In the Fenton and photo-Fenton process, the pH value of the
solution was set at 2.6±0.1 by the addition of a H2SO4 solution
before startup, then a given weight of iron salt was added.
The iron salt was thoroughly mixed with the formaline waste
before the addition of a given volume of hydrogen peroxide. For
photo-Fenton process, the time at which the ultraviolet lamp
was turned on was considered as time zero or the beginning
of the experiment which was taking place simultaneously with
the addition of hydrogen peroxide. As presented in the literature
[23], Fenton and photo-Fenton reactions cannot occur at
pH > 10. Therefore, the reactionwas stopped instantly by adding
NaOH to the reaction mixtures and quenched by adding Na2SO3
to remove H2O2 before analysis. During the experiments, samples
were withdrawn from the reactor at several time intervals
for analysis.