1.5. Treatment via adsorption and ultraviolet radiation
Recently, more innovative methods have been directed
toward the treatment of oily wastewater. For example,
Sokker et al. (2011) investigated the adsorption of crude oil
with an initial concentration of 0.5–30 g/L by a hydrogel of
chitosan-based polyacrylamide prepared by radiationinduced
graft polymerization. Their results showed that the
hydrogel, which was prepared at a concentration of 40%
acrylamide and at a radiation dose of 5 kGy, showed high
efficiency in removal of crude oil of 2.3 g/g at pH 3. A new
cotton-based hydrogel nanocomposite was successfully prepared
by free-radical graft copolymerization of acrylamide
and acrylonitrile onto fabric followed by insertion of Ag
nanoparticles, by Hosseinzadeh and Mohammadi (2014). The
resulting nanocomposite exhibited superhydrophilic and
superhydrophobic properties, and the pH of zero point charge
of the hydrogel nanocomposite was 6.5. Li et al. (2012) studied
the use of biosurfactants in controlling bubble behavior in the
flotation method instead of chemosynthetic surfactants.
They verified that the addition of 0.04 mmol/L of tea saponin
as a biosurfactant decreased the ratio of bubbles by 33%, and
it reduced the terminal velocity of the bubbles by 35% and
constricted the bubble trajectory by 27%. Therefore,
biosurfactants had the effect of a flotation method by
increasing the density and specific surface area of the
bubbles while reducing the bubble size. Rasheed et al. (2011)
treated petroleum refinery wastewater by ultrasounddispersed
nanoscale zero-valent iron (NZVI). They studied
the influence of NZVI dosage and initial pH on COD removal
percentage. The optimum initial pH was found to be 5 and the
optimum dosage of NZVI was 0.15 g/L.
Moreover, Kang et al. (2011) studied