While insolubilization and solidification are mainstream mercury treatment methods in the USA and Europe as well as Japan, soil washing with chelator or acid and heating and vaporization of contaminated soil (heating temperatures of 600 to 1000°C) as late techniques are being proposed. However, these emerging techniques have a few drawbacks, such as very high treatment costs for high-temperature heating or chemical washing, and the possibility of changing the natural soil characteristics. In order to overcome these drawbacks, we have undertaken fundamental laboratory work research to develop more suitable remediation technology. The method proposed in this paper, technically a soil heating method, uses catalysts and physico-chemical oxidation and reduction reaction, which allow heating temperature to be as low as 200 to 300°C and even allows treatment of mercuric silfide, considered to be the most stable mercury form among all mercury compounds. Our preliminary experiments with 2000 mg-Hg·kg^-1 dry weight artificially contaminated soil and heating temperature 300°C showed that around 99% Mercury was removed.

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Nonylphenol (NP) is a biodegradation product of nonionic surfactant nonylphenol ethoxylates (NPEO) and has been known as an endocrine disrupting chemical. Analytical method of NP is presented in this paper. The method includes solid phase extraction for aqueous samples or Soxhlet extraction for solid samples and normal-phase column chromatography followed by GC-MS in SIM mode. For 1l water sample, the limit of quantification was 15ng·l^-1. This is one to two orders of magnitude more sensitive than the previous methods used for monitoring in Japan. The method was applied to environmental samples (i.e. river waters, sediments, sewage effluents, and biological tissues) to demonstrate distribution and behavior of NP in Tokyo metropolitan area. NP concentrations in the river water range from 0.051 to 1.08 μg·l^-1. NP concentration levels were found to be higher in the Sumidagawa River than that of the Tamagawa River. In the river water samples, 5 to 60% of NP existed in particulate phase, indicating a necessity to measure particulate NP for future monitoring. NP was found also in sediments (3.6 to 10.4μg·g^-1 dry weight) and mussels (∼0.17 μg·g^-1 dry weight). These values were approximately three orders of magnitude higher than those in river water on weight basis, suggesting NP accumulation in these solid media.

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Philodina erythrophthalma is one of the species of bdelloid rotifer belonging to micrometazoa. It is known that these species play an important role in contribution toward getting transparency from wastewater treatment system. The fixation of these species in bioreactor is effective for enhancement of floculation and solid-liquid separation. The purpose of this study is to make clear the fixation ability of P. erythrophthalma to the attached media by changing the pore sizes of the media. The following results were obtained. It was made clear that the sticking ability of the rotifer to the attached media depends on its pore size of the media. In the case of the pore size of the media is larger than about 300μm, which is the average length of rotifer, the rotifer sticks to the media quickly after inoculation to the reactor, and is easy to get into the media. The shape and the pore size of the media were the most important factors of the fixing efficiency to the packed media.

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Generally, an impermeable plate has been used as the substratum of rotating biological contractors (RBC). In this study, ‘wire nets’ are used for the permeable substratum of RBCs. As a result, the following findings were elucidated : (1) The substrate removal rate of the permeable substrata is higher than that of the impermeable ones due to bio-mass existing in the space of the substratum and the increase of bio-film thickness. (2) The stable treatment performances are attained in case of short- and long-term change of loading. (3) After detaching bio-film from the substratum, the substrate removal rate of the permeable substratum is not decreased by reactivating of the remained bio-film. Concluding from the above results, when permeable substratum is used in RBCs and any detachment is occurred on the bio-film, the detachment face retrieves a new bio-film surface. Dominant microorganisms in the deep bio-film can be activated. Then it is predicted that the substrate removal rate increases more than the one in the impermeable substratum.

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A tetrachloroethylene (PCE)-degrading mixed culture was obtained from the drainage sediment of a dry-cleaning factory in where PCE was used. Although the mixed culture was unable to be subcultured with keeping PCE degradation activity, the addition of autoclaved or heated soils at 200°C and 600°C into subculture medium was effective to maintain PCE degradation activity. That effect was observed in all heated soil samples used in this study and zeolite, but lost in acid-treated samples. Therefore, the factor effective to maintain PCE degradation activity was supposed to be metals in the soil samples or “habitat” in soils and zeolite for PCE-degrading bacteria. That mixed culture could dechlorinate PCE to cis-1, 2-DCE via trichloroethylene (TCE), and degrade TCE and carbon tetrachloride, but not trichloroethane, chloroform and dichloromethane. The PCE degradation activity was optimized at about pH7 and 30°C.

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Biological anoxic-oxic activated sludge process, which treated domestic wastewater, was investigated to examine the effects of SRT and DO on nitrogen removal and emission of N₂0, which is causing global warming. The results obtained were as follows: The greater part of N₂0 emission was observed through nitrification, that amounted to about 4.5 times as that through denitrification. Alternation of SRT or MLSS, to some extent, had no influence on N₂0 emission through denitrification in anoxic tanks, as far as the nitrogen removal was made effectively under appropriate nitrogen loading. The amount of N₂0 emitted through nitrification at the run of 10-days SRT reaced about twice as that at the run of 20-days SRT, which led to that enough SRT could suppress N₂0 emission through nitrification. Besides, keeping high nitrification efficiency was important for suppression of N₂0 emission. It was clarified that control of carrying DO into the anoxic tank by nitrified water could reduce N₂0 emission through denitrification in anoxic tanks.

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Abundance and spacial distribution of nitrifying bacteria in aerobic biofilm consortia were investigated by using fluorescent in situ hybridization (FISH) with 16SrRNA-targeted oligonucleotide probes. The biofilms were developed in a novel reactor named downflow hanging sponge-cubes (DHS), which was employed as a cost-effective aerobic post-treatment unit after an UASB anaerobic pre-treatment unit receiving municipal sewage. Microscopic direct counting of nitrifying bacteria detected by the FISH technique was carried out to disintegrated biofilm samples, which were obtained by squeezing the sponge-cubes at different reactor height locations. The cell enumeration suggested that the DHS biomass contained 1.4×10⁹-1.2×10⁸ cells·ml^-1 cube of Nitrosomonas and 1.8×10⁸-0.15×10⁸ cells·ml^-1-cube of Nitrobacter, giving the presence ratio to total cells (detected by DAPI-staining) at 1.4% and 0.18%, respectively. Cell concentrations of both nitrifying bacteria were well correlated with ammonia-oxidizing and nitrite-oxidizing activities evaluated by batch tests. Application of the FISH technique to thinsectioned intact biofilm revealed that both Nitrosomonas and Nitrobacter were rather present in the interior space of sponge-cubes, as attached onto sponge materials. A relatively small amount of Nitrosomonas was observed only until 50μm-depth outer layer of the thick biofilm formed on the surface of sponge-cubes.

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