Abstract
The effect of water circulation on the treated water quality of Johkasou was evaluated through cluster and principal component analyses of the measurement results for three Johkasou units that had different usage conditions (the ratio of the practical to the designed number of users being 0.8, 0.14 and 0.29, respectively). Water circulation promoted denitrification, leading to decreases in the concentration of total nitrogen in the water after treatment; however, it did not bring about observable changes for the removal of BOD. Cluster and principal component analyses showed that all water quality indices could be classified into two groups relating to the organic loadings and nitrification-nitrification, respectively. Statistically weak correlation revealed between these two groups suggests that water circulation is effective for the removal of nitrogen; however, for the removal of BOD, different approaches are necessary.
