• Transactions of the Korean hydrogen and new energy society
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• v.30 no.3
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• pp.269-275
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• 2019

This study was conducted to evaluate the microbial communities in coupled system of a microbial electrolysis cell and an anaerobic digestion. Glucose, butyric acid, propionic acid and acetic acid were used as substrates. The maximum methane production and methane production rate of propionic acid respectively were $327.9{\pm}6.7mL\;CH_4/g\;COD$ and $28.3{\pm}3.1mL\;CH_4/g\;COD{\cdot}d$, which were higher than others. Microbial communities' analyses indicated that acetoclastic methangens were predominant in all systems. But the proportion of hydrogenotrophic methanogens was higher in the system using propionic acid as a substrate when compared to others. In coupled system of a microbial electrolysis cell and anaerobic digestion, the methane production was higher as the distribution of hydrogen, which was generated by substrate degradation, and proportion of hydrogenotrophic methanogens was higher.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.12
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• pp.682-688
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• 2015

Effect of electrode spacing on the performance of microbial electrolysis cells(MECs) for treating sewage sludge was investigated through lab scale experiment. The reactors were equipped with two pairs of electrodes that have a different electrode spacing (16, 32 mm). Shorter electrode distance improved the overall performance of MEC system. With the 16 mm of electrode distance, the current density was $3.04{\sim}3.74A/m^3$ and methane production was $0.616{\sim}0.804Nm^3/m^3$, which were higher than those obtained with 32 mm of electrode spacing ($1.50{\sim}1.82A/m^3$, $0.529{\sim}0.664Nm^3/m^3$). The COD removal was in the range of 34~40%, and the VSS reduction ranged 32~38%. As the current production increased, VSS reduction and methane production were increased possibly due to the improved bioelectrochemical performance of the system. Methane production was more affected by current density than VSS reduction. These results imply that the reducing the electrode spacing can enhance the methane production and recovery from sewage sludge with the decreased internal resistance, however, it was not able to improve VSS reduction of sewage sludge.

• Journal of the Korea Organic Resources Recycling Association
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• v.31 no.4
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• pp.41-49
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• 2023

This study examined the effect of input substrate concentration on hydrogen production of microbial electrolysis cells. To compare the performance of MEC according to the input substrate concentration, six laboratory-scale MEC reactors were operated by sequentially increasing the input substrate concentration from 2 g/L of sodium acetate, to 4 g/L, and 6 g/L. The current density, hydrogen production, and SCOD removal rate were analyzed, and energy efficiency and cathodic hydrogen recovery were calculated to compare the performance of MEC. The maximum volumetric current density was obtained at 4 g/L condition (76.3 A/m³) and it decreased to 19.0 A/m³, when the input concentration was increased to 6 g/L, which was a 75% decrease compared to the 4 g/L input condition. Maximum hydrogen production was obtained also at 4 g/L condition (47.3 ± 16.8 mL), but maximum hydrogen yield was obtained at 2 g/L input condition (1.1 L H₂/g COD_in). Energy efficiencies were also highest in 2 g/L condition; the lowest result was observed at 6 g/L condition. Maximum electrical energy efficiency was 76.4%, and the maximum overall energy efficiency was 39.7% at 2 g/L condition. However, when the substrate concentration increased to 6 g/L, the performance was drastically decreased. Cathodic hydrogen recovery also showed a similar tendency with energy efficiency, with the lowest concentration condition showing the best performance. It can be concluded that operating at low input substrate concentration might be better when considering not only hydrogen yield but also energy efficiency.

• Membrane and Water Treatment
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• v.11 no.4
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• pp.283-294
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• 2020

This work aims at studying the feasibility of continuous removal of mixed heavy metal ions from simulated zinc plating wastewaters by coupling a microbial fuel cell and a microbial electrolysis cell in batch and continuous modes. The discharging voltage of MFC increased initially from 0.4621 ± 0.0005 V to 0.4864 ± 0.0006 V as the initial concentration of Cr⁶⁺ increased from 10 ppm to 60 ppm. Almost complete removal of Cr⁶⁺ and low removal of Cu²⁺ occurred in MFC of the MFC-MEC-coupled system after 8 hours under the batch mode; removal efficiencies (REs) of Cr⁶⁺ and Cu²⁺ were 99.76% and 30.49%. After the same reaction time, REs of nickel and zinc ions were 55.15% and 76.21% in its MEC. Cu²⁺, Ni²⁺, and Zn²⁺ removal efficiencies of 54.98%, 30.63%, 55.04%, and 75.35% were achieved in the effluent within optimum HRT of 2 hours under the continuous mode. The incomplete removal of Cu²⁺, Ni²⁺ and Zn²⁺ ions in the effluent was due to the fact that the Cr⁶⁺ was almost completely consumed at the end of MFC reaction. After HRT of 12 hours, at the different sampling locations, Cr⁶⁺ and Cu²⁺ removal efficiencies in the cathodic chamber of MFC were 89.95% and 34.69%, respectively. 94.58%, 33.95%, 56.57%, and 75.76% were achieved for Cr⁶⁺, Cu²⁺, Ni²⁺ and Zn²⁺ in the cathodic chamber of MEC. It can be concluded that those metal ions can be removed completely by repeatedly passing high concentration of Cr⁶⁺ through the cathode chamber of MFC of the MFC-MEC-coupled system.

• Journal of the Korea Organic Resources Recycling Association
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• v.27 no.4
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• pp.25-33
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• 2019

Operating characteristics of a 30 L microbial electrolysis cell (MEC) for producing biogas from sewage sludge was studied. During the 32-day inoculation period, carbon dioxide concentration decreased and methane concentration increased with operating time, and the overall methane content of biogas was 69.1% with a production rate of 171.6 mL CH₄/L·d. In fed-batch experiments for 6 operating cycles, CH₄ concentration of 66.5~77.2% was obtained at a production rate of 184.9~372.9 mL CH₄/L·d, COD, TS and VS removal efficiency ranged from 28.2 to 42.1%, 20.7 to 37.5% and 18.5 to 36.9%, respectively. The MEC system was observed to be stabilized as operating cycles were repeated after inoculation. In the last operating cycle, 5221 mL/L of methane was produced with CH₄ yield of 316.7 L CH₄/kg COD_rem, and the energy recovery was 73%.

• Journal of the Korea Organic Resources Recycling Association
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• v.29 no.2
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• pp.31-38
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• 2021

The aim of this study is to evaluate the possibility of treating slaughterhouse by-products using microbial electrolysis cells (MECs). The diluted pig liver was fed to MEC reactors with the influent COD concentrations of 772, 1,222, and 1,431 mg/L, and the applied voltage were 0.3, 0.6, and 0.9 V. The highest methane production of 5.9 mL was obtained at the influent COD concentration of 1,431 mg/L and applied voltage of 0.9 V. In all tested conditions, COD removal rate was increased as the influent COD concentration increased with average removal rate of 62.3~81.1%. The maximum methane yield of 129~229 mL/g COD was obtained, which is approximately 80% of theoretical maximum value. It might be due to the bioelectrochemical reaction greatly increased the biodegradability of pig liver. Future research is required to improve the methane yield and digestibility through optimizing the reactor design and operating conditions.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.2
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• pp.82-88
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• 2017

MET (Microbial Electrochemical Technology), such as MFC (Microbial Fuel Cell) and MEC (Microbial Electrolysis Cell), is a promising technology for producing sustainable biogas from an anaerobic digester (AD). At current stage, however, the most likely limiting factors, large internal resistances, should be overcome for successful scale up of this technology. Various researchers reported that application of electrode materials containing high current density, increase of ion strength and conductivity, configuration of electrode are good methods for minimizing internal resistances. Recently, stainless steel is receiving great attention because of not only high performance and durability but also low cost. Therefore, in this study, we evaluate electrochemical characteristics and biogas production rate using various electrode materials and configuration (graphite carbon coated with catalysts ($GC-C_M$) or not (GC), stainless steel mesh (SUS-M) and plate (SUS-P)). As the results, current densities of $GC-C_M$, GC, SUS-P, SUS-M were 2.03, 1.36, 1.04, $1.13A/m^2$, respectively. Methane yields of $GC-C_M$, GC, SUS-P, SUS-M were 0.27, 0.14, 0.19, 0.21 $L-CH_4/g-COD_{rem}$., respectively. Stainless steel shows high current density and methane yield, which are similar as graphite carbon coated with catalysts.

• Journal of the Korea Organic Resources Recycling Association
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• v.27 no.4
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• pp.51-59
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• 2019

In this study, the influence of anaerobic digested sludge and 50 mM PBS (phosphate buffer solution) mixing ratio (1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7) on hydrogen production and inoculation period were examined. MECs were operated in fed-batch mode with an applied voltage of 0.9 V. As a result, in the 1:1 mixing ratio reactor, 9.8-20.9 mL of hydrogen was produced with the highest hydrogen content of 66.8-79.6%. Hydrogen gas production and power density increased from after 12 days of inoculation for the 1:1 mixing ratio reactor. In case of 1:2, 1:3 and 1:4 mixing ratio reactor, the hydrogen gas production was 3.7-7.1 mL and the hydrogen gas content was 5.8-65.8%. The hydrogen gas yield in 1:5, 1:6 and 1:7 ratio reactors, was 0.50-0.69 mL and hydrogen content range was 1.8-7.1%. The mixing ratio was found to be suitable for hydrogen production and inoculation period by mixing ratio up to 1:4.

• Journal of the Korea Organic Resources Recycling Association
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• v.26 no.4
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• pp.53-61
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• 2018

Anaerobic digestion (AD) is one of the most widely used process that can convert the organic fraction of waste activated sludge (WAS) into biogas. However, most researched actual methane yields of anaerobic digester (AD) on lab scale is lower than theoretical ones. Bioelectrochemical, anaerobic digester was used to increase methane yield from waste activated sludge. The influence of anaerobic digestion sludge and raw sludge mixing ratio (3:7, 5:5) on methane yield and organic matter removal efficiency were explored. As a result, when the mixing ratio of bioelectrochemical anaerobic sludge was 5:5 compared with 3:7, the highest methane yields were 294.2 mL $CH_4/L$ (0.63 times increase) and 52.5% (7.5% increase), the bioelectrochemical anaerobic digester(5:5) was more stable in the pH, t otal alkalinity and VFAs, respectively. These results showed that the increase in the mixing ratio of anaerobic digestion sludge was found to be effective for maintaining the stable performance of bioelectrochemical anaerobic digester.

• Journal of Life Science
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• v.34 no.7
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• pp.500-508
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• 2024

Recently, there has been increasing interest in enhancing the indoor air quality, particularly in response to the growing utilization of public facilities. The focus of this study was on assessing the efficacy and safety of an air sterilizer equipped with electrolytic salt catalysts. To that end, we evaluated the antimicrobial activity of the vapor spraying from the air sterilizer and its cytotoxicity in condensed form on human cell lines (HaCaT, BEAS-2B, and THP-1). Against the test organisms, which comprised five bacterial strains (Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium) and one fungal strain (Candida albicans), the air sterilizer exhibited relatively high antimicrobial activities ranging from 10.89 to 73.98% following 1 and 3 hr of vapor spraying, which were notably time-dependent. Importantly, cytotoxicity assessments on human cells indicated no significant harmful effect even at a 1.0% concentration. Comprehensive safety evaluations included morphological observations, gene expression (Bcl-2, Bax) tests, and FACS analysis of intracellular ROS levels. Consistent with previous cytotoxicity findings, these estimates demonstrated no significant changes, highlighting the air sterilizer's safety and antimicrobial activities. In a simulated 20-hr operation within an indoor environment, the air sterilizer not only showed an 89.4% removal of total bacteria but also a 100.0% removal of Escherichia sp. and fungi. This research outlines the potential of the developed electrolytic salt catalyst air sterilizer to effectively remove indoor microbial pollutants without compromising human safety, underscoring the solution that it offers for improving indoor air quality.