Fig. 1(m) and (n) shows that an increase in H2O2/Fe2+ molar ratio and H2O2/PW (ml/l) improves the color removal. According to Fig. 2(c), (d), (m) and (n), an increase in H2O2/Fe2+ molar ratio (2.8 and 4.1 for COD and color removals, respectively) and H2O2/PW (1.53 ml/l and 1.73 ml/l for COD and color removals, respectively) decreases the removal efficiency. As illustrated in Table 5, the optimum H2O2/PW (ml/l) and H2O2/Fe2+ molar ratio are 2.14 and 4.99, respectively in the EF-Al. These data are 1.23 and 3.65 in the EF-Fe. These results are in good agreement with the literature. This may be due to that Fenton’s reaction mechanisms would change and some side reactions would occur. It seems that excessive hydrogen peroxide has a scavenging effect on hydroxyl radicals (Eq. (11)):