The objective of this study was to develop a new technology to mitigate the concentration of hydrogen sulfide in sewer pipe by using conductive concrete. Experimental results showed that the concentration of hydrogen sulfide significantly decreased by using conductive concrete, and the effectiveness lasted during 66 days experiment. Also found was that elemental sulfur was observed after 66 days experiment in sludge for conductive concrete, whereas this tread was not observed for ordinary Portland cement. These results demonstrated that conductive concrete provides an electron pathway from deposited sludge in the bottom of sewer pipe to oxygen dissolved in surface water and as a result, the electron generated from hydrogen sulfide oxidation in anaerobic environment was accepted by oxygen via conductive concrete. Finally, regarding the mechanism responsible for hydrogen sulfide oxidation, chemical oxidation was the dominant process and biological process did not play a siginificant role.

 2, 4-dichlorophenoxyacetic acid (2, 4-D) is persistent in water environment and harmful to human body. It is reported that 2, 4-D in aqueous solution can be decomposed by the advanced oxidation process (AOP). However, no clear experimental results have been reported on the decomposition mechanism of 2, 4-D.

 This paper aims to unveil the decomposition mechanism of 2, 4-D by advanced oxidation process using H₂O₂, O₃ and UV in laboratory batch experiments. We reported previously that H₂O₂/O₃/UV and H₂O₂/UV systems are able to generate hydroxyl radical efficiently.

 The results of experiment show that 2, 4-D could be decomposed rapidly by the action of hydroxyl radical generated in H₂O₂/O₃/UV and H₂O₂/UV systems. In this case, dechlorination and degradation of 2, 4-D occurred simultaneously due to non-selective decomposition. On the other hand, selective decomposition without hydroxyl radical was occurred slowly with mineralization of 2, 4-D. In addition, the mineralization pathways of 2, 4-D were estimated from the performance of several decomposition products analyzed by LC/MS/MS and others.

 In this study, the up-flow velocity in the UASB reactor fed with municipal sewage was changed stepwise, and the influence on number of anaerobic protozoan cells and protozoan community was measured. Number of protozoan cells increased by rising the up-flow velocity in the range of 2.4 to 14.4 m/day, but the number of the ciliates decreased sharply due to a washout occurred at 22.4 m/day. Predominant species of anaerobic protozoa present in UASB were Metopus palaeformis, Metopus contortus, Chaenomorpha sp., and Plagiopyla sp, which accounted for about 60% of all 18S rRNA genes. Dominant species of protozoa changed in a short period of time under higher up-flow velocity conditions.

 The concentrations of earthy and musty odor compounds were measured for 123 samples of treated wastewater taken from 25 treatment plants. 2, 4, 6-trichloroanisole was detected from 22 treatment plants with the average concentration of 8.4 ng/L out of the 25 target plants with the detection limit of 1 ng/L. Geosmin was detected from 24 treatment plants with the average concentration of 8.4 ng/L. The concentrations of 2, 4, 6-TCA and geosmin in the treated wastewater was usually higher than their odor thresholds, while the contribution of 2-MIB to the odor of treated wastewater was considered not to be significant. Higher cooncentrations of the target odorous compounds were detected for large-scale wastewater treatment plants compared with those for small-scale plants with the oxidation ditch process. 2, 4, 6-TCA was produced in the aeration tanks in the activated sludge process whereas the chlorination process (disinfection) did not affect the concentration of odorous compounds in the treated wastewater.

 Main objectives of this study are to know the behavior of microplastics in wastewater treatment processes and to estimate the loading to Lake Biwa. Four wastewater treatment plants which are separate sewer system were investigated. Microplastics bigger than 100 micrometer were sampled in wastewater treatment processes, and influent and effluent were sampled in order to know the behavior of microplastics which size were 10 to 100 micrometer. As the results of this study, 30 components were identified from wastewater, treated water, sludge, and scum. Concentration of MPs in influent was 158 to 5,000 pieces/m³. Concentration of MPs in effluent was 0.3 to 2.2 pieces/m³, and it was similar to the concentration of MPs in surface water of Lake Biwa. On the other hand, removal efficiency of MPs which size was 10 to 100 micrometer was 76.3%. It was not enough to remove the MPs smaller than 100 micrometer by the rapid sand filtration. The sum of MPs loading from four wastewater treatment plants was estimated to be 501,630 pieces/day, it was close to the total MPs loading from rivers around Lake Biwa in a fine day.

 This study revealed characteristics of dissolved organic matters (DOM) transformation during soil aquifer treatment (SAT) by comparison to Anaerobic-anoxic-oxic(A2O) treatment. SAT pilot-scale column experiment was conducted. Primary effluent from wastewater treatment plant, A2O treated water and SAT effluent were fractionated using DAX-8, XAD-4 and ion exchange resins. Each fraction was investigated functional groups by FT-IR and 1H-NMR techniques. As the results of these DOM analysis, hydrophilic neutral, transphilic and hydrophobic acids fractions account for 80.8% of residual DOM after SAT. Residual DOM included original DOM in primary effluent and produced DOM during SAT by bioactivity.

 Although trihalomethanes formation potential (THMsFP) was able to be reduced during both A2O treatment and SAT, it was found that the THMsFP of hydrophilic-neutral(HiN) fraction and its specific THMsFP were increased after SAT. Biodegradation by-products could be one of the main HiN components which increase the THMsFP. It is necessary to understand the behavior of the fraction when SAT effluent is used for drinking water source.

 Suspended particles in treated water accumulate in water distribution pipes and cause discolouration of tap water by resuspension due to hydraulic disturbance. This study aimed to model particle accumulation in drinking water distribution system and compare different countermeasure for managing accumulation process. A simple, empirical model for particle accumulation with water velocity as the main parameter was developed based on lab-scale adhesion experiment simulating different velocities. Analysis of water samples collected during unidirectional flushing was also conducted and the amount of accumulated matters was estimated to be 0.18-3.0 g/m². These data were utilized for calibration of the accumulation model. The model was then applied to the target distribution network to estimate a distribution of the accumulated matters. The total amount of equilibrium accumulation in the network was calculated to be 23.8 kg. Scenario analysis was also conducted assuming 1) reduction of suspended solids (SS) concentration in treated water, 2) downsizing of distribution pipes to increase water velocity, and 3) regular flushing. The effects of each countermeasure was quantitatively compared and appropriate management strategy was discussed at the viewpoint of inner-pipe environment.

 It is important to estimate the degree of waste that may result from natural disasters such as large earthquakes and tsunamis to effectively plan for disaster waste management. More specifically, it is especially crucial to estimate the quantity of hazardous chemical waste that a disaster may yield to plan environmental protection measures and proper waste treatment. To estimate such a phenomenon, it is necessary to first determine the amount of chemical substance present in a specific area. This study makes such an estimation for Osaka Prefecture by calculating the ratio between the amount of chemical substances released and transferred and the amount of chemical substances handled. The value of the ratio is termed the "handling coefficient." Notably, while information about the release and transfer of chemicals is published nationwide under the pollutant release and transfer register (i.e., "PRTR") system, that on the handling of chemicals is only available at the limited number of local governments level. This study investigates whether the handling coefficient differs by the fiscal year and, moreover, by local government. Ultimately, the difference between the years proved smaller than that between local governments. This paper argues that the larger difference between regions is due to the differences in the types of industries or industrial processes in each area.

 Various Life Cycle Cost (LCC) -based pipe replacement models have been developed to more effectively replace deteriorating water supply pipes under limited financial resources. However, seismic risk, an important aspect of water supply management, has not been included in LCC because of the complex stochastic process involved. This study proposes a monetization method of seismic risk as an expected value by using the multi-event model (a type of Probabilistic Seismic Hazard Assessment often used in Japan) to examine a list of possible earthquakes from the earthquake catalog developed by Japan’s government, and give occurrence probabilities for each earthquake. Applying this method to a virtualized water supply system in seismically active area showed that inclusion of seismic risk factors hastened the replacement timing of non-seismic-resistant pipes by five to fifteen years. The study also demonstrated significant seismic risk reduction by replacing Cast Iron Pipes (CIPs), which are especially outdated and vulnerable. Thus, immediately replacing CIPs may yield substantial LCC reduction as well as seismic risk.

 In order to quantitatively understand the effect of aggregation of bacteria in water on the inactivation effect by UV, UV irradiation is performed on a sample containing E. coli that has been aggregated using alginic acid and calcium ions, and the inactivation effect is determined by the cultural method. The aggregation state of E. coli was adjusted with initial E. coli concentration (10⁶, 10⁷, 10⁸ CFU/mL) and calcium ion concentration (0, 10, 20 mM). As a result, aggregation affected the inactivation effect only when the initial E. coli concentration was 10⁸ CFU/mL, and the inactivation effect was minimized at a calcium ion concentration of 20 mM. This is because when initial E. coli concentration was 10⁸ CFU/mL, it is considered that there were enough E. coli blocking E. coli from UV. This study suggested that the initial E. coli concentration and the size of flocks in the sample affect the inactivation effect of E. coli.

 In order to reveal the effect of pulsed UV irradiation on microorganism inactivation, inactivation efficiency of E. coli was compared between pulsed UV irradiation and continuous UV irradiation using deep UV-LED. For pulsed irradiation, following two methods were used; switching electric current and blocking UV by rotating shutter. Inactivation efficiency per time did not differ between continuous UV and pulsed UV by rotating shutter. However, pulsed UV by switching electric current showed higher inactivation efficiency than continuous UV. It is suggested that the reason of the higher inactivation efficiency was the improvement of luminous efficiency caused by temperature fall of the LED.

 Basic research on the occurrence and growth mechanism of cyanobacteria as well as methods to prevent growth have been studied for many years. However, excessive cyanobacteria growth is still occurring frequently in lakes and reservoirs in various places. In recent years, ecological engineering methods have been considered due to their sustainability and energy saving nature. In this study, the hypothesis of whether diatom Nitzschia palea has the growth inhibitory effect on Microcystis aeruginosa (NIES-102) and the water blooms (Microcystis spp. collected from the pond) will be investigated. Moreover, since the wavelength of the optimal light for algae and cyanobacteria to grow varies depending on the species, investigation of the wavelength which suppresses the growth of M. aeruginosa will also be carried out. This will be done in combination with using the competitive nature of N. palea and by using LED irradiation. The results of the empirical investigation showed that in the high nitrogen concentration conditions, the growth of M. aeruginosa was inhibited by the addition of N. palea. However, despite the addition of N. palea and the silicate nutrient to the water blooms collected from the pond, it was not possible to confirm the growth inhibition of the cyanobacteria bloom. In the monoculture, irradiation of blue LED causes N. palea to grow, while M. aeruginosa had suppressed growth. Also, the growth of M. aeruginosa was suppressed by about 78% when compared to the used of monoculture and by adding N. palea under the condition of irradiating yellow LED at 25°C.

 In this study, the insolubilization of arsenate in water and soil samples was investigated using potassium ferrate (K₂FeO₄) produced by a wet chemical method. In water samples, the addition of K₂FeO₄ decreased the dissolved As(III) concentration, while the dissolved As(V) concentration was increased, suggesting the oxidation of As(III) to As(V) with K₂FeO₄. The As(V) concentration was decreased to less than 10 μg/L with a further increase in Fe dosage due to coprecipitation with ferric hydroxide produced via reduction of ferrate ion. In soil samples, the total dissolved As concentration was about 50 μg/L in the leaching test using pure water before iron addition, and the As(III) concentration was much greater than the As(V) concentration. The addition of K₂FeO₄ decreased the concentration of As(III) leachable from the soil to less than 10 µg/L at less iron dosage compared to that of FeCl₃. However, a larger amount of K₂FeO₄ was required to lower the total concentration of dissolved arsenic to less than 10 μg/L. Selective extraction of As from the treated soil samples based on the modified BCR method showed that the addition of K₂FeO₄ transformed reducing agent-extractable As into less extractable form. This finding suggests that K₂FeO₄ would be useful for reducing the potential leachability of arsenic from treated soil after being returned to the underground.

 In this study, we focus on potential colloid-facilitated transport in forest soils of radioactive Cs released by the Fukushima Daiichi Nuclear Power Plant accident in March 2011. We set the column experiments using colloidal Cs solution and dissolved Cs solution. The result of column experiments revealed that about 79% of resolved Cs flowed in soil adsorbed on soil and about 86% colloidal Cs flowed in soil effluent without delay caused by cation exchange. It was also revealed that flow peak in the case of 300mm/hr rainfall and 30mm/hr rainfall was appeared at almost the same moment but more Cs infiltrate into soil without adsorption in the case of 300mm/hr railfall.

 Recently, microplastics (MPs) have been getting attention worldwide due to its potential for environmental impacts. However, one of the challenges of MPs studies is the comparison of various studies is difficult because there is no authorized method for measuring MPs. It is important to understand the characteristics and sources of MPs pollution in each region in order to reduce the load of MPs. In this study, we reported that the occurrence of MPs in road dust and river surface water in Kathmandu city, Nepal as an example of developing countries in Asia. In addition, we compared these results with that in Da Nang City (Vietnam) and Kusatsu City (Japan), which were conducted in the same way by authors. The results showed that the average MPs concentrations were 25.7~339 pieces/m² (n=4) in road dust and 600~45, 600 pieces/m³ (n=5) in river surface water (Bagmati River and Bisunumati River). In terms of composition, polyethylene and rubber plastics accounted for 40 % and 18 % of all MPs in road dust, while 70 % of MPs in river surface water were detected as acrylic plastics. The average sizes of MPs were significantly larger (p<0.01) in river surface water (median: 432 μm) than those in road dust (median: 309 μm). As a result, it was suspected that one of the main sources of MPs in river surface water in Kathmandu City is untreated wastewater. Therefore, it was expected that MPs concentrations would decrease after completion of wastewater treatment plant construction.

 Scattered small scale domestic wastewater treatment systems managed by different ministries and their sludge disposal are operated ineffectively. Various types of sludge from small wastewater treatment facilities are analyzed in terms of energy contents, focusing on volatile solids (VS)/ total solids (TS) ratio, calorific value, and anaerobic digestion performance. Higher heating value and biogas production performance in anaerobic digestion are correlated with VS/TS ratio, regardless of sludge types. Sludge in personal on-site wastewater treatment facilities (jokaso) is typically withdrawn once a year, while jokaso sludge withdrawn once every one to three months has higher VS/TS ratio as well as higher biogas production performance of 0.4～0.5 NL/gVS-added, which is similar to that of typical mixed sewage sludge. These results are useful for designing and operating co-digestion, which accepts various types of waste biomass, including small scale wastewater treatment sludge.

 To clarify the microoganisms potentially contributing to anaerobic degradation of octadecane, a comparative analysis of the microbial community structure was performed.The enrichment cultures of methanogenic microbial communities were constructed with two completely mixed reactors using the Niitsu River bottom sediment as a seeding source, and the prokaryotic community was identified. As a result of 16S rRNA gene amplicon sequencing analysis of the sludge in the reactor on day 92 when the reactor supplying octadecane reached stationary state, the bacteria belonging to family Rikenellaceae (Blvii 28), genus Bacteroides and genus Kosmotoga were detected more frequently compared to the reactor that did not supply octadecane. These results indicate that these bacterial species are likely to be potentially contributing to the anaerobic degradation of octadecane in the reactor.

 It`s expected that biogas power generation by methane fermentation will spread for the purpose of utilizing renewable energy. The biochemical methane potential (BMP) is used as the main indicator for assessing the potential to produce methane of a substrate. Resent studies have reported that components in biomass correlated to methane production. The aim of this study was to investigate the influence of chemical components of food waste on the BMP with a special focus on acid detergent fiber (ADF; indicates lignin and cellulose) and lipid with a high theoretical methane potential. Using the variables, poor regression models was found for food waste. The correlation between lipid and BMP was found, with R² of 0.73. The best BMP prediction equation (R² =0.90) was obtained as a result of two-variable regression analyse when ADF and lipids were used as independent variable. The BMP prediction equation is applicable to only a specific food waste, but easy-to-use.

 In this study, we investigated the inactivation of F-specific RNA bacteriophage (FRNAPH) genotypes I, II, III, and IV (GI, GII, GIII, and GIV, respectively) in secondary effluents by chlorine and ultraviolet disinfection and identified surviving FRNAPH strains after disinfection using next generation sequencing (NGS). The resistance of GII–GIV to chlorination was higher than that of GI in batch chlorine disinfection experiments, whereas the resistance of all four genotypes was similar in the FRNAPH-spiked batch chlorine disinfection experiments using the propagated indigenous FRNAPH genotypes in secondary effluents. GI showed the highest persistence to ultraviolet disinfection, followed by GII, GIII, and GIV in batch ultravi-olet disinfection experiments. Two strains belonging to GII were detected by NGS only in both chlorine and ultraviolet disinfected samples, suggesting that these strains may have higher persistence to both the disinfection treatments than that of other FRNAPH strains.

 We investigated change in number of the resistance genes bla_CTX-M and bla_TEM, which are known to be related to ESBL, in activated sludge samples collected at municipal and hospital wastewater treatment plants in Thailand and Japan when the samples were cultured in Luria-Bertani (LB) broth containing a high concentration of antibiotics. The insertion sequences IS26 and ISE_cp1, which are expected to contribute to horizontal gene transfer of the resistance genes, were also quantified in the same sludge samples. The tested antibiotics were amoxicillin (AMPC), ampicillin (ABPC), cefepime (CFPM), meropenem (MRPM) and doripenem (DRPM), all of which are beta-lactam antibiotics, as well as ciprofloxacin (CPFX) and tetracycline (TC). Both resistance genes in all of the sludge samples significantly increased during the cultivation under the existence of AMPC and ABPC. These genes also increased in some samples under the pressure of CPFX, which is often used in medical treatment as alternative to beta-lactam antibiotics, demonstrating the existence of CPFX-resistant ESBL generating bacteria. MRPM-resistant bacteria, which maybe carbapenem-resistant Enterobacteriaceae (CRE), were found in the sludge sample collected at a hospital wastewater treatment plant in Thailand, although they did not seem to have the above resistance genes. The insertion sequences IS26 and ISE_cp1 increased when either of the resistance genes increased in all of the samples added with AMPC and ABPC. The correlation analysis indicates a highly significant contributions of IS26 and ISE_cp1 to the transfers of bla_TEM and bla_CTX-M in the sludge samples, respectively.

 Public concerns have recently emerged due to sanitary microorganism in sanitary sewer overflows (SSOs) from sewerage systems in rainy events. The purpose of this study was to investigate the influence of SSO on chromophoric dissolved organic matter (CDOM) and sanitary microorganisms in a river, Seta River receiving a sewage treatment plant (STP) discharge at the outlet of Lake Biwa. To this end, we conducted field survey during four rainy events whose total rainfalls ranged 10 to 177 mm, and measured CDOM constituents in the STP discharge and the river water. EEM-PARAFAC analysis of CDOM revealed that there are three components of CDOM in the STP discharge and the river water. During the three rainy events, SSOs occurred in the STP. As the results, the CDOM component indicating protein origin in the river water (Comp.2) and summation of the three CDOM components (Comp.f) were confirmed to increase due to untreated sewage discharge in total rainfall events of 28 mm and 68 mm. However, in 177 mm rainfall event when SSOs had occurred before sampling campaign started, Comp.2 did not increase, while Comp. f had gradually increased due to untreated sewage discharge. In addition, in 64 mm and 177 mm rainfall events, increase in sanitary microorganisms in the river water was identified probably due to untreated sewage discharge.

 Suspended solids (SS) formed from various sized particles in wastewater contain organic matter that can be used as energy resource. Since the removal of SS at primary sedimentation process can be regarded as an energy recovery, the heating value distribution by particle sizes would become important.

 In this study, particle size fractionaton for wastewater and sludge samples around primary sedimentation tanks at two wastewater treatment plants (WWTPs) in Japan was performed. Then, the particle size and the organic element (CHN) distributions were clarified. The heating value distributions were elucidated by thermo gravimetry-differential thermal analysis (TG-DTA) and also CHN analysis. Finally, the energy recovery ratio at primary sedimentation tanks in two WWTP.

 As a result, it was confirmed that particles of 250 μm or more were almost recovered in the primary sedimentation tanks. The heating value distributions by particle size showed that the heating value tended to increase as the particle size fraction became smaller, but it was contrary to the tendency of the ignition loss, and the effect of high oxygen content such as toilet paper was observed. The energy recovery ratios in the primary sedimentation tanks were calculated to be 87% and 74%, respectively, but the influence of the particle size distribution itself was more dominant than the heating value distribution according to the particle size.

 This study proposed a flow rate control Ground Source Heat Pump (GSHP) system with a lining borehole ground heat exchanger (LBHE) from the view point of heat storage. To identify basic thermal properties of the LBHE and its surrounding ground, Thermal Response Test (TRT) was conducted. The thermal resistance of the LBHE was 0.025 K/(W/m) from the TRT and 30% lower than the conventional LBHE. In addition, we performed an air heating experiment to examine the effectiveness of the flow rate control. As a results, the water temperature difference between inlet and outlet of the heat exchange plate was about 3℃ and proposed system can work as general GSHP system. Since third day on the experiment, water temperature in the LBHE and its surrounding ground temperatures at 5 p.m. almost recovered to the previous temperature level at 8 a.m. the following morning due to thermal recovering operation. Therefore, it was expected that proposed system enables continuous use of the shallow ground heat. Then, heat exchange rate per unit length of the LBHE was about 50 W/m and about 1.3 times larger than that of double U-tube ground heat exchanger. Consequently, it was found that proposed system can help to save storage energy in the LBHE.

 According to the results obtained in the present study, by adding scrap metal aluminum, hydrogen generation amount significantly increased. For instance, at the presence of 10% metal aluminum, hydrogen generation amount increased to more than 100m³/t-BA from 25.2m³/t-BA and existence of proper addition amount was suggested. Addition of sodium hydroxide increased hydrogen generation speed dramatically. As a result, in excess of 80% of total hydrogen was generated in the first day of the experiment. In the case of BA particle size over 4.75 mm or more, hydrogen generation amount was less than other cases. Hydrogen generation was about 40m³/t when use pilot experiment equipment. This is about 60m³/t less than previous research because of non-warming and weak agitation.

 In this study, we carried out quantum chemical calculations using Gaussian for the oxidative decomposition reaction of phenol by OH•, and investigated the reaction sites of the oxidizing agent in radical reaction and electrophilic reaction. As a result of calculating and comparing the Fukui index at different theoretical levels of HF, B3LYP and M062X, the calculation accuracy of reaction point was found to be high in the order of B3LYP > M062X > HF for the OH• addition to phenol. In addition, the estimation of the reaction point by Fukui index was consistent with the experimental observation for the reactions of intermediate products. In addition to the prediction of reactive sites, we also performed the estimation of reaction rate constants by optimizing the reaction pathway (transition state structure). In this study, we focused on the initial oxidation process in which phenol is converted to catechol (or hydroquinone), but the same method to the other organic trace contaminants can be applicable to theoretically estimate the reaction sites during the oxidative degradation.

 One of the challensges for sewerage development in South East Asia is unexpected low-strength and low-flow influent to domestic wastewater treatment plants, which can cause mismatching between the plant design and influent characteristics. One of the reasons of this unexpected influent characteristics is poor sewer networks in the region. For effective development of sewerage in the region, this study aimed to estimate the change in influent sewage characteristics according to development stages of sewer networks. Taking into account of various conditions of sewer networks, we developed a model to estimate sewage flow, sewage pollution loading, and sewage concentration, employing unit pollution loadings of toilet wastewater and greywater. The model was tested in a residential drainage area of Hue city, Vietnam, and validated by comparing the measured sewage polllution loading and the model-estimated sewage pollution loading at present conditions. The validated model was appied for the same residential area at four development stages of sewer networks. Results indicated that sewer leakage reduction mainly would contribute the increase of sewage flow; an integrated measure of sewer leakage reduction, appropriate greywater discharge to sewers, and septic tank removal would contribute the increase of sewage concentration.

 Facing a phase of developing sewerage in Southeast Asian countries, it is urgent task to establish a methodology to grasp the representative sewage concentration. This study aimed to estimate a relation between sewage sample number and accuracy of computing representative value, and ran simulations with resampling method for raw sewage data observed in Hue, Vietnam. With sequencially observed electron conductivity (EC) data, the simulations were conducted in terms of two parameters: number of samples per day and number of days for sampling. Additionally, we examined a difference in the accuracy of representative value estimation among water quality parameters. Results indicated that number of days for sampling contribute more to the accuracy of computing representative value than number of samples per day. Moreover, for accurate representative value estimation of BOD, COD and TN, more sample numbers likely be required than for SS, TN and EC. The findings of this study based on raw data are expected to contribute on the development of appropriate sewage sampling methodology.

 In order to conserve bay ecosystems, it is important to evaluate impacts of anthropogenic environmental alteration on bioligical communities. In this study, we tested whether assessment based on fatty acid composition analysis could differentiate between two local communities with different distances from a river mouth in Shizugawa Bay. As a result, significant differences in marker fatty acid composition were found between predatory fish and benthic consumers as well as between the two sampling locations. The food web near the river mouth depend relatively more on diatom-derived organic matter, while that of the offshore location depended more on green algae-derived organic matter. These retuslts support that the characteristics of local community and food web structures were evaluated by applying fatty acid composition analysis of consumer organisms. Our results also indicated that predatory fish concentrated EPA and DHA of prey thorugh their assimilation. Particularly to further apply fatty acid compositon analysis of predatory fish for the estimation of food web structures as a method of ecosystem assessment in bays, it is further necessary to quantitatively understand the patterns of fatty acid concentration along trophic levels.

 Unionid mussels play an important role in the cycling and removal of suspended substances from freshwater ecosystems. Unfortunately, their populations are declining worldwide. Although the mechanism for that is unclear, one possible reason may be a reproductive disturbance, because previous studies have reported that the numbers of young and juvenile mussels are few. In this study, we focused on Unio douglasiae nipponensis, which inhabit Lake Hachiro in Akita Prefecture; and we identified when and whether larvae were released by parent mussels. Host fish were also identified. As a result, we discovered that larvae were released from June to July, and that the host fish were gobies (Tridentiger brevispinis). However, juvenile mussels were rare in that location. There is another possibility for unionid mussel reduction, such as the muddy lake bed in Hachiro. To conserve Unio douglasiae nipponensis, further surveys are needed.

 We focus on the phytoplankton biovolume because phytoplankton affects lake water quality at Lake Kasumigaura, Japan. We analyzed the measurement data of cell biovolumes by Ibaraki Kasumigaura Environmental Science Center from FY 2011 to FY 2018, then we listed the phytoplankton cell biovolumes about 162 taxa. Moreover, we multiply cell numbers by cell biovolumes on the respective taxa basis and then sum up them to calculated total biovolumes at 2 research points. Calculated total biovolumes were significantly positively correlated with total biovolume of the previous research at the 2 research points. This result suggested that our list of phytoplankton cell biovolumes have an availability to calculate total biovolume at Lake Kasumigaura. Thus, it could explain clearly the influence of phytoplankton change on lake water quality and ecosystem.

 Invertebrate species DNA of the cytochrome oxidase subunit 1 region were quantified using environmental DNA (eDNA) extracted from river water using quantitative PCR (qPCR). Subsequently, metabarcoding was conducted to obtain the proportion of stream insects of six taxonomic orders (Ephemeroptera, Plecoptera, Trichoptera, Diptera, Odonata, Coleoptera) in the community. Finally, eDNA concentrations of the six taxonomic groups were calculated by multiplying the proportion of each taxonomy and the quantified invertebrate DNA concentration. As a result, aquatic insect eDNA concentrations displayed significant positive correlations with aquatic insect individuals collected by the conventional surber net sampling (Spearman’s rank correlation = 0.74, p < 0.01). Furthermore, positive correlations were observed between the population densities and eDNA concentrations for orders Ephemeroptera, Plecoptera, and Dipetra. These results indicate that the combination of eDNA metabarcoding and qPCR can be an effective way to estimate the abundance of stream insect.

 Suspended oyster aquaculture is one of sources of particulate organic matter (POM) potentially facilitating formations of hypoxia in bottom water of inner bays. While non-feeding oyster aquaculture is generally considered to less affect surrounding environments, substantial amount of POM, such as feces, pseudofeces and exfoliated sessile-organisms on oyster shells and aquaculture facilities deposit to sea bottom. We examined the chemical compositions (carbon and nitrogen stable isotopes, fatty acid compositions) and oxygen consumption rate of POM depositing inside and outside oyster farms in Shizugawa Bay. As a result, the local depositional flux of POM was 2 to 18 times larger inside oyster farms than outside them. It was also found that both the oxygen consumption rate per particulate organic carbon (POC) and the amount of algae fatty acid per POC of depositing POM was lower inside the oyster farms than outside them. Furthermore, those of depositing POM were also lower than those of oyster biodeposits and sessile organisms on oyster shells and farming facilities. These results demonstrate that in the oyster farms, labile fractions of POM was decomposed and significantly reduced in the sedimentation process, and POM depositing to sea floor had relatively higher contents of refractory fractions of POM as well as lower rates of oxygen consumptions per unit mass of POM. It was further estimated that the oxygen consumption of POM from oyster farms accounted for ca. 10% of the total oxygen consumption in the entire area of the inner part of the bay on average.

 Experimental study was carried out in Lake Abashiri where is brackish lake with double-layered formation of freshwater and saltwater. In order to reduce anearobic salt water layer, we installed the oxygen dissolving device (WEP) in the actual waters. As a result of continuously operating the device from icecover period to after snow melting, the flow in the lake was suppressed under the ice, and the rise of dissolved oxygen and the increase of turbidity due to the oxidation of hydrogen sulfide were confirmed in the vicinity of the device. The effect of oxyganation was recognized in the area about 90,000 m² during the two-month operation of the device under the ice. The hydrogen sulfide concentration was confirmed to decreace significantly around the oxygen supply elevation. However, the hydrogen sulfide did not become zero. On the other hand, the flow in the lake was restarted after the snow melt, it was confirmed that the dissolved oxygen and the turbidity were decreased because the oxygen supply effect flowed away with ice break. From the results of water quality analysis, the oxygenation by WEP confirmed hydrogen sulfide around the device reduced by 40%. And also reduced total phosphorus and total nitrogen by 20%. it was found that the water quality of the brackish anaerobic layer can be improved by the dissolved oxygen supply, and the effect becomes clearer as water bodies stagnated.

 Many people are living in floating villages on the Tonle Sap lake (TSL), Cambodia. People in the floating villages, who discharge domestic wastewater without any treatment, are recognized as one of the main sources of pollution of the lake water. On the other hand, they should have risk of health problems posed by using polluted lake water for their daily lives. Since the floating villages seasonally move depending on the change in the lake water level, it is difficult to analyze both the pollution load emitted by the villages and the exposure of villagers to the polluted lake water. In this paper, we tried to characterize the location and movement of the floating villages based on water depth and distance from rivers in the flooded forest analyzed from the satellite images. Analyzing Sentinel 2 images from Vega satellites enabled us to identify the floating villages which showed the seasonal movement. The distribution of such mobile floating villages, as well as immobile villages, was highly dependent on the region of the TSL. Mobile villages were frequently found in west and east regions of the TSL. Floating villages in the north region were immobile, while both types of villages existed in the northeast region and the Tonle Sap river connecting the Mekong river and the TSL. The mobile floating villages tended to locate in shallower rivers, which are surrounded by flooded forests, than the immobile ones in the rainy season. This is probably to avoid big waves on the lake which sometimes endanger the villages. In the dry season, the villages moved to the lake, some of which were 1,000 m away from the mouth of rivers. Based on these findings, we proposed a method to estimate where mobile floating villages are likely to be formed in the TSL.

 This study aimed to clarify the factors affecting water environmental evaluation. We conducted questionnaire to 559 local residents, and analysed by structural equation modelings. As a result, residents who had high interest in nature in childhood, and long residence duration have high level of interest in water environment. However such residents showed negative evaluation for current situations of water plant and exotic fish in the waterside area. Other residents who had close relationship with water resources had high awareness of concervation plan and had good valuation the current situations of cyanobacteria bloom and exotic fish in waterside area. In addition, residents who had high knowledge level of local environmental situation evaluated that water quality is fine. Also residents who had long residence duration has low evaluation of reed community.

 This study aimed to develop a non-destructive method of hollow-fiber membrane breakage detection in water treatment processes using optical fiber sensors. Ten FBG pressure sensors were deployed in a membrane housing, wherein hollow-fiber membranes with varied numbers of cut-off at the inlet and outlet sides of the membrane were installed and the membrane filtration system was operated in a dead-end mode. It was found that the sensitivity of pressure change detection was higher for the conventional pressure gauge than the FBG sensors possibly because two pressure gauges were installed at the inlet and outlet sides of the membrane module, whereas FBG sensors were used for the measurement of the average pressure change in the membrane housing. The predicted filtration pressure reduction by a water flow model within the failed membrane module agreed well with the pressure decreases for the membranes cut at the inlet side, but predicted pressure reduction by the model was greater than the experimental results of membranes cut at the outlet side of the membrane module. The sensitivity of membrane failure detection was significantly improved by using the pressure slope between two neighboring FBG sensors as an indicator. The pressure slope indicator also showed possibility of detecting the position of membrane failure within a membrane housing.

 PVDF hollow-fiber membrane used in a water purification plant was analyzed and compared with the virgin and the artificially aged membranes in order to evaluate the aged membrane condition and to clarify the ageing mechanism. From the results of the bubble point test and the diffusive air flow test, the used membrane became more permeable to air than the virgin membrane, and the analysis of the SEM image of the membrane surface confirmed the increase of the porosity in the used membranes. Slight changes were observed in the molecular weight distribution of the polymer molecule by gel permeation chromatography (GPC) and in the crystallinity by X-ray diffraction (XRD) and attenuated total reflection-Fourier transform infrared spectrometry (ATR-FTIR). On the other hand, in the ATR-FTIR analysis, the attenuation rate of peaks for the used membranes was almost the same between the crystalline phase and the amorphous phase. Furthermore, in SEM analysis of the used membrane, a decrease in the density of PVDF structure and the rougher membrane surface were observed. These results suggested that the ageing of the PVDF hollow-fiber membrane used in a water purification plant was caused by the detachment of PVDF structure including both the crystalline and amorphous phase rather than by the change in crystalline structure or the chain scission of PVDF polymer.

 Anaerobic membrane bioreacter (AnMBR), an combination of methane fermentation and membrane technology, have recently been attracting attention as a creation energy and energy saving wastewater treatment method. AnMBR has not yet been used for treating real sewage because related knowledge is not enough. In this study, long-term continuous treatment experiment of real sewage using AnMBR was conducted to evaluate the treatment performance. Hydraulic retention time (HRT) was shorted stepwise from 24 h to 4 h. As a result, high COD removal efficency (84 to 90%) was obtained in whole experiment. In particular, a high treated water quality with BOD <20 mg / L and COD <60 mg / L was obtained stably at the HRT of 6 to 8 h, which is the typical condition of the conversional activated sludge process. The sludge production yield of An MBR at a HRT of 8h is 0.12 gVSS / gCODrem, which is 1/3 to 1/5 of that for the conversional activated sludge process, and a methane conversion efficiency of influent COD was high as 69.3±3.2 %. A case study comparing the performance between AnMBR and the conversional activated sludge process indicated that the AnMBR would increase the energy recovery efficency by 1.6 times and reduce the excess sludge by half or less.

 Direct treatment of sewage by forward osmosis (FO) using polyamide FO membrane was examined, and the dissolved organic foulant in the sewage was estimated. Filtrated sewage and 3 M sodium chloride solution were used as feed solution (FS) and draw solution, respectively. The permeate flux decreased from 18.7 L/m²/h to 9.9 L/m²/h during 14 h of FO treatment owing to the membrane fouling, whereas the FO membrane rejected 98 % of dissolved organic carbon in FS. The dissolved orgnic matter was partially accumulated in the fouling layer. Analysis using liquid chromatography–organic carbon detection revealed that biopolymer fraction was dominant organic matter in the fouing layer. Although the accumulation of fraction of humic substances, building blocks, and low-molecular weight acids was only 1–2 %, that of biopolymer fraction was above 15 %. The biopolymer fraction is therefore estimated as a key dissolved organic foulant.

 Cyanobacteria have been considered difficult to use as dietary sources by consumers; however, it is unknown whether consumers in eutrophic lakes utilize cyanobacteria. Therefore, fatty acid analysis was used to examine the utilization of cyanobacteria by Bosmina longirostris, Diaphanosoma brachyrum, and adult Copepoda in Lake Hachiro (Akita Prefecture, Japan), which is a eutrophic lake where algal blooms occur every year. The levels of cyanobacterial markers (18:2ω6 and 18:3ω3) in each of the crustacean species increased during the summer bloom period, indicating that the zooplanktons assimilated cyanobacteria. In particular, B. longirostris, the dominant zooplankton species in Lake Hachiro, had the highest cyanobacteria-derived fatty acid content among the analyzed zooplanktons. Our findings indicated that B. longirostris plays an important role in cyanobacteria-derived nutrient transfer to higher trophic consumers in lake food webs.

 We assessed effects of allochthonous water inputs on community structures of primary producers and their productivity in Shizugawa Bay. We collected subsurface sea water from the bay and also waters potentially inflowing into the bay (i.e., river waters, groundwaters, offshore and bottom waters) in September 2017. In the laboratory, each of the allochthonous waters were mixed with the subsurface bay water to mimic the possible mixing of water in the real environment, and the concentration of fatty acid markers of bacteria, greenalgae, diatom and dinofllagelate after a 14-day incubation. As a result, it was found that the response to the treatment differed between the producer groups, and also that there is a competition for nitrogen between the groups. Specifically, bacteria had a higher productivity under conditions of relatively higher nitrate concentration, while productions of algae such as diatom and dinoflagellate were greater under conditions of high phosphate concentration. In addition, community structures of primary producers changed with N/P ratio. Our results further suggest that the composition of fatty acids produced in the inner bay may change significantly due to the change of the quality of the influent waters, so it is necessary to comprehensively manage the bay and surrounding watersheds to protect ecosystems and achieve sustainable fishery production in inner bay systems.

 In this study, we investigated the effect of metal induced oxidative stress on the production of microcystin via the field surveys of lakes dominant with cyanobacteria and laboratory incubation tests. The 16s rRNA gene analysis indicated that the microbial communities are dominated by Microcystis aeruginosa. Measured water quality parameters including chlorophyll a and microcystin per cell number as well as metal concentrations were analyzed by principal component analysis as well as correlation analysis, indicating the relation of microcystin per cell number with metal concentrations such as Ca and Mg. The incubational study using Microcystis aeruginosa (PCC7806 strain) consistently indicated that higher heavy metal (Cu and Zn) concentrations and lower Mg concentrations induced higher oxidative stress and toxin production. These results suggest that it is necessary to focus on the concentration of multiple metals that affect oxidative stress in order to clarify the cause of toxic cyanobacteria in closed waters.

 Grazing experiments were conducted to evaluate survivability of prey bacteria by using three isolated bacterivorous protozoa, Spumella sp. TGKK2, Ochromonas sp. TGPH2, and Bodo sp. TGKH8. Two genetically engineered prey bacteria having marker genes were made from Cupriavidus necator KT1 and Escherichia coli K-12, respectively. Pseudomonas aeruginosa PAO1 was also used as a prey bacterium. Concentrations of these bacteria were adjusted to approximately 1~5 x 10⁸ cells/mL. Grazing rate and final concentration of prey bacterium were changed by combinations of protozoan and bacterium. In common, initial rapid decreases of prey bacteria were observed, then final bacterial concentrations became stable at a certain level ranging from 10⁴ to 10⁶ cells/mL. The genetically engineered C. necator KT1 was also used to evaluate grazing ability of indigenous protozoa in river water, and similar trend in grazing was observed.

 A household-installed water treatment system makes it possible to establish a sustainable water supply in depopulated areas, but the health risks of the system users need to be protected properly because the quality of source water is not always excellent. To manage the users’ health risks, we calculated the microbial risk of Legionella pneumophila (causing a significant pneumonia to the elderly) and chemical risk of disinfection byproducts. It was found that the loss of disability-adjusted life years per peron per year (DALY loss pppy) were significantly below the tolerable disease burden proposed by World Health Organiation (WHO) (10^-6 DALY loss pppy) when the initial concentration of free chlorine in a tank was adjusted to 0.5 mg/L. It takes for about 80 days until cumulative risk of infection exceeds tolerable risk (10^-4 infection/person/year)proposed by USEPA when the presence of Acanthamoeba, the host of L. pneumophila, was assumed in the storage tank of treated water even the injestion ratio of free chlorine was 2.5 mg/L. The disease burden caused by trihalomethane as a disinfection byproduct was about one hundred times smaller than the WHO tolerable disease burden at all conditions of the free chlorine concentration. These result mean that the initial free chlorine concentration of 2.5 mg/L and replacement of membrane after 2 months can be available as critical limits of critical control point in the Water Safety Planning for the household-istalled water treatment system.

 We examined evaluation indexes for deterioration condition and maintenance managent system for drinking water distribution pipeline. Those indexes included resources for human, monetary, and goods and services. Relations among those indexes were investigated and following conclusions were drawn. Ratio of ineffective water was related to pipe material, human resource, monetary resource. Rate of aged pipeline was related to human and monetary resource, as well as maintenance management systems. It was also found that as the water supply population increases, the ratio of ineffective water decreases and the rate of aged pipeline increases. Ratio of pipe material, the number of staff, and the water supply revenue also changed accordingly. Furthermore, there was a tendency to secure human resources in the utilities which implemented wide-area cooperation or public-private partnership. It was also suggested that the maintenance management activity was improving in the wide-area cooperation utilities.

 This study took the imminent variations in water demand to analyse the plan for the renewal of the main distribution pipeline of the water supply network. The water distribution system was divided into three categories (upstream, midstream and downstream) of pipelines on the basis of their extension from the reservoir. This classification was accomplished to ensure the redundancy of the water distribution network after pipe renewal was achieved. The optimal combination of diameter reductions that could secure the effective head necessary for the most advantageous water supply was subsequently examined keeping in mind the fluctuations in water demand.

 Non-seismic joint pipes pipelines were targeted for renewal and three renewal scenarios were formulated according to the importance and age of the pipelines that were to be replaced. The indexes of the minimum effective head, the cost of replacement, the occurrence of backflow and the pumping power expenditure were used to accomplish a comparative analysis of the three renewal scenarios. This situation analysis was conducted to devise the best means of downsizing the new distribution pipeline through the abovementioned method.

 The outcomes of the analysis yielded new knowledge about the renewal plan that incorporated both economy and stable supply via the reduction of the diameter of the distribution mainline.

 This study evaluated a laboratory-scale system of high-solid thermophilic sludge anaerobic digestion with nitrogen and phosphorus recovery. Influent sewage sludge was adjusted to 9-10% total solids (TS) by centrifugation. The anaerobic digester used was a completely-mixed reactor of 2.0 L, and was operated at 55℃ and 20 days hydraulic retention time. Ammonia stripping of digested sludge and its return to the digester reduced total ammonia to 1,760 mgN/L in the digester, achieving VS destruction of 57.8% and methane production of 0.321 NL/gVS. Ammonia stripping was performed at 70℃, initial pH of about 9 for 2 hours, and recovered 20.7% of influent nitrogen as ammonia. Adsorption by porous iron hydroxide at pH 4-5 for 24 hours was employed for phosphate adsorption from digested sludge, and recovered 54.6% of influent phosphorus as phosphate. The acidic pH enabled centrifugal dewatering of digested sludge with only a polymer coagulant, showing capillary suction time of 84 sec and water content of 82.0% at the polymer addition of 1.92%TS. Therefore, this study demonstrated the possibility of high-solid thermophilic sludge anaerobic digestion and concomitant nitrogen/phosphorus recovery.

 In this study, in order to develop the mass production technology necessary for the implementation of edible mushroom cultivation using sewage sludge (dehydrated sludge), mass production test of oyster mushroom medium using dry steam was carried out. As a result, by stirring the medium for 7 minutes with a dry steam stirrer, dehydrated sludge and other medium materials were uniformly stirred, and it was possible to create a medium for mass production. It was also found that the yield characteristics and morphological characteristics of the fruiting bodies of the dry steam injection medium were comparable to the control medium. In addition, CO₂ fertilization test using passion fruit was carried out for the purpose of developing agricultural application technology of CO₂ generated in the mushroom cultivation process. It was apparent that CO₂ fertilization increased the sugar acid ratio of the fruit and improved fruit quality.

 To apply anaerobic digestion for small scale municipal wastewater treatment plant, the effects of rice straw addition on thermophilic digestion of dewatered sludge produced in an oxidation dich plant were examined in a laboratory scale digestor. In the thermophilic digestion experiment of the dewatered sludge (TS 6%) at HRT 15 days, organic acids were accumulated and methane yield was lower than the methane production potential of the sludge. On the other hand, stable methane production could be maintained by the addition of rice straw (3%). Significant differences were observed in both bacterial and archaeal community among mono-digestion and co-digestion sludge. In the digested sludge of co-digestion, higher abundance of Clostridiaceae was detected, estimating that the bacterial group related to decomposition of cellulose. Acetoclastic methane production archaea, Methanosarcina was occupied 59.6 % in detected total archaea. High resistance of Methanosarucina was estimated to achieve stable methane production.