18
K. Ramani et al.
3.4 Methods of Chemical Precipitation for Nitrogen Removal
Another common method of nitrogen removal from wastewater is by precipitating
ammoniacal nitrogen as Magnesium Ammonium Phosphate (MAP), which is also
known as struvite. This method has been widely explored and applied for treatment
of different types of nitrogen rich wastewaters, such as tannery effluents of leather
industries, digester supernatant and in industrial wastewater treatment plants, from
coke plants and nitrogen works to pig farms, sludge liquor and landfill leachate.
Commercial magnesium salts and other magnesium containing by-products are
used as the chemical precipitating agents. Low-cost Mg sources, such as magnesite,
brucite, a by-product of marine salt manufacturing and of the thermal treatment of
meat waste, bone meal, etc., have been assessed for its precipitating potential in the
formation of struvite [58]. The reaction for struvite formation id given as:
Mg
2+
+ PO
3−
+ NH 4
+
+ H 2 O → Mg NH 4 PO 4 6H 2 O ↓
Struvite or Magnesium Ammonium Phosphate (MAP) is a white insoluble crystalline compound comprising equivalent concentration of magnesium, ammonium,
and phosphate [59]. Though, it is completely accepted that this is a potential method,
the usage of costly magnesium salts increases the operational costs, which is a major
limitation of this process [60]. However, using inexpensive sources containing MgO
or Mg(OH) 2 and H 3 PO 4 can greatly reduce the operational cost. For example, ninety
percent of ammonia was removed using MgO as the coagulant during the treatment of
cochineal processed water. In addition, high ammonia removal was achieved during
Coking effluent treatment by using pyrolysate of magnesite as the Mg source.
3.5 Air Stripping for Nitrogen Removal
Air stripping is conventional method used for the removal of volatile gases such as
hydrogen sulfide, hydrogen cyanide and ammonia by driving air through the waste
water. In this method, when alkali is added to the wastewater, non-volatile ammonium
ions (NH 4
+ ) convert to volatile ammonia molecules (NH 3 ), which can be stripped
from the water phase into the gas phase when air is aerated into the water. Then,
by aerating the NH 3 containing air into an acid solution, the NH 3 in the gas phase
can be absorbed and recovered. The related chemical equilibriums include: The
advantages of air stripping lie in its modest reagent costs and easy operation and in
the possibility of recovering the removed nitrogen as ammonium sulphate [55]. Air
stripping is considered as the most attractive for the treatment of the high nitrogen
containing effluent since the cost of one kg of ammonia removal is significantly lower
at high ammonia concentrations.
The process of ammonia stripping generally involves the addition of lime or
caustic chemical in order to increase the pH of the effluent nearly from 10.8 to 11.5
K. Ramani et al.
3.4 Methods of Chemical Precipitation for Nitrogen Removal
Another common method of nitrogen removal from wastewater is by precipitating
ammoniacal nitrogen as Magnesium Ammonium Phosphate (MAP), which is also
known as struvite. This method has been widely explored and applied for treatment
of different types of nitrogen rich wastewaters, such as tannery effluents of leather
industries, digester supernatant and in industrial wastewater treatment plants, from
coke plants and nitrogen works to pig farms, sludge liquor and landfill leachate.
Commercial magnesium salts and other magnesium containing by-products are
used as the chemical precipitating agents. Low-cost Mg sources, such as magnesite,
brucite, a by-product of marine salt manufacturing and of the thermal treatment of
meat waste, bone meal, etc., have been assessed for its precipitating potential in the
formation of struvite [58]. The reaction for struvite formation id given as:
Mg
2+
+ PO
3−
+ NH 4
+
+ H 2 O → Mg NH 4 PO 4 6H 2 O ↓
Struvite or Magnesium Ammonium Phosphate (MAP) is a white insoluble crystalline compound comprising equivalent concentration of magnesium, ammonium,
and phosphate [59]. Though, it is completely accepted that this is a potential method,
the usage of costly magnesium salts increases the operational costs, which is a major
limitation of this process [60]. However, using inexpensive sources containing MgO
or Mg(OH) 2 and H 3 PO 4 can greatly reduce the operational cost. For example, ninety
percent of ammonia was removed using MgO as the coagulant during the treatment of
cochineal processed water. In addition, high ammonia removal was achieved during
Coking effluent treatment by using pyrolysate of magnesite as the Mg source.
3.5 Air Stripping for Nitrogen Removal
Air stripping is conventional method used for the removal of volatile gases such as
hydrogen sulfide, hydrogen cyanide and ammonia by driving air through the waste
water. In this method, when alkali is added to the wastewater, non-volatile ammonium
ions (NH 4
+ ) convert to volatile ammonia molecules (NH 3 ), which can be stripped
from the water phase into the gas phase when air is aerated into the water. Then,
by aerating the NH 3 containing air into an acid solution, the NH 3 in the gas phase
can be absorbed and recovered. The related chemical equilibriums include: The
advantages of air stripping lie in its modest reagent costs and easy operation and in
the possibility of recovering the removed nitrogen as ammonium sulphate [55]. Air
stripping is considered as the most attractive for the treatment of the high nitrogen
containing effluent since the cost of one kg of ammonia removal is significantly lower
at high ammonia concentrations.
The process of ammonia stripping generally involves the addition of lime or
caustic chemical in order to increase the pH of the effluent nearly from 10.8 to 11.5