Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.15, pp.1391-1407, 2011
jmmce.org Printed in the USA. All rights reserved
1391
Impact of pH Variation on Coag-flocculation Behaviour of Chitin
Derived Coag-flocculant in Coal Washery Effluent Medium
M.C. Menkiti
*
and O.D. Onukwuli
Department of Chemical Engineering, Nnamdi Azikiwe University Awka, Nigeria.
*Corresponding author : [e-mail]
ABSTRACT
This work investigates the influence of pH variation on coag-flocculation kinetics and
performance of Chitin Derived Coag-flocculant (CDC) in removal of Suspended and Dissolved
Particles (SDP) from Coal washery effluent (CWE) medium. Key parameters such as rate
constant K
m
, half life τ
1/2,
, and pH etc. were investigated. The best coag-flocculation performance
is recorded at K
m,
of 0.007 l/mg.min, τ
1/2,
of 0.0362min, pH of 8, dosage of 100mg/l and
efficiency E(%) of 99.933. Minimum efficiency (%) > 94.00 was achieved at 30 minutes of coag-
flocculation, establishing CDC as an effective water treatment agent at the conditions of the
experiment.
Keywords: Coal effluent, coag-flocculation, coagulation, chitin, chitosan
1. INTRODUCTION
The biosphere is increasingly exposed to pollution threats in spite of the global efforts to protect
it. Anthropogenic activities are the significant and dominant sources of these threats. The
growing human needs and ceaseless drive to satisfy them have led to the production of varying
forms of harmful wastes that ultimately rest in our aqua systems. The implication is that much of
the water cannot be used without a form of treatment. This situation brings to the fore the needed
impetus to focus on challenges inherent in hydro management, especially in developing countries
where discharge of effluent such as CWE is common.

1392 M.C. Menkiti and O.D. Onukwuli Vol.10, No.15
CWE, emanating from washery unit of coal mining operation depicts elevated concentrations of
organic and inorganic loads [1,2]. Such loads include kaolinite, illite, muscovite, quartz, bacteria,
colloids, virus, color, nitrogen, aromatics, sulphur, phosphorus etc. These contaminants make
CWE a significant environmental pollutant, and thus subject to removal during treatment
processes such as coag-flocculation [3,4].
Coag-flocculation as a treatment procedure has existed for years. The procedure is accomplished
by the addition of ions having opposite charge to that of the particles. Typically, the ion species
are from metal salts, capable of destabilizing stable colloids in suspension, such that they can
agglomerate into settleable floc [5,6]. The application of Al and Fe salts are well established in
the practice, though they are linked with health and cost challenges [6].
Attempts to confront these challenges highlight the persistent search for new substitutes to metal
salts and the current drive to improve the efficiency of existing substitutes [7,8,9]. Among the
established existing substitutes is chitin derived coag-flocculant (CDC), popularly known as
chitosan. CDC is obtained from chitin of crustaceans such as crawfish and crab. CDC, a
polycationic, biodegradable, non-toxic and high molecular weight linear copolymer of
glucosamine and N-acetyl glucoseamine, is soluble and positively charged in acid media and
may therefore be used as eco-friendly coag-flocculant [10,11].
CDC has been widely used as an effective coag-flocculant for a wide variety of suspended solids
in various food and fish processing industries [12,13,14] and suspension containing mineral
colloids in water [11,15,16,17,18]. The reactivity of CDC during coag-flocculation of suspended
and dissolved particles (SDP) results from several mechanisms, including electrostatic attraction,
sorption and bridging. The contribution of each mechanism depends on the pH of the suspension.
In this presnt study, the influence of CDC dosage and CWE pH on the kinetics and coag-
flocculation efficiency of the process were examined. It is expected that the kinetics results will
enrich the existing kinetic data towards development of more efficient and robust coag-
flocculation units that ensure the conservation of the environment.
2. THEORY.
The rate of successful collision between particles of sizes i and j to form particle of size k is [19]:
∑∑
==+
−=
α
ββ
1
),(),(
2
1
ikiBR kji jiBR
k
nnkinnji
dt
dn
…1
where β
BR(i,j)
is Brownian aggregation factor for flocculation transport mechanism, n
i
n
j
is particle
aggregation concentration for particles of size i and j, respectively.

Vol.10, No.15 Impact of pH Variation on Coag-flocculation 1393
It has been established that [19,20]:
η
εβ
TK
B
pBR
3
8
= …2
where K
B
,T ,η, ε
p
are Boltzmann constant, temperature, viscosity and collision efficiency factor,
respectively.
It can be shown that:
mRpBR
KK == εβ
2
1
…3
α
tm
t
NK
dt
dN =−
…4
K
R
is defined as Von Smoluchowski rate constant for rapid coagulation. K
m
is Menkonu coag-
flocculation rate constant accounting for Brownian coag-flocculation transport of destabilized
particles at α
th
order. N
t
is the concentration of SDP at time, t [9,21,22].
Graphical representation of linear form of equation 5 at α=2 provides K
m
from the slope of
equation below:
0
11
N
tK
N
m
+= …5
where N
0
is upper limit of N
t
at t>0. N
0
is N
t
at t=0.
Equation 6 can be solved to obtain coag-flocculation period, τ
1/2
1
02/1
)5.0(
−
=
m
KN τ …6
Equation 2 solved exactly results in generic expression for microscopic aggregation
1
2/1
1
2/1
0
)(
1
1
+
−





+






=
m
m
tm
t
N
N
τ
τ
…7
m=1(monomer), m=2(doublet),m=3(triplet)
Efficiency of coag-flocculation is expressed as:
100(%)
0
0





−
=N
NN
E
t
…8

1394 M.C. Menkiti and O.D. Onukwuli Vol.10, No.15
3. MATERIALS AND METHODS
3.1. Materials Collection, Preparation and Characterization
3.1.1. Coal washery effluent
The effluent was taken from a coal mine located in Enugu, Enugu State, Nigeria. The
characterization of the effluent presented in Table 1 were determined based on standard method
[23].
3.1.2. Crab shell sample
Crab Shell samples (precursor to CDC) were sourced from Nsugbe, Anambra State, Nigeria.
CDC was prepared according to procedure reported by Fernandez-Kim [24]. The characteristics
of the sample on the bases of AOAC standard method [25] are presented in Table 2.
Table 1: Characteristics of coal washery effluent
Parameters Values
pH 2.5200
Turbidity (NTU) 5387.0000
Total hardness(mg/l) 358.0000
Ca hardness (mg/l) 306.0000
Mg hardness (mg/l) 52.0000
Ca
2+(
mg/l) 122.4000
Mg
2+(
mg/l) 15.6000
Fe
2+(
mg/l) 0.2500
SO
4
2-(
mg/l) 72.0000
NO
3
2-(
mg/l) Nil
Cl
-
(mg/l) 184.3400
E.cond(µm/m
2
) 805.2000
TDS (mg/l) 450.9120
TSS (mg/l) 109.6000
T.Coliform Nil
Plate Count 4.0000s
E-Coli Nil
BOD
5
1001.0110

Vol.10, No.15 Impact of pH Variation on Coag-flocculation 1395
Table 2 : Characteristics of coag-flocculant
Parameter CDC
Moisture content (%) 9.7700
Ash content (%) 2.6800
Lipid content (%) 27.1800
Crude protein(%) 44.3800
Carbohydrate(%) 16.2600
3.2. Coag-flocculation Experiments
Experiments were conducted using conventional jar test apparatus. Appropriate dosage of CDC
in the range 100-500mg/l was added directly to 200ml of CWE. The suspension, tuned to pH
range 2-10 by application of H
2
SO
4
/ NaOH was subjected to 2 minutes of rapid
mixing(250rpm),20minutes of slow mixing (20rpm) and followed by 30 minutes of settling.
During settling, samples were withdrawn from 2cm depth and turbidity (converted to SDP in
mg/l) changes measured for kinetic analysis. .
4. RESULTS AND DISCUSSION
The results of the investigation on the coag-flocculation of CWE by CDC are presented and
discussed sequentially as presented below:
4.1 Coag-Flocculation Kinetics
Presented in tables 3-7 are functional kinetics parameters obtained for the coag-flocculation of
CDC in CWE at pH 2, 4, 6, 8, 10 for 100, 200, 300, 400, 500mg/l CDC dosages. Linear
regression coefficient (R
2
) was employed in evaluation of the level of accuracy of fit of the
experimental data on the considered model equation 5. Tables 3-7 indicate that data (with
majority of R
2
> 0.9) were significantly described by the linearized form of equation 4 expressed
as equation 5.
K
m
, determined from the slope of equation 5 is a vital factor that determines the rate of reaction.
Higher K
m
translates to higher rate of coag-flocculation. K
m
is evaluated by fitting the
experimental data on the plot of (1/N) or (1/SDP) against time as can be deduced from equation
5. Representative results for the various dosages and pH as displayed in tables 3-7 are
graphically depicted in Figure 1. It should be noted that the trends for the various dosages and
Ph( not shown) are identical. K
m
(=0.5 β
BR
) as expressed in equation 3 and shown in tables 3-7
recorded maximum and minimum values of 0.007 and 3x10
-5
l/mg.min, respectively. It can be
observed that least values of K
m
were obtained at pH 2. One possible explanation is the
likelihood of excess protonation of the particles, leading to partial or total charge reversal. The

1396 M.C. Menkiti and O.D. Onukwuli Vol.10, No.15
consequence is the prevalence of repulsion of the particle and the attendant poor performance
observed in pH 2. From pH 4 to alkaline condition, CDC can perform satisfactorily but to a
different extent [26,27]. This explains why high and low values of K
m
were obtained at both
acidic and alkaline conditions of CWE.
Another two essential parameters are ε
p
and K
R
. From equations 2 and 3, ε
p
and K
R
could be
evaluated, respectively. It can be deduced from equation 2 that K
R
is a function of K
B
,
temperature and viscosity. Mathematically, it can be expressed as K
R
=fn(T, η). Values of K
R
obtained from Tables 3-7 indicate there is no significant practical variation among the values.
This trend follows minimal variation in the values of temperature and viscosity. At
approximately constant K
R
, ε
p
relates directly to 2K
m
= β
BR
(equation 3). Thus, high ε
p
results in
high kinetic energy providing particle momentum to ensure the overcoming of the electrostatic
repulsive forces by the coag-flocculating particles. It should be noted that high repulsive forces
translate to high zeta potential, which in this present study is relatively high at pH 2. From
theoretical point of view, τ
1/2
, K
R
and ε
p
are believed to be effectiveness factor, understood to
be accounting for the coagulation efficiency before the commencement of flocculation.
The coag-flocculation period, τ
1/2
, is evaluated from equation 6. It can be inferred that τ
1/2
,
=fn(N
0
). It implies that the higher the N
0
, the lesser the τ
1/2 .
This accounts for high settling rate
prevalent among waters with high initial turbidity load. On a broad base, the discrepancies noted
in the results of the functional parameters are due to unattainable assumption that mixing of
CWE particles and CDC throughout the dispersion is 100% efficient before aggregation occurs
[22, 28, 29]. Second account is the interplay between Van der Wall’s forces and the hydro
dynamic interactions which typically alters the theoretical predicted values by a factor of ± 2.
Table 3 : Coag-flocculation kinetic parameters of CDC in CWE at varying pH and 100 mg/l
dosage
Parameters pH=2 pH=4 pH=6 pH=8 pH=10
2.0000 2.0000 2.0000 2.0000 2.0000
R
2
0.9363 0.9574 0.9284 0.9828 0.9268
4E- 05 0.001 0.0009 0.0022 0.0014
8E – 05 0.002 1.8x10
-3
0.0044 0.0028
7.1668 x 10
-12
9.4422 x 10
-12
9.4263 x 10
-12
9.7352 x 10
-12
7.5623 x 10
-12
1.1162 x 10
7
2.1181 x 10
8
1.9095 x 10
8
4.5196 x 10
8
3.7025x 10
8
2.5368 0.0781 0.1128 0.0461 0.0724
10000.0000 322.5806 204.0816 86.9565 476.1905
6.0220 x 10
24
1.9425 x 10
23
1.2289 x 10
23
5.2365x 10
22
2.8676 x 10
23

Vol.10, No.15 Impact of pH Variation on Coag-flocculation 1397
Table 4 : Coag-flocculation kinetic parameters of CDC in CWE at varying pH and 200 mg/l dosage
Parameters pH=2 pH=4 pH=6 pH=8 pH=10
2.0000 2.0000 2.0000 2.0000 2.0000
R
2
0.7962 0.9908 0.9129 0.9209 0.9872
3E- 05 0.0020 0.0023 0.0024 0.0015
6E – 05 0.004 0.4600 0.0048 3 x 10
-3
1.0992 x 10
-11
1.0474 x 10
-11
8.8758 x 10
-12
9.5713 x 10
-12
7.9004 x 10
-12
5.4631 x 10
6
3.8187 x 10
7
5.1826 x 10
8
5.0149 x 10
8
3.7972 x 10
8
3.3825 0.5074 0.5074 0.0422 0.0677
10000.0000 3333.3333 285.1142 57.4713 84.0336
6.0220 x 10
24
2.0073 x 10
24
1.7206 x 10
23
3.4609x 10
22
1.85663 x 10
22
Table 5 : Coag-flocculation kinetic parameters of CDC in CWE at varying pH and 300 mg/l dosage
Parameters pH=2 pH=4 pH=6 pH=8 pH=10
2.0000 2.0000 2.0000 2.0000 2.0000
R
2
0.7970 0.8805 0.7721 0.9349 0.9388
3E- 05 0.0009 0.0017 0.0019 0.0006
6E – 05 1.8 x 10
-3
3.4 x 10
-3
3.8 x 10
-3
1.2x 10
-3
9.8944 x 10
-12
1.0878 x 10
-11
1.0291 x 10
-11
7.8483 x 10
-12
7.9061 x 10
-12
6.0663 x 10
6
1.6546 x 10
8
3.3038 x 10
8
4.8418 x 10
8
1.5178 x 10
8
3.3825 0.1128 0.0596 0.0534 0.1691
50000.0000 322.5806 2564.1025 2500.0000 2500.0000
3.0110 x 10
25
1.9426 x 10
23
1.5441 x 10
24
1.5055x 10
24
1.5055 x 10
24
Table 6 : Coag-flocculation kinetic parameters of CDC in CWE at varying pH and 400 mg/l dosage
Parameters pH=2 pH=4 pH=6 pH=8 pH=10
2.0000 2.0000 2.0000 2.0000 2.0000
R
2
0.9828 0.9576 0.9821 0.9963 0.8194
4E- 05 0.0006 0.0028 0.0010 0.0018
8E – 05 1.2 x 10
-3
5.6 x 10
-3
0.0020 3.6 x 10
-3
1.0180 x 10
-11
1.0335 x 10
-11
8.7400 x 10
-12
8.5143 x 10
-11
8.5552 x 10
-12
7.8585 x 10
6
1.1610 x 10
8
6.4072 x 10
8
2.3489 x 10
8
4.2079 x 10
8

1398 M.C. Menkiti and O.D. Onukwuli Vol.10, No.15
2.5368 0.1691 0.0362 0.1014 0.05663
25000.0000 555.5556 263.1578 88.3333 104.1667
1.5055 x 10
25
3.3456 x 10
23
1.5847 x 10
23
5.0183 x 10
22
6.2727 x 10
22
Table 7 : Coag-flocculation kinetic parameters of CDC in CWE at varying pH and 500 mg/l dosage
Parameters pH=2 pH=4 pH=6 pH=8 pH=10
2.0000 2.0000 2.0000 2.0000 2.0000
R
2
0.9552 0.9501 0.8531 0.9320 0.9862
4E- 05 0.0006 0.0018 0.0026 0.0070
8E – 05 1.2 x 10
-3
3.6 x 10
-3
5.2 x 10
-3
0.0140
9.4882 x 10
-12
1.089 x 10
-11
1.0188 x 10
-11
1.0155 x 10
-11
9.1790 x 10
-12
8..4314 x 10
6
1.1894 x 10
8
3.5335 x 10
8
5.1206 x 10
8
15252 x 10
9
2.5368 0.1690 0.0566 0.0390 0.1449
12500.0000 1428.5714 142.8571 238.0952 212.7659
7.5275 x 10
24
8.6031 x 10
22
8.6031 x 10
22
1.4338 x 10
23
1.2812 x 10
23
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0.080
0.090
010 2030 40
1
/
S
D
P
(
l
/
m
g
)
Time (min)
pH=2
pH=4
pH=6
pH=8
pH=10
Fig. 1: Kinetic profile of SDP removal from CWE by CDC at 100mg/l

Vol.10, No.15 Impact of pH Variation on Coag-flocculation 1399
4.2 Time Evolution of Cluster Size Distribution.
The time evolutions of cluster size distribution are presented in the graphical form of number of
particles as a function of time. By substituting K
m
from equation 5 into 7, the particle
aggregation at a microscopic levels can be predicted graphically by the interaction of singlets
(m=1), doublets (m=2) and triplets (m=3). The singlets, doublets and triplets are composed of
single, double and triple monomers, respectively. Representative results are shown in Figures 2
and 3. The perceived difference in the nature of the curves in response of two different τ
1/2
of
0.0362 and 3.382minutes are demonstrated as case I and caseII, respectively.
Case I This is shown graphically as Figure 2. In this case , the singlet and total particle sum can
be seen to decrease more rapidily. This is evidence of high rate of coag-flocculation supported by
low half life. This can be accounted on the bases of sweep-floc or/ and massive instantaneous
destabilization of the particles. With prevalent low zeta potential in the fluid, the CDC sweep-
floc the particle out of the suspension [30].
Case II This is particle distribution that is associated with coag-flocculation process where there
is absence of excessive entrapment and high shear resistance. The dominating aggregation
mechanisms are charge neutralization in conjunction with low bridging to ensure moderate speed
of coag-flocculation associated with moderate energy barrier in view of gentle nature of the
curves.
0
2E+24
4E+24
6E+24
8E+24
1E+25
1.2E+25
1.4E+25
0510 15 2025 30 35
N
o
o
f
p
a
r
t
i
c
l
e
s
(
/
l
)
Time (min)
Singlet
Doublet
Triplet
Sum
Fig. 2:Temporal particle aggregation profle at minimum half life of 0.0362min

1400 M.C. Menkiti and O.D. Onukwuli Vol.10, No.15
4.3 Time Course % Removal Efficiency for Varying pH and CDC Dosages.
The process efficiency graphically presented in Figures 3-7 are obtained based on the evaluation
of equation 8. They depict the variation of efficiency E(%) as a function of time and pH for
various CDC dosages of 100, 200, 300, 400 and 500mg/l. It was observed that the trends for all
the cases studied are almost identical but with different percentages of efficiency achieved for
particular pH and dosages. This coag-flocculation process was very fast initially with about 99%
efficiency recorded at 3minutes for all cases. The only exception was recorded at pH 2 where
E(%) range between 40 and 60 for Figures 4-8. Practically, 99% of initial SDP load of
19709.20mg/l was removed at 3minutes of coag-flocculation.
The possible explanation for the poor performance at pH 2 could be attributed to hyper
protonation and interactions among numerous chemical species present in CWE. This could
affect the charge balance following complex reaction likely to have been undergone by the
CWE. Arguably, this condition can generate restabalized colloids, causing electrostatic
repulsion among the suspended solids. It could also be observed that the CDC recorded
satisfactory performance from pH 4-10, but to a different extent. It is reported that CDC
performs well in acidic medium because the amine group of CDC is usually protonated by H
+
produced from dissociation of H
2
SO
4
. On the other hand, one possible explanation for the good
alkaline performance is that alkaline cation can favor delamination of the SDP in suspension,
which thereby displays highly accessible surface [11,26]. Another important factor that impacted
the CDC performance in this study is the CDC dosage. Basically, insufficient dosage or over
dosage when confronted with chemical interaction among the chemical species involved in the
process could affect the perceived performance of CDC. At unfavorable conditions, excess CDC
dosage ensures that excess polymer is adsorbed on the particles surfaces, producing restabalized
colloids. The implication is the absence of sites available on the particles surfaces for the
formation of inter particle bridge. However, at favorable conditions, excess CDC can lead to
particle enmeshment that can instantaneously sweep away the SDP from the suspension.
Mechanism of aggregation has possible effects on the influence of dosage on the aggregation
process. It has been reported that effective coag-flocculation could be achieved with much lower
doses of CDC ,especially when complete charge neutralization is not required and the process
guided by combine effects of electrostatic patch and bridging mechanism [11].

Vol.10, No.15 Impact of pH Variation on Coag-flocculation 1401
0
2E+24
4E+24
6E+24
8E+24
1E+25
1.2E+25
1.4E+25
0510 15 2025 30 35
N
o
o
f
p
a
r
t
i
c
l
e
s
(
/
l
)
Time (min)
S inglet
Doublet
Tripl et
S um
Fig.3:Temporal particle aggregation profile at maximum half life of 3.3825min
0
20
40
60
80
100
120
051015 20 2530 35
E
(
%
)
Time (min)
pH=2
pH=4
pH=6
pH=8
pH=10
Fig. 4: Temporal coag-flocculation efficiency profile at 100mg/l and pH varying CWE.

1402 M.C. Menkiti and O.D. Onukwuli Vol.10, No.15
0
20
40
60
80
100
120
051015 20 253035
E
(
%
)
Time (min)
pH=2
pH=4
pH=6
pH=8
pH=1 0
Fig.5: Temporal coag-flocculation efficiency profile at 200mg/l and pH varying CWE
0
20
40
60
80
100
120
0510 15 2025 30 35
E
(
%
)
Time (min)
pH=2
pH=4
pH=6
pH=8
pH=1 0
Fig.6:Temporal coag-flocculation efficiency profile at 300mg/l and pH varying CWE.

Vol.10, No.15 Impact of pH Variation on Coag-flocculation 1403
0
20
40
60
80
100
120
0510 15 2025 30 35
E
(
%
)
Time (min)
pH=2
pH=4
pH=6
pH=8
pH=1 0
Fig.7 :Temporal coag-flocculation efficiency profile at 400mg/l and pH varying CWE.
0
20
40
60
80
100
120
051015 20 2530 35
E
(
%
)
Time (min)
pH=2
pH=4
pH=6
pH=8
pH=1 0
Fig.8: Temporal coag-flocculation efficiency profile at 500mg/l and pH varying CWE.

1404 M.C. Menkiti and O.D. Onukwuli Vol.10, No.15
4.4 Comparative Coag-flocculation Performance Between CDC and Alum.
Figure 9 is the comparative performance chart between CDC and alum at varying pH, 100mg/l
CDC, and 30minutes. The least performance is recorded at pH 2.This is explained by various
reasons adduced earlier in this communication. However, the performance is about 94% for all
the pH considered at this dosage. Similar results(not shown) were obtained for 200, 300, 400 and
500mg/l CDC dosages. The best performance was recorded at pH 8 and 99.933% while the least
was recorded at pH 2 and 94.7537%. The fact is that CDC compares favorably with alum with
advantage of being eco-friendly. Additionally, the use of CDC raises no health concerns, which
is one of the major setbacks in the application of alum in water treatment.
pH=2
pH=4
pH=6
pH=8
pH=10
CDC
95.7195
99.8597
99.8902
99.9333
99.8969
Alum
96.6256
99.8092
99.6661
99.9015
99.8922
92
93
94
95
96
97
98
99
100
101
102
E
(
%
)
CDC
Alum
Fig. 9: Representative comparative coag-flocculation performance between Alum and CDC
for 100mg/l at 30 mins.
5. CONCLUSION
The high level of efficiency achieved within 30 minutes affirms the prevalence of rapid coag-
flocculation, hence the dominance of perikinetics in the removal of SDP from CWE by CDC .
The efficiency of CDC recorded establishes it at a pilot scale and within the experimental
conditions as a veritable treatment agent for the removal of SDP from CWE. The best results
were obtained at pH 8, 100mg/l dosage and 99.933% efficiency.

Vol.10, No.15 Impact of pH Variation on Coag-flocculation 1405
REFERENCES
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flocculation and activated carbon adsorption. Ph.D Thesis. Department of Chemical
Engineering, Nnamdi Azikiwe University, Awka, Nigeria.
[2] Ghose, M.K., 2008; Process of recovering resources from coal washery effluent for
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