Non-destructive 3D imaging and quantification of hydrated biofilm-sediment aggregates using X-ray micro-computed tomography

Abstract

Biofilm-sediment aggregate (BSA) contains a high water content, either within internal pores and channels, or bound by extracellular polymeric substances (EPS) forming a highly hydrated biofilm matrix. Desiccation of BSAs alters the biofilm morphology and thus the physical characteristics of porous media, such as the binding matrix within BSA and internal pore geometry. Observing BSAs in their naturally hydrated form is essential but hampered due to the lack of techniques for imaging and discerning hydrated materials. Generally, imagery techniques (scanning electron microscopy (SEM), transmission electron microscopy (TEM) and focused ion beam nano-tomography (FIB-nt)) involve the desiccation of BSAs (freeze-drying or acetone dehydration), or prevents differentiation between BSA components such as inorganic particles and pore water (confocal laser scanning microscopic (CLSM)). Here, we propose a novel methodology that simultaneously achieves the 3D visualization and quantification of BSAs and their components in their hydrated form at a sub-micron scale using X-ray micro-computed tomography (µ-CT). It enables the high-resolution detection of comparable morphology of multi-phase components within a hydrated aggregate: each single inorganic particle and the hydrated biofilm matrix. This allows the estimation of aggregate density and the illustration of biofilm-sediment binding matrix. This information provides valuable insights into investigations of the transport of BSAs and aggregate-associated sediment particles, contaminants (such as microplastics), organic carbon, and their impacts on aquatic biogeochemical cycling.

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Identifiers

ORCID for Ian H. Townend: orcid.org/0000-0003-2101-3858

ORCID for Kathryn E. Rankin: orcid.org/0000-0002-8458-1038

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