Settling is one of fundamental processes of water treatment, but it needs comparatively large space to install a settling tank. Therefore, it is difficult for some small scale factories to find enough space in their premises to install one. Some experiments were made with some small model settling tanks in which plastic fiber strings with many small loops were stretched covering full cross section perpendicularly to the horizontal flow arranged with some intervals to increase the efficiency of suspended solids removal. It is shown in this paper that the fiber strings in a settling tank improved removal efficiency by preventing short circuit flows, and obstructing suspended solids to pass through the fiber net or adhering them on it.

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Most of algae which affect the filter clogging are slender type diatoms like Synedra, Fragilaria and Asterionella. In this study, model materials for diatoms and sand are used. A deposited amount of diatoms on a grain of a filter, a deposit distribution in the filter and the penetration depth of diatoms in the filter are discussed based on filtration experiments.
The amount of 95 per cent of total deposit is captured within the layer as thick as 30 times of the diameter of a filter grain under the condition of size of a filter grain from 2 to 6 times of diatom length. The ratio of deposited amount on a grain to filter depth is a main factor to estimate the degree of lean of amount of unlateral deposit at the surface layer part of filter layer and it decreases with the diameter of a filter grain. The result in this study shows useful points to design the thickness of filter for protection of filter clogging.

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Seepage impedance caused by clogging which appears in surface water drainage and ground water recharge facilities reduces the operation efficiency. In the mathematical model of the clogging, the filter cake was introduced as the main mechanism. Obtaining the model parameters through a series of experiments, we carried out short term recharge simulations and compared the results with model experiment results. Conducting a shrinking factor and a cracking factor of the cake, we carried out long term recharge simulations and compared the results with the those of an actual recharge basin. These comparisons show good agreements.

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Coagulant-assisted filtration through a dual-media filter, with pH adjusted to 5.5-6, gave an average effluent turbidity of less than 0.5 mg/L at a filtration rate of 120 m/day. The dual-media filter has a coarse medium bed at the upper part and a sand bed at the lower part. The removal efficiency was almost 100% for urbidity and 50-60% for color. Though 80% of the removed flocs were in the coarse medium, the head loss in that part was less than 20% that of the total head loss. The coagulant dosage of 4 mg Al³⁺/L was the optimum for filtration.

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The effects of sulfite or sulfate on anaerobic digestion of excess activated sludge were investigated at 37°C. No inhibition effect was observed up to 4 mM when sulfite was added to the anaerobic digestion adding sulfite system. Biogas production, however, was inhibited by the accumulation of acetate when sulfite was added in the concentration of 8 mM. The optimum concentration of sulfite was 2 mM for the biogas production and 4 mM for the solubilization of VSS of the sludge. The activity of sulfate reducing bacteria was higher when sulfite was added than sulfate was used. In this study, it was confined that sulfite is effective for the solubilization of organic matter.

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Effects of substrate concentration on the hydrogen gas production in acid-forming phase of anaerobic treatment process were investigated using chemostat-reactors. Six reactors were used with the influent glucose concentrations of 1, 000, 3, 162, 10, 000, 31, 620, 100, 000, 316, 200 mg/l, respectively. The SRT of each reactor was set at 4 hours and the reactor temperatures were maintained at 30±1deg;C. The glucose degradation efficiencies of each reactors were decreased with increasing substrate concentrations. The most effective hydrogen production was performed when influence substrate concentration was 10, 000 mg/l. Hydrogen gas was not produced sufficiently in the concentration range of 1, 000-3, 162 mg/l because substrate concentrations were low. The production rate of hydrogen gas did not increase when the substrate concentrations were 100, 000 mg/l or above. Most of the COD_Cr, was not removed from the liquid phase of all reactors at a SRT of 4 hours, which is the most suitable SRT for the highest hydrogen production rate. The effects of glucose concentration on the distribution of total anaerobic bacteria, acid forming bacteria, genus Clostridium and sulfate reducing bacteria were studied by counting colony forming unit.

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A lab-scale UASB reactor was operated over 300 days by feeding a synthetic wastewater composed of sucrose and volatile fatty acids, in order to investigate the granulation mechanism and the microbial structure of retained sludge consortium under thermophilic conditions (55°C).
As a result of establishment of well-settleable, high-activity granuled sludge, the reactor allowed ultimately a volumetric organic loading of 45 kgCOD/m³/day, corresponding to HRT of only 4.2 hours for influent strength of 8000mgCOD/l., with a COD removal efficiency of around 90%. The maximum sludge loading achieved was 3.7 gCOD/gVSS/day, that is 2-3 times as large as that of mesophilically grown sludge.
Methanogenic activities of the retained sludge increased finally up to 60 times for acetate, 25 times for propionate, and 3.5 times for hydrogen as large as those of the seed sludge (thermophilically digested sewage sludge). Relatively low values of the propionate-fed methanogenic activity and the viable cell number of propionate-degrading bacteria, compared to those of other trophic groups, indicate that the propionate breakdown is mostly subject to be a rate-limiting step in thermophilic methane fermentation process.

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In order to clarify the key-mechanisms of self-immobilization of anaerobic sludge consortia, biofilms at various growth stage were obtained over 120 days by installing slide-glass plates as a substratum in an UASB (upflow anaerobic sludge blanket) reactor. Biofilms taken out from the reactor at appropriate time intervals were forwarded to morphological observation with SEM and fluorescence microscopy, extracellular biopolymer analysis and the viable cell counting. The progression of biofilm could be differentiated into four sequent stages: adhesion (until 7 days), clump (8-28 days), conglomerate (29-80 days), and aggregate stage (81-120 days). A strong analogy in self-immobilization of anaerobic microorganisms was observed between biofilm formation and granulation. Entanglement of Methanothrix filaments served to provide other bacterial groups with sites for colonization and to conjoin adjacent microcolonies with each other to form a further extended aggregate. Methanobrevibacter spp. and Methanothrix spp. showed superior capability in adhering to substratum. The population sizes of hydrogenotrophic and acetotrophic methanogens were of the same order of magnitude, i. e. 1.4-1.6×10⁹/g. biomass at the final of the aggregate stage

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The processes of acid supply and consumption were investigated in several lakes in Mt. Norikura alpine. area which were susceptible to acid rain. With regard to acid consumption processes, we measured exchangeable cations of soil from the watershed of the lakes and those of sediments from the lakes themselves. This results of the measurement show Norikura lakes have a small acid-neutralizing capacity as 1/100 that of Lake Nawagaike, which has a normal pH value. With regard to acid supply processes, we observed two types of sulfate ion release from snow particles into the lake water. The first type is a sulfate ion release from snow particles immersed in the lake water at 0°C, which was observed at Lake Kiezuike when snow fell on the lake water at the beginning of June. The second is a sulfate ion release from snow jam, which was observed at Lake Tsurugaike during the snow melting period. At the end of May, the concentration of ion in the lake water was estimated to have increased by 9% by this process. However, it was found that the ion concentration can increase as far as 250%.

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In Hokkaido, we still have many mire fields where specific plants grow. They aregradually disappearing by human activities. We researched the quality of ground water in the mire and studied the water cultivation system that maintains the mire under the natural condition at Sarobetsu Mire. The results are summerized as follows;
(1) The ground water quality of rised bog (located at center of Sarobetsu Mire) is in a unique circumstance, with high concentration of organic matters composed of humic-acid and with low pH, 4.8 on the average.
(2) In the ground water of the upper layer of the raised bog, the concentration of the common inorganic components is low and the composition is similar to rain water. It is absolutely necessary to recharge the ground water by rain water to maintain the natural mire.
(3) In the region of raised bog (Sphgnum moss area), the decomposition activity is extremely low as the concentration of nutrients is low and the organic nutrients are dominant.
(4) While nutrient state of the high water level region of the Sarobetsu Mire is oligotrophic, that of the low ground water level region is eutrophic where inorganic form of nitrogen is dominant.
(5) In the region where bamboo grass invades, the concentration of organic matters and that of dissolved nitrogen (especially inorganic nitrogen) have a positive relationship. Nutrients are in a state liable to dissolve by the bacterial decompositon under the low level of ground water.
(6) Where bamboo grass invades, the concentration of Silicate increases. Influences of geological features should not be disregarded.

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A snowmelt process in snowpack was discussed from the investigation results of snow type profile, water quality profile and volumetric water content profile at Mt.Gassan in Yamagata prefecture. At the snowpack on a slope, the vertical channel in snowcover was observed at the lowest level region in snowpack. At this channel, the snow type was granular snow and snow color was black-like and conductivity was 2-4μS/cm. The horizontal channel in a snow cover was observed as a ice layer at the other slope site. At this ice layer, ion storage and ion release was recognized at the same investigation period. The detail profile of the volumetric water content, w, in snowpack was measured by TDR method. The value of w in channel such as a ice layer and a granular snow showed from 10 to 32% and the value of w in non-channel such as a compacted snow showed from 0 to 3%. There is a clear difference between them, so it is useful to investigate the snowmelt process in a snowpack.

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The quality of water in Abukuma River has been deteriorating and resulting in problems such as water pollution, increasing eutrophication and decreasing of water clarity. We found tiny air bubbles about 5mm diameter on the river bed which are believed to be the products of metabolic processes in the attached biofilm. The air bubbles were collected directly from the river bottom and were analyzed. The composition of the gas in the bubbles were Nitrogen gas of 99.8% and others of H2 and CO₂. In this research, the conditions of the biofilm was also observed, and the activities of microorganisms and the nitrogenous reactions which took place were studied. The numbers of bacteria which were taken from the biofilm in the river bed were also estimated. The flow velocities of the water near the river bed were found to be very low, such as 1-5 cm/sec. At the river bed where bubbles were seen, the VSS/SS value range was from 0.23 to 0.28, but at places where bubbles were not seen, the VSS/SS value range was from 0.10 to 0.14. From this research, it can be concluded that the river bed where the bubbles were found contained a lot of nitrogenious micro-organisms.

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Water pollution of the receiving waters that receive combined sewer overflows (CSOs) from urban sewer pipe systems has been deteriorating and spreading recently. The investigation of reasonable measures to prevent or mitigate the water pollution began to be taken up seriously in the early 1970s. The Public Works Research Institute (PWRI), the Ministry of Construction, has developed a water quality simulation model (PWRI Model) in sewered areas during the mid-1970s and early 1980s. This model, which is usually combined with the RRL method modified by the PWRI to evaluate stormwater runoff, is able to simulate practically the phenomenon in which the pollutants, including BOD, COD, and SS, remaining both on surfaces and in sewers are washed off.
The purpose of this paper is to clarify the adaptability of the model and improve or modify the model if necessary. First, the adaptability was investigated on the basis of the comparisons between observed runoff hydrographs, including pollutographs, and simulated ones in an urban drainage basin which area is about 40 ha. As a result, several methodological problems to be solved were indicated. Second, the modification of the model according to the indications resulted in improving the adaptability considerably.

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For water quality management, it is important to control not only point pollutants load, but also nonpoint pollutants load during wet weather.
In this study, we have first discussed the principles and measures to control nonpoint pollutants load during wet weather. Based on the results, a new drainage system, which takes advantage of both combined and separated drainage systems, has been proposed.
Some simulations on pollutants load behaviors has been performed and the results have shown that the proposed drainage system is possible to collect and treat nonpoint sources more efficiently in comparison with the traditional drainage systems, and very suitable to high-density urban area nonpoint pollutant control.

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Progress in urbanization has caused water-related problems such as large expenditure for water resource exploitation, floods in urban rivers and natural flow rate reduction. Indirect potable reuse of treated wastewater and rainwater infiltration systems are part of major artificial water recycle technologies for solving these problems. In this study, the two systems mentioned above were evaluated in several indices: flow rate, water quality, cost, CO₂ emission, energy consumption and others. The case of the Tama River in the Tokyo metropolitan area was examined.
Indirect potable reuse proved to flatten the flow rate and preserve upstream water environment, while water quality in the lower course became worse than a case without reuse. However, the cost, CO₂ emission and energy consumption were 10% smaller because of diminution of waterworks sizes. The rainwater infiltration systems resulted in 8% increase in the natural flow rate for the main river part and the maximum 80% increase was achieved in a downstream region of the branch rivers. Therefore, 10-20% reduction in terms of COD_mn was obtained in the region, indicating an improvement of the water environment. The rainwater infiltration systems accounted for approximately 10% of the total cost, whereas only 4-5% of the total CO₂ emission and energy consumption was due to the infiltration systems. Thus, they are expected to have environmentally low impact.

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Reuse of wastewater contributes to the decrease in the amounts of water withdrawal as well as its discharges back into receiving water bodies. An integrated system of environmental management with reuse of wastewater will also contribute to enhancement of environmental conservation. This paper deals with a cost allocation problem such that the environmental agency concerned intends to achieve a higher ambient standard of water quality by having water users and the sewerage manager collaborate through developments of a reuse scheme and/or by improving treatment level. The problem is formulated as a multiagent management problem by use of cooperative three person game theory. A set of neccessary conditions for instituting economically viable wastewater reuse systems are derived through mathematical model analyses.

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Membrane filtration of groundwater, which containing iron, manganese and dissolved silica in high concentration, was investigated under continuous filtration. It is considered that the manganese in this raw water does not form the complex compound with organic matter. The membrane filtration after aeration or chlorination is able to remove the iron perfectly. The membrane filtration after chlorination is able to remove the manganese perfectly under high concentrated circulating water. The transmembrane pressure difference depends on the oxidation methods and the flux level. The fouling of membrane depends on the oxide sticked on the surface of membrane. It is able to filtrate more than 70 days within 50 kPa after chlorination under flux of 1m³/m² ·d.

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Fifteen types of ultrafiltration membranes and low pressure reverse osmosis membranes were examined in terms of virus rejection by using several types of coliphages: None of the tested pieces of membranes was complete barrier against Qβ, which is the smallest virus used in this study. Logarithmic rejection coefficient Φ ranged from 3 to 6 for Qβ. Higher rejection was observed for T4, MS2 and two types of indigenous coliphages compared to the Qβ case. Neither molecular weight cutoff value of ultrafiltration membranes nor salt rejection of reverse osmosis membranes had significant relation to rejection of virus. T4 virus which has 80nm of diameter leaked through some of the tested membranes. These phenomena imply membranes have abnormally larger pores which are not included in the main pore size distribution. The velocity variation method was tested to obtain real rejection of virus from observed rejection data. Smaller value of exponent in the laminar flow mass transfer equation than 0.33 was adequate in the case of larger solutes and high flux. Real rejection coefficient of Qβ was estimated 2 to 3 of Φ higher than the observed rejection coefficient.

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The cross flow type ultrafiltration was carried out to evaluate the relation between flux and coagulation state using the results of zeta potential, flux reduction ratio, volumetric sedimentation ratio, the turbidity reduction ratio in Jar test. The concentration of kaolin suspension used in this study was 1000 mg/l. The ion concentration of the raw water was controlled by changing mixing ratio of distilled water and tap water, or with adding NaCl and CaCl₂ solution. As the dispersion state of kaolin suspension was good, the flux of ultrafiltration hardly decreased because of the large negative charge of suspended solid and shearing force under cross flow. If the dispersion state of kaolin suspension was not good, the flux of ultrafiltration was getting small by destabilization of dispersion state. This small change of coagulation state gives large influence on the flux. On the other hand, the cation or coagulant dosage makes coagulated flocs and the resulted large floc and shearing force under cross flow obstructs the cake formation on membrane.

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Mathematical models are developed to evaluate treatment performance in a pre-precipitation and biofilm process which is operated for phosphorus removal and nitrification as well as BOD removal. The biofilm process is a fluidized medium reactor with polyurethane foam. Treatment performance is also evaluated by fractionation method, in which pollutants are separated by particle size with filters (pore size; 105, 1.0 and 0.1 micro-meter). A distribution matrix model is developed to show the change in distribution pattern and concentration of each particle size through precipitation and sedimentation. A mathematical model developed for biofilm reactor, which can simulate the competition between autotrophic and heterotrophic bacteria with respect to attached surface of the medium, is demonstrated to predict the treatment performance (BOD removal and nitrification) by comparing the simulated results with experimental results. With these models, the pre-precipitation and biofilm process is evaluated with respect to hydraulic retention time and recovery of organic sludge by comparing with primary sedimentation and biofilm process. As a result, it is shown to shorten the hydraulic retention time and increase the organic recovery effectively.

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Performance of a denitrification process using polyvinyl alcohol (PVA) as a organic carbon source was investigated by anoxic and aerobic RBC systems at 25°C and 30°C. PVA was well degraded under aerobic condition, but not under anoxic condition. In the experiment using phenol as a co-organic substrate for PVA degradation, the efficiency of denitrification increased from 38% to 84% as the TOC loading rate increased from 1g/m².d to 4.2g/m².d, while PVA-removal and nitrification efficiencies were above 90% throughout all the experiments. In the experiment using PVA as the sole organic carbon source, the efficiencies of PVA removal and nitrification increased with increasing HRT, and reached levels of 95%, and 99%, respectively at an HRT of 10 hours, whereas the efficiency of denitrification reached its maximum value of 78% at an HRT of 8 hours. These results indicated that PVA could be used as a sole electron donor for denitrification and that the optimum HRT for the simultaneous removal of PVA and nitrogen was between 8 and 10 hours. The PVA-decomposing bacteria, nitrifiers, and denitrifiers co-existed in the biofilm, but the populations of PVA-decomposing bacteria and denitrifiers in the surface layer were 1 to 2 orders of magnitude higher than those in middle and bottom layers indicating that the surface layer had a higher denitrifying activity.

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A swine waste which included both urine and feces mixed with waste food oil was treated by Thermophilic Oxic Process. The optimum mixing ratio of waste to the oil was investigated. When the ratio was 10: 1 (v/w), no oil was accumulated in the medium. It was shown that 70 % of calorie was produced from oil and 30 % came from organic matter in swine waste. The long period continuous runing test showed that when the BOD load was 12.5 kg·m^-3·d^-1 and aerationrate was 200 l·m^-3·min^-1 organic carbon was decomposed and no drain water obtained. Also, aminute amount of excess sludge was formed during this period.

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Mutagenic activity of water treated with chlorine dioxide was investigated, focusing on its stability. Chromosomal aberration test using Chinese hamster lung (CHL) cell was carried out to evaluate mutagenic activity. Activity inducing chromosomal aberrations of water treated with chlorine dioxide could be detected after the concentration of chlorite ion decreased. Activity inducing aberrations of humic acids treated with chlorine dioxide at neutral condition was in a range of one third to one half of that of chlorinated solution. It was found that activity inducing aberrations of water treated with chlorine dioxide decreased with hydrolysis reaction. While chloroform was produced with hydrolysis reaction, activity inducing aberrations decreased. The observed hydrolysis rate constant at neutral pH at 20°C was determined to be 0.15 day^-1, and half-life was estimated to be 4.5 days, which were one-eleventh as large as those of chlorinated water. These findings suggest that it is necessary to evaluate the varying mutagenic activities in distribution systems when mutagenic activities of waters treated with chlorine and chlorine dioxide are compared.

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The purpose of our study is to estimate the influence of development activity on shallow sea ecosystems, especially on fish. Fish behavior, based on its preference was revealed to be an essential factor for this purpose. In this paper, fish preference was tested through experimentation on juvenile ocellate puffers. Two waterways were connected to each other at a narrow junction, and different environmental conditions were established for each waterway. Puffer could select the preferred waterway, and the distribution was counted using a video tape recorder (VTR) every minute for 50 minutes. Puffer showed less preference for shade than the shiner, river fish, and showed strong preference for the bottom. The results allowed for the fishes preference to be successfully formulated. This demonstrated the applicability of the formulation method for fish in sea. Then, shiner behavior was tested in a larger tank with several environmental conditions represented. The tank (118 cm long, 49 cm wide, 20 cm depth) was divided into 14 sections, and each section had a different depth, current velocity, plant stem, and shade level. 139 shiner were put in the tank and their distribution was counted using a VTR for 40 minutes. Calculated distribution of shiner by using the formula showed good accordance with observed situation. This result should support the efficiency of the formulation method.

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First, acute toxicity, biodegradability and mutagenisity of 8 commercial household detergents (main surfactants were soap in 3 detergents, synthetic detergents in 3 and the mixture of the both in the remaining 2) and pure nonion- and anion- surfactants were studied, using Microtox assay, BOD meter and Ames' assay, respectively. Next, effects of the detergents on the glucose biodegradation and the mutagen intensity of 4NQO, 2AA and BaP were tested, using BOD meter and Ames' assay.
As a result, detergent which main component was α-SEE showed the highest EC50 value in Microtox assay. Other detergent which main components were LAS, AS and AE showed the lowest EC50 value. The highest biodegradability was found in soap and the lowest was found in α-SFE or LAS detergents. Mutagenicity was not found in any detergent with and without S9-Mix. Detergents with low biodegradability lowered the glucose biodegradation. Synthetic detergents enhance the 4NQO mutagenicity without S9-Mix. In contrast, soap increase the BaP mutagenicity with S9-Mix.

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In order to construct useful transport-chemistry model for large-scale variations of tropospheric trace species, accurate and low computational cost submodel for reaction is needed. Based on sensitivity analysis, Dunker developed a simple method for parameterization of atmospheric chemistry. We have investigated the possibility of applying the method to the equations of tropospheric photochemistry. Since the method was developed for urban air chemistry, some modifications were made. One-dimensional tropospheric model was used to test its accuracy and computational speed. The results indicated little loss of accuracy compared to detailed model simulations of chemistry with high time resolution. In addition, the computation time was reduced by about 2-order of magnitude.

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Albedo effect of anthropogenic Arctic aerosols on climate was estimated through planetary albedo calculation and surface temperature evaluation with two-layer zonal energy balance climate model. Six types of global aerosol models were assumed in the atmospheric boundary layer: Arctic aerosols, subarctic aerosols, continental aerosols, maritime aerosols in Northern Hemisphere, maritime aerosols in Southern Hemisphere and Antarctic aerosols. Optical properties of each type of aerosols were calculated based on chemical characterization. Internal mixing aerosols seriously affect on climate in Arctic Circle. Doubling anthropogenic Arctic aerosols causes 0.3°C increase of surface temperature, whereas the disappearance causes 0.15°C decrease of surface temperature in Arctic Circle.

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With the energy statistics and very precise geographical information the very precise maps of energy consumption in Tokyo were drawn by the method of computer mapping. Computer graphics animation of the annual and diurnal variation of energy consumption in Tokyo was prepared with the calculation in the super computer. These outputs seem to be available as a scenario of anthropogenic heat exhaust, one of the surface boundary conditions for the numerical simulation model of atmospheric environment. The anthropogenic heat in the central Tokyo exceeds 400W/m² in the daytime, especially the maximum value is 1, 590W/m² in winter. The hot water supply in office and hotel occupies 51%. In the suburban area the anthropogenic heat from household sector reaches about 30W/m² in the nighttime.

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In order to evaluate the effect of bacteria-immobilizing pellets in oxic tank, two experimental wastewater treatment processes, namely Process-1 and Process-2, were compared. In Process-1, the hollow immobilizing pellets (0. D. 4mm, I. D. 3mm, density 1.00lg/cm³) were dosed into the oxic tank up to 20% of the reactor volume. Process-2 was operated as a control experiment without pellets. Process-1 showed superiority in suspended solid removal, BOD removal, phosphorus removal, and nitrogen removal over Process-2 especially during winter season, namely, nitrogen removal rate above 70% was maintained at 14°C, with HRT of 6hours and flow rate fluctuation between 0.5 to 2.0 times of the average wastewater flow rate. By further investigating the mechanism of nitrogen removal enhancement by immobilized bacteria, it was concluded that immobilized bacteria not only promoted nitrification and decomposition of organic nitrogen, but they were able to enhance denitrification in the oxic tank.

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The purpose of this study was to investigate solubilization effects on algae by thermal, thermal-alkali, ultrasonic and surfactant-added ultrasonic treatments for enhancing biodegradability of algae for methane production. The solubilization ratio for thermal treatment was increased when temperature was increased, and the effective treatment time was about 30 min. The alkali treatment at 150°C for 30min improved the efficiency of treatment by 60, 50 and 80% for TOC, COD and protein degradation, respectively. Ultrasonic treatment increased the solubilization ratio significantly only in the first 100 min. The ultrasonic treatment was the most effective method. The addition of surfactant improved solubilization efficiency at concentration less than 400 mg/l. The rate of hydrolysis in ultrasonic and thermal treatment was a first-order reaction, one stage. The rate of hydrolysis for fresh algae, k, ranged from 0.019 to 0.023 min^-1 for ultrasonic treatment, 0.012 to 0.018 min^-1 for thermal treatment at 92°C, and 0.009 to 0.013 min^-1 for thermal treatment at 60°C. For ultrasonic treatment, the rate of hydrolysis was higher for protein than for COD, TOC, and carbohydrate, whereas for the thermal treatment, carbohydrate had the highest rate of hydrolysis.

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Filamentous bulking and sulfate reduction in anaerobic-oxic activated sludge system of the municipal plant were examined. The anaerobic-oxic system was sometimes not effective to prevent bulking. When the amount of phosphate release in the anaerobic zone was small and sulfate concentrations were low, filamentous bacteria Type 021N grew predominantly. However the organic substances were remained in the end of anaerobic zone. The sulfate reduction rate was obtained from the anaerobic batch experiment using settled sewage. When the sulfate reducing rate was high, filamentous bulking occurred. Sulfate reduction occurred when the returned sludge was stored in 20°C. The rate of sulfate reduction in the storage experiments also related to the amount of filamentous bacteria. The results showed that sulfate reduction was a course of filamentous bulking due to Type 021N in the actual anaerobic-oxic activated sludge plant.

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The capability of anaerobic-aerobic activated sludge to produce polyhydroxyalkanoate (PHA), a kind of biodegradable plastics, was evaluated in terms of PHA content in the sludge and PHA production rate. Batch experiments were designed to investigate 1) effect of oxygen supply on PHA production, 2) PHA producing capability of sludges from practical anaerobic-aerobic activated sludge plants, and 3) possibility to use an industrial wastewater as the substrate for PHA production. The maximum PHA production observed was 54% of the initial sludge mass. The optimum oxygen supply rate for PHA production was found to be 1.22mgO/min/l. The possibility to use practical sludges and some industrial wastewaters for PHA production was confirmed.

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The amount of sewage that flows into waste water treatment plant, the quality of the sewage, and the pollution load (the product of first two) are not constant; rather, they undergo periodical changes within unit times such as one day, one week, or one year. It often happens that the difference between the maximum and minimum loads is very high at wastewater treatment plant located in sightseeing areas or industrial zones.
Usually, wastewater treatment plant is designed to handle the maximum daily pollution load and is constructed accordingly. However, it is difficult to achieve constant a nd stable performance in the wastewater treatment plant where high loads become concentrated in the specific short: erm of a week or year.
We built a pilot plant and performed the following exp eriments:
We varied the load to ten times per a single day on one cycle in single-stage intermittent aeration system. We changed the amount of withdrawal excess sludge and the anoxic-oxic time ratio, in accordance with a given load, and thereby maintained a constant MLSS and ASRT.
We found that while influent was BOD 150-200 mg/l, SS 140-160 mg/l, T-N 35-50 mg/l. and T-P 3.7-4.3 mg/l, effluent was 4-12 mg/l, 8 mg/l, 2.5-5.9 mg/l and 0.7-1.9 mg/l, respectively. Accordingly, we believe that we have achieve d a constant and stable treatment performance.

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Indicator function of coliphage in regard to viral pollution control was investigated. Concentration of cbliphage in night soil was in the range from less than 10 to 10⁶ PFU·mL^-1. In sewage, coliphage concentration ranged from 10² to 10³ PFU·mL^-1. Calculation based on the concentration in sewage showed that coliphage concentration in night soil should be 1-10⁵ times more than in actual night soil. In diluted night soil, coliphages didn't multiply but they could multiply in diluted night soil when easily assimilable organic matter for host bacteria was added. Suppression of FRNA phage multiplication by RNase was also investigated. RNase inactivated FRNA phage Qβ only at the moment of infection. Some ingredient in night soil decreased efficiency of plating of Qβ by about 15% but did not affect T4 concentration measurement. Coliphage in night soil must multiply after diluted and added some organic matter in sewer pipes. Coliphage concentration, greatly affected by organic matter in the environment, can be assumed to be an indicator for sewage pollution rather than night soil pollution. Both DNA phage and FRNA phage can be applied to the indicators of viral removal in water treatment process, and only FRNA phage can be applied in wastewater treatment process because DNA phage tends to multiply in wastewater treatment process.

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Characteristics on statistical distributions of coliform group density and enterococcus group density were investigated in an aquatic environment. Statistical distributions of both baterial group densities were influenced by the water quality such as suspended solids concentration and so on. The statistical distribution of coliform group density was more sensitive for the water quality than that of enterococcus group density.
In experiments employing the kaolin as the suspended solids, the increase of the kaolin concentration brought decreases of both bacterial group densities, and the degree of decrease of bacterial density was more remarkable in case of coliform group. That is, the presence of kaolin floc in the water sample influences the statistical distribution of coliform group more significantly compared with enterococcus group.
Therefore, results of this study derived that enterococcus group would be much better indicator bacteria than coliform group in the aquatic environment where the suspended solids was involved.

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The sorption of trichloroethylene (TCE) from the vapor phase was investigated by batch sorption experiments. The effects of solid components in natural solids was evaluated with model solid phase system, consisting of five individual model solid phases (humic acid, montmorillonite, amorphous aluminosilicate gel, amorphous iron oxides, and amorphous manganese oxides) and two binary model solid phases (montmorillonite with amorphous aluminosilicte gel and montmorillonite with amorphous iron oxides). The experimental results indicated that swelling clays, which are represented by the montmorillonite, is a dominant sorbent in natural solids. The amorphous metal oxides of aluminosilicate and iron effectively block the sorption site of the swelling clay. The water associated with model solid phases (i. e., moisture content) reduces the sorption. The reduction rate, normalized with respect to the sorption onto each model solid phases of zero moisture content, is greater for the inorganic model solid phases than for humic acid. The sorption experiments with natural solids observed greater reduction rate for the natural solid of low organic carbon content. Therefore, it was hypothesized that moisture content of the swelling clays in a natural solid is smaller than that of the organic matter.

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Some of the environmental factors influencing the growth characterization of the white rot fungus, Phanerochaete chrysosporium, and the degradation of azo dyes (Reactive Red 22 & Sunset Yellow FCF) and chlorinated substances (2, 6-DCP & MCPA) were investigated in shallow batch cultures. The optimum temperature and pH for the growth were around 30°C and 4, respectively. The presence of thiamine was necessary for its growth. The azo dyes were decolorized by the P. chrysosporium under nitrogen-limiting condition. Two chlorinated substances were, however, disappeared under both nitrogen-limiting and nitrogen-sufficient conditions. Adsorption onto the mycelia were also investigated. And it was concluded that these recalcitrant substances were degraded by non-specific mechanisms of this lignin-degrading fungus. The azo dyes were also decolorized by the crude enzymes of lignin peroxydase.

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The viscosity of melted slags is one of the most important control factors in the operation of sewage sludge melting facilities. Therefore it is imperative to understand the features of viscosity dependent on temperature and composition.
However, there are very few measurement data available on the viscosity for melted slag of sewage sludge.
This paper first presents a summary of the basic knowledge about viscosity and then establishes the methods of preparing test samples and the procedures for measuring the viscosity of melted slag at high temperatures using an outer cylinder rotating viscometer. Next the paper reports the results of the viscosity measurments.
These results show that in the case of melted slag of sewage sludge there is a high probability correlation between frequency coefficient and activation energy, which is defined in the Andrade theory. These factors have been previously thought to be independent constants.
Furthermore, this paper suggests a presumptive equation for viscosity with a parameter of activation energy and considers the range and the precision of its application

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