Biosorption
of heavy metals by marine algae Ulva rigida, Cystoseira barbata and Cystoseira crinita
Anna Simeonovaa,
Sevdalina Petkovaa
a Department of Ecology and
Environmental Protection, Technical University-Varna,
1 Studentska str., 9010
Abstract
In this study, the
adsorption properties of three different marine algae (Ulva rigida ( green algae); Cystoseira barbata(brown algae) and Cystoseira crinita (brown algae)) were
investigated. They were collected from the
Keywords:
biosorption,
desorption , heavy metals, marine algae, water treatment
1. Introduction
Heavy metal contamination exists in
aqueous waste streams of many industries, such as metal plating facilities,
mining operations, and tanneries. Heavy metals are not biodegradable and tend
to accumulate in living organisms. To curtail heavy metal pollution problems,
many processes have been developed for the treatment of metal containing waste
waters.
The need for economical, effective
and safe methods for removing heavy metals from waste waters has resulted in
the search for unconventional materials that may be useful in reducing the
levels of heavy metals in the environment. In this light, biological materials
have emerged as an ecofriendly and economic option. Biosorption, which uses the
ability of biological materials to remove and accumulate heavy metals from aqueous solutions, has received
considerable attention in recent years because of few advantages compared to
traditional methods. Biosorption uses cheaper materials such as naturally
abundant algae or byproducts of fermentation industries as biosorbents 1-5
Among the biological materials investigated for heavy metal removal, the
biomass of marine algae otherwise known as seaweeds has been reported to have
high uptake capacities for a number of heavy metal ions. 6-7 Numerous
studies of metal biosorption by brown algae such as Sargassum have been reported in literature.8-11 The role
of the cellular structure, storage polysaccharides, cell wall has been
evaluated in terms of their potential for metal sequestration.
The brown
seaweeds
Sargassum hemiphyllum, Petalinia fascia and Colpomenia sinusa has been
characterized by their number of binding sites.12 Due to their high
number of binding sites Sargassum and Petalinia has been determined to be the most promising for
biosorption application.
Many investigations have been carried out for biosorption of heavy
metals by the other important divisions of algae Green algae (Chlorophyta) and
Red algae (Rhodophyta).13-15 Ulva
reticulate was the focus of the study of Kuppusamy Vijayaraghavan et al.The
influence of several factors such as pH, initial metal concentration and
contact time were analyzed.16 Green algae Cladophora fascicularis was determined by Liping Dend et.al. to be
an effective and economical biosorbent material for the removal of heavy metal
ions.17
In the present study, the biosorption of heavy metal ions such as Cu(II), Zn(II), Pb(II), Ni(II), Cd(II) by
three different marine algae Ulva rigida( green
algae), Cystoseira barbata (brown
algae) and Cystoseira crinita (brown
algae) was investigated. The effect of contact time, concentration of algal
biomass, pH and regeneration were studied.
2. Materials and methods
2.1. Materials
Green algae Ulva rigida and brown algae Cystoseira barbata and Cystoseira crinita are used for investigation of heavy metal ion
sorption. They were collected from the
Heavy metal solutions ware prepared by solving
of Pb(NO3)2, Cu(NO3)2.3H2O,
Ni(NO3)2.6H2O, Zn(NO3)2
and Cd(NO3)2 in deionized water. All reagents
were analytical grade.
2.2. Methods
2.2.1.Preparation of
biomass
Ulva rigida , Cystoseira barbata and Cystoseira crinita were
harvested from
2.2.2. Batch
biosorption studies
All batch biosorption experiments
were carried out by adding 1g of dried biomass to 50 cm3 of heavy metal
ion solutions in Erlenmeyer flasks. The flasks were agitated at 250 rpm for 60
min. The experiments were conducted at room temperature (20oC) at pH
5± 0.5. Samples were taken at regular intervals till equilibrium was reached.
The residual metal concentration in the solution was determined by EDTA
titration. The metal uptake was calculated by the following equation:
where: V - volume of the solution in the contact batch flask(cm3); C0 - initial concentration of the metal ions, mg/dm3; Cf- equilibrium concentration , mg/ dm3; m - weight of the sorbent, g.
Algal mass quantity was varied from 0,1g to 1g to study its influence upon sorption. For studying the influence of pH on the biosorption, experiments were conducted at various initial metal solution pH values of 2-8. To avoid hydroxide precipitation at high pH, ammonium acetate was added.9 All experiments were carried out in triplicate to check the reproducibility of results.
2.2.3. Batch desorption studies
The desorption of heavy metal ions was
carried out using 0,05Ì HNO3 The biosorbents were eluted for 60 min.
After acid elution, deionized water was used to rinse the biomass until the pH
of the wash effluent exceeded 6.0. The regenerated biosorbents then were used
for next sorption. The effect of
regeneration was determined by the following equation-
Where: a1 – metal uptake of the fresh biosorbent;
àn – metal uptake of the regenerated biosorbent
3. Results and
discussion
3.1. Kinetic studies
In the present study the sorption
characteristics of three biosorbents were examined- Ulva
rigida (green algae), Cystoseira barbata(brown algae) and Cystoseira crinita(brown algae) with regard to Pb(II), Cu(II), Ni(II), Cd(II) and Zn(II) ions. The biosorbents were harvested from the
Fig.1. Kinetics of
heavy metal ions uptake onto Ulva rigida
Fig.2. Kinetics of heavy metal ions uptake onto Cystoseira barbata
Fig.3. Kinetics of heavy metal ions uptake onto Cystoseira crinita
Each of the biosorbents showed different
affinity toward heavy metals.This could be explained with the difference in
cell wall composition and the intra group differences which cause significant
differences in the type and amount of metal ion binding to them. The cell wall
consists of variety of polysaccharides and proteins which offers a number of
active sites capable of bindind metal ions 4.The highest uptake of
the investigated biosorbents is shown in table 1. Ulva
rigida exhibited highest uptake with regard to Zn(II) -1,25mgeq/g; Cystoseira barbata to
Cu(II)-2,28mgeq/g
and Cystoseira crinita to
Ni(II)-2,84mg/g. According
to the results for biomass batch sorption the following metal
order was obtained for each biosorbent: Ulva rigida: Zn > Cd > Ni > Cu
> Pb;. Cystoseira barbata: Cu >
Zn > Cd >Ni ~ Pb; Cystoseira
crinita: Ni > Cu > Zn > Cd > Pb.
Table 1. . Heavy metals maximum uptake(mgeq/g) by Ulva rigida, Cystoseira barbata, Cystoseira crinita; initial concentration of metal ions-1g/dm3, pH 5
Metal ions sorbents |
Cu(II) |
Cd(II) |
Ni(II) |
Pb(II) |
Zn(II) |
Ulva
rigida |
0,79 |
1,05 |
0,95 |
0,67 |
1,25 |
Cystoseira
barbata |
2,28 |
1,20 |
0,80 |
0,80 |
1,25 |
Cystoseira
crinita |
1,56 |
1,25 |
2,84 |
0,69 |
1,50 |
The brown algae Cystoseira barbata and Cystoseira crinita exhibited
highest uptake with regard to most of the heavy metal ions. In brown algae
biomass, alginate in the cell wall is the main component responsible for the
metal sorption. It is present in a gel form which appears very porous and easily
permeable.18 This could explain the highest uptake of metal ions.
3.2. Heavy metals
desorption
The exploitation of biosorbents for
removal of heavy metals depends on the efficiency of the regeneration after metal
sorption. The desorption of metals in this study was investigated using dilute
mineral acid 0,05 M HNO3 as desorbing agent. The effect of
regeneration (Ep) was calculated and presented in fig.4, 5 and 6. The three
sorbents exhibited effect of regeneration regarding Pb(II), Cu(II), Zn(II) è Ni(II) under 50% after the II cycle. Good
regeneration and high sorption capacity after multiple cycles showed the three
biosorbents with regard to Cd(II).The most effective regeneration
with regard to Cd(II) was reached by Ulva rigida (82%
after the IV cycle). During regeneration Cystoseira barbata and Cystoseira crinita showed higher mechanical stability than Ulva rigida where the eluation resulted in some changes in
the cell structure of the green algae. Thus, regeneration of the biosorbents
for use in multiple cycles of Cd(II) biosorption- desorption should be
feasible.
Fig.4. Effect of
regeneration of Ulva rigida
Fig.5. Effect
of regeneration of Cystoseira barbata
Fig.6. Effect of regeneration of Cystoseira crinita
3.3.Effect of algae
mass
The effect of Cystoseira
barbata and Cystoseira crinita mass for the removal of Cu(II) and Ni(II) was
studied using algal mass in the range of 100-1000mg. Batch sorption is carried
out till equilibrium was reached and sorption effect was calculated by the
following equation :
E= (
C0- Cf )/ C0 .100, where: C0 -
initial concentration of the metal ions, mg/dm3, Cf-
equilibrium concentration , mg/ dm3. Results showed an increased
uptake of Cu(II) and Ni(II) with the increase of algae quantity( table.2,3). Cystoseira barbata exhibited 90% effect
of Cu(II) sorption at about 1000mg mass.
Table 2.
Effect of sorption of Cu (II) by Cystoseira barbata at different algae mass
mass of
the sorbent |
Co |
Cf |
Å % |
100 mg |
1,9 |
1,59 |
16% |
200 mg |
1,9 |
1,27 |
33% |
500 mg |
1,9 |
1,27 |
33% |
800 mg |
1,9 |
0,95 |
50% |
1000 mg |
1,9 |
0,19 |
90% |
Òable 3. Effect of sorption of Ni (II) by Cystoseira crinita at different algae mass
mass of the sorbent |
Co |
Cð |
Å % |
100 mg |
2,55 |
2,43 |
5% |
200 mg |
2,55 |
2,32 |
9% |
500 mg |
2,55 |
2,08 |
18% |
800 mg |
2,55 |
1,90 |
25% |
1000 mg |
2,55 |
0,54 |
79% |
3.4.Effect of initial solution pH
Marine
algae contain high content of ionizable groups on the cell polysaccharides,
which suggests that the biosorption process could be affected by changes in the
solution pH.3,19 In the present study was investigated the influence
of pH on the sorption uptake of Cystoseira crinita with regard to Ni(II) and Cystoseira barbata to Cu (II).The experiments were carried out at
pH interval 2-8 and the results are presented in fig.7.
Fig.7. Effect of initial pH on heavy metal
sorption
The uptake
for both sorbents showed a sharp increase with an increase in pH from 2.0 to
5.0.This could be explained with the extend of protonation which is determined
by the pH. The amino and carboxyl groups, and nitrogen and oxygen of the
peptide bonds are available for coordination bonding with metal ions. Such bond
formation could be accompanied by displacement of protons4.At lower
pH values (pH=2,3) the concentration of H+ protons was increased and showed preponderance over that of heavy metal ions
which could explain the lower sorption uptake of the algae in this pH range. Both
sorbents reached highest uptake at pH 5(Cystoseira crinita-2,84
mgeq Ni2+/g;
Cystoseira barbata-2,28 mgeq Cu2+/g).
4. Conclusion
The results obtained showed that Cystoseira crinita ,
Cystoseira barbata and Ulva rigida could
be used as efficient biosorbent material for treatment of heavy metal ions.
Highest uptake was reached by Cystoseira crinita for Ni (II) and Cystoseira barbata for Cu(II).The desorption experiments
suggested that the regeneration of the biosorbents was possible for repeated
use especially with regard to Cd(II).The good sorption characteristics
with respect to heavy metals and the availability
of the algae in great quantities in nature, makes these biosorbents very
perspective for successful purification of industrial waters.
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