also shows the COD change at different dosage of active
carbon. Since the waste iron contained Fe and C, they would be
considered as many microcosmic electrodes in the reaction system.
It was found that COD could be reduced when active carbon
was not added. With the addition of active carbon, the reaction of
macroscopical electrodes increased the COD removal efficiency.
In Fig. 4, it is clear that there was a rising trend of COD removal
efficiency with the addition of active carbon. However, as in the
addition of iron, there was no obvious enhancement with further
increase of the active carbon. When the active carbon dosage
was at 10, 15 and 20 g/L, the COD removal efficiencies were
30.9, 33.3 and 35.1%, respectively. Taking both the treatment
effect and cost into consideration, 30 g/L of iron and 10 g/L of
active carbon would be the optimal dosage condition.
and 50 g/L. After 240 min, COD removal efficiency remained
at about 32.0%. It could be concluded there was a transition in
ZVI process between the iron dosage of 20 and 30 g/L. Since an
excess amount of iron would affect the mass transfer efficiency,
30 g/L would be an appropriate dosage. In all batch experiments,
flocs in the sample taken from the reaction system increased
obviously with longer reaction time. The flocs, which were produced
due to the iron corrosion, were brown. With the mixing
and oxidation by aeration, more Fe3+ hydroxides were formed
in the system, which could act as effective coagulant.