Iron, Cobalt, and Gadolinium Transport in Methanogenic Granules Measured by 3D Magnetic Resonance Imaging

Abstract

Description of processes such as bioaccumulation, bioavailability and biosorption of heavy metals in biofilm matrixes requires the quantification of their transport. This study shows 3D MRI measurements of the penetration of free (Fe 2+ , Co 2+ and Gd 3+ ) and complexed ([FeEDTA] 2− and [GdDTPA] 2− ) metal ions in a single methanogenic granule. Interactions (sorption or precipitation) between free metals and the biofilm matrix result in extreme shortening of the spin-spin relaxation time (T 2 ) and a decrease of the amplitude (A 0 ) of the MRI signal, which hampers the quantification of the metal concentration inside the granular sludge matrix. MRI images clearly showed the presence of distinct regions (dead or living biomass, cracks, and precipitates) in the granular matrix, which influenced the metal transport. For the free metal ions, a reactive barrier was formed that moved through the granule, especially in the case of Gd 3+ . Chelated metals penetrated faster and without reaction front. Diffusion of [GdDTPA] 2− could be quantified, revealing the course of its transport and the uneven (0.2-0.4 mmol·L −1 ) distribution of the final [GdDTPA] 2− concentration within the granular biofilm matrix at equilibrium.

Opportunities for visual techniques to determine characteristics and limitations of electro-active biofilms

“…Many nuclei of atoms carry a quantum mechanical spin and thus a magnetic moment (Bartacek et al, 2016). If a strong polarizing magnetic field is used on those nuclei they become magnetized.…”

“…However, MRI has mainly been used in biofilm research to form a 2D or 3D image of the biofilm to show structural biofilm features (Franklin et al, 2015;Neu et al, 2010). For biofilm imaging, magnetic field used can vary from 0.7 to 14.1 Tesla (Bartacek et al, 2016). Caizán-Juanarena et al, 2019 used a magnetic field of 14.1 T to get (28 μm) 3 resolution 3D images of EABfs (Fig.…”

“…At the expense of the 3D image resolution, lower magnetic field of 0.7 Tesla can also be used to perform in-situ observation of the development of the biofilm (Bartacek et al, 2016). With these works, MRI was used to successfully determine the biofilm distribution and its volume with the biggest advantage of not destroying the sample.…”

Granular activated carbon in capacitive microbial fuel cells

“…Existing research studies have mainly focused on biofilm structure, transport of water (i.e. diffusion and flow) and transport of metal ions in and around biofilms structures (Bartacek et al, 2016;Herrling et al, 2017;Manz et al, 2005;Phoenix & Holmes, 2008;Ramanan et al, 2010;Seymour et al, 2004;Wieland et al, 2001), and grown on carriers, even with complex geometry (Graf von der Schulenburg et al, 2008;Herrling et al, 2015Herrling et al, , 2017. Specifically, MRI research on biofilm growth on electrodes has revealed information about diffusion coefficients and metabolic activity (i.e.…”

“…to achieve higher spatial resolutions due to the smaller dimensions of biofilms, but biofilm studies have also been performed at very low field strengths of 0.7 T (e.g. (Bartacek et al, 2016)).…”