The bromate formation model by the reaction of ozone with bromide was fundamentally studied by comparing the experimental results with the numerical simulation results that included bromate formation mechanism proposed by Hoigné or Gunten et al. using the extended SBH model. Upon the addition of phosphate buffer to pure water, the behavior of bromate simulated by this model showed good agreement with the experimental results. But in the case of pure water, the bromate concentration simulated by this model was less than that of the experimental results. On the other hand, it was also founded that, from the results of model simulation and experiment, each showed the different changes in pH.

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The purpose of this study is to remove phosphorous in wastewater by using layer structure inorganic ion exchanger with high selectivity for phosphate anion(TPEX).
The results obtained are as follows.
1)TPEX showed large phosphate removal of 1.43-2.23mmol·g^-1 in phosphorous concentrations of 1-800mgP·l^-1. Maximum removal amount of phosphate ions was obtained around pH value of 7.0.
2)The ion selectivity of various anions in wastewater were in the order of CO₃>PO₄>>SO₄>>C1>>NO₂>NO₃.
3)Residual concentrations of the phosphate ion from rural sewages treated with TPEX were less than 1mg·l^-1.
Talking the results obtained into account, TPEX has been expected as a promising inorganic phosphorous adsorbent.

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In order to improve efficiencies of phoshorus removal at low water temperature, media-added batch activated sludge process combined with droplet method of thick iron solution as a chemical dosing was investigated in a process treating a sewage wastewater.
An thick iron solution is able to be made by heating the crystal of the iron (III) chlorid hexahydrate within one hour at 50-60°C. However, it was shown that the dilution of thick iron solution was necessary to prevent solidification of the solution due to lowering of temperature. The optimal dilution ratio (the ratio of water volume to the volume of thick iron solution) was 0.4 v/v and it was observed the diluted solution did not solidify at 2°C.
Removal efficiency of phosphorus by using the dosage of diluted thick iron solution was remarkably enhanced up to 79-82% at 10°C and it was not observed the inhibitive effect of the dosage on the nitrification and the BOD removal. These results indicate that biological process combined with the droplet method of thick iron solution improve treatment efficiency of phosphorus significantly at low water temperature.
This method could decrease the frequency of maintenance because smaller quantity of dosage is required comparing with the conventional chemical method.

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In this research, the effects of co-existing substances on the decomposition of micropollutants (i.e., 1,2,4-trichlorobenzene (TCB), 1,4-dioxane, and 17β-estradiol) during ozone/hydrogen peroxide (O₃/H₂O₂) process were investigated.
The reaction time for the decomposition of TCB during ozonation increased with the increase of bicarbonate ion, hydroxyl radical (HO·) scavenger, by several ten minutes of magnitude. In the case of O₃/H₂O₂ process, however, the effect of bicarbonate ion on the reaction time of TCB decomposition was a little, therefore, it was less than forty seconds. The effect of H₂O₂ dose on the removal efficiency of TCB for applied ozone dose was greatly observed in the presence of bicarbonate ion. On the other hand, the effect of it was not observed in the presence of humic acid. The effects of humic acid on the ratio of the applied ozone dose per the amount of target compound decomposed (ΔO₃·ΔTarget^-1) were dependent upon the reactivities of target compounds with ozone, that is, highly reactive target for ozone was less affected by humic acid. Also, it was found that the effects of highly reactive compounds for HO· (i.e., humic acid, fulvic acid, and glucose) on the decomposition of TCB were higher than those of less reactive compounds for HO· (i.e., acetate and oxalate ions) when total organic carbon of co-existing substances were identical value.

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If a closed recirculating aquaculture system that need not discharge the effluents is developed, a large amount of the pollutant load on water bodies can be reduced. In this study, rearing experiment of eel were reared in a closed recirculating system. The system consisted of a fish tank, a foam separation unit, nitrification and denitrification units, pH and temperature control units, and a circulation pump. The foam separation unit has an air inhalation-type aerator and supplies numerous bubbles into the rearing water. Fish were fed a commercial diet for 3 months.
The survival rate of eel was 100% during the experiment under the congested condition. The foam separation unit kept oxygen saturation in the rearing water at about 90%. Furthermore, colloidal matters were absorbed on stable foam formed from eel mucus and were removed from the rearing water by foam separation. Ammonia oxidation and the removal of suspend matters were accomplished rapidly at the same time with the nitrification unit, and ammonia concentration and turbidity were kept at less than 0.21mg-N·l^-1 and 0.981 TU, respectively. When the denitrification process was operated, nitrate accumulated in the rearing water was reduced to a concentration less than 7mg-N·l^-1. Based on these results, an intensive aquaculture of freshwater fish such as eel can be achieved by a closed recirculating system.

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Batch Experiments were made in pure cultures of Alcaligenes faecalis under aerobic conditions. NH₄-N, NO₃-N and their mixture (NH₄-N/NO₃-N) were used as the nitrogen sources to test the heterotrophic nitrification and aerobic denitrification functions of A. faecalis. Two carbon (TOC) to total nitrogen ratios (C:N), 5.22:1 and 1:1 were kept and nitrite shock was made to test their influence on the nitrification and denitrification functions of A. faecalis and on N₂O emission. Experimental results showed that: A. faecalis could conduct both nitrification and denitrification. However, the nitrifying and denitrifying rates were strongly influenced by the conditions like the nitrogen sources and the C:N ratio. In the case with NH₄-N as the nitrogen source and the C:N ratio of 5.22:1, the nitrifying rate could be 4.49mgNH₄-N·hr¹, while in the case with NH₄-N/NO₃-N as the nitrogen source and the C:N ratio of 5.22:1, it could be 2.78mgNH₄-N·hr¹. On the other hand, In the case with NO₃-N as the nitrogen source and the C:N ratio of 5.22:1, the denitrifying rate was 0.67mg NO₃-N·hr¹. N₂O emission generation was strongly influenced by the growth status and activity of A. faecalis. The stationary status and low activity led to higher N₂O emission. Among the three nitrogen sources, mixture of NH₄-N and NO₃-N led to most N₂O emission, and NH₄-N led to the least N₂O generation. Therefore, to completely conduct nitrification and avoid the mixing of NH₄-N and NO₃-N will of use to control N₂O emission. A. faecalis could use NO₂-N in its nitrification process. However, the accumulation of NO₂-N led to serious N₂O generation, especially in the case with higher C:N ratio. To avoid NO₂-N accumulation is therefore of importance for reducing N₂O production.

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A laboratory study of photocatalysis was conducted for purification of water contaminants employing a batch scale reactor with thin film TiO₂ catalyst. The reactor was equipped with external light source, germicidal or blacklight lamp. Wavelength bands of irradiation and the direction of incident beam were changed to investigate the effect on degradation of benzene selected as a model compound. The reaction rate constants were evaluated for photocatalytic and photochemical reaction respectively. The shorter wavelength (254nm) was more effective by a factor of 4.4 than 300-400nm when the light was on the side of catalyst surface, while longer wavelength had advantage to penetrate through the catalyst layer or opaque media. The reactivity of photocatalysis was supposed to be closely related to the excitation of molecules by direct photolysis. The production of intermediates was also influenced by wavelength bands. These intermediates degraded in 60 minutes over photocatalyst.

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Physico-chemical properties of dissolved organic matters in river water and ultraviolet irradiated water with or without photocatalyst are examined. Molecular size, hydrophilicity, and adsorbability to solid phase extraction cartridge are identified by 260nm absorbance detection of HPLC, high performance liquid chromatography. Organic constituents were separated into two peaks by HPLC ; one consists of low molecular size substances (below 1000) which had very low adsorbability to solid phase extraction cartridge ; the other consisted of higher adsorbability and higher molecular size, whose 260nm absorbance was degraded by ultraviolet irradiation with TiO₂ photocatalyst. Irradiation of 254nm ultraviolet light (UVC) induced mutagenicity in Salmonella typhymurium TA100 without S9 metabolization. 80 μg·l^-1 of formaldehyde was detected over two-hour UVC irradiation.

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Ozonation is widely used in tap water treatment for removal of musty odor. Active species of ozonation are supposed to be molecular ozone and hydroxyl radical. Dissolved materials in water can affect ozonation, but the relation among ozone, hydroxyl radical and dissolved materials have not been quantitatively analyzed. Batch system would be generally applied to investigate ozone reaction. So, in this study, hydroxyl radical formation during ozonation was investigated using spin trap ESR technique in batch system. The results were compared with that obtained using stopped-flow system.
In case of methylphenols, amounts of DMPO-OH increased in comparison with that without the phenol and reached a constant value. The enhancement effect was similar to the case in which the stopped flow equipment was used. In case of chlorophenols, amount of DMPO-OH was also enhanced but it decreased in a time dependent manner. Decreases in DMPO-OH were dependent on ozone-concentration. In case of 20μM ozone, DMPO-OH generation in batch and stopped flow system were almost the same, when the enhancing effect was calculated using the Y intercept obtained by extrapolating from elimination curves. However, in higher ozone concentration, enhancing effects of phenols in DMPO-OH formation were underestimated compared with that in stopped-flow system. In conclusion, batch system, in addition with stopped-flow system, would be also useful for analyzing enhancing effects of dissolved compounds on ozone reaction when they have moderate enhancing effects.

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The efficiencies of chemical oxidation of organic matter in genuine secondary treated municipal wastewater by using O₃, O₃/UV, O₃/TiO₂, UV/TiO₂, and O₃/UV/TiO₂ methods were compared experimentally. Effects of carbonates on these efficiencies were also investigated. Elimination of carbonates from the water increased TOC reduction efficiency for all the methods. The effect of the carbonates was less significant for the O₃ method than for the other methods. The O₃/UV method was the most effective for reducing TOC under both carbonate-present and decarbonated conditions. The least effective method was the O₃/TiO₂ under the carbonate-present condition, and the UV/TiO₂ method under the decarbonated condition. The catalytic ozone process (O₃/TiO₂) showed a tendency to increase the ozonation at the beginning of the reaction under the decarbonated condition, but the addition of the TiO₂ catalyst inhibited the ozonation under the carbonate-present condition. The photocatalytic oxidation process (UV/TiO₂) did not reduce TOC compared with the other methods, but it could reduce TOC over a long time ; namely after six hours of treatment, TOC reduction efficiency reached 60% under the decarbonated condition and 30% under the carbonate-present condition. And the O₃/UV/TiO₂ method did not show a synergistic effect of ozonation and photocatalytic oxidation.

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In the past few decades, eutrophication in closed water areas has been becoming a serious problem on the use of water for drinking, agriculture, recreation, and other purposes. Especially, excessive phytoplankton growth seriously degrades the environment and aquatic ecosystems; algal blooms, lose of oxygen, fish kills, loss of biodiversity, and other problems. This paper intends to investigate control and prevention of the excessive phytoplankton growth by reducing light levels below those necessary for photosynthesis. To shield sunlight, photochromic (PC) films, which show photochromism such as colorless forms turn to colored forms by ultraviolet irradiation, were prepared. The PC films containing Spironaphthoxazine as a photochromic compound showed excellent photocoloration (75 to 80% absorbance at 600nm) under sunlight irradiation, and they maintained the photocoloration ability, at least longer than a month. However the results of algal growth potential tests with the PC films were the oppsite to what we had expected. While the growth of mixed algal cultures was controlled with the PC films under sunlight irradiation, the application of the PC films was not successful for the prevention of pure cultures M. aeruginosa growth. It was probably attributable to the difference between the wavelength for the PC films' maximum absorbance (approximately 600nm) and the available wavelength for photosynthesis (approximately 680nm). The absorbance at 680nm by PC films was approximately 20%.

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At present, the pollution by organics is a problem for a closed environmental water, in ponds and marshes. As such water as above, contains non- or less-biodegradable organics, represented by humics, in large amounts, their removal by biological treatments can be expected only a little, and many trials to decompose or reform the organics by an oxidation treatment such as ozonation, are being done.
In this study, an electrolytic oxidation treatment which had been conventional methods for organic syntheses and for other purposes was tried. The removal effect of humics was examined with an experimental apparatus of laboratory scale.
As for the electrolytic oxidation treatment, a certain effect for the removal of humics in term of TOC has been shown. And a decrease of a chromaticity has been shown, too. It was also found that there was a strong correlation between the removal ratio of TOC and the quantity of electricity.

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