NMR investigation of water diffusion in different biofilm structures

Abstract

Mass transfer in biofilms is determined by diffusion. Different mostly invasive approaches have been used to measure diffusion coefficients in biofilms, however, data on heterogeneous biomass under realistic conditions is still missing. To non-invasively elucidate fluid-structure interactions in complex multispecies biofilms pulsed field gradient-nuclear magnetic resonance (PFG-NMR) was applied to measure the water diffusion in five different types of biomass aggregates: one type of sludge flocs, two types of biofilm, and two types of granules. Data analysis is an important issue when measuring heterogeneous systems and is shown to significantly influence the interpretation and understanding of water diffusion. With respect to numerical reproducibility and physico-chemical interpretation, different data processing methods were explored: (bi)-exponential data analysis and the Γ distribution model. Furthermore, the diffusion coefficient distribution in relation to relaxation was studied by D-T maps obtained by 2D inverse Laplace transform (2D ILT). The results show that the effective diffusion coefficients for all biofilm samples ranged from 0.36 to 0.96 relative to that of water. NMR diffusion was linked to biofilm structure (e.g., biomass density, organic and inorganic matter) as observed by magnetic resonance imaging and to traditional biofilm parameters: diffusion was most restricted in granules with compact structures, and fast diffusion was found in heterotrophic biofilms with fluffy structures. The effective diffusion coefficients in the biomass were found to be broadly distributed because of internal biomass heterogeneities, such as gas bubbles, precipitates, and locally changing biofilm densities. Thus, estimations based on biofilm bulk properties in multispecies systems can be overestimated and mean diffusion coefficients might not be sufficiently informative to describe mass transport in biofilms and the near bulk.

Heterogeneous diffusion in aerobic granular sludge

“…For the mobile population, self‐diffusivity of water in the granules is reduced compared to the self‐diffusivity of free water. The diffusion coefficients that were found in this study for AGS are in the same order of magnitude as the water self‐diffusion coefficients determined for different anaerobic and aerobic aggregates and biofilms (Beuling et al, 1998; Hornemann et al, 2008; Herrling et al, 2017; Lens et al, 2003, 1997; Phoenix & Holmes, 2008; Renslow, Babauta, Majors, & Beyenal, 2013; Renslow et al, 2010; Vogt, Flemming, & Veeman, 2000).…”

“…In line with the observations in the present study, Phoenix and Holmes (2008) reported relatively little diffusion heterogeneity for a structurally complex phototrophic biofilm. Furthermore, Herrling et al (2017) found there was no clear relation between diffusion and T 2 based on a D‐ T 2 experiment. Thus, T 2 maps are of limited use for the characterization of diffusional properties, despite being relatively easy to obtain.…”

“…However, the lab‐scale reactors were operated with notably different hydrodynamics, influent characteristics, and loading. The wet density of lab‐grown granules is typically reported to be around 1,040 kg/m 3 (Etterer & Wilderer, 2001; Herrling et al, 2017; Winkler, Bassin, Kleerebezem, Van der Lans, & Van Loosdrecht, 2012), although the ash content plays a major role (Winkler, Kleerebezem, Strous, Chandran, & Van Loosdrecht, 2013). The wet density of granules from the Garmerwolde treatment plant was found to be around 1,020 kg/m 3 .…”

Situations Leading to Reduced Effectiveness of Current Hand Hygiene against Infectious Mucus from Influenza Virus-Infected Patients

“…Because mass transfer is limited in biofilms (26,27), a disinfectant solution takes a long time to reach the center of a biofilm. Therefore, bacteria in biofilms are protected from disinfectants and survive longer (26,(28)(29)(30). Human mucus, including sputum, is a viscoelastic substance that shares physical properties with biofilms (31).…”

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.…”