Tetsuo Takakuwa

An improved Richardson-Zaki formula for computing mixed layer composition in binary solid-liquid fluidized beds

In a liquid fluidized bed consisting of binary solid particles differing in size and density, the mixing of the two kinds of particles occurs and the degree of mixing is controlled by an equilibrium force balance relationship. A model to predict the volume fractions of particles in the mixed layer is developed in this paper on the basis of the force balance relationship of each particle species. In describing the drag forces of particle components 1 and 2 in a mixed layer, two hypothetical mono-component beds, bed (1∗) and bed (2∗), are introduced. The bed (i∗) (i=1,2) consists of only one particle component i, and it is assumed that the drag force acting on the particle component i in this bed is equal to that acting on component i in the mixed layer. This assumption, coupled with the Richardson and Zaki formula, leads to a modified Richardson and Zaki formula for computing the composition of the mixed layer in a binary solid-liquid fluidized bed. The validity of this model is tested against experimental data.

A minimal potential energy model for predicting stratification pattern in binary and ternary solid-liquid fluidized beds

Predicting the stratification pattern of a binary or ternary solid-liquid fluidized bed requires not only the calculation of the volume fractions of particles in mixed and mono-component layers but also the specification of the order and the thickness of the layers in the bed. A model was developed for such prediction on the hypothesis that the total potential energy of particles in a bed is minimal. Experiments were carried out for a solid system consisting of glass beads, activated carbon and acrylic particles. The experimental results verified the predicted stratification patterns computed on the basis of the hypothesis adopted in this study.

Simulation of the operational conditions of the full-scale municipal wastewater treatment plant to improve the performance of nutrient removal

Simulation analysis based on a mathematical model is one of the powerful tools for determining the operational conditions for a full scale biological nutrient removal plant. The model that included the Activated Sludge Model No.2 was developed for simulating the performance of the plant in Sapporo City. The investigated plant has the biological reaction basin which consists of the four zones, anaerobicaerobic-anoxic-aerobic phases with the step feed of the primary effluent to the anaerobic and anoxic zones. We performed three experiments to calibrate and verifY our model: (i) Characterization of organic matters in the influent with the OUR test; (ii) Measurement of COD and nutrient concentration at the plant; (iii) Lab-scale batch experiments with the anaerobic-aerobic-anoxic-aerobic phases. The calibrating process showed that no modification of parameter values was required to evaluate the performance and population of the activated sludge. Simulated results showed that the choice of the sewage step feed ratio did not affect the nitrogen removal and that the denitrification rate in the anoxic zone was controlled by the hydrolysis rate of the slowly biodegradable organic matters. The results of the lab-scale experiment and simulation showed that the addition of the readily biodegradable organic matters like fermentation products of the primary settler sludge was effective to improve the performance of nitrogen removal.

Organic matter released from activated sludge bacteria cells during their decay process

Organic matter released from activated sludge bacteria is a considerable issue in the wastewater reclamation process. In this study, we focused 2-keto-3-deoxyoctulosonic acid in the Lipopolysaccharide existed in the gram-negative bacterial cell wall as an index of organic matter released from bacteria, and investigated the fate of 2-keto-3-deoxyoctulosonic acid in the aerated and ultrasonicated activated sludge samples. The results shows 1) 2-keto-3-deoxyoctulosonic acid concentration in the hydrolyzed sample was higher than non-hydrolyzed sample, and this implied that 2-keto-3-deoxyoctulosonic acid existed in the water phase as a monomer and also as a polymer such as Lipopolysaccharide form and their fragments; 2) the value of (2-keto-3-deoxyoctulosonic acid)/(dissolved organic carbon) ratio did not change in the sludge sonication process and was approximately 0.0006, on the other hand, in the bacteria decay process, the ratio varied from zero to approximately 0.0012; 3) the linear relationship was observed between the degraded heterotrophic biomass and the generated 2-keto-3- deoxyoctulosonic acid; and 4) 2-keto-3-deoxyoctulosonic acid might be considered as an index of organic matter originated from activated sludge bacteria cell.