Optimizing the coagulation process in a drinking water
treatment plant – comparison between traditional
and statistical experimental design jar tests
M. Zainal-Abideen, A. Aris, F. Yusof, Z. Abdul-Majid, A. Selamat
and S. I. Omar
ABSTRACT
In this study of coagulation operation, a comparison was made between the optimum jar test values
for pH, coagulant and coagulant aid obtained from traditional methods (an adjusted one-factor-at-a-
time (OFAT) method) and with central composite design (the standard design of response surface
methodology (RSM)). Alum (coagulant) and polymer (coagulant aid) were used to treat a water source
with very low pH and high aluminium concentration at Sri-Gading water treatment plant (WTP)
Malaysia. The optimum conditions for these factors were chosen when the final turbidity, pH after
coagulation and residual aluminium were within 0–5 NTU, 6.5–7.5 and 0–0.20 mg/l respectively.
Traditional and RSM jar tests were conducted to find their respective optimum coagulation conditions.
It was observed that the optimum dose for alum obtained through the traditional method was 12 mg/l,
while the value for polymer was set constant at 0.020 mg/l. Through RSM optimization, the optimum
dose for alum was 7 mg/l and for polymer was 0.004 mg/l. Optimum pH for the coagulation
operation obtained through traditional methods and RSM was 7.6. The final turbidity, pH after
coagulation and residual aluminium recorded were all within acceptable limits. The RSM method was
demonstrated to be an appropriate approach for the optimization and was validated by a further test.
M. Zainal-Abideen (corresponding author)
A. Aris
Faculty of Civil Engineering,
Universiti Teknologi Malaysia,
81310 Johor-Bahru,
Malaysia
E-mail: muzaffar@utm.my
F. Yusof
Z. Abdul-Majid
Faculty of Science,
Universiti Teknologi Malaysia,
81310 Johor-Bahru,
Malaysia
A. Selamat
S. I. Omar
SAJ Holdings Sdn. Bhd.,
P.O. Box 262,
80350 Johor-Bahru,
Malaysia
Key words | coagulation, jar test, one-factor-at-a-time, response surface methodology,
water treatment
INTRODUCTION
Coagulation is one of the most important processes in water
treatment. It is an effective method for the removal of col-
loidal particles in surface water. Many researchers have
applied the coagulation process to treat highly turbid
water (Lin et al. ) and natural organic matter (NOM)
(Zhan et al. ) present in surface water. The process is
also capable of removing arsenic (Hering et al. ) and
residual aluminium (Bérubé & Dorea ) from drinking
water. As a coagulation process has the ability to eliminate
many pollutants from surface and drinking water, the suc-
cess of the process has a direct impact on the reliability of
treatment plant operations and final water quality.
The effectiveness of the coagulation process is
highly dependent on many factors, including dosage of coagu-
lant and coagulant aids and also pH of the operation
(Amirtharajah & O’Melia ). By far, the most common
coagulants used are aluminium sulphate (Al
2
(SO
4
)
3
), ferric
sulphate (Fe
2
(SO
4
)
3
) and ferric chloride (FeCl
3
)( Jiang &
Graham ). Studies on the performance of polymerized
inorganics such as polyaluminium chloride (PACl) (Lin
et al. ) and polyferric chloride (PFC) (Zhan et al. )
as coagulants are actively being carried out. The impact of
pH towards coagulation has also been thoroughly investi-
gated (Gregory & Carlson ; Bérubé & Dorea ;
Zhan et al. ).
It is well established that the choice of coagulants used,
the dosing and the operational pH applied in a coagulation
process make a significant contribution to the operational
cost of the treatment plant. Therefore, it is important to
use the optimum conditions when carrying out coagulation
process so that wastage or unnecessary dosage of the associ-
ated chemicals may be prevented.
496 © IWA Publishing 2012 Water Science & Technology | 65.3 | 2012
doi: 10.2166/wst.2012.561