Nitrogen Removal through Ammonia Release from Holding Ponds
507
detention time (ΔΘ
> 0), lack of wind or great tank depth, the serial tanks would
approach plug flow conditions and
k„k uM ηΔΘ
C n
=
C o
e
h
1 U ~
(19)
If the accumulated residence time is Θ = ηΔΘ, we get eq. (14).
When AQ or the total area of ammonia release ponds is expressed in cm
2 , Q — flow
rate in cm
3 /hr, Θ in hrs and h in cm, then
Θ = ^ Θ
h
Q
And eq. (19) becomes
(20)
_
k u
k l
A Q
C n = C 0 e
Q
(21)
Experimen tal R esu Its
For experimental purposes, lime treatment was applied to the effluent of a five-cell
stabilization pond model* and subsequently ammonia release rates were studied. It had
been found previously that efficient lime treatment of that effluent required a pH of 11
(12), and therefore this was the initial pH in the ammonia release experiment. Because
of the high strength of the raw sewage used in the system, the ammonia concentration
after lime treatment ranged from 50 to 90 mg/1 (as N).
In preliminary experiments the liquid was held outdoors in seven containers of
different sizes with continuous recording of wind velocity and liquid temperature. An
additional container was simultaneously kept indoors, at wind velocity practically nil.
Samples from different depths were drawn once or twice daily and ammonia
concentrations and pH were measured, showing a drop in both. The average relative
concentrations are plotted in semi-logarithmic scale in Fig. 2, which shows that the rate
of evaporation is faster, the smaller the depth and the higher the temperature. Within
each of those experiments wind velocities changed within an ample range.
In order to study separately the wind velocity factor, a special constant-velocity series
was carried out in a wind tunnel equipped with a constant-speed fan. Three tanks, 90, 45
and 30 cm in depth, filled to the same level with a NH 4 C1 solution in distilled water (55
mg/1 as N), pH adjusted to 11.0 with lime milk, were placed at the centre of the tunnel.
Throughout the test, wind velocity was measured with the aid of thermocouple
anemometer scattered about the tunnel, and liquid and air temperatures were recorded.
The first test was carried out at 11.9 km/h and an average water temperature of 24.8°C.
In the second test, the wind velocity was reduced to 4.6 km/h by using a suitable baffle
and the average water temperature was 25.7°C. The third test was carried out in still air
(the fan being only run for a few seconds daily for introducing fresh air through the
tunnel) and an average temperature of 23°C. (Although the temperature was not exactly
the same for the three experiments, it was considered that the range was narrow enough
as to make the effect of temperature negligible in relation to the effect of wind velocity).
Results of relative ammonia concentrations against time, plotted on a semi-logarithmic
This system of treatment was being investigated in relation to the Dan Region Renovation Project.
507
detention time (ΔΘ
> 0), lack of wind or great tank depth, the serial tanks would
approach plug flow conditions and
k„k uM ηΔΘ
C n
=
C o
e
h
1 U ~
(19)
If the accumulated residence time is Θ = ηΔΘ, we get eq. (14).
When AQ or the total area of ammonia release ponds is expressed in cm
2 , Q — flow
rate in cm
3 /hr, Θ in hrs and h in cm, then
Θ = ^ Θ
h
Q
And eq. (19) becomes
(20)
_
k u
k l
A Q
C n = C 0 e
Q
(21)
Experimen tal R esu Its
For experimental purposes, lime treatment was applied to the effluent of a five-cell
stabilization pond model* and subsequently ammonia release rates were studied. It had
been found previously that efficient lime treatment of that effluent required a pH of 11
(12), and therefore this was the initial pH in the ammonia release experiment. Because
of the high strength of the raw sewage used in the system, the ammonia concentration
after lime treatment ranged from 50 to 90 mg/1 (as N).
In preliminary experiments the liquid was held outdoors in seven containers of
different sizes with continuous recording of wind velocity and liquid temperature. An
additional container was simultaneously kept indoors, at wind velocity practically nil.
Samples from different depths were drawn once or twice daily and ammonia
concentrations and pH were measured, showing a drop in both. The average relative
concentrations are plotted in semi-logarithmic scale in Fig. 2, which shows that the rate
of evaporation is faster, the smaller the depth and the higher the temperature. Within
each of those experiments wind velocities changed within an ample range.
In order to study separately the wind velocity factor, a special constant-velocity series
was carried out in a wind tunnel equipped with a constant-speed fan. Three tanks, 90, 45
and 30 cm in depth, filled to the same level with a NH 4 C1 solution in distilled water (55
mg/1 as N), pH adjusted to 11.0 with lime milk, were placed at the centre of the tunnel.
Throughout the test, wind velocity was measured with the aid of thermocouple
anemometer scattered about the tunnel, and liquid and air temperatures were recorded.
The first test was carried out at 11.9 km/h and an average water temperature of 24.8°C.
In the second test, the wind velocity was reduced to 4.6 km/h by using a suitable baffle
and the average water temperature was 25.7°C. The third test was carried out in still air
(the fan being only run for a few seconds daily for introducing fresh air through the
tunnel) and an average temperature of 23°C. (Although the temperature was not exactly
the same for the three experiments, it was considered that the range was narrow enough
as to make the effect of temperature negligible in relation to the effect of wind velocity).
Results of relative ammonia concentrations against time, plotted on a semi-logarithmic
This system of treatment was being investigated in relation to the Dan Region Renovation Project.