NITROGEN REMOVAL THROUGH
AMMONIA RELEASE FROM
HOLDING PONDS
Y. FOLKMAN* and A.M. WACHS
Project Manager, Dan Region Sewage Reclamation Project, Prof. San. Eng.
Tahal Water Planning Ltd., 54 Dan Gavirol Street, Tel Aviv, Israel
INTRODUCTION
During the last decade considerable efforts have been applied to the study of methods
that could be used in nitrogen removal from wastewater. Of special interest are those that
follow lime treatment at high pH values, since this process can be very efficient in
removing from wastewater organic matter, phosphates, bacteria and viruses. Ammonia
stripping towers, after lime treatment, have been used in several instances (1) (2) (3).
Reports on unaided ammonia release from lakes (4), streams (5) and stabilization
ponds (6) point to the possibility of effecting that release by holding lime-treated
effluents in open ponds, a system that could find application in cases where low-cost land
is available and climatic conditions are suitable. The object of this study was to determine
the influence of environmental factors on ammonia release from holding ponds, to obtain
data on the rate of removal and to develop design criteria for such ponds.
INFLUENCE OF pH ON AMMONIA RELEASE
Although much is known on the transition mechanism of ammonia from ions into
dissolved gas and eventual desorption, data on the rate of release and on the influence of
climatic factors are scarce.
For aqueous ammonia, there is equilibrium between its gaseous and ionic states
according to the following equation:
NH 3 + H 2 0 ^ NH 4
+ + OH"
(1)
The reaction is closely dependent on the pH of the water. The ratio of the dissolved
gas in the total ammonia in the water [ΝΗ 4
+ ]τ, as a function of the pH, is given by the
following variant of the equilibrium equation:
[ N H 4 ] T = NH 3 + [NH 4 1
(2)
[ N H 4
+ ] T
1 + %
[H
+
]
*w
when K N is the equilibrium coefficient and K^ = 10"
14 . The pH-dependence of the
gas-to-total ratio is plotted in Fig. 1, which shows that above pH 10, 90% of the ammonia
appear in the form of dissolved gas as against 99% at pH 11. Eq. (1) shows that release of
NH 3 reduces the pH. Lime-treated effluents contain no C0 2 . When they are held for
several days in open ponds, NH 3 is released into the atmosphere and C0 2 is absorbed
503
AMMONIA RELEASE FROM
HOLDING PONDS
Y. FOLKMAN* and A.M. WACHS
Project Manager, Dan Region Sewage Reclamation Project, Prof. San. Eng.
Tahal Water Planning Ltd., 54 Dan Gavirol Street, Tel Aviv, Israel
INTRODUCTION
During the last decade considerable efforts have been applied to the study of methods
that could be used in nitrogen removal from wastewater. Of special interest are those that
follow lime treatment at high pH values, since this process can be very efficient in
removing from wastewater organic matter, phosphates, bacteria and viruses. Ammonia
stripping towers, after lime treatment, have been used in several instances (1) (2) (3).
Reports on unaided ammonia release from lakes (4), streams (5) and stabilization
ponds (6) point to the possibility of effecting that release by holding lime-treated
effluents in open ponds, a system that could find application in cases where low-cost land
is available and climatic conditions are suitable. The object of this study was to determine
the influence of environmental factors on ammonia release from holding ponds, to obtain
data on the rate of removal and to develop design criteria for such ponds.
INFLUENCE OF pH ON AMMONIA RELEASE
Although much is known on the transition mechanism of ammonia from ions into
dissolved gas and eventual desorption, data on the rate of release and on the influence of
climatic factors are scarce.
For aqueous ammonia, there is equilibrium between its gaseous and ionic states
according to the following equation:
NH 3 + H 2 0 ^ NH 4
+ + OH"
(1)
The reaction is closely dependent on the pH of the water. The ratio of the dissolved
gas in the total ammonia in the water [ΝΗ 4
+ ]τ, as a function of the pH, is given by the
following variant of the equilibrium equation:
[ N H 4 ] T = NH 3 + [NH 4 1
(2)
[ N H 4
+ ] T
1 + %
[H
+
]
*w
when K N is the equilibrium coefficient and K^ = 10"
14 . The pH-dependence of the
gas-to-total ratio is plotted in Fig. 1, which shows that above pH 10, 90% of the ammonia
appear in the form of dissolved gas as against 99% at pH 11. Eq. (1) shows that release of
NH 3 reduces the pH. Lime-treated effluents contain no C0 2 . When they are held for
several days in open ponds, NH 3 is released into the atmosphere and C0 2 is absorbed
503