| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1997: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1996: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
After partially freezing waste water, the upper layr of ice contains less waste as waste is naturally concentrated in the lower unfrozen layr of waste water. In this study, waste water contained in a vessel (70 mm in diameter and 210,395,580 mm deep) was frozen from the top downwards by blowing cold ambient air horizontally across the water surface in a freezing room and in outdoor conditions.
1) As the cold ambient air temperature decreased and the air velocity increased, the rate of freezing of the ice layr increased.
2) As the freezing rate increased, the COD concentration in the frozen layr increased and the purifying rate (i.e., COD concentration of frozen layr/COD concentration in waste water) increased. This is due to the fact that when the rate of freezing is too high, the waste is trapped during the ice crystallization process.
3) As the ice layr grew in thickness, the COD concentration of the newest ice also increased. As a result the COD concentration within the ice layr varied with the location within the ice layr, such that the concentration was lowest at the ice surface and increased with ice depth.
4) As wastewater vessels became deeper, the COD concentration in the same depth frozen layr decreased and the purifying rate increased with the depth of the vessels. This is due to the fact that the deeper the vessel, the harder it is for the freezing ice layr to trap waste and the easier it is for waste to escape.
5) Based on the results of this experiment, we were able to develop a predictive equation that relates the COD concentration in the ice layr to the known ambient cold air temperature, the air velocity and the freezing rate. This equation could apply to outdoor condition use.
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