Bioelectromethanogenesis reaction in a tubular Microbial Electrolysis Cell (MEC) for biogas upgrading

The utilization of a pilot scale tubular Microbial Electrolysis Cell (MEC), has been tested as an innovative biogas upgrading technology. The bioelectromethanogenesis reaction permits the reduction of the CO2 into CH4 by using a biocathode as electrons donor, while the electroactive oxidation of organic matter in the bioanode partially sustains the energy demand of the process. The MEC has been tested with a synthetic wastewater and biogas by using two different polarization strategies, i.e. the three-electrode configuration, in which a reference electrode is utilized to set the potential at a chosen value, and a two-electrode configuration in which a fixed potential difference is applied between the anode and the cathode. The tubular MEC showed that the utilization of a simple two electrode configuration does not allow to control the electrodic reaction in the anodic chamber, which causes the increase of the energy consumption of the process. Indeed, the most promising performances regarding the COD and CO2 removal have been obtained by controlling the anode potential at +0.2 V vs SHE with a three electrode configuration, with an energy consumption of 0.47 kWh/kgCOD and 0.33 kWh/Nm3 of CO2 removed, which is a comparable energy consumption with respect the available technologies on the market

Effects of the feeding solution composition on a reductive/oxidative sequential bioelectrochemical process for perchloroethylene removal

Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants due to their improper use in several industrial activities. Specialized microorganisms are able to perform the reductive dechlorination (RD) of high-chlorinated CAHs such as perchloroethylene (PCE), while the low-chlorinated ethenes such as vinyl chloride (VC) are more susceptible to oxidative mechanisms performed by aerobic dechlorinating microorganisms. Bioelectrochemical systems can be used as an effective strategy for the stimulation of both anaerobic and aerobic microbial dechlorination, i.e., a biocathode can be used as an electron donor to perform the RD, while a bioanode can provide the oxygen necessary for the aerobic dechlorination reaction. In this study, a sequential bioelectrochemical process constituted by two membrane-less microbial electrolysis cells connected in series has been, for the first time, operated with synthetic groundwater, also containing sulphate and nitrate, to simulate more realistic process conditions due to the possible establishment of competitive processes for the reducing power, with respect to previous research made with a PCE-contaminated mineral medium (with neither sulphate nor nitrate). The shift from mineral medium to synthetic groundwater showed the establishment of sulphate and nitrate reduction and caused the temporary decrease of the PCE removal efficiency from 100% to 85%. The analysis of the RD biomarkers (i.e., Dehalococcoides mccartyi 16S rRNA and tceA, bvcA, vcrA genes) confirmed the decrement of reductive dechlorination performances after the introduction of the synthetic groundwater, also characterized by a lower ionic strength and nutrients content. On the other hand, the system self-adapted the flowing current to the increased demand for the sulphate and nitrate reduction, so that reducing power was not in defect for the RD, although RD coulombic efficiency was less

Sequential Reductive/Oxidative Bioelectrochemical Process for Chlorinated Aliphatic Hydrocarbons Removal in Contaminated Groundwaters: Fluid Dynamic Characterization of the Scaled-Up Field Test

Chlorinated Aliphatic Hydrocarbons (CAHs) as Perchloroethylene (PCE) and Trichloroethylene (TCE) are worldwide contaminants due to their uncorrected disposal and storage in the past years. An effective remediation strategy for CAHs contaminated groundwaters is the stimulation of dechlorinating microorganisms which can carry out reductive and oxidative reactions that allowed for the complete mineralization of CAHs. More in detail, dehalorespiring microorganisms can reduce PCE and TCE throughout reductive dechlorination reaction (RD) a step happening reaction that remove a chlorine atom from the carbon skeleton of the molecule and replaces it with a hydrogen ion. Hence, aerobic dechlorinating microorganisms oxidize low chlorinated compounds such as cis-dichloroethylene (cDCE) and vinyl chloride (VC) into CO2 using enzymes, such as monooxygenases, to produce instable molecules with oxygen atom like epoxides. The combination of reductive and oxidative dechlorination could maximize the microbial activities allowing to work on the preferred substrates and can be easily tuned by the adoption of bioelectrochemical systems. In these electrochemical devices, an electrodic material interact with so-called electroactive microorganisms, acting like electron acceptor or donor of the microbial metabolism. In this study, a sequential reductive/oxidative bioelectrochemical process developed by the combination in series of two membrane-less microbial electrolysis cells (MECs) has been applied for the treatment of a CAHs contaminated groundwater coming from a polluted site in northern Italy. More in detail, the study presents the development and the validation of the sequential bioelectrochemical process under laboratory conditions and the and subsequent scale-up of the process for a field. The investigation of the laboratory scale performance was conducted by synthetic and real contaminated groundwater while the design and the characterization of the scaled-up process have been obtained with real contaminated in a field test. The scale-up allowed to increase the reactor volume 42 times (from 10 L to 420 L) dividing the reductive and the oxidative sections into 4 different columns with a volume of 105 L (Figure 1). The field test of the bioelectrochemical technology represents the most important scaled-up application in a bioelectrochemical system devoted to the remediation of CAHs contaminated groundwater, thus, it shows an effective solution for the stimulation of microbial activity without the utilization of any chemical in a real environment

Production of Short-chain Fatty Acid from CO2 Through Mixed and Pure Culture in a Microbial Electrosynthesis Cell

The continuous accumulation of atmospheric CO2 requires the development of new technologies for its mitigation. Carbon capture and utilization (CCU) technologies aim to convert CO2 into precious compounds like chemicals and fuels. Biological fixation is an attractive CCU strategy in terms of cost, sustainability and variety of products. Chemoautotrophic microorganisms such as methanogens and acetogens are able to reduce CO2 into acetate and methane, respectively. Acetogens bacteria are able to use CO2 for cell growth through the Wood Liujhundal pathway, moreover, the final precursor (i.e. Acetyl-CoA) of the autotrophic metabolism, is also used in energy metabolism with acetate production as a waste product. Furthermore, it is possible to obtain multicarbon products of autotrophic origin starting from acetyl-CoA and acetate. The biotechnological use of these microorganisms requires the presence of H2 as substrate, which is used as an electron donor in the pathway. This reaction can be sustained by a biocathode in a microbial electrosynthesis cell, in which the reducing power is generated by a polarized electrode. This study proposes the use of a microbial electrosynthesis cell for conversion to acetate in H-cells by either a mixed culture enriched with Acetobacterium woodii or a pure culture of Acetobacterium woodii, to observe the difference in terms of acetate production and reducing power consumption efficiency. The mixed culture was obtained from a mixture of activated sludge and anaerobic digestate, treated by a protocol capable to select acetogenic microorganisms without the use of specific chemical inhibitors (2-Bromoethanesulfonate). Both inoculums were tested at room temperature (25°C) in the cathodic chamber of the H-cell at potentials in the range of -0.7 to -1.1 V vs SHE. The obtained results showed that the enriched mixed culture produced at -0.7 vs SHE a mixture of volatile fatty acids including C4 and C5 molecules with an overall coulombic efficiency of 50%, while at the potential of -0.9 vs SHE methane constituted the main product of the biocathode. The pure culture, on the other hand, showed a specific production of acetate with a coulombic efficiency of 44% at -0.9 vs SHE and 63% at -1.1 vs SHE. Furthermore, a drastic decrease in biocathode biomass was observed in pure culture, suggesting a higher tendency to form biofilms on the electrode unlike the mixed culture, which showed a standard growth profile in the bulk

Metagenomic Analysis Reveals Microbial Interactions at the Biocathode of a Bioelectrochemical System Capable of Simultaneous Trichloroethylene and Cr(VI) Reduction

Bioelectrochemical systems (BES) are attractive and versatile options for the bioremediation of organic or inorganic pollutants, including trichloroethylene (TCE) and Cr(VI), often found as co-contaminants in the environment. The elucidation of the microbial players' role in the bioelectroremediation processes for treating multicontaminated groundwater is still a research need that attracts scientific interest. In this study, 16S rRNA gene amplicon sequencing and whole shotgun metagenomics revealed the leading microbial players and the primary metabolic interactions occurring in the biofilm growing at the biocathode where TCE reductive dechlorination (RD), hydrogenotrophic methanogenesis, and Cr(VI) reduction occurred. The presence of Cr(VI) did not negatively affect the TCE degradation, as evidenced by the RD rates estimated during the reactor operation with TCE (111±2 μeq/Ld) and TCE/Cr(VI) (146±2 μeq/Ld). Accordingly, Dehalococcoides mccartyi, the primary biomarker of the RD process, was found on the biocathode treating both TCE (7.82E+04±2.9E+04 16S rRNA gene copies g−1 graphite) and TCE/Cr(VI) (3.2E+07±2.37E+0716S rRNA gene copies g−1 graphite) contamination. The metagenomic analysis revealed a selected microbial consortium on the TCE/Cr(VI) biocathode. D. mccartyi was the sole dechlorinating microbe with H2 uptake as the only electron supply mechanism, suggesting that electroactivity is not a property of this microorganism. Methanobrevibacter arboriphilus and Methanobacterium formicicum also colonized the biocathode as H2 consumers for the CH4 production and cofactor suppliers for D. mccartyi cobalamin biosynthesis. Interestingly, M. formicicum also harbors gene complexes involved in the Cr(VI) reduction through extracellular and intracellular mechanisms

Electron recycle concept in a microbial electrolysis cell for biogas upgrading

Abstract An innovative strategy to control the metabolism of microorganisms is offered by bioelectrochemical systems in which a graphite-based cathode can be used as electron donor or acceptor. An advanced microbial electrolysis cell is developed to combine CO2 removal from a synthetic biogas in a biocathode and the organic matter oxidation in a bioanode. A novel biogas upgrading approach is presented in which an electron recycle concept is obtained by the combination of CO2 reduction and oxidation. While the bioelectrochemical anodic chemical oxygen demand oxidation provides the electrons necessary for the cathodic CO2 reduction into methane and acetate, the acetate produced by acetogenic microorganisms migrates from the cathode to the anode being oxidized again by the bioanode

Microbial electrolysis cell to enhance energy recovery from wastewater treatment

Energy intensive activate sludge treatment is the most utilized technology for municipal wastewater treatment. However, an innovative way to harvest part of the energy contained in municipal wastewater is offered by the utilization of microbial electrolysis cells (MECs). In an MEC, through the utilization of electro active microorganism, is possible to couple the oxidation organic matter with the generation of value-added reduced products, such as methane, similar to the anaerobic digestion process. MECs typically consist of a bio-anode and a (bio)-cathode separated by an ion exchange membrane (IEM). The addition of external energy usually is required to make the cathodic reaction thermodynamically feasible. Here, a continuous flow methane- producing MEC equipped with an anion exchange membrane was operated in a continuous flow mode for over 60 d at two different poised anode potentials (+ 0.20 and -0.10 V vs. standard hydrogen electrode, SHE) and with a fixed organic load rate (1.08 gCOD/Ld). The MEC showed a high COD removal efficiency (92 ± 1%), with a net energy recovery (122 ± 3 %, at -0.1 V) and low sludge production (0.09 gCOD/gCOD), making its utilization attractive in the frame of low strength wastewater treatment

Sequential reductive/oxidative bioelectrochemical process for groundwater perchloroethylene removal

Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants, microbial communities naturally present in groundwater can reduce CAHs as perchloroethylene (PCE) and trichloroethylene (TCE) to ethylene through reductive dechlorination (RD) reaction while low chlorinated CAHs like cis-dichloroethylene (cis DCE) and vinyl chloride (VC) can be oxidized by aerobic pathways. A combination of reductive and oxidative dechlorination results an effective strategy for the complete mineralization of CAHs. Bioelectrochemical systems (BES) are innovative processes which can be adopted to stimulate both reductive and oxidative dechlorination biomass through polarized electrodes. The present study describes the performances of a an oxidative bioelectrochemical reactor composed by a membrane-less microbial electrolysis cell (MEC) equipped with an internal graphite counterelectrode. In the oxidative reactor the oxygen provided by a mixed metal oxides (MMO) anode stimulated the oxidative dechlorination of the cisDCE contained in synthetic groundwater. Throughout the experimental period, both reductive and oxidative dechlorination pathways were identified due to presence of an internal counter electrode that acted as electron donor. Reductive and oxidative bioelectrochemical reactions, including anions reduction were determined and their relative contribution to the overall flowing current has been quantified in terms of oxidative and reductive coulombic efficiencies

Two phase anaerobic digestion effluents as feedstocks to bioelectromethanogenesis sustenance

In a microbial electrolysis cell (MEC), it is possible to conduct the two main reactions of anaerobic digestion (AD) in two physically separated chambers, by coupling COD oxidation into CO2 (in the bio-anode) to the CO2 removal and reduction into methane (in the bio-cathode), thanks to the transfer of reducing power by the electrical and ionic current. Moreover, AD and MEC can be integrated, by using the MEC to upgrade methane content of the AD biogas while also using residual COD from AD anaerobic digestate, so improving the overall energy efficiency and the quality of the products of conventional AD (Villano et al 2013). However, this approach has not been tested with real substrates yet and concerns also exist on possible fouling and poisoning effects on ionic membrane and/or electrodic material. Here, a continuous-flow 2-chamber MEC was operated under anodic potentiostatic control (at 0.2 vs SHE), to compare its performance by feeding the bio-anode with synthetic vs real substrates; both an anaerobic digestate (from methanogenic stage) and an acidogenic fermentate (from preliminary acidogenic stage) were tested and compared with a synthetic substrate mixture (as described in Zeppilli et al 2014). The MEC was equipped with a proton exchange membrane (PEM) and both electrodic beds made by graphite granules. The cathode chamber was fed by a continuous sparging of a gas mixture of N2/CO2 (70/30 v/v to simulate biogas), whereas a concentrated liquid stream was spilled to counterbalance osmotic water flow across PEM. The MEC performed poorly (23 ± 4 mA) when fed by the anaerobic digestate because its residual COD resulted to be poorly available for anodic oxidation, whereas the mixture of both first and second stage AD effluents gave slightly better performance than the synthetic mixture(60 ± 4 mA vs 50 ± 1 mA, respectively). The latter evidence was not only due to high VFA-content but also to high ammonia concentration. Being ammonia higher than in the synthetic mixture, the percentage of ionic current transported across the PEM by the ammonium instead of the proton was increased from 2 to 20 %. This eventually increased the net generation of the alkalinity in the cathodic chamber and thus bicarbonate concentration in the cathodic spill. Overall, by using the VFA-rich and ammonia-rich mixture of both real effluents, a nitrogen removal rate of 228 mg/Ld was obtained while an average CO2 removal of 3.4 g/Ld was observed in the cathode. Fouling phenomena were observed to decrease the MEC performance, likely due to the high content of suspended solids in both real substrates (in spite of preliminary filtration at around 0.2 mm cut off). However, adverse fouling effects were easily recovered by periodic backwashing of the bio-anode

Carbon dioxide abatement and biofilm growth in Mec equipped with a packed bed adsorption column

In this study, a lab-scale microbial electrolysis cell (MEC) aimed to the biogas upgrading through a methanogenic biocathode has been integrated with an adsorption column to test the possible increase of the biocathode CO2 removal capacity. In the adopted MEC configuration, the oxidation of the organic matter by an anodic biofilm was utilized to partially sustain the energy demand of the bioelectromethanogenesis reaction in the cathodic chamber. Anodic and cathodic biofilms were characterized by cyclic voltammetry (CV) technique which allowed the electron transfer mechanisms characterization in the anodic and cathodic bioelectrochemical reactions. More in detail, while the anodic biofilm showed the presence of a potential direct electron transfer, the cathodic CV suggests a hydrogen mediated mechanism for the CO2 reduction into CH4. The integration of a sorption column and the MEC biocathode showed a negligible effect in the overall biocathode CO2 removal, suggesting the control of the CO2 sorption by a chemical reaction through the alkalinity generation mechanism instead of the gas-liquid mass transfer