Continuous Flow Microbial Electrolysis Cell Research Articles

Evaluation of a mixture of livestock wastewater and food waste as a substrate in a continuous-flow microbial electrolysis cell

While the efficiency of microbial electrolysis cell (MEC) systems has improved remarkably, their application in continuous reactors and wastewater treatment remains poorly understood. This study evaluated the performance of a continuous-flow MEC using livestock wastewater and food waste as substrates. The MEC system achieved a hydrogen production rate of 5.2 L/L/day using acetate as a substrate, and a rate of 2.9–4.6 L/L/day when real wastewater mixtures were used. In terms of chemical oxygen demand (COD) removal, the system demonstrated high efficiency, with values ranging from 42.3 % to 62.2 % depending on the wastewater composition. Volatile fatty acid (VFA) removal reached up to 72.8 %. The current density averaged 9.9 A/m2 with acetate and decreased to 7.0 and 6.1 A/m2 in phases using wastewater, reflecting the adaptation of the microbial community to the more complex substrates. The microbial community was dominated by Firmicutes, Bacteroidetes, Proteobacteria, and Synergistetes, with Proteobacteria showing a particularly high abundance near the anion exchange membrane (AEM) on the anode. The MEC process demonstrates substantial promise as a sustainable technology for both biohydrogen production and wastewater treatment. With further optimization and scaling, MECs could play a crucial role in the circular economy by converting waste into clean energy while simultaneously treating wastewater, offering a pathway toward more sustainable industrial and environmental practices.

Performance of a continuous flow microbial electrolysis cell (MEC) fed with domestic wastewater

In this study, MEC performance was investigated in terms of chemical oxygen demand (COD) removal, hydrogen production rate and energy consumption during continuous domestic wastewater (dWW) treatment at different organic loading rates (OLR) and applied voltages (Vapp). While the COD removal efficiency was improved at low OLRs, the electrical energy required to remove 1g of COD was significantly increased with decreasing the OLR. Hydrogen production exhibited a Monod-type trend as function of the OLR reaching a maximum production rate of 0.30L/(Lrd). Optimal Vapp was found to be highly dependent on the strength of the dWW. The results also confirmed the fact that MEC performance can be optimized by setting Vapp at the onset potential of the diffusion control region.Although low columbic efficiencies and the occurrence of hydrogen recycling limited significantly the reactor performance, these results demonstrate that MEC can be successfully used for dWW treatment.

Performance of a pilot-scale continuous flow microbial electrolysis cell fed winery wastewater

A pilot-scale (1,000 L) continuous flow microbial electrolysis cell was constructed and tested for current generation and COD removal with winery wastewater. The reactor contained 144 electrode pairs in 24 modules. Enrichment of an exoelectrogenic biofilm required ~60 days, which is longer than typically needed for laboratory reactors. Current generation was enhanced by ensuring adequate organic volatile fatty acid content (VFA/SCOD ≥ 0.5) and by raising the wastewater temperature (31 ± 1°C). Once enriched, SCOD removal (62 ± 20%) was consistent at a hydraulic retention time of 1 day (applied voltage of 0.9 V). Current generation reached a maximum of 7.4 A/m(3) by the planned end of the test (after 100 days). Gas production reached a maximum of 0.19 ± 0.04 L/L/day, although most of the product gas was converted to methane (86 ± 6%). In order to increase hydrogen recovery in future tests, better methods will be needed to isolate hydrogen gas produced at the cathode. These results show that inoculation and enrichment procedures are critical to the initial success of larger-scale systems. Acetate amendments, warmer temperatures, and pH control during startup were found to be critical for proper enrichment of exoelectrogenic biofilms and improved reactor performance.

Ni foam cathode enables high volumetric H 2 production in a microbial electrolysis cell

Valuable, “green” H 2 can be produced with a microbial electrolysis cell (MEC). To achieve a high volumetric production rate of high purity H 2, a continuous flow MEC with an anion exchange membrane, a flow through bioanode and a flow through Ni foam cathode was constructed. At an electrical energy input of 2.6 kWh m −3 H 2 (applied cell voltage: 1.00 V), this MEC was able to produce over 50 m 3 H 2 m −3 MEC d −1 (22.8 ± 0.1 A m −2). The MEC had a low cathode overpotential compared to an MEC with Pt-based cathode, because of the high specific surface area of Ni foam (128 m 2 m −2 projected area). The MEC performance however, decreased during 32 days of operation due to an increase in anode and cathode overpotentials. Scaling likely caused the increase in anode overpotential, but it remained unclear what caused the increase in cathode overpotential.

Multi-electrode continuous flow microbial electrolysis cell for biogas production from acetate

Most microbial electrolysis cells (MECs) contain only a single set of electrodes. In order to examine the scalability of a multiple-electrode design, we constructed a 2.5 L MEC containing 8 separate electrode pairs made of graphite fiber brush anodes pre-acclimated for current generation using acetate, and 304 stainless steel mesh cathodes (64 m 2/m 3). Under continuous flow conditions and a one day hydraulic retention time, the maximum current was 181 mA (1.18 A/m 2, cathode surface area; 74 A/m 3) within three days of operation. The maximum hydrogen production (day 3) was 0.53 L/L-d, reaching an energy efficiency relative to electrical energy input of η E = 144%. Current production remained relatively steady (days 3–18), but the gas composition dramatically shifted over time. By day 16, there was little H 2 gas recovered and methane production increased from 0.049 L/L-d (day 3) to 0.118 L/L-d. When considering the energy value of both hydrogen and methane, efficiency relative to electrical input remained above 100% until near the end of the experiment (day 17) when only methane gas was being produced. Our results show that MECs can be scaled up primarily based on cathode surface area, but that hydrogen can be completely consumed in a continuous flow system unless methanogens can be completely eliminated from the system.

Electrodeposition of nickel particles on a gas diffusion cathode for hydrogen production in a microbial electrolysis cell

Gas diffusion cathodes with electrodeposited nickel (Ni) particles have been developed and tested for hydrogen production in a continuous flow microbial electrolysis cell (MEC). A high catalytic activity of electrodeposited Ni particles in such a MEC was obtained without a proton exchange membrane, i.e. under direct cathode exposure to anodic liquid. Co-electrodeposition of Pt and Ni particles did not improve any further hydrogen production. The maximum hydrogen production rate was 5.4 L/L R/day, corresponding to Ni loads between 0.2 and 0.4 mg cm −2. Continuous MEC operation demonstrated stable hydrogen production for over one month. Owing to the fast hydrogen transport through the cathodic gas diffusion layer, the loss of hydrogen production to methanogenic activity was minimal, generally with less than 5% methane in the off-gas. Overall, gas diffusion cathodes with electrodeposited Ni particles demonstrated excellent stability for hydrogen production compared to expensive Pt cathodes.

Hydrogen production in a microbial electrolysis cell with nickel-based gas diffusion cathodes

Gas diffusion cathodes with Ni alloy and Ni catalysts manufactured by chemical deposition were tested for H 2 production in a microbial electrolysis cell (MEC). In a continuous flow MEC, multi-component cathodes containing Ni, Mo, Cr, and Fe, at a total catalyst load of 1 mg cm −2 on carbon support demonstrated stable H 2 production at rates of 2.8 – 3.7 L L R − 1 d − 1 with only 5% methane in the gas stream. Furthermore, a Ni-only gas diffusion cathode, with a Ni load of 0.6 mg cm −2, demonstrated a H 2 production rate of 4.1 L L R − 1 d − 1 . Overall, H 2 production was found to be proportional to the Ni load implying that inexpensive gas diffusion cathodes prepared by chemical deposition of Ni can be successfully used for continuous production of H 2 in a MEC.

High rate membrane-less microbial electrolysis cell for continuous hydrogen production

This study demonstrates hydrogen production in a membrane-less continuous flow microbial electrolysis cell (MEC) with a gas-phase cathode. The MEC used a carbon felt anode and a gas diffusion cathode with a Pt loading of 0.5 mg cm −2. No proton exchange membrane (PEM) was used in the setup. Instead, the electrodes were separated by a J-cloth. The absence of a PEM as well as a short distance maintained between the electrodes (0.3 mm) resulted in a low internal resistance of 19 Ω. Due to an improved design, the volumetric hydrogen production rate reached 6.3 L STP L A − 1 d −1. In spite of the PEM absence, methane concentration in the gas collection chamber was below 2.1% and the presence of hydrogen in the anodic chamber was never observed.