7.7.1 Chemical Inhibitors
In the past decade, ionic liquids (ILs) have gained considerable attention as alternative to commonly used volatile organic compounds (VOCs). These are organic salts
consisting of inorganic anions such as Cl
À , BF 4
À , Br
À , PF 6
À , (CN) 2 N
À , CNS
À ,
AlCl 4
À , etc. which make weak coordination bond with organic cations (Thamke
et al. 2019). They are employed in organic synthesis as solvents and catalysts,
metallic nanoparticle synthesis, biocatalysis, separation of azeotropic mixtures,
CO 2 capture, extractions, etc. (Tzani et al. 2019). Discharge from industries that
manufacture or utilize ILs creates environmental risks. Imidazolium bromide ILs
such as (C 4 mim)Br, (C 6 mim)Br, and (C 10 mim)Br have been found to reduce microbial abundance in soil including AOB and AOA (Cheng et al. 2019).
7.7.2 Biological Inhibitors
Some plant root extracts have been found to act as potential inhibitors of
nitrification.
Brachiaria humidicola grasses are found to possess highest biological nitrification inhibition (BNI) capacity (Subbarao et al. 2017). Root exudates from rice and
Leymus racemosus, which is a family of wheat, also show BNI potential (Sun et al.
2016; Lu et al. 2019). Biological nitrification inhibitors such as 1,9-decanediol,
methyl 3-(4-hydroxyphenyl) propionate (MHPP), and α-linolenic acid (LN) have
been found to inhibit both AOB and AOA population (Lu et al. 2019). However,
different chemical compounds from root extract of same plant produce differing
action on nitrification. For example, sorgoleone, a hydrophobic BNI from sorghum
root extract, causes significant suppression in nitrification, but sakuranetin
(a hydrophilic BNI) also extracted from sorghum root has no nitrification inhibition
potential (Subbarao et al. 2013). Although these compounds play inhibitory role in
nitrification, they find importance in preservation of NH
þ
4 -N in agricultural soil.
AOB and AOA population are also naturally present in terrestrial environments.
Application of nitrogenous fertilizers for crop improvement promotes growth of
AOB, but increase in AOB population alleviates nitrogen from soil and makes it less
available for plants.
7.8 Conclusions
Conventional wastewater treatment processes such as reverse osmosis, electrodialysis, ion exchange, etc. were used way back in the 1990s. Considering the loopholes
in such physical methods, there came a paradigm shift in WWT technologies toward
advanced oxidation processes such as ozonation, electrochemical oxidation, etc. To
7 Nitrogenous Wastes and Its Efficient Treatment in Wastewater
165
In the past decade, ionic liquids (ILs) have gained considerable attention as alternative to commonly used volatile organic compounds (VOCs). These are organic salts
consisting of inorganic anions such as Cl
À , BF 4
À , Br
À , PF 6
À , (CN) 2 N
À , CNS
À ,
AlCl 4
À , etc. which make weak coordination bond with organic cations (Thamke
et al. 2019). They are employed in organic synthesis as solvents and catalysts,
metallic nanoparticle synthesis, biocatalysis, separation of azeotropic mixtures,
CO 2 capture, extractions, etc. (Tzani et al. 2019). Discharge from industries that
manufacture or utilize ILs creates environmental risks. Imidazolium bromide ILs
such as (C 4 mim)Br, (C 6 mim)Br, and (C 10 mim)Br have been found to reduce microbial abundance in soil including AOB and AOA (Cheng et al. 2019).
7.7.2 Biological Inhibitors
Some plant root extracts have been found to act as potential inhibitors of
nitrification.
Brachiaria humidicola grasses are found to possess highest biological nitrification inhibition (BNI) capacity (Subbarao et al. 2017). Root exudates from rice and
Leymus racemosus, which is a family of wheat, also show BNI potential (Sun et al.
2016; Lu et al. 2019). Biological nitrification inhibitors such as 1,9-decanediol,
methyl 3-(4-hydroxyphenyl) propionate (MHPP), and α-linolenic acid (LN) have
been found to inhibit both AOB and AOA population (Lu et al. 2019). However,
different chemical compounds from root extract of same plant produce differing
action on nitrification. For example, sorgoleone, a hydrophobic BNI from sorghum
root extract, causes significant suppression in nitrification, but sakuranetin
(a hydrophilic BNI) also extracted from sorghum root has no nitrification inhibition
potential (Subbarao et al. 2013). Although these compounds play inhibitory role in
nitrification, they find importance in preservation of NH
þ
4 -N in agricultural soil.
AOB and AOA population are also naturally present in terrestrial environments.
Application of nitrogenous fertilizers for crop improvement promotes growth of
AOB, but increase in AOB population alleviates nitrogen from soil and makes it less
available for plants.
7.8 Conclusions
Conventional wastewater treatment processes such as reverse osmosis, electrodialysis, ion exchange, etc. were used way back in the 1990s. Considering the loopholes
in such physical methods, there came a paradigm shift in WWT technologies toward
advanced oxidation processes such as ozonation, electrochemical oxidation, etc. To
7 Nitrogenous Wastes and Its Efficient Treatment in Wastewater
165