Kyu-Jung Chae

Effect of different substrates on the performance, bacterial diversity, and bacterial viability in microbial fuel cells

Four microbial fuel cells (MFCs) were inoculated with anaerobic sludge and fed four different substrates for over one year. The Coulombic efficiency (CE) and power output varied with different substrates, while the bacterial viability was similar. Acetate fed-MFC showed the highest CE (72.3%), followed by butyrate (43.0%), propionate (36.0%) and glucose (15.0%). Glucose resulted in the lowest CE because of its fermentable nature implying its consumption by diverse non-electricity-generating bacteria. 16S rDNA sequencing results indicated phylogenetic diversity in the communities of all anode biofilms, and there was no single dominant bacterial species. A relative abundance of beta-Proteobacteria but an absence of gamma-Proteobacteria was observed in all MFCs except for propionate-fed system in which Firmicutes dominating. The glucose-fed-MFC showed the widest community diversity, resulting in the rapid generation of current without lag time when different substrates were suddenly fed. Geobacter-like species with the most representative Geobactersulfurreducens PCA(T) were integral members of the bacterial community in all MFCs except for the propionate-fed system.

Effects of biofouling on ion transport through cation exchange membranes and microbial fuel cell performance

This study examines the effects of biofouling on the electrochemical properties of cation exchange membranes (CEMs), such as membrane electrical resistance (MER), specific proton conductivity (SC), and ion transport number (t(+)), in addition to on microbial fuel cell (MFC) performance. CEM biofouling using a 15.5 ± 4.6 μm biofilm was found to slightly increase the MER from 15.65 Ω cm(2) (fresh Nafion) to 19.1 Ω cm(2), whereas an increase of almost two times was achieved when the electrolyte was changed from deionized water to an anolyte containing a high cation concentration supporting bacterial growth. The simple physical cleaning of CEMs had little effect on the Coulombic efficiency (CE), whereas replacing a biofouled CEM with new one resulted in considerable increase of up to 59.3%, compared to 45.1% for a biofouled membrane. These results clearly suggest the internal resistance increase of MFC was mainly caused by the sulfonate functional groups of CEM being occupied with cations contained in the anolyte, rather than biofouling itself.

Methanogenesis control by employing various environmental stress conditions in two-chambered microbial fuel cells.

This study examines methanogen activity in microbial fuel cells when exposed to various environmental stresses, such as oxygen, low pH, low temperature, inhibitor (2-bromoethanesulfonate (BES)), and variations in external resistance. Controlling methanogenesis resulted in an increase in Coulombic efficiency (CE) because it was a major cause of electron loss. Methane was mainly produced from aceticlastic methanogenesis, rather than by syntrophic acetate oxidation, with Methanosarcinaceae being the primary contributor. Lowering the resistance from 600 to 50 Omega reduced the methanogenic electron loss by 24%; however, changing the temperature or pH level had little effect. A BES injection was the most potent strategy for the selective inhibition of methanogens without damaging exoelectrogens. The addition of 0.1-0.27 mM BES increased the CE from 35% to 70%. Oxygen stress successfully inhibited methanogens, while slightly suppressing the exoelectrogens, and is believed to be a practical option due to its low operating cost.

A solar-powered microbial electrolysis cell with a platinum catalyst-free cathode to produce hydrogen.

This paper reports successful hydrogen evolution using a dye-sensitized solar cell (DSSC)-powered microbial electrolysis cell (MEC) without a Pt catalyst on the cathode, indicating a solution for the inherent drawbacks of conventional MECs, such as the need for an external bias and catalyst. DSSCs fabricated by assembling a ruthenium dye-loaded TiO(2) film and platinized FTO glass with an I(-)/I(3)(-) redox couple were demonstrated as an alternative bias (V(oc) = 0.65 V). Pt-loaded (0.3 mg Pt/cm(2)) electrodes with a Pt/C nanopowder showed relatively faster hydrogen production than the Pt-free electrodes, particularly at lower voltages. However, once the applied photovoltage exceeded a certain level (0.7 V), platinum did not have any additional effect on hydrogen evolution in the solar-powered MECs: hydrogen conversion efficiency was almost comparable for either the plain (71.3-77.0%) or Pt-loaded carbon felt (79.3-82.0%) at >0.7 V. In particular, the carbon nanopowder-coated electrode without Pt showed significantly enhanced performance compared to the plain electrode, which indicates efficient electrohydrogenesis, even without Pt by enhancing the surface area. As the applied photovoltage was increased, anodic methanogenesis decreased gradually, resulting in increasing hydrogen yield.

Enhanced Coulombic efficiency in glucose-fed microbial fuel cells by reducing metabolite electron losses using dual-anode electrodes.

Glucose-fed microbial fuel cells (MFCs) have displayed low Coulombic efficiency (CE); one reason for a low CE is metabolite generation, causing significant electron loss within MFC systems. In the present study, notable electron loss (15.83%) is observed in glucose-fed MFCs due to residual propionate, a glucose metabolite. In order to enhance the low CE caused by metabolite generation, a dual-anode MFC (DAMFC) is constructed, which are separately enriched by dissimilar substrates (glucose and propionate, respectively) to effectively utilize both glucose and propionate in one-anode chamber. In the DAMFC, propionate ceases to exist as a source of electron loss, and thus the CE increased from 33 ± 6 to 59 ± 4%.

Physicochemical interactions between rhamnolipids and Pseudomonas aeruginosa biofilm layers.

This study investigated the physicochemical interactions between a rhamnolipid biosurfactant and a biofilm layer. A concentration of 300 μg mL(-1) of rhamnolipids, which is around the critical micelle concentration value (240 μg mL(-1)), showed great potential for reducing biofilm. The surface free energy between the rhamnolipids and biofilm layer decreased, as did the negative surface charge, due to the removal of negatively charged humic-like, protein-like, and fulvic acid-like substances. The carbohydrate and protein concentrations composed of extracellular polymeric substances decreased by 31.6% and 79.6%, respectively, at a rhamnolipid concentration of 300 μg mL(-1). In particular, rhamnolipids can interact with proteins, leading to a reduction of the N source and amide groups on the membrane. For carbohydrates, the component ratio of glucosamine was decreased, but the levels of glucose and mannose that form the majority of the carbohydrates remained unchanged. To our knowledge, the present study is the first attempt at studying the interactions of the two phases of rhamnolipids and the biofilm layer, and as such is expected to clarify the mechanism by which rhamnolipids lead to a reduction in biofilm.

Spatial distribution and viability of nitrifying, denitrifying and ANAMMOX bacteria in biofilms of sponge media retrieved from a full-scale biological nutrient removal plant

The spatial distribution and activities of nitrifying and denitrifying bacteria in sponge media were investigated using diverse tools, because understanding of in situ microbial condition of sponge phase is critical for the successful design and operation of sponge media process. The bacterial consortia within the media was composed of diverse groups including a 14.5% Nitrosomonas spp.—like ammonia oxidizing bacteria (AOB), 12.5% Nitrobacter spp.—like nitrite oxidizing bacteria (NOB), 2.0% anaerobic ammonium-oxidizing (ANAMMOX) bacteria and 71.0% other bacteria. The biofilm appeared to be most dense in the relatively outer region of the media and gradually decreased with depth, but bacterial viabilities showed space-independent feature. The fluorescent in situ hybridization results revealed that AOB and NOB co-existed in similar quantities on the side fragments of the media, which was reasonably supported by the microelectrode measurements showing the concomitant oxidation of NH4+ and production of NO3− in this zone. However, a significantly higher fraction of AOB was observed in the center than side fragment. As with the overall biofilm density profile, the denitrifying bacteria were also more abundant on the side than in the center fragments. ANAMMOX bacteria detected throughout the entire depth offer another advantage for the removal of nitrogen by simultaneously converting NH4+ and NO2− to nitrogen gas.

Heavy metal removal from aqueous solutions using engineered magnetic biochars derived from waste marine macro-algal biomass

Despite the excellent sorption ability of biochar for heavy metals, it is difficult to separate and reuse after adsorption when applied to wastewater treatment process. To overcome these drawbacks, we developed an engineered magnetic biochar by pyrolyzing waste marine macro-algae as a feedstock, and we doped iron oxide particles (e.g., magnetite, maghemite) to impart magnetism. The physicochemical characteristics and adsorption properties of the biochar were evaluated. When compared to conventional pinewood sawdust biochar, the waste marine algae-based magnetic biochar exhibited a greater potential to remove heavy metals despite having a lower surface area (0.97m2/g for kelp magnetic biochar and 63.33m2/g for hijikia magnetic biochar). Although magnetic biochar could be effectively separated from the solution, however, the magnetization of the biochar partially reduced its heavy metal adsorption efficiency due to the biochars surface pores becoming plugged with iron oxide particles. Therefore, it is vital to determine the optimum amount of iron doping that maximizes the biochars separation without sacrificing its heavy metal adsorption efficiency. The optimum concentration of the iron loading solution for the magnetic biochar was determined to be 0.025-0.05mol/L. The magnetic biochars heavy metal adsorption capability is considerably higher than that of other types of biochar reported previously. Further, it demonstrated a high selectivity for copper, showing two-fold greater removal (69.37mg/g for kelp magnetic biochar and 63.52mg/g for hijikia magnetic biochar) than zinc and cadmium. This high heavy metal removal performance can likely be attributed to the abundant presence of various oxygen-containing functional groups (COOH and OH) on the magnetic biochar, which serve as potential adsorption sites for heavy metals. The unique features of its high heavy metal removal performance and easy separation suggest that the magnetic algae biochar can potentially be applied in diverse areas that require biosorbents for pollutant removal.

Citric acid and ethylene diamine tetra-acetic acid as effective washing agents to treat sewage sludge for agricultural reuse.

This paper presents the effects of different concentrations of citric acid (CA) and ethylene diamine tetra-acetic acid (EDTA) when used as additive reagents for the treatment of sewage sludge for agricultural use. Herein, both the retention of nutrients and removal of metals from the sewage sludge are examined. The average removal rate for the metals after treatment by CA decreased in the order Cu>Pb>Cd>Cr>Zn, while the rates after treatment by EDTA decreased in the order of Pb>Cu>Cr>Cd>Zn. After treatment with CA and EDTA, total nitrogen and total phosphorus concentrations in the sludge decreased, while the content of available nitrogen and Olsen-P increased. In addition, a multi-criteria analysis model-fuzzy analytic network process method (with 3 main factors and 12 assessment sub-factors) was adopted to evaluate the effectiveness of different treatment methods. The results showed that the optimal CA and EDTA concentrations for sewage sludge treatment were 0.60 and 0.125 mol/L, respectively.

Nitrification and denitrification using biofilters packed with sulfur and limestone at a pilot-scale municipal wastewater treatment plant.

A pilot-scale municipal wastewater treatment plant composed of a fixed film activated sludge (IFAS) system with sulfur–limestone autotrophic denitrification (SLAD) was operated for a year and the influence of different operational factors was investigated. Nitrification efficiency was found to be above 91% at temperatures above 25°C even at short hydraulic residence times (HRTs), but declined to 51±2% when the temperature dropped to 22±3°C. The minimum HRT (HRTmin) to achieve nitrification efficiency>90% was found to be 12 h at temperatures above 25°C. Denitrification efficiencies were found to be 89% and 79% at a nitrate loading of 0.36 kg NO -N m−3 d−1 and at 0.18 kg NO -N m−3 d−1, respectively. The minimum empty bed residence time (EBRT) to achieve denitrification efficiency above 80% without methanol addition was 3 h at a nitrate loading rate of 0.27–0.38 kg NO -N m−3 d−1. The amount of nitrate removed as a function of the sulfate formed was found to be 0.188 g NO -N/g SO . The nitrate load removed by the biofilter as a function of the alkalinity consumed was found to be very close to the theoretical stoichiometric value. The application of the pilot plant was proven to be feasible and the performance of the SLAD system, especially with respect to the minimum EBRT to achieve denitrification efficiency above 80%, the maximum denitrification rate and performance at temperatures below 10°C. To achieve a nitrification efficiency above 90% in the IFAS system, temperature changes and the minimum HRT were found to be the most influential operational parameters.