16
K. Ramani et al.
3.2 Sequential and Continuous Ion-Exchange Operation
In ion exchange operations, ions on the surface of a solid are exchanged for ions
of an identical charge matrices present in the wastewater in which the solid is in
contact. Ion exchange is a general process which can be used to remove undesirable
ions from waste water. Cations (positive ions) are exchanged for hydrogen or sodium,
and anions (negative ions) for hydroxide or chloride ions. Ion exchange using zeolites
is a basic process applied for recovery of ammonia. Zeolites have a porous structure
which is readily available for the trapping of the various cations. Many natural zeolites
materials varying in Si and Al composition are available in which Si rich Clinoptilolite
is the widely used ion exchange column. It has a dual channel system where the
zeolite functions as a molecular sieve. The salient features of Clinoptilolite are high
sorption and ion-exchange capacity, ion exchange selectivity, catalytic activity and
structural temperature stability up to 700–750 °C. In addition, synthetic zeolites with
some improved properties are also produced using silica and alumina as the main
raw materials which further reduces the process economy [55].
The clinoptilolite based ammoniacal nitrogen removal is a cationic ion exchange
reaction. In addition to the ion exchange, ammonia can also be recovered through
the physical adsorption by the structural pores of zeolite. The temperature plays
a main role in determining the efficiency of ammonia removal by adsorption in
which highest ammonia removal is achieved at elevated temperatures. However, the
maximum ammonia removal by clinoptilolite will occur between the pH 4 and 8. The
presence of other cations such as potassium, ammonia, calcium, sodium, magnesium
and other ions in the wastewater can easily be adsorbed by Clinoptilolite and other
zeolite which further results in the diminishing ammonia removal ability [56] (Fig. 3).
3.3 Membrane Processes-Reverse Osmosis and Ultrafiltration
Membrane processes like electrodialysis, ultrafiltration and reverse osmosis play a
significant role in the treatment of nitrogen containing waste water. A membrane is
a phase that acts as a mechanical barrier between the other phases which can be of
solid or a liquid. These efficiently used to the waste water containing nitrogen in the
form of ammonium or nitrate.
Reverse osmosis is highly preferred among the other membrane processes since
its maximum potential in high nitrogen removal and also capable of removing all
forms of nitrogen. Approximately 60–90% of the total nitrogen is being removed
by this process. The major limitations of this process are the membrane fouling
due to accumulation of colloidal substances in the membrane, requirement of pretreatment procedures like chemical clarification and filtration, membrane scaling due
to presence of iron and manganese in the wastewater [57].
Both ultrafiltration and reverse osmosis separate the compounds through a permeable membrane using selective pressure as the driving force. The cut off size for
K. Ramani et al.
3.2 Sequential and Continuous Ion-Exchange Operation
In ion exchange operations, ions on the surface of a solid are exchanged for ions
of an identical charge matrices present in the wastewater in which the solid is in
contact. Ion exchange is a general process which can be used to remove undesirable
ions from waste water. Cations (positive ions) are exchanged for hydrogen or sodium,
and anions (negative ions) for hydroxide or chloride ions. Ion exchange using zeolites
is a basic process applied for recovery of ammonia. Zeolites have a porous structure
which is readily available for the trapping of the various cations. Many natural zeolites
materials varying in Si and Al composition are available in which Si rich Clinoptilolite
is the widely used ion exchange column. It has a dual channel system where the
zeolite functions as a molecular sieve. The salient features of Clinoptilolite are high
sorption and ion-exchange capacity, ion exchange selectivity, catalytic activity and
structural temperature stability up to 700–750 °C. In addition, synthetic zeolites with
some improved properties are also produced using silica and alumina as the main
raw materials which further reduces the process economy [55].
The clinoptilolite based ammoniacal nitrogen removal is a cationic ion exchange
reaction. In addition to the ion exchange, ammonia can also be recovered through
the physical adsorption by the structural pores of zeolite. The temperature plays
a main role in determining the efficiency of ammonia removal by adsorption in
which highest ammonia removal is achieved at elevated temperatures. However, the
maximum ammonia removal by clinoptilolite will occur between the pH 4 and 8. The
presence of other cations such as potassium, ammonia, calcium, sodium, magnesium
and other ions in the wastewater can easily be adsorbed by Clinoptilolite and other
zeolite which further results in the diminishing ammonia removal ability [56] (Fig. 3).
3.3 Membrane Processes-Reverse Osmosis and Ultrafiltration
Membrane processes like electrodialysis, ultrafiltration and reverse osmosis play a
significant role in the treatment of nitrogen containing waste water. A membrane is
a phase that acts as a mechanical barrier between the other phases which can be of
solid or a liquid. These efficiently used to the waste water containing nitrogen in the
form of ammonium or nitrate.
Reverse osmosis is highly preferred among the other membrane processes since
its maximum potential in high nitrogen removal and also capable of removing all
forms of nitrogen. Approximately 60–90% of the total nitrogen is being removed
by this process. The major limitations of this process are the membrane fouling
due to accumulation of colloidal substances in the membrane, requirement of pretreatment procedures like chemical clarification and filtration, membrane scaling due
to presence of iron and manganese in the wastewater [57].
Both ultrafiltration and reverse osmosis separate the compounds through a permeable membrane using selective pressure as the driving force. The cut off size for