Abstract
The biochemical oxygen demand（BOD）and water temperature data of treated water of Johkasou were obtained by the legal inspection of Johkasou located at 160,000 sites in total. These inspections were carried out in each inspection month, and data were collected, tallied, and then analyzed. The results revealed that the water temperature observed at the time of inspection did not affect the average BOD. Instead, a highly linear correlation was observed, indicating that the average water temperature in 4-5 months until the inspection (which lies in the range 11-25 °C) affects the BOD of treatment water. This signifies that the condition of Johkasou observed at a specific time is affected by the cumulative effects of water temperature from a certain time in the past to the time of observation. Furthermore, although earlier inspections of Johkasou have shown that the BOD of treatment water was lower when the water temperature observed at the time of inspection was low, evaluating the moving-average water temperature with respect to the treatment performance of Johkasou reconfirmed that the BOD of treatment water was lower, while the average water temperature was higher, as anticipated in the past.
