contaminated aquarium and found that among all agricultural residues, rice straw is
found to be best for reducing the metals in the polluted aquarium water and
consequently reducing their accumulation in the fish body. Lu et al. (2017) have
applied bamboo and rice straw biochars in metal-contaminated paddy soil; they are
capable of reducing the availability of Cd, Cu, Pb, and Zn by increasing the soil pH.
Shu et al. (2016) applied different forms (dry straw, composted straw, straw
biochar, and straw ash) of rice straw to immobilize Hg in soils by forming methyl-Hg
compound by binding with organic matter present in amended rice straw. Zhang
et al. (2018) have also observed that by incorporating rice straw, there was 28%–
136% enhancement in methyl-Hg levels in contaminated soil by reducing their
availability to the plants. With the enhancement in the level of methyl-Hg in soils,
the microbial activity and dissolved organic matter get increased that consequently
induce the formation of Hg-S-DOM complexes to reduce the phyto-availability of
Hg (Shu et al. 2016; Zhu et al. 2015). Through batch adsorption technique, Akhtar
et al. (2010) have removed Pb(II), Cd(II), Zn(II), and Cu(II) divalent metal ions from
aqueous solutions with the help of rice husk (RHA) after chemical and thermal
activation with 0.1 M HNO 3 and 1 M K 2 CO 3 at 473 K.
Srivastava et al. (2008) have used rice husk ash (RHA) to remove Cd and Zn and
reported the competitive adsorptive removal of Cd(II) and Zn(II) ions from binary
systems using rice husk ash (RHA). A rice husk after some modification has been
used for adsorption of nine heavy metals by Krishnani et al. (2008). Rice husk was
treated with 1.5% alkaline solution and autoclaved at 121
C for 30 min to remove
the lignin (low molecular weight) compounds. The characterization through scanning electron microscope and Fourier transform infrared spectroscopy showed that,
particularly, the calcium and magnesium available at the surface of biomatrix are
responsible for adsorption of heavy metals through ion exchange mechanism. The
adsorption capacity of different heavy metals showed increasing trend having the
order Ni(II) < Zn(II) < Cd(II) < Mn(II) < Co(II) < Cu(II) Hg(II) < Pb(II) < Cr(III).
This treated rice husk has higher adsorption capacity than other kinds of sorbents
(Krishnani et al. 2008). Hegazi (2013) have treated rice husk (20 g) with 13 M
sulfuric acid (100 ml) and heated at 175–180
C for 20 min with stirring at regular
interval. The mixture obtained was black in color. It was filtered and allowed to cool
and finally filtered under vacuum with the help of the Buchner funnel. This treated
sorbent can be used to eliminate up to 20–60 mg/l Fe(II), Pb(II), Ni(II), Cd(II), and
Cu(II) from wastewater of electroplating industries. Elham et al. (2010) reported that
adsorption of Pb and Zn by rice husk is also based upon the amount of adsorbent,
contact time, and pH value of wastewater, which were the factors influencing Zn
(II) and Pb(II) ion sorption.
8.5.2 Use of Sawdust
Along with the rice husk, for removing heavy metals from metal-contaminated
system, sawdust is also used as an attractive low-cost adsorbent. Witek-Krowiak
8 Application of Wastewater in Irrigation and Its Regulation with Special. . .
189
found to be best for reducing the metals in the polluted aquarium water and
consequently reducing their accumulation in the fish body. Lu et al. (2017) have
applied bamboo and rice straw biochars in metal-contaminated paddy soil; they are
capable of reducing the availability of Cd, Cu, Pb, and Zn by increasing the soil pH.
Shu et al. (2016) applied different forms (dry straw, composted straw, straw
biochar, and straw ash) of rice straw to immobilize Hg in soils by forming methyl-Hg
compound by binding with organic matter present in amended rice straw. Zhang
et al. (2018) have also observed that by incorporating rice straw, there was 28%–
136% enhancement in methyl-Hg levels in contaminated soil by reducing their
availability to the plants. With the enhancement in the level of methyl-Hg in soils,
the microbial activity and dissolved organic matter get increased that consequently
induce the formation of Hg-S-DOM complexes to reduce the phyto-availability of
Hg (Shu et al. 2016; Zhu et al. 2015). Through batch adsorption technique, Akhtar
et al. (2010) have removed Pb(II), Cd(II), Zn(II), and Cu(II) divalent metal ions from
aqueous solutions with the help of rice husk (RHA) after chemical and thermal
activation with 0.1 M HNO 3 and 1 M K 2 CO 3 at 473 K.
Srivastava et al. (2008) have used rice husk ash (RHA) to remove Cd and Zn and
reported the competitive adsorptive removal of Cd(II) and Zn(II) ions from binary
systems using rice husk ash (RHA). A rice husk after some modification has been
used for adsorption of nine heavy metals by Krishnani et al. (2008). Rice husk was
treated with 1.5% alkaline solution and autoclaved at 121
C for 30 min to remove
the lignin (low molecular weight) compounds. The characterization through scanning electron microscope and Fourier transform infrared spectroscopy showed that,
particularly, the calcium and magnesium available at the surface of biomatrix are
responsible for adsorption of heavy metals through ion exchange mechanism. The
adsorption capacity of different heavy metals showed increasing trend having the
order Ni(II) < Zn(II) < Cd(II) < Mn(II) < Co(II) < Cu(II) Hg(II) < Pb(II) < Cr(III).
This treated rice husk has higher adsorption capacity than other kinds of sorbents
(Krishnani et al. 2008). Hegazi (2013) have treated rice husk (20 g) with 13 M
sulfuric acid (100 ml) and heated at 175–180
C for 20 min with stirring at regular
interval. The mixture obtained was black in color. It was filtered and allowed to cool
and finally filtered under vacuum with the help of the Buchner funnel. This treated
sorbent can be used to eliminate up to 20–60 mg/l Fe(II), Pb(II), Ni(II), Cd(II), and
Cu(II) from wastewater of electroplating industries. Elham et al. (2010) reported that
adsorption of Pb and Zn by rice husk is also based upon the amount of adsorbent,
contact time, and pH value of wastewater, which were the factors influencing Zn
(II) and Pb(II) ion sorption.
8.5.2 Use of Sawdust
Along with the rice husk, for removing heavy metals from metal-contaminated
system, sawdust is also used as an attractive low-cost adsorbent. Witek-Krowiak
8 Application of Wastewater in Irrigation and Its Regulation with Special. . .
189