MICRO-VIEW BIOCHAR: Visualising and Quantifying Biochar Structure in 3D
This research feature was provided by Tannaz Pak, PhD, CEng FIMMM, FHEI, Associate Professor (Research) at Energy and Environmental Engineering, Teesside University, UK. Tannaz specialises in X-ray micro-CT imaging of biomass and biochar, focusing on quantitative, non-destructive characterisation of pore structure across different feedstocks, pyrolysis conditions, and treatments. This approach allows her to systematically capture how biochar structure develops and varies, which is critical for understanding performance.
Research Abstract
Biochar performance across applications (including soil systems, water treatment, and carbon sequestration) is fundamentally governed by its pore structure. However, this structure is rarely characterised in three dimensions, leaving a clear gap in the ability to systematically link feedstock selection and processing conditions to functional performance.
This work applies X-ray micro-computed tomography (micro-CT) to enable non destructive, quantitative 3D characterisation of biomass and biochar pore architecture. This approach captures how structure evolves from biomass under different pyrolysis conditions and provides measurable descriptors of pore size, connectivity, and accessibility.
Beyond analysis, this research translates complex structural data into high-resolution visualisations and physical 3D models, making biochar structure directly observable and accessible to both specialist and non-specialist audiences.
By providing a quantitative and visual framework for understanding biochar structure, this work enables meaningful comparison between different biochar, more informed material design, and enhanced communication across the sector aligning closely with the International Biochar Initiative’s goals around standardisation, education, and wider adoption.
Key Findings
- Biochar pore structure evolves systematically with processing conditions
X-ray micro-CT reveals clear and measurable changes in 3D pore architecture according to pyrolysis conditions, including the development and expansion of pore networks. - Feedstock and processing conditions directly control structural outcomes
Different biomass types and treatment pathways produce distinct pore geometries, influencing functional performance. - Conventional 2D imaging methods are insufficient for structural characterisation
Techniques such as SEM provide limited, surface-based views and do not capture the three-dimensional connectivity of pore networks, leading to incomplete or potentially misleading interpretations. (Appendix, Figure A1) - 3D imaging enables quantitative, pore-scale metrics
Measurement of pore-size distribution, connectivity and structural heterogeneity enables comparison between different biochar. - Structural and chemical changes do not always align
Our results show that activation may significantly alter surface chemistry (e.g. FTIR) without substantial changes in pore structure at the microscale, highlighting the need for combined analytical approaches. - Visualisation significantly improves understanding and communication
Translating datasets into 3D visualisations and physical models makes biochar structure accessible, supporting engagement with stakeholders, policymakers, and non-specialist audiences. See the accompanying PDF below, Biochar Models.
Method and Evidence
X-ray micro-CT is a well-established technique used in geosciences (e.g. rock characterisation), medical imaging (e.g. diagnostics), and materials science. It enables non-destructive imaging of internal structure of material, producing full 3D reconstruction of material and enabling quantitative analysis of complex structures. In the context of biochar, micro-CT allows direct observation of how biological structures are transformed into carbon architectures. This work applies X-ray micro-CT to enable non-destructive, 3D imaging of biomass and biochar structure. Micro-CT captures the full internal structure of material. We have demonstrated this approach for seaweed-derived biochar (Appendix, Figure A2).
Figure 1: X-ray micro-CT slices of cassava peel biomass and biochar produced at increasing pyrolysis temperatures (300-800°C), including activated biochar. The images show progressive development and expansion of pore structure with temperature, highlighting how processing conditions shape biochar architecture.
Reconstructed 3D volumes are segmented into solid and pore phases, allowing quantitative analysis of structural properties, including pore size distribution, thickness mapping, and pore connectivity through pore network modelling. Within the solid phase the ash and carbon can also be distinguished due to the difference in their X-ray attenuation. Over the past 6-7 years I have applied this approach across a range of feedstocks and processing conditions. For example, imaging of cassava peel biomass and biochar produced between 300- 800°C demonstrates progressive structural transformation, with the development and expansion of pore networks as temperature increases (Figure 1). In contrast, for this sample a bio-chemical activation processes show limited structural change at this scale, despite significant modifications in surface chemistry. The workflow used to translate 3D images into quantitative structural descriptors is summarised in Figure 2.
Figure 2: Workflow for quantitative 3D characterisation of biochar structure. Grayscale image is segmented into solid and pore phases, followed by thickness mapping and pore network modelling (PNM) to quantify pore size distribution and connectivity.
Practical Applications Across the Biochar Value Chain
The ability to characterise biochar structure in 3D provides practical value across the full biochar value chain, particularly in situations where decisions must be made under uncertainty around feedstock, processing conditions, and end-use performance.
At the production stage, this approach is especially valuable when selecting feedstocks and defining pyrolysis conditions for the first time, or when changes in feedstock supply require process adaptation. This is increasingly relevant as biomass resources become more competitive, requiring producers to transition from more conventional feedstock materials such as rice residues, to more abundantly available such as hemp, or other agricultural by-products. In these contexts, X-ray micro-CT enables direct comparison of how different feedstocks and processing pathways translate into pore architecture, supporting more informed and efficient decision-making.
For waste processors handling large and heterogeneous biomass streams, structural imaging provides a means to assess variability within feedstock and its impact on the resulting biochar. This is particularly important where mixed or inconsistent inputs influence product quality. The ability to visualise and quantify structural differences allows identification of variability, detection of anomalies, and improved understanding of how contaminants or irregular materials may affect performance.
In product development and application, linking pore structure to functional behaviour supports a more systematic approach to designing biochar for specific uses. Rather than relying on trial-and-error, structural characterisation provides a complementary basis for selecting or producing biochar with properties suited to particular applications, whether in soil systems, filtration, or other environmental contexts.
From a quality assurance and standardisation perspective, quantitative 3D metrics such as pore size distribution and connectivity offer a reproducible basis for comparing biochar produced under different conditions. This addresses a key challenge in the sector, where materials with similar bulk properties may behave differently in practice due to underlying structural differences.
At the level of policy, carbon markets, and sector-wide adoption, improved understanding of pore architecture provides additional insight into the stability and persistence of biochar. This contributes to more robust recognition of biochar as a long-term carbon storage solution.
Finally, the translation of these datasets into 3D visualisations and physical models enables effective communication across the sector. These tools support engagement with non-specialist stakeholders, facilitate knowledge transfer, and help bridge the gap between technical research and practical implementation.
Conclusions
This work supports IBI’s efforts in advancing biochar standardisation, improving comparability across materials, and strengthening education and awareness through clear, evidence-based understanding of biochar structure.
With over 15 years’ experience in imaging porous media, and the last 6-7 years focused on biochar, I am actively looking to engage with the biochar community to advance the use of 3D structural characterisation as a core component of biochar research and application.
Dr Tannaz Pak, PhD, CEng FIMMM
Associate Professor (Energy and Environmental Engineering), Teesside University, UK
Email: t.pak@tees.ac.uk
Appendix
Measurements extracted from 2D images do not accurately represent 3D pore geometry, and sample preparation introduce artefacts or bias. These limitations restrict the ability to obtain statistically representative, quantitative structural information through applying 2D imaging.
Biochar is commonly structurally characterised using imaging techniques such as scanning electron microscopy (SEM). While SEM provides high resolution images, it is limited to surface or section-based views, and two-dimensional representation of inherently three-dimensional structures. As a result, structural features can be visually inspected but not fully understood.
Figure A1: SEM images and respective measurements for biomass and biochar samples in 2D
Figure A2: Example X-ray micro-CT slices of seaweed-derived biomass (top row), biochar (middle row), and activated biochar (bottom row). Structural transformation during pyrolysis is clearly observed, with the development of pore architecture from biological precursors.
This Figure highlights clear structural differences between biomass, biochar, and activated biochar. Ref: https://doi.org/10.1016/j.biteb.2023.101688