Denitrification of nitrate-polluted water was investigated using a bio-electro reactor which consisted of immobilized denitrifying bacteria electrode as cathode and carbon electrode as anode. In this system, the denitrification occurred with the hydrogen produced by electrolysis of water ; CO₂ and H⁺ derived from electrochemical oxidation of anodic carbon acted as buffer, so, pH was maintained around neutral value. To enhance the denitrification capability of the cathodic biofilm, acetate was also added to the reactor. In the batch experiments, simultaneous use of acetate and hydrogen was observed. The denitrification rate increased with the increase of the concentration ratio between CH₃COO^--C mg·l^-1 and NO₃^--N mg·l^-1 which was given in the form of C/N ; however, acetate remained. The maximum denitrification rate without residual acetate was observed at C/N=1, which corresponds approximately to chemical stoichiometric ratio of the nitrate reduction reaction to nitrogen using acetate as hydrogen donor. In the case of 5 hours of HRT at the continuous experiment, nitrate reduction more than 90% occurred under C/N=1 without residual acetate and nitrite in the reactor effluent and the removal rata was 3.8 times as large as that of the condition without feeding acetate.

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The objective of this study is to determine aerobic and anaerobic biodegradation rates of hexadecane (HEX), phenanthrene (PHE), and anthracene (ANT) using estuarine sediments of Tama River in Tokyo and to estimate degradation potentials of these petroleum hydrocarbons in estuarine sediment of Tama River. Known amounts of these petroleum hydrocarbons were added to sediment slurry prepared by mixing estuarine sediment with bottom water in Tama River (sediment : water=1 : 1 v/v). Sediment slurry was incubated by reciprocal shaking in aerobic and anaerobic condition at 20°C. After sediment slurry was sampled periodically and extracted with ethyl acetate, these petroleum hydrocarbons in sediment were determined by gas chromatography with FID. In aerobic incubation series, the cells number of total heterotrophic bacteria and HEX-, PHE-, or ANT-utilizing bacteria in sediment slurry was determined. Aerobic biodegradation rates of HEX, PHE, and ANT in sediment slurry ranged from 40 μg·g^-1 dry sediment·day^-1 to 70μg·g^-1 dry sediment·day^-1. Anaerobic biodegradation rates of HEX were 5-8 μg·g^-1 dry sediment·day^-1. But, biodegradation of PHE and ANT was not observed during the two-month incubation period. Aerobic degradation of HEX was not affected by existence of PHE or ANT. The mumber of HEX-, PHE- or ANT-utilizing bacteria was 5-10 percentage of total heterotrophic bacteria in estuarine sediment. Biodegradation potentials of petroleum hydrocarbons in estuarine sediment of Tama River calculated from biomass of the utilizing bacteria in estuarine sediment and biodegradation rate per cell of utilizing bacteria in the period of constant biodegradation being observed were 1.0-3.5μg·g^-1 dry sediment·dry^-1 of HEX and 1.2×10^-2-4.2×10^-2μg·g^-1 day sediment·day^-1 of PHE or ANT.

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The conventional vapor extraction technique for soil remediation is fairly effective for the clean-up of unsaturated soil. However, it is difficult to apply this technique to general contaminated sites in Japan where the groundwater level is very high. To solve this problem, the two-phase extraction technique has been developed. In this paper, this technique was applied to a contaminated site and proved fairly effect. Moreover, a prediction analysis of clean-up efficiency is carried out and prediction results are compared with the field data. The analysis model is a simple macro-scopic model, and thermodynamic equibilium states are assumed in the formulation. The two-phase extraction technique is effective in a shallow aquifer and recovery mass from vapor is 5 to 10 times larger than that from groundwater. In addition, surface gas concentrations after remediation are 90% lower than before remediation. The prediction analysis needs quite a large correction factor because this analysis assumed a homogeneous concentration distribution. However, this analysis is effective for rough estimates and is a simple to use.

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The effect of two kinds of herbicide (Simazine, Thiobencarb) on the stability of small-scale microcosm system was investigated. The microcosm system was composed of microanimals as predator (Cyclidium glaucoma, Lepadella sp., Philodina sp., Aeolosoma hemprichi), algae as producer (Chlorella sp., Tolypothrix sp.) and bacteria as decomposer (Pseudomonas putida, bacillus cereus, Acinetobacter sp., Coryneform bacteria). Simazine affected only the growth of Tolypothrix sp. The number of which was measured for l5days after the addition of the herbicide, decreased to a fortieth with the addition of 0.08mg·l^-1 or more, while Thiobencarb affected the growth of Cyclidium glaucoma from 1.0mg·l^-1 in two species cultivation system and from 2.0mg·l^-1 in the microcosm system. The influence was mitigated by the diversity of constituents in the microcosm. A. hemprich was eliminated and the number of Chlorella sp. decreased to a third at above 0.5mg·l^-1 concentration of Thiobencarb. In the microcosm, Simazine was very stable, however the concentration of Thiobencarb decreased to 30% for l5days after the addition of 1.0mg·l^-1. It was found that the toxicity, the influence and the stability of pesticides in aquatic ecosystem were evaluated by the behavior of the constituent microorganisms and pesticides.

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The natural features of estuaries and coastal areas are often seriously damaged due to the discharge of pollutants by human activities, and most natural seashores have disappeared and been replaced by man-made concrete blocks. However, it is a well-known fact that natural seashores have a high self-purification capacity.
The purpose of this study is to develop a new ecotechnologic method to restore the polluted coastal environment by using the artificial beach. The pilot plant of the artificial beach was constructed in the Shiogama Bay, facing the Pacific Ocean. The main merits of this system are a simple structure, free of energy demand, since the tide was used effectively, and purification is carried out by physical and biological filtration through the beach.
The results showed that turbidity was removed effectively and DO was consumed by biological degradation of particulate organic matter and nitrification ; all of these performances depended on both the movement of water and the addition of oxygen caused by the tide ; both were determined by the structure of the beach, which included scale, slope and kind of gravel. The effects of the sectional shape of the beach on the performance are discussed with respect to the results of a numerical simulation.

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Autotrophic denitrification was studied using hydrogen gas as the hydrogen donor. It was confirmed that microorganisms which have the ability of autotrophic denitrification using hydrogen gas are distributed widely. It was concluded that Alcaligenes eutrophus (ATCC 17697), Paracoccus denitrificans (IFO 13301) and Pseudomonas pseudoflava (ATCC 33668) can reduce nitrate to nitrogen gas in the presence of hydrogen gas. The effect of pH value for autotrophic denitrification of these bacteria was not significant within the range of 7 to 8. The effect of temperature on the specific denitrification rate was also examined and the calculated Arrhenius constant was within the range of 44.1 to 63.2 kJ·mole^-1. The specific denitrification rate of A. eutrophus and P. pseudoflava was above 1 mgN·mgSS^-1·d^-1 at 15 degree centigrade. The specific denitrification activity was constant above 10 kPa of partial pressure of hydrogen gas and the Michaelis-Menten half-velocity constant for hydrogen gas was found to be less than 3% of saturation.

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Fifteen strains of Tetrachloroethylene (PCE)-degrading bacteria were isolated on agar plates from contaminated soils and a culture fluid which was acclimated to PCE with a subsoil of pond. Two strains of the isolates and others degraded PCE to trichloroethylene (TCE) and to cis-1,2-dichloroethylene (DCE) via TCE, respectively. Most of identified isolates were Bacillus species, which is the most common genus of bacteria found in soils. The acclimation of PCE-degrading bacteria with a subsoil of pond was performed readily. These results suggest that some indigenous PCE-degrading bacteria which are present in a PCE-polluted environment grow rapidly and readily acquire a higher degrading ability in the presence of favorable organic compounds as electron donors. The best PCE-degrading bacterium (Pseudomonas species) of isolates thoroughly degraded 160mg·l^-1 of PCE to DCE within 4 days at 30°C.

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To clarify the biodegradation of urea in river water, the concentration of urea and the cell number of heterotrophic urea-decomposing and urease active bacteria were examined in three rivers (six sites) located in north Kyushu. There were more urea-decomposing bacteria in the pollutted site (BOD 7.4mg·l^-1, urea 0.114mg·l^-1), 17±30×10² cells·ml^-1, than in the relatively unpolluted site (BOD 1.0mg·l^-1, urea 0.039mg·l^-1), 1.4±1.8×10² cells·ml^-1. The ratio of the average number of urea-decomposing bacteria to heterotrophic bacteria grown on PYG agar medium was 0.28%. However, 55 (30.5%) of 180 strains isolated from river waters contained urease activity.
In biodegradation experiments, urea added to river water at the concentration of 0.2-5mg·l^-1 was not appreciably degraded. The results suggest that, in the river water of below 5 mg·l^-1 of urea, most of the heterotrophic bacteria having urease are not transformed into the urea degrading or assimilating bacteria.

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