As for the EC + Air process, the air was pressed into the electrochemical
process by gas compressor, which strengthens the agitation
and the mass transfer in the electrochemical treatment process, then
many pollutants can easily disperse around the electrode to oxidize directly
and strip out from the wastewater like air stripping technique in
industry. Furthermore, gas diffusion electrodes (GDEs) could also be
formed because O2 in the injected air has poor solubility in aqueous solutions,
and it is first dissolved in the aqueous phase and further transferred
from the bulk to the cathodic surface, which resulted in oxygen
gas being reduced to HO2
−, the conjugate base of H2O2 (Eq. (5)), and
then giving large accumulation of H2O2 about 97.5 mg L−1 since the
acid–base equilibrium between HO2
− and H2O2 has a pKa = 11.64
[16,28]. GDEs possess a large number of active surface sites leading to
a very fast O2 reduction to H2O2, so that some of the harmful substances
in the water can be removed [29,30]. However, the COD value was reduced
to only 1050 mg L−1, and only 77.91% of the COD removal was
reached after 60 min treatment, this is because H2O2 alone is a weak oxidant
in advanced oxidation processes (AOPs) of wastewater treatment,
it is only effective for attacking reduced sulfur compounds, cyanides,
and certain organics such as aldehydes, formic acid, and some nitroorganic
and sulfoorganic compounds [31].