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Sustainable aviation fuels (SAFs) can contribute reduce greenhouse gas emissions compared to conventional fuel. With the increasing SAFs demand, various generations of resources have been shifted from the 1st generation (oil crops), the 2nd generation (agricultural waste), to the 3rd generation (microalgae). Microalgae are the most suitable feedstock for jet biofuel production than other resources because of their productivity and capability to capture carbon dioxide. However, microalgae-based biofuel has a limitation of high freezing point. Recently, a jet biofuel derived from Euglena wax ester has been paying attention due to its low freezing point. Challenges still remain to enhance production yields in both upstream and downstream processes. Studies on downstream processes as well as techno-economic analysis on biofuel production using Euglena are highly limited to date. Economic aspects for the biofuel production will be ensured via valorization of industrial byproducts such as food wastes.

Nitrogen removal in saline wastewater is a challenge of the anaerobic ammonium oxidation (anammox) process, which is dominated by freshwater anammox bacteria (FAB). Candidatus Brocadia and Candidatus Jettenia, the most widely used FABs, have been separately applied and evaluated for their ability to treat saline wastewater. To understand the effect of salinity on nitrogen removal capability when they present together in an anammox granule, we compared two anammox granules: GRN1 was evenly dominated by Ca. Brocadia (42 %) and Ca. Jettenia (43 %), while GRN2 was dominated with mostly Ca. Brocadia (90 %) and a small amount of Ca. Jettenia (1 %). Each granule was inoculated into a continuous column reactor to treat artificial wastewater containing 150 mg NH

Single-stage deammonification (SSD) processes have been successfully operated using the step-feeding strategy to treat high-strength NH

Euglena gracilis (E. gracilis) accumulates paramylon, an immune-functional beta-glucan that can be used as a functional food. Paramylon production is strongly affected by the organic carbon source and the initial pH conditions. Food processing byproducts have attracted attention for microalgal cultivation because of their low cost and abundance of nutrients, including carbon and nitrogen. We investigated the optimal carbon source and its concentration for efficient paramylon production. A spent tomato byproduct (STB) generated from a tomato processing plant was applied for biomass and paramylon production from E. gracilis with respect to the initial pH condition. The highest paramylon concentration (1.2 g L−1) and content (58.2%) were observed with 15 g L−1 glucose. The biomass production increased when STB was used as compared with that when a synthetic medium was used (1.6-fold higher at pH 3 and 2-fold higher at pH 8). The optimal initial pH was determined according to the maximum production of biomass and paramylon. Upcycling the food processing byproduct, STB, can contribute not only to cost reduction of the biorefinery process using E. gracilis but also to environmental remediation by removing organic carbon and nitrogen from the byproducts.

Anaerobic ammonia oxidation (Anammox) is an innovative technology for cost-efficient nitrogen removal without intensive aeration. However, effective control of the competition between nitrite oxidizing bacteria (X

Euglena gracilis produces paramylon, which is a feedstock for high-value functional foods and nutritional supplements. The enhancement of paramylon productivity is a critical challenge. Microalgae growth-promoting bacteria (MGPB) can improve microalgal productivity, however, the MGPB for E. gracilis remain unclear. This study isolated bacteria capable of enhancing E. gracilis growth and paramylon production under mixotrophic conditions. Enterobacter sp. CA3 and Emticicia sp. CN5 were isolated from E. gracilis grown with sewage-effluent bacteria under mixotrophic conditions at pH 4.5 or 7.5, respectively. In a 7-day E. gracilis mixotrophic culture with glucose, CA3 increased E. gracilis biomass and paramylon production 1.8-fold and 3.5-fold, respectively (at pH 4.5), or 1.9-fold and 3.5-fold, respectively (at pH 7.5). CN5 increased E. gracilis biomass and paramylon production 2.0-fold and 4.1-fold, respectively (at pH 7.5). However, the strains did not show such effects on E. gracilis under autotrophic conditions without glucose. The results suggest that CA3 and CN5 promoted both E. gracilis growth and paramylon production under mixotrophic conditions with glucose at pH 4.5 and 7.5 (CA3) or pH 7.5 (CN5). This study also provides an isolation method for E. gracilis MGPB that enables the construction of an effective E. gracilis–MGPB-association system for increasing the paramylon yield of E. gracilis.

Large amounts of food processing byproducts (FPBs) are generated from food manufacturing industries, the second-largest portion of food waste generation. FPBs may require additional cost for post-treatment otherwise cause environmental contamination. Valorization of FPBs into food ingredients by microalgae cultivation can save a high cost for organic carbon sources and nutrients from medium cost. This study reviews FPBs generation categorized by industry and traditional disposal. In contrast with the low-value production, FPBs utilization as the nutrient-abundant medium for microalgae can lead to high-value production. Due to the complex composition in FPBs, various pretreatment methods have been applied to extract the desired compounds and medium preparation. Using the FPB-based medium resulted in cost reduction and a productivity enhancement in previous literature. Although there are still challenges to overcome to achieve economic viability and environmental sustainability, the microalgal transformation of FPBs is attractive for functional food ingredients production.

A flat-panel air-cathode microbial fuel cell (FA-MFC) is known to overcome the low conductivity and biodegradability of domestic wastewater. This study evaluated the normalized energy recovery (NER) based on the volume of wastewater treated (NERV) and chemical oxygen demand (COD) removal (NERCOD) using FA-MFCs with three anode spacing conditions and different flow rates (within a hydraulic retention time of 30 min). Generation of current was similar (11.7 ± 0.5 mA) at different spacings; however, COD removal was affected by the flow rates. The NERV for both acetate and domestic wastewater showed good agreements with the flow rates in all anode spacing conditions. The NERCOD results were negatively correlated with the COD removal rates, independent of the anode spacing. The FA-MFCs yielded an NERCOD of 0.22 kWh/kg-COD from extremely low-strength domestic wastewater (150 mg-COD/L). The FA-MFC has a significant potential as an energy-sustainable wastewater treatment technology.

The present operation and future expansion feasibility of renewable energy at 30 business locations in 12 EBFs in Busan at South Korea were investigated. Currently, 197 GWh/yr of electric power is produced from renewable energies at the EBFs. The largest energy source, except waste heat, is biogas (154 GWh/yr), followed by solar photovoltaic (5.56 KWh/yr) at 11 business locations. A field survey revealed potential production by PV, wind power, and small hydropower of 8.2, 6.2 and 0.751 GWh/yr with associated GHG mitigation of 3620, 2737, and 332 tCO2/yr, respectively, at 26 business locations. A cost-benefit analysis demonstrates that the use of governmental support or private investment could be the most efficient way to introduce renewable energies to EBFs.

Two Sb(III)-oxidizing bacteria were isolated from Sb(III)-contaminated soil. By analyzing the 16S rRNA gene, two isolated strains were designated Shinella sp. NLS1 and Ensifer sp. NLS4. Both strains could oxidize Sb(III) to produce Sb(V) under nutrient-limited conditions. Kinetic studies indicated the NLS1 Sb(III) oxidation rate (Vmax = 0.28 μM min−1, Km = 279.13 μM) was comparable to that of NLS4 (Vmax = 0.32 μM min−1, Km = 248.43 μM). NLS1 could also perform aerobic As(III) oxidation and simultaneous oxidation of Sb(III) and As(III). NLS4 was able to perform Sb(III) oxidation under anaerobic conditions with nitrate as an electron acceptor. NLS1 possesses the aioA gene, which might function as both arsenite and antimonite oxidase, whereas strain NLS4 does not. This implies that Sb(III) oxidation in strains NLS1 and NLS4 occurred through two different pathways. This study demonstrates the potential of both isolates for bioremediation of Sb-contaminated sites.

Microbial fuel cells (MFCs) can treat organic compounds from domestic wastewater without aeration, but an additional procedure is required to remove nitrogen. This study developed a flat-panel air-cathode MFC (FA-MFC) that was comprised of five MFC units connected in series and operated to remove organic and nitrogen compounds from domestic wastewater with a short hydraulic retention time (HRT) of 2.5 h. During eight months of operation, the removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN) increased, reaching 85% and 94%, respectively, and the effluent COD and TN concentrations were 20.7 ± 2.5 mg/L and 1.7 ± 0.1 mg/L, respectively. The greatest removals of COD and TN were in the first and second unit (0.62 kg-N/m 3 /d of TN removal rate). The FA-MFC system allowed simultaneous removals of COD and TN from domestic wastewater, although it led to minimal power output (6.3 W/m 3 in the first unit). Because any abiotic ammonia loss was not found under the supplied potential of ∼1.1 V at a short HRT of 30 min, the biological nitrogen removal was thought as a dominant mechanism for TN removal in the FA-MFCs. Microbial community analysis revealed that, near the cathode, Nitrosomonas -like strains contributed to nitrification and Nitratireductor -like strains led to denitrification. Acidovorax -like strains, known for their metabolic diversity, were ubiquitous and appeared to contribute to organics and nitrogen removal in anode and cathode biofilms. This study provides proof of concept that the FA-MFC system has a promise for energy sustainable wastewater treatment.

A microbial fuel cell (MFC) with multiwall carbon nanotube (CNT) coated stainless steel mesh (SSM) coated anode (S-MFC) was operated with a filtrate generated by the fermentation of municipal primary sludge. The S-MFC's maximum power density (MPD: 69.8–164.9 W/m3) and energy recovery (ER: 0.15–0.60 kWh/kgCOD) were 7–21 times higher than those (3.8–27.3 W/m3 and 0.01–0.11 kWh/kgCOD) of MFC with a graphite felt as an anode (G-MFC). The microbial communities of S- and G-MFCs varied slightly depending on the electrode material. Chloroflexi (23.5%) was dominant in S-MFC, and Proteobacteria (25.3%) in G-MFC. Fermenting bacteria such as Rhodanobacter lindaniclasticus and Anaerolineaceae bacterium were dominated by continuous non-electrochemically active bacteria invasion because the actual fermentation filtrate was directly utilized as the substrate. Nevertheless, the CNT-coated SSM anode and the fermentation filtrate of primary sludge improved the power generation in MFC, which demonstrates the significant potential of this sidestream process for sludge treatment.

Microbial electrochemical technology (MET) that can harvest electricity/valuable materials and enhance the efficiency of conventional biological processes through the redox reaction of organic/inorganic compounds has attracted considerable attention. MET-based anaerobic digestion (AD) systems treating swine manure were operated at different applied voltages (0.1, 0.3, 0.5, 0.7, and 0.9 V) and temperatures (25, 35, and 45 °C). Among the MET-based AD systems with different applied voltages at 35 °C, M4 at 0.7 V showed the highest methane production (2.96 m3-CH4/m3) and methane yield (0.64 m3-CH4/kg-VS). The methane production and yield increased with increasing temperature at an applied voltage of 0.7 V. Nevertheless, the MET-based AD systems (LM at 25 °C and 0.7V) showed competitive AD performance (2.33 m3-CH4/m3 and 0.53 m3-CH4/VS) compared with the conventional AD system (35 °C). The microbial community was affected by the applied voltage and temperature, and hydrogenotrophic methanogens such as M. flavescens, M. hungatei, and M. thermautotrophicus were mainly responsible for methane production in MET-based AD systems. Therefore, the methane production can be enhanced by an applied voltage or by direct interspecies electron transfer because M. flavescens and M. thermautotrophicus were especially predominant in cathode of MET-based AD systems. The MET-based AD systems can help enhance biogas production from swine manure with no significant change in methane content. Furthermore, MET-based AD systems will be a promising AD system through low material development and the optimal operation.

The removal of organics and ammonium from domestic wastewater was successfully achieved by a flat-panel air-cathode microbial fuel cell (FA-MFC). To elucidate the reason for complete ammonium removal in the single-chamber MFCs, microbial communities were analyzed in biofilms on the surface of each anode, separator, and cathode of separator-electrode assemblies (SEAs). The spatial distribution of bacterial families related to the nitrogen cycle varied based on local conditions. Since oxygen diffusing from the air-cathode created a locally aerobic condition, ammonia-oxidizing bacteria (AOB) Nitrosomonadacea and nitrite-oxidizing bacteria (NOB) Nitrospiraceae were present near the cathode. NOB (~12.1%) was more abundant than AOB (~4.4%), suggesting that the nitrate produced by NOB may be reduced back to nitrite by heterotrophic denitrifiers such as Rhodocyclaceae (~21.7%) and Comamonadaceae (~5%) in the anoxic zone close to the NOB layer. Near that zone, the "nitrite loop" also substantially enriched two nitrite-reducing bacterial families: Ignavibacteriaceae (~18.1%), facultative heterotrophs, and Brocadiaceae (~11.2%), anaerobic ammonium oxidizing autotrophs. A larger inner area of biofilm contained abundant heterotrophic denitrifiers and fermentation bacteria. These results indicate that the large-surface SEA of FA-MFC allows counter-diffusion between substrates and oxygen, resulting in interactions of bacteria involved in the nitrogen cycle for complete ammonium removal.

Removal of nitrogen compounds is particularly important domestic wastewater treatment. Our recent study reported the successful removal of nitrogen in single-chamber electroactive biofilm reactors (EBRs) under aeration-free conditions. We hypothesized that the oxygen diffused from the air-cathode is a key factor in the removal of nitrogen in the EBR. If so, the effect of the penetrated oxygen would vary according to the ratio of the air-cathode surface area to the reactor volume (AV ratio) and the hydraulic retention time (HRT). In this study, single-chamber EBRs with three different AV ratios: 125 m2/m3 (EBR-125), 250 m2/m3 (EBR-250), and 500 m2/m3 (EBR-500) were evaluated for the removal of nitrogen under different HRTs of 0.5–6 h. The higher the AV ratio, the greater the increase in nitrification. The total nitrogen (TN) removal efficiency of EBR-125 and EBR-250 decreased as the HRT decreased, while that of EBR-500 increased. EBR-250 showed the highest TN removal (62.0%) with well-balanced nitrification (83.9%) and denitrification (75.1%) at an HRT of 6 h. However, EBR-500 appeared to be superior for practical application because it showed a comparable TN removal (59%) at a substantially short HRT of 1 h. The microbial communities that were involved in the nitrogen cycle varied according to whether the biofilms were located on the anodes, separators, and cathodes but were similar among EBRs with different AV ratios. Nitrifying bacteria were detected in the biofilms that were presented on the cathodes (approximately 7.8% of the total phylotypes), while denitrifying bacteria were mainly found in biofilm that were located on the anodes (approximately 23.3%). Anammox bacteria were also detected on the anode (approximately 3.7%) and in the separator biofilms (approximately 1.9%) of all the EBRs. These results suggest that both the A/V ratio and the HRT could affect the counter diffusion of substrates (NH4+ and organic compounds) and oxygen in the biofilms and allow interactions between a diversity of microorganisms for the successful removal of nitrogen in EBRs. These findings are expected to aid in the development of new applications using EBR for energy-saving wastewater treatment.

The bioremediation of tetrachloroethene (perchloroethene; PCE) contaminated sites generally requires a supply of some fermentable organic substrates as an electron donor. On the other hand, organic substrates can induce the massive growth of microorganisms around the injection wells, which can foul the contaminated subsurface environment. In this study, PCE dechlorination to ethene was performed in a microbial electrochemical system (MES) using the electrode (a cathode polarized at −500 mV vs. standard hydrogen electrode) as the electron donor. Denaturing gel gradient electrophoresis and pyrosequencing revealed a variety of non-Dehalococcoides bacteria dominant in MES, such as Acinetobacter sp. (25.7 % for AS1 in suspension of M3), Rhodopseudomonas sp. (10.5 % for AE1 and 10.1 % for AE2 in anodic biofilm of M3), Pseudomonas aeruginosa (22.4 % for BS1 in suspension of M4), and Enterobacter sp. (21.7 % for BE1 in anodic biofilm of M4) which are capable of electron transfer, hydrogen production and dechlorination. The Dehalococcoides group, however, was not detected in this system. Therefore, these results suggest that a range of bacterial species outside the Dehalococcoides can play an important role in the microbial electrochemical dechlorination process, which may lead to innovative bioremediation technology.

Arsenic and nitrate contaminations in the soil and groundwater have urged the scientific community to explore suitable technologies for treatment of both contaminants. This study reports, for the first time, a novel application of bioelectrochemical systems for coupling As detoxification at the anode and denitrification at the cathode. A similar As(III) oxidation efficiency was achieved when anode potential was controlled by a potentiostat or a direct current (DC) power supply. However, a slightly lower nitrate reduction rate was obtained in reactors using DC power supply during simultaneous operation of nitrate reduction and As(III) oxidation. Microbial community analysis by denaturing gradient gel electrophoresis indicated the presence of some autotrophic As(III)-oxidizing bacteria, including Achromobacter spp., Ensifer spp., and Sinorhizobium spp., that can flexibly switch their original metabolism of using oxygen as sole electron acceptor to a new metabolism mode of using solid-state anode as sole electron acceptor driving for As(III) oxidation under anaerobic conditions. Although further research is required for validating their applicability, bioelectrochemical systems represent a brilliant technology for remediation of groundwater contaminated with nitrate and/or arsenite.

Selenium is said to be multifaceted element because it is essential at a low concentration but very toxic at an elevated level. For the purpose of screening a potential microorganism for selenite bioremediation, we isolated a bacterium, named strain THL1, which could perform both heterotrophic selenite reduction, using organic carbons such as acetate, lactate, propionate, and butyrate as electron donors under microaerobic condition, and electrotrophic selenite reduction, using an electrode polarized at -0.3V (vs. standard hydrogen electrode) as the sole electron donor under anaerobic condition. This bacterium determined to be a new strain of the genus Cronobacter, could remove selenite with an efficiency of up to 100%. This study is the first demonstration on a pure culture could take up electrons from an electrode to perform selenite reduction. The selenium nanoparticles produced by microbial selenite reduction might be considered for recovery and use in the nanotechnology industry.

Recently, bioelectrochemical systems have been demonstrated as advantageous for denitrification. Here, we investigated the nitrate reduction rate and bacterial community on cathodes at different cathode potentials [−300, −500, −700, and −900 mV vs. standard hydrogen electrode (SHE)] in a two-chamber microbial electrochemical denitrification system and effects of sulfate, a common nitrate co-contaminant, on denitrification efficiency. The results indicated that the highest nitrate reduction rates (3.5 mg L−1 days−1) were obtained at a cathode potential of −700 mV, regardless of sulfate presence, while a lower rate was observed at a more negative cathode potential (−900 mV). Notably, although sulfate ions generally inhibited nitrate reduction, this effect was absent at a cathode potential of −700 mV. Polymerase chain reaction–denaturing gradient gel electrophoresis revealed that bacterial communities on the graphite-felt cathode were significantly affected by the cathode potential change and sulfate presence. Shinella-like and Alicycliphilus-like bacterial species were exclusively observed on cathodes in reactors without sulfate. Ochrobactrum-like and Sinorhizobium-like bacterial species, which persisted at different cathode potentials irrespective of sulfate presence, were shown to contribute to bioelectrochemical denitrification. This study suggested that a cathode potential of around −700 mV versus SHE would ensure optimal nitrate reduction rate and counteract inhibitory effects of sulfate. Additionally, sulfate presence considerably affects denitrification efficiency and microbial community of microbial electrochemical denitrification systems.

Euglena gracilis is a promising microalga containing valuable intracellular components such as paramylon with notable immune-functionality. For economic paramylon production, industrial byproducts can be considered as low-priced media. In this study, corn steep liquor and brewers' spent grain were employed as cost-effective media for paramylon production. The paramylon content and yield for E. gracilis cultivated using the corn steep liquor (46.3% w/w and 0.17 g/g) were higher than those using the brewer's spent grain (32.3% w/w and 0.11 g/g). Under the optimized cultural condition of 5% diluted corn steep liquor at an initial pH of 3.5 and temperature of 25 °C, E. gracilis showed the competitive paramylon content (54.2%) and productivity (0.45 g/L/d) compared to those of other studies even without an additional carbon source. This study is the first report on applicability of brewers' spent grain to bioproduction of E. gracilis but it needs further investigation for productivity enhancement. Thus we suggest using corn steep liquor as a sole substrate for E. gracilis is a promising way which shows competent productivity even without any additional substrate such as glucose or fructose. Application of the corn steep liquor as an industrial byproduct can be a successful strategy for efficient and economic paramylon production.

A closed-circuit microbial fuel cell (C-MFC) was operated to investigate the electron flux under fed-batch mode, and the results were compared to those of open-circuit MFC (O-MFC) and a fermentation reactor (F-reactor). The current was the largest electron sink (52.7 % of influent SCOD) in C-MFC, whereas biomass and methane gas were the most significant electron sinks in O-MFC and F-reactor. Interestingly, some of the unknown sink may have accumulated in the electrode of O-MFC. Principal component analysis based on gradient gel electrophoresis profiles showed that the microbial communities were significantly affected by the growth conditions and the presence of electrode, regardless of the circuit connection. Therefore, the electrode and circuit mode might help to control the amount of biomass and enhance the MFC performance.

Single-chamber microbial fuel cells (MFCs) using domestic wastewater (DWW) and milk processing wastewater (MWW) were operated at different organic loading rates (OLRs). The maximum power density (PDmax) and OLR (readily biodegradable COD [RBCOD] and soluble COD [SCOD]) followed the Lineweaver-Burk equation in all influents. The coefficients of determination were 0.9209 and 0.9975 for SCOD and RBCOD, respectively. OLR based on RBCOD showed better power generation function than that based on SCOD. PDmax (2.9-12.2 W/m(3)) in DWW was lower than that (6.9-24.9 W/m(3)) in MWW but the net energy recovery (kWh/kg-SCOD(removed)) in DWW (0.542-1.108) was larger than that in MWW (0.322-0.602). This was attributed to the higher ratio of RBCOD/SCOD (0.44) and the lower values of RBCOD (40 mg/L) in DWW, compared to RBOCD/SCOD (0.11) and RBCOD (110 mg/L) in MWW. Therefore, RBCOD is an important indicator for estimating power generation.

This study aims to enrich Sb(V)-reducing bacterial communities from Sb-contaminated soils using various electron donors for bioremediation of Sb-contaminated sites and recovery of Sb from wastewater. When the organic electron donors were used, Sb(V) reduction rates were 2-24 times faster but electron recoveries were 24-59% lower compared to the culture using inorganic electron donor. The morphological crystallizations of the antimony-reduced precipitates were completely different depending on the electron donor. Different microbial populations were enriched with various electron donors but most commonly, only Proteobacteria and Firmicutes phyla were enriched from a diversified soil microbial community. Geobacter sp. seemed to be an important bacterium in organic electron donors-fed cultures whereas an unclassified Rhodocyclaceae was dominant in inorganic electron donor-fed cultures. The results indicated that organic electron donors especially sugar groups were preferable options to obtain rapid Sb(V)-reduction whereas inorganic electron donor like H2 was better option to achieve high electron recovery.

Single chamber MFC (SMFC) consisted of two separator-electrode assemblies (SEA) using low-pH distillery wastewater (DW) was operated under continuous mode. The electricity generation and microbial community were analyzed according to the external resistance (Rext; 0.1, 0.5, 1, and 5 kΩ). The two SEAs exhibited different electricity generations, despite sharing the same anodic chamber. The SMFC showed the largest maximum power density (PDmax) of 3.7 W/m(3) (SEA 1) and 12.9 W/m(3) (SEA 2) at 5 kΩ. These results demonstrated that low-pH wastewater could be sufficiently used as fuels for electricity generation. Pyrosequencing analysis showed that microbial communities at the phylum level were significantly different according to the Rext. The communities of SEA 1 were slightly different from those of SEA 2. In both SEAs, Firmicutes (>45%) were the most dominant at 0.1 kΩ, while Firmicutes (>34%) and Caldiserica (>34%) were dominant at 5 kΩ. Caldiserica sp. might significantly contribute to electricity generation under low-pH and high-Rext.

Multi-baffled single chamber microbial fuel cells (MBSC-MFCs) were operated with different wastewater sources and organic loading rates (OLRs). As the OLRs increased, the maximum power density (Pmax) in MFCs with an identical influent source also increased. In the case of using a different influent source, Pmax was different even though the MFC had been operated with the similar OLR or hydraulic retention time. Therefore, power generation would be affected concurrently by a range of factors, including the substrate type.

A key criterion in microbial fuel cell (MFC) design is that the bio-electrochemical reaction between bacteria and the bulk solution should occur evenly on the electrode surface in order to improve electricity generation. However, experimental optimization of MFC design over a wide range of conditions is limited. Computational fluid dynamics (CFD) technology makes it possible to evaluate physicochemical phenomena such as fluid flows, mass transfer and chemical reaction, which can assist in system optimization. Twelve MFCs (M1–M12) with different internal structures were subjected to CFD analysis. The dead (DS) and working spaces (WS) of the anode compartment were calculated. The flow patterns of the anodic fluid varied according to the internal structures. The WS where the bio-electrochemical reaction can actually occur varied over the range of 0.14–0.57 m2. Based on the above results, the power densities were estimated under the assumption that a monolayer biofilm was formed on the electrode. M11, with 18 rectangular-type internal structures, showed the largest WS of 0.57 m2 and a theoretical maximum power density of 0.54 W/m2. Although the optimization of the MFC configuration with only CFD analysis remains limited, the present study results are expected to provide fundamental data for MFC optimization.

In order to confirm the effects of the low conductivity and biodegradability of wastewater, flat-panel air-cathode microbial fuel cells (FA-MFCs) were operated by supplying substrates with different volume ratios of domestic wastewater mixed with an artificial medium: the artificial medium only, 25% wastewater, 50% wastewater, 75% wastewater, 100% of wastewater with 500mg-COD/L by adding acetate, and raw domestic wastewater (230mg-COD/L). With the increase of wastewater ratio, the maximum power density and organic removal efficiency decreased from 187 to 60W/m3 and 51.5 to 37.4%, respectively, but the Coulombic efficiency was maintained in the range of 18.0-18.9%. The FA-MFCs could maintain their low internal resistances and overcome the decreasing conductivity. The acetate concentration was more important than the total organics for power production. This study suggests that the FA-MFC configuration has great applicability for practical applications when supplied by domestic wastewater with low conductivity and biodegradability.

The purpose of this study was to identify bacteria that can perform As(III) oxidation for environmental bioremediation. Two bacterial strains, named JHS3 and JHW3, which can autotrophically oxidize As(III)–As(V) with oxygen as an electron acceptor, were isolated from soil and water samples collected in the vicinity of an arsenic-contaminated site. According to 16S ribosomal RNA sequence analysis, both strains belong to the ɤ-Proteobacteria class and share 99% sequence identity with previously described strains. JHS3 appears to be a new strain of the Acinetobacter genus, whereas JHW3 is likely to be a novel strain of the Klebsiella genus. Both strains possess the aioA gene encoding an arsenite oxidase and are capable of chemolithoautotrophic growth in the presence of As(III) up to 10 mM as a primary electron donor. Cell growth and As(III) oxidation rate of both strains were significantly enhanced during cultivation under heterotrophic conditions. Under anaerobic conditions, only strain JHW3 oxidized As(III) using nitrate or a solid-state electrode of a bioelectrochemical system as a terminal electron acceptor. Kinetic studies of As(III) oxidation under aerobic condition demonstrated a higher V max and K m from strain JHW3 than strain JHS3. This study indicated the potential application of strain JHW3 for remediation of subsurface environments contaminated with arsenic.

Nitrate contamination in aquifers has posed human health under high risk because people still rely on groundwater withdrawn from aquifers as drinking water and running water sources. These days, bioelectrochemical technologies have shown a great number of benefits for nitrate remediation via autotrophic denitrification in groundwater. This study tested the working possibility of a denitrifying biocathode when installed into a simulated aquifer. The reactors were filled with sand and synthetic groundwater at various ratios (10, 50, and 100 %) to clarify the effect of various biocathode states (not-buried, half-buried, and fully buried) on nitrate reduction rate and microbial communities. Decreases in specific nitrate reduction rates were found to be correlated with increases in sand/medium ratios. A specific nitrate reduction rate of 322.6 mg m(-2) day(-1) was obtained when the biocathode was fully buried in an aquifer. Microbial community analysis revealed slight differences in the microbial communities of biocathodes at various sand/medium ratios. Various coccus- and rod-shaped bacteria were found to contribute to bioelectrochemical denitrification including Thiobacillus spp. and Paracoccus spp. This study demonstrated that the denitrifying biocathode could work effectively in a saturated aquifer and confirmed the feasibility of in situ application of microbial electrochemical denitrification technology.

Nitrate contamination of water environments can create serious problems such as eutrophication of rivers. Conventional biological processes for nitrate removal by heterotrophic denitrification often need additional organic substrates as carbon sources and electron donors. We tried to accelerate biological denitrification by using bioelectrochemical reactor (BER) in which electrode works as an electron donor. Denitrification activity of 8 environmental samples from various sediments, soils, groundwaters, and sludges were tested to establish an efficient enrichment culture for BER. The established enrichment culture from a soil sample showed stable denitrification activity without any nitrite accumulation. Microbial community analysis by using PCR-DGGE method revealed that dominant denitrifiers in the enrichment culture were Pantoea sp., Cronobacter sakazakii, and Castellaniella defragrans. Denitrification rate (0.08 kg/m 3 ·day) of the enrichment culture in BER with electrode poised at -0.5 V (vs Ag/AgCl) was higher than that (2.1×10 -2 kg/m 3 ·day) of BER without any poised potential. This results suggested that biological denitrification would be improved by supplying potential throughout electrode in BER. Further research using BER without any organic substrate addition is needed to apply this system for bioremediation of water and wastewater contaminated by nitrate.

Microbial fuel cells (MFCs) can convert chemical energy to electricity using microbes as catalysts and a variety of organic wastewaters as substrates. However, electron loss occurs when fermentable substrates are used because fermentation bacteria and methanogens are involved in electron flow from the substrates to electricity. In this study, MFCs using glucose (G-MFC), propionate (P-MFC), butyrate (B-MFC), acetate (A-MFC), and a mix (M-MFC, glucose:propionate:butyrate:acetate = 1:1:1:1) were operated in batch mode. The metabolites and microbial communities were analyzed. The current was the largest electron sink in M-, G-, B-, and A-MFCs; the initial chemical oxygen demands (COD ini ) involved in current production were 60.1% for M-MFC, 52.7% for G-MFC, 56.1% for B-MFC, and 68.3% for A-MFC. Most of the glucose was converted to propionate (40.6% of COD ini ) and acetate (21.4% of COD ini ) through lactate (80.3% of COD ini ) and butyrate (6.1% of COD ini ). However, an unknown source (62.0% of COD ini ) and the current (34.5% of COD ini ) were the largest and second-largest electron sinks in P-MFC. Methane gas was only detected at levels of more than 10% in G- and M-MFCs, meaning that electrochemically active bacteria (EAB) could out-compete acetoclastic methanogens. The microbial communities were different for fermentable and non-fermentable substrate-fed MFCs. Probably, bacteria related to Lactococcus spp. found in G-MFCs with fermentable substrates would be involved in both fermentation and electricity generation. Acinetobacter -like species, and Rhodobacter -like species detected in all the MFCs would be involved in oxidation of organic compounds and electricity generation.

A submerged type microbial fuel cell (MFC) system, which consisted of six readily exchangeable air–cathode MFCs, was evaluated for continuous treatment of low-strength domestic wastewater. When supplied with synthetic wastewater (COD 100 mg/L), the system showed increasing maximum power densities from 191 to 754 mW/m 2 as COD loading rates increased (0.20–0.40 kg/m 3 /day). COD removal efficiencies decreased with increased COD loading rates but the effluent COD concentrations met the relevant effluent quality standard (COD Mn 20 mg/L) at all conditions. The system was then operated with domestic wastewater (c.a. 100 mg COD/L) at 0.32 and 0.43 kg/m 3 /day. The system showed much lower power densities (116–149 mW/m 2 ) at both loading rates, compared to synthetic wastewater. Anodic microbial communities were completely different when the wastewater type was changed. These results suggest that the newly developed MFC system could be applied to treat low-strength domestic wastewater without requiring any additional organic removal stage.

Microbial fuel cells (MFCs) have been considered to be a promising technology in the field of sustainable and renewable energy. An MFC is a system for generating electricity from organic compounds using microorganisms as a bio-catalyst. In the anode chamber of MFCs, microorganisms degrade organic compounds, such as glucose, acetate and ethanol, etc., and the electrons produced from this degradation are transferred to the anode as an electron acceptor. The microorganisms capable of transferring electrons to the anode are called “exoelectrogens”. Exoelectrogens function as electrochemically active bacteria, capable of transferring electrons from their cell body to outside of the cell, and play an important role in electricity generation (7, 8). In general, there are direct and indirect ways for exoelectrogens to transfer electrons. Microorganisms transfer electrons directly by developing a biofilm on the anode surface or indirectly through electron shuttles that exist in the anodic suspension. Current can be generated from differences in the potential due to the movement of electrons; they contribute to the production of electricity in both ways; however, such information on electron transfer mechanisms is still insufficient to understand the physiology of the exoelectrogen, the ecology of anodic microbial communities on the electrodes, and the relationship between the exoelectrogen and other bacteria. Therefore, the identification and characterization of exoelectrogens are the most significant factors for increasing the efficiency of transfer electrons and producing higher power via MFCs (7, 8). Methods for the isolation of exoelectrogens from the anode of MFCs can be categorized as follows: dilution to extinction and plating methods. The plating method is known as a generally convenient method to isolate exoelectrogens from MFC anodes. So far, a great number of exoelectrogens isolated from MFC anodes have been reported. There have also been many investigations on these bacteria, such as Clostridium butyricum(10), Aeromonas hydrophila(13), Rhodoseudomonas palustris(17), Aeromonas sp. (2) and Acrobacter butzleri(3). The main advantage of the plating method for their isolation is the conventional and relatively convenient experimental process. With plating, however, it is possible that it will discover not only exoelectrogens but also other bacteria that are not able to transfer electrons extracellularly on an MFC anode. The exoelectrogens identified by the plating method are also known as dissimilatory Fe (III) reducing bacteria, which are able to reduce insoluble iron (7). One reason is that the media for metal-reducing bacteria have been used to isolate exoelectrogens, even though not all of the microorganisms growing in the media are exoelectrogens. Therefore, microorganisms were generally identified by their electrochemical activity after isolation (by plating). It was impracticable to observe the electrochemically activity of bacteria discovered in the microbial community in MFCs. Moreover, the cultivation-dependent method, the plating method, is well known for significant limiting the numbers and populations of bacteria that represent the entire microbial community. The dilution to extinction method, a different and cultivation-independent method for the isolation of exoelectrogens devised in previous studies, is an alternative method that enables exoelectrogens to be isolated by continuous monitoring of the electricity produced in MFCs. With this method, dominant strains of anode respiring bacteria or the electrochemically active microbial community can be isolated. Ochrobactrum anthropi(20) and Comamonas denitrificans(16) have been reported as microorganisms isolated via the dilution to extinction method. O. anthrophi YZ-1 isolated from U-tube MFCs using the dilution to extinction method showed lower maximum current density of 708 mA/m2, but higher coulombic efficiency of 93% than the mixed culture (1730 mA/m2). They produced current using a wide range of substrates (acetate, lactate, propionate, butyrate, glucose, sucrose, cellobiose, glycerol, and ethanol) (20). Most of the defined strains isolated by the plating method have revealed the capability of reducing metals. It is unclear whether electrochemically active metal-reducing bacteria can significantly affect electricity generation; thus it should be considered that metal-reducing bacteria are really major exoelectrogens in MFC. However, previous studies have generally been carried out using a single method, or with different studies using different inocula, which have made it difficult to collectively compare studies. Thus, in this study, we used two methods, the dilution to extinction and plating methods, to identify and to isolate exoelectrogen. Through dilution to extinction experiments using a U-tube MFC, we tried to reduce the diversity of the exoelectrogenic community and to identify exoelectrogen. Then we isolated iron-reducing bacteria from the anodic microbial community of U-tube MFC by the plating method, and they were compared to the exoelectrogen identified using U-tube MFC.

A biofilm process with the attached bacterial growth onto ceramic media was applied to remove carbonaceous and nitrogenous pollutants from nonpoint water source. The packing ratios of ceramic media were 0.05 and 0.15 (v/v). Thereafter, the reactors were operated intermittently in sequencing batch mode with different cycle periods: 0, 5, 10 and 15 d. The COD and NH4 +-N removal efficiencies were investigated under different operating conditions, such as media packing ratio, temperature and interevent period. Additionally, polymerase chain reaction (PCR)-denaturing gel gradient electrophoresis (DGGE) and INT-dehydrogenase activity (DHA) tests were conducted to observe the microbial community and activity in the biofilm. Consequently, the removal efficiency of the organic matter after 8 h remained stable, even with longer interevent periods, regardless of the packing ratio. The interevent period and packing ratio seemed to have no significant influence on the COD removal efficiency. However, stable nitrification efficiency, with longer interevent period, was only achieved with a packing ratio of 0.15. Therefore, a packing ratio above 0.15 was required to simultaneously achieve stable COD removal and nitrification efficiency. The DGGE profiles revealed that the prevalent microorganism species were changed from that of the seeded activated sludge into those detected in the sediments. Due to the prevalence of microorganisms related to the sediment, their activities did not decrease, even after a 15 d interevent period.