Effect of NH₄-N in dilution water on BOD concentration of water treated by johkasou, which has some high concentration of nitrogen, was investigated. Three kinds of dilution water, that is distilled water, standard dilution water without adding NH₄Cl and standard dilution water were used for BOD measurement.
BOD of such water that was in the tank for biological treatment in which nitrification reaction progressed and that contained some sludge showed a high weight of N-BOD. NH₄-N in dilution water contributed greatly to N-BOD when the dilution factor was large. It was found that nitrification of NH₄Cl added in the standard dilution water processed in the early stage of BOD decomposition.
Concentration of (NH₄+NOx)-N resulting from water in the BOD bottles was calculated based on data obtained in the previous surveys. It seems that no inorganic nitrogen was needed to add into the standard dilution water, because nitrogen concentration of water measured in this study was found to be higher than that in the standard dilution water.

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For the ecological risk assessment, extrapolation from toxicological data obtained at the individual level into effects at the population level is required. We review the analytical methods for translating chronic toxicity data into the effect on propensity of populations (population growth rate or intrinsic rate of population increase). Actual ecotoxicological data have two major problems, i.e., 1) only a very small fraction of chemicals-species combinations has been examined for chronic toxicity, and 2) it is not feasible for many test species to execute the life-cycle test. As analytical methods in order to circumvent these limitations of data, we focus on the extrapolation method and the life history sensitivity analysis, and discuss these methods in the context of ecological risk assessment. The cxtrapolation method is to infer missing chronic toxicity data from regression of known chronic data to acute data, or from regression of chromic data between different species or life stages. From the inferred and the directly estimated chronic toxicity data, the effect of chemicals to population growth rate is estimated. The life history sensitivity analysis estimates the relative importance of life stages in terms of intrinsic rate of natural increase, and reduces the life table evaluation by excluding the unimportant life stages. These analytical methods that apply the ecological theory may be important for future ecotoxicological data analysis embedded in the ecological risk assessment.

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A biofilm model was presented to investigate the design and operation factors of the bio-electro reactor on nitrification. The biofilm model consists of molecular diffusion, substrate utilization and electrochemical reaction. The concept of an effectiveness factor (Ef) was introduced to estimate the effects of applying electric current. The mathematical model showed that the effect of applying electric current was large when bulk DO concentration is low and biofilm is thick. Both the calculated and observed results also showed the possibility of a simultaneous nitrification-denitrification treatment in a single bio-electro reactor. The electrochemically enhanced nitrification rate calculated using the biofilm model was comparable to the experimental result.

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A simulation test method (called TOC-HANDAI) was modified to examine the effect of microorganisms cell order regulation for biodegradation of surfactants.
Microorganisms cell order in the suspension used as an inoculum was made in the same order (10³, 10⁴, 10⁵) by controlling the volume of river water for filtrate in every season.
Each eight surfactants and commercial detergents were tested for 14 days with shaking at 25°C in the dark. Samples were drawn periodically and biodegradation was determined by measuring the remaining TOC.
Biodegradation rate of most surfactant using 10³ cell order inoculum was very different from using 10⁴ and 10⁵ orders during 14 days, though the results which were obtained with the other order inoculum corresponded well. Using the low cell order inoculum, biodegradability of the same surfactant showed wide fluctuation in every season, but using higher cell orders (10⁴, 10⁵) inoculum always showed stable results.
These results suggest that the regulation of microorganisms cell order is useful method which can stabilize the degradation rate and decrease the fluctuation on the simulation test.

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The preservation of water quality and natural environment is increasingly important among the industrialized society. Effluent discharge standards employed by Environment Agency, Japan Federal Government have prevented rivers, lakes, and oceans from the pollution by human activities. The number of novel man-made hazardous substances produced by industries is increasing according to the year, resulted in conventional discharge standards ineffective to preserve natural ecological environment. A novel monitoring parameters to detect unknown pollutants sensitively are need to be investigated.
In this study, the population change in the benthic fauna was used to monitor environmental effect of disinfection agent on rivers. Two separate streams of treated sewage are compared by this method. One stream is treated by chlorine for the disinfection, and ozone treatment were employed for the other stream.
The stream disinfected by chlorine changed benthic fauna drastically compared to that by ozone. The population diversity of the benthic fauna in the river receiving the ozone treated stream was larger than that in the river receiving the chlorinated stream. In conclusion, ozone treatment found to be more effective to preserve the natural ecological environment of the river.

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Ecotoxicological data using life table evaluation are reviewed and analyzed with the power function model. Life table evaluation and population growth experiments are proposed as experimental procedures that provide demographic parameters (e.g. intrinsic rate of natural increase) relevant for calculating extinction risk due to pollutant exposure. Totally 47 concentration vs. intrinsic rate data sets were collected and analyzed with two indices in the power function model, α and β. The α-value is the concentration at which the intrinsic rate of increase drops off below zero due to exposure and the β-value represents curvature of the response. The α-values, which represent strength of ecological toxicity, are highly correlated with acute LC₅₀s. It is indicated that the α-values are indirectly predictable from acute LC₅₀s. Such statistical extrapolation may be useful for ecological risk assessment based on extinction probability of populations.

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