## 3 Results
### Rainfall's Impact on Influent and Effluent Wastewater Parameters  
The seasonal variations in rainfall directly influenced the influent concentrations of various wastewater parameters, while the effluent quality remained consistently within the regulatory limits illustrated in Figure 5,b. This section analyzed the impact of the rainfall on each parameter for both the influent and effluent stages.. The influent pH displayed minimal variation, ranging narrowly from 7.58 during October (1.74 mm rainfall) to 7.79 in December (1.60 mm rainfall). This consistency indicates that the rainfall had a negligible impact on the pH of the incoming wastewater, likely due to the influent's buffering capacity. Similarly, the effluent pH remained stable, ranging from 7.55 in November (3.67 mm rainfall) to 7.90 in August (3.34 mm rainfall). These results demonstrate the treatment process's ability to maintain optimal pH levels irrespective of rainfall-induced variations. The total phosphorus concentrations in the influent varied seasonally, with higher values being observed during drier months, such as 4.36 mg/L in December (1.60 mm rainfall), and lower values during wetter months, like 2.76 mg/L in June (4.12 mm rainfall). This pattern suggests that reduced rainfall limits dilution, leading to higher phosphorus concentrations. The effluent phosphorus levels, however, remained low and consistent, ranging from 0.19 mg/L in September (6.18 mm rainfall) to 0.47 mg/L in August (3.34 mm rainfall), reflecting the treatment system's effectiveness in removing phosphorus regardless of the seasonal rainfall variability. The influent chemical oxygen demand (COD) levels also showed an inverse relationship with the rainfall, peaking at 507 mg/L during December's dry period (1.60 mm rainfall) and decreasing to 361.19 mg/L in the wetter month of June (4.12 mm rainfall). These results indicate that organic pollutants in the influent were more concentrated during periods of lower rainfall. The effluent COD concentrations remained low throughout the year, ranging from 16.06 mg/L in August (3.34 mm rainfall) to 22.76 mg/L in December (1.60 mm rainfall), underscoring the system's high efficiency in COD removal under varying conditions. Figure 5: Wastewater parameters in the influent (In) and effluent (Out) with respect to rainfall. (a) Rain impacts on BOD, TSSs, N Total, (b) rain impacts on pH, P Tot, COD. The biochemical oxygen demand (BOD\({}_{5}\)) in the influent displayed a seasonal trend similar to that of the COD, with higher values being observed in drier months (278.43 mg/L in December at 1.60 mm rainfall) and lower concentrations in wetter periods (190.24 mg/L in June at 4.12 mm rainfall). This pattern reflects reduced dilution during low-rainfall periods. The effluent BOD\({}_{5}\) levels, however, were consistently low and well-controlled, ranging from 2.48 mg/L in December (1.60 mm rainfall) to 3.57 mg/L in October (1.74 mm rainfall), demonstrating the system's effectiveness in meeting regulatory requirements. The influent total suspended solids (TSSs) followed an inverse relationship with the rainfall, with higher concentrations being observed in drier months (194 mg/L in December at 1.60 mm rainfall) and lower levels in wetter months (154.24 mg/L in June at 4.12 mm rainfall). Rainfall appears to dilute suspended solids in the influent. The effluent TSS concentrations were consistently low, ranging from 2.19 mg/L in May (4.74 mm rainfall) to 3.50 mg/L in July (8.00 mm rainfall), indicating the treatment system's robustness in removing suspended solids across all rainfall conditions. The influent total nitrogen concentrations were higher during drier periods, such as the 39.86 mg/L seen in December (1.60 mm rainfall), and lower during wetter months, with 26.49 mg/L in June (4.12 mm rainfall). This trend suggests that reduced rainfall concentrates nitrogenous pollutants in the influent.