Environmental Engineering Reference
In-Depth Information
decomposition of organic waste (Goyal et al., 2005), the availability of heavy
metals, such as lead (Pb) and cadmium (Cd) decrease due to bioaccumulation
of these metals andformation oforgano - complex compoundsduring this
process (Shahmansouri et al., 2005; Bhattacharya and Chattopadhyay, 2006).
Despite the formation of these organo-metal complexes, there is a possibility
that entire cadmium is not assimilated or accumulates and moreover, it can
prove toxic to the invertebrates. Composting can be often challenging for
metallic wastes, such as cadmium as the increase in concentration beyond a
tolerable limit can often inhibit the microbial growth as well as affect overall
organism structure of earthworm community.
3.4. Electro Coagulation
Another way for cadmium removal from industrial wastewater is by
electrocoagulation process without using any chemical material. The technique
only uses transfer of aluminum ion electrons to cadmium in the form of metal.
In this method, cadmium precipitates and that precipitate could be used for
removal and recycling of cadmium or inertization of the same.
The details of reactions occurring in the electrocoagulation process as
proposed by Mahvi and Bazrafshan, in 2007 are shown below:
AlAl
3+
+ 3e¯ (anode).
(1)
3H
2
O + 3e¯ 3/2H
2
+ 3OH¯ (cathode)
(2)
In addition, Al
3+
and OH¯ ions generated at electrode surfaces react in the
bulk wastewater to form aluminum hydroxide:
Al
3+
+ 3OH¯Al(OH)
3
(3)
If the anode potential is sufficiently high, secondary reactions may occur
at the anode, such as direct oxidation of organic compounds and of H
2
O or Cl¯
present in wastewater:
2Cl¯ Cl
2
+ 2e¯
(4)
2H
2
O O
2
+ 4H
+
+ 4e¯
(5)
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