29.3 Potential Solutions
To address some of the abovementioned needs, research must focus on physicochemical processes that create low residual salinity. Promising options fitting into
this requirement involve physicochemical-based processes (membranes, evaporation, sorption), biotechnologies, and advanced oxidation processes (AOPs) using
ferrates and ozone microbubbles. Some of the most promising approaches meeting
the identified requirements have been summarized before, with the emphasis on their
principle, potential applications, performances, and challenges.
29.3.1 Physicochemical Processes
1. Filtration uses membranes, which are classified into microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). Specific filtering
features of these membranes (pore size, surface charge, and hydrophobicity)
determine the contaminant type that can be retained. Several mechanisms including adsorption, electrostatic repulsion, and sieving are involved in the removal of
CECs from municipal and industrial wastewater. MF is widely used to treat
municipal and industrial wastewater as it can be used at atmospheric pressure.
However, MF is not useful for the removal of CECs from municipal and
industrial wastewater as this system is not able to remove contaminants of size
<1 μm (Rodriguez-Narvaez et al. 2017). With a pore size ranging from 1 to
100 nm, UF is able to remove a wide variety of CECs including plasticizers
(bisphenol A, bis(2-ethylhexyl)phthalate, butyl benzyl phthalate), herbicides
(atrazine), pharmaceuticals (17α-ethynylestradiol, naproxen, diclofenac)
(Rodriguez-Narvaez et al. 2017; Yoon et al. 2007). Operating at low pressure,
NF can also be used for CECs removal from municipal and industrial wastewater
because of its small pore size (between 1 and 10 nm), with removal yields higher
than 50% for most of CECs and 90% for pharmaceuticals (Bolong et al. 2009;
Gogoi et al. 2018). Relative to previous membrane systems, the use of hydraulic
pressure as the driving force to separate CECs from wastewater allowed better
efficiency as such systems are able to remove particles of size <1 nm. For
example, ibuprofen, naproxen, fenoprofen, gemfibrozil, and ketoprofen have
been removed for up to 95–99% (Rodriguez-Narvaez et al. 2017). To prevent
the fouling of membranes, commonly encountered during wastewater treatment,
specific conditions must be maintained and backwashing using harsh chemicals is
used to clean the membrane when required. Another limitation of RO is the
necessity to remineralize the water after the treatment because of the nonselective
removal of the elements and to adjust the pH, which increases the treatment costs.
Given the molecular weight and size of Se species, only NF and RO can be
effective in Se removal (Sandy and DiSante 2010). Indeed, RO was found
effective in Se removal below 5 ppb, at pilot and full scale, while NF was less
594
C. M. Neculita et al.
To address some of the abovementioned needs, research must focus on physicochemical processes that create low residual salinity. Promising options fitting into
this requirement involve physicochemical-based processes (membranes, evaporation, sorption), biotechnologies, and advanced oxidation processes (AOPs) using
ferrates and ozone microbubbles. Some of the most promising approaches meeting
the identified requirements have been summarized before, with the emphasis on their
principle, potential applications, performances, and challenges.
29.3.1 Physicochemical Processes
1. Filtration uses membranes, which are classified into microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). Specific filtering
features of these membranes (pore size, surface charge, and hydrophobicity)
determine the contaminant type that can be retained. Several mechanisms including adsorption, electrostatic repulsion, and sieving are involved in the removal of
CECs from municipal and industrial wastewater. MF is widely used to treat
municipal and industrial wastewater as it can be used at atmospheric pressure.
However, MF is not useful for the removal of CECs from municipal and
industrial wastewater as this system is not able to remove contaminants of size
<1 μm (Rodriguez-Narvaez et al. 2017). With a pore size ranging from 1 to
100 nm, UF is able to remove a wide variety of CECs including plasticizers
(bisphenol A, bis(2-ethylhexyl)phthalate, butyl benzyl phthalate), herbicides
(atrazine), pharmaceuticals (17α-ethynylestradiol, naproxen, diclofenac)
(Rodriguez-Narvaez et al. 2017; Yoon et al. 2007). Operating at low pressure,
NF can also be used for CECs removal from municipal and industrial wastewater
because of its small pore size (between 1 and 10 nm), with removal yields higher
than 50% for most of CECs and 90% for pharmaceuticals (Bolong et al. 2009;
Gogoi et al. 2018). Relative to previous membrane systems, the use of hydraulic
pressure as the driving force to separate CECs from wastewater allowed better
efficiency as such systems are able to remove particles of size <1 nm. For
example, ibuprofen, naproxen, fenoprofen, gemfibrozil, and ketoprofen have
been removed for up to 95–99% (Rodriguez-Narvaez et al. 2017). To prevent
the fouling of membranes, commonly encountered during wastewater treatment,
specific conditions must be maintained and backwashing using harsh chemicals is
used to clean the membrane when required. Another limitation of RO is the
necessity to remineralize the water after the treatment because of the nonselective
removal of the elements and to adjust the pH, which increases the treatment costs.
Given the molecular weight and size of Se species, only NF and RO can be
effective in Se removal (Sandy and DiSante 2010). Indeed, RO was found
effective in Se removal below 5 ppb, at pilot and full scale, while NF was less
594
C. M. Neculita et al.