Page 257 - Materials Chemistry, Second Edition

238 Life Cycle Assessment of Wastewater Treatment

in wastewater are kept in solution by electrical charges (Heidmann and Calmano,
2008). At the point when these and other target particles are neutralized by particles
of opposite electrical charge originating from the electro-coagulation system, they
move toward becoming destabilized and forming a stable shape. After this, metal-
lic particles combine into greater flocs and can be removed easily (Rajkumar and
Palanivelu, 2004; Borba et al., 2006). Water particles are hydrolyzed at the cathode
at the same time. Two diverse components proposed for iron anodes can be found in
the following mechanisms:

Mechanism I
In the anode:

4 Fe (s) → 4 Fe 2+ (aq) + 8e − (11.1)

In the cathode:

+
−
8 H ( aq + 8 e → 4 H 2g() (11.2)
)
In solution:
(
+
4 Fe 2+ ( aq + 1 H O l +0 2 () O 2g → 4 FeOH) 3s () + 8 H ( aq) (11.3)
)
()
Mechanism II
In the anode:
Fe s() → Fe 2+ ( aq) + 2e − (11.4)

In the cathode:

−
−
2 H O l() + 2e → H 2g() + 2 OH ( aq) (11.5)
2
In solution:
FeOH)
−
Fe 2+ ( aq + 2 OH ( aq → ( 2s () (11.6)
)
)
Metal ions created at the anode and hydroxide ions created at the cathode react in the
aqueous medium to create different hydroxide species depending on the pH; for example,
2+
−
2+
Fe(OH) , Fe(OH) , Fe(OH) , Fe(OH) , and Fe(OH) . The iron hydroxides coagulate
4
2
3
and settle to the bottom of the solution (Mollah et al., 2004; Vasudevan et al., 2011).
11.5.6.2 Electro-Flotation
Electro-flotation uses modest increases of hydrogen and oxygen gases produced
by water electrolysis, keeping in mind the end goal to buoy toxins up to the sur-
face of the effluent. Electro-flotation can be used as part of a blend with aluminum
electro-coagulation.