To obtain fundamental insights into the potential implementation of anaerobic digestion without heating at wastewater treatment plants, on-site maintenance data were analyzed, and laboratory experiments under varying digester temperature conditions were conducted. Anaerobic digestion performance was evaluated by calculating the digestion rate from the concentrations of total solids and volatile solids. Higher digestion rates were confirmed under higher digester temperatures. In the laboratory experiments where the operational temperature was switched from mesophilic (35°C) to psychrophilic (15°C) conditions, biogas production was observed when a sufficient acclimation period was provided. It was confirmed that the maximum achievable digestion ratio was equivalent under both mesophilic and psychrophilic conditions, although the reaction rate constant was lower under the psychrophilic condition. Microbial community analysis from these experiments revealed an increase in Methanosarcina genus after approximately 300 days of acclimation to lower temperatures. These findings suggest that anaerobic digestion without heating or at low temperatures is feasible.

 In recent years, many studies have been conducted on the effects of additives on the anaerobic digestion process. In this study, steelmaking slag was used as an additive in the anaerobic digestion of sewage sludge and its effect was investigated. Batch anaerobic digestion experiments were conducted by adding converter slag and blast furnace slag with different compositions. The results showed that the addition of converter slag increased the CH₄ content in the biogas by removing CO₂ from the biogas through the carbonation reaction between the Ca contained in the slag and the CO₂ in the biogas. When converter slag (2 g/L) was added to mixed sludge anaerobic digestion, the CH₄ content increased from 66% to 71% and the CH₄ yield increased 1.8 times compared to the control. On the other hand, the addition of blast furnace slag had no effect. The Fe content of the converter slag was higher than that of the blast furnace slag, suggesting that Fe compounds in the converter slag may have contributed to the increase in CH₄ yield.

 The objective of this study is to replicate the acidification process due to trace element deficiency in methane fermentation of food waste, while identifying the change patterns of various indicators of methane fermentation and environmental conditions and examining the correlations between monitoring indicators to provide a foundation for realizing control methods and automatic monitoring. Using a completely mixed reactor with a mesophilic temperature and a HRT of 30 days, a long-term continuous experiment of methane fermentation using food waste without trace elements as the substrate was conducted, and two acidification processes were replicated while continuously monitoring each parameter and analyzing their correlations. As a result, the acidification process due to trace element deficiency was identified through indicators such as organic matter decomposition rate, biogas production, organic acid accumulation, and variations in pH and alkalinity, and was replicated twice. Moreover, among the automatically detectable parameters, linear correlations between CO₂ ratio, pH, and ORP were identified, along with significant correlations between gas production rate, CO₂ ratio, pH and alkalinity 6.5, TVFAs, and TVFAs/alkalinity 6.5.

 A new process for centralized anaerobic digestion of dewatered sludge is proposed in this study. Hydrothermal treatment of dewatered sludge was performed. Water was then added to the hydrothermally treated sludge and dewatering was performed to extract organic matter to the liquid phase. The resulting liquid was used as a substrate for an anaerobic membrane bioreactor (AnMBR) to produce biogas. The solubilization ratio of dewatered sludge was 20.9% after 1 hour of hydrothermal treatment at 150°C. The water content of the dewatered residue was 76.6%. The organic-rich liquid was recovered and fed to the AnMBR. The AnMBR was operated by shortening the HRT step by step. As a result, the HRT could be shortened to 5 days without accumulation of volatile fatty acids. The biogas production rate and the methane yield were 1.74 L/L/d and 0.25 L/g-COD, respectively, when the HRT was 5 days. When the HRT was shortened to 2 days, the transmembrane pressure reached 50 kPa due to membrane fouling. Membrane cleaning at the end of the AnMBR operation indicated that reversible fouling was dominant.

 To mitigate global warming, seaweeds or marine algae are expected to capture carbon dioxide directly from the atmosphere. With the aim to transplant it to the coastal areas in the future, we tried to culture a brown algae Sargassum horneri, which is frequently found in the coastal area in Japan at a low cost using composted sewage sludge as a locally available nutrient source. As a fundamental study, we mixed 1 L seawater and 10 g composted sewage sludge and collected its supernatant as composted sewage sludge (CSS) extract. Then, the brown algae was grown at 20 °C in the seawater mixed with CSS extract at 0%, 1%, 10%, and 20% for seven weeks, replacing the mixture of seawater and CSS extract every week. As the result, the algal growth was observed only in the seawater with 1% CSS extract, achieving the maximum values of full length and fresh weight which were 1.2 and 2.1 times larger than those in the seawater without CSS extract, respectively. On the other hand, the extract application at 10% and 20% to the seawater significantly inhibited the algal growth, probably due to the oversupplies of ammonium and phosphorus from CSS. The algae grown in the seawater with 1% CSS extract had photosynthetic pigments at the comparable concentrations to those grown in the seawater without CSS extract, while they had less contents of heavy metals. These results revealed the potential of CSS to supply nutrients for seaweed growth but the size of brown algae grown in this study was not enough for its transplantation to the coastal areas, motivating further studies to use CSS more effectively.

 Recently, sewage sludge has been attracting attention as a stable domestic source of fertilizer raw materials. In Europe and the United States, however, it has been found to contain per/polyfluoroalkyl compounds (PFAS) in sewage sludge, and there is a movement to establish regulations on fertilizer use. However, knowledge of PFAS in sewage sludge in Japan is lacking. In order to clarify the actual status of PFAS contamination, this study analyzed dewatered cake from 34 sewage treatment plants across Japan for 30 types of PFAS. The total concentrations of the 30 PFASs were 4.6-370 ng/g-dry, with PFOS being the most prominent PFAS, and many long- and short-chain PFASs such as PFHxA, PFNA, PFUnDA, etc. were also detected. The concentrations of PFOS tended to be significantly higher in anaerobic digested sludge. PFOA, PFNA, and PFUnDA showed a slight tendency to increase in concentration with inorganic dewatering aids. It is necessary to pay attention to PFOS concentrations and their trends in order to expand the use of fertilizers in the same way as in Europe and the United States.

 In this study, we carried out a laboratory-scale investigation of the flocculation, concentration, and dewatering of the green alga Chlorella sorokiniana and the diatom Chaetoceros simplex var. calcitrans using polymer flocculants and slurries made with dried microalgae powder. The flocculation experiments were conducted using five different polymer flocculants, with variations in flocculant addition ratio, agitation conditions, and slurry pH. We then conducted gravity concentration and centrifugal dewatering experiments on the formed aggregates, varying the centrifugal strength. The results showed that fast and long agitation produced a higher recovery ratio of exceeding 98%. However, flocculants with larger molecular weights exhibited increased flocculation efficiency under conditions of slow agitation. pH fluctuations from 6 to 8 resulted in a maximum difference of 24.1% in recovery ratio when the flocculant addition ratio was 1%, but almost no change when the addition ratio was 3% or higher. The flocculant with the highest cationic degree in the range of this study showed high recovery rates of approximately 90% at a 2% addition ratio and over 95% at a 3% addition ratio for both microalgae species. The water content of aggregates decreased to about 65% for C. sorokiniana and about 72% for C. simplex var. calcitrans after centrifugal dewatering, suggesting that the dewaterability of algae varies depending on the substances constituting their surface. As the centrifugal intensity was increased, the water content converged to a constant value, which is about 65% for C. sorokiniana and about 70% for C. simplex var. calcitrans, indicating that efficient dewatering cannot be achieved with strong centrifugal separation. By flocculation and concentration, the volume of C. sorokiniana and C. simplex var. calcitrans were reduced to about 1/180 and 1/77, respectively, compared to those before flocculation. Centrifugal dewatering at 700 G or higher further reduced the volume of C. sorokiniana by about one-half and C. simplex var. calcitrans by one-third, respectively.

 This study dealt with phosphorus recovery based on acid extraction from sewage sludge incineration ash combining inorganic chemicals with solid-liquid separation. The recovery of iron and aluminum was also investigated. The recovery method consisted of three steps: after the acid extraction, the acid-extracted solution was adjusted to the pH of 3.0, 3.5, 4.0 or 5.0, and finally separated into calcium phosphate, iron hydroxide and aluminum solution fractions. The phosphorus recovery efficiency of 69-82% was obtained in the calcium phosphate fraction, and the efficiency reached a maximum at the pH of 4.0. The recovery efficiency of iron and aluminum was 55-90% and 75-82%, respectively. The calcium phosphate obtained had a sufficiently low content of heavy metals, but the purity and concentration of iron and aluminum obtained in each faction were evaluated to be insufficient.

 The Japanese eel, Anguilla Japonica, is an essential fish for Japanese. However, the population of Japanese eels has been drastically decreasing. Fish stray into water intakes of dams and weirs and are consumed. There are methods to control fish behavior to prevent straying by using their senses such as sight. Fish have the ability to recognize colors. However, there is no information on the effects of hue, value and chroma of color, on the swimming characteristics of Japanese eels. In this study, the hue, value and chroma of the side and bottom walls colors of a circular pool were changed, to investigate the effects of the three color attributes on the swimming characteristics of Japanese eels. It was found that value was more dominant than hue and chroma in influencing swimming characteristics of Japanese eels. Further, it was also found that when the color of value was changed from black to white, the rate of returning back to low value area and the spent time in the low value area increased, whereas the entering rate into high value area decreased.

 This study attempted to evaluate changes in the spawning habitat of ice goby in the brackish waters of the Muromi River over the past 10 years, based on spawning conditions obtained from field surveys and changes in spawning fitness determined by a generalized linear model. Although the number of spawning sites and plots were in a decreasing trend, the area around the pier of the Muromi New Bridge and the area where spawning grounds were constructed consistently functioned as the main spawning habitat. Although changes in the shape of the sandbars were observed, the spawning area did not change significantly in the 500 m downstream of the weir. However, in recent years, spawning sites have been limited to areas with

 Wild sweetfish (Plecoglossus altivelis) or Ayu in Japanese has cucumber-like and watermelon-like aromas produced in the de-composition of ingested algae, while cultured one has less of these aromas due to the absence of algae in their feed. In this study, microalgae were incubated using treated municipal wastewater (TWW) without any exogenous nutrients and used for the experiment to add the aromas to the cultured sweetfish. In the experiment, the microalgae incubated in TWW were mixed with artificial feed at a ratio of 0 to 30% by weight and fed to the cultured sweetfish for two weeks before the harvest. The incubation in TWW found the dominant class of algae was Chlorophycese, which is belonging to green algae, followed by Diatoma. Of the class of Chlorophyces, the dominant species was Chlorococcales sp., regardless of sampling dates in June and July 2023. In some dates of sampling, Oxyphotobacteria, a bluegreen algae, were detected. Feeding these incubated algae to the cultured sweetfish did not affect the concentration of cucumber-like and watermelon-like aromas such as 3, 6-Nonadien-1-ol and 2, 6-Nonadienal in the fish meat regardless of the amount of fed microalgae but increased them in the fish guts, demonstrating that the sweetfish cultured with the microalgae could obtain such desirable aromas. Additionally, the concentrations of musty off-flavor (2, 4, 6-Trichloroanisole, 2-methylisoborneol, and geosmin) and musk flavor (Galaxolide (HHCB) and Tonalid (AHTN)) components in the fish guts under the microalgae-feeding condition were higher than those without the microalgae-feeding, suggesting that the microalgae incubated in TWW might have these undesirable flavors. This study revealed the feasibility of our idea to give the cultured ayu cucumber-like and watermelon-like aromas by feeding microalgae incubated TWW, although further investigation is needed to determine an optimum condition for microalgae feeding which give these aromas to cultured sweetfish without musty and musk flavors.

 In this study, we attempted to cultivate Artemia for a long period of time utilizing microalgae that naturally proliferate from municipal wastewater treated water with the activated sludge method. As a result of two weeks of culture under natural conditions using only treated municipal wastewater as a substrate, green algae with Scenedesmus quadricauda as the dominant species proliferated. In the component analysis of algal biomass, ash (36%) was detected in the highest proportion, and the proportions of protein and lipid were lower than that of Chlorella. Microalgae derived from urban wastewater treatment plant contained a greater variety of fatty acids, and the proportion of unsaturated fatty acids was higher than that of Chlorella. In a feeding experiment of Artemia, under conditions in which microalgae derived from treated municipal wastewater were fed, initial growth was slower than that of the comparison Chlorella, but it survived for over 70 days and grew to adults. The birth of nauplii was also confirmed, indicating that microalgae derived from treated wastewater are effective as food for the long-term rearing of Artemia.

 This research aimed to establish an energy-creating, low-carbon resource recovery system suitable for the reclamation of concentrated Johkasou sludge. The system consists of (1) high-efficiency anaerobic digestion using a high-solid anaerobic membrane bioreactor (AnMBR) for energy recovery and (2) nitrogen removal and phosphorus recovery using the HAP based one-stage partial nitritation and anammox (PNA) process. The high-solid AnMBR was continuously operated throughout a year to investigate the bioenergy production, material flow and seasonal impacts of concentrated Johkasou sludge. The greatest biogas production rate was observed during summer (0.63 L/L/d), owing to the high total organic and solid content. The material flow results revealed that 46.5–52.4% total COD and 50.2–58.0% carbon was converted to biogas. A hydroxyapatite-based one-stage partial nitritation/anammox (HAP-PNA) process was combined with an AnMBR treating concentrated organic sludge for permeate polishing, focusing on the enhancement of phosphorus recovery by influent Ca/P ratio optimization, alkalinity control and the effect of HAP formation on nitrogen removal. The reactor operated at the nitrogen loading rate of 0.73 kg-N/m³/d and realized 81.6% nitrogen removal efficiency (NRE) and 0.6 kg-N/m³/d nitrogen removal rate. The phosphorus removal efficiency (PRE) and sludge settleability were significantly enhanced by the addition of calcium, and a maximum PRE of 73.2% was achieved when the influent Ca/P ratio was 2.7. The reactor showed high stability and nitrogen removal performance, even when the phosphorus removal rate/nitrogen removal rate ratio was as high as 0.12. This study demonstrates the excellent capability of the one-stage HAP-PNA process for permeate treatment with high phosphorus content. The energy recovery rates ranged from 8.69 to 9.96 kJ/g-VSfed and the system energy self-sufficiency rates ranged from 149-203%. The results demonstrated that the innovative system yielded high energy conversion efficiency and could realize energy positive.

 As CO₂ emission reduction and resource recovery have become common challenges globally, biomethanation technology is regarded as one potential solution. In biomethanation reactors, although the diversity and interactions of microorganisms are complex, their variations significantly impact fermentation efficiency which requires quantitative analysis. This study conducted a long-term continuous experiment in a 15L AnMBR (anaerobic membrane bioreactor) to evaluate the changes in decarbonization efficiency and microbial community structure under different carbon loading. The results showed that at a carbon loading rate of 1.0 g-C/L/d, the decarbonization rate reached over 85%. When carbon loading increased, the dominant microbial species in the reactor shifted from the methane-producing archaeon Meth-anosarcina (17.7%) to the hydrogenotrophic methanogen Methanobacterium (39.4%), which led to a high CH₄ production rate (67 mL/gVSS/h). It was indicated that utilizing a filtration membrane for solid-liquid separation can maintain a high concentration of methanogenic archaea and improve the reactor's decarbonization efficiency and CH₄ production.

 Adsorptive removal of nine antibiotics from water sample and sewage treatment effluent was investigated using biochar (BC) derived from durian peel. Although adsorption capacities of BC for antibiotics in water sample were lower compared to commercial activated carbon (AC), antibiotics concentrations were decreased with an increase in BC dosage. Adsorption isotherm and kinetics of BC for clarithromycin were fitted to Langmuir model and pseudo second order rate model. Maximum adsorption capacity was 5.16 mg/g, which was comparable to the result from other study. Adsorption efficiency of antibiotics except sulfamethoxazole in sewage treatment effluent increased with an increase in BC dosage and showed more than 80%. Therefore, BC would be useful as environmentally friendly adsorbent for antibiotics removal from the effluent applied to agriculture.

 Feeding protein-rich forage rice irrigated with treated municipal wastewater for fattening pigs at 5-6 months of age was reported to improve the quality of its meat in our previous study. However, this feeding practice has a concern regarding the potential transmission of antimicrobial-resistant bacteria and resistance genes from the treated wastewater to the pigs. In this study, we investigated the antimicrobial resistance of Escherichia coli isolated from 9 pigs (test) at 6 month of age, which were fed the wastewater-irrigated forage rice for 55 days, at a pig farm in Yamagata, Japan, comparing the isolates from other 9 pigs (control) fed the same cultivar of rice produced in the conventional farming practice. Forty-three strains of E. coli were isolated from the fecal samples collected from 16 of 18 fattening pigs, including 22 strains from 8 test pigs and 21 strains from 8 control pigs. Antimicrobial susceptibility testing revealed 24 of 43 isolates, with 10 isolates from 5 test pigs and 14 isolates from 7 control pigs, were resistant to tetracycline, chloramphenicol, kanamycin, ampicillin, or sulfamethoxazole/trimethoprim. No significant difference in resistant rates to any of these five antimicrobials were found between the test and control pigs (p > 0.05). The 24 isolates of resistant E. coli were characterized by the detection of antimicrobial-resistance genes using PCR analysis and the classification using multi-locus sequencing typing. Twelve types of resistance genes associated with the above five antimicrobials were detected from the isolates, with the similar profile between test and control pigs. Moreover, the resistant isolates were classified into six sequence types (STs), which were consistent across the two groups of pigs. These findings suggest that feeding the wastewater-irrigated forage rice to fattening pigs at 5-6 months of age caused negligible impacts on the occurrence of antimicrobial resistant E. coli in their intestines.

 A study was conducted to investigate the presence of E. coli and antibiotic-resistant E. coli at 15 sites, including 8 tidal rivers flowing into Urado Bay in Kochi Prefecture and a beach outside the bay. Water samples were collected during both fair weather and rainy conditions. The results showed an increase in bacterial counts during rainfall compared to fair weather. Based on the relationship among rainfall patterns, bacterial counts, and the salinity of water samples, it is suggested that increased microbial loads from upstream river areas and the bay's seawater could be potential sources of contamination during rainfall. A trend was also observed where greater total rainfall was associated with a larger increase in bacterial counts in the rivers. Additionally, at locations where seawater from Urado Bay flows back upstream, a detailed investigation of bacterial count variations was conducted through continuous water sampling during both fair weather and rainfall. The findings confirmed that during fair weather, the backflow of seawater from Urado Bay led to a reduction in the number of E. coli and antibiotic-resistant E. coli in the rivers due to dilution and other effects. During rainfall, both seawater from Urado Bay and runoff from upstream river areas could be a sources of contamination.

 Antimicrobial substances in river water and in-stream organic matter (suspended fine particulate organic matter (SFPOM), attached algae and bentic fine particulate organic matter (BFPOM)) were analysed in rivers whose catchment area is an agricultural and livestock farming region, and the behaviour and distribution of antimicrobial substances between rivers was studied. The results of the measurement of 14 antimicrobial substances common to water and each organic matter in the river showed that 10, 3, 7 and 5 antimicrobial substances were detected in river water, SFPOM, attached algae and BFPOM, respectively. In addition, a comprehensive analysis of 74 antimicrobial substances in organic matter in rivers showed that 11, 38 and 24 antimicrobial substances were detected from SFPOM, attached algae and BFPOM, respectively, although at trace concentrations, suggesting that antimicrobial substances in rivers show different distribution and behaviour depending on the type of organic matter, survey period and sampling point.

 We investigated the prevalence and characterization of antibiotic-resistant Escherichia coli in dent corn fields using sewage-based fertilizers in Tsuruoka City, Yamagata, Japan. Over a period of four months, between June and September 2023, 21 soil samples were collected in the fields that utilized composted sewage sludges and liquid centrate from sludge dewatering as sewage-based fertilizers. For comparison, an additional 27 soil samples were collected in the fields using pig manure, chemical fertilizers, and no fertilizer. The findings of quantifying the amount of E. coli in the samples detected in 48 soil samples in the early growing stage and after harvesting at the concentration ranging from 3.0×10¹ to 1.4 ×10³ CFU/g. The detection rate and concentration were not significantly affected by the application of sewage-based fertilizers. Antibiotic susceptibility tests using 18 antibiotics demon-strated that 15 (31.2%) of the 48 isolates were resistant to ciprofloxacin (13.2%), amikacin (13.2%), and ampicillin (7.5%). To identify the host origin of E. coli, phylogenetic groups analysis and MLST analysis were performed. The main phylogenetic groups were classified A (15 isolates) and B1 (15 isolates) which were normally detected in livestock hosts. The 15 isolates were classified as ST720, which has been reported in environmental isolates. These findings indicate that the identified E. coli did not come from sewage sludge sources, but rather from external environmental factors, such as surrounding fields and wildlife.

 In recent years, aquatic biodiversity surveys using environmental DNA (eDNA) have been conducted, but the behavior of eDNA remains largely unknown. In this study, we investigated the temporal variation of eDNA concentration of the Plecoglossus altivelis and Stenopsyche marmorata. As a result, the DNA of S. marmorata was detected from night to morning, while the DNA of P. altivelis was detected throughout the day. This may be related to the migratory and spawning habits of S. marmorata from evenings to mornings. Moreover, the detection frequency of S. marmorata increased when using a filter with a smaller pore diameter (0.20 µm) compared to a filter with a larger pore diameter (0.65 µm) typically used for eDNA analysis.

 Although the accuracy of environmental DNA (eDNA) detection is influenced by biological and environmental conditions, eDNA dynamics in turbid water is not well understood, precluding establishment of eDNA surveys in turbid water area. In this study, we evaluated the effect of different turbidity conditions on aqueous eDNA fate with different states. Water samples under five turbidity conditions (0, 20, 50, 100, and 200 ppm) were designed by mixing riverbed sediment and either distilled water or aquarium water rearing common carps (Cyprinus carpio). We filtered the turbid water samples using two types of glass fiber filters with different pore sizes and quantified carp eDNA using digital PCR. Consequently, as turbidity increased, the concentration of eDNA also increased; however, under high turbidity conditions, the eDNA concentration tended to decrease. These findings suggest that eDNA recovery is higher at moderate levels of turbidity owing to the adsorption of eDNA and the influence of PCR inhibitors.

 Environmental DNA (eDNA) has attracted attention to evaluate the abundance and distribution of rare species in aquatic environments such as rivers, lakes, and sea. Recently, with the development of technologies for eDNA analysis, it has been applied for diverse purposes, including the detection of invasive alien species and the protection of endangered species. In this study, we developed an analytical assay that uses eDNA to determine the abundance of fish species to understand the habitat conditions of Masu salmon (Oncorhynchus masou), which are important fishery resources. Quantitative PCR using the TaqMan probe assay was employed to estimate the populations of the target species. The developed assay successfully provided the amount of eDNA reflecting the population density in the breeding tanks, and was established as an effective and labor-saving assay to determine the abundance of O. masou spp. To understand the migration ecology of O. masou masou, field surveys were conducted once a month from July to November 2021 at nine sites on the Akagawa River in Yamagata, Japan. The analysis of samples obtained in the survey using the developed assay demonstrated that the amount of eDNA in O. masou spp. varied significantly depending on the month (p = 0.016), reaching a maximum (1.3×10⁶ copies/s) in October. This fluctuation indicates the effects of upstream migration and spawning activities of anadromous Masu salmon from the coastal area. The eDNA of O. masou spp. was not detected in the Otori River (AK1) throughout the study period, which was consistent with the actual habitat distribution of Masu salmon in the Akagawa River. The eDNA analysis developed in this study may be used not only to understand the seasonal migration ecology of O. masou spp. but also to identify the upper boundary of the run and spawning grounds.

 Fishways have been constructed to eliminate the obstruction of fish migration by dams and weirs. Fishway research over the years has focused mainly on swimming fish, but in recent years, benthic fish such as eels have also become a target. In Europe and the United States, fishways for eels with brushes and studs on the bottom of fishway have been proposed. However, specifications of studs suitable for migration of eels are not always clear. In this study, diameters of studs on bottom of eel-ladder were varied 12-60 mm, and total length of eels was varied 150-300 mm, to analyze effects of these studs on their migratory behavior. Under experimental conditions, diameter of stud suitable for migration depended on total length of Japanese eel, and 10-20% of total length was found to be appropriate. Future studies to determine whether similar criteria can be applied to Japanese eels with total lengths ranging from less than 150 mm to more than 300 mm are expected to provide partial design guidelines for eel-ladder that facilitate migration of Japanese eels and contribute to conservation of Japanese eels.

 This study applied a microbial fuel cell (MFC) to a small sewage treatment system (Johkasou) with iron electrolysis for phosphorus removal and evaluated its impact on treatment performance. The laboratory-scale reactor consisted of a 2.1L anaerobic and 1.4L aerobic tank, with the MFC installed in the anaerobic section and the iron electrolysis device in the aerobic section. An open circuit condition was also operated to compare the performance. The MFC demonstrated a maximum power density of 31 W/m² based on the cathode area. The removal of organic matter and nitrogen did not significantly change with or without applying the MFC. However, the phosphorus removal efficiency improved by 10% when the MFC was applied. The average amount of iron valence in the anaerobic sludge was estimated by the X-ray Absorption Near Edge Structure analysis (XANES). The results indicated that the valence of iron was 2.4 with the application of the MFC and 2.6 without it, suggesting that the MFC maintained iron in more reducing conditions. Additionally, the FePO₄ generated by iron electrolysis decreased in the anaerobic tank with the application of the MFC, suggesting a change in phosphorus retention form.

 Membrane bioreactor (MBR) process is superior to the conventional activated sludge (CAS) process in many aspects of wastewater treatment, and it is expected to perform better in terms of virus removal compared to CAS. However, the virus concentration in MBR-treated wastewater often falls below the limit of detection (LOD), making it difficult to measure with conventional detection techniques. In this study, we modified the efficient and practical virus identification system with enhanced sensitivity for membrane (EPISENS-M) method, originally developed for raw sewage, to a low-concentration version applicable to MBR-treated wastewater. We could successfully lowered the LOD to 0.1 copies/L. This improved method demonstrated the ability to quantify pathogenic viruses in effluents from an MBR treating municipal wastewater with approximately 100 to 1000 times the sensitivity of traditional detection techniques. Additionally, the virus removal rates calculated from the measured values showed a log reduction of 4 log₁₀ or higher for each virus, significantly higher than that of CAS. The modified EPISENS-M method for low-concentration ranges is useful for quantitatively evaluating the virus removal performance of MBR systems.

 Cultivation of forage rice using treated wastewater for irrigation can contribute to food security in Japan which imports most of fertilizer and livestock feed. In this study, we investigated the greenhouse gases (GHG) emitted from forage rice cultivation in a real paddy field irrigated with treated municipal wastewater (test field) and compared them with those in the conventional rice paddies cultivated with chemical fertilizers (control field). The total emissions of GHG, integrating methane and nitrous oxides, were 7506 ± 3588 kgCO₂-eq/ha in the test field, which were not significantly different from that (7035 ± 3207 kgCO₂-eq/ha) in the control field. However, in the more comprehensive approach, the GHG emissions could be reduced by 819 kgCO₂-eq/ha in the test field, where treated wastewater is reused instead of fertilizer application, mainly due to the reduction of CO₂ emission during the production and transportation of the chemical fertilizers used in the control field.

 In this study, we focused on nitric oxide (NO), which is now being elucidated as the dominant factor in nitrous oxide (N₂O) production by ammonia-oxidizing bacteria (AOB). In order to contribute to the development of technology for reducing N₂O production in full-scale wastewater treatment plants, we experimentally verified the possibility of extending the scope of the basic theory of N₂O production control by utilizing NO as the engineering indicator to complex microbial systems including denitrifying bacteria as well as AOBs. We designed the simple method for testing NO and N₂O production using disposable syringes and tested activated sludge collected from a wastewater treatment plant. The results showed that NO production is the dominant factor in the conversion rate and production rate of N₂O indicated by activated sludge in anaerobic, aerobic, and anoxic all biological reaction tanks. These results indicate the possibility of controlling N₂O production by comprehensively observing the NO-mediated interactions of complex microbial systems, such as nitrifying and denitrifying bacteria.

 The reduction of gaseous nitrous oxide (N₂O) emissions from wastewater treatment processes is required for the decarbonization of wastewater treatment plants, but the actual fluctuations in N₂O emissions have not yet been clarified. In this study, we conducted continuous monitoring of N₂O emissions from two wastewater treatment processes using an automatic gas analyzer. As a result of continuous monitoring for approximately four months, long-term, medium-term, and short-term fluctuations in N₂O emissions were revealed and the effects of influent water quality were evaluated. The results indicated that N₂O emissions may fluctuate due to the effects of water temperature in the biological reaction tank and influent nitrogen concentration, and that continuous monitoring is effective in clarifying the factors that affect N₂O emissions. Based on these results, it is necessary to review the N₂O emission coefficient and to study operational methods to reduce N₂O emissions.

 Effect of irrigation management when using treated municipal wastewater to cultivate forage rice on emission was analyzed by applying DNDC-Rice model, which simulates the dynamics of biochemical reaction in the soil, to find out effective irrigation condition for reducing GHG emission. According to the model analysis, nitrous oxide emission increased when mid-season drainage was done twice or triple. Methane emission decreased conversely, and total GHG emission converted to equivalent CO2 emission by multiplying GWP of methane and nitrous oxide has also decreased. It was also found that methane emission and total GHG emission decreased if nitrogen included in WWTP was consist of nitrate nitrogen, not ammonia nitrogen. It was shown that GHG emission from paddy field for cultivating forage rice with WWTP effluent could be reduced when irrigation condition was changed compared to conventional irrigation.

 Lake Barato is an oxbow lake isolated from the Ishikari River. It is used for fishing and recreation, and there is much interest in its water quality. The water quality of the Lake Barato has improved compared to the period when eutrophication was severe. However, the water quality of Lake Barato has not been studied in detail in recent years. There has also been no assessment of phosphorus release from lake sediments and related metal elements in lake sediments. In this study, lake water and sediment core samples were collected at high frequency to investigate phosphorus release from lake sediments in the Lake Barato. As a result, lake stratification was observed during the summers of 2022 and 2023, and phosphorus release from lake sediments have been enhanced during these periods. During summer, the phosphorus release rate from lake sediments was 7.89 mg-P/m²/d. The lake sediments were rich in iron, which is characteristic of lakes in peatlands. Iron-bound phosphorus was abundant in lake sediments and might contributes to phosphorus release from lake sediments.

 In order to understand the effects on water bodies when dissolved oxygen is supplied to anoxic saltwater containing hydrogen sulfide, we made long-term chemical analytical tracking of water quality change after hydrogen sulfide were oxidized intentionally. We carried out experiment for 90 days under the external conditions of dissolved oxygen supply and brightness of light. As a result of experiment, it was revealed that sulfur oxidation occurred independently of light. and it was cleared that carbon dioxide was used as the oxygen source under anaerobic conditions and that nutrients were consumed. In addition, it was revealed that molar ratio of sulfur to carbon was 1:1 on anaerobic sulfur oxidation reaction. Furthermore, when hydrogen sulfide was completely oxidized, Anaerobic condition was continued for approximately 2 weeks. After that, when exposed to light, green algae was grown. And it was confirmed that dissolved oxygen was supplied through photosynthesis. It has been confirmed that nutrients and carbon dioxide are consumed during plankton growth. Considering the reuse of anoxic bottom water, it was suggested that reducing nutrients and carbon dioxide in bottom water was possible by detoxifying hydrogen sulfide.

 A model structure, as well as model equations and parameters tailored to the characteristics of the water body, is essential due to the uncertainties in the output values of the ecosystem model. In this study, sparse identification was applied to time series data of water quality state variables generated by the ecosystem model to evaluate its applicability. The results indicated that the correct equation forms and optimal parameters were identified for phytoplankton, particulate organic matter, dissolved organic nitrogen, and dissolved organic carbon. The application of sparse identification to actual observed data suggests the potential for identifying model equations and parameters that reflect the characteristics of the water body and reduce uncertainties in the ecosystem model. On the other hand, for dissolved organic phosphorus, phosphate phosphorus, ammonia nitrogen, and nitrate nitrogen, sparse identification proved challenging. The applicability of sparse identification appears to be influenced by the candidate functions for constructing the library and the amount of time variation of state variables.

 In order to cope with the decrease in the number of operation managers at wastewater treatment plants, it is important to develop and introduce AI technology that can reproduce the operation of skilled managers and contribute to transfer operation know-how. In this study, a questionnaire survey was conducted to understand the demand for AI technology and the operation items that AI technology can guide in wastewater treatment. The results indicated that AI technology could be utilized at wastewater treatment plants, in particular, to help operation managers decide the set values of airflow rate of reaction tanks and excess sludge withdrawal rate, and that there is a certain level of demand for AI technology from operation managers. In addition, we introduced AI technology to an actual wastewater treatment plant to support response decisions and operations, and conducted a demonstration experiment. The AI's inferences for 12 operational items were compared with the judgments of the skilled managers at the wastewater treatment plant, and the results showed that the judgments agreed in approximately 90%. This result indicates that AI technology can be used to help operation managers make decisions on the actual operation of wastewater treatment plants.

 The objective of this study was to determine a centralized (collective treatment) or decentralized (individual treatment) domestic wastewater treatment system based on a multidimensional evaluation. Cost per household, greenhouse gas (GHG) emissions, digester gas potential, and phosphorus recovery potential were formulated as a function of household density for collective and individual treatment systems, respectively. The results suggested that the household density at which these index values are in equilibrium between centralized and decentralized systems was lower than 40 persons per hectare, which has been the profit bifurcation point. The allocation of collective and individual treatments was determined to minimize the sum of the weights of the four indicators using the simulated annealing for a hypothetical residential area with an appropriate spatial distribution of houses. The best mix of centralized and decentralized treatment that can minimize costs and GHG emissions was clarified. The results also suggested that infrastructure hybridization with food waste collection system and novel elemental technologies are necessary to achieve energy independence for a wastewater treatment plant.

 A sewage treatment plant simulator was used to evaluate the effects of energy saving and energy production measures on reducing power consumption and GHG emissions at four medium-sized sewage treatment plants with treatment capacities ranging from 50,000 m³/day to 100,000 m³/day. When introducing energy-saving measures aimed at reducing the amount of aeration air, the energy-saving effect was 4.5-18.6%, less than 20%. On the other hand, with energy production measures, the self-sufficiency rate was expected to increase from 11 to 50% by introducing digestion gas power generation, and it was calculated that the self-sufficiency rate would improve to 21 to 88% by combining excess sludge solubilization and MLSS reduction measures. Simultaneous implementation of energy saving and energy production measures further improved the self-sufficiency rate to 24-99%, and approximately the same effect was expected over the year. When evaluating the GHG reduction effect using the CO2 offset rate, the CO2 offset rate was 57% even at A-STP, which had almost reached power independence, with direct emissions remaining from water treatment. The CO2 offset rate of B-STP for nitrification suppression was 26%. C-STP, with sludge incineration, had the second highest CO2 offset rate at 43%, as the amount of sludge to be treated was reduced due to the introduction of the anaerobic digestion for energy generation. The CO2 offset rate of advanced D-STP was 19% because of the advanced treatment.

 Renewable energy is being introduced in Japan with the aim of achieving a decarbonized society, but maintaining a balance between electricity supply and demand is a challenge. Therefore, a method of procuring regulating power in the market and utilizing power through demand response is being considered. In this study, we evaluated the demand-response power of multiple air conditioners for buildings, but found that the tracking error was large, making it difficult to utilize the power in the market. Next, a method to compensate for the tracking error by combining storage batteries was investigated, and it was found that storage batteries with a capacity of 128.6 kW or more were necessary. Furthermore, in an experiment in which ventilation control was also combined, it was found that the power consumption of the air conditioner could be changed by 23.0% to 53.7%, indicating that the storage battery and ventilation control could be used together to supplement the tracking error.

 Chitosan has been used in agriculture as a soil ammendment and as a soil deodorizer in composting. However, the effects of chitosan on soil after application are not fully understood. In this study, we incubated bacteria in soil with and without chitosan addition. The physico-chemical properties of the soil and the biological properties by gene analysis were determined. The chitosan application increased the soil content of nitrate nitrogen throughout the incubation and promoted nitrification in the soil. DNA was recovered from the treated soil by pre-treatment with phosphate buffer, although chitosan is known to inhibit DNA extraction. The chitosan application significantly changed the bacterial community structure and increased the relative abundance of Streptomycetales, Sphingobacteriales, Xanthomonadales, Cytophagales, etc. Functional prediction analysis using PICRUSt2 suggests that ammonia was supplied to the soil by deamination of chitosan during chitosan metabolism.

 This study aimed to isolate essential urease-producing bacteria required for biocementation using a down-flow hanging sponge (DHS) reactor and an isolation chip (ichip). As a result, almost all urea was decomposed to ammonium in the DHS reactor. Additionally, microbial community structure analysis based on 16S rRNA gene sequencing revealed the presence of various urease-producing bacteria in the DHS reactor. The isolated microorganisms not only possessed urease activity but also exhibited urea decomposition rates comparable to those of S. pasteurii. Analysis of the 16S rRNA gene of the isolated microorganisms showed high genetic similarity to S. pasteurii. Furthermore, the Sporosarcina genus and Bacillus genus accounted for only 1% of the microbial community structure. This suggests that combining DHS reactors with the ichip method allows for the isolation and cultivation of microorganisms with low abundance within the DHS reactors.

 Complete Ammonia Oxidation (Comammox) bacteria are a group of bacteria that perform both ammonia oxidation and nitrite oxidation in a two-step nitrification reaction, and are expected to be applied to new wastewater treatment technologies. On the other hand, the Nitrospira group, to which Comammox bacteria belong, contains a mixture of Comammox bacteria and bacteria that only perform conventional nitrite oxidation, and identification methods based on rRNA approaches cannot distinguish between the two groups. In this study, to solve this problem, we established a technique to identify Comammox bacteria by simultaneous multiple staining of the Nitrospirae phylum by rRNA-FISH and amoA-mRNA by CARD-FISH at the single cell level. In order to detect amoA-mRNA of Comammox bacteria by FISH method, we investigated the conversion of previously reported primers used for PCR to FISH probes in this study. The NtspamoA-359r probe targeting the amoA gene of many Comammox bacteria showed a high ΔG_overall of -15.01 kcal/mol and a high fluorescence intensity, indicating that it may be a useful probe for the detection of amoA-mRNA in Comammox bacteria.

 This study aimed to develop a highly sensitive method for visualizing the functional genes of microorganisms possessing endogenous peroxidase activity. We combined Hybridization Chain Reaction (HCR)-fluorescence in situ hybridization (FISH), a high-sensitivity FISH method that does not rely on enzymatic reactions, with click chemistry capable of specific binding of alkyne-azide. First, Escherichia coli containing plasmids with functional genes as a model microorganism was used to optimize the concentration and reaction time of click chemistry. Our results revealed that extending of the reaction time of click chemistry was more effective than increasing the concentration of Cu²⁺ for specific detection. Secondly, we attempted to visually detect the functional genes of anammox bacteria in a mixed sample of sludge from a bioreactor containing anammox bacteria and a pure culture of methane-producing archaea. As a result, only anammox bacteria were detected, with methane-producing archaea remaining undetected. These results indicate that our method allows for the visualization of functional genes of microorganisms in the environmental samples without being influenced by endogenous peroxidase activity. Moreover, it can be combined with microbial sorting devices for whole-genome analysis to elucidate the metabolic pathways of specific uncultured microorganisms.

 Microplastics (MPs) remain in the aquatic environment for long periods due to their persistence, and there are concerns that they may adversely affect aquatic ecosystems. On the other hand, there is the problem that the number of research cases on MPs for aquatic organisms has been limited in Japan. In this study, we aimed to understand the actual presence of MPs in the digestive tract of freshwater fish and the relationship between MPs in the digestive tract of fish and their habitat. In the survey of MPs in the digestive tract of Gnathopogon elongatus elongatus, there was a significant difference in the number of MPs between the June and October samples, suggesting the effect of activation of its feeding behaviour during the breeding season. In the survey of MPs in the sediment, Polyester fibers were the most abundant MPs in the sediment, suggesting that fibrous MPs sourced from laundry wastewater flow into the Shokanji River and Shokanji Pond and are deposited in the sediment environment. Comparison of the components of MPs in the digestive tract of G. elongatus elongatus and MPs in the sediment indicated that it also ingests MPs present in the sediment when preying on benthic organisms.

 Highway road dust is considered to have a high potential of pollution by trace toxic substances derived from automobiles such as heavy metals and PAHs (polycyclic aromatic hydrocarbons) due to heavy traffic volume of highway, which leads to concern about ecotoxicity in the water environment due to these substances. In this study, ecotoxicity tests on highway road dusts were conducted to show toxicity levels of the highway road dusts. And a couple of new concepts of ecotoxicity evaluation index were also proposed, and ecotoxicity fluctuation of highway road dust was calculated using the index. The followings were done and found. The toxicity level of highway road dust differs depending on the seasons such as winter and non-winter. The significant toxicity was not observed, on average, until the dust ratio is more than 11.20% for winter season and more than 55.11% for non-winter season. In addition, the concepts of C-NOEC (Confidence Interval Based NOEC) and F-NOEC (Cumulative Frequency Based NOEC) were shown as new toxicity evaluation indexes related to NOEC (No Observed Effect Concentration), and their availabilities were examined. Furthermore, the toxicity fluctuation characteristics of highway dusts were shown by calculating the risk ratio using these indexes and content ratios of PAHs.

 Chlorination of natural organic matters (NOM) in water could produce disinfection byproducts (DBPs) that are harmful to human bodies. In this study, we used ultra-high resolution mass spectrometry to identify the molecular formulas of NOM precursors of DBP after different water treatment processes (e.g., UV irradiation, activated carbon adsorption) and also to determine the changes in the molecular properties of NOM and their impacts to the DBP formation. A machine learning (ML) model was developed to predict the number of DBP formula from the molecular properties of NOM. A comparison of models using Pycaret showed that the catboost model had high prediction accuracy, suggesting that the molecular weight and carbon oxygen ratio are factors that have a significant impact on DBP formation. The results suggest that changes in the molecular properties of NOM, such as saturation degree and aromaticity (due to the UV irradiation treatment) may facilitate the number of DBP molecular formula formed.

 As a result of the introduction of strongly acidic hot spring water from the Tamagawa river system for power source development, Lake Tazawa became an acidic lake and the independent ecosystem is no longer functioning. As a countermeasure, Tamagawa neutralization treatment facility began in 1991 but Lake Tazawa's pH hovers around 5.2 and the effects of the neutralization treatment facility are still unknown. In this study, we conducted a short-term chronic toxicity test using aquatic organisms at three locations in Lake Tazawa-Tamagawa river system: Tamagawa neutralization treatment facility, Tamagawa Dam and Lake Tazawa, and compared before and after adjusting the pH to 6.7. As a result, the toxicity unit (TU) in the downstream direction of the Tamagawa Neutralization Plant, Tamagawa Dam, and Lake Tazawa showed a tendency to decrease, and in particular, the decrease in TU value up to Tamagawa Dam and the immediate improvement in toxicity were significant. Regarding the pH adjustment effect, a positive effect was observed in the treated water of the neutralization treatment facility.