Characterization and optimization of anodes for microbial electrochemical technologies treating wastewater

Abstract: Microbial electrochemical technologies (METs) can produce power from renewable sources or produce platform chemicals from carbon dioxide. They are developed within a highly multi-disciplinary and dynamic research environment with the aim to contribute to the global energy transition towards sustainable and renewable energy production, energy efficient remediation, and bioproduction processes. This work has carried the development of METs significantly forward on three different levels.
(1) Engineering: Existing reactor designs are analyzed in detail and rated. Furthermore, a new reactor concept for the integration of METs into wastewater treatment is presented and characterized. (2) On the biological level, different inoculation strategies for the improvement of anode performance are described and (3) On the methodological level (bio-)electrochemical methods to characterize and evaluate METs are revised.
1.The highlight of this work is the development of a new reactor concept (Chapter 5) based on the findings of the analysis and rating of existing reactor designs (Chapter 2.4). The new reactor concept aims at the production of electricity for reducing the overall energy consumption of wastewater treatment and is realized as a combination of METs and membrane bioreactors. It was granted with a German and European patent and the novelty of this development is an anode which is simultaneously used as microfiltration membrane in sidestream crossflow configuration. To evaluate the feasibility of such an anode, the concept is proved using sintered porous stainless steel with G. sulfurreducens and an acetate-based synthetic medium. Resulting current densities were increased up to 4-fold compared to a standard bioelectrochemical anode setup. E.g. a stainless-steel filter of the grade 0.5 µm solely used as anode, achieves current densities of 4 A m−2 in a standard setup and > 15 A m−2 when it is simultaneously used as filtration element in crossflow configuration. To test the feasibility of this new reactor treating wastewater, it is subsequently operated as anaerobic membrane reactor (AnMBR) and the degradation of chemical oxygen demand (COD) monitored. These experiments show, that significant conversion of COD to electrical current on the filter used as anode takes place. The COD removal achieves up to 450 mg L-1 showing great potential for increasing treatment efficiencies and having a polishing effect on the effluent from an AnMBR.
2.Another option to push METs forward is the optimization of the catalytic performance of the biofilm-electrode interface (Chapter 4). It is often reported, that cathodes limit the overall performance. But a closer look into the studies shows, that these results are mostly obtained when running the anodes with a synthetic medium containing high concentrations of acetate. When using more realistic environments, the anode performance is worse and can very well become limiting. To determine and optimize the anode performance treating municipal wastewater, continuous experiments have been conducted and different inoculation strategies were applied to parallel experiments. To optimize the anode performance, a highly specialized microbiologic consortium of the species Geobacter and Shewanella was pre-grown prior to the operation with municipal wastewater. These species are known to deliver high current densities. Interestingly the pre-grown multispecies biofilm did not significantly improve current densities compared to the inoculation with sewage sludge or with no inoculation at all. All experiments reach 0.42 – 0.65 A m-2 after 20 days of operation, while operation with the pre-grown multispecies biofilm running on synthetic medium achieves 4.07 A m-2. The species of the pre-grown biofilm were barcoded to be able to analyze how much of the original biofilm remained and it was revealed that 99 % of the original biofilm is detached. The good news is that no inoculation is needed to run anodes: electroactive bacteria are present in wastewater and will attach, enrich and produce current.
3.The methods to characterize METs are derived from the electrochemistry field and described in Chapter 3. They are well known and established. But there are limitations when applying to biological systems as the electrolytes mostly have low conductivities and are predefined by the characteristics of the waste streams that are used in the aimed application. These low conductivities provoke an increase of two error sources: the iRu-drop and junction potential. Furthermore, electrodes with high surface areas and thus high double layer capacitance are used for the growth of a biofilm which is used as catalyst. This can lead to capacitive currents that superimpose the biocatalytic current of interest. These problems are often not considered or quantified in publications and as a consequence, studies are hard to compare and systematical development of METs for application is slowed down. To contribute to the meaningful characterization of different bioelectrochemical approaches and form a solid methodological basis, methods to quantify the Ru and double layer capacitance are evaluated and their significant influence on the recording of polarization curves is quantitatively shown. Exemplary, in a standard BES setup, potentials can diverge by more than 200 mV from the actual potential, and more than 40% of a recorded electrode current can originate from the electrode material's double layer capacitance. In a last step, solutions and recommendations for the succesful application of electrochemical methods is described.
This work addresses the development of METs and gives a comprehensive overview on engineering, biological, and methodological approaches. It reviews reactor designs and (bio)electrochemical methods in detail to form a sound foundation on which a completely new MET concept is developed and characterized

Object Details

• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch
• Notes: Universität Freiburg, Dissertation, 2019

Classification and Topics

• Classification: Elektrotechnik, Elektronik
• Keyword: Sewage ; Anodes

Contributors, Places and Time

• Event: Veröffentlichung
• (where): Freiburg
• (who): Universität
• (when): 2019
• Creator: Madjarov, Joana
• Contributor: Zengerle, Roland ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Further information

• DOI: 10.6094/UNIFR/151588
• URN: urn:nbn:de:bsz:25-freidok-1515889
• Rights: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Last update: 14.08.2025, 10:47 AM CEST