Momeni 2012). Another novel photocatalyst based on silver nanoparticles and
colemanite ore waste was employed to remove reactive Yellow 86 and 21 in single
and multiple dye mixtures. Ag-colemanite ore waste proved to be a reusable and
cheap photocatalyst causing the removal of dyes from both single and binary
systems under optimized conditions of highly acidic pH, 100 mg/L beginning
concentration, duration of 1.25 h, and photocatalyst dose of 1.0 g L
À1 (Yola et al.
2014).
17.3.3 Electrochemical Treatment
Electrochemical methods such as electrocoagulation offer many advantages over
existing physiochemical and membrane separation methods. For instance,
electrocoagulation utilizes the electron as a unique reagent, thus reducing the cost
sludge production while increasing safety and selectivity. In a typical
electrocoagulation method, a metal electrode functions as anode where electrolytic
oxidation produces the coagulant (Singh et al. 2013). Iron or aluminum electrodes
have gained popularity not only because of economic and commercial advantages
but also due to the favorable mechanism of action, i.e., the formation of metal oxides
and hydroxides that increases adsorption (Zidane et al. 2008). Aluminum and
stainless steel electrodes employed for a simulated reactive dyebath solution
revealed the superiority of stainless steel electrodes, particularly for decolorization.
The mechanism behind color and chemical oxygen demand removal was attributed
to coagulation and adsorption at extremely basic pH (Kabdaşlı et al. 2009).
Reactive Blue 140 and disperse red 1 were subjected to decolorization via
electrochemical technique both in single and mixed form using iron and aluminum
electrodes. The experiment optimized several parameters such as type and distances
of the electrode, current density, and process duration to achieve effective color
removal. At a particular current density, iron displayed better treatment of both
Reactive Blue 140 and disperse red 1 than aluminum, and the energy consumption
was 1kWh.m
À3 for over 96% decolorization of both dyes (Phalakornkule et al.
2010). Another report suggested superior efficiency and operating cost of aluminum
over iron electrodes in the application of electrocoagulation for decolorization of
Levafix brilliant blue E-B. The aluminum electrode achieved 99% decolorization in
less than 30 min at a current density of 100 A/m
2 , electrolyte concentration of 5 mM,
and initial pH of 5.5. The operational cost and energy usage were calculated to be as
$2.9 per m
3 and 16.9 kWh/m
3 , respectively (Akbal et al. 2011).
Aluminum electrodes were applied in the electrocoagulation of 19 dye in a flowthrough cell under varying reaction parameters. Optimum values for electrolyte
(NaCl) concentration, dye concentration, current density, and pH are 4.0 g L
À1 ,
10 ppm, 160A m
À2 , and 6.5, respectively, to achieve about 95% decolorization
(Mollah et al. 2010). The feasibility of electrocoagulation was compared with
ozonation to decolorize diazo-, anthraquinone-, and aniline-based colorants. Both
processes removed nearly 99% of diazo and aniline dyes, whereas the ozonation also
634
R. S. Ashraf et al.
colemanite ore waste was employed to remove reactive Yellow 86 and 21 in single
and multiple dye mixtures. Ag-colemanite ore waste proved to be a reusable and
cheap photocatalyst causing the removal of dyes from both single and binary
systems under optimized conditions of highly acidic pH, 100 mg/L beginning
concentration, duration of 1.25 h, and photocatalyst dose of 1.0 g L
À1 (Yola et al.
2014).
17.3.3 Electrochemical Treatment
Electrochemical methods such as electrocoagulation offer many advantages over
existing physiochemical and membrane separation methods. For instance,
electrocoagulation utilizes the electron as a unique reagent, thus reducing the cost
sludge production while increasing safety and selectivity. In a typical
electrocoagulation method, a metal electrode functions as anode where electrolytic
oxidation produces the coagulant (Singh et al. 2013). Iron or aluminum electrodes
have gained popularity not only because of economic and commercial advantages
but also due to the favorable mechanism of action, i.e., the formation of metal oxides
and hydroxides that increases adsorption (Zidane et al. 2008). Aluminum and
stainless steel electrodes employed for a simulated reactive dyebath solution
revealed the superiority of stainless steel electrodes, particularly for decolorization.
The mechanism behind color and chemical oxygen demand removal was attributed
to coagulation and adsorption at extremely basic pH (Kabdaşlı et al. 2009).
Reactive Blue 140 and disperse red 1 were subjected to decolorization via
electrochemical technique both in single and mixed form using iron and aluminum
electrodes. The experiment optimized several parameters such as type and distances
of the electrode, current density, and process duration to achieve effective color
removal. At a particular current density, iron displayed better treatment of both
Reactive Blue 140 and disperse red 1 than aluminum, and the energy consumption
was 1kWh.m
À3 for over 96% decolorization of both dyes (Phalakornkule et al.
2010). Another report suggested superior efficiency and operating cost of aluminum
over iron electrodes in the application of electrocoagulation for decolorization of
Levafix brilliant blue E-B. The aluminum electrode achieved 99% decolorization in
less than 30 min at a current density of 100 A/m
2 , electrolyte concentration of 5 mM,
and initial pH of 5.5. The operational cost and energy usage were calculated to be as
$2.9 per m
3 and 16.9 kWh/m
3 , respectively (Akbal et al. 2011).
Aluminum electrodes were applied in the electrocoagulation of 19 dye in a flowthrough cell under varying reaction parameters. Optimum values for electrolyte
(NaCl) concentration, dye concentration, current density, and pH are 4.0 g L
À1 ,
10 ppm, 160A m
À2 , and 6.5, respectively, to achieve about 95% decolorization
(Mollah et al. 2010). The feasibility of electrocoagulation was compared with
ozonation to decolorize diazo-, anthraquinone-, and aniline-based colorants. Both
processes removed nearly 99% of diazo and aniline dyes, whereas the ozonation also
634
R. S. Ashraf et al.