South African Journal of Chemical Engineering 36 (2021) 134–141
Contents lists available at ScienceDirect
South African Journal of Chemical Engineering
journal homepage: www.elsevier.com/locate/sajce
Ammonia removal form municipal wastewater by air stripping process: An
experimental study
Arezoo Zangeneh a, Sima Sabzalipour a, *, Afshin Takdatsan a, b, Reza Jalilzadeh Yengejeh a,
Morteza Abullatif Khafaie a, c
a
b
c
Department of Environmental Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran
Department of Environmental Health Engineering, School of Health, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
Department of Public Health, School of Health, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
Air stripping
Ammonia removal efficiency
Air-water ratio
Municipal wastewater treatment plants
This study was aimed to evaluate ammonia removal efficiency (ARE) in the air stripping process in different
operating conditions for wastewater with a low concentration of ammonia such as municipal wastewater
treatment plants (WWTPs) on the laboratory scale. The experiments were performed at different pH (9.7 ± 0.26,
10.93±0.16 and 11.94±0.32), temperature (34.25±0.44, 38.57±3.4 and 40.5 ± 7.68 in ◦ C), initial concentration
(26.98 -47.34, 19.49 -47.48 and 41–98 in mg/L) and air-water (G/L) ratio (60:1, 70:1 and 80:1). The results
showed that ARE in the operating conditions (initial NH+
4 concentration 26.98 -98 mg/L, pH 9.4–12.38, tem­
perature 34–45.8 ◦ C and G/L 60:1–80:1) was increased from 6.6% to 98% with the range of 1 to 14 h. Based on
the results, ARE with 1 standard deviation (SD) increase per unit of pH, temperature and initial NH+
4 concen­
tration was 13.03%, 3.99% and 2.3%, respectively. Also, based on multivariate regression model at high and low
G/L, temperature and pH had the most significant effect on ARE for a synthetic solution as well as a municipal
WWTPs stream, respectively. ARE (91%) was obtained during the stripping process of synthetic and actual
municipal wastewater.
Abbreviations
ARE
Ammonia removal efficiency
Cin
NH+
4 concentrations in influent water (mg/l)
Cout
NH+
4 concentrations in effluent water (mg/l)
G/L
Air-water ratio
gr/L
Gram /liter
h
Hour
mg/L
Milligram/Liter
Mol/L
Mole/Liter
NH3
Ammonium ion gaseous form
NH4
Ammonium ion aqueous form +
NaOH
Sodium hydroxide
NH4Cl
Ammonium chloride
N.A
Not available
pH
A measure of acidity or alkalinity of a solution
Qa
Air flow rate
R
Removal (%)
SD
TN
V
WWTPs
Standard Deviation
Total Nitrogen
Solution volume
wastewater treatment plants
1. Introduction
Ammonium (NH+
4 ) nitrogen can enter the aquatic environment via
direct means (e.g. municipal effluent discharges) and indirect means (e.
g. agricultural activities) (EPA, 2013; Liu et al., 2019) . Therefore,
municipal wastewater treatment plants (WWTPs), landfills, mines,
agriculture and animal rearing operations are the largest sources of
ammonia wastewater pollution (Roch, 2015). Domestic wastewater is
usually composed of 60–70% ammonium nitrogen and 30–40% organic
nitrogen (Deng, 2014; Roch, 2015). The range of ammonium ion con­
centration varies from 20 to 100 mg/L in municipal wastewater (Ash­
rafizadeh and Khorasani, 2010). Bacteria use a small amount of NH+
4 for
cellular synthesis and the remainder, mainly as ammonia nitrogen, is
* Corresponding author.
E-mail addresses: ar.zanganeh60@gmail.com (A. Zangeneh), salipour@iauahvaz.ac.ir (S. Sabzalipour), afshin_ir@yahoo.com (A. Takdatsan), R.jalilzadeh@
iauahvaz.ac.ir (R.J. Yengejeh), Khafaie-m@ajums.ac.ir (M.A. Khafaie).
https://doi.org/10.1016/j.sajce.2021.03.001
Received 26 October 2020; Received in revised form 10 February 2021; Accepted 5 March 2021
Available online 8 March 2021
1026-9185/© 2021 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
A. Zangeneh et al.
South African Journal of Chemical Engineering 36 (2021) 134–141
eventually exiting along with the outlet stream from the treatment plant
(Wang et al., 2006). Also, based on the regulations of European Legis­
lation and WHO, the maximum allowable ammonia concentration in
surface water is less than 1.5 mg/L and 0.2 mg/L respectively (Jeong
et al., 2013). NH+
4 has a hazardous and toxic effect on the human health
only if its intake exceeds the capacity of detoxification and the allowed
limits (Gupta et al., 2015).
NH+
4 in municipal and industrial wastewater is an important
contaminant due to its toxic effects on aquatic organisms and eutro­
phication (Rajitha et al., 2020; Zhang et al., 2020). Therefore, to protect
the environment and human health, it is necessary to remove NH+
4 from
wastewater (Xie et al., 2009). For the removal of nitrogen from waste­
water, different processes such as physico-chemical and biological
(García-Martínez et al., 2017; Muloiwa et al., 2020; Rahmani et al.,
2020) are used . Due to the harmful effects of high concentrations of
ammonium on the microorganisms (in the biological treatment process),
the use of alternative methods based on physico-chemical processes has
been suggested (Capodaglio et al., 2015; Zhu et al., 2017). Currently,
several physico-chemical technologies are available for nitrogen
removal from wastewater: Ammonia and steam stripping; selected ion
exchange; breakpoint chlorination and struvite precipitation, Trickle
bed reactors (TBRs) (Capodaglio et al., 2015; Dasgupta and Atta, 2020;
Hasanoglu et al., 2010; Kartohardjono et al., 2015; Kinidi et al., 2018; Li
et al., 2020). Nevertheless, most of these treatments are still experi­
mental and special attention should be paid to the use of the air stripping
process to remove ammonium ions with low concentration and other
volatile compounds from solution. In several cases, to achieve high
ammonia removal rate, the air stripping process is considered as a
desirable solution (Campos et al., 2013; Ferraz et al., 2013; Taşdemir
et al., 2020; Yilmaz et al., 2010). Ammonia stripping has already been
successfully applied to concentrated wastewater treatment such as in­
dustrial landfill leachate (Gotvajn et al., 2009), Municipal solid waste
(MSW) landfill leachate (Viotti and Gavasci, 2015), petrochemical in­
dustry wastewater (Prather, 1959), swine manure (La et al., 2014),
mineral fertilizers and anaerobic digestion (Guˇstin and Marinˇsek-Logar,
2011; Walker et al., 2011); While very few applications are known in
Municipal wastewater treatment (Capodaglio et al., 2015). The aqueous
form (NH+
4 ) and gaseous form (NH3) as the ammonium ion in aqueous
solutions exist together in equilibrium according to Eq. (1):
NH4 + + OH− ⟷ NH3 + H2 O
air
used in addition to concentrated wastewater treatment for municipal
wastewater treatment with a low concentration of ammonium ion
(20–100 mg/l). In addition, in this study, a comparison is made between
the efficiency of ammonium ion removal during the stripping process of
synthetic wastewater and the actual municipal wastewater (primary
sedimentation tank (PST) effluent). Many studies have recommended an
air-to-water flow ratio of 3000:1 to remove ammonium ions The aim of
this study was to investigate the efficiency of the stripping process for
ammonium ion removal with air to water ratios of less than 3000:1.The
results of this study show that the air-to-water flow ratio is as low as 60:
1, 70: 1 and 80:1 Can be used to remove ammonium ions from municipal
wastewater, which can be prevented from increasing the costs of using
electricity for Aeration. In this study, optimum points and operating
conditions including temperature, pH, and effective flow ratio to remove
ammonium ions from solution (as well as a municipal wastewaterʼ
stream), which is effective in selecting operating conditions in municipal
wastewater treatment plants, was obtained.
This study aimed to evaluate Ammonia removal efficiency (are) in
the air stripping process for wastewater with low concentration of
ammonia such as municipal wastewater treatment plants (WWTPs) and
to obtain optimal operating conditions, on a laboratory scale. In this
study, optimum points and operating conditions including temperature,
pH, and effective flow ratio to remove ammonium ions from solution (as
well as a municipal waste water stream), which is effective in selecting
operating conditions in municipal wastewater treatment plants, was
obtained.
2. Methods
2.1. Design of air stripping tower
For the air stripping experiments, one stripping tower of plexiglass
(1 m height x 10 cm internal diameter) was constructed in the lab- and
pilot-scale experiments (Eddy, 2003). A schematic diagram of the
experimental setup is shown in Fig. 1. The tower was packed with the
media packing type Kaldness 3 (Kavian Media Kaldness, Kavian Co,
Iran) and with 25 × 10 mm diameter. Counter-current packed tower
with the height of the packing was 0.6 m used in this study (Eddy, 2003;
Hanira et al., 2016). Table 1 shows the characteristics of the packed
column and the pilot-scale lab experimental setup for the air stripping of
Ammonia. Plastic media packing was selected in this work to increase
(1)
Ammonium is removed in the stripper process by increasing pH and
converting ammonium ion (NH+
4 ) to ammonia gaseous form (NH3)
(Kinidi et al., 2018). Some important parameters that have been re­
ported to affect ammonia stripping performance are pH, air-water (G/L)
ratio, water and ambient air temperature, contact time/stripping time,
column height, NH+
4 concentration of wastewater, hydraulic wastewater
loading and packing depth (Deng, 2014; Hanira et al., 2016; Kinidi et al.,
2018).
However, pH and temperature are more effective (Guo et al., 2010;
Sengupta et al., 2015). In ammonia stripping, caustic (NaOH) or lime is
added to enhance pH (Alam and Hossian, 2009). The liquid temperature
can also affect the ammonia removal efficiency (ARE) (Deng, 2014).
Also, the rate of contaminant removal in the air stripping process is
influenced by G/L ratio(Wang et al., 2006). To improve removal effi­
ciency, ammonia stripping is usually operated by a counter-current
packed stripping tower with media packing. The media packing in­
creases the surface area of the contaminated water that is exposed to the
air (Abdullahi et al., 2014; Blauvelt, 2009; Deng, 2014). Air stripping
has been suggested for the treatment of concentrated wastewater
treatment (Capodaglio et al., 2015). This study was aimed to evaluate
ARE in the air stripping process for wastewater with a low concentration
of ammonia with a synthetic solution as well as a WWTPs stream in
different operating conditions on the laboratory scale.
The results of this study show that the air stripping method can be
Fig. 1. A Schematic diagram of the pilot-scale lab experiment for the air
stripping of Ammonia.
135
A. Zangeneh et al.
South African Journal of Chemical Engineering 36 (2021) 134–141
effluent to evaluate the comparison of ARE during the stripping process
between synthetic wastewater and actual wastewater, the actual
wastewater for pilot feeding was prepared from Ahvaz Municipal
Wastewater Treatment Plant (WWTPs). Characteristics of actual waste­
water used as influent of air stripping pilot are presented in Table 2.
Table 1
Characteristics of the packed column and the pilot-scale lab experimental setup
for the air stripping of Ammonia.
Parameter
Set 1
Wastewater flow rate (L/min)
Air flow rate (L/min)
Air-water ratio (G/L)
Air speed velocity (m/s)
Packing volume
Packing area
Column diameter
Height of packing
Packing Type
0.42
0.5
25
35
60
70
0.05
0.07
4.71 × 10− 3 m3
2
3
725 m /m
0.1 m
0.6 m
Kaldness 3 (25 × 10 mm)
Set 2
Set3
0.56
45
80
0.09
2.3. Analysis
Visual characteristics of air stripping system and statistical specifi­
cations of input pH, temperature and initial NH+
4 concentration, which
included 590 observations, were presented. To evaluate the effects of
change in the efficiency of system in ammonium removal, a linear
regression model was conducted which included R as the dependent
variable and pH, temperature and NH+
4 as the independent variables. The
amount of change in R for 1 SD change was reported in the independent
variable. Also, a subgroup analysis was performed to evaluate the best
functional performance of the system at a different G/L ratio. All the
analyses were conducted by STATA version 14 (STATA Corporation,
College Station, TX).
the level of liquid-air contact and to improve ARE. The temperature
controller module (Model XH-W3001) and the heating element were
used, which maintained the process at the programmed temperature.
The choice of temperature was based on the temperature range of other
studies (Campos et al., 2013; Lin et al., 2012). The pilot set-up
comprised a receiver tank (sample feed; total volume 20 L). The
airflow rate was supplied by using a diffused aerator (HAILEA Aq. air
pump, 45 L/min). A Rota meter was utilized to regulate and maintain
the wastewater flow rate and airflow rate in the fixed range. As the Fig. 1
shows, (1) Electronic switch and temperature controller; (2) heating
system; (3) feed tank; (4) water pump; (5) water valve;(6) water flow
meter; (7) air stripping column; (8) airflow meter; (9) air pump; (10)
water recycle tank; (11) gas outlet; (12) gas outlet valve.
3. Results and discussion
3.1. Effect of initial ammonia concentration and pH on ARE
In this study, after the pilot reached a stable state, ARE was examined
under different operating conditions during 48 days using synthetic
solutions containing different initial NH+
4 concentrations in 3 sets
(0.53–0.94, 0.38–0.94 and 0.82–1.96 g/L). Blackwell et al. demon­
strated that synthetic solutions had a similar behavior to their solutions
to evaluate the efficiency of removing volatile pollutants by the stripper
process (Blackwell et al., 1979). ARE, based on Eq. (2) for initial and
effluent NH+
4 concentration (26.98–47.34, 19.49–47.48 and 41–98 in
mg/L) and (25.186 − 40.40, 13.67–14.99 and 18–1.82 in mg/L) were
6.6–14% (after 1–1.5 h of operation), 28–68% (after 2.5–3.5 h of
operation) and 56–98% (after 4–14 h of operation), respectively (Fig. 2).
Fig. 2 shows Effect of initial NH4+concentration on are in different
operation times.
The effect of pH (9.7 ± 0.26, 10.93 ± 0.16 and 11.94 ± 0.32.32) and
initial NH+
4 concentration (26.98–47.34, 19.49–47.48 and 41–98 in mg/
L) on the are in the air stripping process is shown in Fig. 3. This
Figure shows at the original pH (9.4), no significant removal of NH+
4
(26.98 mg/L) was achieved as minimum are (6.6%) (influent=26.98
mg/L, effluent= 25.186 mg/L) at 1 h, while optimum is for 98 mg/L
NH+
4 concentration was 98% at pH of 12.38 (influent=98 mg/L, efflu­
ent=1.82 mg/L) and 14 h, respectively. The results of this study
demonstrated that synthetic solutions can be used to evaluate the effi­
ciency of the ammonium removal by air stripping process for waste­
water with a low concentration of ammonium. Thus, in this study, for
synthetic wastewater with initial concentrations range from 19.49 to 98
mg/L, maximum ARE (98%) was achieved in 14 h. While, in a similar
work, in the treatment of landfill leachate with a low concentration of
ammonium (74–220 mg/L) with the maximum removal of ammonium
89%, 24 h was required (Marttinen et al., 2002).In another study, the
highest efficiency of ammonium ions removal by air stripping process
was noted at the level of 50.6%, with an initial pH value of 10.5, after 12
h (Seruga et al., 2020).
Linear regression analysis showed that increasing inlet NH+
4
2.2. Material and process
In this study, to determine ARE in the air stripping process, the effect
of parameters such as pH, temperature, G/L ratio and initial concen­
tration of ammonium was investigated. All the experiments were per­
formed at 3 sets pH (9.7 ± 0.26, 10.93±0.16, 11.94±0.32) and 3 sets
temperature (34.25±0.44, 38.57±3.4, 40.5 ± 7.68 in ◦ C) to remove
ammonium during 48-day periods of operation within 1 to 14 h. Studies
showed that synthetic solutions can be used to evaluate the efficiency of
the air stripping process for wastewater treatment (Jenkins et al., 2007);
So, to evaluate the effect of initial ammonium concentration on the air
stripping process in terms of removing ammonium from municipal
WWTPs, synthetic wastewater was prepared by dissolving 0.3–2 g
ammonium chloride (from NH4Cl salt (Merck)) in distilled water in feed
tank (20 L), which was similar to the concentrations of ammonia in the
municipal wastewater. The pH was adjusted using 6 and 25 mol/L of
NaOH (Merck). Samples (10 mL) were taken in regular periods and from
the feed solution to measure NH+
4 concentration and pH. The quantities
of ammonia and Total nitrogen in the wastewater samples were deter­
mined based on the standard method for the examination of water and
wastewater with reagents and chemicals from Merck by the Nessleri­
zation method (preparation of Nessler reagent and preparation of stan­
dard solutions) and spectrophoto meter (HACH, DR. 5000, Germany) at
425 nm wavelength (method 4500-C and method 4500-N). The pH
samples were measured by a pH meter (WTW 720, Inolab, Germany)
(WPCF, 1989). During the experiment, the pressure drops measured
were very low and an air-water ratio range of equivalent to G/L ratios of
60:1, 70:1, and 80:1 was selected based on other studies (Hanira et al.,
2016). Gas Alert Extreme NH3_BW Technologies by Honeywell sensor
(BW Gas Alert Extreme NH3 Gas Detector) were used to measure
ammonia gas in contaminated air. Ammonia removal efficiency (% Eff.)
was calculated based on Eq. (2):
%Ammonia Eff. =
Cin − Cout
× 100
Cin
Table 2
Characteristics of actual wastewater used as influent of air stripping pilot and
evaluate of ARE.
(2)
Where Cin and Cout are
concentrations in influent and effluent
water in mg/L, respectively (Jafari et al., 2014; Sahu, 2019).
Wastewater characteristics: Primary sedimentation tank (PST)
NH+
4
136
Parameter
Unit
Value
pH
NH+
4
TN
–
mg/L
mg/L
9.14
61.04
70.19
A. Zangeneh et al.
South African Journal of Chemical Engineering 36 (2021) 134–141
Fig. 4. Comparing initial NH4+ concentrations and pH on ARE in synthetic and
actual wastewater.
Fig. 2. Effect of initial NH4+concentration on ARE in different opera­
tion times.
wastewater and actual wastewater.
To evaluate and the comparison of ARE during the stripping process
between synthetic wastewater and actual wastewater with the same
influent NH+
4 concentrations (59.6 mg/L synthetic wastewater, 61.04
mg/L actual wastewater) was examined. Based on results, As shown in
Fig. 4, are in actual wastewater was 91% with average of pH 11.94 at 7 h
and ARE in synthetic wastewater was 91% with average of pH 11.86 at 6
h. The Results of this study demonstrated that, despite a slightly higher
actual wastewater average of pH 11.94 than synthetic wastewater
average of pH 11.86, the time required to remove ammonium ions was
equal to 7 and 6 h for actual municipal from PST effluent with influent
NH+
4 concentration 61.04 mg/Land effluent concentration 5.36 mg/L
and synthetic wastewater with influent NH+
4 concentration 59.6 mg/L
and effluent concentration 4.98 mg/L, respectively. This time difference
can be attributed to the presence of surfactants and other chemical
compounds in actual wastewater, which increases the time required to
transfer the ammonium ion mass from the liquid phase to the gas phase
and demonstrates the need to use anti-foam materials for evaluating
removal efficiency by the stripper process.
Surfactants and other interfering agents in the composition of liquids
complicate the air stripping and lead to the formation of significant
foaming in pilot and laboratory tests, which indicates the need to use
antifoams in the pilot and laboratory tests. The presence of surfactants
also prevents the mass transfer of volatile compounds from the liquid
phase to the gas phase (Lowe et al., 1999), which leads to an increase in
the time required to transfer the mass from the liquid phase to the gas
phase. Another study shows that increasing foam production reduces the
removal efficiency in the process(Seruga et al., 2020).
Fig. 3. Effect of initial NH4+concentration and pH on ARE.
concentration led to increasing ARE, and a significantly positive rela­
tionship was observed between inlet ammonium concentration and the
removal efficiency (p = 0.000), which was similar to another study
(Jafari et al., 2014). This indicates that ammonia nitrogen removal is a
function of initial NH+
4 concentration (Cotman and Gotvajn, 2010;
Lubensky et al., 2019). Also, the results of this study demonstrated that
ARE rose from 6.6% to 98% as pH increased from 9.4 to 12.38. The
reason was the increase in the conversion of Ammonium ion to the
gaseous form at higher pH and shift of the equilibrium chemical reaction
to the right side according to Eq. (1). In this study there was a significant
association between pH and ARE (p = 0.000) .The maximum ARE was
obtained at higher pH and concentrations of NH+
4 . These results were in
agreement with those of other studies (Hossini et al., 2016a; Ozyonar
et al., 2012). When pH is higher, i.e. around 11 or 12, air stripping is
much more effective, especially in terms of ammonia removal (Blauvelt,
2009). Linear regression statistical analysis showed that the stripping pH
(18.62: 0.95% CI, 15.13–22.09) and initial concentration of ammonia
(0.12:0.95% CI, 0.01–0.24) were the factors that led to ARE increasing;
this increase in ARE was more effective with the pH increase than the
increase in the initial ammonia ion concentration. So, we observed, with
an increase per unit of pH and initial concentration, ARE increased by
almost 12% and 2.3%, respectively (change in removal (R) for 1 stan­
dard deviation (SD) change in the independent variable). Therefore, pH
had the most significant effect on stripping due to converting NH+
4 ion to
NH3 gas according to NH+
4 /NH3 equilibrium. Fig. 4 shows the compar­
ison of initial NH+
4 concentrations and pH on ARE in synthetic
3.2. Effect of temperature on ARE
Temperature also has an important effect on stripping, as higher
temperature reduces the solubility of gasses in water (Liehr et al., 2006;
Maile et al., 2017). In this study, the impact of temperature 34.25±0.44,
38.57±3.4 and 40.5 ± 7.68 in ◦ C was investigated and linear regression
analysis showed the significant temperature effect on are (p = 0.000). As
shown in Fig. 5,the maximum is (98%) was obtained at 45.8 ◦ C, while
the lowest ammonia removal (6.6%) was observed at 34 ◦ C .Thus, free
ammonia concentration increased with the increasing temperature. As
the result of reducing the solubility of NH3 gas in wastewater by Henry’s
constant; better ARE was observed at higher operating temperature
(more than 40 ◦ C). This was similar to other studies that increasing the
temperature of the feed tank results in higher removal efficiency in the
air stripping process (Değermenci et al., 2012; Ding et al., 2006; Meh­
dipourghazi et al., 2015; Viotti and Gavasci, 2015). Based on the results,
ARE was increased with rising in the unit of pH (13.03%) and temper­
ature (3.99%) values (change in R for 1 SD change in the independent
variable). However, the effect of pH (20.368: 0.95% CI, 17.87–22.85)
137
A. Zangeneh et al.
South African Journal of Chemical Engineering 36 (2021) 134–141
Fig. 6. Comparing initial NH+
4 concentrations and temperature on ARE in
synthetic and actual wastewater.
ratio increased the transfer of ammonia into the air phase, which was the
same as another study (Hanira et al., 2016; Lin et al., 2012). Also, in the
study conducted by Sonaka et al., A positive relationship between G/L
ratio and ammonia removal efficiency was obtained(Sonaka et al.,
2016). The results of this study demonstrated that the maximum ARE
was 98% for wastewater with a low concentration of 98 mg with the G/L
ratio 80:1. In other similar studies for the removal of ammonium ions in
wastewater with the concentration of 123 and 150 mg and efficiency of
88.3 and 90, G/L ratio of 3000 and 2925 was required in Air stripping
process, respectively (Bui et al., 2020; Jia et al., 2017). Fig. 7 shows the
change in ARE with a 1 SD increase in a unit of pH, temperature and
initial concentration at different G/L ratios (60:1, 70:1 and 80:1). Re­
sults are related to the multivariate regression model and the error bar
indicates a 95% confidence interval. This result demonstrated that ARE
increased with an increase in temperature and G/L ratio (60:1, 70:1 and
80:1). Furthermore, with increasing G/L ratio, the temperature had the
most significant effect on the efficiency of stripping processing, because
increased temperature caused a decrease in solubility, increases in
Henry’s coefficient and, hence, improvement in removal efficiency
(Zareei and Ghoreyshi, 2011).Also, the combined effect of high tem­
perature and G/L ratio resulted in accelerated removal (Kamarden et al.,
2014), while at a low G/L ratio, pH had the most significant impact on
ARE. According to the results of this study, pH and temperature were the
most important factors affecting ARE (change in R for 1 SD change in the
independent variable); but, in the multivariate regression model
(different G/L ratios (60:1, 70:1 and 80:1)), with increasing G/L ratio,
the temperature had the most significant effect on the efficiency of
stripping processing. In contrast, at a low G/L ratio, pH had the most
significant impact on ARE for the air stripping processing in wastewater
with a low concentration of ammonia in a synthetic solution as well as a
WWTPs.
According to other studies, pH and temperature are the most
important factors influencing the efficiency of volatile compounds by
the air stripping processing (Guo et al., 2010; Sengupta et al., 2015);
however, which parameters are more effective in the removal of
ammonia from wastewater with low concentrations of ammonium ion at
different G/L ratios has been less studied. Table 5 shows the comparison
of the present study and previous works on ARE in wastewater with a
low concentration of ammonia by the air stripping process.This study
was aimed to evaluate ARE form wastewater with a low concentration of
ammonium ion by the air stripping process. It is suggested for future
works to examine the effects of time, Henry’s constant and other pa­
rameters on the mass transfer constant in detail.
Fig. 5. Effect of temperature on ARE.
was more significant than temperature (0.587: 0.95% CI, 0.35–0.81) for
ammonia removal from the solution. This result was in agreement with
other the findings of other studies that have investigated ARE by an air
stripping process (Hossini et al., 2016b) .
Change in ARE per 1 SD increase in a unit of pH, temperature and
initial NH+
4 concentration is shown as a univariate and multivariate
regression model in Table 3. Error bar indicates 95% confidence inter­
val. Fig. 6 demonstrates the comparison of initial NH+
4 concentrations
and temperature on ARE in synthetic wastewater (with average of
39.66 ◦ C) and actual municipal wastewater (with average of 40.69 ◦ C)
from PST effluent.
3.3. Effect of airflow on ARE
Air-water (G/L) ratio is an important parameter that has an impact
on the removal rates of ammonia in water (Guˇstin and Marinˇsek-Logar,
2011). Many studies have recommended the G/L ratio of 3000: 1 for the
removal of ammonia (Eddy, 2003). The results of this study showed that
the G/L ratio as low as 60:1, 70:1 and 80:1 can be used to remove
ammonium ions from municipal wastewater treatment with low con­
centration. Experimental values of G/L ratio in our trial were chosen
based on the other studies about the air stripping process (Hanira et al.,
2016).
Table 4 shows the trend of removal efficiencies of ammonia at
different G/L ratios and the concentration of ammonia. The results of
this study showed that the G/L ratio 60: 1, 70: 1 and 80: 1 can be used for
ammonia removal in the air stripping system with the maximum ARE of
14%, 68% and 98%. That indicates the need for less aeration than the
3000: 1 ratio and reduction in the cost of power consumption by the
pump for aeration.
These results indicated that ARE increased with increased G/L ratio
(p = 0.000). In this study, with increasing G/L ratio from 60:1 to 80:1,
the maximum ARE (98%) was at G/L ratio of 80:1 because higher G/L
Table 3
Change in ARE per 1SD increase in a unit of pH, temperature and NH+
4 initial
concentration.
Model 1
Model 2
pH
Changes (95% CI)
Initial concentration
Changes (95% CI)
Temperature
Changes (95% CI)
4. Conclusion
13.625 (12.1–15.23)
10.792 (8.574–13.01)
10.733 (8.99–12.48)
3.155 (0.974–5.357)
5.949 (3.855–7.842)
4.325 (4.063–5.921)
According to the results of this study, ARE in the air stripping process
with increasing the initial NH+
4 concentration, pH, temperature and G/L
ratio from 26.98 to 98 mg/L, 9.4 to 12.38, 34 to 45.8 ◦ C and 60:1 to 80:1
Model 1: Univariate regression model.
Model 2: Multivariate regression model.
138
A. Zangeneh et al.
South African Journal of Chemical Engineering 36 (2021) 134–141
Table 4
Change in ARE at different G/L ratios and concentrations of ammonia.
Air-water ratio (G/L)
Ammoniaconcentration in (mg/L)
Min
Max
Ammoniaconcentration out (mg/L)
Min
Max
Ammonia removalefficiency (%R)
Min
Max
G/L (60)
G/L (70)
G/L (80)
26.98
19.49
41
25.186
13.67
18
6.6
28
56
47.34
47.48
98
40.40
14.99
1.82
14
68
98
initial concentration, respectively (change in ARE per 1 SD increase
in the independent variable).
5 At high and low G/L, temperature and pH had the most significant
effect on ARE per 1 SD increase in the unit of pH, temperature and
initial concentration based on a multivariate regression model
(different G/L (60:1, 70:1 and 80:1)), respectively.
Funding source
This research did not receive any specific grant from funding
agencies in the public, commercial, or not-for-profit sectors.
Credit author statement
Fig. 7. Change in ARE per 1 SD increase in a unit of pH, initial concentration
(NH4) and temperature at different G/L ratios (60, 70 and 80). The results are a
multivariate regression model. Error bar indicates 95% CI.
According to the results of this study, ARE in the air stripping process
with increasing the initial NH+
4 concentration, pH, temperature and G/L
ratio from 26.98 to 98 mg/L, 9.4 to 12.38, 34 to 45.8 ◦ C and 60:1 to 80:1
was increased from 6.6% to 98% within 1 to 14 h. The results of this
study showed that the air stripping method can be used in addition to
concentrated wastewater treatment for municipal wastewater treatment
with a low concentration of ammonium ion (26.98 − 98 mg/L). In
comparing ARE during the stripping process of synthetic wastewater and
actual municipal wastewater from PST effluent, similar ARE (% 91)
results were obtained with the only time difference that can be resulted
from the presence of surfactants and need for anti-foams in ammonia
removal by air stripping process.
The results of this study demonstrated that:
was increased from 6.6% to 98% within 1 to 14 h. The results of this
study showed that the air stripping method can be used in addition to
concentrated wastewater treatment for municipal wastewater treatment
with a low concentration of ammonium ion (26.98 − 98 mg/L). In
comparing ARE during the stripping process of synthetic wastewater and
actual municipal wastewater from PST effluent, similar ARE (% 91)
results were obtained with the only time difference that can be resulted
from the presence of surfactants and need for anti-foams in ammonia
removal by air stripping process.
The results of this study demonstrated that:
1 The air stripping process can be used in addition to concentrated
wastewater treatment to remove ammonia with a low concentration
from WWTPs with high efficiency (% 98).
2 The strong influence of pH on ARE was due to changes in NH+
4 /NH3
equilibrium and converting NH4+ ion to NH3 gas.
3 ARE increased at higher operating temperatures due to reduced
solubility of NH3 gas in wastewater according to Henry constant.
4 pH˃ Temperature˃ NH+
4 initial concentration had the most significant
effect on ARE per 1 SD increase in the unit of pH, temperature and
1 The air stripping process can be used in addition to concentrated
wastewater treatment to remove ammonia with a low concentration
from WWTPs with high efficiency (% 98).
2 The strong influence of pH on ARE was due to changes in NH+
4 /NH3
equilibrium and converting NH4+ ion to NH3 gas.
3 ARE increased at higher operating temperatures due to reduced
solubility of NH3 gas in wastewater according to Henry constant.
4 pH˃ Temperature˃ NH+
4 initial concentration had the most significant
effect on ARE per 1 SD increase in the unit of pH, temperature and
Table 5
Comparing the ARE in wastewater with a low concentration of ammonia by air stripping.
Wastewater Type
Ammonia concentration
(mg/L)
Ammonia Removal
(%)
Temperature(
◦
C)
(G/L) ratio
pH
Time
(h)
Reference
Synthetic Municipal
26.98 − 47.34
19.49 − 47.48
41–98
59.6
61.04
74–220
34.25±0.44
38.57±3.4
40.5 ± 7.68
39.66
40.69
20
20
50
60
70
80
80
80
10 (Air flow rate)
9.7 ± 0.26
10.93±0.16
11.94±0.32
11.86
11.94
11
11
14
1–1.5
2.5–3.5
4–14
6
7
24
24
2
This work
10.5
*N.A
11
11
12
12
12
13
21
2
3
5
Industrial
Petroleum refinery
wastewater
123–366
6.6–14
28–68
56–98
91
91
89
89
88.3–66.8
100
85
25
Synthetic
10–500
Acetylene purification
wastewater
125±2
125±2
125±2
100
100
91
91
91
50
40
60
50
40
Low strength leachates
*
Qa/V [m3/ (h•L)]; Qa: Airflow rate; V: Solution volume; N.A: Not available.
139
3000–2000
Air flow
rate: 8495. 1 L of
air/gal
*0.13
0.13
*0.5
0.5
0.5
(Marttinen et al.,
2002)
(Jia et al., 2017)
(Prather, 1959)
(Değermenci et al.,
2012)
(Zhu et al., 2017)
A. Zangeneh et al.
South African Journal of Chemical Engineering 36 (2021) 134–141
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in the independent variable).
5 At high and low G/L, temperature and pH had the most significant
effect on ARE per 1 SD increase in the unit of pH, temperature and
initial concentration based on a multivariate regression model
(different G/L (60:1, 70:1 and 80:1)), respectively.
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Declaration of Competing Interest
The authors declare no potential conflict of interest regarding the
publication of this work.
Acknowledgement
The present study is extracted from a Ph.D. dissertation in Environ­
mental Engineering, Ahvaz Branch, Islamic Azad University.
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