have a significant impact on categories such as marine and freshwater eutrophication and terrestrial acidification, while second-generation systems are limited by the intensive processing steps needed for delignification, typically involving the use of chemicals and/or energy. LCA in early stages of the production of bio-based building blocks, rather than on the manufacture of biofuels or bioplastics, allows the precise identification of the environmental burdens that may be influencing the overall environmental profile of a biorefinery.

Pyrolysis of invasive woody vegetation for energy and biochar has climate change mitigation potential

Woody plant encroachment in agricultural areas reduces agricultural production and is a recognised land degradation problem of global significance. Invasive native scrub (INS) is woody vegetation that invades southern Australian rangelands and is commonly cleared to return land to agricultural production. Clearing of INS emits carbon to the atmosphere, and the retention of INS by landholders for the purpose of avoiding carbon emissions has been incentivized in Australia as an emission reduction strategy. Retaining INS, however, means land remains relatively unproductive because INS negatively impacts livestock production. This desktop study examined whether clearing INS to return an area to production, and pyrolysing residues to produce biochar, has the potential to provide climate change mitigation (the "pyrolysis scenario"). The syngas produced via pyrolysis was assumed to be used to generate electricity that was fed into the electricity grid and avoided the production of electricity from existing sources. In addition, the biochar was assumed to be applied to soils used for wheat production, giving mitigation benefits from reduced N₂O emissions from fertiliser use and reduction in the use of lime to ameliorate soil acidity. Relative to clearing INS and burning residues in-situ, the pyrolysis scenario resulted in a reduction in radiative forcing of 1.28 × 10^-4 W m² ha^-1 of INS managed, 25 years after clearing, and was greater than the reduction of 1.06 × 10^-4 W m² ha^-1 that occurred when INS was retained. The greatest contribution to the climate change mitigation provided by the pyrolysis scenario came from avoided emissions from grid electricity production, while avoided N₂O and lime emissions made a relatively minor contribution towards mitigation.

Environmental sustainability of biofuels: a review

Biofuels are being promoted as a low-carbon alternative to fossil fuels as they could help to reduce greenhouse gas (GHG) emissions and the related climate change impact from transport. However, there are also concerns that their wider deployment could lead to unintended environmental consequences. Numerous life cycle assessment (LCA) studies have considered the climate change and other environmental impacts of biofuels. However, their findings are often conflicting, with a wide variation in the estimates. Thus, the aim of this paper is to review and analyse the latest available evidence to provide a greater clarity and understanding of the environmental impacts of different liquid biofuels. It is evident from the review that the outcomes of LCA studies are highly situational and dependent on many factors, including the type of feedstock, production routes, data variations and methodological choices. Despite this, the existing evidence suggests that, if no land-use change (LUC) is involved, first-generation biofuels can-on average-have lower GHG emissions than fossil fuels, but the reductions for most feedstocks are insufficient to meet the GHG savings required by the EU Renewable Energy Directive (RED). However, second-generation biofuels have, in general, a greater potential to reduce the emissions, provided there is no LUC. Third-generation biofuels do not represent a feasible option at present state of development as their GHG emissions are higher than those from fossil fuels. As also discussed in the paper, several studies show that reductions in GHG emissions from biofuels are achieved at the expense of other impacts, such as acidification, eutrophication, water footprint and biodiversity loss. The paper also investigates the key methodological aspects and sources of uncertainty in the LCA of biofuels and provides recommendations to address these issues.

Recent Developments in Low iLUC Policies and Certification in the EU Biobased Economy

The development of a sustainable biobased economy (BBE) in Europe is associated with several challenges. Amongst others, lessons learned from the development of the biofuel sector and the complex debate around land use change associated with a growing demand for biomass have to be considered when developing BBE policies. In that regard, strategies to identify and verify feedstocks with low potential risks for direct and indirect land use change (iLUC) impacts are of specific importance. Complementing existing efforts to assess iLUC with modelling activities, the European Commission (EC) has proposed a risk-based approach, aiming to differentiate high and low iLUC risk biomass. Amongst others, different additionality measures can be used to produce certified biomass with low iLUC risk. However, a comprehensive overview and analysis of these additionality measures and the challenges related to their integration in an integer verification approach is still missing. Therefore, we analyse European Union (EU) policies dealing with iLUC, iLUC risk assessment studies, certification approaches, and iLUC modelling studies to identify and develop additionality practices potentially applicable in certification and to show how the potential application of the proposed measures could be realised and verified in practice. We identified five potential practices for low iLUC risk biomass production, which are likely to be used by market actors. For each practice, we identified methods for the determination of low iLUC risk feedstock and products. Finally, our review includes recommendations for follow-up activities towards the actual implementation of additionality measures in biomass certification schemes.

Water-energy-food nexus of bioethanol in Pakistan: A life cycle approach evaluating footprint indicators and energy performance

Water, energy, and food are the most basic and essential sectors for human welfare. However, an inextricable nexus and competition exists among these sectors. Production of molasses-based bioethanol is an interesting case resulting in the production of different food and energy materials while consuming water, energy, land, and other raw materials, throughout its life cycle. This paper briefly describes the nexus among water, energy, and food for bioethanol in Pakistan and its environmental implications. A life cycle approach has been used for evaluating four footprint categories including the carbon, ecological, water scarcity, and energy footprints along with an energy analysis of bioethanol. In comparison to conventional gasoline, bioethanol would have benefits in terms of lesser greenhouse gas emissions, better use of productive land, and superior energy performance, but, this will be at the expense of higher impacts in terms of water scarcity. Therefore, considering only a single aspect could result in inadvertent trade-offs that may go unnoticed. The quantified values would help accomplish integrated resource management along with their utilization within limits so as to be available for other uses. This study could help in developing strategies for optimal management of resources to maximize the synergies and minimize the possible trade-offs.

Techno-environmental assessment of the green biorefinery concept: Combining process simulation and life cycle assessment at an early design stage

The Green biorefinery (GBR) is a biorefinery concept that converts fresh biomass into value-added products. The present study combines a Process Flowsheet Simulation (PFS) and Life Cycle Assessment (LCA) to evaluate the technical and environmental performance of different GBR configurations and the cascading utilization of the GBR output. The GBR configurations considered in this study, test alternatives in the three main steps of green-biorefining: fractionation, precipitation, and protein separation. The different cascade utilization alternatives analyse different options for press-pulp utilization, and the LCA results show that the environmental profile of the GBR is highly affected by the utilization of the press-pulp and thus by the choice of conventional product replaced by the press-pulp. Furthermore, scenario analysis of different GBR configurations shows that higher benefits can be achieved by increasing product yields rather than lowering energy consumption. Green biorefining is shown to be an interesting biorefining concept, especially in a Danish context. Biorefining of green biomass is technically feasible and can bring environmental savings, when compared to conventional production methods. However, the savings will be determined by the processing involved in each conversion stage and on the cascade utilization of the different platform products.

Can farmers mitigate environmental impacts through combined production of food, fuel and feed? A consequential life cycle assessment of integrated mixed crop-livestock system with a green biorefinery

This study evaluates environmental impacts of an integrated mixed crop-livestock system with a green biorefinery (GBR). System integration included production of feed crops and green biomasses (Sys-I) to meet the demand of a livestock system (Sys-III) and to process green biomasses in a GBR system (Sys-II). Processing of grass-clover to produce feed protein was considered in Sys-II, particularly to substitute the imported soybean meal. Waste generated from the livestock and GBR systems were considered for the conversion to biomethane (Sys-IV). Digestate produced therefrom was assumed to be recirculated back to the farmers' field (Sys-I). A consequential approach of Life Cycle Assessment (LCA) method was used to evaluate the environmental impacts of a combined production of suckler cow calves (SCC) and Pigs, calculated in terms of their live weight (LW). The functional unit (FU) was a basket of two products "1kg_LW-SCC+1kg_LW-Pigs", produced at the farm gate. Results obtained per FU were: 19.6kg CO₂ eq for carbon footprint; 0.11kg PO₄ eq for eutrophication potential, -129MJ eq for non-renewable energy use and -3.9 comparative toxicity units (CTU_e) for potential freshwater ecotoxicity. Environmental impact, e.g. greenhouse gas (GHG) emission was primarily due to (i) N₂O emission and diesel consumption within Sys-I, (ii) energy input to Sys-II, III and IV, and (iii) methane emission from Sys-III and Sys-IV. Specifically, integrating GBR with the mixed crop-livestock system contributed 4% of the GHG emissions, whilst its products credited 7% of the total impact. Synergies among the different sub-systems showed positive environmental gains for the selected main products. The main effects of the system integration were in the reductions of GHG emissions, fossil fuel consumption, eutrophication potential and freshwater ecotoxicity, compared to a conventional mixed crop-livestock system, without the biogas conversion facility and the GBR.

Coproducts performances in biorefineries: Development of Claiming-based allocation models for environmental policy

This study revisited the fundamentals of allocation to joint products and proposed new models for allocating common greenhouse gases emissions among coproducts of biorefineries. These emissions may account for more than 80% of the total emissions of greenhouse gases of the biorefineries. The proposed models optimize the reward of coproducts for their compliance to environmental requirements. They were illustrated by a case study of wheat straw biorefinery built on the literature. Several scenarios were considered with regard to the grain yield, field emissions of greenhouse gases, allocation between grain and straw and policy requirements. The results conform to the expectations and are sensitive to the policy targets and to the environmental performance of the counterpart system. Further research works are necessary to achieve a full application to complex processes. However, the proposed models are promising towards assessing the simultaneous compliance of coproducts of a biorefinery to environment policy requirements.

Changes in carbon footprint when integrating production of filamentous fungi in 1st generation ethanol plants

Integrating the cultivation of edible filamentous fungi in the thin stillage from ethanol production is presently being considered. This integration can increase the ethanol yield while simultaneously producing a new value-added protein-rich biomass that can be used for animal feed. This study uses life cycle assessment to determine the change in greenhouse gas (GHG) emissions when integrating the cultivation of filamentous fungi in ethanol production. The result shows that the integration performs better than the current scenario when the fungal biomass is used as cattle feed for system expansion and when energy allocation is used. It performs worse if the biomass is used as fish feed. Hence, integrating the cultivation of filamentous fungi in 1st generation ethanol plants combined with proper use of the fungi can lead to a reduction of GHG emissions which, considering the number of existing ethanol plants, can have a significant global impact.