3.3. The roles of oxidation and coagulation
The typical Fenton wastewater treatment process includes four
stages: pH adjustment, oxidation, neutralization and coagulation,
as well as solid–liquid separation. The organics are removed by
both oxidation and coagulation [3]. The perturbation plots (Fig. 3)
showedthat initialpHsignificantly influenced importance of oxidation
relative to coagulation [3], where the effects of all the factors
at the center point in the design space are compared. Except for
the interaction term X2X3, the other linear terms (X1, X2 and X3),
quadratic terms (X1
2, X2
2 and X3
2) and the interaction terms (X1X2
and X1X3) were statistically significant for oxidation COD removal
(Table 3). The addition of H2O2 (X2) had an expected linear positive