High performance spiral wound microbial fuel cell with hydraulic characterization

Scaling up of dual-chamber microbial electrochemical systems - An appraisal using systems design approach

Impetus to minimise the energy and carbon footprints of evolving wastewater resource recovery facilities has promoted the development of microbial electrochemical systems (MES) as an emerging energy-neutral and sustainable platform technology. Using separators in dual-chamber MES to isolate anodic and cathodic environments creates endless opportunities for its myriad applications. Nevertheless, the high internal resistance and the complex interdependencies among various system factors have challenged its scale-up. This critical review employed a systems approach to examine the complex interdependencies and practical issues surrounding the implementation and scalability of dual-chamber MES, where the anodic and cathodic reactions are mutually appraised to improve the overall system efficiency. The robustness and stability of anodic biofilms in large-volume MES is dependent on its inoculum source, antecedent history and enrichment strategies. The composition and anode-respiring activity of these biofilms are modulated by the anolyte composition, while their performance demands a delicate balance between the electrode size, macrostructure and the availability of substrates, buffers and nutrients when using real wastewater as anolyte. Additionally, the catholyte governed the reduction environment and associated energy consumption of MES with scalable electrocatalysts needed to enhance the sluggish reaction kinetics for energy-efficient resource recovery. A comprehensive assessment of the dual-chamber reactor configuration revealed that the tubular, spiral-wound, or plug-in modular MES configurations are suitable for pilot-scale, where it could be designed more effectively using efficient electrode macrostructure, suitable membranes and bespoke strategies for continuous operation to maximise their performance. It is anticipated that the critical and analytical understanding gained through this review will support the continuous development and scaling-up of dual-chamber MES for prospective energy-neutral treatment of wastewater and simultaneous circular management of highly relevant environmental resources.

Computational and experimental analysis of organic degradation positively regulated by bioelectrochemistry in an anaerobic bioreactor system

Methane production was tested in membrane-less microbial electrolysis cells (MECs) under closed-circuit (R_CC) and open-circuit (R_OC) conditions, using glucose as a substrate, to understand the regulatory effects of bioelectrochemistry in anaerobic digestion systems. A dynamic model was built to simulate methane productions and microbial dynamics of functional populations, which were colonized in groups R_CC and R_OC during the start-up stage. The experiment results showed significantly greater methane production in R_CC than R_OC, the average methane production of R_CC was 0.131 m³/m³/d, which was 1.4 times higher than that of R_OC (0.055 m³/m³/d). The simulation results revealed that bioelectrochemistry had a significant influence on the abundance of microorganisms involved in acidogenesis and methanogenesis. The abundance of glucose-uptaking microorganisms was 87% of the total biomass in R_OC without applied voltage, which was 20% higher than that in R_CC (67%) when external voltages were applied between the anode and cathode. The abundance of hydrogenotrophic methanogens in R_CC was 6% higher than that in R_OC. The simulation results were verified through 16S rDNA high-throughput sequencing analysis. An electron balance analysis revealed that alteration of the acidogenesis type led to more acetate and hydrogen production from glucose fermentation, compared with the situation without bioelectrochemistry. An additional pathway from acetate to hydrogen was introduced by bioelectrolysis. These two factors resulted in significant enhancement of methane production in R_CC. Bioelectrolysis process directly contributed to 26% of the total methane production after the start-up stage. When the applied voltages were cut down or decreased, R_CC could maintain considerable methane productions, because the microbial communities and electron transfer pathways were already formed. Starting-up with high voltage, but operating under low voltage, could be an energy-favorable strategy for accelerating biogas production in bioelectro-anaerobic bioreactors.

Ambient CO2 capture and storage in bioelectrochemically mediated wastewater treatment

This study reports that wastewater can be used to capture and store CO2 directly from ambient air and produce energy. The proof-of-concept system consisted of an ion exchange resin column that captures and concentrates ambient CO2 using a moisture-driven cycle. The concentrated CO2 was then transferred into a microbial electrochemical carbon capture (MECC) reactor for carbon sequestration and hydrogen production. Data from an average batch cycle showed that approximately 8mmol/L CO2 was captured in the MECC cathode when 0.14g/LCOD was removed in the anode. With 90% hydrogen conversion efficiency, the energy intensity and CO2 absorption from the process could be 11.3kJ/gCOD and 0.49gCO2/gCOD respectively. If the proposed process is applied, over 68milliontons of atmospheric CO2 can be captured yearly during wastewater treatment in the US, which equates to significant economic values if CO2 taxes were to be implemented more widely.

Geophysical Monitoring of Hydrocarbon-Contaminated Soils Remediated with a Bioelectrochemical System

Efficient noninvasive techniques are desired for monitoring the remediation process of contaminated soils. We applied the direct current resistivity technique to image conductivity changes in sandbox experiments where two sandy and clayey soils were initially contaminated with diesel hydrocarbon. The experiments were conducted over a 230 day period. The removal of hydrocarbon was enhanced by a bioelectrochemical system (BES) and the electrical potentials of the BES reactors were also monitored during the course of the experiment. We found that the variation in electrical conductivity shown in the tomograms correlate well with diesel removal from the sandy soil, but this is not the case with the clayey soil. The clayey soil is characterized by a larger specific surface area and therefore a larger surface conductivity. In sandy soil, the removal of the diesel and products from degradation leads to an increase in electrical conductivity during the first 69 days. This is expected since diesel is electrically insulating. For both soils, the activity of BES reactors is moderately imaged by the inverted conductivity tomogram of the reactor. An increase in current production by electrochemically active bacteria activity corresponds to an increase in conductivity of the reactor.

The tubular MFC with carbon tube air-cathode for power generation and N,N-dimethylacetamide treatment

A continuous flow microbial fuel cell (MFC) was assembled with carbon tube air-cathode and carbon felt anode. The organic solvent N,N-dimethylacetamide (DMAC) was used as the only carbon source for power generation. After the adaptive phase, the cell potential was gradually increased from 0.15 to 0.45 V with 200 Ω of external resistor during 150 h of operation. The calculated power density of this MFC was 100 mW L(-1) when the cell potential was 0.45 V. The reversible redox peaks of carbon tube were obtained in cyclic voltammogram between -0.5 and -0.25 V under aerobic circumstance. The removal rate of DMAC was 15-50% after treatment with hydraulic retention time of 12 min. The results indicated that it is possible to realize the power extraction from DMAC wastewater in the form of electricity by the bioconversion process of MFC.

Optimized matching modes of bioelectrochemical module and anaerobic sludge in the integrated system for azo dye treatment

In this work, three matching modes (relative positions, catholyte flow sequences, and flow regimes) of bioelectrochemical module and anaerobic sludge were evaluated and optimized for azo dye treatment in the integrated system with embedding modular bioelectrochemical system into anaerobic sludge reactor. Results showed that it was favorable to operate this integrated system under the condition of 1/4 cathode soaking into sludge with spiral distributor in down-flow direction. Current, electrochemical impedance spectroscopy and pH clearly demonstrated the important role of 1/4 soaking in electron/proton transfer. The down-flow direction flowed through electrode zone and then sludge zone could benefit to the efficient use of cathode and improve AO7 treatment. Furthermore, the positive effect of spiral catholyte distributor might be due to its promoting role in mixing and creating a spiral flow channel around the cathode electrode-microbes-solution interface. These results exhibited great potential for matching modular bioelectrochemical system with anaerobic treatment process.

A lab-scale anoxic/oxic-bioelectrochemical reactor for leachate treatments

A membraneless, liter-scale bioelectrochemical reactor with both bioanode and biocathode was established for landfill leachate treatment. Anoxic/oxic (A/O) zones at anode compartment and cathode compartment, respectively, were connected with a reflux to facilitate nitrogen removal. With raw landfill leachate of 17,500-22,600 mg L(-1) chemical oxygen demand (COD) and 1170-1490 mg L(-1) NH4(+)-N, the tested reactor removed 89.1±1.6% of chemical oxygen demand and 99.2±0.1% of NH4(+)-N at 3.0 kg COD m(-3) d(-1). The corresponding maximum power density was 2.71±0.09 W m(-3), with internal resistance of 46.7±1.6 Ω and open circuit voltage of 727±7 mV. The species of Pseudomonas, Desulfovibrio, Bacillus, Enterococcus, Pelospora, Dehalobacter dominated the anodic community, while those of methylotrophs, Rhodobacter, Verrucomicrobiaceae, Geobacter, Flavobacterium, Thauera, Desulfovibrio and Aeromonas dominated the cathodic community. The proposed A/O bioelectrochemical reactor is a prototype for practical treatment of landfill leachate at affordable costs.

Pluggable microbial fuel cell stacks for septic wastewater treatment and electricity production

Septic tanks and other decentralized wastewater treatment systems play an important role in protecting public health and water resource for remote or developing communities. Current septic systems do not have energy production capability, yet such feature can be very valuable for areas lack access to electricity. Here we present an easy-to-operate microbial fuel cell (MFC) stack that consists a common base and multiple pluggable units, which can be connected in either series or parallel for electricity generation during waste treatment in septic tanks. Lab studies showed such easy configuration obtained a power density of 142±6.71mWm(-2) when 3 units are connected in parallel, and preliminary calculation indicates that a system that costs approximately US $25 can power a 6-watt LED light for 4h per day with great improvement potential. Detailed electrochemical characterizations provide insights on system internal loss and technology advancement needed.