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Item type:Publication, Access status: with files , Selective bioelectrochemical purification of propionate from food waste hydrolysate(Elsevier, 2026-12-21); ; Dark fermentation enables hydrogen production while generating propionate-rich streams from food waste. However, efficient separation of propionate from short-chain fatty acid (SCFA) mixtures remains challenging and costly in the downstream processes. Therefore, strategies enabling selective purification of propionate prior to separation from the fermentation broth are highly desirable. In this study, a bioelectrochemically assisted bench-scale process was developed as a proof-of-concept pretreatment to enhance selective purification of propionate prior to downstream processing. A single-chamber rotating disc bioelectrochemical reactor (RDBER) was used to selectively purify the hydrolysate via enhancing the consumption of butyrate by an electroactive biofilm of a recently published butyrate-oxidizing microbial consortium. In the RDBER, different hydraulic retention times (HRTs) without and with pH control were evaluated to investigate their effects on propionate fraction among SCFAs and process stability. The results show that with a pH of 7.0–7.3 and an HRT of 8 days, a propionate fraction of up to 95.5% can be achieved, with its concentration doubling compared to the feed. These results demonstrate the potential of this process as a pretreatment step prior to downstream separation, with the aim of reducing separation complexity and enhancing propionate recovery.Publicationtype: Journal Article15 7 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Design approach and performance of a scalable granular packed bed biofilter for electro-fermentationBioelectrochemical systems (BES) represent a promising technology for the production of energy, energy carriers, and chemicals; however, their implementation in industrial applications faces significant challenges related to scalability. In this study, we introduce a novel, scalable, single-chamber BES in which the working electrode is realised as a packed bed of electrically conductive equal-sized spheres made from a graphite-polymer composite. The reactor has a total volume of 3.56 L and a packed bed volume of 1.66 L with an electrode surface area of 1.06 m². A model microbial electrolysis / electro-fermentation of lactate to acetate was catalysed by the exoelectrogenic bacterium Shewanella oneidensis , achieving a maximum current density of 430 mA m<sup>-2</sup> at an anode potential of 300 mV relative to the standard hydrogen electrode.Publicationtype: Journal Article19 6 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Efficiency and process development for microbial biomass production using oxic bioelectrosynthesis(Elsevier, 2025-03); ; ; ; Rosa, Luis F. M.Autotrophic microbial electrosynthesis (MES) processes are mainly based on organisms that rely on carbon dioxide (CO2) as an electron acceptor and typically have low biomass yields. However, there are few data on the process and efficiencies of oxic MES (OMES). In this study, we used the knallgas bacterium Kyrpidia spormannii to investigate biomass formation and energy efficiency of cathode-dependent growth. The study revealed that the process can be carried out with the same electron efficiency as conventional gas fermentation, but overcomes disadvantages, such as the use of explosive gas mixtures. When accounting only for the electron input via electrical energy, a solar energy demand of 67.89 kWh kg–1 dry biomass was determined. While anaerobic MES is ideally suited to produce methane, short-chain alcohols, and carboxylic acids, its aerobic counterpart could extend this important range of applications to not only protein for use in the food and feed sector, but also further complex productsPublicationtype: Journal Article24 22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A scalable, rotating disc bioelectrochemical reactor (RDBER) suitable for the cultivation of both cathodic and anodic biofilmsThis study discusses the construction and operation of a membrane-less bioelectrochemical reactor that employs rotating working electrodes with a surface area of up to 1 m2. As a proof-of-principle for an aerobic microbial electrosynthesis process, Kyrpidia spormannii was cultivated in the reactor. Optical coherence tomography was used to examine the spatial distribution of the cathodic biofilm. After 24 days 87 % of the cathode surface was covered with biofilm that was characterized by a radial increase in its biovolume towards the circumcenter of the electrodes reaching up to 92.13 μm3 μm−2. To demonstrate the versatility of the system, we further operated the reactor as a microbial electrolysis cell employing a co-culture of Shewanella oneidensis and Geobacter sulfurreducens. Anodic current densities of up to 130 μA cm−2 were measured during these batch experiments. This resulted in a maximum production rate of 0.43 L of pure hydrogen per liter reactor volume and day.Publicationtype: Journal Article33 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Enrichment of phosphate-accumulating organisms (PAOs) in a microfluidic model biofilm system by mimicking a typical aerobic granular sludge feast/famine regime(Springer, 2022-01-15); ; ; ; Wastewater treatment using aerobic granular sludge has gained increasing interest due to its advantages compared to conventional activated sludge. The technology allows simultaneous removal of organic carbon, nitrogen, and phosphorus in a single reactor system and is independent of space-intensive settling tanks. However, due to the microscale, an analysis of processes and microbial population along the radius of granules is challenging. Here, we introduce a model system for aerobic granular sludge on a small scale by using a machine-assisted microfluidic cultivation platform. With an implemented logic module that controls solenoid valves, we realized alternating oxic hunger and anoxic feeding phases for the biofilms growing within. Sampling during ongoing anoxic cultivation directly from the cultivation channel was achieved with a robotic sampling device. Analysis of the biofilms was conducted using optical coherence tomography, fluorescence in situ hybridization, and amplicon sequencing. Using this setup, it was possible to significantly enrich the percentage of polyphosphate-accumulating organisms (PAO) belonging to the family Rhodocyclaceae in the community compared to the starting inoculum. With the aid of this miniature model system, it is now possible to investigate the influence of a multitude of process parameters in a highly parallel way to understand and efficiently optimize aerobic granular sludge-based wastewater treatment systems. Key points • Development of a microfluidic model to study EBPR. • Feast-famine regime enriches polyphosphate-accumulating organisms (PAOs). • Microfluidics replace sequencing batch reactors for aerobic granular sludge research.Publicationtype: Journal ArticleScopus© Citations 5 52 173 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Biological biogas upgrading in a membrane biofilm reactor with and without organic carbon sourceBiogas upgrading is a necessary step to minimize the CO2 of raw biogas and to make it suitable for gas liquefaction or introduction into the national gas grid. Biomethanation is a promising approach since it converts the CO2 to more methane on site, while taking advantage of the organisms responsible for biogas production in the first place. This study investigates the suitability of a pseudo-dead-end membrane biofilm reactor (MBfR) for ex-situ biogas upgrading using biogas as sole carbon source as well as for additional acetoclastic methanation when an organic carbon source is provided. Results prove that the concept of MBfR is especially advantageous for ex-situ hydrogenotrophic methanation of biogas CO2, yielding high product gas qualities of up to 99% methane. It is discussed that cross-flow membrane operation could reduce mass flux of inert methane through membranes, attached biofilms, and reactor liquid, and, thus, improve methanation space time yields.Publicationtype: Journal ArticleScopus© Citations 12 49 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Extracellular riboflavin induces anaerobic biofilm formation in Shewanella oneidensis(BioMed Central, 2021-06-03); ; ; ; Background: Some microorganisms can respire with extracellular electron acceptors using an extended electron transport chain to the cell surface. This process can be applied in bioelectrochemical systems in which the organisms produce an electrical current by respiring with an anode as electron acceptor. These organisms apply flavin molecules as cofactors to facilitate one-electron transfer catalyzed by the terminal reductases and in some cases as endogenous electron shuttles. Results: In the model organism Shewanella oneidensis, riboflavin production and excretion trigger a specific biofilm formation response that is initiated at a specific threshold concentration, similar to canonical quorum-sensing molecules. Riboflavin-mediated messaging is based on the overexpression of the gene encoding the putrescine decarboxylase speC which leads to posttranscriptional overproduction of proteins involved in biofilm formation. Using a model of growth-dependent riboflavin production under batch and biofilm growth conditions, the number of cells necessary to produce the threshold concentration per time was deduced. Furthermore, our results indicate that specific retention of riboflavin in the biofilm matrix leads to localized concentrations, which by far exceed the necessary threshold value. Conclusion: This study describes a new quorum-sensing mechanism in S. oneidensis. Biofilm formation of S. oneidensis is induced by low concentrations of riboflavin resulting in an upregulation of the ornithine-decarboxylase speC. The results can be applied for the development of strains catalyzing increased current densities in bioelectrochemical systems.Publicationtype: Journal ArticleScopus© Citations 26 117 227 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Propionic acid production from food waste in batch reactors: Effect of pH, types of inoculum, and thermal pre-treatmentIn this study, lab-scale batch fermentation tests were carried out at mesophilic temperature (30 °C) to examine the influence of inoculum type, pH-value, and thermal pretreatment of substrate on propionic acid (PA) production from dog food. The selected inocula comprised a mixed bacterial culture, milk, and soft goat cheese. The batch tests were performed at pH 4, pH 6, and pH 8 for both, untreated and thermally pretreated food. Results show that the production of PA and volatile fatty acids (VFAs) in general were significantly dependent on the chosen inoculum and adjusted pH value. The maximum PA production rates and yields were determined for the cheese inoculum at pH 6 using untreated and pretreated dog food. PA concentration reached 10 g L−1 and 26.5 g L−1, respectively. Our findings show that by selecting optimal process parameters, an efficient PA production from model food waste can be achieved.Publicationtype: Journal ArticleScopus© Citations 32 43 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Enhanced production of propionic acid through acidic hydrolysis by choice of inoculumBACKGROUND: In this study, the enhancement of propionic acid production from a model feedstock mimicking kitchen waste was investigated. For that purpose, two operational runs of a semicontinuous anaerobic hydrolysis reactor were carried out at pH 6.0 ± 0.1 and mesophilic (30 °C) temperature. Two different types of inocula, a mixed microbial culture selected over 24 months for growth on cellulose and a culture contained in goat cheese were compared. RESULTS: The results show that the goat cheese inoculum was significantly more efficient for propionic acid (PA) production. The highest propionic acid concentration achieved amounted to 139 mmol L−1 at a yield of 23.3 mg g−1 volatile solids (VS), which was 55% greater than what was achieved with the mixed culture. Furthermore, it was observed that propionic acid production was enhanced by a combination of high hydraulic retention time (HRT) with low organic loading rate (OLR), ensuring sufficient time for complete processing of the complex organic substrates. The fermentation could be kept in a stable process of propionic acid production at HRT of 20 days and a rather low OLR of 11.1 g L−1 day−1 VS. CONCLUSION: Our results give a better understanding of PA production in semicontinuous mode, applying optimized process parameters and selecting the adequate microbial community for inoculation. This study provides important information for the improvement of PA production from complex substrates for future industrial application. © 2020 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).Publicationtype: Journal Article35 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Assessing and modeling biocatalysis in field denitrification beds reveals key influencing factors for future constructions(2021-01-01); ; ; Environmental contamination with fertilizers is threatening biodiversity in many ecosystems due to nitrate-based eutrophication. One opportunity for a cost-efficient nitrate elimination are denitrification beds in which a microbial community thrives under anoxic conditions with polymeric plant material as a carbon and an electron source. Incoming nitrate is used as electron acceptor and reduced to molecular nitrogen. Projects realizing denitrification beds in field scale are sparse and robust data on their efficiency throughout the year mostly not available. This study analyzed the nitrate elimination efficiency and microbiology of a 216 m3 denitrification bed over the time course of more than three years. Phylogenetic as well as transcriptomic analysis revealed that the reactor contained a biofilm community growing on the surface of the wood chips and a planktonic community. Both differed in composition but their variance was affected only to a minor extend by seasonal temperature changes. Cellulose degradation was mainly conducted by the biofilm population while denitrification was mostly conducted by the planktonic community. Methanogens were detectable only to a very minor extend. Using online data from the nitrate concentration of in- and outflowing water as well as a hydrological model to predict the water inflow, it was possible to establish a process model that sufficiently describes the denitrification process. This model clearly indicates that the denitrification efficiency is mostly impacted by temperature and hydraulic retention time. It also suggests that the simple design of the denitrification bed most likely leads to different flow paths through the reactor depending on the volumetric flow rate. This study allows for the first time a robust estimation of the necessary reactor size for nitrate removal in a moderate continental climate setting. It also suggests how future denitrification beds could be improved for better performance.Publicationtype: Journal ArticleScopus© Citations 12 35