Effects of sulfate and sulfide on methanogenesis were examined in a sulfate-poor anaerobic sludge that had been acclimated with glucose as a carbon source for more than 3 years. Bacterial sulfide production occurred immediately when sulfate was added into the sludge. High density of sulfidogens (10¹⁰-10¹¹ cells per g VSS) should inhabit in the sludge. At the same time methanogenesis was inhibited and the maximum inhibition was 53% of the initial methanogenesis at 0.6mM of sulfate. Up to 3mM of sulfide stimulated the methanogenesis, but more than 5mM of sulfide inhibited markedly the methanogenesis. These results show that high density of sulfidogens maintained by their fermentation from substrates under sulfate-poor environments and inhibited partially methanogenesis under sulfate-rich environment because of sulfidogens's predominant utilization of competitive substrates between sulfidogens and methanogens.

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Optimal harvest management to obtain maximum yield of waterhyacinth is studied theoretically and experimentally. Theoretical analysis, based on logistic curve for a growth of waterhyacinth, shows that maximum yield is obtained by constantly harvesting only growth parts of it and keeping the population density of S_m/2 (S_m : saturation value of logistic eq.).
However, it also shows that its yield hardly depends on a harvest period of waterhyacinth up to 30 days if the value of S_m/2 is between upper and lower density of population in the period. These conclusions were supported by two experiments : Experiment I for 9 months and Experiment II for 15 months in a natural pond. Mean yield and nitrogen removal in the later experiment with the harvest management, which followed almost the above mentioned technique, were up to about 90% of theoretical maximum yield (S_mλ /4) and maximum nitrogen removal (S_mλ N/4) (λ : growth coefficient in logistic eq., N : total nitrogen content in tissues of waterhyacinth).

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Effects of sulfate load on substrates utilization for sulfidogens and methanogens were investigated in anaerobic sludge that had been acclimated with glucose under various sulfate loads (0 to 0.475mmol SO₄^2-·l^-1·d^-1). Methanogenesis was decreased with increasing sulfate load and the methane production rate was decreased by 23% at 0.475mmol SO₄^2-·l^-1·d^-1 compared with no sulfate load sludge. When sulfate reduction was inhibited by the addition of molybdate in sulfate load sludge, methane production rate was the same as that in no sulfate load sludge. At the same time, the utilization rates of propionate and acetate by sulfidogens were increased, but that of acetate, hydrogen and formate by methanogens were decreased with increasing sulfate load. The utilization rate of propionate by syntrophic hydrogen-producing acetogens also decreased. These results showed that sulfidogens competed for acetate with methanogens and for propionate with syntrophic hydrogen-producing acetogens in high sulfate load condition.

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An enzymatic method was applied to the determination of ammonia in natural water. A sample solution containing ammonia was mixed with a glutamate dehydrogenase (G1DH), reduced nicotinamide adenine dinucleotide phosphate (NADPH) and 2-oxoglutarate. The decrease in the absorbance intensity caused by the disappearance of NADPH by this reaction was measured at 340 nm. We report here the application of this enzymatic method to determine ammonia in seawater, lake water and river water and compare the enzymatic method with ordinary indophenol blue colorimetry.
There was a linear relationship (r²=0.999) between peak height and ammonia concentration over the range 0-29 μM. The low concentration of measurement was about 0.5 μM for a sample volume of 250 μl. The interference effect of amino acids and urea at concentrations of 50 mgl^-1 was negligible. Good agreement was found between the enzymatic method and ordinary indophenol blue colorimetry.

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Using XAD-2 resin and Ames' assay, mutagenicity of tap waters and the River Shinano waters in Niigata Prefecture of Japan were measured during the winter period from 1988 to 1990 with the test strain of TA100.
Without S-9, maximum, minimum and average mutagenicity for 26 tap waters were 133 ngl^-1, N. D. and 31 ngl^-1 as 4NQO. In contrast, with the addition of S-9, mutagenicity were reduced by the average of 91.5%. Mutagenicity of tap waters gained by the rapid sand filtration of river water were much stronger than those by the slow sand filtration of river water and/or the direct supply of groundwater.
On the other hand, maximum, minimum and average mutagenicity for the 9 River Shinano waters without S-9 were 18 ngl^-1, 5 ngl^-1 and 13 ngl^-1 in terms of 4NQO. Mutagen intensity was reduced by the average of 28.4% with the addition of S-9. High correlation coefficients were found between the river water mutagenicity and “permanganate value, ammonia, total phosphorus and/or BOD”. It is understood that the mutagenicity of the River Shinano was closely related to the organic matter which comes from ordinary human life and animal excretion in the basin.

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