New microbial electrosynthesis system for methane production from carbon dioxide coupled with oxidation of sulfide to sulfate.

Microbial electrosynthesis system (MES) is a promising method that can use carbon dioxide, which is a greenhouse gas, to produce methane which acts as an energy source, without using organic substances. However, this bioelectrical reduction reaction can proceed at a certain high applied voltage when coupled with water oxidation in the anode coated with metallic catalyst. When coupled with the oxidation of HS- to SO42-, methane production is thermodynamically more feasible, thus implying its production at a considerably lower applied voltage. In this study, we demonstrated the possibility of electrotrophic methane production coupled with HS- oxidation in a cost-effective bioanode chamber in the MES without organic substrates at a low applied voltage of 0.2 V. In addition, microbial community analyses of biomass enriched in the bioanode and biocathode were used to reveal the most probable pathway for methane production from HS- oxidation. In the bioanode, electroautotrophic SO42- production accompanied with electron donation to the electrode is performed mainly by the following two steps: first, incomplete sulfide oxidation to sulfur cycle intermediates (SCI) is performed; then the produced SCI are disproportionated to HS- and SO42-. In the biocathode, methane is produced mainly via H2 and acetate by electron-accepting syntrophic bacteria, homoacetogens, and acetoclastic archaea. Here, a new eco-friendly MES with biological H2S removal is established.

Biological methane production coupled with sulfur oxidation in a microbial electrosynthesis system without organic substrates.

Methane is produced in a microbial electrosynthesis system (MES) without organic substrates. However, a relatively high applied voltage is required for the bioelectrical reactions. In this study, we demonstrated that electrotrophic methane production at the biocathode was achieved even at a very low voltage of 0.1 V in an MES, in which abiotic HS- oxidized to SO42- at the anodic carbon-cloth surface coated with platinum powder. In addition, microbial community analysis revealed the most probable pathway for methane production from electrons. First, electrotrophic H2 was produced by syntrophic bacteria, such as Syntrophorhabdus, Syntrophobacter, Syntrophus, Leptolinea, and Aminicenantales, with the direct acceptance of electrons at the biocathode. Subsequently, most of the produced H2 was converted to acetate by homoacetogens, such as Clostridium and Spirochaeta 2. In conclusion, the majority of the methane was indirectly produced by a large population of acetoclastic methanogens, namely Methanosaeta, via acetate. Further, hydrogenotrophic methanogens, including Methanobacterium and Methanolinea, produced methane via H2.

Multiple organic substrates support Mn(II) removal with enrichment of Mn(II)-oxidizing bacteria.

Three different organic substrates, K-medium, sterilized activated sludge (SAS), and methanol, were examined for utility as substrates for enriching manganese-oxidizing bacteria (MnOB) in an open bioreactor. The differences in Mn(II) oxidation performance between the substrates were investigated using three down-flow hanging sponge (DHS) reactors continuously treating artificial Mn(II)-containing water over 131 days. The results revealed that all three substrates were useful for enriching MnOB. Surprisingly, we observed only slight differences in Mn(II) removal between the substrates. The highest Mn(II) removal rate for the SAS-supplied reactor was 0.41 kg Mn⋅m-3⋅d-1, which was greater than that of K-medium, although the SAS performance was unstable. In contrast, the methanol-supplied reactor had more stable performance and the highest Mn(II) removal rate. We conclude that multiple genera of Comamonas, Pseudomonas, Mycobacterium, Nocardia and Hyphomicrobium play a role in Mn(II) oxidation and that their relative predominance was dependent on the substrate. Moreover, the initial inclusion of abiotic-MnO2 in the reactors promoted early MnOB enrichment.

Stormwater inflow loading of polycyclic aromatic hydrocarbons into urban domestic wastewater treatment plant for separate sewer system.

Polycyclic aromatic hydrocarbons (PAHs) are common contaminants present in wastewater, and determination of their sources is important for their management in the environment. In this study, stormwater loading of PAHs during rainfall periods was evaluated for sewage inflow into a wastewater treatment plant (WWTP) for a separate sewer system. To accomplish this, sewage inflow volumes, suspended solid concentrations, and PAH concentrations were measured during eight rainfall events and on two no-rainfall days at the inlet of the plant. Based on a comparison between the rainfall and no-rainfall loading quantified by the measurements, excess PAH loadings with stormwater were evaluated for the rainfall events. The relationship between rainfall intensity and stormwater loading was then used to evaluate long-term stormwater loadings of water and PAHs. Their contributions to the sewage inflow were 0.7% and 1.0% for 1 year for water and the sum of 16 measured PAHs, respectively. Our measurements and estimates demonstrate that direct stormwater inflow is not a primary source of PAHs to the plant for this separate sewer system.

Integrated biological-physical process for biogas purification effluent treatment.

Biogas purification via water scrubbing produces effluent containing dissolved CH4, H2S, and CO2, which should be removed to reduce greenhouse gas emissions and increase its potential for water regeneration. In this study, a reactor built with air supplies at the top and bottom was utilized for the treatment of biogas purification effluent through biological oxidation and physical stripping processes. Up to 98% of CH4 was removed through biological treatment at a hydraulic retention time of 2 hr and an upper airflow rate of 2.02 L/day. Additionally, a minimum CH4 concentration of 0.04% with no trace of H2S gas was detected in the off gas. Meanwhile, a white precipitate was captured on the carrier showing the formation of sulfur. According to the developed mathematical model, an upper airflow rate of greater than 2.02 L/day showed a small deterioration in CH4 removal performance after reaching the maximum value, whereas a 50 L/day bottom airflow rate was required to strip the CO2 efficiently and raise the effluent pH from 5.64 to 7.3. Microbiological analysis confirmed the presence of type 1 methanotroph communities dominated by Methylobacter and Methylocaldum. However, bacterial communities promoting sulfide oxidation were dominated by Hyphomicrobium.

Pollutants removal from synthetic wastewater by the combined electrochemical, adsorption and sequencing batch reactor (SBR).

Wastewater filtration is considered the main solution to water shortages. Here, we treated synthetic wastewater by combining treatment techniques, namely, electrochemical oxidation and adsorbent added sequencing batch reactor (SBR). One beaker with a working value of 1500 mL was applied in this contemporary study. In the upper part of the beaker, an anode and a cathode (Ti/RuO2-IrO2) were arranged in parallel for the electrochemical oxidation process. Sodium sulfate (Na2SO4) with a concentration of 2.5 g/L was added as the electrolyte. The voltage and current were set to 7.50 V and 0.40 A, respectively. Aeration was conducted at the bottom of the beaker. Then, 15% working value of the reactor was filled by activated sludge, and 85% working value of the reactor was added with synthetic wastewater. In addition, 1.50 g/L of powdered cockleshell was added in the reactor. Response surface methodology was used for statistical analysis. In synthetic wastewater, concentrations of COD, ammonia, phenols and chromium were 2500 mg/L, 2500 mg/L, 100 mg/L and 100 mg/L, respectively. pH and reaction time (h) were considered as independent factors. A total of 2430 mg/L biochemical oxygen demand, 2500 mg/L ammonia, 90.0 mg/L phenols, and 84.0 mg/L chromium were eliminated at the optimum reaction time (72.9 min) and pH (6.5). The energy consumption value was 6.5 (kWh kg-1) at the optimum operating conditions. This study indicated that this combined treatment system exhibited high performance.

Nitrogen removal using an anammox membrane bioreactor at low temperature.

Membrane bioreactors (MBRs) have the ability to completely retain biomass and are thus suitable for slowly growing anammox bacteria. In the present study, an anammox MBR was operated to investigate whether the anammox activity would remain stable at low temperature, without anammox biomass washout. The maximum nitrogen removal rates were 6.7 and 1.1 g-N L⁻¹ day⁻¹ at 35 °C and 15 °C, respectively. Fluorescence in situ hybridization and 16S rRNA-based phylogenetic analysis revealed no change in the predominant anammox species with temperature because of the complete retention of anammox biomass in the MBR. These results indicate that the predominant anammox bacteria in the MBR cannot adapt to a low temperature during short-term operation. Conversely, anammox activity recovered rapidly after restoring the temperature from the lower value to the optimal temperature (35 °C). The rapid recovery of anammox activity is a distinct advantage of using an MBR anammox reactor.

PAH contents in road dust on principal roads collected nationwide in Japan and their influential factors.

Fifty-four road dust samples were collected from principal roads (n = 37) and residential roads (n = 17) nationwide in Japan from March 2010 to November 2012. Sixteen polycyclic aromatic hydrocarbons (PAHs) and ignition loss (IL) were determined. The total PAH contents ranged from 62 to 6,325 ng g(-1) with a geometric mean of 484 ng g(-1). The IL ranged from 0.8 to 17% with a mean of 6%. The PAH contents were correlated with the IL contents, and the IL contents were dependent on the population density. From the PAH pattern analysis, the PAHs from road dust are considered to be mainly from diesel emissions.

Unique episymbiotic relationship between Candidatus Patescibacteria and Zoogloea in activated sludge flocs at a municipal wastewater treatment plant.

Candidatus Patescibacteria, also known as candidate phyla radiation (CPR), including the class-level uncultured clade JAEDAM01 (formerly a subclass of Gracilibacteria/GN02/BD1-5), are ubiquitous in activated sludge. However, their characteristics and relationships with other organisms are largely unknown. They are believed to be episymbiotic, endosymbiotic or predatory. Despite our understanding of their limited metabolic capacity, their precise roles remain elusive due to the difficulty in cultivating and identifying them. In previous research, we successfully recovered high-quality metagenome-assembled genomes (MAGs), including a member of JAEDAM01 from activated sludge flocs. In this study, we designed new probes to visualize the targeted JAEDAM01-associated MAG HHAS10 and identified its host using fluorescence in situ hybridization (FISH). The FISH observations revealed that JAEDAM01 HHAS10-like cells were located within dense clusters of Zoogloea, and the fluorescence brightness of zoogloeal cells decreased in the vicinity of the CPR cells. The Zoogloea MAGs possessed genes related to extracellular polymeric substance biosynthesis, floc formation and nutrient removal, including a polyhydroxyalkanoate (PHA) accumulation pathway. The JAEDAM01 MAG HHAS10 possessed genes associated with type IV pili, competence protein EC and PHA degradation, suggesting a Zoogloea-dependent lifestyle in activated sludge flocs. These findings indicate a new symbiotic relationship between JAEDAM01 and Zoogloea.

Physiological characterization of an anaerobic ammonium-oxidizing bacterium belonging to the "Candidatus scalindua" group.

The phylogenetic affiliation and physiological characteristics (e.g., Ks and maximum specific growth rate [µmax]) of an anaerobic ammonium oxidation (anammox) bacterium, "Candidatus Scalindua sp.," enriched from the marine sediment of Hiroshima Bay, Japan, were investigated. "Candidatus Scalindua sp." exhibits higher affinity for nitrite and a lower growth rate and yield than the known anammox species.

Occurrence of per- and polyfluoroalkyl substances in aquatic environments and their removal by advanced oxidation processes.

Per- and polyfluoroalkyl substances (PFAS), one of the main categories of emerging contaminants, are a family of fluorinated organic compounds of anthropogenic origin. PFAS can endanger the environment and human health because of their wide application in industries, long-term persistence, unique properties, and bioaccumulation potential. This study sought to explain the accumulation of different PFAS in water bodies. In aquatic environments, PFAS concentrations range extensively from <0.03 (groundwater; Melbourne, Australia) to 51,000 ng/L (Groundwater, Sweden). Additionally, bioaccumulation of PFAS in fish and water biota has been stated to range from 0.2 (Burbot, Lake Vättern, Sweden) to 13,900 ng/g (Bluegill samples, U.S.). Recently, studies have focused on PFAS removal from aqueous solutions; one promising technique is advanced oxidation processes (AOPs), including microwaves, ultrasound, ozonation, photocatalysis, UV, electrochemical oxidation, the Fenton process, and hydrogen peroxide-based and sulfate radical-based systems. The removal efficiency of PFAS ranges from 3% (for MW) to 100% for UV/sulfate radical as a hybrid reactor. Therefore, a hybrid reactor can be used to efficiently degrade and remove PFAS. Developing novel, efficient, cost-effective, and sustainable AOPs for PFAS degradation in water treatment systems is a critical area of research.

Ecophysiological role and function of uncultured Chloroflexi in an anammox reactor.

The coexistence of uncultured heterotrophic bacteria belonging to the phylum Chloroflexi has often been observed in anaerobic ammonium oxidation (anammox) reactors fed with synthetic nutrient medium without organic carbon compounds. To determine if coexisting Chloroflexi in anammox reactors scavenge organic matter derived from anammox bacterial cells, the present study was conducted to investigate the substrate uptake pattern of the uncultured Chloroflexi present in an anammox reactor and to clarify if they take up microbial products derived from anammox bacterial cells. To accomplish this, combined microautoradiography and fluorescence in situ hybridization (MAR-FISH) was conducted. Phylogenetic analysis revealed that 36% of the clones analyzed in this study were affiliated with Chloroflexi. The sequence similarities to Anaerolinea thermophila and Caldilinea aerophila within the phylum Chloroflexi were only 81.0-88.7% and 80.3-83.8%, respectively. The uncultured Chloroflexi were found to incorporate sucrose, glucose, and N-acetyl-glucosamine. The (14)C-tracing experiment revealed that the uncultured Chloroflexi were clearly MAR-positive, indicating the utilization of decaying anammox bacterial cell materials. Taken together, these results indicate that coexisting uncultured Chloroflexi in anammox reactors scavenge organic compounds derived from anammox bacterial cells.

Influence of temperature and salinity on microbial structure of marine anammox bacteria.

Anaerobic ammonium oxidation (anammox) is a type of biological oxidation mediated by a group of Planctomycete-like bacteria. Members of the genus Candidatus Scalindua are mainly found in marine environments, but not exclusively. This group is cultured using different inoculums and conditions; however, its optimal growth conditions are not clear. Additionally, little information is known about the factors that influence the activity and the selection of a population of marine anammox bacteria. This study was conducted to investigate the influence of temperature and salinity on the marine anammox community. To accomplish this, an up-flow fixed-bed column reactor was operated, and quantitative fluorescence in situ hybridization (FISH) with probes specific to dominant marine anammox bacteria was conducted. Anammox activity was observed at 20 and 30 °C, but not at 10 °C. A nitrogen removal rate of 0.32 kg TN m(-3) day(-1) was obtained at 20 °C. These results suggest that temperature affects the activity (nitrogen removal rate) of anammox bacteria, while salinity does not affect the activity in the marine anammox biofilm.

Development of anammox reactor equipped with a degassing membrane to improve biomass retention.

In up-flow anammox reactors, one of the contributing factors to biomass wash-out is the adherence of nitrogen gas produced by the anammox reaction to biomass. In this study, we operated an up-flow anammox reactor equipped with a degassing membrane to minimize the biomass wash-out from the reactor by separating the produced gas from the biomass. In addition, both the effect of degassing on the anammox reactor performance and the durability of the membrane submerged in the anammox reactor were investigated. The results show that the use of the degassing membrane in the anammox reactor could (1) improve the biomass retention ability (by separating the produced gas from the biomass), and (2) increase the component ratio of anammox bacteria in the reactor. In addition, degassing could reduce the N(2)O emission produced in the reactor (for the gas selectivity of the degassing membrane). No membrane fouling was observed even after 2 months of operation without washing, indicating an advantage to the use of the degassing membrane.

PAHs concentration and toxicity in organic solvent extracts of atmospheric particulate matter and sea sediments.

The concentration of polycyclic aromatic hydrocarbons (PAHs) and the toxicity to marine bacteria (Vibrio fischeri) were measured for the organic solvent extracts of sea sediments collected from an urban watershed area (Hiroshima Bay) of Japan and compared with the concentrations and toxicity of atmospheric particulate matter (PM). In atmospheric PM, the PAHs concentration was highest in fine particulate matter (FPM) collected during cold seasons. The concentrations of sea sediments were 0.01-0.001 times those of atmospheric PM. 1/EC50 was 1-10 L g(-1) PM for atmospheric PM and 0.1-1 L g(-1) dry solids for sea sediments. These results imply that toxic substances from atmospheric PM are diluted several tens or hundreds of times in sea sediments. The ratio of the 1/EC50 to PAHs concentration ((1/EC50)/16PAHs) was stable for all sea sediments (0.1-1 L µg(-1) 16PAHs) and was the same order of magnitude as that of FPM and coarse particulate matter (CPM). The ratio of sediments collected from the west was more similar to that of CPM while that from the east was more similar to FPM, possibly because of hydraulic differences among water bodies. The PAHs concentration pattern analyses (principal component analysis and isomer ratio analysis) were conducted and the results showed that the PAHs pattern in sea sediments was quite different to that of FPM and CPM. Comparison with previously conducted PAHs analyses suggested that biomass burning residues comprised a major portion of these other sources.

Metabolic Potential of the Superphylum Patescibacteria Reconstructed from Activated Sludge Samples from a Municipal Wastewater Treatment Plant.

Patescibacteria are widely distributed in various environments and often detected in activated sludge. However, limited information is currently available on their phylogeny, morphology, and ecophysiological role in activated sludge or interactions with other microorganisms. In the present study, we identified microorganisms that interacted with Patescibacteria in activated sludge via a correlation ana-lysis using the 16S rRNA gene, and predicted the metabolic potential of Patescibacteria using a metagenomic ana-lysis. The metagenome-assembled genomes of Patescibacteria consisted of three Saccharimonadia, three Parcubacteria, and one Gracilibacteria, and showed a strong positive correlation of relative abundance with Chitinophagales. Metabolic predictions from ten recovered patescibacterial and five Chitinophagales metagenome-assembled genomes supported mutualistic interactions between a member of Saccharimonadia and Chitinophagales via N-acetylglucosamine, between a member of Parcubacteria and Chitinophagales via nitrogen compounds related to denitrification, and between Gracilibacteria and Chitinophagales via phospholipids in activated sludge. The present results indicate that various interactions between Patescibacteria and Chitinophagales are important for the survival of Patescibacteria in activated sludge ecosystems.

Environmental Factors Affecting the Community of Methane-oxidizing Bacteria.

Methane-oxidizing bacteria (MOB) are ubiquitous and play an important role in the mitigation of global warming by reducing methane. MOB are commonly classified into Type I and Type II, belonging to Gammaproteobacteria and Alphaproteobacteria, respectively, and the diversity of MOB has been examined. However, limited information is currently available on favorable environments for the respective MOB. To investigate the environmental factors affecting the dominant type in the MOB community, we performed MOB enrichment using down-flow hanging sponge reactors under 38 different environmental conditions with a wide range of methane (0.01-80%) and ammonium concentrations (0.001-2,000| |mg N L-1) and pH 4-7. Enrichment results revealed that pH was a crucial factor influencing the MOB type enriched. Type II was dominantly enriched at low pH (4-5), whereas Type I was dominant around neutral pH (6-7). However, there were some unusual cultivated biomass samples. Even though high methane oxidation activity was observed, very few or zero conventional MOB were detected using common FISH probes and primer sets for the 16S rRNA gene and pmoA gene amplification. Mycobacterium mostly dominated the microbial community in the biomass cultivated at very high NH4+ concentrations, strongly implying that it exhibits methane oxidation activity. Collectively, the present results revealed the presence of many unknown phylogenetic groups with the capacity for methane oxidation other than the reported MOB.

Bioelectrical Methane Production with an Ammonium Oxidative Reaction under the No Organic Substance Condition.

The present study investigated bioelectrical methane production from CO2 without organic substances. Even though microbial methane production has been reported at relatively high electric voltages, the amount of voltage required and the organisms contributing to the process currently remain unknown. Methane production using a biocathode was investigated in a microbial electrolysis cell coupled with an NH4+ oxidative reaction at an anode coated with platinum powder under a wide range of applied voltages and anaerobic conditions. A microbial community analysis revealed that methane production simultaneously occurred with biological denitrification at the biocathode. During denitrification, NO3- was produced by chemical NH4+ oxidation at the anode and was provided to the biocathode chamber. H2 was produced at the biocathode by the hydrogen-producing bacteria Petrimonas through the acceptance of electrons and protons. The H2 produced was biologically consumed by hydrogenotrophic methanogens of Methanobacterium and Methanobrevibacter with CO2 uptake and by hydrogenotrophic denitrifiers of Azonexus. This microbial community suggests that methane is indirectly produced without the use of electrons by methanogens. Furthermore, bioelectrical methane production occurred under experimental conditions even at a very low voltage of 0.05| |V coupled with NH4+ oxidation, which was thermodynamically feasible.

Modelling of wet deposition of atmospheric polycyclic aromatic hydrocarbons by the consecutive measurements in an urban area, Japan.

The wet deposition for particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) was modelled from the consecutive measurements of atmospheric concentration and wet deposition for particulate matter and PAHs in Higashi-Hiroshima city, Japan. In order to estimate the model in detail, the wet deposition was classified with that from gaseous and PM phase. The gaseous PAHs assumed to be dissolved into raindrops according to Henry's constant, and the PAHs attached on atmospheric PM were assumed to be trapped with PM. The PM was classified with coarse (>7 µm) and fine (0.6-7 µm) PM for the calculation of trap. PM and PAHs depositions estimated with the wet deposition model were compared with measured data. The ratios of the measured to the estimated values of PM and PAHs gave close agreement with measurements (0.41-4.29 (1.35: average) for PM and (0.32-3.83 (1.42)) for PAHs) regardless of precipitation. The depositions of PAHs of liquid and particulate phase were on the other hand significantly different from those from gaseous and PM phases respectively. From those differences, the transfer from particulate to liquid phase was suggested to occur during the precipitation.

PAHs emission source analysis for air and water environments by isomer ratios - Comparison by modified Cohen's d.

Possible emission sources of PAHs in air and water environments were discussed by a comparison between the data sets of emission sources and environmental fields using five isomer ratios. The similarity of a pair of the datasets of different sources or environment fields for each isomer ratio was evaluated by a newly developed modified effect size d, and the mean of those for the five isomer ratios was applied as an index of similarity. From the analysis, diesel emission and/or biomass burning residues were considered to be major emission sources for almost all the datasets of environments. The pollution loading and path to the PAHs loading of coastal sediments in Hiroshima bay area were examined and it was inferred emission sources was consistently assigned by these newly developed indicators of isomer ratios. Diesel and/or biomass burning were considered to be major sources for the west side area of the bay and the biomass burning was considered to be for the east side area. Further, it was evaluated the west side area, which confronts the Hiroshima city downtown area more directly, was more similar to diesel, and the east side area, which is a bit remoted to the urban central was more similar to the biomass burning. This newly developed method would be a promising alternative application of isomer ratio analysis.