Sophie Parsons’s research while affiliated with University of Bath and other places

Concerns relating to the potential environmental and land-use impacts associated with terrestrial energy crops have sparked an interest in the alternative use of marine feedstocks, such as seaweed (macroalgae). In contrast to terrestrial crops farming seaweed does not require the input of freshwater or chemical fertiliser and does not compete for land required by food crops. Seaweed remains a largely untapped source of valuable polysaccharides, proteins, fatty acids, and pigments which can be purified, or used as feedstock in the production of platform chemicals. Recently, Life cycle assessment (LCA) has been used to evaluate the potential environmental impacts arising from the use of seaweed feedstocks, predominately in the production of bioenergy. There are a range of different methods which can be used to cultivate and harvest seaweed for further downstream processing. These include land- and tank-based methods, nearshore and offshore cultivation, as well as integrated multitrophic aquaculture. As interest in seaweed cultivation in Europe grows, it is important to understand the associated environmental impacts. To date, a number of LCAs have assessed these different cultivation methods, either in isolation or as part of a wider seaweed biorefining product system. This work aims to bring these studies together—identifying where specific environmental hotspots lie within the cultivation and harvesting processes, and to understand the role of different design aspects. Overall, this review identifies challenges relating to future cultivation system design and LCA methodology.

Purpose Algal research has been dominated by the use of marine biomass (mainly microalgae) as feedstock in the production of second-generation biofuels, albeit with limited economic success. A promising alternative strategy is the valorisation of seaweed (macroalgae), with the cascaded extraction of its high-value components, as well as lower-value components further downstream, under the ‘biorefinery concept’. The goal of this study was to assess the environmental performance of one such marine biorefinery situated in the UK. Methods Attributional life cycle assessment (LCA) was conducted on a hypothetical marine biorefinery coproducing fucoidan, laminarin, protein and alginate/cellulose packaging material (target product), from cultivated Saccharina latissima. The functional unit was the production of 1 kg of packaging material. A total of 6 scenarios were modelled, varying in coproduct management methodology (system expansion, mass allocation or economic allocation) and applied energy mix (standard or green energy). Sensitivity analysis was also conducted, evaluating the systems response to changes in allocation methodology; product market value; biomass composition and transport mode and distance. LCA calculations were performed using OpenLCA (version 1.10.3) software, with background processes modelled using the imported Ecoinvent 3.6 database. Environmental impacts were quantified under ReCiPe methodology at the midpoint level, from the ‘Heirarchist’ (H) perspective. Results and discussion The overall global warming impacts ranged from 1.2 to 4.52 kg CO2 eq/kg biopolymer, with the application of economic allocation; 3.58 to 7.06 kg CO2eq/kg with mass allocation and 14.19 to 41.52 kg CO2eq/kg with system expansion — the lower limit representing the instance where green electricity is used and the upper where standard electricity is employed. While implementing the green energy mix resulted in a 67% reduction in global warming impacts, it also incurred a 2–9 fold increase in overall impacts in the categories of terrestrial acidification, human non-carcinogenic toxicity, land-use and terrestrial ecotoxicity. Economic allocation resulted in burden shifting most favourable to the packaging material pathway. Conclusions This study demonstrates that the road to environmental optimisation in marine biorefineries is fraught with trade-offs. From the perspective of LCA — and by extension, the eco-design process that LCA is used to inform — when evaluating such product systems, it serves to strike a balance between performance across a broad spectrum of environmental impact categories, along with having consideration for the nature of energy systems incorporated and LCA methodological elements. Graphical Abstract

Purpose Derelict fishing gear (DFG) is one of the most abundant and harmful types of marine litter that gets increasingly retrieved from the ocean. However, for this novel waste stream recycling and recovery pathways are not yet commonly established. To identify the most suitable waste management system, this study assesses the potential environmental impacts of DFG waste treatment options in Europe. Methods This study applies an attributional life cycle assessment (LCA) to four DFG waste treatment scenarios, namely a mechanical recycling, syngas production, energy recovery and landfill disposal. The scope spans from the retrieval and transport processes to pre- and end-treatment steps until the outputs are sent to landfill or assumed to substitute products or energy. Primary data was collected from retrieval and waste treatment trials in Europe. Contribution, sensitivity and uncertainty analyses were conducted using the LCA software SimaPro and ReCiPe as the impact methodology. Results and discussion The results show that the mechanical recycling and energy recovery achieve the lowest potential environmental impacts. The syngas production and landfill disposal scenario are not environmentally competitive because they require too much electricity, or their avoided production credits were too small to offset their emissions. Unlike the pre-treatment and transport processes, the retrieval and end-treatment processes have a significant impact on the overall results. The transport distances, energy mix and market and technological assumptions are least sensitive, while changes to the waste composition significantly affect the results. Especially a reduced lead content benefits the human toxicity impact potential of the landfill disposal scenario. The uncertainty analysis showed that the results are very robust in nine of twelve impact categories. Conclusions This is the first LCA study that compares waste treatment options for marine litter. The results indicate that a disposal of DFG is hazardous and should be replaced with mechanical recycling or energy recovery. While this may be technologically possible and environmentally beneficial, economic and social factors should also be considered before a final decision is made. To further reduce environmental impacts, marine litter prevention should play a more important role. Graphical abstract

Background Heterotrophic single-cell oils (SCOs) are one potential replacement to lipid-derived biofuels sourced from first-generation crops such as palm oil. However, despite a large experimental research effort in this area, there are only a handful of techno-economic modelling publications. As such, there is little understanding of whether SCOs are, or could ever be, a potential competitive replacement. To help address this question, we designed a detailed model that coupled a hypothetical heterotroph (using the very best possible biological lipid production) with the largest and most efficient chemical plant design possible. Results Our base case gave a lipid selling price of $1.81/kg for ~ 8,000 tonnes/year production, that could be reduced to$1.20/kg on increasing production to ~ 48,000 tonnes of lipid a year. A range of scenarios to further reduce this cost were then assessed, including using a thermotolerant strain (reducing the cost from $1.20 to$1.15/kg), zero-cost electricity ($1.12/kg), using non-sterile conditions ($1.19/kg), wet extraction of lipids ($1.16/kg), continuous production of extracellular lipid ($0.99/kg) and selling the whole yeast cell, including recovering value for the protein and carbohydrate ($0.81/kg). If co-products were produced alongside the lipid then the price could be effectively reduced to$0, depending on the amount of carbon funnelled away from lipid production, as long as the co-product could be sold in excess of $1/kg. Conclusions The model presented here represents an ideal case that which while not achievable in reality, importantly would not be able to be improved on, irrespective of the scientific advances in this area. From the scenarios explored, it is possible to produce lower cost SCOs, but research must start to be applied in three key areas, firstly designing products where the whole cell is used. Secondly, further work on the product systems that produce lipids extracellularly in a continuous processing methodology or finally that create an effective biorefinery designed to produce a low molecular weight, bulk chemical, alongside the lipid. All other research areas will only ever give incremental gains rather than leading towards an economically competitive, sustainable, microbial oil.

Background Heterotrophic single cell oils (SCOs) are one potential replacement to lipid derived biofuels sourced from first generation crops such as palm oil. However, despite a large experimental research effort in this area, there are only a handful of techno-economic modelling publications. As such, there is little understanding of whether SCOs are, or could ever be, a potential competitive replacement. To help address this question we designed a detailed model that coupled a hypothetical heterotroph (using the very best possible biological lipid production) with the largest and most efficient chemical plant design possible. Results Our base case gave a lipid selling price of $1.81 / kg for ~8,000 tonnes / year production, that could be reduced to$1.20 /kg on increasing production to ~48,000 tonnes of lipid a year. A range of scenarios to further reduce this cost were then assessed, including using a thermotolerant strain (reducing the cost from $1.20 /kg to$1.15 /kg), zero cost electricity ($1.12/kg), using non-sterile conditions ($1.19 / kg), wet extraction of lipids ($1.16 / kg), continuous production of extracellular lipid ($0.99 /kg) and selling the whole yeast cell, including recovering value for the protein and carbohydrate ($0.81 /kg). If co-products were produced alongside the lipid then the price could be effectively reduced to$0, depending on the amount of carbon funnelled away from lipid production, as long as the co-product could be sold in excess of $1/kg. Conclusions The model presented here represents an ideal case that which while not achievable in reality, importantly would not be able to be improved on, irrespective of the scientific advances in this area. From the scenarios explored, it is possible to produce lower cost SCOs, but research must start to be applied in three key areas, firstly designing products where the whole cell is used. Secondly, further work on the product systems that produce lipids extracellularly in a continuous processing methodology or finally that create an effective biorefinery designed to produce a low molecular weight, bulk chemical, alongside the lipid. All other research areas will only ever give incremental gains rather than leading towards an economically competitive, sustainable, microbial oil.

Background Palm oil is the most commonly used crop oil worldwide, and is used predominantly for food, in the chemical industry and for biofuels. It is mainly cultivated in areas with biodiverse and carbon-rich rainforest which has given rise to large increases in greenhouse gas (GHG) emissions and significant impacts to biodiversity. There is therefore substantial interest in finding an alternative to palm oil. Heterotrophic single cell oils (SCOs) are one potential replacement as these are able to mimic the lipid profile of palm oil in a way that other terrestrial and exotic crop oils cannot. But, despite a large experimental research effort in this area, there are only a handful of techno-economic modelling publications. As such, there is little understanding of whether SCOs are, or could ever be, a potential competitive replacement to palm oil. To help address this question we designed a detailed model that coupled a hypothetical heterotroph (using the very best possible biological lipid production) with the largest and most efficient chemical plant design possible. Results Our base case gave a lipid selling price of $2.01 / kg for ~8,000 tonnes / year production, that could be reduced to$1.54 /kg on increasing production to ~48,000 tonnes of lipid a year. A range of scenarios to further reduce this cost were then assessed, including using a thermotolerant strain (reducing the cost from $1.54 /kg to$1.47 /kg), zero cost electricity ($1.48/kg), using non-sterile conditions ($1.05 / kg), wet extraction of lipids ($1.48 / kg), continuous production of extracellular lipid ($0.76 /kg) and selling the whole yeast cell, including recovering value for the protein and carbohydrate ($1.14 /kg). If co-products were produced alongside the lipid then the price could be effectively reduced to$0, depending on the amount of carbon funnelled away from lipid production, as long as the co-product could be sold in excess of $1/kg. Conclusions The model presented here represents an ideal case that which while not achievable in reality, importantly would not be able to be improved on, irrespective of the scientific advances in this area. From the scenarios explored, however, it should still be possible to produce lower cost SCOs, but research must start to be applied in three key areas, firstly designing products where the whole cell is used, displacing products that contain palm oil rather than attempting to produce an exact refined palm oil substitute. Secondly, further work on the product systems that produce lipids extracellularly in a continuous processing methodology or finally that create an effective biorefinery designed to produce a low molecular weight, bulk chemical, alongside the lipid. All other research areas will only ever give incremental gains rather than leading towards an economically competitive, sustainable, microbial oil.

The past decades have seen an increasing interest in developing pathways to produce bio-based chemicals from lignocellulosic biomass and organic waste as renewable resources. Using biomass as a source of chemical building blocks is critical to a future sustainable chemical industry. The successful development of bio-chemicals will also have a profound impact in terms of the innovations of new polymers and materials, new solvents, and new bio-active compounds. This article provides a broad review of conventional thermal heating, microwave processing, and biochemical processing for the production of value-added bio-based chemicals. The potentially important but currently little exploited microwave-assisted processes are given particular attention and the microwave-specific, non-thermal effects are explored. The comparative merits of different approaches are evaluated from the techno-economic and environmental perspectives. The opportunities of integrated biorefineries are articulated, with the aim to actualize carbon-efficient valorization of lignocellulosic biomass and organic waste for synthesizing an array of products.

BACKGROUND Macroalgae are gaining increasing interest as an important biomass feedstock. Yet when valorising marine biomass, the presence of salt can pose a substantial obstacle to the effectiveness of downstream biological and chemical processes, as well as the engineering infrastructure required. Accordingly, dewatering, washing and drying are often considered the first and crucial primary steps in processing marine biomass such macroalgae. The high costs of these processes can make further marine biorefinery commercialisation prohibitive. This investigation assesses simple pre‐treatments for macroalgal biomass in saltwater, thereby reducing the freshwater footprint, and removing the need for an energy‐intensive washing and drying stage. RESULTS Using acid and basic catalysts, the carbohydrate and soluble protein components were fractionated into a soluble aqueous phase, for further fermentation and a solid phase suitable for hydrothermal liquefaction. The presence of saltwater was found to aid the fractionation process, solubilising more of the biomass. The use of H2SO4 produced more monosaccharides, whereas NaOH solubilised higher levels of biomass at lower temperatures. The aqueous phase was demonstrated to be suitable for biological processing with the salt tolerant yeast Metschnikowia pulcherrima, and the residual solids suitable for processing via hydrothermal liquefaction. CONCLUSION By contrast with existing pre‐treatment strategies, we demonstrate that an entirely salt‐based biochemical conversion route is a potentially viable option. For the first time this work demonstrates that, rather than a hindrance, the presence of saltwater can be advantageous, and could provide an alternative, more cost‐effective pathway to achieving a successful macroalgal‐based biorefinery.

The expansion of palm oil cultivation in recent decades has led to substantial increases in greenhouse gas emissions and biodiversity loss from carbon-rich tropical forest. Because of this, there is increased focus on replacement of palm oil in industrial and consumer products. Plant oils like rapeseed and sunflower oil, exotic oils such as coconut oil and shea butter, and microbial single cell oils have been suggested as potential replacements. Here, we review each of these options from a technical, environmental and economic perspective, including the option to improve the sustainability of existing palm oil cultivation practices. Increasing concerns about the impacts of palm oil cultivation have led to a growing focus on how to replace palm oil in commercial applications. This Perspective analyses replacement options—from a technical, environmental and economic angle—and how to make current cultivation practices more sustainable.

Oleaginous microalgae and yeast are of increasing interest as a renewable resource for single cell oils (SCOs). These have applications in fuels, feed and food products. In order to become cost competitive with existing terrestrial oils, a biorefinery approach is often taken where several product streams are valorised alongside the SCO. Whilst many life cycle assessment (LCA) and Techno-economic (TEA) studies have employed this biorefinery approach to SCO production, a systematic analysis of their implications is missing. This review evaluates the economic and environmental impacts associated with the use of coproducts. Overall, protein production plays the greatest role in determining viability, with coproduct strategy crucial to considering in the early stages of research and development.