2013 年 1 巻 1 号 p. 111-124
The ability of a gas dissolving device to improve the DO condition of water is evaluated using the oxygen transfer rate. Usually the oxygen transfer rate is measured in mixing-type treatment, where air bubbles are released in the water tank. This method, however, has some disadvantages, such as that it cannot be used for compressed-type gas dissolving devices and that it requires the evaluation of the overall gas transfer coefficient. The present study proposes a convenient method of evaluating the oxygen transfer rate which is applicable to gas dissolving devices of both compressed and pressure-free types, applicable to water with an arbitrary DO concentration, and does not require the evaluation of the overall gas transfer coefficient. Evaluation of DO improvement is done using the equivalent DO increment, devised to eliminate the influence of the DO concentration of the water before treatment. The value of the oxygen transfer rate is represented as the value at a temperature of 20 degrees Celsius. Laboratory experiments to check the method have shown that the proposed method of measurement is valid.
