## 3 Results
### Impact of Rainfall on WWTP Efficiency  
Figure 7 illustrates the monthly rainfall and efficiencies of the wastewater treatment plant parameters.  
The phosphorus removal efficiency showed slight fluctuations corresponding to the rainfall patterns. During months with higher rainfall, such as July (8.00 mm) and May (4.74 mm), the phosphorus removal efficiency ranged between 86% and 94%. In months with lower rainfall, such as October (1.74 mm) and December (1.60 mm), slightly higher phosphorus removal efficiencies of 94% and 93%, respectively, were observed. This indicates that increased rainfall does not significantly compromise phosphorus removal, though minor variations occur during rainfall extremes.  
The COD removal efficiency remained stable across varying rainfall conditions, with the WWTP consistently achieving high efficiencies. For example, in months of higher rainfall, such as May (4.74 mm) and July (8.00 mm), the efficiencies were 96% and 95%, respectively. Similarly, months with lower rainfall, like October (1.74 mm) and December (1.60 mm), also maintained a COD removal efficiency of 96%. These results demonstrate that COD removal is not highly sensitive to seasonal rainfall changes, reflecting the robustness of the treatment system.  
Figure 6: Monthly temperature and efficiency of wastewater treatment plant parameters.  
The BOD removal efficiency was consistently high throughout the year, remaining above 95% irrespective of the rainfall levels. In higher rainfall months, such as July (8.00 mm) and September (6.18 mm), the BOD removal efficiency ranged from 98% to 99%. During lower rainfall months, like October (1.74 mm) and December (1.60 mm), the efficiencies were similarly high, reaching 98% and 99%. This consistent performance indicates that the BOD removal is effective regardless of rainfall variations.  
The TSSs removal efficiency was also unaffected by changes in the rainfall, maintaining a high efficiency at or above 98% throughout the year. For instance, during higher rainfall months, such as May (4.74 mm) and September (6.18 mm), the TSSs removal efficiencies were 98% and 99%, respectively. In lower rainfall months, such as October (1.74 mm) and December (1.60 mm), the efficiencies remained at 98%. This demonstrates the resilience of the treatment process in managing suspended solids under varying rainfall conditions.  
The nitrogen removal efficiency exhibited a more noticeable sensitivity to rainfall variations. During months with higher rainfall, such as July (8.00 mm) and May (4.74 mm), the nitrogen removal efficiency was slightly lower, ranging between 75% and 77%. In contrast, months with lower rainfall, such as October (1.74 mm) and December (1.60 mm), showed higher nitrogen removal efficiencies from 80% to 81%. This trend suggests that reduced rainfall may improve nitrogen removal, possibly due to higher influent nitrogen concentrations during drier conditions.  
The ammonium removal efficiency remained consistently at 100% across all months, irrespective of the rainfall. Both higher rainfall months, such as July (8.00 mm) and September (6.18 mm), and lower rainfall months, like October (1.74 mm) and December (1.60 mm), demonstrated no significant variation in ammonia removal efficiency. This underscores the robustness of the ammonia removal process, which operates effectively and independently of seasonal rainfall patterns.  
In summary, while the rainfall showed minor impacts on the removal efficiencies of phosphorus and nitrogen, other parameters, including the removal efficiencies of COD, BOD, TSSs, and ammonium, remained largely unaffected. The WWTP demonstrated high resilience and consistent performance across varying rainfall conditions.