In order to increase the efficiency of biological treatment systems, such as purification tanks for domestic wastewater, a fluidized bed biofilm filtration process that uses open cylindrical carriers (filter media) has been studied. With this process, the authors have achieved increased efficiency in the removal of organic matter and enhanced solid-liquid separation performance.
For less than 20 mg·l^-1 BOD and less than 10 mg·l^-1 SS in the effluent, when the filling ratio for the fluidized bed part is at 45%, the BOD volumetric loading must be less than 1.4 kg BOD₅·m^-3·d^-1 and the BOD surface loading must be less than 5.7 g BOD₅·m^-2·d^-1. To estimate the average inflow pattern of domestic wastewater and with an operation where 3Q water volume is recirculated per day, the filter height must be more than 200 mm and the filtration rate must be less than 1.0 m·h^-1.
Through retail investigation of various design conditions, a fluidized bed biofilm filtration part has been designed for 5 persons and compared with the current contact aeration process. The volume of the fluidized bed part (aerobic treatment part) ranges from 0.1 to 0.25 m³ depending on the filling ratio, or 10 to 25% of the 1.0 m³ of a contact aeration tank. The biofilm filtration part, which carries out solid-liquid separation, has a volume of 0.045 - 0.1 m³, or 17 - 33% of the 0.3 m³ of a sedimentation tank.
Thus, the volume necessary for the biological treatment part plus the solid-liquid separation part has been significantly reduced, with increased efficiency. Future use of this system is therefore quite feasible.

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Wastewater containing fluoride is released by various industries. In 2001, the effluent standard for fluoride was revised from 15 to 8 mg·l^-1 in Japan. The aim of this study was to develop a simplified method for high-quality treatment of fluoride in wastewater. The calcium fluoride method is one of the conventional methods of removing fluoride from wastewater. However, the concentration of fluoride in the effluent obtained by this method has not been considered suitable based on the new effluent standard. In this paper, the effect of CO₂ in the atmosphere on the reaction between calcium ion and fluoride ion was assessed based on chemical equilibrium. It is found that CO₂ in the atmosphere interferes with fluoride removal efficiency and produces a large amount of sludge by forming calcium carbonate. In order to confirm these phenomena, experiments using real wastewater under normal and degassed conditions were carried out not only by measuring the fluoride concentration in the wastewater, but also by characterizing the properties of the formed sludge. As a result, the calcium fluoride method under degassed conditions is suggested to be a very promising method for treatment of wastewater containing fluoride from the viewpoint of minimum emission.

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A new optimization technique for establishing control setpoints for an activated sludge process based on Activated Sludge Model No.2d (ASM2d) and Genetic Algorithm (GA) has been developed. Process performance predicted by ASM2d, which was compared with the data measured at an existing wastewater treatment plant and confirmed to be sufficiently reliable, was used as the objective function in determining new setpoints by the proposed optimization technique. It has been shown that this technique can determine the combinations of good setpoints that would yield effluent nitrogen and phosphorus concentrations below 10mg-N·l^-1 and 1mg-P·l^-1, respectively. Moreover, these setpoints were found to be economically advantageous in comparison with other operational conditions. The proposed new optimization technique is expected to make significant contributions to the enhancement of biological nutrient removal in the activated sludge process.

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Phosphorus removal in water was examined using charoal made from industrial waste materials such as magnetic cards, and magnetic tapes. The efficiency of phosphorus removal by the magnetic card charcoal was two times higher than those by the magnetic tape charcoal and the activated carbon of special grade. From adsorption isotherms, the parameters, k and n^-1, in the Freundlich equation (q=kcⁿ-1) were estimated to be 12.6 mg-P·g^-1 and 0.22, respectively. The phosphorus removal mechanism will be discussed by comparing the effect of carbonization temperature (600-800°C) on phosphorus adsorption efficiency. The phosphorus removal mechanism is mainly chemical adsorption. It is considered that metallic ions on the surface of charcoal become active sites of adsorption.

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