Electrifying enzymatic bioproduction

A microbial battery couples waste degradation to a specific enzymatic production process. This is enabled by the uncoupling of the waste oxidation process from the enzymatic bioproduction via redox cathodes. The approach can be attractive for small-scale, local production of chemicals from water and/or CO2

A current-driven six-channel potentiostat for rapid performance characterization of microbial electrolysis cells

Knowledge of the performance of microbial electrolysis cells under a wide range of operating conditions is crucial to achieve high production efficiencies. Characterizing this performance in an experiment, however, is challenging due to either the long measurement times of steady-state procedures or the transient errors of dynamic procedures. Moreover, wide parallelization of the measurements is not feasible due to the high measurement equipment cost per channel. Hence, to speedup this characterization and to facilitate low-cost, yet widely parallel measurements, this paper presents a novel rapid polarization curve measurement procedure with a dynamic measurement resolution that runs on a custom six-channel potentiostat with a current-driven topology. As case study, the procedure is used to rapidly assess the impact of altering pH values on a microbial electrolysis cell that produces H-2. A $\times 2$ - $\times 12$ speedup could be obtained in comparison with the state-of-the-art, depending on the characterization resolution (16-128 levels). On top of this speedup, measurements can be parallelized up to $6\times$ on the presented, affordable-42-per-channel-potentiostat

DSA to grow electrochemically active biofilms of Geobacter sulfurreducens

Biofilms of Geobacter sulfurreducens were grown on graphite and on dimensionally stable anodes (DSA) in medium that did not contain any soluble electron acceptor. Several working electrodes were individually addressed and placed in the same reactor to compare their electrochemical behaviour in exactly the same biochemical conditions. Under constant polarization at 0.20Vversus Ag/AgCl, the electrodes were able progressively to oxidize acetate (5 mM), and average current densities around 5Am−2 and 8Am−2 were sustained for days on DSA and graphite, respectively. Removing the biofilm from the electrodes led the current to zero, while changing the medium by fresh one did not disturb the current when contact to air was avoided. This confirmed that the biofilm was fully responsible for the electro-catalysis of acetate oxidation and the current was not due to the accumulation of compounds in the bulk. Cyclic voltammetries performed during chronoamperometry indicated that the oxidation started above 0.05V versus Ag/AgCl. The difference in maximal current values obtained with DSA and graphite was not linked to the biofilm coverage ratios, which were of the same order of magnitude in the range of 62–78%. On the contrary, the difference in maximal current values matched the ratio of the average surface roughness of the materials, 5.6 m and 3.2 m for graphite and DSA, respectively

Electricity-assisted production of caproic acid from grass

Background: Medium chain carboxylic acids, such as caproic acid, are conventionally produced from food materials. Caproic acid can be produced through fermentation by the reverse beta-oxidation of lactic acid, generated from low value lignocellulosic biomass. In situ extraction of caproic acid can be achieved by membrane electrolysis coupled to the fermentation process, allowing recovery by phase separation. Results: Grass was fermented to lactic acid in a leach-bed-type reactor, which was then further converted to caproic acid in a secondary fermenter. The lactic acid concentration was 9.36 +/- 0.95 g L-1 over a 33-day semi-continuous operation, and converted to caproic acid at pH 5.5-6.2, with a concentration of 4.09 +/- 0.54 g L-1 during stable production. The caproic acid product stream was extracted in its anionic form, concentrated and converted to caproic acid by membrane electrolysis, resulting in a >70 wt% purity solution. In a parallel test exploring the upper limits of production rate through cell retention, we achieved the highest reported caproic acid production rate to date from a lignocellulosic biomass (grass, via a coupled process), at 0.99 +/- 0.02 g(-)L(-1) h(-1). The fermenting microbiome (mainly consisting of Clostridium IV and Lactobacillus) was capable of producing a maximum caproic acid concentration of 10.92 +/- 0.62 g L-1 at pH 5.5, at the border of maximum solubility of protonated caproic acid. Conclusions: Grass can be utilized as a substrate to produce caproic acid. The biological intermediary steps were enhanced by separating the steps to focus on the lactic acid intermediary. Notably, the pipeline was almost completely powered through electrical inputs, and thus could potentially be driven from sustainable energy without need for chemical input