Bioremediation of Lead(II) from Polluted Wastewaters Employing Sulphuric Acid Treated Maize Tassel Biomass

doi:10.4236/ajac.2013.412083

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American Journal of Analytical Chemistry, 2013, 4, 689-695

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

http://dx.doi.org/10.4236/ajac.2013.412083

Open Access AJAC

Bioremediation of Lead(II) from Polluted Wastewaters

Employing Sulphuric Acid Tr eated Maize Tassel Biomass

Mambo Moyo, Linda Chikazaza

Department of Chemical Technology, Midlands State University, Gweru, Zimbabwe

Email: moyom@msu.ac.zw

Received September 30, 2013; revised October 29, 2013; accepted November 15, 2013

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

cited.

ABSTRACT

The ability to modify a waste by-product precursor, maize tassel biomass using sulfuric acid as the activating agent with

specific focus on Lead(II) ion from water has been proposed. The treating of maize tassel using sulphuric acid is be-

lieved to enhance sorption capacity of Lead(II) ions. For this, batch adsorption mode was adopted for which the effects

of initial pH, adsorbent dosage, contact time and initial concentration were investigated. Consequently, it was found that

the adsorbent capacity depends on pH; since it increases up to 4.5 and then decreases. The highest percentage of Lead(II)

ion removal was achieved in the adsorbent dosage of 1.2 g and at an initial concentration of 10 mg/L metal ion. In an

attempt to determine the capacity and rate of Lead(II) removal, isotherm and kinetic data were modeled using appropri-

ate equations. To this end, the adsorption data fitted best into the Langmuir model with an R2 (0.9997) while kinetically

the Lead(II) adsorption followed the pseudo-second-order model. Furthermore, as a way to address issues related to

sustainability, maize tassel is recommended since the process is considered to be a dual solution for environmental

cleaning. From one side, it represents a better way to dispose the maize tassel which has no use after fertilization and on

the other hand it is an economic source of carbonaceous materials.

Keywords: Maize Tassel; Adsorption; Removal; Wastewater Treatment, Lead(II) Ion

1. Introduction

The presence of heavy metals in the environment poses a

serious and complex environmental and public problem

due to their non-degradability [1]. Among the heavy

metals, Lead (Pb) is very toxic because it is carcinogenic

in nature [2]. Lead is the most significant toxin of the

trace metal ions, and human exposure is through inges-

tion of food and water, and inhalation. Lead affects mainly

the peripheral nervous system and hematopoietic, renal,

gastrointestinal, cardiovascular and reproductive systems.

According to World Health Organization [3], the permis-

sible level for Pb in drinking water is 0.05 mg/L. Conse-

quently, the occurrence of very low concentration levels

of lead in drinking water is considered as highly toxic

and requires more efficient removal, extraction, and treat-

ment methodologies.

The removal of metals from water has been previously

achieved by various methods such as ion exchange, pre-

cipitation, oxidation, reduction and membrane filtration

[4,5]. Currently, adsorption technology using cheap, eas-

ily available agricultural plants, algal biomass and cyano-

bacteria has increased in recent years. However, the use

of raw sorbents in adsorption may cause problems since

most plants contain a green pigment known as chloro-

phyll (sparingly soluble in water) and some organic mat-

ter may be leached out, consequently affecting the taste

and colour of the treated waters [6,7]. In spite of the ver-

satility of commercial activated carbon as an adsorbent in

wastewater treatment with its high surface area, micro-

porous characteristics, and high adsorption capacity; its

high cost and loss during the regeneration restrict its ap-

plications in developing countries [8,9]. Given these dis-

advantages, efforts have now been geared towards intro-

ducing low cost precursors that can serve as alternative

sources for water cleaning after modification using dif-

ferent activation agents. In the recent years, modified

sorbents derived from locally available materials such as

Ceiba pentandra hulls [8], Euphorbia rigida [10], ha-

zelnut husks [11], wheat bran [12], coirpith [13], and

coconut shell [14] have received increasing attention for

the removal and recovery of heavy metals from water

M. MOYO, L. CHIKAZAZA

690

and wastewater systems.

Maize tassel is an inexhaustible, non-edible, mesopor-

ous and renewable polymeric material resource, which is

discarded as waste by most farmers after fertilization

[15]. Hence, the present study aims to assess the applica-

bility of acid treated maize tassel for the adsorptive re-

moval of Lead(II) from aqueous solution and to investi-

gate the effect of operating parameters on the adsorption

process. The parameters studied include contact time,

initial Lead(II) concentration, adsorbent dosage and ini-

tial solution pH.

2. Materials and Methods

2.1. Modification of Maize Tassel

The maize tassel was collected from Morris farm in

Northlea, Gweru, Zimbabwe. Maize tassel was plucked

off the woody parts of the maize plant, thoroughly washed

with water and sun dried for 5 days. The dry biomass

was milled and then fractionated using 100 - 300 µm

analytical sieves. Then, the modification was prepared

according to reported procedure [16-18]. Briefly, the frac-

tionated maize tassel powder (200 g) was weighed in a

clean dry beaker of capacity 1 L containing (200 mL,

97% H2SO4 for 24 h) followed by refluxing in a fume

hood for 4 h. After cooling, the reaction mixture was

filtered, and the filtrate was washed repeatedly with ul-

tra-pure water and soaked in 1% NaHCO3 solution to

remove any remaining acid. The sample was then washed

with distilled water until the pH of the acid treated maize

tassel was between 6 - 7, dried in an oven at 120˚C over-

night and kept in a glass bottle until use.

2.2. Characterization of Prepared Acid Treated

Maize Tassel

The bulk density, loss of mass on ignition, simple spe-

cific surface area, pH and moisture content of the acid

treated maize tassel were determined following reported

procedures [19,20]. Briefly, for bulk density, acid treated

maize tassel was transferred to a 10 mL measuring cyl-

inder of about 1.0 cm diameter. Sufficient quantity of

powder was added to occupy a volume of 10 mL under

the condition, and it was subsequently weighed. The bulk

density was expressed as grams per litre (the weight of

the acid treated maize tassel filling a graduated cylinder

on gentle tapping, divided by the volume of the cylinder

10 mL). The loss of mass on ignition was done by

weighing 15 g of the acid treated maize tassel and put

inside furnace at constant temperature of 600˚C for 2 h.

After roasting, the sample became charred and was re-

moved from the furnace then put in a desiccator for

cooling. The residual product was then weighed, and the

difference in mass represented the mass of organic mate-

rial present in the sample. For moisture content, 10 g of

acid treated maize tassel was weighed into a crucible and

heated in the oven for 5 h at constant temperature of

105˚C. The sample was then removed and put in a desic-

cator in so that moisture from atmosphere could not be

absorbed. The sample was reweighed. This procedure was

repeated several times until a constant weight was ob-

tained. The difference in the mass constitutes the amount

of moisture content of the adsorbent







23 21

%moisture 100ww ww  (1)

where w

w1 is weight of crucible,

w2 is initial weight of crucible with sample,

w3 is final weight of crucible with sample.

2.3. Preparation of Synthetic Solution

A stock solution of Lead(II) ion (1000 mg/L) was pre-

pared by dissolving Pb(NO3)2 (Merck, South Africa) in

ultra-pure water (resistivity ˃ 18 MΩ·cm−1). The pro-

gressive dilution procedure of the stock solution was

employed in the preparation of working solutions. The

pH of the working solutions was adjusted to the required

value with 0.1 M·NaOH or 0.1 M·HCl. All the chemicals

used were of analytical reagent grade.

2.4. Batch Adsorption Studies

A weighed amount of acid treated maize tassel was in-

troduced into stoppered reagent bottles containing vari-

ous concentrations with 100 mL aqueous solutions of

Lead(II) ions. The suspensions were shaken at room tem-

perature (25˚C ± 1˚C) using a mechanical shaker for a

prescribed time at 160 rpm. The solutions were filtered

through Whatman 42 filter paper and the residual con-

centration of metal ion was determined by AAS method.

The effects of concentration (10 - 50 mg/L), contact time

(5 - 300 min), solution pH (2 - 12) and adsorption dose

(0.1 - 2.5 g) were studied. The percentage of removed

Lead(II) ions (R%) in solution was calculated by using

Equation (2):





100

%ie



 (2)

The amount of metal adsorbed by acid treated maize

tassel was calculated from the difference between metal

quantity added to the biomass and metal content of the

supernatant using Equation (3):





CCV



 (3)

where qe is the metal uptake (mg metal adsorbed per g

adsorbent), Ci and Ce are the initial and equilibrium metal

concentration in solution (mg/L), V is the volume of the

solution (mL) and M is the weight of acid treated maize

Open Access AJAC

M. MOYO, L. CHIKAZAZA 691

tassel (g).

2.5. Desorption Studies

For the desorption studies, contact was made between 1.2

g of acid treated maize tassel and a 100 mL Lead(II) so-

lution. After Lead(II) ion sorption, the acid treated maize

tassel was filtered, washed three times with ultra-pure

water to remove residual Lead(II) ions on the surface,

and kept in contact with different concentrations (0.05 -

0.3 mol/L) of 100 mL·HCl solution. The mixtures were

shaken in a rotary shaker for 60 min. The filtrates were

analyzed to determine the concentration of Lead(II) ions

after desorption using AAS.

2.6. Adsorption Isotherms

In the present study, the equilibrium data for the ad-

sorbed Lead(II) ions onto acid treated maize tassel was

expressed using Langmuir and Freundlich isotherm. The

Freundlich isotherm [21] is given by Equation (4):

eFe

qKC (4)

The parameters can be linearized by taking logarithms

to find the parameters KF and n:

ln lnln

qK C

e

(5)

A plot of ln qe versus ln Ce gives a straight line and KF

and n can be calculated from the intercept and slope, re-

spectively. The linear form of the Langmuir isotherm

model [22] can be represented by Equation (6):

max max

11 11

qqbq C









(6)

A plot of 1/qe versus 1/Ce was found to be a straight

line with 1/qmax as intercept and 1/qmax b as slope and

hence qmax and b can be calculated. In addition, a dimen-

sionless constant called separation factor, RL can be used

to express an essential feature of Langmuir isotherm

[23]:

RaC

 (7)

where, Cm is the initial concentration of Lead(II). The

value of RL indicates the type of the isotherm to be either

unfavorable when RL ˃ 1, linear if RL = 1, favorable if 0

˂ RL ˂ 1 or RL = 0.

2.7. Adsorption Kinetics

The pseudo-second order model has been widely used for

adsorption for the following reasons: it does not have the

problem of assigning an effective adsorption capacity,

the adsorption constant capacity, rate constant and initial

adsorption rate can all be determined from the equation

without knowing any parameter beforehand [24]. Hence

in the present study, adsorption of Lead(II) ions on acid

treated maize tassel has been described by pseudo-sec-

ond-order model [18]. The general form of the pseudo-

second-order kinetic model:

kq  (8)

where qe and qt (mg/g) are the amounts of the Lead(II)

ions sorbed at equilibrium and at time t (min), respec-

tively and k2 (mg/g·min) is the second order rate constant.

The slope of the plot (t/qt) versus t gives the value of qe

and from the intercept k2 can be calculated

3. Results and Discussion

3.1. Physicochemical Characteristics of Acid

Treated Maize Tassel

The physico-chemical characteristics like pH, moisture

content, bulk density, surface area, and loss of mass on

ignition were determined and given in Table 1.

3.2. Effects of Dosage

The effect of biomass dosage on the biosorption of Pb (II)

ions was studied using biomass dosage in the range 0.1 -

2.5 g (Figure 1). As shown in Figure 1, the percentage

removal increases sharply from 58.5% to 92.2%, but be-

yond this, the percentage removal did not increase sig-

nificantly and reached a maximum at 92.3%. This phe-

nomenon can be due to the greater availability of activity

sites or surface area making easier penetration of the

Lead(II) ions to the adsorption sites and increasing this

number had no effect after equilibrium is reached. These

results are in agreement to other results reported in lit-

erature [2,25].

3.3. Effect of pH

The effect of initial pH of a solution is a major factor

used to determine the adsorption property of an adsorb-

ent from wastewater. The possible reasons are its effects

on the chemistry of the ions and the activity of functional

groups (carboxylate, phosphate and amino groups) on the

cell walls [12]. As shown in Figure 2, there is an in-

Table 1. Characteristics of the acid treated maize tassel

developed from maize tassel.

Parameter Value

pH 6.9

Moisture (%) 0.3

Bulk density (g·mL−1) 0.52

Surface area (m2/g) 250

Particle size range 100 - 300 µm

% Loss of mass on ignition 0.7

Open Access AJAC

M. MOYO, L. CHIKAZAZA

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Figure 1. Dosage versus percentage removal of Lead(II) ion

(contact time: 60 min; pH 5.4; initial concentration 10 mg/L;

Error bar = ±S.D. and n = 3).

Figure 2. pH against percentage removal of Lead(II) ion

(contact time: 60 min; dosage 1.2 g; initial concentration 10

mg/L; Error bar = ±S.D. and n = 3).

crease in the quantity of adsorbed Lead(II) ions onto acid

treated maize tassel by increasing pH of the medium up

to a maximum value of pH 5.4. At low pH values, the

adsorbent is positively charged since the pH is lower than

the isoelectric point or point of zero charge (PZC) [26].

Hence the removal yield of Lead(II) ions is very low due

to the electrostatic repulsion forces between positively

charged H3O+ and Pb2+ ions. Thereafter the adsorption

percentage decreased in alkaline medium perhaps due to

the formation of Pb(OH)2 and soluble hydroxyl com-

plexes such as PbOH+, aqueous Pb(OH)2 and Pb(OH)3−

and adsorbent was deteriorated with the accumulation of

metal ions making true adsorption studies impossible

[25,27]. The results obtained in this study showed that

the acid treated maize tassel is more effective in remov-

ing Lead(II) ions from an aqueous system with more than

94% removal as compared to raw maize tassel 75% [28];

physically prepared AC 78% [29]. Therefore, pH 5.4 was

selected to be the optimum pH for all further studies.

3.4. Effect of Agitation Time and Initial

Concentration

The effect of agitation time is one of the important fac-

tors when designing batch sorption systems for eco-

nomical wastewater treatment plant application [13]. As

shown in Figure 3, the relationship between agitation

time and Lead(II) ion sorption onto acid treated maize

tassel at different initial Lead(II) concentrations is deter-

mined by plotting the percentage biosorption of Lead(II)

ion against agitation time for the interaction time inter-

vals of between 2 to 300 min.

It was observed that 52%, 60%, 65% and 70% of

Lead(II) ions was removed in the first 2 min for the dif-

ferent concentrations 10, 20, 30 and 50 mg/L respec-

tively and the process was rapid up to 60 min reaching

91.8%. Beyond 60 min, the percentage of biosorption is

almost constant indicating the attainment of equilibrium

conditions. The presence of adequate external surface area

on the acid treated maize tassel may have boosted the

rate of adsorption to be fast in the initial stages which

was followed by a slower internal diffusion process, which

maybe the rate determining step. From the observed ad-

sorption trend of Lead(II), the binding may be through

van der Waals forces of attraction present on the surface

of the acid treated maize tassel. Therefore, all other ex-

periments were conducted at an agitation time of 60 min.

The effect of initial concentration on the percentage

removal is also shown in Figure 3. The concentration

range from 10 to 50 mg/L for the metal ion has been

studied. The removal of Lead(II) ions by acid treated

maize tassel was found to decrease with increase in ini-

tial Lead(II) concentration. The observed behavior can be

attributed to the increase in the amount of Lead(II) ions

to the unchanging number of available active sites on the

acid treated maize tassel. Hence, more metal ions were

left in solution. Thus it can be said that removal of

Lead(II) ion is highly concentration dependent.

3.5. Interference Studies

The selectivity of the acid treated maize tassel on the

adsorption efficiency of Lead(II) were studied in the

Figure 3. Agitation time against percentage removal Lead

(II) ion (concentrations: a to d: 10 to 50 mg/L, adsorbent

dosage: 1.2 g; pH: 5.4, Error bar = ± S.D. and n = 3).

Open Access AJAC

M. MOYO, L. CHIKAZAZA 693

presence of anions such as F−, Cl−, 3, NO 2



and

and cations such as Fe2+, Mg2+, Ca2+, Na+ and K+.

There was no significant reduction in the adsorption of

Lead(II) when the concentration of the above ions in-

creased up to 50 mg/L in aqueous solution. It can be

concluded that with proper treatment of the industrial

wastewater, adsorption of Lead(II) ions on the surface of

the adsorbent up to 94% in the presence of the studied

anions and cations up to 50 mg/L is possible.

PO 

3.6. Isotherm and Kinetics Study

Figures 4(a) and (b) show the Langmuir isotherm and

the Freundlich adsorption isotherm respectively. The

Freundlich constants n and KF, Langmuir constants b and

qmax and the correlation coefficient R2 are given in Table

2. The calculated value of Freundlich constant n is within

the range (0.1 < n < 1), reported in literature [30] show-

ing that adsorption is favorable. However, the linearized

equation did not give a good correlation for the removal

of Lead(II) onto acid treated maize tassel, indicating that

Lead(II) adsorption by acid treated maize tassel fits bet-

ter to the Langmuir model than to the Freundlich model.

The calculated RL was 0.62 indicating that the adsorption

of the Lead(II) was a favorable process. The plot of t/qt

versus t is shown in Figure 4(c). The values of k2 and qe

were 0.135 g/mg min and 2.02 mg/g respectively. The R2

value was 0.998, indicating a chemisorptions process.

3.7. Treatment of Industrial Wastewater

The suitability of the sulphuric acid treated maize tassel

for the removal of Lead(II) was tested with the leachates

from an electroplating plant. The leachate sample pH was

maintained between 5.4 - 5.9 and the determined compo-

sition of leachate from an electroplating plant is tabulated

in Table 3.

The treatment of Lead(II) in leachates was signifi-

cantly good (p < 0.05). Almost 93.9% removal from

wastewater was possible with 1.2 g of the adsorbent.

Thus, the results corroborate well with what is obtained

from the batch adsorption mode conducted for Lead(II)

removal in synthetic wastewater samples. Furthermore,

preliminary treatment of the leachates is essential before

application of acid treated maize tassel as the adsorbent.

3.8. Desorption Studies

For wastewater treatment, the successful application of

desorption reduces the dependence on thermal activation,

incineration, and land disposal, which directly or indi-

rectly increases environmental pollution. In this study,

effect of HCl concentration on the desorption of Lead(II)

ion is shown in Figure 5. It can be observed that desorp-

tion rate increases with the increase in HCl concentration

but attained a constant at 0.2 M·HCl.

(a)

(b)

(c)

Figure 4 (a) Langmuir isotherm; (b) Freundlich isotherm

for Lead(II) ion removal; (c). Pseudo-second-order kinetic

fit for Lead(II) adsorption.

Table 2. Langmuir and Freundlich constants for Lead(II)

adsorption using acid treated maize tassel.

Adsorption isotherm Parameter Value

Langmuir qmax (mg/g) 37.31

b (L/mg) 0.062

R2 0.9997

Freundlich KF 0.077

n 0.482

R2 0.9515

4. Conclusion

The present study showed that acid treated maize tassel

can be used for the effective removal of Lead(II) ions

Open Access AJAC

M. MOYO, L. CHIKAZAZA

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Table 3. Composition of leachates sample from an electro-

plating plant.

Parameter Value

pH 3.9

Total dissolved salts (mg/L) 5056.44

Turbidity (NTU) 1.22

Electrochemical conductivity (μmhos/cm) 3044.28

COD (mg/L) 30.56

Chloride (mg/L) 320.58

Sulphate (mg/L) 1005.56

Calcium (mg/L) 95.35

Lead (mg/L) 98.28

Zinc (mg/L) 18.25

Figure 5. Effect of different HCl concentrations on desorp-

tion of Lead(II) ion (concentrations: a to d: 10 to 50 mg/L

Error bar = ±S.D. and n = 3).

from wastewater. Lead(II) adsorption was found to be pH

dependent and maximum removal was observed at pH

5.4. An increase in the acid treated maize tassel dosage

leads to an increase in Lead(II) ions removal due to a

corresponding increase in the number of active sites. The

Langmuir adsorption isotherm was demonstrated to pro-

vide the best correlation (R2 = 0.9997) for the adsorption

of Lead(II) ions onto acid treated maize tassel confirming

monolayer coverage. Adsorption obeyed a pseudo-sec-

ond-order model. It can be concluded that the acid treated

maize tassel from maize tassel adds to the global discus-

sion of its cost-effective utilization in wastewater treat-

ment.

5. Acknowledgements

The authors are grateful for the Department of Chemical

Technology, Midlands State University, Gweru, Zimbab we

for providing facilities.

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