Biobased Materials and Carbon Storage
By A. Clare
Biobased materials are those that comprise of one or more substances derived from biomass. Biomass often includes feedstocks obtained from agricultural or forestry raw materials, algae or biowaste. These materials provide an alternative to traditional fossil-based products, therefore; enabling an opportunity to decrease dependence on fossil resources.
Carbon sequestration is the storage element of the carbon cycle and one form occurs when plants absorb CO2 from the atmosphere during photosynthesis. This biomass can subsequently be incorporated into materials to produce biobased products, which may store this carbon for a number of years. Although this form of carbon storage is technically reversible (as carbon emissions can be re-emitted at a materials end of life), it delays the radiative forcing and can offset current anthropogenic emissions.
Carbon negative products and sustainable production
The inclusion of biomass in products can create new carbon pools, preventing previously absorbed carbon from re-entering the atmosphere. The longer the lifetime of these products, the later the carbon pool is emptied. Although incorporating biomass can significantly reduce the carbon footprint of a product, the success of the product being carbon negative (and sequester carbon) relies on the production volume of the product absorbing more atmospheric CO2 than it emits. During the processing stage, the emissions deriving from energy use and transport need to be less than the amount of carbon stored by the product. Furthermore, not all biobased materials are 100% biobased. Some materials may also include fossil components to increase performance. The addition of fossil-based resources may drastically increase the footprint of a product; therefore, this must also be considered when determining if a product is carbon neutral.
Reduction in greenhouse gas emissions (GHGs) is the prime environmental benefit of producing bio-based products, with these benefits regarded as very important by NGOs and public procurement officers. In addition to the processing stages, emissions also need to be low during upstream processes. The biobased content of a product is not an indicator of sustainability – it simply demonstrates how much of the product is derived from biomass (whether produced sustainably or not). Although renewable, biomass sustainability relates to the impacts of sourcing and subsequent processing. The biomass should be produced sustainably, with minimal effects on biodiversity, soil quality, water quality and social well-being. For example, if land previously used for food production is diverted to produce bio-based products, the existing demand will need to be met by other means (e.g., diverting non-agriculture land elsewhere). This indirect land-use change may also result in a significant increase in GHG emissions. Furthermore, sustainability is also influenced by whether biomass is harvested to produce bio-based materials or comes from waste.
End of life
Biobased materials provide alternative end-of-life (EoL) options relative to conventional counterparts; however, they can also enter traditional EoL processing routes (e.g., landfill, recycling, incineration). Ensuring biobased materials sequester more carbon than they emit also includes those emissions produced during end-of-life processes (and the transport of the material to these processes). Different routes release various amounts of emissions - see Table 1. Emissions from landfills are high and incineration and closed-/open-loop processes emissions are similar. Alternatively, anaerobic digestion and composting produce the least amount of emissions. Biobased products can be beneficial as they can often be recycled or, even better, composted at end-of-life – enabling to meet all forms of circular thinking (Figure 1).
Table 1 - 2021 Emission factors for different disposal methods using household residual waste (tonnes) as the waste type example
Biobased materials which are also of fossil origin are often recycled. Mechanical processes separate the bio- and fossil components. If this sorting process cannot be carried out – for example, due to low volumes – the materials are likely to enter an incineration process instead. Compostability correlates with circularity and enables the production of new biomass. The resulting biomass can be collected through biowaste collection and either composted or used as biogas to produce renewable energy. These materials are likely only to degrade under industrial composting conditions, as compostable means; a product degrades under specific controlled conditions (involving temperature, time humidity, and microorganisms present). Materials that enter anaerobic digestion at end-of-life; can be used to generate biogas (albeit largely methane), with the remaining sludge residue able to be applied as an agriculture nutrient.
Figure 1 – Circular thinking during the production of biobased materials.
Biobased materials can replace many fossil-based products whilst greatly reducing a products carbon footprint and fitting into the circular economy model. However, to be classed as sustainable, other factors must also be considered -to ensure the product is sustainable across its entire lifecycle. Biomass must be cultivated and produced sustainably, whereas production should use minimal energy and, the origins of processing agents should also be considered. Without careful consideration of the whole life’s impacts, the benefits of replacing fossil feedstocks to reduce GHG emissions may come at a cost of other environmental impacts. Furthermore, many industrial materials have the potential to be replaced by biobased counterparts; however, the performance and cost of their production is also an important consideration.