generating more and more OH radicals which remove the dye
by degrading it into smaller molecules (Fu et al., 2010). However,
removal efficiency would decrease when Fe2+ addition
was higher than 3 mg L1. It can be seen from Fig. 3 that
the optimal dosage was 3 mg L1 of Fe2+ (73% color and
32.5% COD removal). This is possibly due to the reaction
leading to the Fe2+ and OH recombination. Therefore, the
oxidation of organic pollutants was hindered at high Fe2+
concentration (Li et al., 2009).
Fe2þ þ OH ! Fe3þ þ HO