In order to make Fe particles and air play the role in removal pollutants
in refinery wastewater simultaneously, both Fe particles and air
were introduced in the electrochemical process in primary wastewater
condition (EC + Fe + Air) and about 3 of the pH value after adjusted
(EC + Fe + Air + pH 3), respectively. It is clear from Fig. 2 that the
COD value reduced continuously to 777.3 mg L−1, and 83.65% of COD
removal was reached after 60 min treatment in the EC+Fe+Air process.
High COD removal in the EC+Fe+Air process can be ascribed to
the cooperative action of efficient GDEs and three-dimensional electrodes
of high specific surface area. At present, the test results showed
that the concentration of H2O2 is 136.4 mg L−1. Furthermore, reasonable
current densities were electrogenerated and large numbers of the
mass transfer coefficients of the injected air in this process increased
the removal rate of pollutants. Nevertheless, the COD value of refinery
wastewater in the EC + Fe + Air process cannot reach grade III
(500 mg L−1) of wastewater discharge standards in fact [32].
While the COD decreased notably in the first 10min, it thendecreased
to 479.4mg L−1 slowly in the following 50 min in the EC+Fe+Air+pH
3 process. The largest COD removal of about 89.91% in Fig. 2 might be
attributed not only to the cooperative action of efficient GDEs and
three-dimensional electrodes, but also to the formation of •OH, a very
powerful oxidizing agent. The addition of Fe particles is oxidized to
Fe2+ at the anode (Eq. (6)), and about 184 mg L−1 of H2O2 is generated
at the cathode from O2 in the injected air during the electrochemical reaction
process according to the electrode potentials (Eq. (7)), then the