Application of Ferrate as Coagulant and Oxidant Alternative for Purifying Saigon River Water

VNU Journal of Science: Earth and Environmental Sciences, Vol. 36, No. 4 (2020) 1-7 
1 
Original Article 
Application of Ferrate as Coagulant and Oxidant Alternative 
for Purifying Saigon River Water 
Tran Tien Khoi1, Nguyen Dang Hoang Chuong2, Hoang Gia Phuc1, 
Nguyen Thi Thuy3, Nguyen Nhat Huy2, 
1International University, Vietnam National University Ho Chi Minh City, 
6 Linh Trung, Thu Duc, Ho Chi Minh, Vietnam 
2Ho Chi Minh City University of Technology, Vietnam National University Ho Chi Minh City, 
268 Ly Thuong Kiet, Ward 14, Ho Chi Minh, Vietnam 
3Ho Chi Minh City University of Food Industry, 140 Le Trong Tan, Tay Thanh, Ho Chi Minh, Vietnam 
Received 06 August 2019 
Revised 09 December 2019; Accepted 17 December 2019 
Abstract: In this study, we aimed to use ferrate as an all-in-one alternative for the removal of 
chlorine-consumed compositions such as organic, color, turbidity, iron, and manganese in river 
water for water supply purposes. Ferrate (FeO42-) was simultaneously employed as coagulant and 
oxidant for purification of Saigon River water in order to reduce the formation of disinfection by-
products in the produced tap water. The Jartest was conducted using both ferrate for raw river water 
and poly-aluminum chloride (PAC) for chlorinated water to determine the optimum concentration 
of chemicals and pH values as well as comparing the effectiveness of ferrate and traditional 
coagulation with pre-chlorination technology for surface water purification. Results showed that 
ferrate could be used to remove organic compounds with high efficiency of 86.2% at pH 5 - 6 and 
ferrate concentration of 16 mgFe/L. Moreover, the removal efficiency for turbidity, color, and iron 
were at least 90%, indicating that ferrate would be a very promising alternative for chlorine and 
PAC for water purification. 
Keywords: ferrate, natural organic matters removal, water purification, DBPs control. 
1. Introduction 
Saigon River is the main source for tap water 
supply in Ho Chi Minh City, where water quality 
is degraded year by year due to the poor 
upstream pollution management [1]. For 
maintaining the tap water quality, more chlorine 
________ 
 Corresponding author. 
 E-mail address: nnhuy@hcmut.edu.vn 
 https://doi.org/10.25073/2588-1094/vnuees.4425 
is using by Tan Hiep Water Treatment Plant 
(THWTP) in Ho Chi Minh City (Vietnam) for 
pre-oxidation of natural organic matters 
(NOMs), ammonia, iron, and manganese as well 
as to prevent algae growth in treatment units. 
This increasing use of chlorine of the plant could 
increase in disinfection by-products (DPBs) 
T.T. Khoi et al. / VNU Journal of Science: Earth and Environmental Sciences, Vol. 36, No. 4 (2020) 1-7 2 
formation in tap water [2], which were found in 
tap water samples of Ho Chi Minh City [1]. 
During disinfection and chlorination processes, 
chlorine (Cl2 gas) is dissolved, hydrolyzed, and 
reacted with NOMs as well as bromide ion in 
water to form trihalomethanes (THMs, a typical 
type of DBPs) [3-5]. The formation of THMs in 
water is dependent on chlorine concentration, 
concentration and property of NOMs, pH, 
temperature, and bromide ion. Most of DPBs are 
harmful to human health while some are 
recognized as carcinogens [6,7]. The control of 
DBPs is mainly focused on the use of 
disinfectant and the removal of NOMs content in 
water by proper operation of water treatment 
plant and pollution control of water source. 
Methods for DPBs control and reduction include 
using alternative disinfectants (e.g. chloramine, 
chlorine dioxide, ozone, UV, and potassium 
permanganate), DPBs precursor removal (e.g., 
by enhanced coagulation with activated carbon 
(AC)/ozonation/nanofiltration, bio-filtration, ion 
exchange, AC adsorption, and membrane 
filtration), and removal of DBPs formed in water 
(e.g., by air stripping, reverse osmosis, AC 
adsorption, and photocatalysis) [8-10]. In case of 
Saigon River water treatment, DPB precursor 
removal could be the most effective method for 
the prevention of DPBs formation and looking 
for a multifunctional chemical that could remove 
both NOMs and other pollutants is particularly 
needed. On the other hand, ferrate (FeO42-) has 
attracted many attention because of its high 
oxidation ability and onsite supplying of ferric 
coagulant, which could be very potential as a 
green solution for surface water, ground water, 
and wastewater treatment [11-15]. Most of the 
studies focused on synthetic water sample for 
organics removal. There is very limited information 
on the use of ferrate for treatment of actual river 
water at supply water treatment plant as an 
alternative for pre-chlorination, algae growth 
prevention, oxidation, and coagulation- flocculation. 
This study is aimed to use ferrate as an 
alternative chemical for purification of Saigon 
River water as input water for tap water supply 
in order to reduce the formation of DBPs. Effects 
of pH and ferrate concentration were 
investigated for obtaining the optimum operation 
condition. The performance of ferrate was also 
compared with those of traditional pre-oxidation 
with chlorine and subsequent coagulation with 
poly-aluminum chloride (PAC). 
2. Materials and Methods 
Saigon River water samples were taken at 
Hoa Phu Pumping station of THWTP (Ho Chi 
Minh City, Vietnam), preserved in a storage 
room at 4oC, and used within 3 days. Before each 
experiment, the water sample with desire volume 
was let in ambient environment for increasing 
the temperature to 20oC. For comparison 
purpose, the pre-chlorinated water samples at 
THWTP were also taken for traditional chemical 
coagulation test. 
Solid ferrate was synthesized in the laboratory 
followed a previous published procedure using 
analytical grade chemicals [16,17], then stored 
in a desiccator, and used within 1 month. Other 
chemicals used for analys ... d 
the coagulation efficiency. However, higher 
concentration had the benefit of oxidation under 
acidic condition, and more ferrate means more 
oxidant for removal of NOMs and colored 
compounds, proven by the increase of NOMs 
and color removal efficiency with the increase of 
ferrate concentration. 
Fig. 1. Effect of ferrate concentration on turbidity, 
NOMs (as COD), and color removal efficiency (at pH 5). 
Figure 2 illustrates the effect of pH on the 
removal of turbidity, NOMs, and color in raw 
river water. Results showed that the performance 
of ferrate strongly depended on pH of the 
environment, which determines the decay rate of 
ferrate as well as its characteristic and its role 
mainly as coagulant or oxidant. For turbidity, the 
removal efficiency reached the highest value of 
97.6% at pH 6 and concentration of 8 mgFe/L 
and remained stable at higher concentrations. 
This proven the relatively stable coagulation 
ability of ferrate at pH 6, which involving both 
colloid charge neutralization and sweep 
flocculation by amorphous iron hydroxide 
precipitates [14]. The removal of NOMs and 
color at pH 6 was similar to those at pH 5, 
indicating the effect of both coagulation (i.e. 
predominant at pH 6) and oxidation (i.e. 
favorable at pH 5) capability of ferrate. 
Moreover, the removal efficiency of turbidity, 
NOMs, and color mostly decreased when pH 
increased from 6 to 7, 8, and 9 due to the 
decrease of ferrate oxidation ability and slow 
decomposition of ferrate at neutral or basic 
condition. High ferrate concentration at high pH 
environment also produces more precipitates 
which could even increase the color and turbidity 
of water. And the mechanism mainly depended 
0
20
40
60
80
100
4 8 12 16 20
R
e
m
o
v
a
l 
e
ff
ic
ie
n
cy
 (
%
)
Ferrate concentration (mgFe/L)
Turbidity
COD
Color
T.T. Khoi et al. / VNU Journal of Science: Earth and Environmental Sciences, Vol. 36, No. 4 (2020) 1-7 4 
on the sweep flocculation at high ferrate 
concentration for relative stable colloid at 
neutral or high pH value. It can be concluded that 
ferrate have both oxidation and coagulation 
functions, but these two abilities were not 
optimized at the same pH condition. Therefore, 
pH 6 was chosen as optimum condition due to 
the high removal efficiency of turbidity, NOMs, 
and color in water, as well as less chemical 
consumption for neutralization. 
Fig. 2. Effect of pH and ferrate concentration on (a) 
turbidity, (b) NOMs, and (c) color removal. 
Fig. 3. Effect of pH and PAC concentration on (a) 
turbidity, (b) NOMs, and (c) color removal. 
In comparison with ferrate, the experiments 
using PAC at different concentrations (5-25 
mg/L) and pH (6-8) were conducted with pre-
chlorinated water sample from THWTP. Results 
in Figure 3 reveal similar trends in the removal 
of turbidity, NOMs, and color regardless pH 
value, possibly because of the only coagulation 
function of PAC. The highest removal 
efficiencies were 97.8, 84.6, and 87.7% for 
0
20
40
60
80
100
4 8 12 16 20
T
u
r
b
id
it
y
 r
e
m
o
v
a
l 
(%
)
Ferrate concentration (mgFe/L)
pH5 pH6 pH7
pH8 pH9
(a)
0
20
40
60
80
100
4 8 12 16 20
C
O
D
 r
e
m
o
v
a
l 
(%
)
Ferrate concentration (mgFe/L)
pH5 pH6 pH7
pH8 pH9
(b)
-20
0
20
40
60
80
100
4 8 12 16 20
C
o
lo
r
 r
e
m
o
v
a
l 
(%
)
Ferrate concentration (mgFe/L)
pH5
pH6
pH7
pH8
pH9
(c)
20
40
60
80
100
5 10 15 20 25
T
u
r
b
id
it
y
 r
e
m
o
v
a
l 
(%
)
PAC concentration (mg/L)
pH6
pH7
pH8
(a)
20
40
60
80
100
5 10 15 20 25
C
O
D
 r
e
m
o
v
a
l 
(%
)
PAC concentration (mg/L)
pH6
pH7
pH8
(b)
20
40
60
80
100
5 10 15 20 25
C
o
lo
r
 r
e
m
o
v
a
l 
(%
)
PAC concentration (mg/L)
pH6
pH7
pH8
(c)
T.T. Khoi et al. / VNU Journal of Science: Earth and Environmental Sciences, Vol. 36, No. 4 (2020) 1-7 5 
turbidity, NOMs, and color, respectively, at pH 
7 and PAC concentration of 20 mg/L. These high 
removal efficiencies prove that the pre-
chlorination step has enhancement effect on the 
removal of NOMs and color via oxidation and 
precipitation of dissolved contaminants such as 
iron and manganese by chlorine. In addition, the 
excess use of PAC showed insignificant negative 
effect on turbidity and color removal as ferrate. 
However, ferrate was superior in terms of NOMs 
removal since it provided the removal efficiency 
of 86.2% as compared to the efficiency of 84.6% 
achieved by the combination of pre-chlorination 
and PAC at pH 6 – 7 and PAC concentration of 
20 mg/L. This showed a very potential 
application of ferrate as oxidant and coagulant 
for practical water treatment which could reduce 
the formation of DBPs while maintain high 
treatment efficiency of the water treatment plant. 
Since Fe3+ is a product of ferrate treatment, 
iron removal efficiency using ferrate and PAC 
was investigated to find either ferrate provide 
negative or positive effect on iron removal. At a 
low concentration of 4 mgFe/L, ferrate was not 
only unable to remove iron in raw water sample 
(initial concentration of 0.8 mg/L) but also 
increased iron content in the treated water (2.95 
– 3.30 mg/L in pH range of 5 – 9), which did not 
meet the limit of National technical regulation on 
drinking water quality (QCVN 01:2009/BYT, 
0.3 mg/L). With the increase of ferrate 
concentration, iron removal was enhanced, as 
can be seen from Figure 4. It was also clear that 
increase of pH value from 5 - 9 resulted in the 
decrease of iron removal efficiency. This trend 
can be explained by the low decay ability of 
ferrate which resulted in high iron content in 
water sample. However, with the increase of 
ferrate concentration, the removal of iron was 
significantly improved and reached the highest 
efficiency of 96.4% at concentration of 20 
mgFe/L and pH 5 due to the strong oxidation of 
ferrate under acidic condition. The iron removal 
was also tested using PAC for pre-chlorinated 
water with a high removal efficiency of 98.8% at 
PAC concentration of 25 mg/L due to the 
coagulation enhancement via oxidation of iron 
by chlorine. Although the efficiency was not 
high as current technology of pre-oxidation by 
chlorine and coagulation by PAC, ferrate still 
have high ability to removal total iron in water 
with suitable concentration and pH. 
Fig. 4. Effect of pH and concentration on iron 
removal using (a) ferrate and (b) PAC. 
Manganese usually co-exists with iron in 
organic colloidal form in surface water. The 
removal of manganese requires oxidation of 
dissolved Mn(II) species to Mn(IV) precipitates, 
which is done by chlorine oxidation in THWTP. 
In this study, ferrate was applied as alternative to 
remove manganese and the results are presented 
in Figure 5. As can be seen, a relative stable 
removal efficiency of manganese was achieved 
at around 50% in a wide range of pH and ferrate 
concentration. Actually, manganese 
concentrations before (0.2 mg/L) and after 
treatment (< 0.1 mg/L) were low and both met 
the standard (0.3 mg/L, QCVN 01:2009/BYT). 
These indicate the less dependence of 
manganese removal on coagulation- flocculation 
-40
-20
0
20
40
60
80
100
8 12 16 20
Ir
o
n
 r
e
m
o
v
a
l 
(%
)
Ferrate concentration (mgFe/L)
pH5
pH6
pH7
pH8
pH9
(a)
40
60
80
100
5 10 15 20 25
Ir
o
n
 r
e
m
o
v
a
l 
(%
)
PAC concentration (mg/L)
pH6
pH7
pH8
(b)
T.T. Khoi et al. / VNU Journal of Science: Earth and Environmental Sciences, Vol. 36, No. 4 (2020) 1-7 6 
by ferrate. This low efficiency also implies that 
manganese is more stable and harder to be 
oxidized and hydrolyzed than iron under the 
tested condition. 
Fig. 5. Effect of pH and concentration on manganese 
removal using ferrate. 
4. Conclusion 
The use of ferrate could significantly reduce 
the formation of DBPs due to the reduction of 
both NOMs and chlorine consumption during 
the purification of Saigon River water as input 
water for water supply. Experiment results 
showed that ferrate is very potential and 
effective for river water purification in terms of 
turbidity, NOMs, color, iron, and manganese 
removal. Both pH and ferrate concentration had 
strong effect on the performance of ferrate for 
water treatment. Ferrate is more effective under 
acidic condition (i.e. pH range of 5-6) due to its 
both roles as oxidant and coagulant. The suitable 
pH is at 6 while ferrate concentration could be 
chosen based on the purification purposes (e.g. 
low concentration of 8 mg/L for turbidity and 
maybe higher concentration up to 16 mgFe/L for 
NOMs removal). In some conditions, ferrate is 
not as a good coagulant as PAC but the removal 
efficiency using ferrate was higher or 
competitive with pre-chlorination and 
coagulation due to its oxidation property. Future 
works should focus on the mechanism of iron 
and manganese removal in river water 
purification as well as the formation/reduction of 
DBPs 
References 
[1] V.N. Trang, L.D. Phuong, N.P. Dan, B.X. Thanh, 
C. Visvanathan, Assessment on the 
trihalomethanes formation potential of Tan Hiep 
Water Treatment Plant, J Water Sustain 2 (2012) 
43-53. https://doi.org/10.11912/jws.2.1.43-53. 
[2] R. Sadiq, M.J. Rodriguez, Disinfection by-
products (DBPs) in drinking water and predictive 
models for their occurrence: a review, Sci. Total 
Environ. 321 (2004) 21-46. https://doi.org/10. 
1016/j.scitotenv.2003.05.001. 
[3] S. Chowdhury, P. Champagne, P.J. McLellan, 
Models for predicting disinfection byproduct 
(DBP) formation in drinking waters: a 
chronological review, Sci. Total Environ. 407 
(2009) 4189-4206. https://doi.org/10.1016/j.scito 
tenv.2009.04.006. 
[4] T. Bond, J. Huang, M.R. Templeton, N. Graham, 
Occurrence and control of nitrogenous 
disinfection by-products in drinking water – A 
review, Water Res. 45 (2011) 4341-4354. 
[5] S.D. Richardson, M.J. Plewa, E.D. Wagner, R. 
Schoeny, D.M. DeMarini, Occurrence, 
genotoxicity, and carcinogenicity of regulated and 
emerging disinfection by-products in drinking 
water: a review and roadmap for research, 
Mutation Research/Reviews in Mutation Research 
636 (2007) 178-242. https://doi.org/10.1016/j.mrr 
ev.2007.09.001. 
[6] E. Agus, N. Voutchkov, D.L. Sedlak, Disinfection 
by-products and their potential impact on the 
quality of water produced by desalination systems: 
a literature review, Desalination 237 (2009) 214-
237. https://doi.org/10.1016/j.desal.2007.11.059. 
[7] C.G. Graves, G.M. Matanoski, R.G. Tardiff, 
Weight of evidence for an association between 
adverse reproductive and developmental effects 
and exposure to disinfection by-products: a critical 
review, Regul. Toxicol. Pharmacol. 34 (2001) 
103-124. https://doi.org/10.1006/rtph.2001.1494. 
[8] A. Matilainen, M. Vepsäläinen, M. Sillanpää, 
Natural organic matter removal by coagulation 
during drinking water treatment: A review, Adv. 
Colloid Interface Sci. 159 (2010) 189-197. 
[9] T. Chaiket, P.C. Singer, A. Miles, M. Moran, C. 
Pallotta, Effectiveness of coagulation, ozonation, 
and biofiltration in controlling DBPs, Journal 
(American Water Works Association) 94 (2002) 
40
45
50
55
60
4 8 12 16 20
M
a
n
g
a
n
e
se
 r
e
m
o
v
a
l 
(%
)
Ferrate concentration (mgFe/L)
pH5 pH6 pH7
pH8 pH9
T.T. Khoi et al. / VNU Journal of Science: Earth and Environmental Sciences, Vol. 36, No. 4 (2020) 1-7 7 
81-95. https://doi.org/10.1002/j.1551-8833.2002. 
tb10251.x. 
[10] A. Matilainen, M. Sillanpää, Removal of natural 
organic matter from drinking water by advanced 
oxidation processes, Chemosphere 80 (2010) 351-
365.  
2010.04.067. 
[11] K. Prabhat Rai, J. Lee, S.K. Kailasa, E.E. Kwon, 
Y.F. Tsang, Y.S. Ok, K.-H. Kim, A critical review 
of ferrate(VI)-based remediation of soil and 
groundwater, Environ. Res. 160 (2018) 420-448. 
https://doi.org/10.1016/j.envres.2017.10.016. 
[12] A. Talaiekhozani, M.R. Talaei, S. Rezania, An 
overview on production and application of ferrate 
(VI) for chemical oxidation, coagulation and 
disinfection of water and wastewater, Journal of 
Environmental Chemical Engineering 5 (2017) 
1828-1842. https://doi.org/10.1016/j.jece.2017. 
03.025. 
[13] V.K. Sharma, Potassium ferrate(VI): an 
environmentally friendly oxidant, Adv. Environ. 
Res. 6 (2002) 143-156. https://doi.org/10.1016/ 
S1093-0191(01)00119-8. 
[14] J.-Q. Jiang, B. Lloyd, Progress in the development 
and use of ferrate(VI) salt as an oxidant and 
coagulant for water and wastewater treatment, 
Water Res. 36 (2002) 1397-1408. https://doi.org/ 
10.1016/S0043-1354(01)00358-X. 
[15] D. Ghernaout, M.W. Naceur, Ferrate(VI): In situ 
generation and water treatment – A review, 
Desalination and Water Treatment 30 (2011) 319-
332. https://doi.org/10.5004/dwt.2011.2217. 
[16] K.T. Tien, N. Graham, J.-Q. Jiang, Evaluating the 
coagulation performance of ferrate: A preliminary 
study, ACS Symp. Ser 985 (2008) 292-305. 
https://doi.org/10.1021/bk-2008-0985.ch017. 
[17] N. Graham, T. Khoi, J.-Q. Jiang, Oxidation and 
coagulation of humic substances by potassium 
ferrate, Water Sci. Technol. 62 (2010) 929-936. 
https://doi.org/10.2166/wst.2010.369. 
[18] J.-Q. Jiang, S. Wang, A. Panagoulopoulos, 
Comparative performance of potassium ferrate 
(VI) in drinking water and sewage treatment, 
Proceedings of the 9th International Conference 
on Environmental Science and Technology, 
Rhodes Island, Greece (2005) 1-3. https://doi.org/ 
10.1080/19443994.2014.938303. 
[19] V.K. Sharma, R. Zboril, R.S. Varma, Ferrates: 
Greener Oxidants with Multimodal Action in 
Water Treatment Technologies, Acc. Chem. Res. 
48 (2015) 182-191. https://doi.org/10.1021/ar 
5004219.