Environmental Assessment: Life Cycle Assessment of biofuels from seaweed using the MacroFuels concept

Introduction

The objective of the MacroFuels project is to advance the technologies for producing liquid transportation biofuels from cultivated seaweed (or macroalgae). As a result, it is hoped that it will be possible to provide more sustainable transport fuels.

The MacroFuels concept sets out to progress the technologies for producing third generation biofuels from seaweed by assessing current system design concepts. These designs are informed by lab scale testing, field trials and modelling completed within the other work packages of the MacroFuels project. The biofuels production scenarios targeted as part of the MacroFuels concept are:

• Bio-ethanol via fermentation (EtOH process);

• Bio-butanol and bioethanol via ABE (acetone, butanol and ethanol) fermentation (ABE Process); and

• Bio-furanics via biphasic reaction with toluene and water, and reaction with bio-butanol and hydrogen.

This study reports an environmental life cycle assessment (LCA) of those biofuels which could be produced under the MacroFuels concept. The LCA evaluates the full value chain and thereby provides a better understanding of the potential environmental impacts of the large-scale cultivation of seaweed and its use as a feedstock for the production of biofuels.

A key driver for the development of biofuels in Europe is the renewable Energy Directive (2018/2001/EC) (the RED). The RED sets a target of 14% of energy for transport to come from renewable sources by 2030. For a biofuel to count towards this target, it must fulfil certain sustainability criteria set out in the RED with respect to greenhouse gas (GHG) emissions and should be identified as no / low risk for additional impacts from indirect land use change. Indirect land use change can increase the net GHG emissions from terrestrial crops used as biofuels, but seaweed is seen as a low risk crop in this context, as it is grown in the sea and will not displace land used to grow food.

Goal and Scope of the Study

The goal of this LCA was to conduct a ‘cradle-to-grave’ assessment of the MacroFuels concept. This will inform its future development by appraising the potential environmental impact of producing biofuels from seaweed for use as transport fuels and allow comparison of the calculated GHG emissions of these fuels with reported values for those produced from other sources.

The objectives of the LCA are as follows:

1. To increase MacroFuels’ understanding of the life cycle environmental impacts of the biofuels from seaweed concept;

2. Identify where the main environmental impacts occur (the so-called ‘hotspots’) in the full value chain for the production of biofuels from seaweed to support the design of systems for seaweed cultivation and processing to biofuel;

3. Compare the life cycle impacts of the ethanol, butanol and furanic fuels produced; and

4. Benchmark the biofuels assessed under the MacroFuels project against:

a. Equivalent conventional, fossil-based, fuels and currently available biofuels; and

b. Sustainability criteria for GHG emissions under the Renewable Energy Directive (2018/2001).

Product System Studied and Functional Unit

The study investigates the potential environmental impacts of the following products produced via the three processes outlined above. An important step in both the EtOH and ABE processes is the hydrolysis of the seaweed prior to fermentation. This can be completed by either acid hydrolysis or enzyme hydrolysis and both processes are considered, as follows.

• Ethanol (EtOH process - acid hydrolysis);

• Ethanol (EtOH process - enzyme hydrolysis);

• Ethanol (ABE process - acid hydrolysis);

• Ethanol (ABE process - enzyme hydrolysis);

• Butanol (ABE process - acid hydrolysis);

• Butanol (ABE process - enzyme hydrolysis);

• Furanics fuel additive; and

• Furanics fuel (10%) / bio-butanol (90%) blend

The functional unit this study is defined as:

1 MJ of biofuel used as transport fuel in an internal combustion engine.

Life Cycle Stages Considered

The LCA carried out was ‘cradle-to-grave’. This means that all significant life cycle stages associated with the product systems studied were considered, from raw materials, through processing and production, to distribution, use, waste collection, recycling or management at end of life.

Energy and material inputs were traced back to the extraction of resources, and emissions and wastes from each life cycle stage were quantified. Figure 0-1 shows the system boundary of the LCA.

Figure 0-1 System boundaries of LCA based on life cycle of biofuel from seaweed according to the MacroFuels concept

The Macrofuels concept considers a biorefinery with a processing capacity of 1.2 Mtonne seaweed (dw) per year, as this equivalent to that of an existing large bioethanol plant in the port of Rotterdam, the Netherlands. 

Seaweed cultivation

The study assumes that only brown seaweed (Saccharina latissimi) is used as feedstock in the EtOH and ABE processes and only red seaweed (Palmaria palmate) is used as feedstock for the furanics process. It has been assumed that two harvests a year of these crops is possible. The cultivation systems and yields for both seaweeds are assumed to be the same.

The design of the seaweed cultivation system was based on a concept published in open literature (Groenendaal, Vandendaele, & Vroman, 2017; Sioen, 2015). The growing substrate for the seaweed is sheetnets, made from polyester non-woven material, held horizontally in the water by chains and bouys and arranged in repeating segments for a total effective area of the seaweed field of 18,460 ha. This will produce 1.2 Mtonne seaweed (dw) per year for the biorefinery.

Processing seaweed to biofuel

The data for processing seaweed to biofuel have been sourced from MacroFuels deliverable 6.2, Techno-economic Evaluation and Health and Safety Risk Assessment. Table 0-1below summarises the production processes for each scenario considered in the Macrofuels concept.