Coag-Flocculation Kinetics of <i>Mucuna sloanei</i> Seed for Phosphorus Removal from Waste Water

doi:10.4236/ajac.2013.412088

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American Journal of Analytical Chemistry, 2013, 4, 732-738

Published Online December 2013 (http://www.scirp.org/journal/ajac)

http://dx.doi.org/10.4236/ajac.2013.412088

Open Access AJAC

Coag-Flocculation Kinetics of Mucuna sloanei Seed for

Phosphorus Removal from Waste Water

Kamoru Akinpelu Babayemi1*, Okechukwu Dominic Onukwuli2, Matthew Chukwudi Menkiti2,

Akindele Oyetunde Okewale3

1Department of Chemical Engineering, Anambra State University, Uli, Nigeria

2Department of Chemical Engineering, Nnamdi Azikiwe University, Awka, Nigeria

3Department of Chemical Engineering, Landmark University, Omuaran, Nigeria

Email: *[email protected]

Received October 2, 2013; revised November 15, 2013; accepted November 25, 2013

tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly

cited.

ABSTRACT

Mucuna sloanei (MS) an environmentally friendly biomass was used as a coagulant for treatment of phosphorus con-

taining waste water. The study evaluates the coag-flocculation efficiency of MS and its functional kinetic parameter

response to varying pH and dosage of the waste water effluent. Coag-flocculation reaction order α, coag-flocculation

rate constant K, and coagulation period τ1/2 were determined. The maximum coag-flocculation performance (97.4%) is

recorded at rate constant, K of 1.24 × 10−4 l/mg·min, dosage of 400 mg/l, pH of 8 and coagulation period τ1/2 of 0.100

min while the minimum (61%) is recorded at K of 3 × 10−5 l/gm·min, dosage 100 mg/l, pH of 2 and τ1/2 of 8.900 mins.

The results confirm that MS coagulant is an effective coagulant obeying the theory of fast coagulation in the conditions

of the experiments.

Keywords: Coag-Flocculation; Mucuna slonaei; Phosphorus

1. Introduction

Coagulation is an established process for transforming

small particles into larger aggregates (flocs) and for ad-

sorbing dissolved organic matter onto particulate aggre-

gates so that these impurities can be removed in subse-

quent sedimentation and filtration stages [1].

Coag-flocculation of waste water may be accomplished

with any of the common water coagulants including lime,

iron and aluminum salts and synthetic polymers.

However, the search for a better alternative to conven-

tional coagulants has become an important challenge in

the water treatment process with the aim of minimizing

the detrimental effects associated with the use of such

coagulants. The use of coagulants of biological origin has

become imperative. Some of the coagulants and floccu-

lants of biological origin that have been used include

Chitosan [2], tannins [3], aqueous extract of the seed of

Moringa Oleifera [4], extract of Okra, nirmali seed [5]

and Mucuna sloanei which is the subject of the study.

Mucuna sloanei are wild plants found in some parts of

the semi and sub-Saharan and tropical zones of Africa.

The seeds are edible and are used for the thickening of

soups in some parts of Nigeria. They possess unique

characteristic behavior in hot water displaying different

degrees of the viscoelastic properties [6]. The seeds are

toasted for easy removal of the hull or par-boiled and

then ground to obtain a fine powder or paste, when wet

milled. The powder may be used as recipes of some food

items and in beverages [7]. Consumption of Mucuna as

food has also been reported from Mozambique and Ma-

lawi [8].

Mucuna gum is a galactomannan consisting of D-ga-

lactose and D-mannose as the main sugars [9]. The en-

dosperm was found to constitute 67.15% of the whole

seed with about 32.6% as gum. It may also be a rich

source of crude protein [10].

The chemical and nutritional evaluation of the raw

seed of M. sloanei suggested that this could be a rich

source of crude protein after cooking. The galactoxy-

loglucan isolated from the cotyledon consists of Glc:Xyl:

Gal in a molar ratio of 1:8:1.7:1.0 and a molar mass of

1.6 × 106 g·mol−1 [11]. This work, however, attempts to

*Corresponding author.

K. A. BABAYEMI ET AL. 733

explore and generate interest in the utilization of Mucuna

sloanei (MS) seed as a coagulant. Coag-flocculation per-

formance and kinetic of MS under various pH of the in-

dustrial waste effluent are also investigated.

2. Materials and Methods

The sample of Mucuna sloanei seed was sourced from a

village market, in Ihiala, Anambra State. The seeds were

dried, dehulled and ground into fine power after which it

was sieved through 0.2 mm sieve. The fraction with par-

ticle size less than 0.2 mm was then processed into a co-

agulant using standard method [12].

The jar test was conducted based on standard Bench

Schale Nehelometric method (single angle procedure) for

the examination of water and waste water [13,14] using

model WZS-185MC Turbidimeter, Gulenhamp magnetic

stirrer and Delta 320 pH meter.

The percentage of turbidity removal was calculated

using Equation (1)

Removal efficiency





100 (1)

where C0 and C are the initial and residual concentration

of the waste water effluent respectively.

Theoretical Principle

The rate of flocculation is a function of the particles

(count) concentration C, and the intensity of Brownian

motion characterized by the diffusivity D. Consideration

of the particle diffusion flux in a mono dispersed system

toward a particle of radius “a” (chosen as the central one)

on the basis of Fick’s equation yields an expression for

the rate of decrease in the particle number.

cKC



 (2)

Integrating Equation (1) gives

lnln ln





 



 (3)

From which

and



can be determined from a

plot of d

ln d







against .

ln C

In Equation (1), K is coagulation rate constant/colli-

sion frequency

α: is the order of coagulation reaction

C: is the concentration of the particles (TSS)

It has been shown by some researchers that for the

conditions described above [15].

8πKR



D

(4)

where

2Ra



From Einstein’s equation [16]





KTB (5)

where B is the friction factor, T is the absolute tempera-

ture (0K) and KB is the Boltzman constant (Molar gas

constant per particle).

For the simplest case of a smooth spherical particle of

radius “a” immersed in a fluid of viscosity µ, B is given

by Stoke’s relation.

6π





(6)

Putting Equation (6) into Equation (5) gives

6π



 (7)

But 2Ra





Therefore 2

6π3π

TKT

DRR







(8)

Putting Equation (8) into Equation (4) gives

8π

3π3

KT KT





















(9)

Putting Equation (9) into Equation (2) when 2





yields





 





(10)

Applying the method of separable variable and inte-

grating Equation (2) within the following limits:

At t = 0, C = c0 at t = t, C = C, yields

cKt

 (11)

Integrating Equation (11) above yields

 (12)

Multiply both sides of Equation (12) by C0 to give

CCKt

C (13)

Making “C” the subject of the formular, yields



111

CCKt t



















(14)

Let





1CK



 (15)

Therefore Equation (14) becomes







(16)

When t





then Equation (16) becomes

Open Access AJAC

K. A. BABAYEMI ET AL.

734

11 2

C



(17)

Thus at 0



. This quantity is called the co-

agulation period, which is the time during which the ini-

tial concentration of particles is halved. For Brownian

coagulation of mono dispersed particles at early stage (t

≤ 30 minutes), the time evolution of the cluster-size dis-

tribution for colloidal particle is usually described thus:

 

d1,,

ij in

jn i

Cijcc incc





 





(18)

where d

t is the rate of change of concentration of

particle of size n (concentration/time).

β is a function of the coag-flocculation transport mecha-

nism. The appropriate value of β for Brownian transport

is given by [15].

BR P





 (19)

where KB is Boltzman’s constant (J/K)

T is Absolute temperature (K)

For Brownian aggregation at early stages (t ≤ 30 min-

utes) Equation (18) can be solved exactly, resulting in the

expression [16].



CKC





































(20)

Recall from Equation (15)











, Putting Equa-

tion (15) in Equation (20)

We have























(21)

Let 2





 and put in Equation (21)













 (22)

Equation (22) gives general expression for particle of

n-th order. Hence for primary particles (n = 1)



10 2

















(23)

For twins (n = 2)



20 3



























(24)

For triplets (n = 3)



30 4



















(25)

The process of aggregation is a complicated phe-

nomenon. Analysis shows that Equation (16) holds for

the overall concentration of all particles, which mono-

tonically decreases in time like the number of primary

particles:







 (26)

Linearising Equation (26) gives

111

CC C







 (27)

where a plot of 1



versus t gives

Slope =





, Intercept =

Now that





can be obtained from slope of Equation

(27) while the theoretical quantities



 is found with the

aid of Equation (15) [16].

CK KTC





 (28)

As 0





Therefore,



80.5 4

tKT CKTC





(29)

where 12

t is coagulation period/half life.

In the work of [16] it was shown that the coagulation

rate constant could be determined by monitoring the chan-

ges in the turbidity of the coagulation liquid with time.

The particle concentration during early stages of co-

agulation can be determined directly, by visual particle

counting or indirectly from turbidity measurement [17].

3. Results and Discussion

Figures 1-5 show the effect of coagulant dosage on the

turbidity removal at various pH. It can be seen from the

figure that turbidity removal increases with increase in

coagulant dosage. Figures 1-4 show the removal effi-

ciency as function of time for various MS coagulant

dosages at pH of 2, 4, 6 and 8 respectively. It can be seen

from the figure that the removal efficiency increases very

fast within the first ten minutes for a particular dosage

after which a decrease in efficiency began to set in. The

figures also show that the removal efficiency of MS co-

Open Access AJAC

K. A. BABAYEMI ET AL. 735

0 20406080100

t, mi n

100mg/l

200mg/l

300mg/l

400mg/l

500mg/l

Figure 1. Coagulation efficiency profile for varying MS

dosage at pH = 2.

100

0 20406080100

t, m in

100mg/l

200mg/l

300mg/l

400mg/l

500mg/l

Figure 2. Coagulation efficiency profile for varying MS

dosage at pH = 4.

100

120

0 20406080100

t, m in

100mg/l

200mg/l

300mg/l

400mg/l

500mg/l

Figure 3. Coagulation efficiency profile for varying MS

agulant increases with dosage. However, in Figure 5, it

dosage at pH = 6.

was observed that as pH was increased further to 10, the

100

120

0 20406080100

t, m in

100mg/l

200mg/l

300mg/l

400mg/l

500mg/l

Figure 4. Coagulation efficiency profile for varying MS

dosage at pH = 8.

100

0 20406080100

t, m in

100mg/l

200mg/l

300mg/l

400mg/l

500mg/l

Figure 5. Coagulation efficiency profile for varying varyin

rate of removal began to decrease. It could be deduced

occulation parameters at various

9000 with the

MS dosage at pH = 10.

from the above observation that the optimum turbidity

removal of MS coagulant occurred at the optimum pH of

8 and 400 mg/l dosage.

The values of coag-fl

sages and pH are presented in Tables 1 to 5 above.

The R2 and coag-flocculation rate constant K contained

in the various tables were determined from plots 1/ct

versus time as shown in Figures 6 to 10.

The values of, R2, being greater than 0.

ception of the results at pH of 2, are satisfactory and

this confirms the theory of perikinetic as the controlling

mechanism of coag-flocculation under study [18]. The-

highest value of K is recorded for 400 mg/l at pH of 8

while the least value is recorded for K at pH of 2 as pre-

sented in Table 4. The corresponding value of τ1/2 is

0.100 min at pH of 8 and 400 mg/l dosage. For pH of 2,

and 400 mg/l dosage, τ1/2 is 8.900 mins. This indicates

that the best coagulation performance could be achieved

Open Access AJAC

K. A. BABAYEMI ET AL.

Open Access AJAC

736

MS at varying pH and 100 mg/l dosage.

Parameters pH = 10

Table 1. Coagulation kinetic parameters of

pH = 2 pH = 4 pH = 6 pH = 8

K (l/

8.60 × 1025

4.45 × 1025

3.31 × 1025

2.89 × 1025 5.18 × 10

mg·min)

βBR (l/mg·min)

εp (l/mg)

τ1/2 (min)

C0 (mg/l)

(Np)0

.0 × 10−3

2.0000

0.5870

3 × 10−5

6 × 10−5

40 × 1012

8.900

373

0 × 10−3

2.0000

0.9540

2 × 10−4

2.4 × 10−4

2.18 × 1013

2.200

373

.0 × 10−3

2.0000

0.9794

8 × 10−4

3.6 × 10−4

3.30 × 1013

1.400

373

.0 × 10−3

2.0000

0.9840

0 × 10−4

4.0 × 10−4

3.60 × 1013

1.300

373

1.0 × 10−3

2.0000

0.9713

6 × 10−5

1.2 × 10−6

1.10 × 1013

4.400

373

Table 2. Coagulation kinetic parameters MS at varying pH and 200 mg/l dosage.

Parameters pH = 10

pH = 2 pH = 4 pH = 6 pH = 8

K (l/

8.37 × 10

3.37 × 10

2.59 × 1025

2.47 × 1025

3.79 × 1025

mg·min)

βBR (l/mg·min)

εp (l/mg)

τ1/2 (min)

C0 (mg/l)

(Np)0

.0 × 10−3

2.0000

0.7070

3 × 10−5

6 × 10−5

5.4 × 1012

8.900

373

.0 × 10−3

2.0000

0.9836

.8 × 10−4

3.6 × 10−4

3.30 × 1013

1.400

373

0 × 10−3

2.0000

0.9749

4 × 10−4

4.8 × 10−4

4.40 × 1013

1.100

373

0 × 10−3

2.0000

0.9854

6 × 10−4

5.2 × 10−4

4.70 × 1013

1.000

373

1.0 × 10−3

2.0000

0.9742

2 × 10−4

2.4 × 10−4

2.20 × 1013

2.200

373

Table 3. Coagulation kinetic parameters MS at varying pH and 300 mg/l dosage.

Parameters pH = 10

pH = 2 pH = 4 pH = 6 pH = 8

K (l/

8.06 × 1025

3.25 × 1025

1.68 × 1025

1.44 × 1025

3.49 × 10

mg·min)

βBR (l/mg·min)

εp (l/mg)

τ1/2 (min)

C0 (mg/l)

(Np)0

.0 × 10−3

2.0000

0.7420

3 × 10−5

6 × 10−5

5.4 × 1012

8.900

373

0 × 10−3

2.0000

0.9738

8 × 10−4

3.6 × 10−4

3.30 × 1013

1.400

373

.0 × 10−3

2.0000

0.9616

7 × 10−4

9.4 × 10−4

8.54 × 1013

0.500

373

.0 × 10−3

2.0000

0.9610

6 × 10−4

1.1 × 10−5

1.01 × 1014

0.400

373

1.0 × 10−3

2.0000

0.9696

2 × 10−4

2.4 × 10−4

2.18 × 1013

2.200

373

Table 4. Coagulation kinetic parameters MS at varying pH and 400 mg/l dosage.

Parameters pH = 10

pH = 2 pH = 4 pH = 6 pH = 8

K (l/

8.00 × 1025

3.07 × 1025

1.08 × 1025

1. 4

7.22 × 1024 3.37 × 1025

mg·min)

βBR (l/mg·min)

εp (l/mg)

τ1/2 (min)

C0 (mg/l)

(Np)0

0 × 10−3

2.0000

0.6830

3 × 10−5

6 × 10−5

5.4 × 1012

8.900

373

0 × 10−3

2.0000

0.9844

9 × 10−4

3.8 × 10−4

3.45 × 1013

1.400

373

0 × 10−3

2.0000

0.9703

9 × 10−4

1.58 × 10−5

1.44 × 1014

0.300

373

.0 × 10−3

2.0000

0.9576

24 × 10−

2.48 × 10−5

2.25 × 1014

0.100

373

1.0 × 10−3

2.0000

0.9850

1 × 10−4

2.0 × 10−4

1.81 × 1013

2.600

373

Table 5. Coagulation kinetic parameters MS at varying pH and 500 mg/l dosage.

Parameters pH = 10

pH = 2 pH = 4 pH = 6 pH = 8

K (l/mg·min)

βBR (l/mg·min)

εp (l/mg)

τ1/2 (min)

C0 (mg/l)

(Np)0

2.0000

0.6830

3 × 10−5

6 × 10−5

5.4 × 1012

8.900

373

7.76 × 1025

2.0000

0.9840

2.3 × 10−4

4.6 × 10−4

4.18 × 1013

1.100

373

2.59 × 1025

2.0000

0.9749

8.9 × 10−4

17.8 × 10−4

1.61 × 1014

0.300

373

1.02 × 1025

2.0000

0.2764

4.1 × 10−4

8.2 × 10−4

7.45 × 1013

0.600

373

7.22 × 1024

2.0000

0.9882

1.5 × 10−4

3.0 × 10−4

2.72 × 1013

1.700

373

2.83 × 1025

0 × 10−3 0 × 10−3 .0 × 10−3 .0 × 10−3 1.0 × 10−3

K. A. BABAYEMI ET AL. 737

y = 3E-05x + 0.005

0.587R² =

y = 3E-05x + 0.

R² =

y = 3E-05x + 0.005

R² = 0.742

y = 3E-05x + 0.006

R² = 0.683

y = 3E-05x + 0.006

R² = 0.656

0.00E+00

1.00E-03

2.00E-03

3.00E-03

4.00E-

5.00

6.00

8.00E-03

9.00E-03

020406080

, l/mg

t, mi n

005

0.707

E-03

00E-03

100mg/l

200mg/l

300mg/l

400mg/l

500mg/l

Figure 6. Kinetic plot of 1/Ct versus time for MS dosage at

pH = 2.

y = 0.00012x + 0.00663

R² = 0.95395

y = 0.00018x + 0.00661

1.50E-02

1/C

, l/mg

R² = 0.98357

y = 0.00018x + 0.00750

R² = 0.97381

y = 0.00019x + 0.00787

R² = 0.98441

y = 0.00023x + 0.00903

R² = 0.99126

0.00E+00

5.00E-03

1.00E-02

2.00E-02

2.50E-02

0 20406080

t, m in

100mg/l

200mg/l

300mg/l

400mg/l

500mg/l

Figure 7. Kinetic plot of 1/Ct versus time for varying MS

dosage at pH = 4.

y = 0.00018x + 0.00706

R² = 0.97935

y = 0.00024x + 0.00767

4.00E-02

1/C

, l/mg

y = 0.00020x

R² = 0.974 94

y = 0.00047x + 0.00721

R² = 0.96167

y = 0.00079x + 0.00542

R² = 0.97028

y = 0.00089x + 0.00574

R² = 0.97486

0.00E+00

1.00E-02

2.00E-02

3.00E-02

5.00E-02

6.00E-02

7.00E-02

0 20406080

t, mi n

100mg/l

200mg/l

300mg/l

400mg/l

500mg/l

Figure 8. Kinetic plot of 1/Ct versus time for varying MS

dosage at pH = 6.

of MS coagulant at K = 1.24 × 10−3 (mg·min)−1 and τ1/2 =

0.100 mins.

+ 0.00808

8397R² = 0.9

y = 0.00026x

R² =

y = 0.00056x + 0.00725

R² = 0.96106

y = 0.00041x + 0.01534

R² = 0.27636

y = 0.00124x + 0.00228

R² = 0.95768

0.00E+00

1.00E-02

2.00E-02

3.00E-02

5.0

0 20406080

1/C

, l/mg

t, m in

0.98535

0.00826

4.00E-02

0E-02

6.00E-02

7.00E-02

00E-02

9.00E-02

100mg/l

200mg/l

300mg/l

400mg/l

500mg/l

Figure 9. Kinetic plot of 1 C

t versus time for varying MS

dosage at pH = 8.

y = 0.00006x + 0.00801

R² = 0.97133

1.50E-02

, l/mg

y = 0.00012x + 0.00848

R² = 0.97417

y = 0.00010x + 0.01125

R² = 0.98499

y = 0.00015x + 0.01238

R² = 0.98821

0.00E+00

5.00E-03

2.00E-02

2.50E-02

0 20406080

t, mi n

y = 0.00012x + 0.00963

R² = 0.96961

1.00E-02

200mg/l

300 g/lm

400mg/l

500mg/l

Figure 10. Kinetic plot of 1/Ct versus time for varying MS

dosage at pH = 10.

At nearly invariant values of K, εp relates directly to

2K = βBR. The consequence is that high εp results in high

kinetic energy to overcome the zeta potential. The impli-

cation is that the double layer is either reduced or the

colloids destabilized to actualize low τ1/2 in favour of

high rate of coagulation [18].

re obtai previous researches

[19].

4. Conclusion

The removal efficiency E > 80% recorded at the opti-

mum pH of 8 and dosage of 400 mg/l supported by the

value of τ1/2 = 0.100 minute presents the potential of

Mucuna sloanei as a source of organic derived coagulant

applicable in large scale water treatment. The obtained

results are in agreement with previous works [19].

The results show that high values of τ1/2 correspond to

low εp and K, an indication of repulsion in the system.