In situ Biofilm Quantification in Bioelectrochemical Systems by using Optical Coherence Tomography

Abstract

Detailed studies of microbial growth in bioelectrochemical systems (BESs) are required for their suitable design and operation. Here, we report the use of optical coherence tomography (OCT) as a tool for in situ and noninvasive quantification of biofilm growth on electrodes (bioanodes). An experimental platform is designed and described in which transparent electrodes are used to allow real‐time, 3D biofilm imaging. The accuracy and precision of the developed method is assessed by relating the OCT results to well‐established standards for biofilm quantification (chemical oxygen demand (COD) and total N content) and show high correspondence to these standards. Biofilm thickness observed by OCT ranged between 3 and 90 μm for experimental durations ranging from 1 to 24 days. This translated to growth yields between 38 and 42 mgCODbiomass gCODacetate −1 at an anode potential of −0.35 V versus Ag/AgCl. Time‐lapse observations of an experimental run performed in duplicate show high reproducibility in obtained microbial growth yield by the developed method. As such, we identify OCT as a powerful tool for conducting in‐depth characterizations of microbial growth dynamics in BESs. Additionally, the presented platform allows concomitant application of this method with various optical and electrochemical techniques.

Spotlight on the Energy Harvest of Electroactive Microorganisms: The Impact of the Applied Anode Potential

“…A whole arsenal of techniques have been applied for shedding light on the fundamentals of EET and EAM. These include, for instance, cyclic voltammetry, confocal resonance Raman microscopy, differential electrochemical mass spectrometry, nuclear magnetic resonance spectroscopy, and optical coherence tomography (Fricke et al, 2008; Virdis et al, 2012; Alves et al, 2015; Kubannek et al, 2018; Molenaar et al, 2018). However, a comprehensive thermodynamic analysis of the energy fluxes during EET is still missing.…”

Determining incremental coulombic efficiency and physiological parameters of early stage Geobacter spp. enrichment biofilms

“…This includes i) studies under steady-state conditions to minimize the influence of pH, e.g., by application of a flow cell [44], ii) inclusion of modeling approaches [68] or spatial-temporal analysis, iii) comparison of Geobacter spp. pure and enrichment cultures to assess the influence of minor species in the biofilm, and iv) minimally invasive measuring the biomass with, e.g., optical coherence tomography for an improved normalization of the derived parameters [69]. Especially the experimental setup (two-chamber systems), age of the examined biofilms (early stage vs. mature biofilms), and anode potential (i.e., different EET pathways) [70][71][72] are of utmost importance.…”

Granular activated carbon in capacitive microbial fuel cells

“…The relation found was 2340.3 C mg -1 N (R 2 = 0.98), which is half of that recently found for bioanodes in flat (FTO) electrodes, i.e. 4982.2 C mg -1 N (Molenaar et al, 2018). The lower value obtained in this study could relate to a lower microbial activity of the biofilm or to a higher nitrogen content of the same, although it is difficult to say since the bioanodes measured in that latter study were grown between 1 to 24 days.…”

“…Generally, all granules followed the same growth pattern, with a maximum current around 3 days after inoculation and a steady-state current of 65-71% of the maximum current after 1 week of growth. This shape seems to be typical for potential controlled bioanodes as previously reported in literature (Molenaar et al, 2018), which could relate to an increased ionic diffusion resistance due to the formation of a thicker biofilm (Sun et al, 2016). Nevertheless, nutrients and substrate were continuously supplied (acetate concentration was maintained >5mM) and the solution was continuously stirred.…”