• Energy Research

Incumbent clinker production practices fall short of meeting carbon-emission neutral targets, pressing the need to implement waste valorization approaches in cement plants to mitigate environmental impacts. However, there is a lack of knowledge on the future environmental performance of emerging waste-to-heat and fuel upcycling in clinker manufacturing. This study examines the prospective life cycle impacts of (1) solid recovered fuel (SRF) utilization and (2) on-site marine fuel production using integrated fluidized bed pyrolysis to substitute fossil fuels in clinker production and marine transportation. Environmental impacts are projected between 2025 and 2050 by applying learning effects in the foreground life cycle inventory and shared socioeconomic pathways (SSP1, SSP2), extended with the 1.9 W m−2 representative concentration pathway (SSP2-RCP1.9), in the background system. The highest decarbonization progress (−538.9 kg CO2-eq (t clinker)−1) is achieved under the SSP2-RCP1.9 development trajectory, driven by avoidance of emissions from waste management systems and converting biogenic carbon-rich municipal solid waste resources. The predicted CO2-eq impacts are found to be lower than the point source emission from raw meal calcination in several SSP scenarios, indicating that carbon-emission neutrality is attainable in combination with retrofitted carbon capture, utilization, and storage (CCUS) technologies. The assessment highlights the potential for burden shifting to other environmental impacts, e.g., particulate matter formation (+37.0 % by 2050), pointing to the need to evaluate additional pyrolysis oil upgrading and NOX emission mitigation strategies. Overall, synergizing waste pyrolysis with clinker production is found to be favourable due to (i) improved energy requirements, (ii) reduced fossil fuel use and impacts on climate change and ecosystem quality, and (iii) high potential for technological learning-driven environmental progress.

Information on biodegradation kinetics of biodiesel fuels is a key aspect in risk and impact assessment practice and in selection of appropriate remediation strategies. Unfortunately, this information is scattered, while factors influencing variability in biodegradation rates are still not fully understood. Therefore, we systematically reviewed 32 scientific literature sources providing 142 biodegradation and 56 mineralization half-lives of diesel and biodiesel fuels in various experimental systems. The analysis focused on the variability in half-lives across fuels and experimental conditions, reporting sets of averaged half-life values and their statistical uncertainty. Across all data points, biodegradation half-lives ranged from 9 to 62 days, and were 2-5.5 times shorter than mineralization half-lives. Across all fuels, biodegradation and mineralization half-lives were 2.5-8.5 times longer in terrestrial systems when compared to aquatic systems. The half-lives were generally shorter for blends with increasing biodiesel content, although differences in number of data points from various experiments masked differences in half-lives between different fuels. This in most cases resulted in lack of statistically significant effects of the type of blends and experimental system on biodegradation half-lives. Our data can be used for improved characterization of risks and impacts of biodiesel fuels in aerobic aquatic and terrestrial environments, while more experiments are required to quantify biodegradation kinetics in anaerobic conditions. Relatively high biodegradability of biodiesel may suggest that passive approaches to degrade and dissipate contaminants in situ, like monitored natural attenuation, may be appropriate remediation strategies for biodiesel fuels.

The imperative of a widespread, climate-neutral industrial transition necessitates adopting sustainable-by-design e-ammonia production practices. However, as is the case with early-stage technologies, its full potential in decarbonization and substituting conventional infrastructure at higher manufacturing readiness levels remains unknown. While learning and scaling effects offer insights into future potentials through historical observations, a collection of learning-by-doing, learning-by-searching and scaling data is absent for emerging green transition-related technologies. This study addresses the knowledge gap by building on economic learning theory and combining it with process virtualization to develop an explorative and normative framework for (i) synthesizing environmental learning rates for first-of-a-kind (FOAK) technologies and (ii) using them in prospective life cycle assessment. We consecutively develop and scale 12 e-ammonia processes designing green hydrogen production, ammonia synthesis, and air separation units using ASPEN Plus® V11 software to construct environmental learning curves (R2> 0.95). The quantified environmental learning effects, harmonized with shared socioeconomic pathways, show the technology's comprehensive potential to evolve into an eco-efficient nth-of-a-kind production line following a 2.5 doubling of experience by 2050. The cumulative environmental progress is driven by a short technology doubling time and moderate to high 3.1-23.4% environmental learning and scaling rates. Prospective projections that involve learning and scaling effects in the foreground system markedly outperform scenarios that consider environmental progress solely in background life cycle inventories. Therefore, future-oriented sustainability assessments need to account for advancements in both foreground and background inventories simultaneously to support and guide eco-friendly technological developments effectively.

Macroalgae cultivation shows potential for the application as emerging feedstock for microbial fermentation to produce biochemicals. However, metal residues in macroalgae might affect the fermentation capacity of relevant microorganisms. This aspect is currently not considered when selecting macroalgae and microorganism species for microbial fermentation. To consider this aspect for selecting viable macroalgae and microorganism species, we link metal exposure in bioreactors from macroalgae residues to ecotoxicological test results for relevant microorganisms. Our results indicate that estimated bioreactor concentrations for most metals are below microorganism effect levels. For copper and hexavalent chromium, however, reactor concentrations might exceed relevant effect levels for at least some considered microorganism species. Adjusting water hardness in the bioreactor as well as selecting algae harvest location and macroalgae species might minimize metal exposure to fermenting microorganisms, in support of optimizing the biorefining process for biochemical production. (Less)

Hydrothermal carbonization of biowaste with energy recovery was evaluated as a biowaste treatment technology using attributional life cycle assessment carried out in line with ISO 14044. Results show that important differences were observed for individual impact categories. Hydrothermal carbonization outperformed all other incumbent technologies in three impact categories and performed on par with anaerobic digestion and composting in the climate change category, where impact scores across three different wet biowaste streams ranged from -0.014 to -0.032 kg CO2 equivalents per kg of wet biowaste treated. However, it performed the worst in those environmental impacts which address resource depletion, including mineral, fossil and renewable resource depletion. This stresses the need to include all impact categories when evaluating environmental performance of biowaste treatment technologies. Differences in the ranking between different midpoint categories corroborate earlier studies suggesting that the general waste hierarchy might not necessarily apply to hydrothermal carbonization of biowaste.

The merits of temporary carbon storage are often debated for bio-based and biodegradable plastics. We employed life cycle assessment (LCA) to assess environmental performance of polyhydroxyalkanoate (PHA)-based plastics, considering multiple climate tipping as a new life cycle impact category. It accounts for the contribution of GHG emissions to trigger climate tipping points in the Earth system, considering in total 13 tipping elements that could pass a tipping point with increasing warming. The PHA was either laminated with poly(lactic acid), or metallized with aluminum or aluminum oxides to lower permeability of the resulting plastics toward oxygen, water vapor and aromas. The assessments were made accounting for potential differences in kinetics of evolution of greenhouse gases (CO2, CH4) from bioplastic degradation in the end-of-life. Results show that: (1) PHA films with high biodegradability perform best in relation to the climate tipping, but are not necessarily the best in relation to radiative forcing increase or global temperature change; (2) sugar beet molasses used as feedstock is an environmental hot spot, contributing significantly to a wide range of environmental problems; (3) increasing PHA production scale from pilot to full commercial scale increases environmental impacts, mainly due to decreasing PHA yield; and (4) further process optimization is necessary for the PHA-based plastics to become attractive alternatives to fossil-based plastics. Our study suggests that multiple climate tipping is a relevant impact category for LCA of biodegradable bioplastics.

Polyhydroxyalkanoates (PHA) are bio-based and biodegradable alternatives to conventional plastic types and have the potential to reduce the environmental impacts along the life cycle. In comparison to already established production routes for PHA (heterotrophic production) based on renewable feedstock like glucose (first generation feedstock), novel production routes, such as the photoautotrophic production of PHA based on CO2 as feedstock (third generation feedstock) could offer new perspectives with regard to the reduction in the environmental impacts. To quantify the environmental impacts of PHA produced via photoautotrophic and heterotrophic production pathways, life cycle assessment (LCA) methodology based on ISO 14040/44 was applied, thus conducting a first of its kind comparative study for PHA based on third generation feedstock. The results show that the photoautotrophic production of PHA has advantages in comparison to heterotrophic PHA based on glucose originating from corn as feedstock in all the assessed environmental impact categories, thus showing the environmental potential of novel production routes for bioplastics. Additionally, the results of the LCA show that the chloroform-based extraction method, commonly used in the downstream processes of both the technologies, has a significant contribution of environmental impacts in the production of PHA. Therefore, the reduction of chloroform loss during the extraction process can reduce its environmental impact. Our results indicate that PHA production from CO2 using the photoautotrophic production route is a promising technology with regard to the environmental impacts when compared to the heterotrophic production based on glucose feedstock.

Abstract To enable quantifying environmental performance of products and technologies in relation to Planetary Boundaries, there is a need for life-cycle impact assessment (LCIA) methods which allow for expressing indicators of environmental impact in metrics corresponding to those of the control variables in the Planetary Boundaries framework. In this study, we present such a methodology, referred to as PB-LCIA. Characterization factors for direct use in the LCIA phase of a life cycle assessment, or other life-cycle based assessment, were developed for a total of 85 elementary flows recognized as dominant contributors to transgressing specific Planetary Boundaries. Exception was made for “biosphere integrity” and “introduction of novel entities” where a Planetary Boundary is yet to be defined for the latter and characterization models are considered immature for the former. The PB-LCIA can be used to quantify the share of the “safe operating space” that human activities occupy, as was illustrated by calculating indicator scores for about 10,600 products, technologies and services exemplifying several sectors, including materials, energy, transport, and processing. The PB-LCIA can be used by companies interested in gauging their activities against the Planetary Boundaries to support decisions that help to reduce the risk of human activities moving the Earth System out of the Holocene state.