Evaluating the Sustainability and Environmental Performance of Commercially Applicable Marine Biorefineries

: (Alternative Format Thesis)

Abstract

Macroalgae (or ‘seaweed’) is a high-productivity and renewable resource. Owing to its diverse chemical composition, macroalgae can be transformed into a variety of products serving numerous industries including (but not limited to) Food and Beverage, Cosmetics, Chemicals, Pharmaceuticals, Nutraceuticals, Textiles, Agriculture, Energy, and Packaging. The conversion of macroalgal biomass is made possible through biorefineries. Unlike traditional manufacturing systems that often focus on producing a single target product, marine [seaweed] biorefining systems operate in a cascading manner, allowing for the co-production of a multitude of marketable products.

Seaweed biorefining is an emerging technology in Europe, and Life Cycle Assessment (LCA) is recognised as a key tool for ensuring its sustainable establishment. While the majority of peer-reviewed literature in the field of Marine Biorefinery systems has primarily addressed the conversion of algal biomass into energy products, the potential for converting seaweeds into high-value products hasn't been extensively explored, especially from an environmental assessment perspective.

This thesis encompasses a series of LCA projects evaluating the environmental performance of various marine biorefining product systems that utilise seaweed as feedstock, and that are situated in the United Kingdom. It provides insights into how best to navigate the establishment of this emerging technology, both from a methodological and a design perspective, in a way that ensures positive environmental outcomes. And vitally, how derived seaweed-based products might fare in the commercial landscape.

Commencing the investigative segment of this thesis, an LCA study was conducted evaluating the environmental performance of a Marine Biorefinery co-producing four medium-to-high value co-products from cultivated brown seaweed: fucoidan, laminarin, protein, and polymeric packaging material (target product). This exploratory study served as a foundational assessment of the dynamics in seaweed product systems, specifically in relation to LCA methodology. While energy decarbonisation proved a powerful tool in reducing overall climate change impacts, it inadvertently led to increased emissions in other environmental categories, such as terrestrial acidification, human non-carcinogenic toxicity, land-use, and terrestrial ecotoxicity. Moreover, the study reveals the significant influence of co-product management procedures have on LCA outcomes.

Next followed the conceptualisation and cradle-to-gate LCA of a biorefinery producing a alginate/cellulose composite biopolymer from cultivated Saccharina latissima, and a recalcitrant carbon-rich biochar product derived from the pyrolysis of the macroalgal solids waste stream. This combined carbon capture and utilization with long-term carbon sequestration via biochar burial – a mechanism by which the emissions associated with the production of the macroalgal biopolymer are offset.

The scope of this study evaluating the environmental performance of this biochar-integrated seaweed-to-biopolymer biorefinery was then expanded to encompass the evaluation impacts associated with biopolymer product end-of-life and biochar application. Adopting a cradle-to-grave approach enabled the determination of the system's potential for achieving net carbon negativity. Adding a further layer of context, life cycle assessment was coupled with techno-economic assessment, unveiling biopolymer production routes that are both environmentally friendly and cost-competitive.

In the final instance, this work pivots to the assessment of seaweeds utility as feedstock in a biorefinery deriving high-value sustainable ingredients – specifically as a carbohydrate source fuelling the fermentation of oleaginous yeast Metschnikowia pulcherrima, which is subsequently harvested to derive refined single-cell oil a substitute for commercially produced palm oil. Whilst the biorefining routes using seaweed as feedstock result in overall global warming impacts significantly lower than commercial palm oil, the alternative use of molasses and bread waste feedstocks offered superior environmental outcomes.

Date of Award	2 Oct 2024
Original language	English
Awarding Institution	University of Bath
Supervisor	Chris Chuck (Supervisor), Hannah Leese (Supervisor) & Sophie Parsons (Supervisor)