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

Groundwater Bioremediation through Reductive Dechlorination in a Permeable Bioelectrochemical Reactor

A new membrane-less bioelectrochemical reactor configuration was developed for contaminated groundwater remediation. The new bioelectrochemical reactor configuration was inspired by the utilisation of a permeable reactive barrier (PBR) configuration with no separation membrane. The corresponding reactive zones were created by using graphite granules and mixed metal oxide (MMO) electrodes to stimulate the reductive and oxidative biological degradation of chlorinated aliphatic hydrocarbons. In the present study, the PBR-like bioelectrochemical reactor has been preliminarily operated with synthetic contaminated groundwater, testing the reductive dechlorination activity on cis-dichloroethylene (cisDCE). Moreover, to assess the effects of competing anions presence for the electron donor (i.e., the cathode), the synthetic wastewater contained sulphate and nitrate anions. In the PBR-like reactor operation, nearly all cisDCE was removed in the initial sampling port, with only VC detected as the observable RD product. During the same biotic test of the PRB reactor, the presence of both the reductive dechlorination and anions reduction was confirmed by the complete nitrate reduction in the cathodic chamber of the PRB reactor. On the contrary, sulphate reduction showed a lower activity; indeed, only 25% of the influent sulphate was removed by the PRB reactor

Role of the Electroactive and Non-electroactive Surface Area (EASA and nEASA) for Electroactive Biofilms in Bioelectrochemical Systems

The role of the electroactive surface area (EASA) and of the non-electroactive surface area (nEASA) was studied to better understand electroactive biofilm’s (EAB) growth and performance in four different systems. Those systems consisted in four 1L glass bottles filled with mineral medium and substrates, a stainless-steel cathode and a bioanode. Four different types of bioanode were assembled in order to study the EASA and nEASA role. A potentiostat controlled the anodic potential, which was fixed in every system at + 0.2 V vs SHE (standard hydrogen electrode). To measure the EASA of every system, cyclic voltammetries (CVs) were carried out at different scan rates. Comparing them with the one obtained with a reference system, each EASA is easily calculated. The nEASA, instead, was measured calculating the geometric volume. The obtained results demonstrate the fundamental role of the EASA and, moreover, the necessity to reduce as much as possible the nEASA in order to enhance the performance

Renewable gases production coupled to synthetic wastewater treatment through a microbial electrolysis cell

This study describes the use of a microbial electrolysis cells for the production of gaseous biofuels sustained by the oxidation of a synthetic wastewater. During the overall experimental investigation, the MEC’s bioanode removed on average 855 ± 57 mgCOD/d producing an average electric current of 66 ± 7 mA which was diverted into gaseous biofuels like biomethane, biohydrogen and biohythane. Three different MEC cathodic configurations were investigated selecting the electrodic materials (graphite granules GG, and mixed metal oxide MMO) and operating conditions (pH of the catholyte, additional sorption chamber). Biomethane production increased from 26 ± 4–102 ± 8 meq/d when the MMO electrode was used with respect to GG electrodic material. In contrast, the MMO electrode in combination with a CO2 sorption chamber was successfully utilized for simultaneous H2 production and CO2 sorption from a N2/CO2 mixture which simulates an anaerobic digestion biogas. The combination of H2 production and CO2 sorption allowed to obtain a gaseous mixture composed of 9% H2, 5% CO2, and 80% N2 that according to the assumption of replacing the N2/CO2 mixture with real biogas corresponded to a commercial-grade biohythane. Overall, the results highlight the potential of MECs as an efficient approach for biogas upgrading, allowing biohythane production increasing CH4 content and lowering CO2 concentration

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

Evaluation of the biological treatment of a real contaminated groundwater through reductive dechlorination biostimulation

Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants due to improper utilization in past industrial activity. Anaerobic reductive dechlorination, where bacteria use CAHs as electron acceptors, is crucial for bioremediation. Environmental conditions, such as nutrient availability and electron donors (i.e., molecular hydrogen), can influence the effectiveness of bioremediation processes. Also, bioremediation strategies like bioaugmentation (i.e., the supply of the enriched dechlorinating consortium) and bio-stimulation (i.e., the supply of electron donor) can improve CAHs removal performances. Here, a microcosm study is presented to assess the effectiveness of bioaugmentation with an enriched dechlorinating consortium for groundwater remediation. Target contaminants used were tetrachloroethane (TeCA), trichloroethylene (TCE) and sulphate ion. Various conditions, including biostimulation and bioaugmentation approaches were tested to evaluate the feasibility of biological treatment. Operating conditions, i.e., mineral medium and lactate, facilitated the dechlorination of TCE into ETH, leading to an increase in the dechlorinating population (Dehalococcoides mccartyi) to 67% of the total bacteria, with reductive dechlorination (RD) rates up to 7 µeq/Ld. Conversely, the RD performance of microcosms with real contaminated groundwater was negatively affected by the combined presence of TeCA and sulphate, indicated by a low abundance of D. mccartyi (<3%) and low RD rates (up to 0.39 µeq/Ld), suggesting that the native microbial population lacked the capacity for effective dechlorination. Moreover, the principal component analysis plot highlighted distinct groupings based on microbial community across different microcosm conditions, indeed, microbial community structures dominated by D. McCarty were associated with higher reductive dechlorination rates while non-augmented and non-stimulated microcosms reflected distinct microbial communities dominated by non-dechlorinating taxa. Additionally, RD decreased (48, 23, 22, and 14 µeq/Ld) with increasing sulphate concentrations (0, 150, 225, and 450 mgSO4 -2/L), further demonstrating the inhibitory effect of sulphate in the treated contaminated groundwater. Overall, this study highlights the complex interplay between environmental conditions, treatment strategies, and microbial communities in driving dechlorination processes. Specifically, the effectiveness of reductive dechlorination is heavily influenced by the availability of electron donors and the composition of the medium or groundwater, which can drive significant shifts in microbial community dynamics, either supporting or hindering the reductive dechlorination process

Bioelectrochemical Organic Matter Conversion Into Hydrogen, Comparison of Different Polarization Strategies

Hydrogen plays a pivotal role in the decarbonization of the fuel industry as both an energy vector and a chemical, however most of the available technologies still heavily rely on fossil fuels and sustainable processes are still unused due to their higher operational costs. MECs are devices based on the utilization of electroactive microorganisms that can interact with polarized electrodes (usually graphite-based), using them as the final electron acceptor for their metabolism. The use of a bioanode capable of oxidizing the organic substances contained in wastewater makes it possible to utilize part of the chemical energy present in the reduced waste compounds for the generation of green hydrogen, reducing the required (theoretical) potential by 85% compared to conventional electrolysis (+1.23 V vs +0.187 V). This study aims to compare two different polarization strategies of a microbial electrolysis cell aimed at hydrogen production coupled with the oxidation of synthetic wastewater. The study clearly showed the advantage of using potentiostatic polarization over galvanostatic polarization due to lower energy consumption during the potentiostatic polarization mode. Indeed, galvanostatic polarization promoted the loss of biological activity due to kinetic limitations in the biological reactions. Consequently, water oxidation on graphite granules occurred in the anodic chamber, increasing the anodic potential up to 0.95 V vs. SHE

Bioelectrochemical Nitrate Reduction in a Continuous Flow Microbial Electrolysis Cell

High Nitrate concentrations in groundwater present considerable public health hazards. This study examines a dual-chamber Microbial Electrolysis Cell (MEC) reactor, consisting of two cylindrical borosilicate glass chambers (cathode and anode), for nitrate reduction from synthetic groundwater, using enriched mixed cultures from Venice Lagoon sediments. Different cathodic potentials were tested, with -450 mV vs. SHE used during batch mode and -450 mV, -550 mV, and -750 mV vs. SHE potentials, with three different Hydraulic Retention Times of 0.63, 1.35, and 0.38 days, tested during continuous flow mode. The highest Denitrification Rate of 72.58 ± 19.28 mgL -1 d -1 was achieved at -750 mV vs. SHE with a low HRT of 0.38 day. Comparisons between biotic and abiotic conditions at -750 mV vs. SHE and 0.63 day HRT showed slightly higher rates in biotic environments (59.01 ± 9.88 mgL -1 d -1 vs. 45.41 ± 1.17 mgL -1 d -1 ). The study highlights the potential of MEC technology for efficient nitrate reduction in groundwater

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