2.3.1 Bench-Scale Process
Cho et al. (2011) applied the EK process for the removal of salts, such as nitrate,
chloride, sulfate, sodium, calcium, and potassium, from agricultural soil. Kim et al.
(2010) effectively removed sodium and chloride from tidelands soil by EK remediation. They observed that effective remediation is directly proportional to the
operation time of the EK process. Results showed complete removal of sodium in
the tidelands and a significant amount of chloride removal (58.5%) after 10 days of
the EK process. Furthermore, they observed that sodium and chloride concentration
directly influences the reduction in electrical conductivity of the soil, about 65.5% of
the original value. Removal efficiency was reduced after 10 days of the EK process,
and correspondingly the energy consumption increased. Lee et al. (2012a, b) demonstrated the effect of electrode materials for reduction of salinity/saline salts from
the soil. Sodium and chloride ions were effectively removed from the soil using a
dimensionally stable anode (DSA), with platinum (Pt), Fe, and boron-doped diamond (BDD) electrodes, with average removal ranges about 97% or more and 98%
or more of sodium and chloride, respectively. Similarly, Cho et al. (2010) also
attempted removal of nitrates from agricultural soil at various voltage gradients, of
1, 2, and 3 V/cm applied for 2 and 4 days. They achieved 80% and 99% of nitrate
removal at 2 and 4 days of the EK process, respectively. Kim et al. (2010) also
observed higher sodium than chloride removal efficiency during EK remediation.
They explained that the chloride ions may produce a complex with calcium and
magnesium, such as [CaCl]
+ and/or [MgCl]
+
, which move towards the cathode by
electromigration. Generally, chloride ions move towards the anode by
electromigration during the process, and the high concentration of chloride in the
anolyte solution may inhibit chloride removal by back-diffusion into the soil section
from the electrolyte chamber (Kim et al. 2010). In addition, the chloride removal
process may be interrupted by the electro-osmotic flow. On the other hand, sodium
ions are removed by electromigration and electro-osmosis processes because both
processes act in the same flux direction (Cho et al. 2009).
2.3.2 A Pilot- and Field-Scale Process
Some investigators have attempted the removal and reduction of salts and soil
electrical conductivity in pilot and field tests in contaminated agricultural soil
(Choi et al. 2012; Kim et al. 2013a, b, 2012a, b, c; Lee et al. 2012a, b, 2013).
Choi et al. (2012) achieved excellent results in the removal of sodium, chloride, and
nitrate (>90%) in the field application of the EK process using a voltage gradient of
0.8 V/cm for 60 days, but they could not reduce the electrical conductivity of the soil
to the recommended value of 2.5 dS/m for crop cultivation. The removal efficiency
was about 80% and 60% at the top and bottom layers of the soil, respectively. Kim
et al. (2011) observed that the nitrate removal was higher than chloride concentration
for 14 days of ex situ EK processing in the hexagonal electrode arrangement system
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S. Annamalai and M. Sundaram
Cho et al. (2011) applied the EK process for the removal of salts, such as nitrate,
chloride, sulfate, sodium, calcium, and potassium, from agricultural soil. Kim et al.
(2010) effectively removed sodium and chloride from tidelands soil by EK remediation. They observed that effective remediation is directly proportional to the
operation time of the EK process. Results showed complete removal of sodium in
the tidelands and a significant amount of chloride removal (58.5%) after 10 days of
the EK process. Furthermore, they observed that sodium and chloride concentration
directly influences the reduction in electrical conductivity of the soil, about 65.5% of
the original value. Removal efficiency was reduced after 10 days of the EK process,
and correspondingly the energy consumption increased. Lee et al. (2012a, b) demonstrated the effect of electrode materials for reduction of salinity/saline salts from
the soil. Sodium and chloride ions were effectively removed from the soil using a
dimensionally stable anode (DSA), with platinum (Pt), Fe, and boron-doped diamond (BDD) electrodes, with average removal ranges about 97% or more and 98%
or more of sodium and chloride, respectively. Similarly, Cho et al. (2010) also
attempted removal of nitrates from agricultural soil at various voltage gradients, of
1, 2, and 3 V/cm applied for 2 and 4 days. They achieved 80% and 99% of nitrate
removal at 2 and 4 days of the EK process, respectively. Kim et al. (2010) also
observed higher sodium than chloride removal efficiency during EK remediation.
They explained that the chloride ions may produce a complex with calcium and
magnesium, such as [CaCl]
+ and/or [MgCl]
+
, which move towards the cathode by
electromigration. Generally, chloride ions move towards the anode by
electromigration during the process, and the high concentration of chloride in the
anolyte solution may inhibit chloride removal by back-diffusion into the soil section
from the electrolyte chamber (Kim et al. 2010). In addition, the chloride removal
process may be interrupted by the electro-osmotic flow. On the other hand, sodium
ions are removed by electromigration and electro-osmosis processes because both
processes act in the same flux direction (Cho et al. 2009).
2.3.2 A Pilot- and Field-Scale Process
Some investigators have attempted the removal and reduction of salts and soil
electrical conductivity in pilot and field tests in contaminated agricultural soil
(Choi et al. 2012; Kim et al. 2013a, b, 2012a, b, c; Lee et al. 2012a, b, 2013).
Choi et al. (2012) achieved excellent results in the removal of sodium, chloride, and
nitrate (>90%) in the field application of the EK process using a voltage gradient of
0.8 V/cm for 60 days, but they could not reduce the electrical conductivity of the soil
to the recommended value of 2.5 dS/m for crop cultivation. The removal efficiency
was about 80% and 60% at the top and bottom layers of the soil, respectively. Kim
et al. (2011) observed that the nitrate removal was higher than chloride concentration
for 14 days of ex situ EK processing in the hexagonal electrode arrangement system
194
S. Annamalai and M. Sundaram