Mercurials have been released into the environment by geological or anthropogenic activities. Organomercurial compounds such as methylmercury are known as toxic compounds. Therefore, organomercurials should be monitored to keep clean environments. However, chemical species of organomercurials are not easily detected separately or individually.
In this study, we tried to detect organomercurial compounds by using a bacterial gene-expression system. A series of mer operon-luciferase (mer-lux) transcriptional fusion plasmids (pHYΔB3Lux and pHYB3Lux) was constructed to evaluate the gene expression system with a new organomercury lyase gene merB3 from Bacillus megaterium MB1. A plasmid (pGR1A) encoding mer operon genes from O/P_merR1 to merA isolated from B. megaterium MB1 was used as a transacting gene expression vector with the mer-lux transcriptional fusion plasmids into a same host bacterial cell. The transformants that carry a set of two plasmids (pHYΔB3Lux+pGR1A or pHYB3Lux+pGR1A), respectively) were used for detection of organomercurials. The experimental results showed that the transformant with pHYΔB3Lux+pGR1A responded to only mercury chloride (MC). On the other hand, the transformant with pHYB3Lux+pGR1A responded and detected MC and the all organomercurials tested in the study. Therefore, the bacterial strain which possess a gene expression system of mer-lux transcriptional fusion was useful to detect organomercurials with distinction from inorganic mercury.

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In order to establish a methodology for the optimization of a water treatment process in terms of its total toxicity reduction, we proposed a simple method for describing changes in the concentrations of a toxic chemical and of its derivatives, and changes in the total toxicity derived from these chemicals. Dichlorvos (DDVP), an organophosphate, was selected as a model chemical, and the toxicity of the treated water was evaluated by the growth inhibition of cultured human cells. In a series of experiments, although original DDVP was rapidly degraded, its oxidation intermediate (DDVP' and DDVP'') was produced and strongly affected the total toxicity of the treated water. Changes in the concentrations of these chemicals and the total toxicity were well described by a simple numerical model. By using this model, we predicted the effects of ozone concentration, pH, and ozonation time on the total toxicity reduction during ozonation of DDVP at the level of the environmental standard. Such a methodology proposed in this work would be useful for choosing an better treatment process and also in optimizing the running conditions.

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Inactivation of bacteria in water by the phtocatalytic oxidation and repression of the photoreactivation were studied. By counting bacteria with Standard Plate Count (SPC) method and heterotrophic bacteria in the river water, the inactivation and photoreactivation effects under the condition of 254nm-ultraviolet irradiation and that of the black light (maximum intensity: 352nm (300nm-440nm) ) irradiation was examined. The inactivation effect by 254nm-ultraviolet irradiation was particularly remarkable than the black light irradiation, while the oxidative degradation potential was almost equivalent. And it was proved that the photoreactivation of bacteria could be suppressed by using the photocatalyst with 254nm-ultraviolet irradiation. Generation of aldehydes was confirmed in the 254nm-ultraviolet irradiation with photocatalyst of tap water, river water, and groundwater, however, their amount were very limited in typical reaction time for inactivation.

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This study was carried out to clarify the effects of bacterial adhesion on powdered activated carbon (PAC) on bacterial activity using nitrate reduction activity E. coli K-12. E. coli K-12 was incubated with or without PAC. Additional amount of PAC ranged from 300 to 5,000mg·l^-1 at 7.75×10⁷ cells·ml^-1 or from 20 to 90mg·l^-1 at 1.78×10⁸ cells·ml^-1 of E. coli K-12. The cells concentration was also changed from 2.23×10⁷ to 1.58×10⁸ cells·ml^-1 at a constant concentration of PAC, 1,000mg·l^-1. High specific nitrate reduction rate was observed in cultures with PAC than those without PAC. The specific nitrate reduction rate increased with the increase in the ratio of adhered cells to total cells. The relationship between the specific nitrate reduction rate and the ratio of adhered cells to total cells was expressed by first order proportional equation. The results indicate that the adhesion of bacteria on activated carbon stimulates bacterial activity. The stimulation of bacterial activity did not result in adsorption of substrate, products or oxygen on PAC, therefore, it must depend on the interaction between adhered bacteria and the surface property of PAC.

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T-N removal performance was investigated using observed data on rural sewerage facilities with anaerobic and aerobic submerged filters. It was found that probability distribution of T-N in influent and effluent of rural sewerage facilities obeyed normal distribution or logarithmic normal distribution, T-N removal in anaerobic filter tank was assumed to depend primarily on influent T-N concentration, influent of NO_x-N/T-N rate, and SS reduction in anaerobic filter tank. Because effluent NO_x-N/T-N rate of contact aeration tank also will be determined from hydraulic loading (hydraulic detention time), it is clear that recirculation ratio shall be related to influent NO_x-N/T-N rate of anaerobic filter tank. It is suggested that influent NO_x-N/T-N rate of anaerobic filter tank may be affected significantly by recirculation ratio so that T-N removal shall be governed from recirculation ratio. It is possible that effluent T-N concentration and influent NO_x-N/T-N rate of anaerobic filter tank can be predicted by recirculation ratio and effluent NO_x-N/T-N rate from flow equation tank. Consequently, it is important that control of SS and hydraulic detention time is effective to maintain T-N removal efficiency in anaerobic filter tank. T-N removal in contact aeration tank is also influenced by influent T-N and SS reduction.

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