Advances in Chemical Engineering and Science, 2012, 2, 490-503
http://dx.doi.org/10.4236/aces.2012.24060 Published Online October 2012 (http://www.SciRP.org/journal/aces)
Treatment of Pulp and Paper Mill Wastewater with
Various Molecular Weight of PolyDADMAC Induced
Flocculation with Polyacrylamide in the Hybrid System
M. A. A. Razali1,2, Z. Ahmad1, A. Ariffin1*
1School of Material and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, Nibong Tebal, Penang,
Malaysia
2Research and Development Department, Global Network Technology SdnBhd, Bentong, Malaysia
Received August 1, 2012; revised September 4, 2012; accepted September 12, 2012
ABSTRACT
Flocculation studies between dual polymers on pulp and paper mill wastewater are reported in this paper. The effects of
different molecular weights of polyDADMAC and different dosages of Polyacrylamide (PAM) were studied. The mo-
lecular weights of polyDADMAC used were 8.8 × 104, 10.5 × 104 and 15.7 × 104 g/mol. The flocculation performance
was analyzed in jar tests with PolyDADMAC and Polyacrylamide dosages ranging from 0.4 - 2.0 mg·L−1 and 0.4 - 8.0
mg· L −1 respectively. A higher molecular weight and a 6.0 mg·L−1 dosagepolyDADMAC gave the highest level of floc-
culation based on turbidity and TSS removal. In addition, increasing the molecular weight of PolyDADMAC increased
ζ potential values approaching zero. This indicated that polyDADMAC acts as a destabilizer. Based on TSS, the addi-
tion of PAM will improve the size of microflocs created by polyDADMAC. It demonstrates that PAM acts as a bridger
between microflocs.
Keywords: Flocculation; PolyDADMAC; Polyacrylamide; Zeta Potential; Molecular Weight
1. Introduction
Much research has concluded that flocculation is an effi-
cient and cost effective method for water and wastewater
treatment [1-4]. Flocculation can be defined as a process
that makes finely dispersed particles aggregate and form
large floc [5]. Flocculation is promoted by the addition of
organic or inorganic chemicals. In recent years, the use
of synthetic polyelectrolytes as flocculants for the re-
moval of suspended solids in wastewater treatment has
become a widely used practice.
There have been several studies on hybrid polyelec-
trolytes systems to improve the flocculation of suspended
particles in wastewater [6-9]. Dual flocculants often offer
advantages over a single component flocculant, such as
better control of flocculation kinetics and improved floc
strength. According to Yu and Somasundaran [6], floc-
culants showed limited flocculation while being used
alone, but achieved good flocculation when used together.
Chitikela and Dentel [10] propose that hybrid cationic
polyelectrolyte conditioning is more effective than single
polyelectrolytes. These dual flocculant approaches were
attempts by different branches of industry, both mineral
processing [11-13] and paper making [14,15].
The first research on this topic was conducted by Britt
[16] in regards to the paper making industry. He ob-
served that a dual flocculant promoted higher floccula-
tion, but the aggregates were very fragile and, hence,
easily redispersed by an applied shear. To overcome this
problem, a new technique was tested by using a combi-
nation of cationic and anionic polymers. The cationic
polymer was used to flocculate the slurry to the point
where no solids were detected in the supernatant, fol-
lowed by the addition of an anionic polymer. Results
from this technique exhibited increased firmness when
compared to the single polymer test. Most previous stud-
ies explored a combination of cationic and anionic poly-
mers, with the exclusion of Swerin et al. [17], who stud-
ied the absorbtion and flocculation rates when using two
cationic polymers. They used different molecular weights
of polyDADMAC and PAM, but only covered the floc-
culation process on microcrystalline cellulose (MCC). To
date, there are no studies of different of molecular weight
of polyDADMAC and PAM for pulp and paper mill
wastewater particles.
The pulp and paper mill industry consumes a large
amount of water and therefore discharges a large amount
*Corresponding author.
C
opyright © 2012 SciRes. ACES

M. A. A. RAZALI ET AL. 491
of wastewater [18]. The large amount of wastewater con-
stitutes one of the major sources of aquatic pollution. The
bleaching process produces the largest volume of pollut-
ants, which generates several chlorinated compounds via
chlorination and others toxic organic compounds such as
lignin. Highly toxic materials are formed from lignin and
its derivatives, while recalcitrant compounds are respon-
sible for the high BOD and COD [19]. In addition to be-
ing highly toxic, lignin and its derivatives are also
mutagenic [20]. Lignin causes death to zooplankton and
fish, and profoundly affects the terrestrial ecosystem [21].
Therefore, it is obligatory that the effluent from pulp and
paper mills is treated before entering receiving waters.
This study employs different molecular weights of
cationic polyDADMAC and different dosages of emul-
sion polyacrylamide in pulp and paper mill wastewater
samples. The objective of this work was to investigate
the synergistic effects of addition of different molecular
weights of polyDADMAC on the flocculation of pollut-
ants present in pulp and paper mill wastewater using a
constant molecular weight of emulsion polyacrylamide. ζ
potential of the supernatant, the turbidity, total suspended
solids (TSSs) and chemical oxygen demand (COD) con-
centrations were measured as the evaluating parameters.
2. Experimental
2.1. Materials
Pulp and paper mill wastewater was collected from the
wastewater treatment plant equalization tank of a paper
mill in Penang, Malaysia, in accordance with ASTM E
300-03. This factory produces about 3000 metric tons of
tissue paper a month and produces 96 m3 of wastewater
per ton of paper produced. The characteristics of the
wastewater collected from the factory are similar to those
found in previous studies [20,21]. The polyDADMAC
flocculants used in this study were radically synthesized
with various monomer concentrations. The molecular
weights were obtained by synthesizing various monomer
concentrations, as shown in Table 1. The molecular
weights were calculated based on intrinsic viscosity val-
ues. The ζ potential of each polyDADMAC at pH 7 were
determined and also shown in Table 1. The cationic
polyacrylamides (PAM) used in this study were supplied
by Global Network Technology SdnBhd, Malaysia. Mo-
lar mass of this PAM is 10 MDa. Distilled water was
Table 1. Molecular weight and ζ potential for polyDAD-
MAC samples.
Prepared samples Molecular weight (g/mol) ζ potential (mV)
PDM01 8.8 × 104 40.15
PDM02 10.5 × 104 42.10
PDM03 15.7 × 104 48.60
used to prepare all the polyDADMAC and emulsion
Polyacrylamide feedstock solutions of 0.1% respectively.
2.2. Experimental Procedure
A jar test was performed with the conventional jar appa-
ratus (VelpScientifica FC6S model) using 500-ml waste-
water samples. Different combinations of PolyDADMAC
molecular weights (as shown in Table 1), polyDAD-
MAC dosages (0.4, 0.8, 1.2, 1.6, 2.0 mg·L−1) and PAM
dosages (0.4, 2, 4, 6 and 8 mg·L−1) were tested. The se-
lected PolyDADMAC dosage and Molecular weight was
added to 500 ml of wastewater and stirred for a period of
2 min at 200 rpm. This was followed by slow mixing for
10 min at 35 rpm. Selected polyacrylamide dosages were
then introduced into the wastewater samples 45 seconds
after the polyDADMAC additions. The flocs formed were
allowed to settle for 5 min. After settling, the turbidity,
TSSs, Zeta potential and COD of the supernatants were
determined. The experiments were repeated several times
to obtain an average value.
2.3. Analytical Techniques
COD was evaluated using COD vials (Hach, United
States) with different sensitivity ranges. Sample digestion
was performed in a DRB200 reactor (Hach) over 2 hours
at 150˚C. Solutions being tested for sample digestion
were cooled at room temperature before being measured
by a DRB200 Digital Reactor, 15-Wells (Hach). The
supernatant turbidity before filtration was measured with
a turbidity meter (from Lovibond). A pH meter (Cyber-
Scan model, Eutech Instruments, Singapore) was used to
measure the pH of the solutions. The TSS concentration
was determined by filtering a well-mixed sample through
a glass fiber filter (GA 55, Advantec, Japan), and the
residues retained on the filter were dried in an oven at
103˚C for 60 min prior to weighing. The ζ potential was
determined with a Malvern Mastersizer 2000.
3. Results and Discussions
In this study, it was hypothesized that polyDADMAC
would perform as a charge neutralizer while PAM would
perform as a bridger. The addition of polyDADMAC into
the pulp and paper mill wastewater was proven to desta-
bilize the stability of negatively charged particles. The
destabilization process caused particle-particle attraction
and created microflocs. The incorporation of PAM to the
system immediately increased the size of flocs. Loop and
tails in PAM chains were able to absorb into particles
and create bridges between particles, thus increasing the
size of microflocs, as shown in Figure 1(c). Figure 1 is a
video caption of the above mentioned flocculation proc-
ess.

M. A. A. RAZALI ET AL.
492
units of DADMAC. In addition, each repeating unit of
DADMAC brings one positive charge. According to
Subramanian (1999), it has been accepted that one of the
factors of the flocculation process is charge neutraliza-
tion [22]. Increasing repeating units will increase the
positive charge, thus improving the charge neutralization
or destabilization of negative particles. Increasing the
molecular weight also allows for larger loops and ends to
develop, and therefore yeilds more space to attract sus-
pended particles [23]. This phenomenon was consis-
tentwith the study by Zang et al. [24] on reed pulp sus-
pension. Zang observed that increasing the positive
charge increased flocculation efficiency.
(a) (b)
Figure 2 also shows that high level flocculation an-
doptimal dosing for this system occurred at 1.2 mg·L−1 of
polyDADMAC dosage. A dosage lower than 1.2 mg·L−1
can cause a decrease in turbidity removal (gap between
lowest and highest molecular weight) with an increase in
PAM dosage, as shown in Table 2. This phenomenon
may be due to charge repulsion between both polyelec-
trolytes. Initially, at a low dosage of PAM, the negative
charge of particles is destabilized by polyDADMAC.
The addition of PAM creates bridges between microflocs
produced by polyDADMAC. Increasing the polyDAD-
MAC molecular weight improved the efficiency of floc-
culation due to an increase in negative charge destabili-
zation. After a certain dosage of PAM, saturation oc-
cured. Excessive amounts of PAM create charge repul-
sion, thus reducing the level of flocculation. This phe-
nomenon is illustrated in Figure 3. According to Lee
[25], excessive additional PAM doses seem to deteriorate
inter-particle flocculation efficiencies which contribute
from conformational changes of absorbed PAM mole-
cules on particles surfaces.
(c)
Figure 1. Pulp and paper mills wastewater: (a) Without any
polymers; (b) Addition of polyDADMAC; (c) Addition of
polyacrylamide.
3.1. Effect on Turbidity Removal
The influence of the molecular weight of PolyDADMAC,
with several PAM dosages, on turbidity removal is
shown in Figure 2. Generally, turbidity removal in-
creased with an increasing molecular weight. At the 0.4
mg· L −1 dosage of PAM, PDM03 showed higher floccu-
lation turbidity removal than PDM01 and PDM02, which
were lower in molecular weight. This observation was
thought to be caused by the contribution of polyDAD-
MAC chains. Chains of polymer are directly related to
the repeating unit, which at high molecular weights of
polyDADMAC gave longer chains and many repeating
3.2. Effect on Total suspended solids
The removal of TSSs from pulp and paper mill wastewa-
er, following treatment with different molecular weights t
40
50
60
70
80
90
100
0.2 0.40.6 0.811.2 1.41.6 1.822.2
Turbidity Removal (%)
Dosage (mg·L
−1
)
PDM01
PDM02
PDM03
(a)

M. A. A. RAZALI ET AL. 493
40
50
60
70
80
90
100
0.2 0.4 0.60.811.2 1.4 1.6 1.
Turbidity Removal (%)
Dosage (mg·L
−1
)
8 2 2.2
PDM01
PDM02
PDM03
(b)
40
50
60
70
80
90
100
0.2 0.4 0.60.811.2 1.41.6 1.
Turbidity Removal (%)
Dosage (mg·L
−1
)8 2 2.2
PDM01
PDM02
PDM03
(c)
40
50
60
70
80
90
100
0.2 0.4 0.60.811.2 1.4 1.6 1.
Turbidity Removal (%)
Dosage (mg·L
−1
)
8 2 2.2
PDM01
PDM02
PDM03
(d)
0
10
20
30
40
50
60
70
80
90
100
0.2 0.4 0.6 0.811.2 1.41.6 1.
Turbidity Removal (%)
Dosage (mg·L
−1
)82 2.2
PDM 01
PDM 02
PDM 03
(e)
Figure 2. Effect of different molecular weight of PolyDADMAC on turbidity removal at (a) 0.4; (b) 2.0; (c) 4.0; (d) 6.0; and (e)
8.0 PAM dosages (mg·L−1).

M. A. A. RAZALI ET AL.
494
Table 2. Turbidity removal deviation at different PAM dosage.
PAM Dosage (mg·L−1) Shift (between PDM 01 and PDM03)
0.4 24
2.0 17
4.0 23
6.0 7
8.0 7
negativelychargedbefore additionofpolyelectrolytes
Destabilizationby polyDADMACandbridges byPAM
restablizationoccur breaksome ofthe bridges
O
NH2
O
NH 2
ONH2
ONH2
O
H2N
O
H2N
O
H2N
O
H2N
N+
N+
N+
N+
N+
N+
N+
N+
O
NH2
ONH2
O
NH2
O
NH2
O
NH2
O
NH2
O
NH2
O
H2N
O
NH 2
ONH
Figure 3. Illustration of saturation and restabilization phenomenon.
of polyDADMAC, with the addition of various PAM
dosages, is shown in Figure 4. Turbidity removal and
TSS removal results are similar. A log-linear model cre-
ated by Packman et al. [26] showed a strong positive cor-
relation between TSS and turbidity (R2 = 0.96) with a
regression equation of ln(TSS) = 1.32 ln(NTU) + C with
C is not significantly different than zero. Approaching
the value 1 for “R2” indicates that there is a linear rela-
tionship between both results. According to Pavanelli
and Bigi [26,27], turbidity is mainly due to particles in
suspension. From this figure, the highest molecular
weight gives the highest level of TSS removal. Charge
neutralization creates condensed particles. In addition,
the destabilization process is believed to occur concur-
rently with a bridging mechanism for higher molecular
weights. Increasing molecular weights greatly increases
the number of unoccupied absorption sites [28]. Increas-
ing the unoccupied absorption sites increases the ten-
dency for more microflocs to agglomerate. Similar out-
comes were observed by Denkov [29], in which the sus-
pended solid removal was higher at higher molecular
weights. It was observed that the 1.2 mg·L−1 poly-
DADMAC dosage showed the highest turbidity removal
for all PAM dosages, except 4.0 mg·L−1. This indicates
that 1.2 mg·L−1 is the optimum dosage for turbidity re-
moval in this system.
The effects of PAM dosage on TSS removal can be
split into two stages. The first stage is from 0.4 - 0.8
mg· L −1, while the second stageis from 1.2 mg·L−1 and
above. It was observed that the optimal dosage had no
significant effect on TSS removal. TSS removal achieved
for different PAM dosages with constant molecular
weights of polyDADMAC were similar, as shown in
Table 3.
Below the polyDADMAC optimal dosage, TSS re-
moval increased with the increasing dosage of PAM.
TSS removal started to decrease after a certain dosage, as
shown in Table 4. Similar to theturbidity removal results,
increasing the PAM dosage increased the probability
bridging mechanisms would occur. The increase of
bridging increases the size of flocs, hence increasing the
amount filtered. The filtered amount is related to TSS
removal. Increasing turbidity removal will increase the
filtered amount. However, TSS removal decreased with

M. A. A. RAZALI ET AL. 495
dosages higher than 4.0 mg·L−1. This was caused by
steric stabilization. At the dosage of 4.0 mg·L−1, the sur-
face particles became saturated and therewere no ab-
sorbable sites available for PAM to perform the bridging
process. Excessive PAM chains led to steric stabilization
and caused the deflocculation of particles in solution, as
shown in Figure 5. A part of the PAM segments was
strongly absorbed into the particles’ surfaces, while other
segments were the stabilizing moiety that extends out
from the surface into the solution. When two particles
approached each other, the extended PAM chains of the
stabilizing block came into contact and caused a repul-
sive force that prevented the particles from aggregating
[30].
3.3. COD Removal
Figure 6 presents the COD removal from pulp and paper
mill wastewater treated with different molecular weights
of polyDADMAC, with the addition of PAM in various
dosages. Maximum COD removal efficiency was 98.6%,
and was achieved by PDM02 at a dosage of 1.2 mg·L−1
and a PAM dosage of 6.0 mg·L−1. It should be noted that
COD removal results were in contrast to the turbidity and
TSS removal. The highest COD removal was achieved
by PDM02, while the best results in regards to turbidity
and TSS were achieved by PDM03. However, in all three
results, COD removal increased from PDM 01 to PDM
02.
40
50
60
70
80
90
100
0.2 0.4 0.6 0.811.2 1.4 1.6 1.822.2
TSS removal (%)
Dosage (mg·L
−1
)
PDM01
PDM02
PDM03
(a)
40
50
60
70
80
0.20.71.21
TSS Removal (%)
Dosage (mg·L
−1
)
90
100
.72.2
PDM01
PDM02
PDM03
(b)
40
50
60
70
80
0.20.4 0.60.811.21.4 1.61.
TSS Removal (%)
Dosage (mg·L
−1
)
90
100
8 22.2
PDM 01
PDM 02
PDM 03
(c)

M. A. A. RAZALI ET AL.
496
40
50
60
70
80
90
100
0.2 0.4 0.6 0.811.2 1.4 1.6 1.8
TSS removal (%)
Dosage (mg·L
–1
)2 2.2
PDM01
PDM02
PDM03
(d)
40
50
60
70
80
90
100
0.2 0.4 0.6 0.811.2 1.4 1.6 1.8
TSS Removal (%)
Dosage (mg·L
–1
)
2 2.2
PDM 01
PDM 02
PDM 03
(e)
Figure 4. Effect of polyDADMAC dosage on TSS removal at (a) 0.4; (b) 2.0; (c) 4.0; (d) 6.0; and (e) 8.0 PAM dosages (mg·L–1 ).
Table 3. TSS removal at optimal dosage of PDM03 with different of PAM dosage.
PAM Dosage (mg·L–1) TSS removal (mg·L–1)
0.4 92.6
2.0 95.8
4.0 94.7
6.0 94.0
8.0 95.8
Table 4. TSS removal at 0.4 mg·L–1 dosage of PDM01 with different of PAM dosage.
PAM Dosage (mg·L–1) TSS removal (mg·L–1)
0.4 50.0
2.0 63.7
4.0 75.3
6.0 60.5
8.0 60.0

M. A. A. RAZALI ET AL. 497
Particles before saturated
O
NH2
ONH2
ONH2
O
H2N
O
H2N
O
NH2
ONH
O
NH2
2
(a)
Steric stabilization occured
O
NH2
O
H2N
O
NH2
O
NH2
O
NH2
O
NH2
O
H2N
O
H2N
O
H2N
O
NH2
O
NH2
O
NH2
O
NH2
O
NH2
O
NH2
O
NH2
O
H2N
O
NH
2
O
NH2
O
NH2
(b)
Figure 5. Illustration particles before saturated and steric stabilization occurred.
50
55
60
65
70
75
80
85
90
95
100
0 0.5 1 1.5 2
COD Removal (%)
Dosage (mg·L
–1
)2.5
PDM 01
PDM 02
PDM 03
(a)

M. A. A. RAZALI ET AL.
498
50
55
60
65
70
75
80
85
90
95
100
00.511.5
COD Removal (%)
Dosage (mg·L
–1
)22.5
PDM 01
PDM 02
PDM 03
(b)
50
55
60
65
70
75
80
85
90
95
100
00.511.5
COD Removal (%)
Dosage (mg·L
–1
)
22.5
PDM 01
PDM 02
PDM 03
(c)
50
55
60
65
70
75
80
85
90
95
100
00.511.
COD removal (%)
Dosage (mg·L
–1
)
522.5
PDM 01
PDM 02
PDM 03
(d)

M. A. A. RAZALI ET AL.
499
50
60
70
80
90
100
110
00.511.5
COD removal (%)
Dosage (mg·L
–1
)22.5
PDM01
PDM02
PDM03
(e)
Figure 6. Effect of PolyDADMACdosages on COD removal at (a) 0.4; (b) 2.0; (c) 4.0; (d) 6.0; and (e) 8.0 PAM dosages
(mg·L–1).
Generally, COD removal increases with increasing
molecular weight, as observed from PDM01 and PDM02.
However, the COD removal started to decrease with in-
creasing molecular weights (PDM03 to PDM02). In ac-
cordance with the results obtained by Tavares [31], the
increase of COD removal from PDM 01 to PDM02 is
related to the increase of lignin removal from the waste-
water. Decreasing levels of lignin in wastewater reduces
oxidation, thus increasing COD removal. The decrease of
COD removal from PDM02 to PDM03 is likely caused
by polyDADMAC flocculants being discharged along
with water, instead of with the suspended solid.
3.4. ζ Potential Measurement
ζ Potential measurement is an evaluation method for de-
termining the stability and instability of colloidal disper-
sions. The measurement of ζ potential is a function of the
surface charge of the particles. Particles tend to agglom-
erate when the value of ζ potential is closer to zero
(isoelectric point) [32]. Figure 7 shows that PDM03
shows a ζ potential value closer to zero than others. The
value closest to zero was achieved at a dosage of 1.2
mg· L −1 polyDADMAC and a PAM dosage of 8.0 mg·L−1,
which was −0.06 mV. This indicates that increasing the
molecular weight of PolyDADMAC shifts the ζ potential
value closer to zero. The factors of being more positively
charged and higher in molecular weight destabilized the
negative charge through van der walls forces. Floccula-
tion started to occur when the attractive van der Waals
forces were equal to the repulsive electrostatic force.
However, there was no significant difference in ζ po-
tential value for different dosages of PAM, as shown in
Table 5. PAM has a much less significant effect on ζ
potential compared to polyDADMAC. It is known that ζ
potential is a good indicator of the magnitude of repul-
sive forces between particles. In this system, the addition
of polyDAdMAC destabilized the particles, resulting in
big changes in the ζ potential value, and created micro-
flocs. Many particles became closer to each other, but
still few agglomerates formed. Bridgers were created by
PAM chains increase the agglomerates formed hence
reduced the ζ potential value a small amount.
PDM 01 and PDM 02 showed positive values after op-
timal dosing, while PDM 03 showed a negative value
with PAM dosages of 0.2 mg·L−1 and 0.2 mg·L−1. PDM
01 and PDM 02 resulted in values of 10.3 and 4.01 mV
respectively. Meanwhile, PDM 03 resulted in −7.75 mV.
This is possibly contributed to deflocculation. Excessive
amounts of polyDADMAC causes charge repulsion, thus
creating stability between particles. Meanwhile, exces-
sive amounts of PAM cause saturation, thus breaking the
bridges, although microflocs still exist. Zhou and Frank
(2006) conclude that the positive value of ζ potential
achieved is contributed to the bridging mechanism, while
charge neutralization is more dominant if the ζ potential
achieved is a negative value [33].
4. Conclusion
TSSs, the reduction of turbidity, COD removal, and ζ
potential were studied using dual polyelectrolytes as a
hybrid flocculant method in treating pulp and paper mill
Table 5. ζ Potential of wastewater after treatment by dif-
ferent dosage of PAM and constant polyDADMAC dosage
at 1.2 mg·L–1.
PAM Dosage (mg·L–1) ζ Potential (mV)
0.4 −1.12
2.0 −1.08
4.0 −1.12
6.0 −0.06
8.0 −1.32

M. A. A. RAZALI ET AL.
500
-25
-20
-15
-10
-5
0
5
10
15
00.511.5
ζ Potential (mV)
PolyDADMACDosage (mg·L
–1
)
22.5
PDM01
PDM02
PDM03
(a)
-25
-20
-15
-10
-5
0
5
10
15
00.511.
ζ Potential (mV)
PolyDADMACDosage (mg·L
–1
)
522.5
PDM01
PDM02
PDM03
(b)
-25
-20
-15
-10
-5
0
5
10
15
00.511.
ζ Potential (mV)
PolyDADMACDosage (mg·L
–1
)
522.5
PDM 01
PDM 02
PDM 03
(c)

M. A. A. RAZALI ET AL. 501
-20
-15
-10
-5
0
5
10
15
00.511.5
ζ Potential (mV)
PolyDADMAC Dosage (mg/L)
22.5
PDM 01
PDM 02
PDM 03
(d)
-25
-20
-15
-10
-5
0
5
10
15
00.511.
ζ Potential (mV)
PolyDADMACDosage (mg·L
–1
)
522.5
PDM 02
PDM 03
PDM 04
(e)
Figure 7. Effect of PolyDADMAC dosages on ζ Potential at (a) 0.4; (b) 2.0; (c) 4.0; (d) 6.0; and (e) 8.0 PAM dosages (mg·L–1).
wastewater. In this system, PolyDADMAC functions as a
charge destabilizer, while PAM (the loops and tails of the
chains link the microflocs) acts as a bridger. Another
conclusion is that the highest flocculation occurs at a
lower value of the ζ potential. Decreasing the value of the
ζ potential decreased the repulsive forces between parti-
cles, and thus increased the occurrence of flocs.
5. Acknowledgements
The authors wish to acknowledge the financial support
provided by MOSTI science fund (1001/pbahan/814131)
and Global Network Technology (GNT) SdnBhd.
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