Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.3, pp.279-298, 2011
jmmce.org Printed in the USA. All rights reserved
279
Coag-Flocculation Studies of Afzelia Bella Coagulant (ABC) in Coal
Effluent Using Single and Simulated Multi Angle Nephelometry
M.C. Menkiti* and O.D. Onukwuli
Department of Chemical Engineering, Nnamdi Azikiwe University, Awka, Nigeria.
*Corresponding author:
Telephone: [phone]
ABSTRACT
Following the need for the use of environmentally friendly, renewable resource in industrial
processes, this work explores the potential of an effective application in pilot scale of Afzelia
bella seed as a coag-flocculant. The study evaluates the coag-flocculation efficiency and
functional kinetic parameter response to varying pH and dosage of coal washery effluent and
ABC respectively. The maximum coag-flocculation performance is recorded at rate constant,
K of 3.3333 x 10-3m3/kg.s, dosage of (0.3 and 0.2kg/m3); pH of 2 and coagulation period, τ1/2
of 28.1216 s while the minimum is recorded at K of 1.6667 x 10-4m3/kg.s, dosage of 0.2kg/m3,
pH of 10 and τ1/2 of 562.365 s. The least value of coag-flocculation efficiency, E (%)>89.00.
Simulated and unsimulated values of rate constants Ks and K respectively are in close
agreement, validating the concept of perikinetics. The potential of ABC as an effective
organic coag-flocculant has been established. The results confirm that theory of rapid coag-
flocculation holds for the aggregation of coal washery effluent using ABC and at the
conditions of the experiment.
Keywords: Afzelia bella; coag-flocculation; coal effluent; kinetics; nephelometry.
1. INTRODUCTION
1.1 Background
In waste water treatment operations, the process of coag-flocculation (coagulation /
flocculation) is employed to separate suspended solids from waste effluent; via floc formation
[1, 2, 3, 4,]. Among the factors that can affect the formation of the flocs are temperature, pH,
effluent quality e.t.c. [5].

280 M.C. Menkiti and O.D. Onukwuli Vol.10, No.3
Coag-flocculation can be achieved by the use of inorganic substances (alum, FeCl3 e.t.c) and
natural organic derivatives. However, the caog-flocculation behaviors of these inorganic
aggregates agents are well documented with little or no attention given to the study of the
animal and plant material as a potential source of organic derived coagulant. To this end,
focus is hereby given to the study of a plant material, Afzelia bella bean, as a potential source
of coagulant derivative. Afzelia bella is a leguminous plant, rich in protein, fat and starch. It is
a native to tropical climate such as Eastern Nigeria [6].
Afzelia bella is an edible, non-toxic and biodegradable substance. Previous results obtained in
its thickening properties highlight promise of renewable material with extensive application
in water treatment technology.
However, in spite of the abundance of Afzelia bella in our local communities in Nigeria, little
or no comprehensive work has been reported on its coag-flocculating application. Against
this backdrop, this work endeavors to explore and generate interest in the utilization of
Afzelia bella as a coagulant. In line with this, the work focuses on coag-flocculation
performance and kinetics of ABC under varying pH of coal washery effluent (a typical
medium for this kind of study) using single and simulated multi angle light scattering
techniques. Thus if well harnessed and developed, ABC can be an alternative to or be used in
conjunction with the inorganic coagulant. Ultimately, post usage handling and health
challenges posed by the inorganic coagulant can be reduced.
1.2 Theoretical Principles and Model Development
For a uniformly coag-flocculating equilibrium phase with negligible influence of external
forces [7]:










nTP
i
ii n
G
G
,,
 a constant ….1
And
dx
dC
C
TK
fi
i
B
d …2
Where G is the total Gibbs free energy
ni is the number of moles of component i
μi is chemical potential
Ci is concentration
x is diffusion distance
fd is viscous drag force.
B K is Boltzmann’s constant (J/K)
T
is Absolute temperature (K)
But from Ficks law

Vol.10, No.3 Coag-Flocculation Studies of Afzelia Bella 281









dx
dC
C
B
f
D
i
id …3
Where D′ is diffusion coefficient
B is friction factor
Comparing equation 2 and 3 generates Einstein’s equation:
B
TK
DB

 …4
For similar phase, the rate of successful collision between particles sizes i and j (mass
concentration/time) to form particle of size k is [8, 5]:
Nij = εp β (i,j) ninj …5
where
εp = collision efficiency
β(i,j) = collision factor between particles of size i and j
ninj = particle concentration for particles of size i and j, respectively.
Assuming monodisperse, no break up and bi particle collision, the general model for
perikinetic coag-flocculation is given as [9, 5]:
ki
i
ji
kji
knnkinnji
dt
dn  


1
),(),(
2
1
 …6
where dt
dnk is the rate of change of concentration of particle of size k (concentration /
time).

is a function of the coag-flocculation transport mechanism.
The appropriate value of

for Brownian transport is given by [10]:


TKB
pBR 3
8
 …7
The generic aggregation rate of particles (during coagulation / flocculation) can be derived by
the combination of equations 6 and 7 to yield:

t
tKN
dt
dN  …8
Where t N is total particle concentration at time
t
,

kt nN (mass / volume)
K is the Menkonu coag-flocculation rate constant for th  order.
 is the order of coag-flocculation process .
Meanwhile BR K 
2
1
 …9
Also, RpBR K


2 …10
Combining equations 8,9 and 10 produce:
 dt
dNt


tRp NK ….11
Where R
K is the Von smoluchowski rate constant for rapid coagulation [11].

282 M.C. Menkiti and O.D. Onukwuli Vol.10, No.3
However DaKR

 8 ….12
aRp2 ….13
Where a is particle radius.
From Einstein’s equation:B
T
KD B 

From Stoke’s equation :aB

6 ….14
where η is the viscosity of the coag-flocculating fluid
Combining equations 11 to14 gives:



t
B
p
tN
TK
dt
dN
3
4
 …15
Comparing equations 8 and 15 show:


TK
KB
p
3
4
 ...16
For perikinetic aggregation,

theoretically equals 2 as would be shown below [12, 7]:
From Fick’s law,
dR
dN
RDJ t
pf
2
4 

 ..17
Integrating equation 17 at initial conditions0

t
N,aR2

:



pt
RN
Nt
p
pf dN
R
dR
D
J
020
4 
...18
Thus 0
8aNDJ f


…19
For central particle of same size undergoing Brownian motion, the initial rate of rapid
coag-flocculation is:
0 NJ
dt
dN
pf
t
 …20
2
0
3
4N
TKB
p


...21
2
3
4
t
B
pN
TK


 at 0t
Hence, from equation 21,2

For 2

; equivalence of equation 8 yields:
2 KN
dt
dN 
Hence:
  tN
NdtK
N
dN
0
2
0
…22
Thus
0
1
1
N
Kt
N
 ...23
Plot of


N
1 Vs
t
produces a slope of K and intercept of
0
1N.

Vol.10, No.3 Coag-Flocculation Studies of Afzelia Bella 283
For the evaluation of coagulation period (21

), from Equation 23:




















KN
t
N
N
0
0
1
1
...24
Where 





KN0
1

…25
Hence:
  /1
0
t
N
N  …26
When


t
, equation 26 becomes
2
0
N
N …27
Therefore as 2100 ;5.0


 NN
Hence
 KN0
21 5.0
1
  ...28
For Brownian (perikinetic) aggregation at early stages (t≤30 minutes), equation 6 can be
solved exactly, resulting in the generic expression


1
1
0
)(
1




m
m
tm
t
t
N
N


...29
Where


2

Hence, for singlets (m=1)













2
01
1
1

t
NN ...30
For doublets (m=2)















3
02
1


t
t
NN ...31
For triplets (m=3)















4
2
03
1


t
t
NN ….32
Also for the coagulating phase, the intensity of light scattered from suspension of
monodispersed phase is described as [11]:


)()(21)0,(),( 2qACqIqI md
mmd  

 ….33
Where I(q, Τd) is the intensity of light scattered by the initially unaggregated suspension ;
Τd = t / τ′ (dimensionless time)

284 M.C. Menkiti and O.D. Onukwuli Vol.10, No.3
q is the scattering wave vector
 


5.0sin
4
0
0
nq 







 …34
where λ0 is the wave length of the laser incident light in Vacuum, (λ0 =2πa / 6)
n0 is the refractive index of the suspending medium
θ is the scattering angle
Am is the form factor for an aggregate consisting of m primary particles.
a is radius of particles sphere.
If the coagulating medium obeys the Rayleigh-Gans-Debye (RGD) approximations, then


m
i
m
jij
i
mqr
qr
qA
1
sin
)( …35
Where rij is the centre-to-centre separation of primary particles i and j in the given m-fold
aggregate. The summation accounts for all pairs of particle centers in the aggregate.
The expression for the scattered intensity in view of many possible configurations
arising from larger aggregates is:








 

)()(2
)1(
sin
21)0,(),( 3
3
0
0qAC
qd
qd
qIqI md
mm
d
d
d …36
The form factors are given by an average of all contributing structures where d0 is hard core
interaction diameter of singlets.Differentiating equation 36 as t→0, yields:



















)()(2
)1(
sin
21
),(
)0,( 3
3
0
0
0
qAC
qd
qd
dt
d
dt
tqdI
qI
I
md
mm
d
d
t
…37














0
0
0
0
sin
),(
)0,( qd
qd
N
dt
tqdI
qI
I
BR
t

…38
Using simulated version of equation 38, KS (simulated K) can easily be determined at several
scattering angles. A plot of
0
0
0
sin ),(
)0,( qd
qd
Vs
dt
tqdI
qI
I
t






 gives a slope of N0βBR from where
(KS)t→0 could be determined.
2. MATERIALS AND METHODS.
The sample of Afzelia bella was sourced from Nsugbe,Anambra State, Nigeria and processed
to ABC based on the work reported by Adebowale and Adebowale [13].
The jar test was conducted based on standard Bench scale Nephelometric method (single
angle procedure) for the examination of water and waste water [14, 15] using model WZS-
185 MC Turbidimeter, APPNo 688644A Gulenhamp magnetic stirrer and mettler Toledo
Delta 320 pH meter.
For the simulation, excel package was used while d0 = 1μm [16, 7] and no [17] were
generated from literature and simple experiment respectively.

Vol.10, No.3 Coag-Flocculation Studies of Afzelia Bella 285
3. RESULTS AND DISCUSSION
3.1 Coag-flocculation Parameters
The values of caog-flocculation reaction parameters are presented in Tables 1 to 6. For all
cases of dosages and pH, the value of α is 2, though with the exception of few, the
corresponding value of R2 is generally >0.9. This result actually emphasizes its consistency
with Von Smoluchowski theory of coagulation. Meanwhile, it should be noted that α relates
with K inversely. Since K is rate per concentration and K is associated with energy barrier
(KT), it is understandable that for higher α to be obtained, lower K is a necessary condition
for such phenomenon [12]. K (=0.5βBR) values appreciably are less sensitive to a given pH as
the dosage of ABC changes from 0.1kg/m3 to 0.5kg/m3 .This may be as a result of situation
where same or similar coag-flocculation mechanism is controlling the process. Also, the
variation in KR is generally minimal; following insignificant changes in values of temperature
and viscosity of the coag-flocculation medium.
At nearly invariant values of KR ,εP relates directly to 2K= βBR .The consequence is that high
εP results in high kinetic energy to overcome the zeta potential. The implication is that the
double layer is either reduced or the colloids destabilized to actualize low τ1/2 in favor of high
rate of coagulation. The results show that high values of τ1/2 corresponds to low εP and K,
and indication of repulsion in the system. τ1/2 values lie within the range of previous works
where milliseconds had been reported [7].
Table1: Coag-flocculation Functional parameters for varying pH and constant dosage of
0.1kg/m3 ABC
Parameter pH=2 pH=4 pH=6 pH=8 pH=10

2 2 2 2 2
2
R
0.976 0.907 0.989 0.944 0.937
K
(m3/kg.s) 1.667 x 10-3 3.333 x 10-4 1 x 10-3 3.333 x 10-4 1.667 x 10-4
Br

(m3/kg.s) 3.333 x 10-3 6.667x10-4 2x10-3 6.667x10-4 3.333x10-4
R
K(m3/s) 1.273x10-17 1.470x10-17 1.274x10-16 1.470x10-16 1.470x10-16
p

( kg-1) 2.618x1014 4.535x1012 1.570x1013 4.535x1012 2.268x1012
)(
2
1s

56.237 281.19 93.748 281.191 562.365

c
SP 0(kg/m3) 0.417 1.25 0.526 1 1.667

c
p
N0(m-3) 2.5 x 1026 7.5 x 1026 3.1694 x 1026 6.0221 x 1026 10.0371 x 1026
r
(kg/m3.s) 1.667x10-3 c2 3.333x10-3 c2 1x10-3 c2 3.333x10-4 c 1.667x10-4 c

286 M.C. Menkiti and O.D. Onukwuli Vol.10, No.3
Table2: Coag-flocculation Functional parameters for varying pH and constant dosage of
0.2kg/m3 ABC
Parameter pH=2 pH=4 pH=6 pH=8 pH=10

2 2 2 2 2
2
R
0.977 0.866 0.991 0.982 0.893
K
(m3/kg.s) 3.333 x 10-3 3.333 x 10-4 1.167 x 10-3 3.333 x 10-4 1.667 x 10-4
Br

(m3/kg.s) 6.667 x 10-3 6.667x10-4 3.333x10-3 6.667x10-4 3.333x10-4
R
K(m3/s) 1.639x10-17 1.6250x10-16 1.639x10-16 1.625x10-16 1.625x10-16
p

( kg-1) 4.072x1014 4.102x1012 2.034x1013 4.102x1012 2.051x1012
)(
2
1s

28.122 281.191 80.337 281.19 562.366

c
SP 0(kg/m3) 0.526 1.25 0.526 1 1.667

c
p
N0(m-3) 3.167x 1026 7.528 x 1026 3.346 x 1026 0.675E-4 0.675E-4
r
(kg/m3.s) 3.333 x 10-3c2 3.333x10-4c2 1.167x10-3 c2 3.333x10-4 c2 1.667x10-4 c2
Table3: Coag-flocculation Functional parameters for varying pH and constant dosage of
0.3kg/m3 ABC
Parameter pH=2 pH=4 pH=6 pH=8 pH=10

2 2 2 2 2
2
R
0.983 0.620 0.968 0.996 0.9347
K
(m3/kg.s) 3.333 x 10-3 3.333 x 10-4 1.167 x 10-3 1.500 x 10-3 1.667 x 10-4
Br

(m3/kg.s) 6.667 x 10-3 6.667x10-4 3.333x10-3 3x10-3 3.333x10-4
R
K(m3/s) 1.303x10-16 1.315x10-16 1.307x10-16 1.333x10-16 1.242x10-16
p

( kg-1) 5.117x1013 5.069x1012 2.551x1013 2.251x1013 2.684x1012
)(
2
1s

28.122 281.191 80.337 62.486 562.365

c
SP 0(kg/m3) 0.434 1.429 0.526 0.526 1.667

c
p
N0(m-3) 2.614x 1026 8.603 x 1026 3.168 x 1026 3.168 x 1026 10.037x1026
r
(kg/m3.s) 3.333 x 10-3c2 3.333x10-4c2 1.167x10-3 c2 3.333x10-4 c2 1.667x10-4 c2

Vol.10, No.3 Coag-Flocculation Studies of Afzelia Bella 287
Table 4: Coag-flocculation Functional parameters for varying pH and constant dosage of
0.4kg/m3 ABC
Parameter pH=2 pH=4 pH=6 pH=8 pH=10

2 2 2 2 2
2
R
0.922 0.403 0.851 0.979 0.934
K
(m3/kg.s) 3.333 x 10-3 1.667 x 10-4 3.333 x 10-4 1.667 x 10-3 1.667 x 10-4
Br

(m3/kg.s) 6.667 x 10-3 3.333x10-4 6.667x10-3 3.333x10-3 3.333x10-4
R
K(m3/s) 1.130x10-16 1.231x10-16 1.130x10-16 1.242x10-16 1.243x10-16
p

( kg-1) 5.902x1013 2.708x1012 5.902x1013 2.684x1013 2.683x1012
)(
2
1s

28.122 562.366 281.193 56.237 562.237

c
SP 0(kg/m3) 0.100 1.429 1.111 0.556 1.429

c
p
N0(m-3) 0.602x 1026 8.603 x 1026 6.891 x 1026 3.346 x 1026 8.603x1026
r
(kg/m3.s) 3.333 x 10-3c2 1.667 x 10-4c2 3.333 x 10-4c2 1.667 x 10-3c2 1.667x10-4 c2
Table 5: Coag-flocculation Functional parameters for varying pH and constant dosage of
0.5kg/m3ABC
Parameter pH=2 pH=4 pH=6 pH=8 pH=10

2 2 2 2 2
2
R
0.921 0.549 0.986 0.979 0.934
K
(m3/kg.s) 3.333 x 10-3 3.333 x 10-4 5.000 x 10-4 1.667 x 10-3 1.667 x 10-4
Br

(m3/kg.s) 6.667 x 10-3 6.667 x 10-4 10.000x10-4 3.333x10-3 3.333x10-4
R
K(m3/s) 1.587x10-16 1.408x10-16 1.587x10-16 1.408x10-16 1.121x10-16
p

( kg-1) 4.200x1013 4.735x1012 3.151x1012 2.367x1013 2.974x1012
)(
2
1s

28.119 281.191 187.459 56.237 562.366

c
SP 0(kg/m3) 0.769 1.429 1.111 0.323 1.429

c
p
N0(m-3) 0.602x 1026 8.603 x 1026 6.891 x 1026 3.346 x 1026 8.603x1026
r
(kg/m3.s) 3.333 x 10-3c2 3.333 x 10-4c2 5.000 x 10-4c2 1.667 x 10-3c2 1.667x10-4 c2

288 M.C. Menkiti and O.D. Onukwuli Vol.10, No.3
Table 6: Representative values of K (Experimental) and Ks (Simulated) at varying
dosage and pH
pH Dosage(kg/m3) N0(Particles / m3) d0(μm) K(m3/kg.s) KS(m3/kg.s)
2 0.1 2.509 x 1026 1.0 1.667 x 10-3 1.594 x 10-3
4 0.1 7.528 x 1026 1.0 3.333 x 10-4 3.321 x 10-4
6 0.1 3.169 x 1026 1.0 1x 10-3 9.466 x 10-4
8 0.1 6.022 x 1026 1.0 3.333 x 10-4 3.321 x 10-4
10 0.1 1.004 x 1027 1.0 1.667 x 10-4 1.494 x 10-4
2 0.1 2.509 x 1026 1.0 1.667 x 10-3 1.594 x 10-3
2 0.2 3.169 x 1026 1.0 3.333 x 10-3 3.155 x 10-3
2 0.3 8.603 x 1026 1.0 3.333 x 10-3 3.487 x 10-3
2 0.4 0.602 x 1026 1.0 3.333 x 10-3 3.321 x 10-3
2 0.5 4.631 x 1026 1.0 3.333 x 10-3 3.240 x 10-3
Meanwhile, the values of K (now KS) from equation 38 determined from the simulated
light scattering model are in strong agreement with K (from equation 23) determined from
experimental jar test. These results underscore the concept of Brownian (rapid) coag-
flocculation at early time even in situation where independent procedures were employed in
the determination of the parameters. The representative’s plots for the determination of K and
KS (simulated K) are presented in Figs 1 to 4.
Fig 1: Selected representative plots of 1/SP Vs time based on minimum
2
1

y = 1E-05x + 0.0006
R2 = 0.9366
y = 1E-05x + 0.0006
R2 = 0.8932
y = 1E-05x + 0.0006
R2 = 0.9347
y = 1E-05x + 0.0007
R2 = 0.934
y = 1E-05x + 0.0007
R2 = 0.934
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0510 1520 2530 35
Time x(60 sec)
1/SP(m3/kg)
0.1kg/m
3
at pH=10
0.2kg/m
3
at pH=10
0.3kg/m
3
at pH=10
0.4kg/m
3
at pH=10
0.5kg/m
3
at pH=10
Linear (0.1kg/m
3
at
pH=10)
Linear (0.2kg/m
3
at
pH=10 )
Linear (0.3kg/m
3
at
pH=10)
Linear (0.4kg/m
3
at
pH=10)
Linear (0.5kg/m
3
at
pH=10)

Vol.10, No.3 Coag-Flocculation Studies of Afzelia Bella 289
Fig 3: Initial intensity changes Vs. interference factor at 0.1kg/m
3
ABC
-6E+22
-4E+22
-2E+22
0
2E +22
4E +22
-0.08 -0.06 -0.04 -0.0200.020.040.06
sin (qd
0
) / qd
0
[1/I(q,0)][dI(K,0)/dt](s
-1
)
pH=2
pH=4
pH=6
pH=8
pH=10
Fig 2: Selected representative plots of 1/SP Vs Time based on maximum
2
1

y = 0.0001x + 0.0024
R2 = 0.9755
y = 0.0002x + 0.0019
R2 = 0.9767
y = 0.0002x + 0.0023
R2 = 0.983
y = 0.0002x + 0.001
R2 = 0.9215
y = 0.0002x + 0.0013
R2 = 0.9209
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
010203040
Time x(60 Sec)
1/SP(m3/kg)
0.1kg/m
3
at pH=2
0.2kg/m
3
at pH=2
0.3kg/m
3
at pH=2
0.4kg/m
3
at pH=2
0.5kg/m
3
at pH=2
Linear (0.1kg/m
3
at pH=2)
Linear (0.2kg/m
3
at pH=2)
Linear (0.3kg/m
3
at pH=2)
Linear (0.4kg/m
3
at pH=2)
Linear (0.5kg/m
3
at pH=2)
Fig 4: Initial intensity change Vs. interference factor for ABC at pH of 2
-5E+23
-4E+23
-3E+23
-2E+23
-1E+23
0
1E+23
2E+23
3E+23
-0.08 -0.06 -0.04 -0.02 00.02 0.04 0.06
sin (q,d0) / qd0
[1/I(q,0)][dI(K,0)/dt] (s-
1
)
0.1kg/m
3
0.2kg/m
3
0.3kg/m
3
0.4kg/m
3
0.5kg/m
3

290 M.C. Menkiti and O.D. Onukwuli Vol.10, No.3
The discrepancies in K, KR and


c
SP 0are explained by the unattainable assumption that
mixing of particles and ABC throughout the dispersion is 100% efficient before any
aggregation occurs. The effect of this limitation will be local increase in particle ratios during
the mixing phase given uneven distribution of particles / ABC complexes [18]. Another
account is the interplay between the Vander Waal forces and the hydrodynamic interactions
which typically alters the theoretically predicted parameter values by a factor of ±2.However,
other additional short range forces may represent the most likely explanation for any other
remaining discrepancies [19, 20].
3.2 SP (kg/m3) Vs Time plots
The SP Vs Time plots are presented in Figs 5 to 9. The common trend is that SP reduces with
time. This is because as single particles flocculate into large aggregates and settle, the
turbidity of the dispersion decreases and the transmission intensity increases. This behavior
reflects the complex dependence of turbidity (hence coag-flocculation) on particle number
(dropping) and particle size (increasing) over time [18]. The rapid settling of the flocculated
particle is shown in Figs 5 to 9 where 90% of the initial SP concentration of 21204.72mg/l
were removed at the 3rd minute. This is supported strongly by the values of τ1/2 recorded in
Tables 1 to 5 where the highest and least coag-flocculation were achieved at pH of 2 and 10
respectively.
Fig 5:Plot of SP vs Coag-flocculation Time at varying pH and constant
dosage of 0.1kg/m
3
0
200
400
600
800
1000
1200
1400
1600
1800
0 10203040
Timex(60 sec)
SPX(1 0
-3
kg/m
3
)
pH=2
pH=4
pH=6
pH=8
pH=10

Vol.10, No.3 Coag-Flocculation Studies of Afzelia Bella 291
Fig 6:plot of SP Vs Coag-floccul ation Ti me at varyi ng pH and constant
dosage of 0.2kg/m
3
0
200
400
600
800
1000
1200
1400
1600
1800
0 10203040
Time x (60 sec)
SP x (10
-3
kg/m
3
)
pH=2
pH=4
pH=6
pH=8
pH=10
Fig 7:plot of SP Vs Coag-flocculation Time at varying pH and constant
dosage of 0.3kg/m
3
0
500
1000
1500
2000
2500
0 10203040
Time x (60 sec)
SP x (10
-3
kg/m
3
)
pH=2
pH=4
pH=6
pH=8
pH=10
Fig 8:Pl ot of SP Vs Coag-flocculation Time at varying pH and constant
dosage of 0.4kg/m
3
0
500
1000
1500
2000
2500
0 10203040
Time x (60 sec)
SP x (10
-3
kg/m
3
)
pH=2
pH=4
pH=6
pH=8
pH=10

292 M.C. Menkiti and O.D. Onukwuli Vol.10, No.3
Fig 9:P lot of SP Vs Coag-flocculation Time a t varying pH and constant
dosage of 0. 5kg/ m
3
0
500
1000
1500
2000
2500
0 10203040
Time x (60 sec)
SP x (10
-3
kg/m
3
)
pH=2
pH=4
pH=6
pH=8
pH=10
3.3 Efficiency E (%) vs. time
Plots of E (%) Vs time are presented in Figs 10 to 14. The E (%) indicates the effectiveness
of ABC to remove suspended particle (turbidity) form the effluent. The plots show that the
least E > 89.00 justifies the effectiveness of ABC. This collaborates with the values of τ1/2
and real life application of coag-flocculation in which 90% of the particle removal is usually
achieved within the first five minutes of the process. Observation shows that the best coag-
flocculation was achieved at pH of 2 followed by 6 and 8.
Fig 10:Pl ot of E(%) Vs Coag-flocculati on Timeat varying pH and
constant dosage of 0.1kg/m
3
92
93
94
95
96
97
98
99
100
0 10203040
Time x (60 sec)
E (%)
pH=2
pH=4
pH=6
pH=8
pH=10

Vol.10, No.3 Coag-Flocculation Studies of Afzelia Bella 293
Fig 11:Plot of E(%) Vs Coag-fl occulati on Time at varying pH and
consta nt dosage of 0 .2kg/m
3
91
92
93
94
95
96
97
98
99
100
010203040
Time x (60 sec)
E (%)
pH=2
pH=4
pH=6
pH=8
pH=10
Fig 12:P lot of E Vs Coag-flocculation Time at varying pH and constant
dosage of 0.3kg/m
3
90
92
94
96
98
100
010203040
Time x (60 sec)
E (%)
pH=2
pH=4
pH=6
pH=8
pH=10
Fig 13:P lot of E Vs Coag-flocculation Time at varying pH and constant
dosage of 0.4kg/m
3
88
90
92
94
96
98
100
010203040
Time x (60sec)
E (%)
pH=2
pH=4
pH=6
pH=8
pH=10

294 M.C. Menkiti and O.D. Onukwuli Vol.10, No.3
Fig 14:P lot of E vs Coag-flocculation Time at varying pH and constant
dosage of 0.5kg/m
3
88
90
92
94
96
98
100
010203040
Time x (60sec)
E (%)
pH=2
pH=4
pH=6
pH=8
pH=10
3.4 E (%) vs. pH
This is presented in Fig 15. It indicates the performance of various doses of ABC at varying
pH. Interestingly, all the doses have a similar trend having their maxima at pH=2 and minima
at pH=10.All doses have the same E at pH of 2,indicating that dose does not affect the E(%)
at pH of 2.
3.5 E (%) vs. Dosage (kg/m3)
This is presented in Fig 16. The optimum dosages are 0.1kg/m3 and 0.3kg/m3 at E =
99.3722% and pH =2.It confirms the observation made in fig 15.pH of 10 has the least E(%)
for all the dosages.
Fig 15: Plot of E(%) Vs pH at 30 min for varying dosages
94
95
96
97
98
99
100
024 681012
pH
E (%) 0.1kg/m
3
0.2kg/m
3
0.3kg/m
3
0.4kg/m
3
0.5kg/m
3

Vol.10, No.3 Coag-Flocculation Studies of Afzelia Bella 295
Fig 16:P lot of E(% ) Vs Dosages at varying pH and constant Time
94
95
96
97
98
99
100
00.10.20.30.40.50.6
Dosage(kg/m
3
)
E(%)
pH=2
pH=4
pH=6
pH=8
pH=10
3.6 Time Evolution of the Cluster Size Distribution
The representative plots (here Ni given in particles / m3) are presented in Figs 17 and 18. The
discussion is presented in two cases as follows:
Case I: Consider Fig 17. The particle distributions expected in a typical coag-flocculation
process is shown here. The curves Ni Vs. t, beginning with twins (doublets) passes through a
maxima because they are absent at the initial instant (t=0, N2=0) and at the end of coag-
flocculation process (t=∞, N2=0).The number of primary particles (singlets) can be seen to
decrease more rapidly than the total number of particles. For all consolidated particles, the
curves pass through maxima whose height lowers with an increase consolidation.
The curves are expected in coag-flocculation where there is absence of excessive colloidal
entrapment and high shear resistance. Mainly, the dominant mechanism in these graphs are
charge neutralization combined with low bridging to ensure moderate speed of coag-
flocculation. The discrete nature of formation of N1, N2, and N3 is associated with moderate
energy barrier.
Case II: Consider Fig 18.This is the case in which the values of N3 and ∑Ni are close such
that their variation with time is near same. Also, similar trend with respect to N2 and Ni is
obtained. The plot indicates that there exists a wide margin of difference in concentration
values between the pair of (N3 and ∑Ni) and (N2 and Ni).The implication is the existence of
high shear force and resistance to collision. This is clearly demonstrated by the value of τ1/2
which is the highest recorded. This is an indication of high zeta potential associated with the
process.

296 M.C. Menkiti and O.D. Onukwuli Vol.10, No.3
4. CONCLUSION
The efficiency of ABC recorded presents it as a potential source of organic derived coagulant
that can be applied in large scale water treatment .The optimum dosages , pH and τ1/2 for the
coag-flocculation are (0.3kg/m3 and 0.2kg/m3) , 2 and 28 seconds respectively. The obtained
results are generally in agreement with previous works [5, 11, 20, 21] and in conformity with
perikinetic theory.
NOMENCLATURE
K :Menkonu coag-flocculation reaction rate constant
βBR: Collision factor for Brownian Transport
εp: Collision Efficiency
τ1/2: Coagulation Period / Half life
E: Coag-flocculation Efficiency
Fig 17: Time evolution of th e cluster size distribution for
2
1

= 28.1216
0
2E+27
4E+27
6E+27
8E+27
1E+28
1.2E+28
1.4E+28
0 102030 40
Time x (60 Sec)
No of particle / m3
N1 (No of particle / m
3
)
N2 (No of particle / m
3
)
N3 (No of particle / m
3
)
∑N (No of particle / m
3
)
Fig 18: Time evolution of the cluster size distribution for
2
1

= 562.365
0
2E+27
4E+27
6E+27
8E+27
1E+28
1.2E+28
1.4E+28
0 102030 40
Time x (60 sec)
No of particle / m3
N1 (No of particle / m
3
)
N2 (No of particle / m
3
)
N3 (No of particle / m
3
)
∑N (No of particle / m
3
)

Vol.10, No.3 Coag-Flocculation Studies of Afzelia Bella 297
R2: Coefficient of Determination
α: Coag-flocculation reaction order
-r: Coag-flocculation reaction rate

c
SP 0: Computed initial suspended particle (kg/m3)
Jf :Flux
fd: Drag force
KS : K value obtained from simulation.
ABC: Afzelia bella coagulant
do : Hard core interaction diameter of the primary particle.
a: Radius of the primary particle
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