(Khuntia et al. 2013, 2014; Ryskie et al. 2019). Previous findings showed good
efficiency of wet Fe(VI) in NH 3 removal from synthetic and actual gold mine
effluents (Gonzalez-Merchan et al. 2016), but increased residual salinity in
treated water from the oxidant (Gonzalez-Merchan et al. 2018). Noteworthy,
wet Fe(VI) preparation involves the oxidation of an Fe(III) salt (sulfate, chloride,
or sulfate) under alkaline conditions (NaOH) using an oxidant (NaOCl). Previous
findings also showed good efficiency of ozone microbubbles in NH 3 and metal
removal, from synthetic and actual effluents (Ryskie et al. 2019). A major
drawback of the AOPs is often the creation of residual salinity. Further tests are
required for evaluating the influence of bubbles size, the simultaneous removal of
other oxidizable contaminants present in the water, as well as aquatic toxicity of
final effluent.
29.3.2 Biological Processes
Biological processes are commonly used to remove organic compounds from
municipal and industrial wastewater and inorganic contaminants from mine water
(precipitation as sulfides). Performances of biological treatments are dependent on
microorganism activities. Various factors including water composition, loading rate,
type of media, temperature, and aeration rate can alter the microbial activity and
therefore the efficiency of treatment. Consequently, biological treatment is susceptible to the presence of toxin or excess of nutrients in water, seasonal and loading rate
changes, and shock. The main drawbacks of biological treatments are related to
fouling and filter clogging phenomenon as well as careful control of operating
conditions to favor microbial activities. As discussed earlier, conventional biological
processes such as activated sludge are not very effective in removing recalcitrant
organic CECs from municipal and industrial wastewater. Anaerobic processes can
be effective but the degradation of organic compounds is quite slow. Moreover,
several studies reported that anaerobic processes are not efficient for the removal of
pharmaceuticals, personal care products, and endocrine disrupting compounds. This
can be explained because these CECs are present in much lower concentrations than
other organic contaminants, reducing the portion of these contaminants that can be
effectively degraded (Adeleye et al. 2016). To improve the performances of biological treatment to remove organic CECs from water, it can be combined with physical
treatments such as MF or UF. For example, studies reported that membrane bioreactors (MBRs), which combined an activated sludge process with a membrane
process (MF or UF) are extensively used in wastewater treatment plants to remove
organic compounds from municipal and industrial wastewater (Rodriguez-Narvaez
et al. 2017). However, there are only few papers reporting on the performances of
MBRs for the degradation of CECs (Sui et al. 2011; Yang et al. 2011). According to
these studies, only easily biodegradable CECs (such as caffeine, diclofenac, trimethoprim, acetaminophen, ibuprofen, tetracycline) can be efficiently removed from
wastewater (60–100%), whereas low biodegradable ones (such as metoprolol,
598
C. M. Neculita et al.
efficiency of wet Fe(VI) in NH 3 removal from synthetic and actual gold mine
effluents (Gonzalez-Merchan et al. 2016), but increased residual salinity in
treated water from the oxidant (Gonzalez-Merchan et al. 2018). Noteworthy,
wet Fe(VI) preparation involves the oxidation of an Fe(III) salt (sulfate, chloride,
or sulfate) under alkaline conditions (NaOH) using an oxidant (NaOCl). Previous
findings also showed good efficiency of ozone microbubbles in NH 3 and metal
removal, from synthetic and actual effluents (Ryskie et al. 2019). A major
drawback of the AOPs is often the creation of residual salinity. Further tests are
required for evaluating the influence of bubbles size, the simultaneous removal of
other oxidizable contaminants present in the water, as well as aquatic toxicity of
final effluent.
29.3.2 Biological Processes
Biological processes are commonly used to remove organic compounds from
municipal and industrial wastewater and inorganic contaminants from mine water
(precipitation as sulfides). Performances of biological treatments are dependent on
microorganism activities. Various factors including water composition, loading rate,
type of media, temperature, and aeration rate can alter the microbial activity and
therefore the efficiency of treatment. Consequently, biological treatment is susceptible to the presence of toxin or excess of nutrients in water, seasonal and loading rate
changes, and shock. The main drawbacks of biological treatments are related to
fouling and filter clogging phenomenon as well as careful control of operating
conditions to favor microbial activities. As discussed earlier, conventional biological
processes such as activated sludge are not very effective in removing recalcitrant
organic CECs from municipal and industrial wastewater. Anaerobic processes can
be effective but the degradation of organic compounds is quite slow. Moreover,
several studies reported that anaerobic processes are not efficient for the removal of
pharmaceuticals, personal care products, and endocrine disrupting compounds. This
can be explained because these CECs are present in much lower concentrations than
other organic contaminants, reducing the portion of these contaminants that can be
effectively degraded (Adeleye et al. 2016). To improve the performances of biological treatment to remove organic CECs from water, it can be combined with physical
treatments such as MF or UF. For example, studies reported that membrane bioreactors (MBRs), which combined an activated sludge process with a membrane
process (MF or UF) are extensively used in wastewater treatment plants to remove
organic compounds from municipal and industrial wastewater (Rodriguez-Narvaez
et al. 2017). However, there are only few papers reporting on the performances of
MBRs for the degradation of CECs (Sui et al. 2011; Yang et al. 2011). According to
these studies, only easily biodegradable CECs (such as caffeine, diclofenac, trimethoprim, acetaminophen, ibuprofen, tetracycline) can be efficiently removed from
wastewater (60–100%), whereas low biodegradable ones (such as metoprolol,
598
C. M. Neculita et al.