Coagulation of Humic Water with Fenton Reagent

Abstract

An iron (II) and hydrogen peroxide mixture, also called ‘Fenton’s reagent’, produces an extremely strong oxidizing agent the hydroxyl radical OH●. Recent publications by several authors have shown that use of Fenton’s reagent could be considered for use in water treatment, due to its very effective oxidation of specific organic substances like pesticides. Another advantage of Fenton’s reagent is that it does not produce bromates. Iron (III), which is the other reaction product of Fenton’s reagent, could certainly act as coagulant in the treated water.

There are some differences between coagulation with Fe³⁺ and that with Fenton’s reagent. Optimal dose of iron in the case of Fenton’s reagent depends on interactions between the alkalinity (pH) and H₂O₂/Fe²⁺ ratio. For the same concentration of humic substances in model humic water (5 mg/l of HS) the optimal dose varied from 40 μmol/l to 110 μmol/l of Fe, depending on the other variables. Residual colour, residual UV absorbance (254 nm) and residual iron also depend on interactions between initial alkalinity, coagulation pH, iron dose, and H₂O₂/Fe²⁺ ratio. No values of optimal pH or iron dose can be given or recommended as guide values at this time. It seems that optimal iron doses are lower when Fenton’s reagent is used rather than iron (III). The H₂O₂/Fe²⁺ ratio should not drop below 0.5 but, on the other hand, there is only a slight improvement when it exceeds 0.5.