The Limits of Three‐Dimensionality: Systematic Assessment of Effective Anode Macrostructure Dimensions for Mixed‐Culture Electroactive Biofilms

Abstract

This study analyzes the biofilm growth and long‐term current production of mixed‐culture, electrochemically active biofilms (EABs) on macrostructured electrodes under low‐shear‐force conditions. The channel dimensions were altered systematically in the range 400 μm to 2 mm, and the channel heights were varied between 1 and 4 mm to simulate macrostructures of different scales. Electrodes with finer‐structured surfaces produced higher current densities in the short term owing to their large surface area but were outperformed in the long term because the accumulation of biomass led to limitations of mass transfer into the structures. The best long‐term performance was observed for electrodes with channel dimensions of 1×4 mm, which showed no significant decrease in performance in the long term. Channels with a diameter of 400 μm were overgrown by the biofilm, which led to a transition from 3 D to 2 D behavior, indicating that structures of this scale might not be suitable for long‐term operation under low‐shear‐stress conditions.

Redox Potential Heterogeneity in Fixed‐Bed Electrodes Leads to Microbial Stratification and Inhomogeneous Performance

“…For unknown reasons, both reactors experienced a decrease in current production at day 58. Eventually, the limit of three‐dimensionality was reached around this moment [7,45] . Therefore, the formed biomass at the granules started to hinder mass transfer processes (i. e., supply of acetate to EAM and removal of counter ions from biofilm towards liquid) at key positions within the 3D network, i. e., between the granules or in granule pores.…”

Optimal Geometric Parameters for 3D Electrodes in Bioelectrochemical Systems: A Systematic Approach

“…We chose these duct diameters to span one order of magnitude to create a solid database for model calculations. Secondly, on the basis of our preceding study, in this size range a significant impact of biofilm growth or clogging was not to be expected. The number of ducts incorporated in the graphite electrodes was adjusted to obtain equal total surface areas for all 4 electrodes in each run (Table S1).…”

“…They include carbon cloth, graphite felt, fiber‐based electrode structures, carbon brushes, granular electrodes, layered structures, foams or sponges, and carbonated electrodes derived from natural or artificial precursors. A dense packing however can give rise to other limitations such as the clogging of the structure by biomass or electrochemical limitations owing to an unfavorable geometry and the typically low conductivity of solutions used in BES . While bioanodes are usually designed with the possible bottlenecks in mind, the bottlenecks have not been quantified to an extent that would enable optimization of electrode structure towards a specific application.…”

Studying the Impact of Wall Shear Stress on the Development and Performance of Electrochemically Active Biofilms

“…The relative current onset times were calculated from the slope of the exponential phase (of the first feeding cycle) and were normalized with respect to the highest value for each series . Relative current densities were calculated by normalizing the current densities of each series with respect to the highest value at the highest current density (relative maximum current density) or at the end of the experiment (relative final current density) . Experiments were operated for over one month (Figure a, b, c and d, long‐term) or around 2 weeks (Figure e and f, short‐term) corresponding to 6 replicates for the calculation of onset times and relative maximum current densities (Figure ) and 4 replicates for the calculation of relative final current densities (Figure ).…”

“…Additionally, the influence of higher shear forces on biofilms of EAB could be of interest for systems with considerably increased volume flows. Higher volume flows may be of interest in the context of wastewater treatment as they can be applied non‐continuously (e. g. pulsed flow operation) to remove excess biomass from the system and avoid clogging of bioanodes which has been shown to be a significant factor for performances losses in BES …”