One of the major concerns of lake management in nutrient rich areas is the potential for algal blooms. Large algal population can clog filters in water supply systems and cause heavy damage to various uses of water resources. Simulation models can be used to predict the potential for algal blooms and thus can be used to help estimate the effective use of alternative management strategies.
This paper discusses a stochastic model for simulating short-term variation of spatial pattern of harmful blue-green algae in a lake. This model is theoretically derived on the basis of the Markov process and simplified for practical application. The basic idea of this model is as follows;(1) Algal growth mechanism in two-dimensional water body is separated into two functional elements-growth and transportation of algae, which are formulated as growth probability and tranport probability respectively.(2) Growth probability is estimated by the analysis of the data observed in the actual occurrence of algal bloom and transport probability by the lake flow simulation model considering wind effect. Each probability is described as the matrix notation for calculation. This model is applied to the southern part of Lake Biwa, and the ability of the model is examined. As a result, it is found that this model is a helpful tool to predict algal bloom and from the standpoint of simulation the initial condition setting is dominant factor for prediction of short-term spatial variation of algal bloom in lake.

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A multi-component dynamic model for phosphorus in the bottom sediment-water system of Lake Kasumigaura, a highly eutrophic and shallow lake, was developed to obtain quantitative information on the sediment-water interactions. The model was calibrated and the sensitivity analysis of the model parameters conducted to identify the deficiency of our knowledge at present and to determine future research needs. Good agreement between the model calculations and observed data of phosphorus release flux and phosphorus concentrations in the sediment was noted. The phosphorus dynamics of the upper layer (0-1cm) of the sediment seem to regulate the phosphorus transportation between sediment and water. Further studies on the particulate phosphorus sedimentation flux from the overlying water to the sediments and the adsorption-desorption of phosphorus between liquid and solid phases in the sediment were found to be necessary from the sensitivity analysis.

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To understand the dynamic changes in water qualities near the mouth of influent rivers, some metals and nutrients compositions of. particulate matter and sediment were measured in Takahamairi Bay in Lake Kasumigaura. Near the mouth those compositions changed seriously and inside of the lake most of those compositions varied longitudinally in proportion to the log of the volume before reaching each point. In the influent rivers, high correlation coefficients among Ti, POC, PON, PP concentrations of particulate matter were found. Inside of the lake, similar relations were observed except for PP. Two components model and three components model on the basis of Ti content and chlorophylla content were successfully applied to the explanation on those compositions. The variations of some compositions could be also accounted for by the meteorological, hydraulic, chemical conditions of the lake. In the case of POC, PON, Ti, Mn, chlorophylla etc., the compositions of sediment which have little change were closely associated with and could be a useful tool for the estimation of those averages of particulate matter in the water just above the sediment.

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We discussed basic characteristics of seasonal variation of sediment compositions in the previous report. In this paper we deal with the rapidity and extent of the variation of sediment composition.
The main results are as follows. When the surface sediment size became finer, the fresh water inflow to the estuary was about 100m³/s (5.6m³/s/100km²) and the change was completed in about 10 days. On the other hand, the change becoming coarser was completed in a day. In this case the fresh water inflow was over 400m³/s (22m³/s/100km²). Judging from the change of longitudinal distributions of sediment size, finer particles always exist from the river mouth to the bay, and the extent to which finer particles are dominant expands upstream from spring to summer. When finer particles in the surface sediment were dominant, the thickness of the sediment layer where the finer particles were dominant was several centimeters in the middle reaches of the estuary. The time lag between the variation of the concentrations of the sediment constituents and the sediment size was not found due to the observation at intervals of 2 days.

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The forms of heavy metal compounds in urban river muds were fractionated by various solvent extraction methods. And by these examined date and its principle component analysis the pollution characteristics and the sources of heavy metals were analyzed. The results are as follows:
(1) It is possible to determine the artificial origin heavy metals (Secondary deposits) by 0.5N HCl extraction method, and origin bounding ones by 6%H₂O₂ extraction method and absorptive state, oxides and carbonates by 10%HOAc extraction method.
(2) The concentration of urban river heavy metals is high in Zn, Cu, Pb of 0.5N HCl soluble metals (Secondary deposits), especially in Zn.
(3) The heavy metals in the urban river muds are composed of ones in natural soil particles (Primary deposits) with much Fe and Mn, and ones in artificial deposits (Secondary deposits). When urban drainage flows into river, heavy metals (Cu, Mn, Zn, etc.) contained in 6 %H₂O₂ soluble matters become rich and the proportion of 10, %HOAc soluble metals becomes high.
(4)The artificial origin heavy metals are much contained in silt and clay. But there is not a great difference between the patterns of the ratio of each concentration to the total concentration in each analyzed grain size. So the influences of pollution come to entire muds.

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The final purpose of this study is to evaluate and control the inflowing amount of nutrients into closed water area. For the first step to this purpose, the process of nutrient transfer and change in a river was studied. There have been many studies that dealt with the detailed profile of the process, but few which considered the whole system in good balance. In this paper, the total system of a river was studied using computer simulation method based on continuous data for a long period which contain nutrients concentration at up and downstream observation points in one river, sediment amount within these two points, and flow rate. As the results, it became clear that the effects of sedimentation and wash out of suspended matters, adsorption of soluble phosphorus, removal of soluble nitrogen and dissolution of COD might play an important part in the process of nutrient transfer and change in a river. Those effects have been considered little before.

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Etoh and Kurita have presented expressions of efficiency of storagetreatment systems to reduce non-point pollutant runoff for some special conditions; extremely large or small capacity of a storage or treatment facility, and the volume of water which is treated during average interstorm duration, is equal to average runoff volume of single storms. By combining these results, an approximate expression of the efficiency for a general condition is introduced, which may be simple and accurate enough for practical applications. Values of efficiency of existing systems are calculated both by the expression and by simulations. They agree well with each other, which may prove practical validity of the present expression.

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removal of floating matter by a algae trap is caused by transport of the matter into the trap by overtopping wave. To simulate this process, a surface tension was introduced into the Simplified Marker and Cell method. The simulation shows that the removal is strongly accelerated by surface tension. This acceleration is also shown by experiments.

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Basin Wide Ecological Models (BAWEM) with simply compartmentalized environment are developed for forecasting and evaluating fate of chemicals. These models show sufficient applicability to the test chemicals classified into five categories according to the emission process to the environment. The first version of the BAWEM described in the steady-or unsteady-equilibrium state is used for the priority setting of chemicals. To compare the magnitude of chemical risk potential with that of other chemicals, the concentrations of chemicals in biota derived from acceptable daily intake (C_bADI) and maximum acceptable toxicant concentration (MATC, calculated from O.1×LC50) are selected for the chemical risk standardizing indices. The following results are obtained by the model simulations:
(1) The simulated concentration level of test chemicals in water, sediment and biota showed almost the same order of magnitude of the observed concentration level of them.
(2) Chlordane was recently designated as a specific indicator of the risky chemicals. Some of the other test chemicals were found to have high risk potential than that of chlordane.

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The presence of organohalogenated compounds in drinking water supplied by public water supply is the matter of the management of environmental carcinogen. This paper dealed with the behaviour of trihalomethanes (THM), chloralhydorate (CH), trichloroacetic acid (TCA), dichloroacetic acid (DCA) which are considered the final products of the reaction between organic substances and chlorine in water purification process.
Both of THM and TDOX (sum of CH, TCA and DCA) present about 15% of Total Organic Halides (TOX) in tap water. The formation of CH, TCA and DCA as well as that of THM are affected by the reaction conditions such as chlorine concentration, pH, reaction time and temperature. CH was confirmed to the chlorinated intermediate in the course of organochlorinate formation reaction, and CH produced TCA in neutral pH range or chloroform in high pH range by the hydrolysis of itself. TCA produced DCA by dechlorination of itself. But there were observed the presence of other intermediates of DCA than TCA in the experiment.

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Experimental studies have been undertaken on the chemical change of Hg vapour (H°g) by corona discharge to investigate the possibility of Hg removal technique, The species of gasses used were compound gas (C gas) and exhaust gas of a municipal refuse incinerator (E gas). C gas or (E+C) gas including about 0.5 mg-Hg/m³ was led to small-scale cylinder (inside diameter: 56.5mm, discharge electrode diameter: 0.26mm, length: 250mm), and there corona discharge (positive or negative corona) was generated, The gas exhausted from the cell was led to gas wash bottle (distilled water), and then H°g concentration was measured continuously.
H°g removal efficiency increased as corona power was increased, and decreased as gas temperature was increased, The H°g removal mechanism is suggested as follows; In case of the gas including O₂ and no HCe, H°g reacts with O₃ or O generated by corona discharge to O form HgO. In case of the gas including even low concentration of HCe, H°g reacts with HCe to form HgCe2 markedly.
Intermittent discharge resulted in effective H°g removal, H°g changed to watersoluble form after passing EP of a municipal refuse incinerator.

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Settling and thickening properties of biological sludge, produced in the sewage treatment plants, have been deteriorated. It would be caused mainly by the reduction of solid content in the biological sludge. This paper presented the experimental results on the improvement of the settling and thickening properties of biological sludge by mixing it with chemical sludge, produced in the water treatment plants. Dewatering property was also very much improved by the mixing of biological and chemical sludge. Chemical sludge coagulated in a lower ALT ratio improved more the physical properties of biological sludge. It was demonstrate that chemical sludge adsorbed the orthophosphate by the surface coordination reaction. Surface coodination reaction was examined by the acid-base titration.

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Utilization of incinerated ash and smelted slag from sewage sludge as construction materials were put into field experiments. Results are as follows;
a. Incinerated ash of dewatered sludge conditioned by lime can he utilized as an embankment material, a fill material, a subbase course material, and as a soil improvement material for the-hardening of soft ground. b. Air-cooled smelted slag can be applied to the base course material and the concrete material. c. The properties of smelted slag can be greatly improved by crystallization. d. It is also confirmed that plate slag, cubic slag and lemon-shaped slag can be made.

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Extraction of inorganics especially Na, K, Cd and Pb from waste incinerator fly ash was studied by using column soaking and batchwise shaking tests.
Pb and Cd were re-sorbed onto fly ash matrices after they had been extracted into a solvent. The extraction rates to contents by shaking were at maximum 92% and 3.7% on Cd and Pb respectively. No significant difference was observed on K and Na extraction between batchwise shaking and column soaking, while other cations were extracted more by shaking than column soaking.
Discussing extraction kinetics by the results of column soaking, it was revealed that the extraction rates of K and Na were proportional to K and Na remaining in fly ash matrices. A model which assumes that these soluble contents are localized on the surface of fly ash matrices forming small particles is proposed.

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Optimum allocation method was proposed and simulation studies were executed for allocating monitoring wells around an assumued municipal solid waste burial site by use of a computer. The problem to allocate monitoring wells was formulated as a multi-attribute design problem and was tried to solve based on utility assessment techniques, under the conditions where environmental parameters such as permeability, porosity, diffusivity, distribution coefficient and so on were given as stochastic variables in each given range, and where attribute utility functions were given as fuzzy information.
Two dimensional convective dispersion equation was solved numerically under stochastic environmental parameters to get travel time distribution of a hazardous material, which should be used for determining fuzzy expectation of each attribute under appropriate conditions. Some examples of optimum well allocations were shown and the characteristics of the optimum alternatives and the proposed allocation method were examined.

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Solute transport in sand columns under steady unsaturated moisture flow was studied experimentally and theoretically using Cl-ion and Cr (VI) as tracer materials. These materials were trans ported through sand column, showing non-sigmoidal breakthrough curves.
The mathematical procedures, proposed in this paper, for evaluatin g sorptive solute transport in unsaturated sand column are to be devided into two steps. The first step is identification of soil moisture flow model. Multi-component flow model for evaluating the breakthrough curves for non-sorptive solute (Cl-ion) is examined. The second step is identification of sorption-desorption model. Sorption-desorption model for evaluating the breakthrough curves for sorptive solute (Cr (VI)) is identified, under multi-component moisture flow model determined in the first step.
These procedures were applied on those experimental results persued in this study using unsaturated sand column system. Some valuable results were obtained.
(1) Soil moisture flow in sand columns was simulated well by the two-component moisture flow model.
(2) Observed breakthrough curves for Cr (VI) were simulated well by the mathematical model, where sorptive Cr (VI) takes two stable physico-chemical forms in the aqueous solution used in this study.

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The denitrification processes in the soil columns of 10-20cm in diameter and 40-45 cm in depth are investigated under the continuous unsaturated-flow conditions. More than 90% of NO₃^--N applied as KNO3 solution (20mgN/l) was removed when the partial pressure of O₂ in the soil is 2-4% and the C/N ratio adjusted by CH₃OH is 2.0.
The evolution of the denitrification rate profile calculated by the reactive convectio-dispersive equation using experimentally obtained concentration profiles of NO₃^--N showed that the denitrification takes place within 20cm in depth.
A tracer experiment using ¹⁵N has revealed that ¹⁵N0₃^- is quantitatively converted to ³⁰N₂.

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The effect of temperature on acetate removal rates within a methanogen attached biofilm reactor was studied theoretically and experimentally. A mathematical biofilm model was developed considering the dependencies of substrate diffusion and decomposition rates on temperature, furthermore the relations between removal rates and the non-dimensional parameters which specified treatment characteristics were also examined. Isothermal experiments on mesophilic acetate treatments were carried out, and the non-dimensional parameters, i. e. biofilm property (Ms) and operation parameter (Pes), were obtained. Then, non-isothermal experiments were executed, and the variations of the acetate removal rates with temperature were examined and analized by using the present model.
The following results were obtained.
(1) Treatment characteristics of acetate were evaluated accurately in a range of 15-37°C by using the normalized biofilm property (Ms), operation parameter (Pes) and the activation energy (ΔE) of substrate decomposition rate.
(2) The effect of temperature on acetate removal rates differed with organic loading rates, but the activation energy (ΔE) was regarded as a constant value of 12.1 kcal/mol.
(3) Acetate was converted to methane at a yield of 0.91 mol-CH₄/mol-Ace except when the temperature was less than approximately 10°C.

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Two continuous flow experiments were conducted using a multi-staged up flow sludge blanket reactor applied to a methane fermentation process for the treatment of a medium strength industrial wastewater. The first experiment was made to investigate the temperature dependence of the UASB process performance in the range of 25°C to 15°C with a mixture of starch and sucrose as a substrate at four fixed loading rates, 3.0, 4.5, 6.0 and 9.0 KgCOD/m³· day. At the higher loading rate and/or the lower temperature, i. e., at temperatures lower than 19°C for a loading rate of 6.0 KgCOD/m³·day and at lower than 21°C for 9.0KgCOD/m³·day the process performance of methanogenesis remarkably deteriorates due to the accumulation of undegraded starch grains into the granular sludge. This phenomenon results in the failure of methane fermentation process because the liquefication of solid substrate may be a limiting step of the overall process.
The second experiment was performed to examine the sludge granulation process during a start-up period of UASB system using two types of reactor configuration fed on a mixture of volatile fatty acids. The filamentous growth of Methanothrix genus is a deterministic factor of the sludge granulation, causing high biomass retainment in the reactor as well as enrichment of high activity methanogenic bacteria. Furthermore, crystallization of Calcium-Phosphate (CaHPO₄· 2H₂0) is valid for an artificial enhancement of sludge granulation, leading a shortening of start-up period of UASB reactor.

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An activated sludge process using membrane units for solidliuqid separation was investigated. This system achieved more than 95% of COD removal under the large variation of experimental conditions, such as organic loading, composition of influent organic materials and the pore size of used membranes. Large molecular organic matters were accumulated in the supernatant of mixed liquor in the aeration tank: the molecular weight of the accumulated substances was estimated more than 100, 000 by gelchromatogram. The compositions of effluent from different pore size membranes were almost the same. The filtration rate through membranes increased as the pore size increased in the range of molecular weight cutoff between 10, 000 and 300, 000 of ultrafiltration membranes. However, the filtration rate did not change with changes in the pore size over that range and dropped sharply beyond the limit va lue of the pore size which was estimated between 1μm and 10μm because of the clogging inside the membranes.

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The characteristics of activated sludge and the process performance were investigated as the function of sludge retention time (SRT, expressed as ts), using the continuous treatment process with synthetic wastewater. Then, numbers of dominant bacteria were isolated and identified at SRTs of 2-day, 5-day, 10-day and 15-day, and the constitutional ratio of isolates was discussed. Consequently, the following results were obtained;
(1) Pseudomonas sp. or Alcaligenes sp., Flavobacterium sp., Coryne-form bacteria including Arthrobacter sp. were isolated as dominant bacteria of activated sludge. A few Micrococcus sp. and Bacillus sp. were also isolated. However, some few isolated ones, including both gram-negative and gram-positive bacteria could not be identified.
(2) Bacterial population was changed with the SRT. Most of bacteria were classified as Pseudomonas sp. or Alcaligenes sp. with 2-day and 5-day SRT, and the ratio of Flavobacterium sp. and Coryne-form bacteria increased with the increase of SRT.
(3) It was found that the characteristic of activated sludge and the process performance were closely related to the constitutional ratio of dominant bacteria in activated sludge.

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Pilot-scale experiments were conducted to clarify the design conditions. and operation control method of the sequencing batch activated sludge process (SBASP) for municipal wastewater treatment.
The removal performances of organic matter, nitrogen and phosphorus were evaluated based on the results of the pilot-scale survey. The aeration time required for one cycle can he predicted from the obtained relationship between modified BOD-SS loading and BOD₅ removal efficiency.
Settling characteristics of sludge blanket in the reactor and characteristics of the excess sludge production for SBASP were also investigated. It was found out that the initial settling velocity of sludge blanket can he predicted from both the MLSS concentration and the water temperature and that the settling time required for one cycle can he determined practically by predicting the initial settling velocity of sludge blanket.
Design conditions and design procedures peculiar to the SBASP system were proposed using the results obtained.

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In any sequencing batch activated sludge process, it has become one of the principal aims to remove nitrogen by utilizing effectively the organic substrate in raw-waste water. The influence of feeding and aerating conditions and also the behaviour of the related substrates during operation were studied by the laboratory experiments characterized by feeding pattern and the ratio of operating times without and with aerations [At/Ot] in one cycle. The main results are as follows:
1) Nitrogen removal efficiency was higher and more stable in the case of step-feeding than single-feeding methods.
2) It was effective for denitrification to supply raw wastewater under withoutaeration in all experimental conditions.
3) The optimum ratio of At/Ot was 0.6 in the anaerobic step-feeding methods.
4) Most of the soluble COD and soluble organic nitrogen which accumulated in the sludge during the feed were decomposed and oxidized during successive aeration. In the course of next feeding, the oxidized nitrogen was denitrified consuming the feeded soluble COD.

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An experimental program was conducted to investigate what kinds of organic substrates were anaerobically absorbed by the activated sludge grown with anaerobic sequence. A rapid substrate uptake and the concurrent phosphate release were observed when the sludge was fed with acetate, propionate, n-and iso-butyrates, and n-valerate, but no PHB accumulation took place except when the sludge absorbed acetate. The sludge also took up under anaerobic conditions various metabolic key substrates such as lactate, pyruvate, fumarate, malate, oxalacetate, but citrate and oxoglutarate were unabsorbable for the sludge. Amino acids such as glutamate, asparate, alanine, serine were also anaerobically absorbed, but the glutamate uptake accompanied no ammonium release. Methanol, ethanol, iso-propanol, n-buthanol appeared to be inert to the sludge. Phosphate release was almost proportional in quantities to the substrate uptake, but acetate analogues such as formate, iodoacetate, glycolate, glyoxylate stimulated an extensive phosphate release despite no apparent uptake of these organics was observed. The significance of the anaerobic substrate uptake and its relation with the phosphate release were discussed.

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In this study the influence of return flow phosphorus load on the performance of the anaerobic-oxic biological phosphorus removal process as well as the behavior of removed phosphorus in the sludge treatment process were investigated in order to obtain information for optimum sludge treatment for the process. A full scale wastewater treatment plant was used for the study.
The following findings were obtaine d as the results of the study.
(1) With anaerobic digestion in the sludge treatment process about 60% of phosphorus amount which was removed as excess sludge was again released in the sludge treatment process.
(2) In the case when gravity thickened sludge was directly dewatered without anaerobic digestion, phosphorus amount which corresponds to removed phosphorus amount as excess sludge could he discharged as sludge cake out of the process.
(3) It is considered that in order to obtain mean effluent T-P concentration lower than 0.5mg/l, the ratio of return flow phosphorus load to that of inflow should be less than 50% for reactor HRT 5.6hours. In additio n to that, return flow phosphorus load, especially that of the belt press filtrate should be equalized before ret urned.

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The biological reactions were modelled and were treated kinetically, concerning the process analysis for the design and maintenance for the simultaneous removals of organics and nitrogen from the sewage by means of the activated sludge process with a single reactor in which the multi-reactions proceed in parallel. The organics oxidation, nitrification and denitrification reaction-rates were derived from Monod-type functions for the substrates concerning in their reactions and the change of the water quality was expressed by combining the foregoing rate equations and mass balances.
The activated sludge investigated was cultivated in an oxidation ditch with an artificial sewage, and the kinetic parameters of the Monod-type functions were determined from the results of the batch method. The water quality of the mixed liquor calculated numerically as a function of time using the kinetic equations suggested was found to be in good agreement with the experimental results, and the kinetic model and parameters evaluated seem to be practically useful in the process analysis.

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General models for evaluating the simultaneous removal of organic substances and nitrogen compounds in a steady-state biofilm were presented, especially taking account of the production of secondary substrates in the biofilm mainly from the lysis of microorganisms and the utilization of the substrates by denitrifiers in some unoxic part of the biofilm. Preliminarily the production of the secondary substrates was studied, and these model were solved numerically, and compared with experimental results. Main conclusions are as follows.
1) Production of the secondary substrates was proved by the result that the concentration of some organic substances and nitrogen compounds increased in the bulk liquid around a biofilm or a small bag containing activated sludge while areating without substrate addition.
2) The secondary substrates could be oxidized and utilized for denitrification.
3) Concentration distribution profiles of oxygen, organic substrates, NH₄-N, NO_x-N and alkalinity obtained, from the models explained well the relationship among oxidation, nitrification and denitrification, and mass transport.
4) The models were fairly verified with the experimental results on the organic substrate removal.

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