How sustainable is biomass-derived carbon feedstock?

As the petrochemical industry continues to explore circular models, biomass is envisaged as playing a key role beside recycling and captured carbon – but how sustainable is it, really? Jed Thomas 

Biomass-derived carbon, often championed as a renewable energy source, presents a complex sustainability profile that warrants thorough examination.  

While it offers potential benefits in reducing reliance on fresh petroleum and therefore, improving circularity, its environmental impact, particularly concerning soil health and carbon offset credibility, is multifaceted.  

It seems possible to ensure the sustainability of this feedstock, if we’re very careful about how much is used and the practices deployed by producers. 

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Does renewable carbon degrade topsoil? 

The extraction of biomass for chemical production can lead to soil degradation, especially when agricultural residues, essential for biomass-derived carbon feedstocks, are removed without adequate management.  

These residues are vital for maintaining soil organic matter, which supports soil structure, fertility, and moisture retention.  

Their removal can result in diminished soil health and increased erosion – which, in turn, exposes more stored carbon to the air, forming and releasing carbon dioxide. 

A 2024 report by the materials research non-profit the World Resources Insitute outlines three principles for sustainably sourcing biomass:¹ 

• Prioritize wastes, residues, and by-products: though, WRI admit that this poses a risk to ‘soil health and ecological functioning’, such that ‘More research is needed to determine the appropriate amount [...] that should be left on farms and forest floors to maintain soil health.’ 

• Forestry material should come from ecologically managed forests: without built-in sustainability, an expanding biomass industry is likely to produce even greater deforestation.  

• Grown carbon removal crops should be limited to native species on marginal land: this is to ensure that ‘natural or protected lands’ do not lose ‘large natural carbon stores in soil or aboveground vegetation’, which could make the whole business net-emitting. 

Practices like cover cropping and mulching are essential for preserving soil integrity. They contribute organic matter, suppress weeds, and enhance nutrient cycling. 

However, diverting biomass from these practices to energy production can compromise these benefits. For instance, utilizing crop residues for bioenergy instead of soil cover can reduce soil organic carbon, leading to poorer soil health.  

Research from 2024 discusses the use of ‘low-value woody biomass’, which is produced as part of routine forest management, as a feedstock for biochar, a substance used to improve soil properties and sequester carbon in soil.²

The problem, of course, is that this places pressure on the use of that residue for the chemicals industry, especially if there are concerns about the sequestration credentials. 

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Is biomass actually carbon neutral? 

The classification of biomass as carbon-neutral is contentious.  

While the carbon released during biomass combustion is theoretically offset by the carbon absorbed during plant growth, this balance is not always achieved in practice. 

Factors such as land-use changes, cultivation practices, and biomass transportation can result in net carbon emissions.  

An op ed published in Environmental Research Letters back in 2018 suggests that for agricultural or forestry residues to be carbon neutral, it must meet two criteria:³ 

• It cannot be grown for the purpose of burning or utilising, i.e. it must be a genuine waste or by-product.  

• Within a period of time consequential for climate actions, its emissions must be negligible, i.e. it can’t take 50 years for a given biomass source to recycle its carbon emissions. 

Of course, it may seem like combustion is irrelevant when we’re talking about feedstocks for chemicals manufacture but if biomass-derived chemicals end up in landfill, incineration is a likely outcome given today’s status quo in waste management. 

Similarly, the possibility that biomass-derived feedstocks will be counted as carbon offsets raises another concern. It has long been debated in climatology whether or not offsetting is a legitimate concept. 

For instance, another op ed, published this time in Nature’s World View section, by Professor Kevin Anderson from the University of Manchester in 2012 states that: ‘Carbon offsetting is without scientific legitimacy and is dangerously misleading.’⁴  

His argument is that carbon offsetting can ‘stimulate further emissions’ by, for example, increasing demand for flights, releasing greater quantities of carbon that we don’t have the capacity to offset. 

There is a related criticism of offsetting which is that it may prevent effective reductions in the atmospheric concentration of carbon dioxide – as it were, offsetting ‘clogs up’ available sequestration capacity, leaving historic emissions untouched. 

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In the case of biomass-derived carbon feedstocks for chemical manufacture, then, how these feedstocks are categorised by regulators, whether they are a form of sequestration (carbon-negative) or an offset (carbon-neutral).  

The sustainability of biomass-derived carbon is intricately linked to land management practices, soil health considerations, and the authenticity of carbon offset claims.  

To harness its potential benefits, it is imperative to adopt practices that preserve soil integrity, ensure genuine carbon sequestration, and promote ecological balance. This necessitates a holistic approach that integrates sustainable agriculture, responsible biomass sourcing, and rigorous carbon accounting. 

¹ Biomass can fight climate change, but only if you do it right. Audrey Denvir and Haley Leslie-Bole. World Resources Institute. 2024.

² Role of biochar made from low-value woody forest residues in ecological sustainability and carbon neutrality. Ghosh et al. Soil Science Society of America Journal. 2024.  

³ Not carbon neutral: Assessing the net emissions impact of residues burned for bioenergy. Mary S Booth. Enviromental Research Letters. 2018.

⁴ The inconvenient truth of carbon offsets. Prof. Kevin Anderson. Nature: World View. 2012.