Abstract
Ability of the gas dissolving device to improve the DO condition of water is evaluated by using the oxygen transfer rate. Usually the oxygen transfer rate is measured in the mixed type treatment where air bubbles are released in the water tank. This method, however, has disadvantaeges that it can not be used for the compressed type gas dissolving devices and that it requires the evaluation of the overall gas transfer coefficient, etc. 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 the water with arbitrary DO concentration, and does not require the evaluation of the overall gas transfer coefficient. Evaluation of the DO improvement is done by using the equivalent DO increment devised to eliminate the influence of the DO concentration of the water before treatement. The value of the oxygen transfer rate is represented as the value at a temperature of 20 degree celsius. Laboratory experiments to check the method have shown that the proposed method of measurement is valid.
