Recently in Japan it's very important to analyze efficiency of sewage improvement projects for households. But most of research efforts which deal with the efficiency of sewage improvement projects analyze the cost but fail to discuss their benefits. So the purpose of this study is to estimate the net social benefits of sewage improvement projects for households. First, we proposed a new method to estimate benefits of sewage improvement projects based upon hedonic approach supplemented by survey approach before estimating the benefits. Secondly, we estimated the net social benefits of sewage improvement projects in the Tokyo Metropolitan area. We found that net social benefit was negative in KOKUBUNJI CITY. And we found also the net social benefit associated with small scale treatment projects to improve the water quality of the river was lager than that associated with the existing system in MATSUDO CITY.

View full abstract

Hydrological measurements were performed during and after rainfall from April to November in 1990 in the Enokigawa experimental basin close to Hiroshima city. The Enokigawa experimental basin was divided into two parts which were the urbanized lower reaches and the forested upper reaches with headwaters. Water quality of stream did not change remarkably by rainfalls in the urbanized lower reaches. There was also no clear change of water quality of stream in the forested upper reaches, except the SO₄^2- concentration gradually increased in this observation period. The ratios of pre-event water flow (groundwater runoff) to the discharge increment of two storm events were shown to be 73 and 87% by the runoff separation using the ¹⁸0 stable isotope method. These facts imply that the water quality of stream in the upper reaches depends almost on groundwater corresponding to headwaters.

View full abstract

The comparison of soil chemical properties and the condition of Japanese cedar stands in the Kanto-Koshin District were discussed to clarify the possible damaging effects of soil chemical properties. Soil types studied were mainly black soils and brown forest soils. In severely and moderately damaged stands, pH value, percent of base saturation and exchangeable Ca (ex-Ca) concentration were significantly lower and exchange acidity and exchangeable Al (ex-Al) concentration were significantly higher than those of healthy stands, in both black soils and brown forest soils. Though the correlations of factors to damage were similar in both soil types, the levels of base saturation, ex-Al and ex-Ca differed according to the chemical properties and acid buffering capacities of those types. The difference of soil chemical properties observed in damaged stands and healthy stands was assumed to be as follows : Dry deposition, transported from coastal regions of Tokyo Bay, was trapped in cedar tree canopies, then washed into the soils by stem flow and throughfall. Though it was assumed soil chemical properties in this study were not contributing factors to cedar decline, further increased concentration of ex-Al and loss of nutrients (Ca, Mg) could have direct adverse effects.

View full abstract

The diauxic growth in a batch culture with acetic acid and oxalic acid was investigated for the effective biodegradation of organic acids which were produced by ozonolysis of pulp wastewater. As it was necessary to degrade all substrates in a continuous culture with mixed substrates, the stability of the steady state which degrade all substrates was to be examined. Stability of steady states was discussed through the eigen values using the previously proposed diauxic model. The number and stability of steady states varied remarkably with operational conditions such as dilution rate and feed substrate concentrations. The three steady states existed, one was the steady state where both substrates were consumed, another was the steady state where only one substrate was consumed and the other was washout. The operational method was studied to obtain the steady state where both substrates were consumed by the diauxic model.

View full abstract

Reactions of SO₂ with NH₃ were studied at 45-105°C in gaseous mixture of NO, oxygen and nitrogen with and without water. The reactions proceed at reaction temperature lower than 65°C in the presence of 10% water and white powdery reaction products were uniformly deposited on the surface of a reactor and of a fiber filter. From the chemical analysis of the products dissolved in water, the main components of the products were considered to be ammonium sulfate, sulfite, hydrogen sulfate and hydrogen sulfite. The reactions may proceed in absorbed water on the surface of a reactor and a fiber filter.

View full abstract