Takeshi Goda

An eutrophication model of Lake Kasumigaura

Abstract The artificial eutrophication of lakes and reservoirs is recognized worldwide as a serious problem of water quality management. Lake Kasumigaura, the largest shallow lake in Japan, showed the typical signs of eutrophication over the last decades. This is due to the increased nutrient loadings of urbanization, agricultural development and fishing culture. A lot of countermeasures are now being planned and undertaken by local and central governments. In order to accomplish these plans effectively, it is inevitable to comprehend and summarize the total figure of nutrient dynamics in the lake as well as in the surrounding region. In this study, a mathematical model of nutrient dynamics, which is composed of four segments and 14 compartments in each segment, is presented in order to figure out the roles and relations of each compartment to the nutrient cycles. After the fidelity of the model to field and experimental informations was thoroughly checked, the calibrated model was used to get the future status of water quality of Lake Kasumigaura.

Kinetic model of activated sludge metabolism and its application to the response of qualitative shock load

Abstract A series of study for kinetic model of substrate ingestion and metabolism in the activated sludge system was performed. Coefficients included in the proposed model were argued referring to some experimental data. And it was shown that the proposed model can simulate the mechanism of substrate ingestion, metabolism, oxygen uptake rate and the change of sludge activity. The model was applied thereafter to predict the performance of activated sludge suffering the qualitative shock loading, in the completely-mixing system.

Synthesis and analysis of a comprehensive lake model — with the evaluation of diversity of ecosystems

Abstract The development of a model for Lake Kasumigaura is presented. The various steps in this development are discussed and it is demonstrated how the various model versions differ in complexity as more and more processes and details are considered. Furthermore, several restoration methods are discussed making use of the model results. Finally, an evaluation of the diversity is presented.

Entropy analysis of water and wastewater treatment processes

In the environment, due to its physicochemical properties such as action as a solvent in becoming a carrier to waste materials and waste heat, water especially as compared to other environmental media is very susceptible to pollution. Entropy is the measure of disorder of a system. In a closed system, entropy tends to increase. For example, if a compound is dumped in pure water, it is likely that the compound will be dissolved and diffused into whole water body. The meaning of a compound dissolved and diffusing in the water is twofold: (1) increase in entropy of the solution; (2) increase in the extent of pollution. It can be seen that an increase in entropy results in water pollution. Once water is polluted, input energy is required in order to remove the pollutants and purify the water and to decrease the entropy of polluted water. On the other hand, the entropy is created by the irreversibility. The author will show that if the efficiency of water treatment system (N) can be given by entropy production...

Evaluation of thermodynamical efficiency of reverse osmosis process using entropy

Abstract Entropy is the measure of disorder of a system. In a closed system, entropy tends to increase. For example, if a compound is dumped in pure water, it is likely that the compound will be dissolved and diffused into whole water body. The meaning of compound dissolving and diffusing in the water is twofold; (1) increase in entropy of the solution; and (2) increase in the extent of pollution. It can be realized that increase in entropy results in water pollution. Once water is polluted, input energy is required in order to remove the pollutants and purify the water, to decrease the entropy of the aqueous solution. The purpose of water treatment is to decrease the entropy of polluted water. On the other hand, the entropy is created by the irreversibility of the system. We may explain later, that if the efficiency of water treatment system (η) can be given by the rate of decrease in entropy of feed water (ΔS/Δt) and the rate of internal entropy production (dtS/dt), then we can evaluate the thermodynamical efficiency of water treatment systems.

Environmental impacts of sewage sludge applied to cropland

The National Institute for Environmental Studies, Japan (NIES) had pursued special research through 1978–1984, concerning environmental effects due to land application of sewage sludge. This paper summarizes the essential results. In many cases, the repeated application of sewage sludge with more than 3–4 times, or the total amount exceeding 30–50 tons/ha, caused (1) unfavorable soil pH (>7.5 or <6), (2) decreased the numbers of soil microbes, (3) reduced crop yields, and (4) caused abnormal symptoms in some kinds of crop. Ground water quality also changed unfavorably in such a manner as excess nitrate concentration by the above rate of sludge application. However, soil water did not increase algal growth in the absence of PO4 3‐ and chelates (EDTA). The application of sludge stimulated the formation of N2O. It seems that no more sewage sludge should be applied after the soil is loaded by sludge three times or with total amount of 30 tons/ha.

Regression models for estimating storm runoff load and its application to Lake Kasumigaura

Regression models are proposed for accurate estimation of storm runoff load. Regression equations are obtained for the relationship between final cumulative load and flow during direct runoff by each storm event. The models are applied to estimate annual nutrients load by all influent rivers into the Lake Kasumigaura for a model year of average annual rainfall. The load in dry weather is calculated from observed data of all influent rivers. Total annual load for a year is the sum of loads in dry weather days and loads in wet weather days. The ratios of the load in a wet weather day to total annual loads are 29 percent for T‐N, 51 percent for T‐P, 53 percent for T‐COD, 22 percent for D‐N, 22 percent for D‐P and 30 percent for D‐COD.

Kinetic model of algal growth incorporating intracellular carbohydrate and phosphorus pools

A series of studies on a kinetic model of photosynthesis, nutrient ingestion, and metabolism for algal growth were conducted. Coefficients included in the proposed model were examined referring to experimental data on growth of Chlorella sp. It was shown that the proposed model can simulate the mechanism of algal growth, change of intracellular phosphorus content, change of intracellular carbohydrate content, and effects of nutrients on algal growth.