Archived project

Défi H12: Production de bio-hydrogène par électrolyse microbienne (Microbial electrolysis cell (MEC) for bio-hydrogen production)

Goal: Défi H12's research was financially supported by the French National Research Agency (ANR-09-BioE-10 D ́efiH12).

A microbial electrolysis cell (MEC) is used to produce hydrogen by electrolysis of organic matter. An MEC consists of a conventional cathode that provides hydrogen production by electrochemical reduction of water, associated with an anode that oxidizes to carbon dioxide all kinds of organic substrates. This oxidation process is only possible thanks to the development on the anode of a microbial biofilm which acts as an electrocatalyst. Compared with current water electrolysis processes, an MEC operates at 5 to 10 times lower voltages, dividing by a factor of 5 the cost of electrical energy of the hydrogen produced.

Fermentative biohydrogen production processes in mixed cultures convert carbohydrates (e.g. sucrose and glucose) with yields limited to 2-3 moles of hydrogen per mole of hexose and co-produce volatile fatty acids (acetic or butyric acid). ). Fed with acetate, an MEC produces 3 moles of hydrogen per mole of acetate. The coupling of Fermentation + MEC thus ensures a production of 8-9 moles of hydrogen per mole of hexose, a large step towards the theoretical limit of 12 moles of hydrogen per mole of hexose.

The concept of MEC born in 2005 already demonstrates production speeds of the order of several liters of hydrogen per liter of reactor per hour. Several bottlenecks have been identified, including the lack of fundamental knowledge about the mechanisms of electro-microbial catalysis of the anode.

DéfiH12 was an exploratory project that focused on the interdisciplinarity to obtain the fundamental advances needed to design an optimal MEC at pilot scale.

Date: 10 February 2010 - 9 February 2014

Updates
0 new
0
Recommendations
0 new
0
Followers
0 new
19
Reads
0 new
149

Project log

Alessandro Carmona
added a project goal
Défi H12's research was financially supported by the French National Research Agency (ANR-09-BioE-10 D ́efiH12).
A microbial electrolysis cell (MEC) is used to produce hydrogen by electrolysis of organic matter. An MEC consists of a conventional cathode that provides hydrogen production by electrochemical reduction of water, associated with an anode that oxidizes to carbon dioxide all kinds of organic substrates. This oxidation process is only possible thanks to the development on the anode of a microbial biofilm which acts as an electrocatalyst. Compared with current water electrolysis processes, an MEC operates at 5 to 10 times lower voltages, dividing by a factor of 5 the cost of electrical energy of the hydrogen produced.
Fermentative biohydrogen production processes in mixed cultures convert carbohydrates (e.g. sucrose and glucose) with yields limited to 2-3 moles of hydrogen per mole of hexose and co-produce volatile fatty acids (acetic or butyric acid). ). Fed with acetate, an MEC produces 3 moles of hydrogen per mole of acetate. The coupling of Fermentation + MEC thus ensures a production of 8-9 moles of hydrogen per mole of hexose, a large step towards the theoretical limit of 12 moles of hydrogen per mole of hexose.
The concept of MEC born in 2005 already demonstrates production speeds of the order of several liters of hydrogen per liter of reactor per hour. Several bottlenecks have been identified, including the lack of fundamental knowledge about the mechanisms of electro-microbial catalysis of the anode.
DéfiH12 was an exploratory project that focused on the interdisciplinarity to obtain the fundamental advances needed to design an optimal MEC at pilot scale.
 
Nicolas Bernet
added a research item
Even with an increasing interest in scaling-up Microbial Electrochemical Technologies (MET), it is still common to focus on their “fundamentals”. An important example is the production of current density (jmax) by microbial anodes in a three-electrode arrangement (3 EA) configuration, e.g.: a graphite plate of well-defined projected (or geometric) surface area (PSA) and a cathode, both parallel to each other. With such type of anode within a 3 EA configuration, jmax‘s calculation is expected to be straightforward. Nonetheless, certain issues prevail. Occasionally, jmax is wrongly overestimated neglecting the surface of the anode that does not directly face the cathode. Here, grown biofilms of the novel electroactive bacterium Geoalkalibacter subterraneus showed that the actual area of anode that contributes to jmax is the total PSA (or apparent geometric area) immersed in the electrolyte available to form a biofilm regardless the side of the anode that faced or opposed the cathode even in a medium with low conductivity such as urban wastewater, a niche of application for METs. For the sake of normalization, researchers (and especially a “freshman” microbial electrochemist) are encouraged to: A) use the total PSA (or apparent geometric area) immersed in the electrolyte to calculate jmax or B) to cover edges and faces hidden of the anode with an electrical insulator to allow the flow of current on the side of the anode that directly faces the cathode prior calculation of jmax. This normalization can be conducted when the main goal is to quantify (and thus properly report) jmax produced when using (e.g.): a novel i) electroactive bacterium, ii) electrode material or iii) reactor design.
Melanie Pierra
added 2 research items
Biohydrogen production from dark fermentation is limited because of the associated production of organic acids. These by products can be used as substrates in a microbial electrolysis cell (MEC), since electroactive biofilms can completely convert organic matter into hydrogen and carbon dioxide. This work aims at analyzing, in the context of the coupling of those two processes and for each one, the relationship between microbial community structures and the associated macroscopic functions. The originality of this study is to work in saline conditions (30-35 gNaCl/L), which favors the charges transfer in the MEC electrolyte but is poorly studied in dark fermentation. Results showed a high selection of microorganisms in both processes associated to good hydrogen production performances. Some of whom are poorly characterized until now. An iron-enrichment method to enrich electroactive bacteria is also proposed. Finally in coupling situation, the introduction of biomass originated from dark fermentation could result to a decrease of biofilm activity.
Dark fermentation is an intermediate microbial process occurring along the anaerobic biodegradation of organic matter. Saline effluents are rarely treated anaerobically since they are strongly inhibited by high salt concentrations. This study deals with the characterization of microbial communities producing hydrogen under moderate halophilic conditions. A series of batch experiments was performed under anaerobic conditions, with glucose as substrate (5 g L−1) and under increasing NaCl concentrations ranging from 9 to 75 gNaCl L−1. A saline sediment of a lagoon collecting salt factory wastewaters was used as inoculum. Interestingly, a gradual increase of the biohydrogen production yield according to NaCl concentration was observed with the highest value obtained for the highest NaCl concentration, i.e. 75 gNaCl L−1, suggesting a natural adaptation of the sediment inoculum to salt. This work reports for the first time the ability of mixed culture to produce hydrogen in moderate halophilic environment. In addition, maximum hydrogen consumption rates decreased while NaCl concentration increased. A gradual shift of the bacterial community structure, concomitant to metabolic changes, was observed with increasing NaCl concentrations, with the emergence of bacteria belonging to Vibrionaceae as dominant bacteria for the highest salinities.
Alessandro Carmona
added 7 research items
Two different saline sediments were used to inoculate potentiostatically controlled reactors (a type of microbial bioelectrochemical system, BES) operated in saline conditions (35 gNaCl l-1). Reactors were fed with acetate or a mixture of acetate and butyrate at two pH values: 7.0 or 5.5. Electroactive biofilm formation lag-phase, maximum current density production and coulombic efficiency were used to evaluate the overall performance of reactors. High current densities up to 8.5 A m-² were obtained using well-defined planar graphite electrodes. Additionally, biofilm microbial communities were characterized by CE-SSCP and 454 pyrosequencing. As a result of this procedure, two anode-respiring bacteria (ARB) always dominated the anodic biofilms: Geoalkalibacter subterraneus and/ or Desulfuromonas acetoxidans. This suggests that a strong electrochemically driven selection process imposed by the applied potential occurrs in the BES system. Moreover, the emergence of Glk. subterraneus in anodic biofilms significantly contributes to broaden the spectrum of high current producing microorganisms electrochemically isolated from environmental samples.
The aim of this work is to evaluate biohydrogen production from agro-industrial wastewaters and by-products, by combining dark fermentation and microbial electrolysis in a two-step cascade process. Such coupling of both technologies constitutes a technological building block within a concept of environmental biorefinery where sustainable production of renewable energy is expected. Six different wastewaters and industrial by-products coming from cheese, fruit juice, paper, sugar, fruit processing and spirits factories were evaluated for the feasibility of hydrogen production in a two-step process. The overall hydrogen production when coupling dark fermentation and microbial electrolysis was increased up to 13 times when compared to fermentation alone, achieving a maximum overall hydrogen yield of 1608.6 ± 266.2 ml H2/ gCODconsumed and a maximum of 78.5 ± 5.7% of COD removal. These results show that dark fermentation coupled with microbial electrolysis is a highly promising option to maximize the conversion of agro-industrial wastewaters and by-products into bio-hydrogen.