The ecological risk for chemicals should be evaluated from the viewpoint of population-level impact. To date, however, there are still no practical approaches to the assessment of the population-level impact of chemicals in order to develop appropriate plans for chemical management. In an attempt to address this urgent issue, we firstly proposed two population-level approaches based on state-of-the-art approaches to population-level risk assessment. Thereafter, as a case study, we applied the two approaches to the quantitative assessment of the potential impact of 4-nonylphenol (4-NP) on medaka (Oryzias latipes) in terms of reduction of population growth rate (λ). An age-classified projection matrix (daily time-step) model was developed and used as a tool for incorporating life-cycle survivorship and fecundity data obtained for individual-level responses of medaka exposed to 4-NP into population-level responses such as λ. Based on the resulting λs, the two proposed population-level approaches were then examined. The predicted no-effect concentration (PNEC) for population-level impact based on the threshold concentration (defined as the concentration at λ=1), as well as the lowest-observed-effect concentration (LOEC), the non-observed-effect concentration (NOEC), and the maximum-acceptable-toxic concentration (MATC) were then derived. The results suggest values for PNEC ranging between 0.82 and 2.10μg·l^-1 for medaka population growth impact under 4-NP exposure. Although these two approaches still have limitations, current knowledge indicates that they are reasonable and practical approaches to the evaluation of population-level impact.

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A protocol is described for the PCR-DGGE analysis of nirS nitrite reductase genes and its application to analyzing the denitrifying bacterial populations in activated sludge biomass samples from eight plants treating wastewater. A degenerate primer set designed by Braker et al (1998) was modified as 24 primer sets for this purpose. The method uses the 24 primer sets for the PCR analysis of these genes, and was validated against Ralstonia eutropha. With the activated sludge samples, six of the primer sets produced no PCR products under the given conditions. The multidimensional DGGE profiles obtained suggest that similar bacterial populations harboring the nirS gene exist in different plants treating the same type of wastewater. Some of the bands detected by DGGE were common to all biomass samples obtained from different plants, suggesting the presence of common denitrifying populations.

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We have studied and determined the most suitable electrolytic conditions and applied them to the biological filtration process by the electrochemical elution of iron, but have not made it clear whether to apply them to the activated sludge process.
In this study, we examined phosphorus removal, dehydrogenase activity and oxygen uptake rate using an experimental activated sludge system for the electrochemical elution of iron in the laboratory. This method was successful in more than 70% phosphorus removal while maintaining an Fe:P ratio of more than 0.75, a current density 0.25mA·cm^-2 and an intermittent operation of electrolysis. Phosphorus removal technologies based on the electrochemical elution of iron usually require an Fe:P ratio of 1.5. Our results were achieved by combining our system with a biological process that maintains phosphorus. This combined method offers high stability and provides more than two months of phosphorus removal. The electrochemical elution of iron does not negatively affect the performance of the biological treatment. The effluent BOD and nitrogen concentrations were not increased by introducing this method.
Moreover, the unit features a compact design and a low operating cost. In view of this, we consider that phosphorus removal technologies that incorporate electrochemical elution of iron can be provided for any wastewater treatment systems.

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The transcription level of amoA mRNA encoding a subunit of ammonia monooxygenase (amo) in ammonia-oxidizing bacteria (AOB) was quantified by competitive reverse transcription (RT)-PCR methods. The effects of ammonia concentration and dissolved oxygen (DO) on the transcription levels of amoA mRNA and 16S rRNA in AOB were evaluated to conduct batch experiments with nitrifying biofilms taken from a lab-scale reactor treating artificial wastewater. A batch incubation without ammonia resulted in the rapid decrease in the transcription level of amoA mRNA from 2.2 X 10⁵ copies·ng^-1-total RNA to 2.3 X 10⁴ copies·ng^-1 within four hours, while the 16S rRNA transcription level in AOB reduced to almost 50% of the level at the start of incubation. At a subsequent incubation with ammonia for eight hours a slight increase in the transcription level of amoA mRNA occurred, whereas the 16S rRNA transcription level recovered to 80% of the level at the start of incubation. The copy numbers of amoA mRNA and 16S rRNA showed almost fixed values for over eight hours in the absence of dissolved oxygen. RT-PCR will provide a basis for the development of new monitoring technologies and operational strategies for ammonia removal processes.

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Practical application has been delayed regarding domestic wastewater treatment systems used in detached houses that are capable of removing nitrogen and phosphorus simultaneously. The authors have directed their attention to a process that combines carrier fluidized biofilm filtration and iron electrolysis. They studied a treatment system for removing nitrogen and phosphorus simultaneously in terms of its functions, and conducted the performance and verification tests.
The results confirmed that the treated water constantly showed a BOD and T-N of 10 mg·l^-1 or less, an SS of 5 mg·l^-1 of less, and a T-P of 0.7 mg·l^-1 or less on average, although the tests were conducted during a low-temperature period. The phosphorus removal system using iron electrolysis functioned properly during the test period, dissolving an almost theoretical amount of iron, thus contributing to the steady removal of phosphorus. The amount of sludge accumulated after completion of the study reached 13.0-21.6 g·n^-1·d^-1, which corresponds to a 3.8-8.5 g·n^-1·d^-1 increase compared with other systems lacking a phosphorus removal system. It was confirmed that as much as a year's amount of generated sludge can be held in storage even with such an increase.
The present treatment system for removing nitrogen and phosphorus simultaneously was confirmed to be capable of maintaining its design performance. In the future, further investigations on subjects such as condition optimization will be necessary.

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The removals of boron, selenium (IV) and selenium (VI) in a solution of coal fly ash from a power plant (EP ash) were examined using chelating resin (Diaion CRB02, Mistubishi Chem.). Boron, Se (IV) and Se (VI) were removed quantitatively in the pH range 4-7 using the resin. At optimum pHs, the maximum adsorbed quantities were 11.7mg·g^-1 for boron, 9.7mg·g^-1 for Se (IV) and 6.8mg·g^-1 for Se (VI). The adsorbed elements were recovered quantitatively, yielding 98% for boron, 98% for Se (IV) and 88% for Se (VI) with a 1M sulfuric acid solution whose volume is 10times the resin volume. When a solution of EP ash (boron : 2.7mg·l^-1, selenium : 0.06mg·l^-1, sulfate ion : 89.7mg·l^-1), whose volume is 500times the resin volume, was passed through the column at the space velocity of 30h^-1, breakthrough points did not appear by this volume of the sample solution. Thsese results suggest that boron, Se (IV) and Se (VI) in the solution of EP ash can be recovered successfully using the resin.

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