Electro-Flotation
Electro-flotation involves the electrolysis of water that produces hydrogen and
oxygen gas bubbles at both electrodes. The chemical reactions occurring in the
electro-flotation process are shown as follows (Eqs. 11.1, 11.2 and 11.3):
Anode:
2H 2 O l
ð Þ ! 4H
þ
þ O 2 g
ð Þ þ 4e
À
ð11:1Þ
Cathode:
4e
À
þ 4H 2 O l
ð Þ ! 2H 2 g
ð Þ þ 4OH
À
ð11:2Þ
Overall reaction:
2H 2 O l
ð Þ ! 2H 2 g
ð Þ þ O 2 g
ð Þ
ð11:3Þ
where H 2 O (l), H 2 (g), and O 2 (g) are water, hydrogen gas, and oxygen gas,
respectively. The hydrogen ion, hydroxide ion, and electron are denoted as H
+
,
OH
À , and e
À , respectively in the equations above.
The gas bubbles formed at the electrode attach to the oil particles and subsequently rise to the surface where the oil is removed through skimming. Electroflotation demonstrates several strengths, such as (a) excellent oil removal efficiency
of up to 90%, (b) the gas bubbles have uniform and small diameters of 100 μm which
increases the surface area of contact between the oil particles and gas bubbles,
(c) small and compact units that require low maintenance and operating costs, and
(d) the rate of bubble generation can be controlled easily through the manipulation of
current density (Eskin et al. 2015; Mansour and Chalbi 2006; Rubio et al. 2002;
Wang et al. 2010). However, this flotation technique suffers from low throughput,
emission of hydrogen gas bubbles, and high electrode costs (Rubio et al. 2002).
Other Flotation Techniques
Several other types of flotation techniques have also been reported for the oily
wastewater treatment which include jet and column flotations. Jet flotation has
shown its potential for the oily wastewater treatment due to the small air bubbles
production, high throughput, moderate equipment and maintenance costs as it does
not have moving parts, and easy installation (Yu et al. 2017; Rubio et al. 2002).
Santander et al. (2011) set up a modified jet (Jameson) cell in an offshore platform.
The device demonstrated a high oil removal efficiency of around 81% at a high
throughput rate of 24.7 m
3 /h m
2 . The results indicate the great prospects of utilizing
jet flotation in the oily wastewater treatment applications.
11 Oily Wastewater Treatment
361
Electro-flotation involves the electrolysis of water that produces hydrogen and
oxygen gas bubbles at both electrodes. The chemical reactions occurring in the
electro-flotation process are shown as follows (Eqs. 11.1, 11.2 and 11.3):
Anode:
2H 2 O l
ð Þ ! 4H
þ
þ O 2 g
ð Þ þ 4e
À
ð11:1Þ
Cathode:
4e
À
þ 4H 2 O l
ð Þ ! 2H 2 g
ð Þ þ 4OH
À
ð11:2Þ
Overall reaction:
2H 2 O l
ð Þ ! 2H 2 g
ð Þ þ O 2 g
ð Þ
ð11:3Þ
where H 2 O (l), H 2 (g), and O 2 (g) are water, hydrogen gas, and oxygen gas,
respectively. The hydrogen ion, hydroxide ion, and electron are denoted as H
+
,
OH
À , and e
À , respectively in the equations above.
The gas bubbles formed at the electrode attach to the oil particles and subsequently rise to the surface where the oil is removed through skimming. Electroflotation demonstrates several strengths, such as (a) excellent oil removal efficiency
of up to 90%, (b) the gas bubbles have uniform and small diameters of 100 μm which
increases the surface area of contact between the oil particles and gas bubbles,
(c) small and compact units that require low maintenance and operating costs, and
(d) the rate of bubble generation can be controlled easily through the manipulation of
current density (Eskin et al. 2015; Mansour and Chalbi 2006; Rubio et al. 2002;
Wang et al. 2010). However, this flotation technique suffers from low throughput,
emission of hydrogen gas bubbles, and high electrode costs (Rubio et al. 2002).
Other Flotation Techniques
Several other types of flotation techniques have also been reported for the oily
wastewater treatment which include jet and column flotations. Jet flotation has
shown its potential for the oily wastewater treatment due to the small air bubbles
production, high throughput, moderate equipment and maintenance costs as it does
not have moving parts, and easy installation (Yu et al. 2017; Rubio et al. 2002).
Santander et al. (2011) set up a modified jet (Jameson) cell in an offshore platform.
The device demonstrated a high oil removal efficiency of around 81% at a high
throughput rate of 24.7 m
3 /h m
2 . The results indicate the great prospects of utilizing
jet flotation in the oily wastewater treatment applications.
11 Oily Wastewater Treatment
361