Effects of sulfate concentration and COD/S ratio on the methane production and sulfate reduction in the anaerobic degradation of butyric acid were investigated by using an anaerobic chemostat-type reactor at 35°C. The sulfate concentration and COD/S ratio were changed in the ranges of 68 to 1667 mg·l^-1 and 1.5 to 148, respectively. In order to study the competition between the methane producing bacteria (MPB) and sulfate-reducing bacteria (SRB), the COD mass balance, electron flow, sulfur balance and trophic-groups bacterial populations under the different conditions were analyzed quantitatively.
The competition between MPB and SRB was evidently influenced by COD/S ratio. When COD/S ratio was 6.0 or more, the methane production was the main reaction. On the other hand, 67% of the total electron flow was utilized by SRB when COD/S ratio was 1.5. The path way of butyrate degradation and the microflora in the reactor were also affected by COD/S ratio. The numbers of acetate-consuming and H₂-consuming MPB decreased from 10⁶ to 10⁴ MPN·ml^-1 and 10⁶ to 10¹ MPN·ml^-1, respectively, as COD/S ratio decreased from 148 to 1.5. In the reactor in which a small amount of sulfate was added to the substrate, the numbers of butyrate-consuming and acetate-consuming SRB were enumerated as high as 10⁷ to 10⁸ MPN·ml^-1. It is suggested that in sulfate-depleted environment, the butyrate-consuming SRB play an important role in producing H₂ and acetate from butyrate, as well as the acetogenic bacteria.

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Nitrate concentration in the ground water under the paddy field has a seasonal change and relatively high concentration was observed in the summer. There is a weak relationship between water level of the ground water and nitrate concentration. The concentration of dissolved oxygen in the ground water is nearly 0 mg·l^-1 in summer but about 10 mg·l^-1 in winter. This means that denitrification is easier in summer. The change of denitrification rate could not explain why relatively high concentration of nitrate observed in summer.
A numerical model is presented. The model incorporates nitrification of fertilizer in the paddy field, penetration of nitrate into the soil and change of ground water quantity. The model is useful to interpret the mechanism of seasonal nitrate concentration change in the ground water under the paddy field.

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In order to assess the contribution of acid precipitation on water quality of river and lake, the results obtained by batch experiments were analyzed based on chemical equilibrium technique. In this study, four soils collected in Ishikawa Pref. were mixed with an acid solution at various pH. All of the soils contained little carbonates. Sulfate ion was not adsorbed on the soils except one soil sample. It was recognized that cation-exchange and dissolution of aluminum from the soils principally contributed to neutralization of acid precipitation by soils. The amounts of H⁺ ion replaced by exchangeable cations in soil, ΔH⁺, were estimated from the pH value of an acid solution before and after equilibration with soils. From the relationship between values of ΔH⁺ and concentrations of cations released from the soil, it was found that the soil contained some neutral salts. It was suggested that the existence of neutral salts in soils might give overestimates for the value of base saturation of soil. Since the obtained values of ΔH⁺ approximately agreed with sum of cation released from the soil samples, measurement of ΔH⁺ was believed to be simple and useful method to estimate total amounts of exchanged cations.

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Isolation of 2-methylisoborneol (2-MIB) degrading bacteria from environmental water and sediment had been tried and the following results were obtained.
2-MIB degrading bacterium (Strain S6) isolated from a pond sediment was identified as Pseudomonas sp.
The strain formed colonies about 1mm in diameter after 5 days incubation at 25°C. The strain could degrade more than 90% of 4 mg·l^-1 2-MIB in 4 days under an aerobic condition. The degradation of 2-MIB by the strain was proved to be co-metabolism. The strain could partly degrade 2-MIB in autoclaved river water and sediment. Ethanol assimilating bacteria could degrade 2-MIB partly through the acidification of culture media when incubated in ethanol containing media.

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Microorganisms which contribute to the effective production of useful materials as well as substrate decomposition can be kept at a high concentration through the use of a membrane module with a reactor.
This paper reports on our experimental results on methane fermentation using a membrane module. The methane fermentation reactor uses charged raw sludge from the suspended solids separating device (which is much the same as the sludge from the primary settling tank) and the concentrated backwash of the biological aerated filter.
The reduction rate of volatile suspended solids charged into the methane fermentation reactor increased from 76.8% to 84.8% at a reactor temperature of 25°C, and only the raw slugde from the separating device was charged.
When a mixture of the concentrated backwash and the separated sludge from the separating devise were fed to the methane fermentation reactor the reduction rate for volatile suspended solids increased from 52% to 72% at 25°C. Such a high reduction rate of volatile suspended solids can be attributed to the use of the membrane separation system.
Stable operation of the membrane module was achieved under the condition that the SS concentration of the inlet liquid was from 20,000 to 25,000 mg·l^-1 and the membrane linear velocity was 0.6m·S^-1. The recovery of flux was only achieved through back washing.
The power consumption for membrane separation was calculated as 2.15KW·h per m³ of the permeant, provided that both the motor efficiency and pump efficiency were 1.0.

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