## 3 Results and Discussion
### Statistical Analysis
#### 3.2.2 Regression Models: Generation, Calibration and Analysis of Variance
The active compounds of the deshelled _Carica papaya_ seeds coagulant extract filled with surface  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Term**} & **Turbidity Removal** & **Coagulation Activity** \\ \cline{2-3}  & \(p\)**-Value** & \(p\)**-Value** \\ \hline A: Dosage & 0.0005 & 0.0014 \\ B: pH & \textless{}0.0001 & 0.0114 \\ C: Initial turbidity & \textless{}0.0001 & \textless{}0.0001 \\ A \(\times\) B & 0.0015 & 0.0035 \\ A \(\times\) C & 0.0001 & 0.0003 \\ B \(\times\) C & 0.0233 & 0.0400 \\ A \(\times\) A & 0.5013 & 0.0575 \\ B \(\times\) B & \textless{}0.0001 & 0.4608 \\ C \(\times\) C & 0.2898 & 0.0010 \\ A \(\charges explains the strong effect of pH on coagulation activity, which influences the interaction of bio-coagulant with the suspended particles [41; 42]. In combination of the dosage and pH variables, the turbidity removal was increased to the maximum value of 71%. The response surface of turbidity removal as a function of deshelled _Carica papaya_ dosage and initial turbidity is shown in Figure 4b. The surface plot illustrated the effect of wide range of bio-coagulant dosage and initial turbidity at fixed pH of 5.3. It can be seen at low dosage of 50 mg/L, an increase in initial turbidity showed a gradual increment of turbidity removal from about 2.7% to 12.0%. Contrarily, as shown in Figure 4b, the turbidity removal was positive in response to increasing dosage of the deshelled _Carica papaya_ seeds when treating 500 NTU initial turbidity of the synthetic water. However, the highest removal was not observed at the maximum dosage studied, which means that by increasing the dosage is viable up to approximately 160 mg/L. An excess of coagulant above this value causes colloidal particles to stabilize, raising the residual turbidity thus, reducing the turbidity removal. In conjunction with these two variables viz. dosage and initial turbidity, the turbidity removal was able to reach up to 67% at 160 mg/L dosage and the initial turbidity of 500 NTU. Contradictory observation on turbidity removal was shown between the interaction of initial turbidity and pH (Figure 4c). At low pH of 4, the turbidity removal was increased from 14.9% to nearly 100.0% when the initial turbidity was increased from 100 NTU to 500 NTU with the coagulant dosage kept constant at 125 mg/L. The similar positive trend was observed at high pH of 6.5 where the turbidity removal was increased up to 42.9%. Contrarily, at low initial turbidity of 100 NTU, the turbidity removal experienced a significant decrease when the pH was increased from 4.0 to 6.5. The same trend was observed at high initial turbidity of 500 NTU. The turbidity removal decreased from about 90.0% to 43.0% upon the increment of pH. Figure 4: Response surface of the turbidity removal as a function of (**a**) deshelled _Carica papaya_ seeds dosage and pH, (**b**) deshelled _Carica papaya_ seeds dosage and initial turbidity and (**c**) pH and initial turbidity. Figure 5a shows the response surface plots on the significant relationship between the bio-coagulant dosage and pH towards the coagulation activity at a constant initial turbidity of 300 NTU. Based on the figure, at low dosage of 50 mg/L, the coagulation activity was greatly increased as the pH decreased from 6.5 to 4.0. However, at high dosage of 200 mg/L, the change of coagulation activity showed a concave shape profile as the pH decreased from 6.5 to 4.0. This profile suggested that the coagulation activity was increased until a certain point, then it starts to decrease. Similar observation was seen when the dosage was increased. At pH 6.5, the coagulation activity was increased as the dosage increased from 50 mg/L to 200 mg/L. The coagulation activity increased gradually until the dosage reached approximately 140 mg/L. Beyond this dosage, the coagulation activity started to decrease. Restabilization of colloidal particles may take place at this moment, which in turn resulted in low efficiency of coagulation activity.