(Schrank et al. 2004). Cr(VI) has been reported to cause inhibition of growth of the
nitrifying/denitrifying bacteria as well as other heterotrophs (Stasinakis et al. 2002;
Farabegoli et al. 2004). However, being of low-cost and flexible operation, a
sequencing batch reactor (SBR) may provide a sustainable solution to effective
biological treatment as it is feasible for the removal of nitrogen from TWW in the
presence of inhibitors due to selection and enrichment of a particular microbial
species (Farabegoli et al. 2004; Durai and Rajasimmam 2011; Rameshraja and
Suresh 2011; Lofrano et al. 2013).
Sulfide present in TWW primarily inhibits the methanogenesis during its anaerobic treatment, and this might be due to its toxic effect on remediating bacteria,
competition for substrate among the methanogenic and sulfate-reducing bacteria,
and trace element precipitation (Midha and Dey 2008; Rameshraja and Suresh 2011;
Mannucci et al. 2014). Nevertheless, how sulfide creates toxicity and its mechanisms
are still unknown and need to be understood.
Further, constructed wetlands (CWs) are also representing the most promising
wastewater treatment solution (Bharagava et al. 2017c). The phytoremediation of Cr
from TWW uses Brachiaria decumbens, Phragmites australis, and Pennisetum
purpureum CW (Mant et al. 2004). The potential of Typha latifolia, Canna indica,
Stenotaphrum secundatum, Phragmites australis, and Iris pseudacorus for the
phytoremediation of TWW in CW has been also reported, and Typha latifolia and
Phragmites australis were the two dominant plant species (Calheiros et al. 2007).
Plant species, Sarcocornia fruticosa and Arundo donax, during the
phytoremediation of secondary treated TWW in the horizontal subsurface flow
CW effectively reduced the COD and BOD up to 80 and 90%, respectively
(Calheiros et al. 2012). Further, Dunn et al. (2013) have also suggested TWW as a
suitable medium for the growth and cultivation of Arthrospira (Spirulina). Moreover, the chromium salt can be retained in wetlands with nonspecialized supporting
media (Dotro et al. 2012).
However, future research should be focused on (a) understanding of the dynamics
of microbiological processes and correlation between the biotic and abiotic processes in CWs; (b) knowledge of the dynamics of element cycle which might help us
to know the basic mechanism of greenhouse gas emission in CWs; and
(c) understanding of microbial community and plant-microbe interactions to know
the underlying mechanism of pollutant removal in CWs (Carvalho et al. 2017).
Anammox is an emerging technology for wastewater treatment and used to
remove ammonia from TWW during its anaerobic treatment. It is a low-cost and
less energy-intensive biological wastewater treatment process wherein oxidation of
ammonia takes place in the absence of oxygen with nitrite as a favored electron
acceptor. On contrary to conventional nitrification/denitrification process, it consumes less amount of O 2 (up to 50%), has no organic chemicals, and saves high cost
of operation (up to 90%) for sludge disposal (Anjali and Sabumon 2014). Hence, it is
more suitable for the industrial effluents with huge amount of ammonia. On the other
hand, the long time required for its start-up and its reductive nature in the presence of
organic chemicals and NH 4 -N limit its commercial applications (Anjali and
Sabumon 2014). Hence, there is a need to construct a potential consortium able to
do anammox in the presence of organic chemicals. Furthermore, the construction of
534
R. N. Bharagava and G. Saxena
nitrifying/denitrifying bacteria as well as other heterotrophs (Stasinakis et al. 2002;
Farabegoli et al. 2004). However, being of low-cost and flexible operation, a
sequencing batch reactor (SBR) may provide a sustainable solution to effective
biological treatment as it is feasible for the removal of nitrogen from TWW in the
presence of inhibitors due to selection and enrichment of a particular microbial
species (Farabegoli et al. 2004; Durai and Rajasimmam 2011; Rameshraja and
Suresh 2011; Lofrano et al. 2013).
Sulfide present in TWW primarily inhibits the methanogenesis during its anaerobic treatment, and this might be due to its toxic effect on remediating bacteria,
competition for substrate among the methanogenic and sulfate-reducing bacteria,
and trace element precipitation (Midha and Dey 2008; Rameshraja and Suresh 2011;
Mannucci et al. 2014). Nevertheless, how sulfide creates toxicity and its mechanisms
are still unknown and need to be understood.
Further, constructed wetlands (CWs) are also representing the most promising
wastewater treatment solution (Bharagava et al. 2017c). The phytoremediation of Cr
from TWW uses Brachiaria decumbens, Phragmites australis, and Pennisetum
purpureum CW (Mant et al. 2004). The potential of Typha latifolia, Canna indica,
Stenotaphrum secundatum, Phragmites australis, and Iris pseudacorus for the
phytoremediation of TWW in CW has been also reported, and Typha latifolia and
Phragmites australis were the two dominant plant species (Calheiros et al. 2007).
Plant species, Sarcocornia fruticosa and Arundo donax, during the
phytoremediation of secondary treated TWW in the horizontal subsurface flow
CW effectively reduced the COD and BOD up to 80 and 90%, respectively
(Calheiros et al. 2012). Further, Dunn et al. (2013) have also suggested TWW as a
suitable medium for the growth and cultivation of Arthrospira (Spirulina). Moreover, the chromium salt can be retained in wetlands with nonspecialized supporting
media (Dotro et al. 2012).
However, future research should be focused on (a) understanding of the dynamics
of microbiological processes and correlation between the biotic and abiotic processes in CWs; (b) knowledge of the dynamics of element cycle which might help us
to know the basic mechanism of greenhouse gas emission in CWs; and
(c) understanding of microbial community and plant-microbe interactions to know
the underlying mechanism of pollutant removal in CWs (Carvalho et al. 2017).
Anammox is an emerging technology for wastewater treatment and used to
remove ammonia from TWW during its anaerobic treatment. It is a low-cost and
less energy-intensive biological wastewater treatment process wherein oxidation of
ammonia takes place in the absence of oxygen with nitrite as a favored electron
acceptor. On contrary to conventional nitrification/denitrification process, it consumes less amount of O 2 (up to 50%), has no organic chemicals, and saves high cost
of operation (up to 90%) for sludge disposal (Anjali and Sabumon 2014). Hence, it is
more suitable for the industrial effluents with huge amount of ammonia. On the other
hand, the long time required for its start-up and its reductive nature in the presence of
organic chemicals and NH 4 -N limit its commercial applications (Anjali and
Sabumon 2014). Hence, there is a need to construct a potential consortium able to
do anammox in the presence of organic chemicals. Furthermore, the construction of
534
R. N. Bharagava and G. Saxena