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Introduction
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April 2012 - November 2017
August 2006 - March 2009
Publications
Publications (262)
Nitrous oxide-reducing bacteria (N2ORB) are generally considered the only biological sink for the potent greenhouse gas N2O. Although N2O consumption activities by diverse heterotrophic N2ORB have been detected, knowledge gaps remain about the phylogenies, physiologies, and activities of N2ORB. Here, we successfully enriched a methylotrophic N2ORB...
Shifting from ammonia removal to recovery is the current strategy in wastewater treatment management. We recently developed a microaerophilic activated sludge system for retaining ammonia whereas removing organic carbon with minimal N2O emissions. A comprehensive understanding of nitrogen metabolisms in the system is essential to optimize system pe...
Shifting from ammonia removal to recovery is the current strategy in wastewater treatment management. We recently developed a microaerophilic activated sludge (MAS) system for retaining ammonia while removing organic carbon with minimal N2O emissions. A comprehensive understanding of nitrogen metabolisms in the MAS system is essential to optimize s...
The occurrence of the cavitation phenomena in a high-pressure jet device was verified. When water was injected at 4 MPa and 3 L min⁻¹ into the device made of a transparent material, small bubbles were observed, which would be produced by lowered pressure inside. Hydrodynamic simulation revealed that the pressure fell below saturated vapor pressure...
The dynamic change of redox conditions is a key factor in emission of elemental mercury (Hg⁰) from riparian soils. The objective of this study was to elucidate the influences of redox conditions on Hg⁰ emission from riparian soils. Soil suspension experiments were conducted to measure Hg⁰ emission from five Hg-contaminated soil samples in two redox...
N2O-reducing bacteria have been examined and harnessed to develop technologies that reduce the emission of N2O, a greenhouse gas produced by biological nitrogen removal. Recent investigations using omics and physiological activity approaches have revealed the ecophysiologies of these bacteria during nitrogen removal. Nevertheless, their involvement...
Here, we report a genome sequence of Afipia carboxidovorans strain SH125 isolated from an anammox reactor. This facultative anaerobic strain possesses the clade I-type nitrous oxide (N2O) reductase gene, devoid of nitrite- and nitric oxide reductase genes. Deciphering the genome will help explore N2O reducers instrumental in N2O mitigation.
Nitrification is mediated by numerous different microorganisms, but knowledge of their ecophysiologies is insufficient. Leachate in the late stages of landfill operation provides a brackish environment with a high ammonia concentration, and methanol is added as an electron donor for denitrification. Such a unique environment may contain novel nitri...
A complete genome sequence of Marinobacter shengliensis D49 in the class Gamma-proteobacteria was isolated from activated sludge treating landfill leachate. The genome encodes the functional genes for the biosynthesis of ectoine (ectABC), a compatible solute for cosmetics. Deciphering the genome helps pave the way for ectoine production by the isol...
A transition to ammonia recovery from wastewater has started; however, a technology for sustainable nitrogen retention in the form of ammonia and organic carbon removal is still in development. This study validated a microaerophilic activated sludge (MAS) system to efficiently retain ammonia from high-strength nitrogenous wastewater. The MAS is bas...
Iron sulfides-based autotrophic denitrification (IAD) is effective for treating nitrate-contaminated wastewater. However, the complex nitrate transformation pathways coupled with sulfur and iron cycles in IADs are still unclear. In this study, two columns (abiotic vs biotic) with iron sulfides (FeS) as the packing materials were constructed and ope...
Natural gas brine pumped up from below the ground surface contains not only natural gas and iodine, but also high concentrations of ammonia. To sustain healthy water environments, it is important to understand the status of NH4–N in waste brine drained into a public water area after the collection of natural gas and iodine from the brine. In this s...
Lakes are hot spots for methane (CH4) emissions and particulate organic carbon (POC) production, which describes the methane paradox phenomenon. However, the current understanding of the source of POC and its effect on CH4 emissions during eutrophication remains unclear. In this study, 18 shallow lakes in different trophic states were selected to i...
The first global-scale assessment of Sb contamination in soil that was related to mining/smelting activities was conducted based on 91 articles that were published between 1989 and 2021. The geographical variation, the pollution level, the speciation, the influencing factors, and the environmental effects of Sb that were associated with mining/smel...
Lacustrine eutrophication is generally considered as an important contributor of carbon emissions to the atmosphere; however, there is still a huge challenge in accuracy estimating carbon emissions from lakes. To test the effect of widely used space-for-time substitution on lake carbon emissions, this study monitored different processes of carbon e...
In denitrifying reactors, canonical complete denitrifying bacteria reduce nitrate (NO3-) to nitrogen via N2O. However, they can also produce N2O under certain conditions. We used a 15N tracer method, in which 15N-labeled NO3-/nitrite (NO2-) and nonlabeled N2O were simultaneously supplied with organic electron donors to five canonical complete denit...
A transition to ammonia recovery from wastewater has started; however, a technology for sustainable nitrogen retention in the form of ammonia is still in development. This study validated a microaerophilic activated sludge (MAS) system to efficiently retain ammonia from high-strength nitrogenous wastewater. The MAS is based on conventional activate...
Microorganisms possessing N2O reductases (NosZ) are the only known environmental sink of N2O. While oxygen inhibition of NosZ activity is widely known, environments where N2O reduction occurs are often not devoid of O2. However, little is known regarding N2O reduction in microoxic systems. Here, 1.6-L chemostat cultures inoculated with activated sl...
Intensive research on molecular microbiological methods has accelerated the development of cutting-edge technologies, e.g., a high-throughput sequencer, microscopy, and mass spectrometry, at a surprisingly fast pace. The development of these technologies has allowed researchers, whose expertise does not lie in environmental microbiology and microbi...
Agricultural soil is the primary N2O sink limiting the emission of N2O gas into the atmosphere. Although Gemmatimonadetes bacteria are abundant in agricultural soils, limited information is currently available on N2O reduction by Gemmatimonadetes bacteria. Therefore, the effects of pH and temperature on N2O reduction activities and affinity constan...
A membrane-aerated biofilm reactor (MABR) provides bubbleless aeration and direct oxygen supply to a biofilm, achieving excellent aeration efficiency. Despite this advantage, research on membrane material is scarce. Here, we developed a composite membrane with high oxygen permeability and low vapor permeability with polystyrene elastomer (PS) as th...
Soil moisture is a key factor for mercury (Hg) emission from soil. Despite its significance for Hg emissions, the effect of soil moisture on Hg flux and fractions has not been thoroughly investigated. The objective of this study was to elucidate the influences of soil moisture and temperature on Hg fluxes from soils and Hg fractions. A kinetic stud...
Urban rivers receive used water derived from anthropogenic activities and are a crucial source of the potent greenhouse gas nitrous oxide (N2O). However, considerable uncertainties still exist regarding the variation and mechanisms of N2O production in response to the discharge of treated sewage from municipal wastewater treatment plants (WWTPs). T...
Nitrous oxide (N2O) is a highly potent greenhouse gas and ozone-depleting substance, produced and consumed during denitrification. Evaluation of the N2O production and consumption activities of complete denitrifying bacteria is essential for understanding their capacity to act as N2O sinks in engineered systems for cost-effective nitrogen removal v...
Purpose of Review
Improper discharge of industrial effluents would lead to direct contamination of our water, air, and soil systems. Without proper treatment, both these inorganic and organic-matter-containing waste would pose harmful effects towards aquatic organisms, overall water quality, reduction in soil health, and increase in greenhouse gass...
Harnessing nitrous oxide (N2O)-reducing bacteria is a promising strategy to reduce the N2O footprint of engineered systems. Applying a preferred organic carbon source as an electron donor accelerates N2O consumption by these bacteria. However, their N2O consumption potential and activity when fed different organic carbon species remain unclear. Her...
Shallow lakes are considered important contributors to emissions of nitrous oxide (N2O), a powerful greenhouse gas, in aquatic ecosystems. There is a large degree of uncertainty regarding the relationship between N2O emissions and the progress of lake eutrophication, and the mechanisms underlying N2O emissions are poorly understood. Here, N2O emiss...
Atmospheric deposition of reactive nitrogen compounds (Nrs) has been recognized as a threat to plant diversity in terrestrial ecosystems. As a first attempt to investigate the relationship between Nrs deposition and plant diversity loss in Japan, we collected and analyzed the available long-term nationwide monitoring data on annual Nrs deposition a...
In full-scale sewage treatment plants, long-term and high-frequency monitoring is required to mitigate nitrous oxide (N2O) emissions. In this study, the profile of the dissolved N2O concentration in a full-scale oxidation ditch reactor was investigated to determine the variation of the N2O emission factor. It was found that the concentration of dis...
Upcycling wastes into valuable products by mixed microbial communities has recently received considerable attention. Sustainable production of high-value substances from one-carbon (C1) compounds, e.g., methanol supplemented as an external electron donor in bioreactors for wastewater treatment, is a promising application of upcycling. This study un...
Nitrous oxide (N2O), a potent greenhouse gas, is reduced to N2 gas by N2O‐reducing bacteria (N2ORB), a process which represents an N2O sink in natural and engineered ecosystems. The N2O sink activity by N2ORB depends on temperature and O2 exposure, yet the specifics are not yet understood. This study explores the effects of temperature and oxygen e...
The relative locations of AOB, NOB, and DNB were examined for three different kinds of carriers in two types of hybrid biofilm process configurations: integrated fixed-film activated sludge (IFAS) and moving bed biofilm reactor (MBBR) processes. IFAS water resource recovery facilities (WRRFs) used Anodkalness K1 carriers (KC) at Broomfield, Colorad...
Isotopic fractionation factors against ¹⁵N and ¹⁸O during anammox (anaerobic ammonia oxidization by nitrite) are critical for evaluating the importance of this process in natural environments. We performed batch incubation experiments with an anammox-dominated biomass to investigate nitrogen (N) and oxygen (O) isotopic fractionation factors during...
Quantitative PCR (qPCR) is broadly used as the gold standard to quantify microbial community fractions in environmental microbiology and biotechnology. Benchmarking efforts to ensure the comparability of qPCR data for environmental bioprocesses are still scarce. Also, for partial nitritation/anammox (PN/A) systems systematic investigations are stil...
Nitrifying biomass immobilized in a gel has been applied for wastewater treatment, as immobilization results in a high bacterial cell density in the reactor and facilitates easy solid–liquid separation in the settling tank. Herein, the diffusivity, reaction rate, and concentration profile of oxygen in a spherical gel entrapping ammonia-oxidizing ba...
Excess sludge reduction is a central challenge in wastewater treatment, requiring a cost-effective technology. Here, we report the pilot-scale implementation of two Modified Ludzack-Ettinger (MLE) processes with and without a high-pressure jet device (HPJD) as a sludge reduction method based on physically decomposing bacterial cells in activated sl...
Using metagenome sequencing, a nearly complete genome sequence was retrieved for the uncultured Methyloceanibacter sp. strain A49, recovered from an activated sludge system used for landfill leachate treatment at a closed landfill site. The total size and encoded sequences are 3,407,434 bp and 3,280 genes, respectively.
We report a complete genome sequence of Methylosinus sp. strain C49, a methane-oxidizing bacterium (MOB) in the class Alphaproteobacteria , isolated from MOB-enriched biomass. The genome encodes the functional genes for methane oxidation ( pmoA ) and polyhydroxyalkanoate (PHA) biosynthesis ( phaABC ). Deciphering the genome will help research towar...
Shallow lakes are a crucial source of methane (CH4), a potent greenhouse gas, to the atmosphere. However, large uncertainties still exist regarding the response of CH4 emissions to the increasing trophic levels of lakes as well as the underlying mechanisms. Here, we investigate the CH4 emission flux from lakes with different trophic states in the m...
Methane-oxidizing bacteria (MOB) possess the metabolic potential to assimilate the highly potent greenhouse gas, CH4, and can also synthesize valuable products. Depending on their distinct and fastidious metabolic pathways, MOB are mainly divided into Type I and Type II; the latter are known as producers of polyhydroxyalkanoate (PHA). Despite the m...
Acylase is known as a quorum quenching enzyme that degrades N-acyl-homoserine lactones (AHLs), a key signaling molecule in a quorum sensing (QS) mechanism. Acylase I cleaves the acyl-chain in the chemical structures of AHLs, thereby exerting an anti-biofilm effect by the inhibition of bacterial cell–cell communication and resultant secretion of ext...
A high concentration of accumulated volatile fatty acids (VFAs) is one of the most important factors resulting in reactor failure during solid-state anaerobic digestion. In this study, the feedstock-to-inoculum (F/I) ratio (0.5, 2, 3, 4 and 6) and the recovery method after failure (biochar addition or inoculum addition) were investigated in batch s...
We report the complete genome sequence of Pseudomonas putida strain TS312, in the class of Gammaproteobacteria . The strain, isolated from a paper mill, harbors the hdtS gene, encoding N -acyl-homoserine lactone synthase. Deciphering the genome contributes to revealing the mechanisms of quorum sensing and associated biofilm formation in engineered...
Although the deep-layer sedimentary soils excavated from construction sites contain low level of geogenic arsenic (As), remediation is necessary when the As leachability exceeds the environmental standard (10 μg/L) in Japan. In this study, the zero-valent iron (ZVI) amendment followed by dry magnetic separation (ZVI-DMS) was implemented for the tre...
Changes in microbial communities are observed during the long-term operation of activated sludge systems employing an excess sludge reduction technology. Short-term changes are also significant to confirm if key microbes are damaged, but they have not been investigated due to the absence of an appropriate method. We report a methodology to identify...
The recent discovery of nitrous oxide (N2O)-reducing bacteria suggests a potential biological sink for the potent greenhouse gas N2O. While some N2O-reducing bacteria have been described, characterization of more isolates will be required for an application towards N2O mitigation. Here, we describe the successful enrichment and isolation of high-af...
Membrane processes for water purification and wastewater treatment are impacted by biofilm formation, a hotspot for bacterial cell-cell communication, mainly mediated by N-acyl homoserine lactones (AHLs) as signal compounds. Polymer materials for membrane filtration require high water permeability and biofilm deterrents. Therefore, in this study, a...
The diversity and dynamics of microorganisms in engineered ecosystems have a high impact on performance and operational stability. Nitrogen removal from wastewater is one example of such complex and dynamic ecosystems. Following the microbial community composition and its functional potential is highly valuable information for optimizing performanc...
Anaerobic ammonium oxidation (anammox) has been implemented as a cost-effective nitrogen removal process in wastewater treatment. To apply the process to saline wastewater treatment at temperatures below 30 °C, the effectiveness of marine anammox bacteria has been demonstrated in a pilot-scale reactor. Nevertheless, mesophilic conditions, often fou...
Sludge dewatering is an important process for determining the operation cost of sludge disposal. Hence, improving the dewaterability of anaerobically digested sludge containing high water content is of paramount significance. For this challenge, we developed a novel process in which fibrous materials initially collected from a primary sedimentation...
Heterogeneous distribution of substrate and microorganisms and low mass transfer limit methane production dramatically in solid-state anaerobic digestion (SS-AD). To overcome this challenge, this study determined the optimal inoculation strategy (complete premix/slurry application) for reusing solid digestate as inoculum and the optimal leachate ci...
The aims of this study were to investigate the feasibility of partial nitrification (PN) in a sequencing batch reactor (SBR) fed with real wastewater discharged from the washing process at a semiconductor factory, to evaluate the efficacy of online control for nitrite buildup, and to examine the microbial community composition. To this end, online...
Mixing is an important operation in solid-state anaerobic digestion (SS-AD) to improve the mass transfer of the solid phase. This study proposed simple turning by loader in common garage-type digester without commonly used mixer or percolation system (simplified SS-AD). In simplified-SS-AD, turning is conducted in open condition. Thus, oxidation of...
International concern on in silico methodology development of ecotoxicity prediction of chemical substances become one of the hot topics these years. To classify chemical substances based on their structure information and then predict ecotoxicity with Log Kow linear regression empirically for the chemical with a similar structure is the most seen...
The in sillico method to predict the ecotoxicity of chemical substances for reducing animal testing has become attracted attention. A most common model for predicting ecotoxicity classify chemical substances empirically based on functional groups and then predict ecotoxicity with a linear regression by using a descriptor of a chemical substance suc...
This paper discusses the microbial basis and the latest research on nitrous oxide (N2O) emissions from biofilms processes for wastewater treatment. Conditions that generally promote N2O formation in biofilms include (1) low DO values, or spatial DO transitions from high to low within the biofilm; (2) DO fluctuations within biofilm due to varying bu...
Nitrous oxide (N2O) is an important greenhouse gas that can be emitted from wastewater treatment plants (WWTPs). Such emissions are reportedly process specific and related to operational parameters. This study was conducted to clarify spatial and daily variations of N2O in a full-scale activated sludge anoxic/oxic process that consisted of an anoxi...
Heavy metals contaminated soils are a potential exposure hazard to the public. This study demonstrated the application of chlorination and thermal treatment for remediation of heavy metals-contaminated soils on a full-industrial scale. Five soil samples were treated at a soil remediation factory equipped with an internally-heated rotary kiln (lengt...
The effect of reducing alkali consumption in a partial nitritation-anammox process for removing nitrogen from waste brine was investigated. An experiment into the effect of pH on nitrogen removal rate demonstrated that alkali consumption could be decreased by 49% without impairing specific anammox activity (SAA). This was likely due to OH⁻ producti...
We report here a draft genome sequence of Azospira sp. strain I13 in the class Betaproteobacteria , a facultative anaerobic bacterium responsible for nitrous oxide (N 2 O) reduction. Deciphering this genome would pave the way for the use of Azospira sp. strain I13 to facilitate N 2 O consumption in a nitrogen-removing bioreactor emitting N 2 O.
Nitrous oxide (N2O)-reducing bacteria, which reduce N2O to nitrogen in the absence of oxygen, are phylogenetically spread throughout various taxa and have a potential role as N2O sinks in the environment. However, research on their physiological traits has been limited. In particular, their activities under microaerophilic and aerobic conditions, w...
Development of a strategy to mitigate nitrous oxide (N2O) emitted from biological sources is important in the nexus of wastewater treatment and greenhouse gas emission. To this end, immobilization of N2O-reducing bacteria as a biofilm has the potential to ameliorate oxygen (O2) inhibition of the metabolic activity of the bacteria. We demonstrated t...
Excavated soils with low-level As contamination obtained from construction projects during city development have been of great concern in Japan. Water-extractable As represents the most easily mobilized and ecotoxicologically relevant fraction in the soil environment. In the present study, the water-extractability of As in excavated alkaline urban...
Dry anaerobic digestion is a promising technology for the recycling of agricultural waste to produce energy and fertilizer. Adding water to the substrate enables better handling and avoid inhibition caused by high total solid (TS) content in the reactor; however, it also increases leachate and operational costs. To assess the extent to which the am...
The goal of this study was to develop a startup strategy for a high-rate anaerobic ammonium oxidation (anammox) reactor to treat waste brine with high concentrations of ammonium from a natural gas plant. An upflow anaerobic sludge blanket (UASB) anammox reactor with an effective volume of 294 L was fed continuously with waste brine with a salinity...
Novel composite gel beads that entrap ammonia-oxidizing bacteria (AOB) were developed for wastewater treatment. The AOB-entrapping composite gel beads, which were monodispersed and millimeter-sized, were produced by a method that combined suspension-gelation with sedimentation polymerization. This method involves the preparation of calcium alginate...
Leaching of hazardous trace elements from excavated urban soils during construction of cities has received considerable attention in recent years in Japan. A new concept, the pollution potential leaching index (PPLI), was applied to assess the risk of arsenic (As) leaching from excavated soils. Sequential leaching tests (SLT) with two liquid-to-sol...
This study investigated the effect of the feedstock-to-inoculum (F/I) ratio on performance of the solid-state anaerobic co-digestion of pig urine and rice straw inoculated with a solid digestate, and clarified the microbial community succession. A 44-day biochemical methane potential test at F/I ratios of 0.5, 1, 2 and 3 at 55 °C and a 35-day large...
Purpose
In Japan, the excavated soils produced from constructions projects, which contain relatively low levels of arsenic (As), are considered as a potential concern if they could release significant amount of As to the environment. The aim of this study was to investigate the As leaching from excavated alkaline soils and, in particular, the influ...
A membrane-aerated biofilm reactor (MABR) provides a counter-current substrate diffusion geometry in which oxygen is supplied from a gas-permeable membrane on which a biofilm is grown. This study hypothesized that an MABR would mitigate NO and N2O emissions compared with those from a conventional biofilm reactor (CBR). Two laboratory-scale reactors...
The goal of this study was to investigate the effectiveness of a membrane-aerated biofilm reactor (MABR), a representative of counter-current substrate diffusion geometry, in mitigating nitrous oxide (N2O) emission. Two laboratory-scale reactors with the same dimensions but distinct biofilm geometries, i.e., a MABR and a conventional biofilm reacto...
The dry-thermophilic anaerobic digestibility of alternative biomasses to rice straw for pig manure treatment was evaluated. Seven grass and three woody biomasses were subjected to batch dry-thermophilic anaerobic digestion for methane (CH4) production. The CH4 production potential ranged from 109±8.1 to 347±62 m³/t-VS, with woody biomasses showing...
