Tsuno Hiroshi

Mathematical models are developed to evaluate treatment performance in a pre-precipitation and biofilm process which is operated for phosphorus removal and nitrification as well as BOD removal. The biofilm process is a fluidized medium reactor with polyurethane foam. Treatment performance is also evaluated by fractionation method, in which pollutants are separated by particle size with filters (pore size; 105, 1.0 and 0.1 micro-meter). A distribution matrix model is developed to show the change in distribution pattern and concentration of each particle size through precipitation and sedimentation. A mathematical model developed for biofilm reactor, which can simulate the competition between autotrophic and heterotrophic bacteria with respect to attached surface of the medium, is demonstrated to predict the treatment performance (BOD removal and nitrification) by comparing the simulated results with experimental results. With these models, the pre-precipitation and biofilm process is evaluated with respect to hydraulic retention time and recovery of organic sludge by comparing with primary sedimentation and biofilm process. As a result, it is shown to shorten the hydraulic retention time and increase the organic recovery effectively.

Biological nitrification can be inhibited by free NH₃ in wastewater containing high concentrated ammonium. Bio-zeolite reactor is developed in this study. It is a combined physical and biological reactor, in which zeolite is used as both adsorbent of ammonia and attached growth medium for nitrifier. In this reactor, concentration of ammonium nitrogen is kept by ion-exchange under the threshold level which causes the inhibition, and the ammonium nitrogen is nitrified by bacteria grown on the medium (zeolite). It is experimentally shown that ion-exchange and biological nitrification mechanisms occur concurrently, and that adsorption of ammonium nitrogen prevails when its load is larger than the nitrification activity. However, adsorbed ammonium nitrogen is released and nitrified after sufficient growth of nitrifier on the medium, then ion-exchanging capacity of zeolite is regenerated. Thus, stable removal of high concentrated ammonium nitrogen can be obtained, and successful response to stepwise shock loading is also shown without any serious increase of concentration of ammonium nitrogen. Ammonium-nitrogen loading per unit weight of zeolite is shown to be an important design parameter of this reactor, and more than 90% removal of ammonium nitrogen can be accomplished until the loading is increased to 0.15mgN/(g-zeolite·h).

Ammonium nitrogen is a principal material of concern in treated water discharge. Applicability of completely mixed series reactor with polyurethane foam cubes as attached medium to municipal sewage treatment for BOD removal and nitrification was experimentally examined. Nitrifier grew preferably on the polyurethane foam cubes, and its nitrifying activity reached 0.33 (mg N/hr.cube) for the cubes of 8 cm3. BOD removal was completed in 4 hours, and then nitrification began to occur and was completed in 10 hours under the condition of temperature as low as 15 degrees centigrade. The heterotrophic bacteria and nitrifier grew separately in the different cells of the reactor. Nitrification activity was inhibited by some organics included in the influent. The effect of inhibition was severer with increasing DOC.

Fluidized-bed granular activated carbon (GAC) anaerobic reactors have been under development to treat wastewaters which contain high concentration of inhibitory and/or refractory compounds as well as easily biodegradable organic compounds. The processes are characterized by the combined physical and biological removal mechanisms ; that is, adsorption by the GAC medium and biodegradation by the attached bacteria on the medium. A simple mathematical model, which incorporates these two mechanisms and was developed for the artificial waste-water containing 3-ethylphenol and acetic acid, was applied to the simulation of the gasification wastewater treatment after a little modification. The values of constants and coefficients included in the model equations were estimated with values obtained for the artificial wastewater and the experimental data for one case of three cases of the experiment simulated. It was demonstrated that the modified simple model is able to simulate the changes with time in effluent soluble COD, COD retained in the GAC medium and daily methane production under different operational conditions. And qualitative and quantitative relationships between each state variables and predominant mechanisms under each operational condition were discussed through the comparison between experimental data and simulated results.

Design and operational strategies for the coal gasification wastewater treatment with the fluidized-bed granular activated carbon (GAC) anaerobic reactor were discussed with the mathematical model presented. Equations which show the relationships at steady state between treatment performance and operational parameters, such as specific GAC replacement rate, GAC medium mass per reactor volume, superficial hydraulic retention time, influent COD loading, and strength of the wastewater. Critical and optimum growth conditions of the bacteria degrading inhibitory organics were also discussed and operational range of specific GAC replacement rate was determined for supporting the bacterial growth. Stability of the process against the step-increase and step-decrease in the wastewater strength was also discussed with x_A-x_H relation figure and trajectories on the x_A-x_H phase plane.

Fluidized-bed granular activated carbon (GAC) anaerobic reactors have been under development to treat wastewaters which contain high concentration of inhibitory and/or refractory compounds as well as easily biodegradable organic compounds. The processes are characterized by the combined physical and biological removal mechanisms ; that is, adsorption by the GAC medium and biodegradation by the attached bacteria on the medium. A simple mathematical model, which incorporates these two mechanisms and was developed for the artificial waste-water containing 3-ethylphenol and acetic acid, was applied to the simulation of the gasification wastewater treatment after a little modification. The values of constants and coefficients included in the model equations were estimated with values obtained for the artificial wastewater and the experimental data for one case of three cases of the experiment simulated. It was demonstrated that the modified simple model is able to simulate the changes with time in effluent soluble COD, COD retained in the GAC medium and daily methane production under different operational conditions. And qualitative and quantitative relationships between each state variables and predominant mechanisms under each operational condition were discussed through the comparison between experimental data and simulated results.