7 research outputs found
Capacitive Bioanodes Enable Renewable Energy Storage in Microbial Fuel Cells
We developed an integrated system for storage of renewable
electricity
in a microbial fuel cell (MFC). The system contained a capacitive
electrode that was inserted into the anodic compartment of an MFC
to form a capacitive bioanode. This capacitive bioanode was compared
with a noncapacitive bioanode on the basis of performance and storage
capacity. The performance and storage capacity were investigated during
polarization curves and charge–discharge experiments. During
polarization curves the capacitive electrode reached a maximum current
density of 1.02 ± 0.04 A/m<sup>2</sup>, whereas the noncapacitive
electrode reached a current density output of only 0.79 ± 0.03
A/m<sup>2</sup>. During the charge–discharge experiment with
5 min of charging and 20 min of discharging, the capacitive electrode
was able to store a total of 22 831 C/m<sup>2</sup>, whereas
the noncapacitive electrode was only able to store 12 195 C/m<sup>2</sup>. Regarding the charge recovery of each electrode, the capacitive
electrode was able to recover 52.9% more charge during each charge–discharge
experiment compared with the noncapacitive electrode. The capacitive
electrode outperformed the noncapacitive electrode throughout each
charge–discharge experiment. With a capacitive electrode it
is possible to use the MFC simultaneously for production and storage
of renewable electricity
data_sheet_1.PDF
<p>Current challenges for microbial electrosynthesis include the production of higher value chemicals than acetate, at high rates, using cheap electrode materials. We demonstrate here the continuous, biofilm-driven production of acetate (C2), n-butyrate (nC4), and n-caproate (nC6) from sole CO<sub>2</sub> on unmodified carbon felt electrodes. No other organics were detected. This is the first quantified continuous demonstration of n-caproate production from CO<sub>2</sub> using an electrode as sole electron donor. During continuous nutrients supply mode, a thick biofilm was developed covering the whole thickness of the felt (1.2-cm deep), which coincided with high current densities and organics production rates. Current density reached up to −14 kA m<sup>−3</sup><sub>electrode</sub> (−175 A m<sup>−2</sup>). Maximum sustained production rates of 9.8 ± 0.65 g L<sup>−1</sup> day<sup>−1</sup> C2, 3.2 ± 0.1 g L<sup>−1</sup> day<sup>−1</sup> nC4, and 0.95 ± 0.05 g L<sup>−1</sup> day<sup>−1</sup> nC6 were achieved (averaged between duplicates), at electron recoveries of 60–100%. Scanning electron micrographs revealed a morphologically highly diverse biofilm with long filamentous microorganism assemblies (~400 μm). n-Caproate is a valuable chemical for various industrial application, e.g., it can be used as feed additives or serve as precursor for liquid biofuels production.</p
Is There a Precipitation Sequence in Municipal Wastewater Induced by Electrolysis?
Electrochemical
wastewater treatment can induce calcium phosphate
precipitation on the cathode surface. This provides a simple yet efficient
way for extracting phosphorus from municipal wastewater without dosing
chemicals. However, the precipitation of amorphous calcium phosphate
(ACP) is accompanied by the precipitation of calcite (CaCO<sub>3</sub>) and brucite (MgÂ(OH)<sub>2</sub>). To increase the content of ACP
in the products, it is essential to understand the precipitation sequence
of ACP, calcite, and brucite in electrochemical wastewater treatment.
Given the fact that calcium phosphate (i.e., hydroxyapatite) has the
lowest thermodynamic solubility product and highest saturation index
in the wastewater, it has the potential to precipitate first. However,
this is not observed in electrochemical phosphate recovery from raw
wastewater, which is probably because of the very high Ca/P molar
ratio (7.5) and high bicarbonate concentration in the wastewater resulting
in formation of calcite. In the case of decreased Ca/P molar ratio
(1.77) by spiking external phosphate, most of the removed Ca in the
wastewater was used for ACP formation instead of calcite. The formation
of of brucite, however, was only affected when the current density
was decreased or the size of cathode was changed. Overall, the removal
of Ca and Mg is much more affected by current density than the surface
area of cathode, whereas for P removal, the reverse is true. Because
of these dependencies, though there is no definite precipitation sequence
among ACP, calcite, and brucite, it is still possible to influence
the precipitation degree of these species by relatively low current
density and high surface area or by targeting phosphorus-rich wastewaters
Bacteria as an Electron Shuttle for Sulfide Oxidation
Biological
desulfurization under haloalkaliphilic conditions is
a widely applied process, in which haloalkalophilic sulfide-oxidizing
bacteria (SOB) oxidize dissolved sulfide with oxygen as the final
electron acceptor. We show that these SOB can shuttle electrons from
sulfide to an electrode, producing electricity. Reactor solutions
from two different biodesulfurization installations were used, containing
different SOB communities; 0.2 mM sulfide was added to the reactor
solutions with SOB in absence of oxygen, and sulfide was removed from
the solution. Subsequently, the reactor solutions with SOB, and the
centrifuged reactor solutions without SOB, were transferred to an
electrochemical cell, where they were contacted with an anode. Charge
recovery was studied at different anode potentials. At an anode potential
of +0.1 V versus Ag/AgCl, average current densities of 0.48 and 0.24
A/m<sup>2</sup> were measured for the two reactor solutions with SOB.
Current was negligible for reactor solutions without SOB. We postulate
that these differences in current are related to differences in microbial
community composition. Potential mechanisms for charge storage in
SOB are proposed. The ability of SOB to shuttle electrons from sulfide
to an electrode offers new opportunities for developing a more sustainable
desulfurization process
Data_Sheet_1_Development of an Effective Chain Elongation Process From Acidified Food Waste and Ethanol Into n-Caproate.pdf
<p>Introduction: Medium chain fatty acids (MCFAs), such as n-caproate, are potential valuable platform chemicals. MCFAs can be produced from low-grade organic residues by anaerobic reactor microbiomes through two subsequent biological processes: hydrolysis combined with acidogenesis and chain elongation. Continuous chain elongation with organic residues becomes effective when the targeted MCFA(s) are produced at high concentrations and rates, while excessive ethanol oxidation and base consumption are limited. The objective of this study was to develop an effective continuous chain elongation process with hydrolyzed and acidified food waste and additional ethanol.</p><p>Results: We fed acidified food waste (AFW) and ethanol to an anaerobic reactor while operating the reactor at long (4 d) and at short (1 d) hydraulic retention time (HRT). At long HRT, n-caproate was continuously produced (5.5 g/L/d) at an average concentration of 23.4 g/L. The highest n-caproate concentration was 25.7 g/L which is the highest reported n-caproate concentration in a chain elongation process to date. Compared to short HRT (7.1 g/L n-caproate at 5.6 g/L/d), long HRT resulted in 6.2 times less excessive ethanol oxidation. This led to a two times lower ethanol consumption and a two times lower base consumption per produced MCFA at long HRT compared to short HRT.</p><p>Conclusions: Chain elongation from AFW and ethanol is more effective at long HRT than at short HRT not only because it results in a higher concentration of MCFAs but also because it leads to a more efficient use of ethanol and base. The HRT did not influence the n-caproate production rate. The obtained n-caproate concentration is more than twice as high as the maximum solubility of n-caproic acid in water which is beneficial for its separation from the fermentation broth. This study does not only set the record on the highest n-caproate concentration observed in a chain elongation process to date, it notably demonstrates that such high concentrations can be obtained from AFW under practical circumstances in a continuous process.</p
Fluidized Capacitive Bioanode As a Novel Reactor Concept for the Microbial Fuel Cell
The use of granular
electrodes in Microbial Fuel Cells (MFCs) is
attractive because granules provide a cost-effective way to create
a high electrode surface area, which is essential to achieve high
current and power densities. Here, we show a novel reactor design
based on capacitive granules: the fluidized capacitive bioanode. Activated
carbon (AC) granules are colonized by electrochemically active microorganisms,
which extract electrons from acetate and store the electrons in the
granule. Electricity is harvested from the AC granules in an external
discharge cell. We show a proof-of-principle of the fluidized capacitive
system with a total anode volume of 2 L. After a start-up period of
100 days, the current increased from 0.56 A/m<sup>2</sup> with 100
g AC granules, to 0.99 A/m<sup>2</sup> with 150 g AC granules, to
1.3 A/m<sup>2</sup> with 200 g AC granules. Contact between moving
AC granules and current collector was confirmed in a control experiment
without biofilm. Contribution of an electro-active biofilm to the
current density with recirculation of AC granules was limited. SEM
images confirmed that a biofilm was present on the AC granules after
operation in the fluidized capacitive system. Although current densities
reported here need further improvement, the high surface area of the
AC granules in combination with external discharge offers new and
promising opportunities for scaling up MFCs
Controlling Ethanol Use in Chain Elongation by CO<sub>2</sub> Loading Rate
Chain elongation is an open-culture
biotechnological process which
converts volatile fatty acids (VFAs) into medium chain fatty acids
(MCFAs) using ethanol and other reduced substrates. The objective
of this study was to investigate the quantitative effect of CO<sub>2</sub> loading rate on ethanol usages in a chain elongation process.
We supplied different rates of CO<sub>2</sub> to a continuously stirred
anaerobic reactor, fed with ethanol and propionate. Ethanol was used
to upgrade ethanol itself into caproate and to upgrade the supplied
VFA (propionate) into heptanoate. A high CO<sub>2</sub> loading rate
(2.5 L<sub>CO2</sub>·L<sup>–1</sup>·d<sup>–1</sup>) stimulated excessive ethanol oxidation (EEO; up to 29%) which resulted
in a high caproate production (10.8 g·L<sup>–1</sup>·d<sup>–1</sup>). A low CO<sub>2</sub> loading rate (0.5 L<sub>CO2</sub>·L<sup>–1</sup>·d<sup>–1</sup>) reduced EEO
(16%) and caproate production (2.9 g·L<sup>–1</sup>·d<sup>–1</sup>). Heptanoate production by VFA upgrading remained
constant (∼1.8 g·L<sup>–1</sup>·d<sup>–1</sup>) at CO<sub>2</sub> loading rates higher than or equal to 1 L<sub>CO2</sub>·L<sup>–1</sup>·d<sup>–1</sup>.
CO<sub>2</sub> was likely essential for growth of chain elongating
microorganisms while it also stimulated syntrophic ethanol oxidation.
A high CO<sub>2</sub> loading rate must be selected to upgrade ethanol
(e.g., from lignocellulosic bioethanol) into MCFAs whereas lower CO<sub>2</sub> loading rates must be selected to upgrade VFAs (e.g., from
acidified organic residues) into MCFAs while minimizing use of costly
ethanol