## 3 Results and Discussion
### Characteristic Indicators of RBC Failure  
Since the failures were considered to be caused by mechanical aging, the relationship between power consumption and failure in the rotating disk devices was examined, as shown in Figure 5. The figure illustrates the power consumption and operational status of rotating disk device No. 1 and No. 2, which are installed in parallel. Figure 4: Long-term trends in climate and leachate quality at the landfill site. This figure shows the temporal variation in rainfall, atmospheric temperature, influent leachate temperature, pH, and transparency from 2006 to 2023, indicating the relative stability of influent conditions. In the fifth figure, the plots are colored depending on leachate clarity. Since the rotating disk devices operate under constant voltage conditions, an increase in power consumption indicates an increase in load. This is because the torque required to rotate the disks increases due to factors such as mechanical wear, reduced lubrication between components, and increased disk weight resulting from long-term alternating exposure to air and leachate, which leads to calcium precipitation. Therefore, power consumption serves as a relevant parameter related to the failure of rotating disk devices. In particular, a rising trend in power consumption is often associated with the occurrence of abnormal noise, followed in some cases by eventual failure. Figure 4(a) shows the time-series variation in current (top) and operational status (bottom) of the RBC No. 1 over a 17-year period. The blue-shaded area in the top panel  
Figure 5: Relationship between electrical current and RBC behavior. **(a,b)** Time series plots of electrical current for rotating disk devices No. 1 and No. 2, respectively. The blue area indicates normal operation (1.8–2.2 A), while the red area indicates sudden increases in current or expansion of current fluctuations, which often precede abnormal noise or malfunctions. represents the normal operating current range (1.8-2.2 A). Notable events are highlighted with red arrows. The arrows labeled #1-1 and #1-2 indicate periods of sudden current increase, which preceded failure events and were also accompanied by abnormal noise. The arrow labeled #1-3 marks a prolonged period where the current remained consistently above the normal range, even though no abnormal noise was reported. The bottom panel categorizes the operational status based on daily inspection logs into four classes: \"Standby\", \"Normal\", \"Noise\", and \"Failure\". The red-shaded bands correspond to failure periods, showing clear alignment with anomalies in current values. These observations suggest that sudden increases in current and high current levels can serve as effective early indicators of potential mechanical failure, even in the absence of abnormal noise. Figure 5b presents the time-series variation in current (top) and operational status (bottom) of RBC No. 2 over a 17-year period. The arrows labeled #2-1 and #2-2 indicate periods of sudden current increase, both of which were followed by the occurrence of abnormal noise and equipment failure. In contrast, the arrows labeled #2-3 represents a period where the fluctuation amplitude of the current increased significantly, despite remaining within the normal range. The fluctuation amplitude of the current suggests potential instability in the rotational load and serves as an effective early indicator. When the fluctuation exceeds 0.3 A as shown in the arrows labeled #2-3, it can be regarded as an early warning sign of failure. In fact, no previous studies have monitored RBC maintenance information over the long term. However, it is well known that current consumption increases with the rotation speed of the disk [6]. Considering that an increase in self-weight due to scale precipitation on the rotating disk and a decrease in shaft lubricity may increase the torque required for rotation, an increase in the current consumption can be considered an indicator of mechanical service life.