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Journal of Endocytobiosis and Cell Research (2015) 1-7 | International Society of Endocytobiology
zs.thulb.uni-jena.de/content/main/journals/ecb/info.xml

Journal of Endocytobiosis and Cell Research VOL 26 | 2015 1
Journal of
Endocytobiosis and
Cell Research
Uptake and biosorption potential of Pistia stratiotes for Cr6+
Aziz-ud-Din1
, Zeshan Ali2
*, Farrakh Meh-
boob2
and Qaiser Mahmood Khan3
1Department of Genetics, Garden Campus, Hazara Universi‐
ty, Mansehra, Pakistan; 2,*Ecotoxicology Research Institute,
National Agricultural Research Centre, Park Road, Islama‐
bad, PO 45500, Pakistan; 3Soil & Environmental Biotech‐
nology Division, National Institute for Biotechnology &
Genetic Engineering (NIBGE), Faisalabad, Pakistan;
*correspondence to: eco4nd@yahoo.com

Uptake and biosorption potential of Pistia stratiotes for
Cr6+ was examined. The study was conducted in two
phases: in the first phase, the effect of different Cr6+
concentrations on plant weight, leaf number and root
length was determined along with plants uptake poten‐
tial. Higher concentration of Cr6+ (> 8 ppm) had inhibi‐
tory effects on increase in plant weight due to impair‐
ment of the metabolic machinery. Leaf number and
root length showed no increase when exposed to a Cr6+
concentration of ~ 10 ppm. When grown in solutions
containing 2, or 4 ppm Cr6+ concentrations, P. stratiotes
removed 100% of Cr6+. However at increasing concen‐
trations of 6 and 8 ppm, only 50% reduction in respec‐
tive solutions was recorded. In a second phase biosorp‐
tion capacity of dead P. stratiotes was determined. The
optimal pH range for maximum Cr6+ biosorption lied
between 1‐2. Maximum biosorption capacity of dead
biomass was recorded at 200 ppm of the initial Cr6+
concentration. The volume and pH of a Cr6+ solution
passing through the columns were critically important
affecting the biosorption capacity of P. stratiotes. These
findings are important for cost‐effective and environ‐
mental friendly removal of Cr6+ from tannery effluents
which are posing serious risk to human and environ‐
mental health in tannery hubs of Pakistan.

Journal of Endocytobiosis and Cell Research (2015) 1‐7
Category: Research paper
Keywords: Pistia stratiotes, biosorption, Cr6+, environmental
health, tannery

Accepted: 09 January 2015
____________________________________________________________________

Introduction
Chromium (Cr) is an important environmental contaminant
that generates from numerous anthropogenic activities, i.e.
tanning, electroplating, mining, metal finishing, dyes prepa‐
ration, cement industries and preparation of corrosive
paints (Ahn et al. 1999). In last decades its concentration
has consistently increased in different environmental com‐
partments due to elevated municipal and industrial activi‐
ties reciprocal to human demands (Ali et al. 2013a). Cr like
other heavy metals is a serious health risk, i.e. toxic, persis‐
tent, carcinogenic, mutagenic and teratogenic (Gourdon et
al. 1990).
Environmental behaviour of Cr is largely a function of
its oxidation state (Losi et al. 1994). It can exist in various
oxidation states; of which the trivalent form (Cr3+) is most
stable and insoluble in water at neutral pH (Losi et al.
1994). Cr3+ in presence of mild oxidants can easily trans‐
form to hexavalent form (Cr6+) which is highly water solu‐
ble at neutral pH (Cary 1982). Cr6+ is a stronger oxidizing
agent than Cr3+ and this property is likely related to its
higher toxicity for most organisms (Rapoport and Mutter
1995). Cr6+ is described as 500 times more toxic than Cr3+
(Kowalski 1994). Transition between these two forms of Cr
is important for the accumulation tendency, transport and
toxicity in ecological compartments (Smith et al. 1989).
In Pakistan the most important anthropogenic source of
Cr in the environmental compartments is tannery industry
that plays a significant role in the economic uplift of the
country (Ali et al. 2015). There are around 650 registered
tannery units in different cities of Pakistan, i.e. Gujranwala,
Multan, Kasur, Karachi, Peshawar, Sialkot and Sahiwal (Ali
et al. 2013a). Various studies have highlighted higher Cr
levels in the soils, sediments and underground/surface
water of these cities due to unchecked/untreated tannery
industrial effluents (Tariq et al. 2006; Qadir et al. 2008; Ali
et al. 2015). Tannery effluents contain Cr in both oxidation
states, i.e. Cr6+ and Cr+3. Due to higher toxicity, the hexava‐
lent form (Cr6+) has remained a pressing concern in tan‐
nery industrial effluents (Gong et al. 2010). Cr6+ has smaller
size which allows it to breach through the biological mem‐
branes adding to its toxicity. Many efforts have been made
to treat Cr6+ in wastewater to reduce environmental pollu‐
tion (Leland et al. 1978). Conventional methods used for
the treatments and disposal of Cr6+ bearing wastewater
include chemical precipitation, ion exchange, membrane
separation, solvent extraction and adsorption, etc. (Lee et
al. 1998). These methods either are very expensive or re‐
quire extensive electrical/chemical/mechanical inputs
(Farid et al. 2014). Bioremediation and biosorption on the
other hand offer cost‐effective and environment friendly
disposal of Cr6+ bearing wastewaters without any further
environmental peril.
The present research is focused on the bioremediation
and biosorption of Cr6+ using the indigenous aquatic plant
Pistia stratiotes (water lettuce). Water lettuce exists as
common weed in lentic habitats of Pakistan and is a recog‐
nized metal hyperaccumulator (Lu et al. 2010). The basic

Potential of Pistia stratiotes for Cr6+
, Aziz-ud-Din et al.
2 Journal of Endocytobiosis and Cell Research VOL 26 | 2015
aim of this research work is to develop an efficient biore‐
mediation/biosorption method for Cr6+ removal that can be
replicated at national scale in tannery industrial cities for
regular Cr6+ pollution abatement strategies. This study will
also serve as guideline for the legislators and environmen‐
tal managers for the management of Cr6+ contaminated
environments around tanneries.

Material and methods
Sample collection
Fresh and healthy water lettuce (P. stratiotes) plants of
uniform size (number of leaves per plant = 10 ± 2; root
length = 11.5 ± 2 cm) and weight (11.2 ± 1.5 g fresh weight)
were collected from the canal water near Ayub Agricultural
Research Institute, Faisalabad. Collected plants were
washed with tap water followed by distilled water to re‐
move mud, debris and other foreign particles attached to
submerged and aerial plant parts.

Use of P. stratiotes (living plants) for Cr6+ removal
The experiment was performed in a greenhouse in large
plastic tubes of 10 litre capacity. Synthetic Cr6+ solutions
were prepared in distilled water using analytical grade
K2Cr2O7. Nine treatments in triplicate were used to investi‐
gate the phytoremediation potential of P. stratiotes. The
experiment was set up in completely randomised design
with factorial arrangements. Essential nutrients (Cr free)
were also added in each tube to support normal plant
growth and development (Hewitt 1966).

Treatment Concentration
1 distilled water
2 2 ppm Cr6+
3 4 ppm Cr6+
4 6 ppm Cr6+
5 8 ppm Cr6+
6 10 ppm Cr6+
7 12 ppm Cr6+
8 14 ppm Cr6+
9 16 ppm Cr6+

The experiment continued for a period of 28 days. Water
samples after an interval of 7 days were carefully with‐
drawn from the tubes to analyse Cr6+ concentration using
the diphenyl carbazide (DPC) method (Bartlett and James
1988). At the same time plant growth attributes, i.e. plant
weight, number of leaves and roots length were recorded.
Triplicate water Cr6+ levels and plant growth results from
each treatment were averaged and the results are present‐
ed in the Results/Discussion section.

Use of P. stratiotes (dry biomass) for Cr6+ removal
Collected plants were dried in an oven at 60 °C for 48
hours. Plant material was ground with the help of grinder
after complete drying. The obtained powdered dry biomass
was used in pH and biomass‐dependent biosorption stu‐
dies of Cr6+ from synthetic solutions. pH‐dependent bio‐
sorption experiments were set up in Erlenmeyer flasks
(250 ml) containing Cr6+ synthetic solution (100 ppm) and
0.15 g of dried plant biomass. The pH was adjusted with the
help of NaOH and H2SO4. The experiment was conducted in
triplicates at room temperature and at different pH, i.e. 1, 2,
3, 4 and 5. The flasks were placed in a shaker at 150 rpm.
Approximately 1.5 ml of water samples were collected in
Eppendorf tubes at different time intervals. Zero time sam‐
ples were taken from every flask before adding the plant
biomass. Biomass dependent biosorption experiment was
conducted as described above, but the pH was adjusted at
1.5. Different amounts of plant material, i.e. 0.05 g, 0.1 g,
0.15 g, 0.2 g and 0.25 g were weighed and added in differ‐
ent flasks. These flasks were placed on a rotatory shaker
(150 rpm) at room temperature. Zero samples were col‐
lected before adding the biomass. Samples were taken in
Eppendorf tubes at different time intervals for the analysis
of Cr+6.

Cr6+ uptake capacity (q) was determined by the following
equation:
q
V V
g

whereas
Vi = initial Cr concentration,
Vf = final Cr concentration,
g = weight of the biosorbent in g.

Column biosorption of Cr6+ by P. stratiotes dry biomass was
studied using glass columns of 1.5 cm internal diameter at
room temperature. Approximately 2 g of uniformly pow‐
dered Pistia biomass was added from the top and rinsed
with distilled water. The length of the 2 g‐packed column
was 6 cm. Synthetic Cr6+ solution (100 ppm) was passed
through the column from the top at a flow rate of approxi‐
mately 120 ml/h and the eluents were collected in 100 ml
fractions. The working temperature was kept at room tem‐
perature. Column biosorption of Cr6+ by P. stratiotes was
observed at different pH and its breakthrough curve was
studied.

Statistical analysis
Statistical analysis was carried out using Randomised Com‐
plete Block Design (RCBD) and Duncan’s Multiple Range
Test (DMRT).

Results and discussion
Effect of Cr6+ on vegetative growth of P. stratiotes
P. stratiotes weight, leaf number and root length values
recorded from all treatments at increasing days were sub‐
jected to ANOVA (Table 1a, 2a, 3a). Duncan’s Multiple
Range Test (DMRT) of mean weight, leaf number and root
length values at increasing days were estimated and pre‐
sented in Tables 1b, 2b and 3b. The results showed that
treatments, the time after treatments and their interaction
significantly contributed in the overall variance of weight,
leaf number and root length (Table 1a). DMRT of mean
values of weight (Table 1b) showed that the first three
doses were insignificantly different from each other with
respect to weight. Weight values at 14, 21 and 28 days
insignificantly differed from each other, but showed higher
values of weight as observed immediately after the treat‐
ment. The results related to the effect of Cr6+ on plant
weight showed that higher concentration of Cr6+ (> 8 ppm)
had marked inhibitory effects on gain in plant weight. The
effect was more prominent in case of treatment with 10
ppm of Cr6+. It depicts that higher concentration of Cr6+
inhibits the plant growth showing toxicity to the test plant.
In another study, the Cr6+ concentration at around 20 ppm
killed P. stratiotes in three days of exposure (Sen et al.
1987).

Table 1a: ANOVA of weight of P. stratiotes at various time intervals after treatment with Cr6+ during its growth experiments
Source D.F. S.S. M.S. F p
Replication 1 0.716 0.716 1.4045 0.2442 n.s*
Treatment (T) 6 112.357 18.726 36.7286 0 P < 0.001
Day (D) 4 120.343 30.086 59.0086 0 P < 0.001
T x D 24 59.176 2.466 4.836 0 P < 0.001
Error 34 17.335 0.51
Total 69 309.927
n.s* ‐ not significant

Table 1b: DMRT of mean weight of P. stratiotes at various time intervals after treatment with Cr6+
Treatments (mg/l) ↓
Days→ Day 0 Day 7 Day 14 Day 21 Day 28
C B A A A
2.519 3.569 5.455 5.713 5.709
0
B MN IJKLMN EFG CDEF DEFG
4.572 2.095 3.415 5.625 5.95 5.775
2
A KLMN HIJKL ABCD AB A
6.082 2.53 3.94 7.33 8.135 8.475
4
A KLMN HIJKL BCDE ABC AB
5.688 2.52 3.93 6.74 7.555 7.695
6
A IJKLMN GHIJK BCDE ABCDE AB
5.711 2.825 4.18 6.71 7.15 7.69
8
B KLMN IJKLM FGHI DEFG EFGH
4.36 2.51 3.565 4.46 5.765 5.5
10
D LMN KLMN IJKLMN MN N
2.336 2.44 2.49 2.95 1.975 1.825
12
C JKLMN IJKLMN FGHIJ IJKLMN IJKLMN
3.401 2.71 3.46 4.37 3.46 3.005
All mean values under a category which share a common letter are insignificantly different, otherwise they differ at p < 0.05

Table 2a: ANOVA of leaf number of P. stratiotes at various time intervals after treatment with Cr6+ during its growth experiments
n.s* ‐ not significant

Table 2b: DMRT of mean leaf number of P. stratiotes at various time intervals after treatment with Cr6+ during its growth experi‐
ments
C C B A A
4.571 6.5 14.93 20 22.93
0
AB J IJ EFGHIJ CDEF ABC
14.1 4 6.5 13.5 19 27.5
2
A J IJ CDEFG ABCD AB
16.7 4.5 6.5 18 23.5 31
4
A J IJ DEFGH BCDE A
16.4 4.5 6.5 16.5 22.5 32
6
AB J IJ DEFGHI BCDE ABC
15.3 5 6.5 15 22.5 27.5
8
AB J IJ FGHIJ CDEF ABCD
13 4.5 6.5 12 18.5 23.5
10
C J IJ FGHIJ FGHIJ FGHIJ
8.7 5 6 10.5 11.5 10.5
12
BC J HIJ CDEF BCDE GHIJ
12.3 4.5 7 19 22.5 8.5
Replication 1 64.129 64.129 3.9688 0.0544 n.s*
Treatment (T) 6 464.086 77.348 4.787 0.0012 P < 0.01
Day (D) 4 3661 915.25 56.6438 0 P < 0.001
T x D 24 973.2 40.55 2.5096 0.0069 P < 0.01
Error 34 549.371 16.158
Total 69 5711.786

Table 3a: ANOVA of root length of P. stratiotes at various time intervals after treatment with Cr6+ during its growth experiments

Table 3b: DMRT of mean root length of P. stratiotes at various time intervals after treatment with Cr6+ during its growth experiments

C B A AB A
4.143 6.929 8 7.429 8.214
0
C IJ DEFGH CDEFG CDEFG CDEF
7 3.5 7 8 8 8.5
2
A IJ CDEFGH BCD AB A
9.2 3 7.5 10 11.5 14
4
AB IJ CDEFGH BCD BC BC
8.4 3.5 7.5 10 10.5 10.5
6
BC HIJ CDEFG CDEF CDEFGH CDEFG
7.3 4.5 8 8.5 7.5 8
8
BC EFGHI CDEFGH BCDE CDEFG CDEFG
7.7 6 7.5 9 8 8
10
D IJ FGHIJ FGHIJ IJ IJ
4.5 4 5.5 5.5 4 3.5
12
D HIJ FGHIJ GHIJ J GHIJ
4.5 4.5 5.5 5 2.5 5

Cr6+ toxicity is an established phenomenon in aquatic and
terrestrial plants. In Myriophyllum spicatum, an increase in
shoot length was recorded at 0.05 ppm Cr6+ level, however
when its concentration was increased to 1 ppm, linear
reduction in shoot length/weight was recorded. In a study
on three herbaceous plants, i.e.
Trifolium repens, Festuca arundina‐
cea and Medicago sativa, Wang et al.
(2012) demonstrated decrease in
plant height, dry weight of
roots/shoots when exposed to Cr6+
levels exceeding 200 mg/kg in pot
soils. The results regarding the
effects of Cr6+ on leaf number and
increase in leaf number was record‐
ed up to concentration of 8 ppm.
There was relatively small increase
in leaf number at 10 ppm concentra‐
tion. At higher concentration, the
plant showed increase in leaf num‐
ber up to 21 days, but after that it
did not survive. Working on wheat,
Sharma and Sharma (1993) also
showed negative correlation be‐
tween Cr concentration and leaf
number. DMRT mean values of root
length showed that the first four
doses increased the root length while the latter two doses
reduced it. As days after treatment with Cr6+ are concerned,
the values of root length increased with increasing days
after the treatments. There was no or small increase in the
root length of P. stratiotes at 10 ppm while at higher con‐
centration the plant showed reduction in the root length
after the first week. Negative correlation between Cr con‐
centration and root length of different crops has also been
observed by others (Sharma and Sharma 1993; Stiborova et
al. 1986).

Replication 1 0.057 0.057 0.0367 P < 0.001
Treatment (T) 6 198.571 33.095 21.2538 0 P < 0.001
Day (D) 4 151.343 37.836 24.2982 0 P < 0.001
T x D 24 142.857 5.952 3.8226 0.0002 P < 0.001
Error 34 52.943 1.557
Total 69 545.771
Figure 1: Reduction in Cr6+ concentration during growth studies
of P. stratiotes. Treatments were (T1 = 2 ppm, T2 = 4 ppm, T3 = 6
ppm, T4 = 8 ppm, T5 = 10 ppm, T6 = 12 ppm). Data was collected
for four weeks at 7 days interval by growing P. stratiotes plants
on the given concentrations of Cr6+.

Uptake of Cr6+ during growth of P. stratiotes
P. stratiotes eliminated Cr6+ from the solution at a concen‐
trations of 2 and 4 ppm, while at 6 and 8 ppm the Cr con‐
centration is reduced to one half. At 10 ppm the reduction
in Cr concentration in the solution is negligible, whereas
there is no reduction beyond 10 ppm (Figure 1). P. strati‐
otes uptake of Cr is affected by its oxidation state. Cr6+ can
either directly pass through the plasma membrane or via
carriers, i.e. phosphate‐sulfate carriers. Cr3+ on the other
hand cannot use any specific membrane transporters for
inward movements. In trivalent form it simply diffuses
through the plasma membrane by forming lipophilic lig‐
ands. It is evident from these findings that P. stratiotes
efficiently uptakes/concentrates Cr6+ in leaves below 10
ppm concentration and therefore can play a vital role in
recycling Cr6+ from the contaminated industrial effluents.

Cr6+ biosorption studies using dried biomass of P.
stratiotesEffect of different dosage of P. stratiotes
biomass on the biosorption of Cr6+
Five different concentration of biomass of P. stratiotes, i.e.
0.05, 0.1, 0.15, 0.2 and 0.25 g/50 ml, were used for Cr6+
removal from 100 ppm Cr6+ solution. It was found that with
increase in initial biomass, the removal of Cr6+ from the
solution also increased. It has been reported extensively
that the initial concentration of biomass is important and
with increase in biomass, the rate of biosorption is in‐
creased accordingly (Kuyucak 1990).
In this study, 0.05 g biomass/50 ml solution removed
25% Cr6+ and 0.1 g biomass/50 ml of solution removed
63% Cr6+, while the higher amounts, i.e. 0.15 g, 0.2 g and
0.25 g/50 ml removed 100% Cr6+ from the solution con‐
taining initially 100 ppm Cr6+ (Table 4) after 6 hour of shak‐
ing (150 rpm) at room temperature. According to Gadd
(1990) the most probable mechanism is that first the cell
wall comes in contact with metal ions in solution, where the
metal can be deposited on the surface or within the cell
wall structure before interacting with cytoplasm material
or other cellular parts (Gadd 1990; Pereira et al. 2014).
This cell wall uptake may be directed by functional groups
like phosphates, carboxyl groups, amines or phospho‐
diester species. The results of Crist et al. (1988) showed
that the biosorption of heavy metals has two phases: first
phase is attributed to surface adsorption, mainly based on
anion exchange with the participation of carboxyl groups of
uronic acids. The second phase represents the diffusion of
ions into the cell.

Table 4: Effect of different dosages of P. stratiotes dried biomass on Cr6+ biosorption
Biosorbent amount (g) 0.05 0.1 0.15 0.2 0.25
Initial concentration (ppm) 100 100 100 100 100
Concentration after 6 hours (ppm) 75 37 0 0 0
% decrease in Cr6+ concentration 25 63 100 100 100
Uptake capacity (q) (mg/g) 25 31.5 33.33 25 20
Volume of test sample = 50 ml; pH = 1.5

Effect of pH on Cr6+ biosorption
The results showing the effect of different pH levels on the
biosorption of Cr6+ by P. stratiotes are summarized in Table
5. It was observed that maximum biosorption takes place at
lower initial pH. Metal uptake from 100 ppm/50 ml solu‐
tion using 0.15 g of dried biomass of P. stratiotes is 100%,
46%, 15%, 2% and 0% at pH 1, 2, 3, 4 and 5, respectively.
Earlier studies on heavy metal biosorption showed that pH
was the single most important parameter affecting the
biosorption process. Our finding are in agreement with
Cetinkaya et al. (1999) who observed that Cr6+ was more
effectively adsorbed at low pH in different fungal species.

Table 5: Effect of different pH levels on Cr6+ biosorption using
dried biomass of P. stratiotes
pH 1 pH 2 pH 3 pH 4 pH 5
Initial concentra‐
tion (ppm)
100 100 100 100 100
Concentration
after 6 hours
(ppm)
0 54 85 98 100
% decrease in
Cr6+ concentra‐
tion
100 46 15 2 0
Uptake capacity
(q) (mg/g)
33.33 15.33 5 0.67 0
Volume of test sample = 50 ml; Biosorbent amount = 0.15 g

Effect of initial Cr6+ concentrations on biosorption
Results showing the effect of initial Cr6+ concentrations on
the biosorption of Cr6+ by dead P. stratiotes are summarized
in Figure 2. The initial metal ion concentrations remarkably
influenced the equilibrium of metal uptake and adsorption.
Maximum equilibrium uptakes of Cr6+ ions were observed
at 49 mg/g for P. stratiotes at 200 ppm (mg/l) of initial
Cr6+concentration. The increase in loading capacities of
biosorbent with the increase of metal concentration may be
due to higher probability of collusion between metal ions
and biosorbent. Our results showed a positive correlation
between uptake capacity and initial Cr6+ concentration, and
are in agreement with Cetinkaya et al. (1999).
Column biosorption of Cr6+ using dried biomass of P.
stratiotes
Performance of P. stratiotes material for sorption of Cr6+
was estimated by running a number of columns at different
influent pH’s and varying Cr6+ inflow concentration
(50 ppm and 100 ppm).
Column biosorption at different pH
The effects of varying influent pH levels on sorption of Cr6+
on P. stratiotes biomass are represented in Table 6. Three
pH were 1.98, 3.02 and 4.0. The inflow Cr6+ concentration
was 100 ppm and 2 g P. stratiotes biomass was used in
these columns. The results showed that at low pH maxi‐
mum biosorption took place, while with increasing pH; Cr6+
biosorption decreases.

Table 6: Column biosorption of Cr6+ at different pH levels by P.
stratiotes dried biomass
pH (inflow) 1.98 3.02 4.07
% Cr6+ removal 95 6 0.5
After passing 0.5 (L) Cr ppm
in eluents
5 94 99.5
Uptake capacity (q) (mg/g) 21.25 1.5 0.12
Cr6+ concentrations = 100 ppm; pH levels = 1.98, 3.02 and
4.07; Flow rate = 120 ml/h; Biosorbent amount = 2 g; Vo‐
lume treated = 0.5 L

At pH 1.98, 3.02 and 4.07, 95%, 6% and 0.5% Cr6+ was
removed from the solution in the columns, respectively.
The metal uptake calculated after passing 0.5 L of 100 ppm
Cr6+ solution though 2 g of P. stratiotes biomass was 21.25
mg/g, 1.5 mg/g and 0.12 mg/g at pH 1.98, 3.02 and 4.07,
respectively. The results from column sorption are in
agreement with the previous studies on an Azolla Cr6+ sys‐
tem which showed that the optimum pH for Cr6+ binding is
2 ‐ 2.5 (Zhao and Duncan 1997).

Table 7: Column biosorption of Cr6+ (50 ppm and 100 ppm) by P. stratiotes dried biomass
Cr6+ concentrations = 50 ppm & 100 ppm; pH 1.95; Flow rate = 120 ml/h; Biosorbent amount = 2 g; Volume treated = 0.8 L

Gradual breakthrough of Cr6+ removal in column oper‐
ations
A gradual breakthrough curve of Cr6+ removal was ob‐
served in the column elution profiles at 50 and 100 ppm
inflow Cr6+ concentration (Table 7). Cr6+ solution was ap‐
plied to the columns in 100 ml fractions up to 0.8 L. It was
observed that the P. stratiotes biomass in the column is
gradually saturated until it reached 50% removal in case of
100 ppm inflow Cr6+ solution after passing 0.8 liter through
the column (as shown in Figure 3). The phenomenon of
gradual break‐ through is of importance because a column
run is always terminated at some chosen value of Cr6+ con‐
centration in the effluent. Therefore, the capacity of the
sorbents for Cr6+ removal will not be fully utilized in a sin‐
gle bed run. Other researchers have also observed similar
gradual breakthroughs of Cr6+ in their studies on column
sorption of Cr6+ with activated carbon, leaf mould, Sphag‐
num moss peat, coconut husk and palm pressed fibers with
these materials. Physical and chemical sorption was
deemed to be the predominant mechanisms for the remo‐
val of Cr6+ (Tan et al. 1993; Sharma and Foster 1996).

Conclusion
Plants as living or dead biomass can be very useful for the
removal of different kinds of pollutants from various types
of environments. The present study is an attempt to find
out the solution to environmental pollution caused by Cr6+
using P. stratiotes. In the present investigation P. stratiotes
has successfully demonstrated the removal of Cr6+ from the
water with both living and dead plant material. It can be
effectively used in decontamination of tannery effluents
containing Cr6+ in excess quantities. Phytoremediation of
Cr6+ in tannery effluents via P. stratiotes is cost effective, an
economical and environment friendly method that can be
adopted on large scale to prevent environmental damage
caused by this metal.
Volume treated (L) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Cr6+ conc. (50 ppm) 0 0.07 1.2 3.1 4 12 17 21
Cr6+ conc. (100 ppm) 2.5 3.7 5 7.4 11.2 16 25 48
% removal of Cr6+ from 100 ppm solution 97.5 96.5 95 92.6 88.8 84 75 52
Figure 2: Biosorption at initial Cr6+ con‐
centrations by dried biomass of P. strati‐
otes. 50 ml of solution in a flask containing
different concentrations of Cr6+ was sub‐
jected to 2 g of dried biomass of P. strati‐
otes at pH 1.5


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Figure 3: Breakthrough curve for a 2 g biomass column
for the removal of Cr6+. A column was used by adding 2
g of dried biomass of P. stratiotes which was packed in
a length of 6 cm. a total of 0.8 liters of 100 ppm at pH
1.95. Cr6+ solution was passed through the column at a
rate of 120 ml/h. Eluents were collected in 100 ml
fractions.

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