Natural attenuation and remobilization of arsenic in a small river contaminated by the volcanic eruption of Mount Iou in southern Kyushu Island, Japan.

The active volcano Mount Iou, in the southern part of Japan, erupted in 2018 for the first time in approximately 250 years. Geothermal water discharged from Mount Iou had high concentrations of toxic elements, such as arsenic (As), which could seriously contaminate the adjacent river. In this study, we aimed to clarify the natural attenuation of As in the river through daily water sampling for approximately eight months. The risk of As in the sediment was also evaluated using the sequential extraction procedures. The highest As concentration (2000 µg/L) was observed upstream but typically remained below 10 µg/L downstream. Dissolved As was the main form in the river water on non-rainy days. Arsenic concentration in the river naturally decreased through dilution and sorption/coprecipitation with Fe, Mn, and Al (hydr)oxides during flow. However, peaks in As concentration were frequently observed during rainfall events, possibly due to sediment resuspension. Furthermore, the range of pseudo-total As in the sediment was 4.62-14.3 mg/kg. Total As content was highest upstream before decreasing further along the flow. When using the modified Keon method, 44-70% of the total As existed as more reactive fractions associated with (hydr)oxides.

Probing the dynamics of three freshwater Anammox genera at different salinity levels in a partial nitritation and Anammox sequencing batch reactor treating landfill leachate.

Partial nitritation/Anammox was applied to treat NaCl-amended landfill leachate. The reactor established robust nitrogen removal of 85.7 ± 2.4% with incremental salinity from 0.61% to 3.10% and achieved 0.91-1.05 kg N/m3/d at salinity of 2.96%-3.10%. Microbial community analysis revealed Nitrosomonas, Nitrospira, and denitrifiers occupied 4.1%, <0.2% and 10.9%, respectively. Salinity variations impelled the dynamics of Anammox bacteria. Jettenia shifted to Brocadia and Kuenenia at salinity of 0.61%-0.81%. Kuenenia outcompeted Brocadia and occupied 51.5% and 50.9% at salinity of 1.48%-1.54% and 2.96%-3.10%, respectively. High nitrite affinity and fast growth rate were proposed as key factors fostering Brocadia overgrew Jettenia. Functionalities of sodium-motive-force facilitated energy generation and intracellular osmotic pressure equilibrium regulation crucially determined Kuenenia's dominance at elevated salinity. Co-occurrence network further manifested beneficial symbiotic relationships boosted Kuenenia's preponderance. Knowledge gleaned deepen understanding on survival niches of freshwater Anammox genera at saline environments and lead to immediate benefits to its applications treating relevant wastewaters.

Unclassified Anammox bacterium responds to robust nitrogen removal in a sequencing batch reactor fed with landfill leachate.

Treatment of landfill leachate was conducted in a lab-scale sequencing batch reactor (SBR). The SBR was started through inoculating activated sludge with controlling dissolved oxygen of 0.5-1.0 mg/L. Anammox reaction took place within around three months. The SBR established robust nitrogen removal with incremental NLRs of 0.25-2.17 kg N/m3/d. At the final phase, it achieved elevated nitrogen removals of 1.68-1.91 kg N/m3/d. 16S rRNA gene amplicon sequencing analysis revealed Nitrosomonas, unclassified Anammox bacterium, and diverse denitrifying populations coexisted and accounted for 4.02%, 20.05% and 34.69%, respectively. Phylogenic analysis and average nucleotide identity comparison jointly suggested the unclassified Anammox bacterium potentially pertained to a novel Anammox lineage. The functional profiles' prediction suggested sulfate reduction, arsenate reduction and eliminations of antibiotics and drugs likely occurred in the SBR. The finding from this study suggests contribution of unclassified Anammox bacteria in influencing nitrogen budget in natural and engineering systems is currently being underestimated.

A novel reactor combining anammox and Fenton-like reactions for the simultaneous removal of organic carbon and nitrogen at different organic carbon to nitrogen ratios.

A Fenton-like reaction and anaerobic ammonium oxidation (anammox) were combined to construct a novel process named FenTaMox for removing nitrogen (N) and organic carbon (measured as chemical oxidation demand (COD)). Two columns were packed with iron-manganese-sepiolite, a catalyst that uses hydrogen peroxide (H2O2) to catalyze Fenton-like reactions, and inoculated with marine anammox bacteria. During the start-up, marine anammox medium was fed into both columns to acclimate the marine anammox bacteria to iron-manganese-sepiolite. Batch experiments revealed that the marine anammox bacteria were not affected by 60 mgL-1 of H2O2. Next, medium containing glucose and H2O2 was fed into one column as the FenTaMox treatment, while medium containing glucose but no H2O2 was fed into the other column as the control. At a COD/N of 4, FenTaMox exhibited higher removal efficiencies of N and COD compared with that of the control, suggesting the application of FenTaMox for organic carbon- and N- removal.

Efficient transition from partial nitritation to partial nitritation/Anammox in a membrane bioreactor with activated sludge as the sole seed source.

A lab-scale membrane bioreactor (MBR) was employed to carry out the partial nitritation/Anammox (PN/A) process from conventional activated sludge. Seed sludge was cultivated under microaerobic conditions for 10 days before seeding into the MBR. The bacterial community was analyzed on the basis of cloning and sequencing of 16S rRNA gene. Relative slow ammonia oxidation rates (3.2-13.0 mgN/L/d) were established in the microaerobic cultivation period. In the continuous MBR operation, the nitritation was achieved in the first 16 days and the reactor produced a balanced ratio between ammonia and nitrite which favored the proliferation of Anammox bacteria. Efficient transition from PN to PN/A was achieved in two months which was supported by appearance of reddish spots on the reactor inner wall and the concurrent consumption of ammonium and nitrite. The PN/A performed a robust and high-rate nitrogen removal capability and achieved a peak nitrogen removal of 1.81 kg N/m3/d. 16S rRNA gene-based analysis indicated that "Nitrosomonas sp." and "Candidatus Jettenia sp." accounted for ammonia oxidation and nitrogen depletion, respectively. Denitratisoma facilitated denitrification in the reactor. The present study suggested that a pre-cultivation of seed sludge under microaerobic conditions assists fast realization of PN and further convoyed efficient transition from PN to PN/A. Knowledge gleaned from this study is of significance to initiation, operation, and control of MBR-PN/As.

Effects of structural vulnerability of flat-sheet membranes on fouling development in continuous submerged membrane bioreactors.

The relationship between fouling development in a continuous laboratory-scale membrane reactor (MBR/Lab) and the membrane material was investigated using flat-sheet membranes prepared from four materials (polyvinylidene difluoride (PVDF), polyethersulfone, chlorinated polyvinyl chloride, and polytetrafluoroethylene). Further, the characteristics of the suspension liquid in MBR/Lab were compared with those of samples from actual wastewater treatment plants. It was found that, in addition to the membrane material's own characteristics, the structural vulnerability of the membranes had a determining effect on fouling development. The PVDF membrane showed the highest transmembrane pressure during MBR operation and its surface experienced significant damage because of the shearing stress caused by aeration, resulting in the penetration of the membrane by the fouling compounds. The characteristics of suspension liquid in MBR/Lab were almost similar to those in the MBR at a night-soil treatment plant and the aeration tank of a sewage treatment plant.

Changes of nitrogen-removal performance and that of the bacterial community in a mixed culture comprising freshwater and marine anammox bacteria under averaged environmental condition.

Nitrogen-removal processes using anammox bacteria are expected to achieve high-rate removal while remaining economical, and their practical applications have been investigated. However, anammox bacteria still have unfavorable characteristics for practical use, including susceptibility to a change in environmental conditions. In this study, with an aim of exploring the adaptability of mixed anammox bacteria to environmental conditions, the shift of nitrogen-removal performance and bacterial community in a mixed culture comprising freshwater anammox bacteria (FAB) and marine anammox bacteria (MAB) were investigated by a continuously stirred tank reactor (CSTR). The CSTR inoculated with the mixed anammox bacteria was operated for 180 days under an averaged condition between freshwater and marine conditions with a temperature of 27.5 °C and a synthetic medium with 15 g/L NaCl was used. Nitrogen-removal performance became stable after 114 days and more than 90% of nitrogen that was loaded into the reactor was removed in the range of nitrogen loading rate 0.07-0.42 kg N/m3/d. After operating at 0.42 kg N/m3/d for one month, a biomass sample was taken and its bacterial community was analyzed by clone-library analysis using a partial sequence of 16S rRNA. Among the clones of anammox bacteria that were made by an anammox-bacteria-specific primer, 97% of them were MAB and only 3% were FAB. These results indicate that the bacterial community including anammox bacteria was evidently changed due to environmental conditions and that the averaged condition in this study was suitable for marine bacteria rather than freshwater bacteria.

Understanding nitrate contamination based on the relationship between changes in groundwater levels and changes in water quality with precipitation fluctuations.

There are growing concerns about nitrate contamination in Kumamoto City, where >700,000 people completely depend on groundwater as a source of drinking water. We found that some groundwater samples showed considerably different nitrate concentrations although their sampling locations were close to one another, and we speculated that this phenomenon was due to the differences in subsurface geological properties. In order to verify this hypothesis, we carried out temporally intensive long-term monitoring of the groundwater levels and water qualities at three of the closely related sampling wells, and the results revealed that the changes in water level and water quality were different at each well. The water level at well T1, where nitrate concentrations ranged from 12 to 26 mg N/L, showed a significantly sensitive and unique response to heavy rain, which indicated that the subsurface at this site might be highly permeable; this would have allowed for the influent water to easily reach the groundwater aquifer over a short period. However, wells T2 and T3, which were located within 0.6 and 1.9 km from well T1, respectively, had nitrate concentrations that were lower than that in well T1 (4.5-8.0 mg N/L) and showed only gradual responses to heavy rain. These observations suggest that the highly permeable subsurface properties in the vicinity of well T1 contributed to the more serious nitrate contamination in well T1 than those at wells T2 and T3. This study demonstrates the importance of temporally intensive, long-term monitoring for capturing changes in groundwater level and water quality with precipitation fluctuations, and we showed how this approach can lead to a better understanding of the nitrate contamination situation.

High growth potential and nitrogen removal performance of marine anammox bacteria in shrimp-aquaculture sediment.

Anaerobic ammonium oxidation (anammox) bacteria were enriched in continuous packed-bed columns with marine sediment. One column (SB-C) was packed with only marine sediment collected from a shrimp-aquaculture pond, and another column (SB-AMX) was inoculated with marine anammox bacteria (MAB) as a control. These columns were continuously fed with natural or artificial seawater including ammonium (NH4+) and nitrite (NO2-). The SB-AMX showed anammox activities from the beginning and continued for over 200 days. However, the SB-C had no nitrogen removal performance for over 170 days. After adding a bicarbonate solution (KHCO3) to the sediment-only packed column, anammox activity was observed within 13 days. The column exhibited a nitrogen removal efficiency (NRE) of 88% at a nitrogen loading rate (NLR) of 1.0 kg-N·m-3·day-1, which was comparable to the control one. A next-generation sequencing analysis revealed the predominance of MAB related to "Candidatus Scalindua spp.". In addition, the co-occurrence of sulfur-oxidizing denitrifiers was observed, which suggests their symbiotic relationship. This study suggests the applicability of MAB for in-situ bioremediation of nitrogen-contaminated marine sediments and reveals a potential microbial interaction between anammox and sulfur-oxidizing communities responsible for nitrogen and sulfur cycling in marine aquaculture systems.

One-stage partial nitritation and anammox in membrane bioreactor.

Partial nitritation and anammox (PN/A) was applied in a lab-scale membrane bioreactor (MBR) to investigate its technical feasibility for treating ammonium-rich wastewater with low C/N ratio. The bacterial community was analyzed by molecular cloning and 16S rRNA sequence analysis. Partial nitritation (PN) was first realized in MBR by seeding aerobic activated sludge. With dissolved oxygen control, a steady effluent mixture with NO2 (-)-N/NH4 (+)-N ratio of 1.13 ± 0.08 was generated from the PN process. Subsequently, the MBR was seeded with anammox biomass on day 59. After running 300 days, the one-stage PN/A achieved a maximum nitrogen removal rate of 1.45 kg N/m(3)/day at the nitrogen removal efficiency of 89.5 %. Microbial community analysis revealed that Nitrosomonas sp. HKU and Nitrosospira sp. YKU corresponded to nitritation; meanwhile, Candidatus Brocadia TKU sp. accounted for nitrogen removal of the PN/A system. Specifically, Nitrosomonas sp. were enriched in the reactor at the PN/A phase and then conquered Nitrosospira sp. to be the predominant ammonia oxidizers. Nitrite oxidizers and denitrifiers were detected in symbiosis with aforementioned microbes. Denitrification promised potential plus nitrogen depletion. The present one-stage PN/A process allows a significant decrease in operational costs compared with classical nitrification/denitrification.

Nitrogen removal properties in a continuous marine anammox bacteria reactor under rapid and extensive salinity changes.

Salinity tolerance is one of the most important factors for the application of bioreactors to high-salinity wastewater. Although marine anammox bacteria (MAB) might be expected to tolerate higher salinities than freshwater anammox bacteria, there is little information on the effects of salinity on MAB activity. This study aimed to reveal the nitrogen removal properties in a continuous MAB reactor under conditions of rapid and extensive salinity changes. The reactor demonstrated stable nitrogen removal performance with a removal efficiency of over 85% under salinity conditions ranging from 0 to 50 g/L NaCl. The reactor performance was also well maintained, even though the salinity was rapidly changed from 30 to 50 g/L and from 30 to 0 g/L. Other evidence suggested that the seawater medium used contained components essential for effective MAB performance. Bacterial community analysis using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) showed that planctomycete UKU-1, the dominant MAB species in the inoculum, was the main contributor to anammox activity under all conditions. The PCR-DGGE using a universal bacterial primer set showed different DNA band patterns between the reactor biomass sample collected under conditions of 75 g/L NaCl and all other conditions (0, 30, 50 and freshwater-medium). All DNA sequences determined were very similar to those of bacterial species from marine environments, anaerobic environments, or wastewater-treatment facilities.

Application of a modified conceptual rainfall-runoff model to simulation of groundwater level in an undefined watershed.

Groundwater level simulation models can help ensure the proper management and use of urban and rural water supply. In this paper, we propose a groundwater level tank model (GLTM) based on a conceptual rainfall-runoff model (tank model) to simulate fluctuations in groundwater level. The variables used in the simulations consist of daily rainfall and daily groundwater level, which were recorded between April 2011 and March 2015 at two representative observation wells in Kumamoto City, Japan. We determined the best-fit model parameters by root-mean-square error through use of the Shuffled Complex Evolution-University of Arizona algorithm on a simulated data set. Calibration and validation results were evaluated by their coefficients of determination, Nash-Sutcliffe efficiency coefficients, and root-mean-square error values. The GLTM provided accurate results in both the calibration and validation of fluctuations in groundwater level. The split sample test results indicate a good reliability. These results indicate that this model can provide a simple approach to the accurate simulation of groundwater levels.

Kinetic study on nitrogen removal performance in marine anammox bacterial culture.

Kinetics of anaerobic ammonium oxidation (anammox) reaction in marine anammox bacterial culture was first investigated. The nitrogen removal performance of the reactor was compared with prediction of Monod model, modified Stover-Kincannon model, first-order and the Grau second-order substrate removal models. Based on calculations, Monod model, modified Stover-Kincannon model and the Grau second-order model proved to be more appropriate to describe the nitrogen removal kinetics of the reactor than first-order model with high determination coefficients of 0.993, 0.993 and 0.991, respectively. According to the modified Stover-Kincannon model, the maximal substrate removal rate (rm) and saturation rate constant (KB) were suggested as 7.37 and 6.41 g N/L/d, respectively. In addition, in light of the Monod model, the saturation concentration (Ks) and the maximal specific substrate removal rate constant (Rm) were determined to be 0.107 g/L and 0.952 g N/g MLVSS/d, respectively. Moreover, model evaluation was carried out by assessing the linear correlation between measured and predicted values. Both kinetics study and model evaluation showed that Monod model, modified Stover-Kincannon model and the Grau second-order substrate removal models could be used to describe the kinetic behavior or design of the marine anammox reactor.

Temperature effect on nitrogen removal performance and bacterial community in culture of marine anammox bacteria derived from sea-based waste disposal site.

Anaerobic ammonium oxidation (anammox) bacteria have been detected in variety of marine environment in recent years, however, there have been only a few studies on their characteristics in the culture. The aim of this study is to reveal the effect of temperature on nitrogen removal ability and bacterial community in a culture of marine anammox bacteria (MAAOB). The MAAOB were cultured from the sediment of a sea-based waste disposal site at the North Port of Osaka Bay in Japan. The maximum nitrogen removal rate (NRR) was observed at 25°C in the MAAOB culture, and it decreased both at below 20°C and over 33°C. The activation energy of the MAAOB culture was calculated to be 54.6 kJ mol(-1) in the 5°C to 30°C range. No significant change in bacterial community according with temperature (5-37°C) was confirmed in the results of polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE). Meanwhile, a number of bacteria related to the oxidation-reduction reaction of sulfur were confirmed and it is speculated that they involved in the activity of MAAOB and nitrogen removal ability in the culture.

Enrichment culture of marine anaerobic ammonium oxidation (anammox) bacteria from sediment of sea-based waste disposal site.

The present study investigates the enrichment of anaerobic ammonium oxidation (anammox) bacteria in the marine environment using sediment samples obtained from a sea-based waste disposal site and discusses the construction of marine anammox bioreactor. Enrichment of bacteria related to Candidatus Scalindua wagneri along with simultaneous removal of nitrite and ammonium ions was observed in the continuous bioreactor culture under a total nitrogen loading rate of 0.4 kg-N m(-3) day(-1).

Microbial ecology of a perchlorate-reducing, hydrogen-based membrane biofilm reactor.

The hydrogen-based membrane biofilm reactor (MBfR) has been shown to reduce perchlorate to below 4 microg/L, but little is known about the microbial ecology of this or other hydrogen-based reactors, especially when influent perchlorate concentrations are much lower than the influent oxygen and nitrate concentrations. Dissimilatory (per)chlorate-reducing bacteria (PCRB) can use oxygen as an electron acceptor, and most can also use nitrate. Since oxygen and nitrate can be reduced concurrently with perchlorate, they may serve as primary electron acceptors, sustaining PCRB when the perchlorate concentrations are very low. We studied five identical MBfRs, all seeded with the same inoculum and initially supplied with oxygen, or oxygen plus nitrate, in the influent. After 20 days, perchlorate was added to four MBfRs at influent concentrations of 100-10,000 microg/L, while the fifth was maintained as a control. One day after perchlorate addition, the MBfRs displayed limited perchlorate reduction, suggesting a low initial abundance of PCRB. However, perchlorate reduction improved significantly over time, and denaturing gradient gel electrophoresis (DGGE) analyses suggested an increasing abundance of a single Dechloromonas species. Fluorescence in-situ hybridization (FISH) tests showed that the Dechloromonas species accounted for 14% of the bacterial count in the control MBfR, and 22%, 31%, and 49% in the MBfRs receiving nitrate plus 100, 1000, and 10,000 microg/L perchlorate, respectively. The abundance was 34% in the MBfR receiving oxygen plus 1000 microg/L perchlorate. These results suggest that oxygen is more favorable than nitrate as a primary electron acceptor for PCRB, that PCRB are present at low levels even without perchlorate, and that the presence of perchlorate, even at low levels relative to nitrate or oxygen, significantly enhances selection for PCRB.

Kinetics of a hydrogen-oxidizing, perchlorate-reducing bacterium.

This paper provides the first kinetic parameters for a hydrogen-oxidizing perchlorate-reducing bacterium (PCRB), Dechloromonas sp. PC1. The qmax for perchlorate and chlorate were 3.1 and 6.3 mg/mgDW-day, respectively. The K for perchlorate was 0.14 mg/L, an order of magnitude lower than reported for other PCRB. The yields Y on perchlorate and chlorate were 0.23 and 0.22 mgDW/mg, respectively, and the decay constant b was 0.055/day. The growth-threshold, Smin, for perchlorate was 14 microg/L, suggesting that perchlorate cannot be reduced below this level when perchlorate is the primary electron-acceptor, although it may be possible when oxygen or nitrate is the primary acceptor. Chlorate accumulated at maximum concentrations of 0.6-4.3 mg/L in batch tests with initial perchlorate concentrations ranging from 100 to 600 mg/L. Furthermore, 50 mg/L chlorate inhibited perchlorate reduction with perchlorate at 100 mg/L. This is the first report of chlorate accumulation and inhibition for a pure culture of PCRB. These Chlorate effects are consistent with competitive inhibition between perchlorate and chlorate for the (per)chlorate reductase enzyme.

Effect of inoculum conditioning on hydrogen fermentation and pH effect on bacterial community relevant to hydrogen production.

The effect of conditioning for a variety of inoculums on fermentative hydrogen production was investigated. In addition, the effects of pH condition on hydrogen fermentation and bacterial community were investigated. The effect of conditioning on hydrogen production was different depending on the inoculum types. An appreciable hydrogen production was shown with anaerobic digested sludge and lake sediment without conditioning, however, no hydrogen was produced when refuse compost and kiwi grove soil were used as inoculums without conditioning. The highest hydrogen production was obtained with heat-conditioned anaerobic digested sludge, almost the same production was also obtained with unconditioned digested sludge. The pH condition considerably affected hydrogen fermentation, hydrogen gas was efficiently produced with unconditioned anaerobic sludge when the pH was controlled at 6.0 throughout the culture period and not when only the initial pH was adjusted to 6.0 and 7.0. Hydrogen production decreased when the culture pH was only adjusted at the beginning of each batch in continuous batch culture, and additionally, bacterial community varied with the change in hydrogen production. It was suggested that Clostridium and Coprothermobacter species played important role in hydrogen fermentation, and Lactobacillus species had an adverse effect on hydrogen production.

Isolation of aryl-phosphate ester-degrading bacterium from leachate of a sea-based waste disposal site.

An aryl-phosphate ester (APE)-degrading bacterium was isolated from the leachate of a sea-based waste disposal site. The isolated APE-degrading bacterial strain YS-57 grew well in a medium containing glucose and NaCl, and degraded two types of APE:tricresyl phosphate and triphenyl phosphate. The optimal temperature, pH, and NaCl concentration for the growth of strain YS-57 were 30 degrees C, 7.0, and 1.0%, respectively. Strain YS-57 grew at an APE concentration of 25 mg/l without being inhibited. APEs were degraded by the supernatant of the medium in which strain YS-57 was cultured, suggesting that the APE-degrading enzyme was released into the extracellular space in the logarithmic growth phase. The 16S rDNA sequence of strain YS-57 showed 95.6% similarity to that of Roseobacter gallaeciensis and the morphological properties were also comparable. Consequently, strain YS-57 was closely related to the genus Roseobacter.

Estrogenic chemicals and estrogenic activity in leachate from municipal waste landfill determined by yeast two-hybrid assay.

Estrogenic activity and estrogenic chemicals in landfill leachate were investigated by yeast two-hybrid assay and chemical analysis. Leachate sample extracted by liquid-liquid extraction with dichloromethane at pH 7.0 showed a higher dose-response curve than sample extracted at pH 3.0. or than sample extracted by solid phase extraction at either pH 7.0 or 3.0. The fraction extracted at pH 3.0 specifically inhibited not only growth of yeast but also estrogenic activity in this assay, suggesting that it contained anti-estrogenic chemicals. The greatest contributor to estrogenic activity among the chemicals identified in leachate extract was bisphenol A, with an estimated contribution ratio of 84%. The contribution ratios of 4-nonyl phenol (4-np) and 4-tert-octyl phenol (4-t-op) were estimated at 1.0%, and 0.1%, respectively, while natural estrogens such as 17beta-estradiol or estrone were below detection limit, so that their contribution ratio was estimated at no more than 10%. The estrogenic activity of leachate was decreased by aeration treatment alone after 7 days, and was no longer detected after 22 days. Concentrations of bisphenol A, 4-np and 4-t-op likewise decreased with aeration.