The primary purpose of this research was to assess the applicability of the cascade aerator in a passive treatment system for ferruginous mine drainages to increase efficiency and reduce the size of the passive treatment system. Two experiments of different aeration methods were executed: the air diffuser experiment and the cascade aerator experiment. Through the air diffuser experiment, it was verified that the main mechanisms that occur in the mine drainage were gas exchanges with the atmosphere, Fe(II) oxidation and subsequent precipitation. Aeration from the air diffuser accelerated the increase in DO and prompted the decrease in CO 2 , where the latter affected the eventual increase in pH level. Together with the increase in DO and pH, it can be concluded that the aeration has a clear effect on boosting the oxidation rate of Fe(II). The predictive model which was proposed in this research proved its applicability by reasonably estimating the changes in water qualities of the mine drainage. The aeration efficiency by the cascade aerator was chiefly influenced by drop height of the mine drainage, not by water qualities or depths of plunge pools. Various Fe(II) oxidation rates by the different heights of cascade aerator could be estimated by the predictive model using only initial water qualities and rate constants. Through series of experiments it is suggested that in a passive treatment system, a cascade aerator with even a relatively slight elevation of one step (70 cm) can effectively boost the Fe(II) oxidation rate of mine drainages of net alkaline.

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This research focused on the optimum design of a cascade aerator to enhance the efficiency of an oxidation pond in a passive treatment system for remediating ferruginous mine drainage. For this purpose, various aeration experiments with aerators of different drop heights (0-4 m) and formations (types A and B) were executed on mine drainage. Type A simply drops the mine drainage into the oxidation pond while type B sprays the mine drainage and retains it for 8 min in each step. The efficiency enhancement of the oxidation pond was strongly dependent on the increase in pH and DO of the mine drainage discharged into the pond. The water quality improved with the increase in drop height but especially showed better effect with type B. The reasons for this result were attributed to the increase of contact surface and retention time of the mine drainage. The cascade aerator, therefore, should be designed to be as high as possible with the assistance of spraying form and retention time of the mine drainage to maximize the efficiency of the oxidation pond. These effects could be evaluated by calculating required areas of the oxidation pond for 95% of Fe(2+) oxidation.

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