functional groups which can absorb solar radiation or other radiation directly, hence
effectively degraded by photolysis and indirect photodegradation. Organic pollutants can undergo direct photolysis by absorbing light which are then capable to
produce a chemical transformation (Verlicchi and Zambello 2014). Some compounds are sensitive to photodegradation, like ketoprofen and naproxen, and can
easily be degraded by expose (Hijosa-Valsero et al. 2010).
Sorption This process plays a key role in determining the environmental transport
and fate of organic chemicals (Wen et al. 2012). Sorption is the process by which
one substance takes up or holds another substance. Whether or not a PPCP will
adsorb to the substrate is related to the compounds sorption distribution coefficient
(Kd) and the properties of the substrate present. For example, compounds that are
moderately hydrophilic tend not to bind to organic matter (Hijosa-Valsero et al.
2010). Some pharmaceutical compounds can sorb to sediments within the wetland
bed, soil, as well as plant roots. Sorption mechanism can depend on many factors,
including compound’s properties (e.g., chemical structure, water solubility, hydrophobic characteristics, acid/base properties, etc.) and soil characteristics (e.g.,
composition of soil organic matter, redox potential, temperature, pH, etc.)
(Zhang et al. 2014). Suspended particles from wastewater are retained in a wetland
bed; sorption of dissolved organic contaminants on soil, organic carbon, mineral
surfaces, and biofilms coating the gravel bed can be an important process for
removal of pharmaceutical products (Tatum 2015). It is to mention here that
some compounds sorption may require lengthy time from weeks to months to
reach equilibrium (Wen et al. 2012).
Parameters of CW that influence the removal efficiency of PPCPs: The physical
features and parameters of the constructed wetland include the type of flow, feeding
strategies, planted vs unplanted, type of planted plants, type of substrate, HRT, and
hydraulic loading rates (HLR). Other variables include temperature, season, pH,
amount of sunlight, type and number of microbes present, etc. which vary depending
on geographical location. Removal percentages are mainly dependent on temperature, HRT, and loading rate and are highly variable between systems (Hussain and
Prasher 2011; Zhu and Chen 2014). Moreover, wetland type selection will depend
on regional practices, climatic considerations, the nature of the pollutants and their
loads, aesthetics, health and wildlife concerns, land and topographical limitations,
etc. As water consisting suspended particles and dissolved contaminants passes
through a wetland, the contaminants can be physically removed from the water
flow as the suspended particles settle down due to gravity or they may be become
trapped by vegetation or the dissolved chemicals are sorbed to the bed soil through
the phase partitioning process (Conkle et al. 2012). Plants are considered to favor
removal of pharmaceuticals. Once pharmaceutical are bioaccumulated and
translocated by plants, they generally undergo three transformation stages:
(i) chemical modification (reductions, oxidations, hydrolysis); (ii) conjugation
(with sugars, glutathione, amino acids); and iii) sequestration (conjugates are
converted to other conjugates and deposited in plant vacuoles or bound to the cell
wall and lignin) (Zhang et al. 2014). High redox potentials encourage aerobic
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S. Khan et al.
effectively degraded by photolysis and indirect photodegradation. Organic pollutants can undergo direct photolysis by absorbing light which are then capable to
produce a chemical transformation (Verlicchi and Zambello 2014). Some compounds are sensitive to photodegradation, like ketoprofen and naproxen, and can
easily be degraded by expose (Hijosa-Valsero et al. 2010).
Sorption This process plays a key role in determining the environmental transport
and fate of organic chemicals (Wen et al. 2012). Sorption is the process by which
one substance takes up or holds another substance. Whether or not a PPCP will
adsorb to the substrate is related to the compounds sorption distribution coefficient
(Kd) and the properties of the substrate present. For example, compounds that are
moderately hydrophilic tend not to bind to organic matter (Hijosa-Valsero et al.
2010). Some pharmaceutical compounds can sorb to sediments within the wetland
bed, soil, as well as plant roots. Sorption mechanism can depend on many factors,
including compound’s properties (e.g., chemical structure, water solubility, hydrophobic characteristics, acid/base properties, etc.) and soil characteristics (e.g.,
composition of soil organic matter, redox potential, temperature, pH, etc.)
(Zhang et al. 2014). Suspended particles from wastewater are retained in a wetland
bed; sorption of dissolved organic contaminants on soil, organic carbon, mineral
surfaces, and biofilms coating the gravel bed can be an important process for
removal of pharmaceutical products (Tatum 2015). It is to mention here that
some compounds sorption may require lengthy time from weeks to months to
reach equilibrium (Wen et al. 2012).
Parameters of CW that influence the removal efficiency of PPCPs: The physical
features and parameters of the constructed wetland include the type of flow, feeding
strategies, planted vs unplanted, type of planted plants, type of substrate, HRT, and
hydraulic loading rates (HLR). Other variables include temperature, season, pH,
amount of sunlight, type and number of microbes present, etc. which vary depending
on geographical location. Removal percentages are mainly dependent on temperature, HRT, and loading rate and are highly variable between systems (Hussain and
Prasher 2011; Zhu and Chen 2014). Moreover, wetland type selection will depend
on regional practices, climatic considerations, the nature of the pollutants and their
loads, aesthetics, health and wildlife concerns, land and topographical limitations,
etc. As water consisting suspended particles and dissolved contaminants passes
through a wetland, the contaminants can be physically removed from the water
flow as the suspended particles settle down due to gravity or they may be become
trapped by vegetation or the dissolved chemicals are sorbed to the bed soil through
the phase partitioning process (Conkle et al. 2012). Plants are considered to favor
removal of pharmaceuticals. Once pharmaceutical are bioaccumulated and
translocated by plants, they generally undergo three transformation stages:
(i) chemical modification (reductions, oxidations, hydrolysis); (ii) conjugation
(with sugars, glutathione, amino acids); and iii) sequestration (conjugates are
converted to other conjugates and deposited in plant vacuoles or bound to the cell
wall and lignin) (Zhang et al. 2014). High redox potentials encourage aerobic
146
S. Khan et al.