The Application of the Dynamic Life Cycle Assessment (dLCA) Framework to Guide Sustainable Design of Emerging Technologies

應用動態生命週期評價框架指導新興技術的可持續性發展

Student thesis: Doctoral Thesis

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Award date27 Aug 2021

Abstract

Life cycle assessment (LCA) is increasingly required to conduct the systematic life cycle-based evaluation at a very early stage of technology development. Especially for emerging technologies are constantly rapidly developing and regarded as capable of changing the status quo. When quantifying the environmental impacts for those emerging technologies, the inherent lack of detailed datasets for emerging technologies contributes to significant uncertainties, making the adoption of traditional assessment approaches challenging. The two main aspects discussed throughout the thesis, process optimization and material selection, can be further improved to reduce the uncertainty. This thesis proposes a dynamic LCA (dLCA) approach to address these inherent uncertainties through iterative collaborative research between LCA modelers and experimentalists at the forefront of developing emerging technologies.

The first project evaluates the environmental impacts of the emerging waste valorization technology by adopting the dLCA framework. The large and increasing amount of solid waste generated each year in cities makes solid waste management one of modern society's most pressing issues. While the most efficient solution is to prevent waste generation in the first place, it is necessary to bio-based convert organic waste streams into value-added products ranging from compost to biomaterials and bioenergy. It is also a viable way to divert waste streams away from saturated landfills. Microbial biosurfactants are surface-active molecules that are naturally produced by a range of microorganisms. They have advantages over chemical surfactants, such as lower toxicity, higher biodegradability, anti-tumor, and anti-microbial properties. Sophorolipids (SLs) are one of the most promising biosurfactants representing the largest share of the biosurfactant market. Researchers are developing novel approaches for SL production by utilizing renewable feedstocks and advanced separation technologies. However, challenges still exist regarding the consumption of materials, enzymes, and electricity, primarily fossil based. Researchers lack a clear understanding of the associated environmental impacts. It is imperative to quantify and optimize the environmental impacts of this emerging technology very early in its design phase to guide a sustainable scale-up. From a collaborative perspective, wherein LCA experts work with experimentalists to quantify environmental impacts and provide recommendations for optimizing the SL production pathway. Studies that have analyzed the environmental sustainability of microbial biosurfactant production are very scarce in the literature. Hence, in this work, we explore the possibility of applying LCA to evaluate SL production's environmental sustainability. A dLCA framework that quantifies the environmental impacts iteratively, is proposed and used to assess SL production. The first traversal of the dLCA is associated with selecting an optimal feedstock, and results identified food waste as the optimal feedstock. The second traversal compared fermentation coupled with alternative separation techniques. It highlighted that the fed-batch fermentation of food waste integrated with the in-situ separation technique resulted in less environmental impacts.

After quantifying the environmental performances for food waste-derived SL production, the second project explores the associated environmental sustainability by extending the scale from lab to industry, with the assistance of techno-economic analysis (TEA). Sophorolipid production through bioconversion of organic waste streams is a promising solution, regarded as an emerging valorization technology. It is imperative to quantify and optimize this emerging technology's environmental impacts very early in its design phase to guide its scale-up towards maximizing its sustainability. LCA and TEA are widely applied for retrospective quantification of environmental impacts of technologies ready for implementation. TEA can provide detailed data on the downstream purification processes for industrial SL production. The refined SLs are produced through either crystallization and freeze-drying for SL crystals or ultrafiltration for SL syrup. Industrial-scale production leads to electricity demand for 1 kg SLs more reasonable, further resulting in tremendous reduction on the environmental impacts per functional unit. The corresponding global warming potential (GWP) values were 7.9 kg CO2 eq. and 5.7 kg CO2 eq. per kg SL crystal and syrup, compared with the GWP for 1 kg of crude SL (second traversal, 273.0 kg CO2 eq.). Integrated with the Ashby-like charts, this project can prioritize future research questions to guide the sustainable design of emerging waste valorization technology through iterative traversal of the dLCA framework. The Ashby-like charts based on the LCA and TEA results at the pilot plant highlight the trade-offs between systemic environmental costs and economic benefits for design decisions. Also, given the variation in the composition of waste streams for different regions, such a systematic evaluation of the environmental and economic implications will steer the selection of SL production pathways keeping location-specific sustainability in mind. This project's completion will provide new knowledge on potential unforeseen consequences associated with the eventual implementation of a full-scale waste-derived SL production plant.

The third project focuses on one of the most popular fluoropolymers in the market, polyvinylidene fluoride (PVDF), widely used in emerging technologies. It is commonly used as pipes and cables, binder material, and membrane materials. Lately, PVDF is being examined for batteries, biomedical research, chemical engineering, and wastewater management applications. These PVDF applications cover most emerging technologies, which can be attributed to its outstanding physicochemical properties. With the global demand for PVDF in diverse technologies increasing significantly, it is imperative to quantify the environmental impacts associated with its production. LCA methodology is a standardized approach for evaluating the environmental impacts of novel materials. However, most previous LCA studies have not accounted for PVDF in a scientifically rigorous manner. While compiling the life cycle inventory (LCI) on PVDF, several kinds of surrogates were chosen to bridge the data gap, rather than establishing the new dataset for PVDF. We investigate the similarity and difference between PVDF and popular surrogates regarding the synthesis pathways, adopting surrogates to replace PVDF. Due to using these surrogates, the GWP values calculated in the literature vary significantly, with a difference of 60.7 kg CO2 eq. between the highest and lowest estimates. After evaluating the life cycle environmental profiles of those commonly used surrogates, we find that the application of surrogates is hardly reliable. Additionally, the PVDF inventory dataset is underestimated. For this reason, we model the PVDF production process according to the synthesis approach and assess the cradle-to-gate impacts, which creates lower uncertainty. The impact assessment on the PVDF inventory dataset results in an acceptable GWP value (55.8 kg CO2 eq.), but a high cumulative energy demand (CED, 756 MJ-Eq), due to the significant demand for chlorine during the production of vinylidene fluoride (VDF). Notably, this is the first study to develop a detailed LCI for PVDF involved in emerging technologies. Against the unreliable PVDF surrogates commonly existed in the LCA works, the first PVDF inventory dataset has been successfully established with acceptable sensitivity and variability levels.

After evaluating the inventory dataset of PVDF, the fourth project aims to develop and demonstrate the dLCA framework to guide the sustainable design and selection of emerging electrospun membranes for dyeing wastewater treatment technologies. Membrane distillation (MD) for water desalination and purification has been gaining prominence to address the issues relating to water security and destruction of aquatic ecosystems not just in Hong Kong, but also globally. Recent advances in the electrospun membranes (E-PH membrane via electrospinning and PDMS/PVDF hybrid electrospun membrane via electrospraying) for MD have improved anti-fouling wetting performance. However, the environmental and human health impacts associated with the production and use of novel electrospun membranes are unclear. In order to develop sustainable electrospun membranes, it is imperative to quantify and analyze the trade-offs between membrane performance and impacts at the early stages of research on novel membranes. LCA is an appropriate tool to systematically account for environmental impacts, such as carbon emissions, all the way from raw material extraction to the disposal of any product, process or technology. The inherent lack of detailed datasets for emerging technologies contributes to significant uncertainties, making the adoption of traditional LCA challenging. This project presents a novel dLCA framework that holistically assesses the sustainability of electrospun nanofibrous membranes through collaborative research between life cycle researchers and membrane engineers.

These results can guide experimentalists to optimize those processes further. Besides, LCA modelers can also improve the environmental sustainability of emerging technologies. Resultant datasets can be iteratively used in subsequent traversals to account for technological changes and mitigate the corresponding impacts before scaling up. The successful application of dLCA will be transformative in its capacity to advance the understanding of the trade-offs between systemic environmental costs and economic benefits for design decisions.