| This study has been performed to investigate influence of the change of recycle ratio on phosphorus removal in ASA(Advanced Step Aeration) system. Results have it that : as results of experiments with recycle ratios of 0.3Q, 0.5Q and 1.0Q and 10 days of fixed sludge retention time. SS removal efficiencies were stable over 90% in all conditions. COD and BOD removal efficiencies with recycle ratios of 0.3Q and 0.5Q were almost the same over 90% but in recycle ratio of 1.0Q COD and BOD removal efficiencies were reduced to the range from 87 percent to 88 percent. NO₃-N removals in the anoxic sludge tank with recycle ratios of 0.3Q, 0.5Q and 1.0Q were 94.3%, 93.7 and 87.7, respectively, therefore, in the recycle ratio of 0.3Q the highest removal efficiency was revealed. In condition of the recycle ratio of 0.3Q Anoxic sludge tank minimized the nitrite and nitrate inhibition in the return activated sludge and maximized phosphorus release through the stable DO control. In C/P ratio of 19 : 1 phosphorus release rate(K_(PR)) in the anaerobic tank with the recycle ratio of 0.3Q was 2.89㎎P/gMLSS·hr and in the recycle ratios of 0.5Q and 1.0Q phosphorus release rate(K_(PR)) could be shown as 2.69㎎P/gMLSS·hr and 1.80㎎P/gMLSS·hr, respectively. Phosphorus uptake rates(K_(PU)) in the aerobic tank could be described as 1.42㎎P/gMLSS·hr in the recycle ratio of 0.3Q, 1.37㎎P/gMLSS·hr in the recycle ratio of 0.5Q and 1.15㎎P/gMLSS·hr in the recycle ratio of 1.0Q, respectively. As a result of, the very highest phosphorus release rate(K_(PR)) and phosphorus uptake rates(K_(PU)) were revealed in the recycle ratio of 0.3Q. Phosphorus removal efficiencies in ASA system according to recycle ratios were 83.9 percent in the recycle ratio of 0.3Q, 80.5 percent in the recycle ratio of 0.5Q and 71 percent in the recycle ratio of 1.0Q, respectively. Conclusively, it is recommended that the recycle ratio of 0.3Q be maintained to ensure effective phosphorus removal in ASA system. |
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