In situ probing and evaluation of two different electrode materials in bio electrochemical systems by means of Optical Coherence Tomography on automated robotic platform

Carbon-based and stainless steel-based materials are widely utilized as anode/cathode electrodes in bio electrochemical systems (BESs) due to its low capital cost, high conductivity and large specific surface area. Carbon-based materials such as carbon veil are mostly applied in lab-scale reactors because of its versatile shape and configuration. Moreover, stainless steel type materials show higher strength and are easier to incorporate within flow field. Optical coherence tomography (OCT) as an image technique is a suitable method to monitor biofilm growth and fluid-structure interactions at the meso-scale. In BESs, investigating bulk-biofilm interface (fluid-structure interactions) is of particular interest to optimize the mass transfer under suitable hydrodynamic condition and enhances the overall effectivity of BESs systems. To extend the knowledge about the influence of different anode electrodes as substratum on OCT monitoring and quantification, the biofilm structural properties analyzed by OCT image processing and bioelectrochemical systems performance were compared.  

A custom-designed dual-chamber setup was constructed by two transparent optical flow cells and fixed in the automated monitoring platform (Evobot). Herein, we applied OCT to in-situ characterize and quantify the biofilm structure properties on two different anode electrodes (carbon veil-CV and porous stainless steel-SS) as substratum in microbial fuel cell (MFC) mode.  3D OCT dataset analysis presented 3 structural parameters for biofilm-carbon veil interface and 5 structural parameters for biofilm-stainless steel interface, separately. Biofilm volume (BioV) was calculated to compare CV and SS anode electrodes.

In this study, a time-series of biofilm development was performed on both CV and SS materials. At the fourth day, the biofilm almost covered the entire anode surface and achieved 97% substratum coverage. Afterwards the biofilm grew mostly in vertical direction. With the further biofilm growth along height the electric resistance increased and power production gradually reached the equilibrium. Nevertheless, both materials did not show predominant advantage on power production. Furthermore, a relatively small error appeared on quantitative analysis of Biofilm volume using stainless steel. Whereas, the predictability of biofilm volume on the carbon veil anodes was hindered by the appearance of shadowing effects. Thus, it can be concluded that stainless steel flat plate electrode is preferable as anode material to investigate the interaction between biofilm structure, hydrodynamic conditions and mass transfer in BESs via OCT.