1,720,993 research outputs found
Biohydrogen production from xylose by fresh and digested activated sludge at 37, 55 and 70 °C
No full textTwo heatetreated inocula, fresh and digested activated sludge from the same municipal wastewater
treatment plant, were compared for their H2 production via dark fermentation at mesophilic (37 C),
thermophilic (55 C) and hyperthermophilic (70 C) conditions using xylose as the substrate. At both 37
and 55 C, the fresh activated sludge yielded more H2 than the digested sludge, whereas at 70 C, neither
of the inocula produced H2 effectively. A maximum yield of 1.85 mol H2 per mol of xylose consumed was
obtained at 55 C. H2 production was linked to acetate and butyrate production, and there was a linear
correlation (R2 1⁄4 0.96) between the butyrate and H2 yield for the fresh activated sludge inoculum at
55 C. Approximately 2.4 mol H2 per mol of butyrate produced were obtained against a theoretical
maximum of 2.0, suggesting that H2 was produced via the acetate pathway prior to switching to the
butyrate pathway due to the increased H2 partial pressure. Clostridia sp. were the prevalent species at
both 37 and 55 C, irrespectively of the inoculum type. Although the two inocula originated from the
same plant, different thermophilic microorganisms were detected at 55 C. Thermoanaerobacter sp.,
detected only in the fresh activated sludge cultures, may have contributed to the high H2 yield obtained
with such an inoculum
OpenTCC: An open source low-cost temperature-control chamber
No full textMicrobial electrochemical technologies (MET) are emerging systems for environmental
applications such as renewable energy production or pollution remediation. MET research
often requires stable temperatures and low levels of electromagnetic interference. Due to
the presence of electrical wires and sensors, heating MET using water jacket recirculation
can raise safety issues, whereas heating coils may affect the results of electrochemical analyses.
The proposed open-source temperature-control chamber (OpenTCC) aims to provide
a low-cost solution for controlling temperature (in the range 20–55 C) while simultaneously
reducing the electromagnetic interferences caused by switching mode power supplies.
OpenTCC consists of a light and cheap structure, incorporating eight heating pads
and two Peltier-cooling modules powered by open-source electronic circuits. Its hardware
is controlled by an Arduino microcontroller and a Python interface which provides datalogging
and serve as a basis for programable temperature cycles. The system has a modular
design to allow stacking several independent modules. OpenTCC provides a reliable and
tunable temperature control at lower costs than currently available commercial temperature
controllers and provides a platform for field-specific upgrades. Though optimized for
MET, Open-TCC can be adapted to other laboratory applications due to its flexible design
Gauging sediment microbial fuel cells using open-circuit auxiliary electrodes
No full textThis study examines the use of open circuit (OC) auxiliary electrodes to monitor changes on the bulk potential in
a sediment microbial fuel cell (SMFC). This complements the cell voltage and electrode potential measurement
obtained in closed circuit (CC), helping to understand the limitations of the system and facilitating its optimization.
Duplicate SMFCs were equipped with electrode grids containing integrated CC and OC electrodes. Current
densities up to 20 mA/m2 were obtained with the CC electrode pairs. The OC auxiliary electrodes showed a stable
bulk potential around 0.7 V with cathode and anode potentials at 0.5 and -0.2 V vs SHE, respectively. A clear
correlation between OC and CC potential was observed, which allowed to identify technical problems (such as
oxygen intrusion to the anode or faulty electrode connections) and detect the causes of power limitation without
disconnecting the CC electrodes. Thus, OC auxiliary electrodes are useful to optimize SMFC installation and
facilitate troubleshooting, particularly in environments with variable bulk potentials such as intertidal zones
Microbial electrochemical technologies: Electronic circuitry and characterization tools
No full textMicrobial electrochemistry merges microbiology, electrochemistry and electronics to provide a set of technologies
for environmental engineering applications. Understanding the electronic concepts is crucial for effectively
adopting these systems, but the importance of electronic circuitry is often overlooked by microbial electrochemistry
researchers. This review provides the background on the electronics and electrochemical concepts
involved in the study of microorganisms interacting with electricity, and their applications in microbial electrochemical
technology (MET). The potentiostat circuitry is described along with its working principles. Electrochemical
analyses are presented together with the rational and parameters employed to study MET devices
and electroactive microorganisms. Finally, future directions are delineated towards the adoption of MET, and the
related electronics, in environmental engineering applications
Fermentative hydrogen production from cheese whey with in-line, concentration gradient-driven butyric acid extraction
No full textHydrogen (H2) generation from cheese whey with simultaneous production and extraction
of volatile fatty acids (VFAs) was studied in UASB reactors at two temperatures (20 and
35 C) and pH values (5.0 and 4.5). The extraction module, installed through a recirculation
loop, was a silicone tube coil submerged in water, which allows concentration-driven
extraction of undissociated VFAs. Operating conditions were selected as a compromise
for the recovery of both H2 and VFAs. Batch experiments showed a higher yield (0.9 mol H2
mol 1 glucoseeq.) at 35 C and pH 5.0, regardless of the presence of the extraction module,
whereas lower yields were obtained at pH 4.5 and 20 C (0.5 and 0.3 mol H2 mol 1 glucoseeq., respectively). VFAs crossed the silicone membrane, with a strong preference for butyric
over propionic and acetic acid due to its higher hydrophobicity. Sugars, lactic acid and
nutrients were retained, resulting in an extracted solution of up to 2.5 g L 1 butyric acid
with more than 90% purity. Continuous experiment confirmed those results, with production
rates up to 2.0 L H2 L 1 d 1 and butyric acid extraction both in-line (from the UASB
recirculation) and off-line (from the UASB effluent). In-line VFA extraction can reduce the
operating costs of fermentation, facilitating downstream processing for the recovery of
marketable VFAs without affecting the H2 production
Carboxylic acids production and electrosynthetic microbial community evolution under different CO2 feeding regimes
No full textMicrobial electrosynthesis (MES) is a potential technology for CO2 recycling, but insufficient information
is available on the microbial interactions underpinning electrochemically-assisted reactions. In this
study, a MES reactor was operated for 225 days alternately with bicarbonate or CO2 as carbon source,
under batch or continuous feeding regimens, to evaluate the response of the microbial communities,
and their productivity, to dynamic operating conditions. A stable acetic acid production rate of
9.68 g m-2 d-1, and coulombic efficiency up to 40%, was achieved with continuous CO2 sparging, higher
than the rates obtained with bicarbonate (0.94 g m-2 d-1) and CO2 under fed-batch conditions
(2.54 g m-2 d-1). However, the highest butyric acid production rate (0.39 g m-2 d-1) was achieved with
intermittent CO2 sparging. The microbial community analyses focused on differential amplicon sequence
variants (ASVs), allowing detection of ASVs significantly different across consecutive samples. This analysis,
combined with co-occurence network analysis, and cyclic voltammetry, indicated that hydrogenmediated
acetogenesis was carried out by Clostridium, Eubacterium and Acetobacterium, whereas
Oscillibacter and Caproiciproducens were involved in butyric acid production. The cathodic community
was spatially inhomogeneous, with potential electrotrophs, such as Sulfurospirillum and Desulfovibrio,
most prevalent near the current collector. The abundance of Sulfurospirillum positively correlated with
that of Acetobacterium, supporting the syntrophic metabolism of both organisms
Silicone membrane contactors for volatile fatty acid (VFA) separation from cheese whey
No full textThe effect of pH and extraction temperature on flux, recovery, mass transfer coefficient and separationfactor of volatile fatty acids (VFAs) and alcohols from synthetic solutions and cheese whey fermentatewas investigated using a silicone membrane contactor with water as extractant. The silicone membraneallowed extraction of undissociated acids only, resulting in substantially higher recovery efficiencies at pH3 than at pH 5. Furthermore, the non-porous silicone membrane favoured extraction of longer chain overshorter chain acids. Caproic acid was extracted with the highest flux of 1.30 (± 0.02) g m−2h−1in shorttime (32 h), with a 41.5 % recovery efficiency at pH 3 and 20◦C, indicating the feasibility of its selectiveseparation from the VFA mixture. A similar trend was observed for alcohols, with butanol being extracted with a 39 % recovery efficiency at 40◦C, against 32 % and 19 % of propanol and ethanol, respectively, whilethe mass transfer coefficients were not affected by temperature. When applying the silicone membrane contactor to real cheese whey fermentate at pH 3, butyric and acetic acid were extracted with 21.5 % and7% recovery efficiency, respectively, suggesting the feasibility of the contactor for VFA recovery from real fermentate
Temperature control as key factor for optimal biohydrogen production from thermomechanical pulping wastewater
No full textThis study evaluates the use of non-pretreated thermo-mechanical pulping (TMP) wastewater as a potential
substrate for hydrogen production by dark fermentation. Batch incubations were conducted in a
temperature gradient incubator at temperatures ranging from 37 to 80 ◦C, using an inoculum from a thermophilic,
xylose-fed, hydrogen-producing fluidised bed reactor. The aim was to assess the short-term
response of the microbial communities to the different temperatures with respect to both hydrogen yield
and composition of the active microbial community. High throughput sequencing (MiSeq) of the reversely
transcribed 16S rRNA showed that Thermoanaerobacterium sp. dominated the active microbial community
at 70 ◦C, resulting in the highest hydrogen yield of 3.6 (±0.1) mmol H2 g−1 CODtot supplied. Lower
hydrogen yields were obtained at the temperature range from 37 to 65 ◦C, likely due to consumption of
the produced hydrogen by homoacetogenesis. No hydrogen production was detected at temperatures
above 70 ◦C. Thermomechanical pulping wastewaters are released at high temperatures (50–80 ◦C), and
thus dark fermentation at 70 ◦C could be sustained using the heat produced by the pulp and paper plant
itself without any requirement for external heating
Selective enrichment of biocatalysts for bioelectrochemical systems: A critical review
No full textMicrobial electrochemical technologies (MET), also known as bioelectrochemical systems (BES), use microorganisms
as biocatalysts to recover valuable resources like bioelectricity, hydrogen, nutrients, metals, and industrial
chemicals from wastes and wastewaters. MET are therefore expected to play a key role in waste management
and reduction of the carbon footprint in the near future. However, considerable fundamental and
technological challenges still need to be addressed before using MET in practice. Rapid start-up, as well as an
efficient and stable performance, are the pre-requisites to achieve commercialization of MET. Although considerable
advancements have been made in this field in the past two decades, no general conclusion has been
drawn about how to start-up BES in the most efficient manner. This review aims to survey and critically analyze
start-up strategies proposed in the literature to favor a fast and efficient establishment of electrochemically
active microorganisms onto bioanodes or biocathodes and promote their activity over a long period of operation.
Various aspects of BES start-up, including inoculum selection, elimination of competitive microorganisms, and
selection of operational parameters for enrichment of electroactive biofilms are covered. In summary, inoculation
with already enriched culture, imposing of an anode potential or using polarity reversal at the cathode
are the potential methods for ensuring fast and efficient BES start-up. Electrode configuration and hydrodynamic
conditions are also major aspects to be considered for biofilm formation and development
Composition and role of the attached and planktonic active microbial community in mesophilic and thermophilic xylose-fed microbial fuel cells
No full textA mesophilic (37 C) and a thermophilic (55 C) two-chamber microbial fuel cell (MFC) were studied and
compared for their power production from xylose and the microbial communities involved. The anodeattached,
membrane-attached, and planktonic microbial communities, and their respective active
subpopulations, were determined by next generation sequencing (Illumina MiSeq), based on the
presence and expression of the 16S rRNA gene. Geobacteraceae accounted for 65% of the anodeattached
active microbial community in the mesophilic MFC, and were associated to electricity
generation likely through direct electron transfer, resulting in the highest power production of
1.1 W m 3. A lower maximum power was generated in the thermophilic MFC (0.2 W m 3), likely due to
limited acetate oxidation and the competition for electrons by hydrogen oxidizing bacteria and
hydrogenotrophic methanogenic archaea. Aerobic microorganisms, detected among the membraneattached
active community in both the mesophilic and thermophilic MFC, likely acted as a barrier for
oxygen flowing from the cathodic chamber through the membrane, favoring the strictly anaerobic
exoelectrogenic microorganisms, but competing with them for xylose and its degradation products. This
study provides novel information on the active microbial communities populating the anodic chamber of
mesophilic and thermophilic xylose-fed MFCs, which may help in developing strategies to favor
exoelectrogenic microorganisms at the expenses of competing microorganisms
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