Hg²⁺ ions in water are reduced to metalic mercury and vaporized in the Ferrite treatment, which is an oxidation reaction of ferrous and heavy metal hydroxide by aeration. But the behavior of mercury is not known in detail.
In this paper, condition of Hg²⁺ reduction, the rate of metalic mercury volatilization from water, merucury concentration of filtrate and the dissolution of mercury from magnetite suspension at pH 1-7 were studied in the oxidation of Fe (OH)₂ suspension contained HgCl₂ 5-20mg·l^-1 by aeration at 45-75°C.
The suitable condition for reducing Hg²⁺ ions to metalic mercury was initial pH≥9 and Fe²⁺/Hg²⁺ (mol/mol)≥50.
The rate of metalic mercury volatilization was controlled by the reaction temperature and the condition of aeration, and the volatilization rate equation was obtained. We found that mass transfer coefficient of mercury, K_La-Hg, was proportional to (K_La-O2)^1.5.

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Competition of blue-green algae Microcystis aeruginosa and Phormidium tenue in chemostat was simulated to determine what was the cause of species shift among them. The model consists of 8 equations including Droop's equation, growth of algae depends on internal nutrient content. Simulation of growth of M. aeruginosa and P. tenue at N:P supply ratio 5 to 40 almost agreed with experimental data. It was suggested that outcome of competition in chemostat could be predicted by the simulation model. Differences in kinetic constants such as Q_min (minimum cell quota) and ρ_max(maximal nutrient uptake rate) were assumed to be causes of change in weight ratio of each algae with increase in N:P supply ratio in chemostat, suggesting species shift among blue-green algae in lakes occurs due to differences in kinetic constants for growth and nutrient uptake. At N:P supply ratio <60 (P was fixed), total dry weight of M. aeruginosa and P. tenue in competition calculated with the model increased with increase in N:P supply ratio.

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Competitive interaction between sulfate-reducing bacteria (SRB) and methane producing bacteria (MPB) for hydrogen and for acetate in anaerobic degradation of long chain fatty acids (LFAs) was investigated using two different sludge consortia: the one (referred to as R1) grown in a sulfate-free medium and the other (R2) in a sulfate-rich medium. Both sludges were cultivated in parallel for six months in a fill-and-draw mode on palmitate (C 16, saturated LFA).
R1 sludge finally reached a very low sulfate-reducing activity (SRA, 0.019 gCOD·gVSS^-1·d^-1) and a very high methaneproducing activity (MPA, 10.1 gCOD·gVSS^-1·d^-1) for hydrogen-fed vial test: the ratio of SRA/MPA (both on the basis of COD equivalent) was only 0.0019. On the contrary, R2 sludge was characterized by a high hydrogen-fed SRA (1.15 gCOD·gVSS^-1·d^-1) and by a low hydrogen-fed MPA (0.0093 gCOD·gVSS^-1·d^-1): the SRA/MPA ratio was 123. The results of hydrogen-trophic MPN enumeration showed a similar tendency: the SRB/MPB ratios were 1/10^3.6 and 10^2.0 for R1 and R2 sludge, respectively. Therefore, degradation of palmitate into acetate was performed by a symbiosis between proton-reducing acetogenic bacteria (PRB) and MPB in R1 sludge, whereas by a syntrophic association between PRB and SRB in R2 sludge.

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Effects of substrate C/N ratio on the spatial distributions of ammonia-oxidizing bacterial population and their activities in biofilms were investigated by fluorescent in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide probes and the use of microelectrodes. The increase in substrate C/N ratio (i.e., addition of acetate) immediately intensified the interspecies competition for oxygen between ammonia-oxidizing bacteria and heterotrophic bacteria, and consequently resulted in deterioration of ammonium oxidation rate especially in the surface of the biofilm. This decrease in the ammonium oxidation rate in the surface could explain a steep spatial gradient of ammonia-oxidizing bacterial population within the biofilms cultured at high substrate C/N ratios.
Furthermore, development of the spatial distributions of ammonia-oxidizing bacteria and their activities within the biofilm was followed during biofilm development. The active ammonium oxidation zone gradually shifted from the upper layer to the inner layer of the biofilm, which corresponded with the development of the spatial distributions of ammonia-oxidizing bacteria within the biofilm. Based on in situ analyses of microbial structure and activity, we discussed on mechanisms of population dynamics of ammonia-oxidizing bacteria in biofilms.

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Lake Kojima is one of the most eutrophicated lakes in Japan. This artificial lake is located in southern area of Okayama prefecture, and was made in 1962 as a reservoir for many paddy fields. This study was conducted to make clear species composition of phytoplankton and its seasonal changes in Lake Kojima in a period from April 1993 to March 1998, and obtain the basic informations which will be supplied for the environmental protection plan for Lake Kojima.
The results obtained can be concluded as follows :
1) 36 genera phytoplankton, that is, 5 genera of Cyanophyceae, 9 genera of Bacillariophyceae, 18 genera of Chlorophyceae, 1 genus of Phytoflagellata and 3 genera of Euglenophyceae, were observed in Lake Kojima from April 1993 to March 1998 (FY1993-1997).
2) Chlorophyceae was dominant in species composition and Bacillariophyceae was dominant in cell number, and Auracoseira italica, Melosira varians and Cyctotella spp. were recognized as dominant species in Lake Kojima through a year.
3) The diversity index (H') showed a mode of spring ≥autumn>summer≥winter.
4) Cyanophyceae showed negative correlationship, Bacillariophyceae and Phytoflagellata showed positive correlationships, and Chlorophyceae and Euglenophyceae did not show clear correlationships with rise of T-N/T-P mass ratio.
5) The T-N/T-P mass ratio lowers in summer because of effect of inflow loading from paddy field, but Lake Kojima has enough condition for water bloom because the absolute values of nutrient salts are high.
6) Main Cyanophyceae which formed water bloom were Microcystis aeruginosa and Anabaeba spiroides, and the dominant species for water bloom was recognized as Oscillatoria in 1970s, Microcystis in 1980s, and Anabaena in 1990s.

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Reaction products of chlorophenols with laccase were investigated. Chlorohydroquinone and 4-chlorocatechol of reaction products in solution obtained from reaction of 2,4-dichlorophenol with laccase were identified by GC/MS and HPLC. Similarly, dichlorodihydroxybenzene and trichlorodihydroxybenzene were estimated as a reaction product of 2,4,6-trichlorophenol and 2,3,4,6-tetrachlorophenol with laccase, respectively. The color of solution was changed to light pink after enzymatic reaction of 2,4-dichlorophenol with laccase. The color of solution disappeared after it was reduced by addition of sodium hydrosulfite. It was concluded the formation of chloro-p-benzosemiquinone caused light pink color in enzymatic reaction. This result was supported with calculated UV/VIS spectrum of chloro-p-benzosemiquinone by ZINDO program.

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Application of comet assay (single cell gel electrophoresis assay) to detect DNA damaging potential in the environmental water was examined in this study. Cultured human lymphocyte cell line was served as target organism and contacted in vitro with concentrated leachate samples from a waste landfill. Dose-response relationship was confirmed with positive DNA damaging reagents (B(a)P and 4NQO). Comet assay could detect statistically positive DNA damage in 3-folds concentrated leachate with S9mix metabolic activation. DNA damaging potential in the samples seemed to be caused by ash, which consists most of disposed wastes on the landfill. Differences of detection sensitivity and characteristic between comet assay and conventional microbiological mutagenic tests were also discussed.

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