1.4.1 Physical Treatments
1.4.1.1 Air Stripping
It is usually implemented for the removal of volatile contaminants through a
straightforward transfer from the aqueous phase to the gas phase. Air stripping is
an excellent alternative to distillation, which is not economically feasible. It can be
performed in the simplest cases by spraying, bubbling, or mechanical dispersion
(e.g., cascade). All the stripping systems work in counterflow to the wastewater in
order to increase the amount of contaminant extracted according to mass transfer
laws. The use of high surfaces for transfer processes is required. In basic systems, the
wastewater flow to be treated is either sprayed at the top of a long column or
scattered and uniformly distributed within a packed bed of solid material. However,
volatile contaminants are usually organic and surfactants are generally used to
extract contaminants from soils. The higher the surfactant concentration is, the
lower the removal efficiency is in the vapor phase, because of the enhanced
contaminant stabilization in the aqueous phase and then, the increase of the apparent
Henry constants (Lipe et al. 1996). Foam production resulting from the decreased
surface tension between the air and the water phases by surfactants (Sect. 1.3.2) may
hinder a fast fluids circulation in the column. In that case, vacuum stripping of VOCs
in nonionic surfactant solutions in co-current mode, or even better membrane
pervaporation have been used for the removal of BTEX, naphthalene, and chlorinated compounds (Jiang et al. 1997; Abou-Nemeh et al. 1999; Kim et al. 2007; Topf
et al. 2013). Field-tests assessments have been mainly carried out on
TCE-contaminated groundwater at low surfactant concentrations and needed ultrafiltration for surfactant recovery before reuse (Sabatini et al. 1998; Vane et al. 2001).
The principle of membrane pervaporation is explained in the next section.
1.4.1.2 Membrane Filtration
The filtration of colloids and solutes requires membrane technologies since classical
filtration cannot retain particles smaller than few microns. A membrane is a thin
selective barrier (about 200 μm thick) separating two compartments which enables
the transfer of molecules or colloids thanks to a driving force. The driving force is a
gradient between the two compartments either pressure or compound concentration
or electric field. The efficiency of a membrane system is characterized by its
volumetric flux (m
3 s
À1 m
À2 ), its recovery (defined as the ratio of permeate flow
to feed flow) and the rejection, R, which is the fraction of molecules or solids that is
retained by the membrane and calculated as:
32
N. Fatin-Rouge
1.4.1.1 Air Stripping
It is usually implemented for the removal of volatile contaminants through a
straightforward transfer from the aqueous phase to the gas phase. Air stripping is
an excellent alternative to distillation, which is not economically feasible. It can be
performed in the simplest cases by spraying, bubbling, or mechanical dispersion
(e.g., cascade). All the stripping systems work in counterflow to the wastewater in
order to increase the amount of contaminant extracted according to mass transfer
laws. The use of high surfaces for transfer processes is required. In basic systems, the
wastewater flow to be treated is either sprayed at the top of a long column or
scattered and uniformly distributed within a packed bed of solid material. However,
volatile contaminants are usually organic and surfactants are generally used to
extract contaminants from soils. The higher the surfactant concentration is, the
lower the removal efficiency is in the vapor phase, because of the enhanced
contaminant stabilization in the aqueous phase and then, the increase of the apparent
Henry constants (Lipe et al. 1996). Foam production resulting from the decreased
surface tension between the air and the water phases by surfactants (Sect. 1.3.2) may
hinder a fast fluids circulation in the column. In that case, vacuum stripping of VOCs
in nonionic surfactant solutions in co-current mode, or even better membrane
pervaporation have been used for the removal of BTEX, naphthalene, and chlorinated compounds (Jiang et al. 1997; Abou-Nemeh et al. 1999; Kim et al. 2007; Topf
et al. 2013). Field-tests assessments have been mainly carried out on
TCE-contaminated groundwater at low surfactant concentrations and needed ultrafiltration for surfactant recovery before reuse (Sabatini et al. 1998; Vane et al. 2001).
The principle of membrane pervaporation is explained in the next section.
1.4.1.2 Membrane Filtration
The filtration of colloids and solutes requires membrane technologies since classical
filtration cannot retain particles smaller than few microns. A membrane is a thin
selective barrier (about 200 μm thick) separating two compartments which enables
the transfer of molecules or colloids thanks to a driving force. The driving force is a
gradient between the two compartments either pressure or compound concentration
or electric field. The efficiency of a membrane system is characterized by its
volumetric flux (m
3 s
À1 m
À2 ), its recovery (defined as the ratio of permeate flow
to feed flow) and the rejection, R, which is the fraction of molecules or solids that is
retained by the membrane and calculated as:
32
N. Fatin-Rouge