order to describe or reproduce the real water conditions in the river, we propose a method for adjustment of the observed data which we obtained in our river survey. By using these adjusted parameters, the mass-balances of flux and pollutants hold well, so we define it as a“reasonable water condition.” And also, these reasonable parameters were used in models based on the Streeter-Phelps equation describing self purification in a river. The results predicted by these model studies were then compared with the actual conditions in the Tama River. In some cases it was possible, and permissible, to make modifications to the model which improved the agreement between the predicted and the observed results;in other cases, this was not permissible.

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Water qualities related to lake eutrophication such as water temperature, secchi depth, concentration of suspended matters, chlorophyll-a, nutrients, etc., were observed in Lake Kasumigaura by three types of survey; 1) monthly survey at ten points for 1976-1982, 2) daily observation for two months, 3) hourly observation for several days. Some statistical analyses were applied to those data and the fundamental features of the variation were investigated. First, the type of frequency distribution, typical pattern of seasonal and horizontal variations, and the relationship of those were obtained. Some water qualities such as chlorophyll-a, PON, POC, etc., which are almost all produced in the lake, have nearly same characteristics in the time and horizontal variations and their types of frequency distribution are varied from lognormal type near the river mouth to normal one in the center of the lake. Second, the magnitudes of variance for hourly, daily, seasonal variations were compared, and it was found that hourly and daily variations have nearly same order of seasonal one in the summer. Third, the short and long term effects of meteorological conditions to water qualities were examined and the singular conditions were separated to evaluate their effects.
These results are discussed at the view point of sampling method and some informations were proposed for the sampling method which would give the more accurate estimation of lake eutrophic conditions.

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Inner basin drainage shall be planned with flood water level in main stream and characteristics of sub-basin. Sewerage system is merely an alternatives. Systems approach are available for decision-making process of this comprehensive inner basin drainage problem. This paper gives strategy for inner basin drainage system planning.
Submerged areas are evaluated by backwater simulation. Drainage capacity are measured by annually expected submerged area for three cases. First is the case that flood water level exceeds its design level, second is that pump well level is fixed at its designed level throughout the drainage, and third is that pump well level is kept under the critical flow level of the sewer. Then, pattern analysis for such attributes about drainage capacity suggests whether external river improvement should be conducted and what kind of sewerage reconstruction may be effective.

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Return Period of a Reservoir Capacity can be estimated from the occurrence curve of the yearly required volumes calculated by such as the Mass-Curve Method. However, the practical data processing method for the estimation has been little discussed because of the past limited data.
In this paper, from a case study of the severe drought in the Fukuoka area in 1978, the data over 60 years are collected, simulated and analyzed as a computer work, from which some practical estimation methods of the return period are shown such as follows, 1) the quantitative relations between the number of data and the precision of the estimated return period are shown as examples, 2) the distribution functions employed for the occurrence curve are compared among log-normal, Gumbel, and so forth, the result of which shows that the number of data is more important than the selection of the functions, and 3) a new stochastic treatment is required for calculated volumes by Mass-Curve Method before plotting for the occurence curve.
The authors propose to employ a new probability of full condition of a reservoir at the beginning of the dry period, because the hypothesis of the full condition in the Mass-Curve Method leads a great deal of stochastic error for the final estimation of the return period.

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Water resources problems and stability of watei supply make waterworks area-wide. Area-wide waterworks is to be planned with consideration of such as regional climate and history, that is, hydrological and socio-economical aspect and histories of water-works.
This paper gives the background information of area-wide waterworks and tries to identify its future policy making. Waterworks system is classified three levels according to area-wide size. The regional characteristics are paternized. Questionnaire data analysis gives the relation between area-wide size and regional characteristics. At the result, we get the conclusion that the supplydemand gap and the scale of kernel cities affect the area-wide size of waterworks.

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A method of prediction for suspended sediment concentration in quiescent state has been developed. Based on the mass balance equations for suspended cohesive particles of each size and the assumption of the similarity of particle size distributions, two partial differential equations concerning suspended sediment concentration and sediment mass flux as dependent variables were derived. The two specific overall parameters characterizing a normalized particle size distribution function and a coagulative characteristic of particles are obtained in these equations. The vertical concentration distribution and the depositional rate of suspended sediment in water can be computed numerically by the above equations with properly choosed two parameters. In order to check the numerical computed results, experiments of settling were carried out with cohesive clay in seawater. Total suspended sediment weight per unit area was measured for various initial sediment concentrations. The numerical computed results presented in this study coincide with the experimental results except for the high initial sediment concentration. The equations can also be shown applicable to convective-diffusion transport problems.

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Although conventional modeling of mass transport in groundwat er systems is usually assumed to be homogeneous, real aquifers have the heterogeneous structures whose heterogeneity cannot be determined accurately. In this study, the statistical homogeneity i. e. only statistical characteristics are uniform all over the region is assumed for a transmissivity field, and the effect of its heterogeneity and uncertainty on the estimation of groundwater flow and concentration is stochastically analyzed using Monte Carlo technique. Many realizations of a transmissivity field are produced using the method which can generate the two-dimensional random fields of any covariance structure. Then Darcy's equation and the convective dispersion equation are solved for many realizations of the transmissivity field by Galerkin finite element method to estimate the statistical characteristics of the groundwater flow and the concentration. In Monte Carlo tecnique the methodof conditional simulation can be used to generate the realizations of a transmissivity field conditioned by observation data. In this study, the method of conditional simulation which conventionally considers the observation data to be true is extended to take observation noises into consideration. Results of the simulations show that the standard deviations in hydraulic pressure, groundwater flow and concentration and the mean of groud water flow increase as the standard deviation in log transmissivity increases. The coefficient of variation in concentration increases in the region away from the point source of contamination in proportion as the spatial autocorrelation of log transmissivity becomes stronger. The shapes of the distributions of concentration obtained in this study are different from conventional ones obtained with the assumption of homogeneous aquifer. It is shown that the method of conditional simulation can also be effectively used with observation noises and can decrease the uncertainty in the estimation of groundwater systems.

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In enviromental pollution problems, the contamination is predicted by the convective diffusion equation (CDE) as a mathematical model. Nowadays many discretized schemes are proposed for solving the CDE exactly. Then the stability analysis as a necessary condition is firstly implemented to formulate the selection criteria for their schemes. Even though the schemes are stable, there are probably some cases which produce innegligible numerical errors. Therefore the error analysis of numerical solution is necessary for the next step of the stability analysis. The purpose of this studies is to apply the system control theory to the error analysis and then to analize the wave number transfer properties of the several schemes by taking the influence of the initial value into consideration. In this paper the one-dimensional unsteady CDE is employed for the simplicity of discussion and a new error estimation index is proposed. This index is related to both the amplification factor and the initial value, and its availability is investigated by a simple example.

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An ordinary aerobic rotating biological contactor (NBC) has disks which are half submerged in the bulk liquid. In order to estimate the oxygen transfer rate into the biofilm fixed to a rotating disk quantatively, it should be noted that the mechanism be essentially described as unsteady-state diffusion and reaction process, because the biofilm experiences cyclic changes between the air and water phases. In this study, we gave the analytical solutions of differential equations of unsteady-state mass transfer for RBC nitrification process. We calculated the removal rate of ammonium nitrogen from the solutions and compared them with experimental results. The experiments were carried out using a small laboratory-scale RBC unit whose disk diametre was 26 cm. From these results, we could examine effects of rotational speed and disk diametre on the ammonium nitrogen removal rate. Main results were as follows:(1) Reaction mechanism changed from ammonium limitation (substrate limitation) to oxygen limitation at about 5 rpm in this study.(2) At higher rotational speed than 5 rpm, nitrification was limited by oxygen supply and the increase of rotational speed had no effect on the ammonium nitrogen removal rate. However, the dissolved oxygen concentration in the bulk liquid increased with the increase of rotational speed, because the bulk liquid was more aerated as rotational speed increased.(3) It was estimated from the unsteady-state analytical solutions that more than 95% of the amount of oxygen used in the biofilm was supplied from the air under the oxygen limitation and that the maximum ammonium nitrogen removal rate decreased as disk diametre increased.

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A rotating contactor has been used as a biological oxidation process which is referred to a rotating biological contactor (RBC). In the RBC, the rotating velocity is usually very low compared with that in the application of the rotating contactor as a aeration process in order to attach the biofilm to the contactor surface. The oxygen transfer capacity of the RBC is determined by the thickness of diffusion layer and attached-water layer, and the oxygen uptake rate of biofilm. A mathematical model of the oxygen transfer process in the rotating contactor with very low rotating velocity is presented, and simulation and experiment of the same process are carried out to find the relationships between the thickness of diffusion layer and attached-water layer, contactor rotating velocity and contactor size. It is shown that the diffusion layer thickness is inversely proportional to the root of the contactor rotating velocity and the attached-water layer thickness is proportional to the root of the contactor peripheral velocity. A mathematical model of the biological oxidation in the RBC is developed and applied to the nitrification with and without simultaneous carbon oxidation. The nitrification rate is formulated based on the oxygen transfer capacity.

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The frequency distribution of water quality indices in a eutrophic lake is analysed and characterized in connection with their local and seasonal behaviors. Their distribution patterns can be classified into five groups, which are exponential, normal, log-normal and uniform distributions and others. The factors which may influence the distribution patterns are considered to be the acceptance capacity of receiving water, the pollutants loading and the periodicity of indices. The first is connected with the reduction rate of the pollutants by self-purification reaction in the water body. The concentrations of the indices influenced strongly by this factor follow an exponential distribution. The second is on the indices related firmly to pollutant inputs, which patterns are classified into normal or log-normal types. The third factor is the periodicity. The value of the periodic index follows approximately a uniform distribution. On the indices which variations are expected to be caused by the influent of pollutants and periodicity, the shapes of histograms do not show the special distributions. In order to estimate the effects of these three factors on the distribution pattern, the method of Analysis of Variance' is introduced. Two statistical parameters, namely contribution proportions on dates and stations of sampling, are abstracted in the analysis. The contribution proportion on dates seems to represent the periodicity and the other seems to be related to pollution effects. The third parameter which indicates the effect of the acceptance capacity can be expressed by the magnitude of coefficient of variance. Each water quality index is plotted to a three-dementional space with these parameters, so that it is recognized that the characteristics of frequency distributions of water quality indices can be successfully and quantitatively classified by these parameters.

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The contribution of nitrogen release from sediment to total nitrogen loading into lakes were studied in Lake Yunoko and Lake Kasumigaura. Nitrogen flux at the sediment-water interface was estimated by a mathematical model based on the Fick's law. There observed little differences in NH₄-N release flux from sediments of Lake Yunoko throughout the year. NH₄-N release flux in the profoundal zone was greater than that of the littral zone. NI₄-N release flux at the lake center ranged 45 to 65 mg·m^-2·d^-1, whereas NO_x-N (NO₂+NO₃-N) flux from water to sediment was negligible. It was estimated that internal nitrogen loading in Lake Yunoko ranged from 7.3 to 11 kgN.d^-1 and was equivalent to 15-36% of external nitrogen loading. In Lake Kasumigaura NH₄-N and NO_x-N concentrations in interstitial water changed seasonably. Maximum NH₄-N release flux was observed (69-134 mg·m^-2·d^-1) during summer and early autumn. NH₄-N release flux decreased with water temperature (-2-8mg·Em^-2·^-1). NO_x-N flux from water to sediment in Takahamairi Bay was comparable to NH₄-N release flux except summer. Internal/external nitrogen loading ratio during summer in Takahamairi Bay was 0.5. This ratio in the lake center area ranged from 0.5 (winter) to 3.0 (summer).

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Water quality purification using water hyacinth, Eichhornia Crassipes (Mart.) Solms, has attracted from the point of view of energy cost on wastewater treatment systems. Water hyacinth, however, is originally a subtropical flora. Therefore it is necessary to investigate the applicability on temperate climate as Japan. The purpose of this study is to investigate the characteristics of nitrogen uptake and growth of water hyacinth on the temperate climate conditions. Rates of nitrogen uptake and growth were measured in cultures of water hyacinth growing outdoors in continuously flowing nutrient solutions. Either NH₄Cl or NaNO₃ was added as the resource of nitrogen in nutrient solutions. Maximum growth rate coastant k_max was expressed as an exponential function of air temperature, k_max=a [e^{b (T-10)}-1.0](1/hr). This model is a nonlinear function, because experimental results were analyzed using a nonlinear parameter estimation program that employs the method of Gauss-Newton least-squares. As the results a=0.00623 and b=0.0326 were obtained. An empirical model of nitrogen uptake rate of water hyacinth was simulated by the Michaelis-Menten equation with V_max, the maximum specific rate of nitrogen uptake. The total nitrogen uptake rate was caliculated by a mass balance equation with nitrogen in each culture. Half-saturation constants were estimated to be 0.650 mg-N/1 in the case of NH₄Cl as nitrogen resource and 0.893 mg-N/l for NaN0₃. On the other hand, the yield coefficent of water hyacinth was 0.0279mg-DW/mg-N when NH₄Cl, was used as the nitrogen resource.

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Rates of photosynthesis and respiration of biotic communities were measured in large-scale artificial streams and Kanda River. In the artificial streams, two types of bed were prepared - stony one and flat stainless steel one. Water was recirculated in the streams, each of which was polluted with different amount of powdered milk. The metabolic activities of the biotic community in each stream was estimated on both BOD and O₂ balance bases. The results were as follows.
(1) The stream with stony bed, on which a large amount of periphyton was growing, showed lower net productivity or higher purification rate than with flat bed.
(2) The average net productivity, that had minus values in all cases, was proportional to the organic pollutant concentration. The behavior of organic pollutant in the flowing water - stream bed system could be approximately evaluated from the values of net community productivity obtained by TOD and 0₂ balance methods.
The characteristics of biotic product and respiration were surveyed in Kanda River, where algal communities were densly attendant on the concrete bed. O₂ balance method was applied and following results were obtained.
(3) The activities of epibenthic communities was far more dominant than those of flowing suspended ones.
(4) Primary productivity was saturated when light intensity reached 5klux-10klux. The increment in light intensity over the limit therefore did not contribute to the primary production.
(5) Daily average values of the community respiration rate exceed those of primary productivity even in Kanda River, which is assumed to be one of the most eutrophicated rivers in Japan.

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For the purpose of leveling up safty in water supply, the quantification of virus concentration in water resource is required, and one of the most important basic data required for the quantification or the quantitative prediction is the decay constant of viruse in natural water. Therefore, the natural decay or inactivation of Coxsackie-B virus is observed and measured in a cirulative channel (diameter 40cm, width 10cm, depth 20cm) in a laboratory. The experimental conditions are controlled in temperature and sunlight. The former is by a regulative heater and the latter is by a window shutter. The results are summarized in the following forms as κ_θ=κ₂₀ (1.175) ^(θ-20), κ₂₀=1.41 (in sunlight condition) and κ'_θ=κ'₂₀ (1.143) ^(θ-20), k'₂₀ =0.87 (in dark condition), where k_θ is the decay constant (1/day) in the first order reaction under the temperature θ(°C). The mechanism of the inactivation is also briefly discussed in this paper.

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The effect of some factors, which are important to design an aerobic sanitary landfill, on aerobic decomposition of artificially made refuse-typical in this nationin laboratory scale, continuously air-forced static piled layer was experimentally discussed. In order to estimate the effect, temperature inside the layer and gas concentration of exhaust, etc. were measured for about one month, followed by calculating the total quantity of carbon-dioxide and water evolution, oxygen consumption, the decrease of dry refuse, etc. Consequently, the variations of temperature and concentration with time have 2 or 3 peaks within about 2 weeks and chief decomposed component seems to be hydrocarbon. The decreased weight of dry refuse attains to 30-40% of initial refuse and to 2-4 times more than volatile matter of garbage and the decreased weight of summer-type refuse is defferent from that of winter-type refuse. Anaerobic duration till start of aerating less than 2 days has little effect on decomposition. Too high and too low piled density of the layer give morse decomposition. Even refuse with such low garbage content as 12% can give steady decomposition. Plastic in refuse, especially film results in worse decomposition. For the purpose of energy saving and speedy decomposition, 1 mol oxygen/d/kg of dry initial refuse, or 110 1 air/d/kg is appropriate. Moisture content of refuse less than 70% is desired for steady decomposition. These conclusions are also useful to understand the phenomena in composting process or semiaerobic sanitary landfill.

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To ascertain the phenomenon by which leachate is collected by a leachate collection pipe, and how much part of leachate flows into the ground and how much is collected by the colletion pipe, (1) we experimented the leachate collection in the experimental sanitary landfill model, and (2) we analyzed seepage flow near the interface between base ground and waste. We got the results: Some part of leachate flows into the ground and the other part of it is collected by the collection pipe.(2) The amount of the leachte that flows into the ground depends only on the seepage characteristics of ground soil and rain fall intensity ie, the excess of the rain fall over seepage capacity of ground soil is collected by the collection pipe.(3) The amouns of leachate that is collected and flows into the ground are affected by the atmospheric pressure.

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Experiments were conducted with an anaerobic fluidized bed to clarify the roles of sulfate-reducing bacteria in organic substance decomposition and acetic acid formation. The fluidized bed was operated in the conditions of the hydraulic retention time 11 ± 1.0 min., the bed expansion ratio 1.10 ± 0.04, the microorganism density 11.8-22.6 gVSS/1, temperature 22.0 ± 1.2°C and pH 7.05±0.45.
Sulfate-reducing bacteria utilized lactate, formate, propionate and ethanol as electron donor. The stoichiometric reactions involved are respectively formulated as follows. 2 CH₃CHOHCOO^- + SO^2-₄ + H₂O → 2 CH₃COO^-+ H₂S + 1/2 H₂O + 3/2 H₂CO₃ + 3/2 OH^- + 1/2 HCO₃^-, 4HCOO^- + 4 H₂O + SO₄^2- + 1/2 H₂CO₃ → H₂S + 5/2 H₂O + 3/2 OH^- + 9/2 HCO₃^-, 4/3 CH₃CH₂COO^- + 8/3 H₂O + 1/2 H₂CO₃ + S0₄^2- → 4/3 CH₃COO^- + 4/3 CO₂ + H₂S + 5/2 H₂O + 1/2 HCO₃^- + 3/2 OH^-, 2 CH₃CH₂OH + SO₄^2- → 2 CH₃COO^- + H₂S + 2 H₂O.
The bacteria, however, did not utilize acetic acid, n- and iso-butyrates, and n- and iso-valerates. Glucose and skim milk were indirectly utilized by the bacteria after conversion of those substrates into various intermediates by coexisting other anaerobic bacteria in the bed. Sulfate-reducing reaction was considered to be unfavourable for the anaerobic process. Since propionate was found to be easily converted to acetic acid by sulfur-reducing bacteria, the positive utilization of sulfur-reducing bacteria may improve the acid formation process in terms of avoiding the build up of propionate which is found to be difficult for methane bacteria to use.

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The effect of oleate on methane production from acetate in anaerobic digestion was examined both in a batch experiment and in continuous culture experiments. These experiments were carried out at 35°C using with a synthetic substrate containing 20000mg/l of acetate as a sole carbon source and with the various concentrations of sodium oleate solution. The change of methane content in gas phase and the residual volatile fatty acids (VFA) indicated that the methane production from acetate was inhibited moderately by the oleate shock loading of 5mg/l and completely by that of 10 mg/1 in the batch experiment. The continuous culture experiments at SRT of 7.4 and 21.6 days suggested that the acetate utilizing methanogenic bacteria could be acclimated to the toxicity of oleate and were not inhibited until the oleate concentration reached about 60 to 70 mg/1. The inhibitory phenomena caused by oleate in methane production from acetate were recognized as a rapid decrease of gas production rate and a rapid increase of residual VFA. At that time it was also observed that the most part of oleate added to the digester was accumulated in sludge (precipitating fraction of mixed liquor after centrifugation in 3000 rpm for 15 min) which contained cells of methanogenic bacteria. The addition of Ca²⁺ ion to the digester which had been just inhibited by oleate was not effective to relieve the inhibition, although it is usually effective to prevent oleate from inhibiting if it is made before the inhibition occurs. On the other hand, oleate of less than 60 mg/1 seemed to have some stimulating effect on the microbial growth and the efficiency of VFA removal or VFA conversion into methane in methanogenesis. It was also shown that oleate could be decomposed to some extent in the digester where methanogenic bacteria were acclimated to oleate.

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The purpose of this paper is to compare the process designs of the secondary wastewater treatment plant which has a diurnal inflow variation by computer simulation. As the result of the simulations, the process design which includes the balancing tank is more advantageous than the process designs which have the surplus capacity or the simpler control systems under the inflow variation.

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The membrane fouling in reverse osmosis is a serious, probrem because it reduces solution flux (J_v) and rejection. In this work, the effects of salt addition on fouling of polymer solute were examined using cellulose acetate membrane. In the case of poly-nonelectrolyte solutions, it was found that J_v changed little and salt rejection was increased slightly due to gel-layer (fouling layer) on each case. In the case of poly-electrolyte solutions, both J_v and salt rejection decreased as the salt concentration increased.
The relationship between the permeability through the gel-layer of poly-electrolyte, CMC, (A_G) and the salt concentration (C_eq) was recognized as follows: In (A_G /A_G) = -aν⁺ In (C_eq) +b (ν⁺ is valence of cation)
It was obtained that there were linear correlations between ln (1- f_obs) and logarithmic concentration (lnC). The addition of multi-valence cation increased the permeation of Na⁺ included in CMC.
These results seemed to be brought about by the deswelling of polymer gel-layer (fouling layer), which cased by the salt addition.

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The purpose of this report is to reveal the denitrification in a aeration tank, which tries to clarify the relation between the mixing and the reaction kinetics. The authors produced the back flow model apparatus and examined the relation of the mixing to the nitorogen removal. Then, we tried a method of velocity analysis from batch tests. Results of these experiments, it became clear as follows.(1) In the plug flow model tank, the more the mixing increase, the more the removal of total nitorogen increase till some mixing point (φmax=0.15).(2) In the complete mixing tank, it was estimated that the reaction of nitrification and denitrification were acted continuously in the low DO level.

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The ultimate biodegration of linear alkylbenzene sulfonate (LAS) in the act ivated sludge process has been studied using the ¹⁴C ring-labeled LAS. By using the methylene blue method and the tracer method, primary degradation and benzene ring degradation were evaluated respectively. In batch experiments, 30-40% of ring carbon was converted to carbon dioxide after 24 hrs' aeration in the acclimated system, but only 2-10% in the unacclimated system. ¹⁴CO₂ evolution and primary degradation proceeded simultaneously, but the rate of ¹⁴CO₂ evolution was slow. In 24 hrs, primary degradation proceeded completely, 46-52% of ring carbon remained in the sludge and 14-18% in the solution in the acclimated system. ¹⁴CO₂ evolution rate was affected by addition of glucose and initial concentration of LAS. This study shows the biodegradation mechanism of LAS in the activated sludge process.

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