3.2. Fenton and photo-Fenton processes
In this step the degradation of formaldehyde and methanol
in formaline waste was explored by means of the very reactive
and oxidizing hydroxyl radicals generated by the Fenton and
photo-Fenton processes.
In order to evaluate the effect of UV light on the degradation
of formaldehyde and methanol, Fenton and photo-Fenton
processes were compared at different concentrations of Fe2+
(6.67 × 10−3, 2.27 × 10−2 and 6.67 × 10−2 M). Initial concentration
of 0.667 M of H2O2 was chosen as the initial conditions.
As seen in Fig. 2(a and b), the removal efficiency of formaldehyde
and methanol treated by the photo-Fenton process was
higher than that by the Fenton process. Results indicated that
the Fe2+ efficiency of the photo-Fenton process with 10 W of
UV light was larger than that of the Fenton process at the same
concentration of Fe2+.
From this experiment set, the degradation of both formaldehyde
and methanol with Fenton process is the results of the
reactions between ferrous ion and hydrogen peroxide. Several
reactions can take place in degradation of formaldehyde and
methanol. However, the mechanisms of these reactions in Fenton’s
process are not yet completely clear and there is much
disagreement in the literature on the exact intermediates that
form including whether or not the hydroxyl radical itself forms
[14,16,17,25]. More recent studies have confirmed the existence
of the ferryl ion (FeVIO2+) as an intermediate and shown evidence
that disfavours the hydroxyl radical as an intermediate