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USE of aquatic plants for the

removal of heavy metals from
wastewater
a a a
R. K. Srivastav , S. K. Gupta , K. D. P. Nigam & P.
b
Vasudevan
a
Department of Chemical Engineering ,
b
Centre for Rural Development and Appropriate
Technology , Indian Institute of Technology , Hauz Khas,
New Delhi‐110016, India
Published online: 24 Feb 2007.

To cite this article: R. K. Srivastav , S. K. Gupta , K. D. P. Nigam & P. Vasudevan (1993) USE
of aquatic plants for the removal of heavy metals from wastewater, International Journal of
Environmental Studies, 45:1, 43-50, DOI: 10.1080/00207239308710877

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 Intern. J. Environmental Studies, 1993, Vol. 45, pp. 43-50 © 1993 Gordon and Breach Science Publishers S.A.
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USE OF AQUATIC PLANTS FOR THE REMOVAL OF

HEAVY METALS FROM WASTEWATER
R. K. SRIVASTAV,* S. K. GUPTA,* K. D. P. NIGAM* and P. VASUDEVAN†
*Department of Chemical Engineering, †Centre for Rural Development and Appropriate
Technology, Indian Institute of Technology, Hauz Khas, New Delhi-110016, India
Downloaded by [University of North Carolina] at 16:16 11 November 2014

(Received in form term May 20, 1993)

The biomass yield, efficiency to uptake heavy metals and metal concentration factor (MCF) were calculated for
Salvinia and Spirodela. These plants were used for the removal of lead and zinc, from their synthetic solutions
of single and mixed groups in laboratory conditions in two different seasons (August-November '90 and
April-July '91). In both seasons the maximum yield was observed for Spirodela in lead solutions, while in case
of zinc solutions the maximum yield was observed for Salvinia in months of August-November '90 and
Spirodela in April-July '91. Metal ion concentration after 14 days of contact time was higher in Spirodela in
both seasons in single group of solutions. But, a similar trend was not observed with mixed group. The metal
ions uptake data show that 70-90 and 50-95 percent removal of lead and zinc by both aquatic plants after first
2 days of contact time for single and mixed group metal ions, respectively. But, the values of 52-73 and 31-69
percent were observed for single and mixed groups, respectively, after 14 days of contact time. MCF for both
aquatic plants was also calculated, and it was found that Spirodela is more effective than Salvinia for the
removal of lead and zinc.
KEYWORDS: Biomass, uptake, Salvinia, Spirodela, lead, zinc, wastewater.

INTRODUCTION

With increasing industrialization, the problem of water pollution is no longer confined to

a few places. Diverse industrial wastes have aggravated the problem of water pollution.
This problem becomes complex because of the qualitative and quantitative differences in
pollution, according to the industries involved, and of the non-degradability of inorganic
pollutants, like heavy metals, which are hazardous when discharged into water body.
The toxic effects of high concentration of heavy metal ingestion on human and animal
life have been known for a very long time. But water pollution by heavy metals has
become acute only in the recent years. Public concern, spurred by incidents, such as the
Minamata disaster, has led to the introduction of strict legislative standards governing
exposure to heavy metals and the discharge of effluents containing these metals. This
problem can be solved by adopting alternative technologies which suit to the situation of
low capital availability, minimum manpower and can also save energy consumption.
There has been considerable interest in using aquatic plants for the treatment of
wastewater by several scientists. The aquatic plants can also be exploited for the removal
of various pollutants like heavy metals from wastewater because of their fast growth rate
and simple growth requirements and ability to absorb the metal ions.1"3
Further, analysis of these plants for metals also can give an indication of the state of
water environment to which they have been exposed. The metal concentrations of plant
materials are higher than in feed water making detection levels less restrictive.4 The

Correspondence: Prof. K. D. P. Nigam

43
 44 R. K. SRIVASTAV ETAL.

absorption of metal ions by aquatic plants depends on the nature and amount of aquatic
plants, their stage of development, earlier treatment as well as the volume of feeding
water and its metal ion content and presence of other dissolved substances.
In the present study, it was proposed to evaluate the heavy metal removal potential of
some of the locally available aquatic plants. A preliminary survey indicated that Salvinia
molesta (Mitch) and Spirodela polyrhiza (schleid), grow easily in the surroundings of
Delhi. Salvinia and Spirodela are free floating aquatic plant. Salvinia has colonised
several parts of the world, notably Africa5 and India,6'7 and has a very good growth rate
under favourable conditions. Spirodela is perhaps the smallest of the flowering plants
and has worldwide distribution, growing on the surface of ponds.89 It has characteristics
which make it potentially useful as an agricultural crop because it reproduces
vegetatively and is among the fastest growing plants.10 The specific growth rate of
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Spirodela is very high 0.1-0.35 gm/gm/day. Each fond absorbs metal ions from the
waterbody through the whole plant and not through a central root system as in other
plants." These aquatic plants are able to grow successfully on wastewater and convert
degradable pollutants directly into protein-rich fodder, while the wastewater is suitable
for irrigation.12
The purpose of this study was to examine the lead and zinc uptake by these two
aquatic plants from their enriched solutions, since environmental pollution by heavy
metals can be a much more serious insidious problem than pollution by organic
substances because they are not degradable by natural processes. The effect of these
metal ions on the biomass growth rate and metal concentration factor were also studied.
Based on these data an aquatic plant wastewater system could be designed and viability
examined.

MATERIALS AND METHOD

The young aquatic plants Salvinia and Spirodela were collected from ponds near Sonia
Vihar (25 km away) and Modinagar city drain (35 km away), respectively, from a north-
east direction from the laboratory. These plants separately kept in cemented tanks near
laboratory containing tap water prior to the start of the experiments. The experiments
were performed in plastic tubs having 10 cm depth and 22 cm diameter with maximum
capacity of 2 litre. In all the experiments 100 gm plant samples (fresh weight) were
placed in 1 litre of solutions and kept under natural conditions. Before the start of the
experiment the plants were cleaned properly by tap water to remove particles from roots
and leaves.
Aquatic plants (Salvinia and Spirodela) were exposed separately to the individual
metal ion solutions of lead [Pb(NC>3)2] and zinc [Zn(NO3)2.6H2O] at nominal
concentration of 1.0, 2.0 4.0 and 8.0 ppm. Aquatic plants were also exposed to mixed
solutions of these metals containing lead 1.0 + zinc 1.0, lead 2.0 + zinc 2.0, lead 4.0 +
zinc 4.0 and lead 8.0 + zinc 8.0 ppm by pipetting appropriate amounts of 1000 ppm stock
solution of each prepared, using deionised distilled water, into a known volume of tap
water. Tap water used for dilution contained (in ppm) Ca 13.8, Cr 0.003, Cu 0.07, Fe
0.13, Ni 0.08, Pb 0.004, Zn 0.12, total dissolved solids 83.8 and pH 7-7.5. One control
group was also used without addition of any metal.
The metal enriched solutions were changed every alternate day, viz. 2nd, 4th, 6th, 8th,
10th and 12th day after the beginning of the experiment. While changing solution some
roots got detached from the plants. Hence the old solutions were filtered through a plastic
mesh and the roots were added to the respective samples. The residual solution after
 HEAVY METAL REMOVAL 45

filtration was analysed for metal concentration to estimate metal ion removal at 2-day
intervals.
The aquatic plants grown in the solutions were weighed after 14 days of contact time
and analysed for metal ion concentrations in both plants. The Metal Concentration Factor
(MCF) was also estimated. The above experiments were conducted in two seasons
(August-November 90 and April-July 91) to find out any seasonal effect on the removal
of Pb and Zn ions by both aquatic plants.

ANALYSIS

As for the methods of analysis, Standard methods were followed13. An Atomic

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Absorption Spectrophotometer model Perkin-Elmer AAS 5000 was used for estimating
metal concentrations in the water and biomass.

RESULTS AND DISCUSSION

1. Biomass Growth
The biomass growth of Salvinia and Spirodela after 14 days of contact in lead and zinc
solutions was compared with the initial fresh weight 1.0, are shown in Table I. The
maximum biomass growth was obtained with a 2 ppm zinc solution in case of Salvinia.
While in case of Spirodela, this was also at 2.0 ppm of lead in both seasons in one group.
In the mixed group of lead and zinc maximum growth was observed with a 1 ppm
solution for Salvinia and 4.0 ppm for Spirodela in August-November 90, and 1 ppm for
Salvinia and 2 ppm for Spirodela in April-July 91, respectively.

TABLE I
Relative growth of aquatic plants in solutions of different concentrations of lead and zinc

August-November' '90 April—July '91

Salvinia Spirodela Salvinia Spirodela
Single Mixed Single Mixed Single Mixed Single Mixed
group group group group group group group group
(Pb+Zn) (Pb+Zn) (Pb+Zn) (Pb+Zn)

Treatment
Lead
1 PPM 1.14 1.11 1.15 1.07 1.13 1.10 1.17 1.13
2 PPM 1.12 1.10 1.16 1.09 1.11 1.07 1.19 1.15
4 PPM 1.10 1.07 1.13 1.10 1.09 1.07 1.15 1.10
8 PPM 1.05 1.08 1.11 1.08 1.07 1.05 1.12 1.08
Zinc
1 PPM 1.13 1.11 1.09 1.07 1.14 1.10 1.17 1.13
2 PPM 1.16 1.10 1.11 1.09 1.14 1.07 1.18 1.15
4 PPM 1.14 1.07 1.15 1.10 1.12 1.07 1.15 1.10
8 PPM 1.12 1.08 1.13 1.08 1.09 1.05 1.11 1.08
Control 1.16 - 1.15 - 1.18 - 1.17 -

Values are based on relative fresh weight (1.0)

 46 R. K. SRIVASTAV ET AL.

It may be seen from Table I that the biomass growth decreased at 8.0 ppm solution of
experiment, showing that higher concentrations inhibit plant growth.

2. Removal of Lead and Zinc

The percentage removal of lead and zinc by Salvinia and Spirodela are shown in Tables
II-V. Maximum removal was at first 2 days for 1.0-8.0 ppm of feed solutions for both
metal ions. The removal rate was 70-93 percent for 1.0-8.0 ppm concentrations over the
first 2 days. The percentage removal continuously decreases with the passage of time
increases. This is indicative of a fast attainment of the saturation state in the plants. A
similar trend was also observed with a mixed group of lead and zinc. Similar results have
been reported for the removal of lead and zinc by using waterhyacinth.1-3'14
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The removal rate was less in a mixed group than in single metal solutions. No
significant effect of seasons was observed. A little but regular variation in the percentage
removal of different concentrations of solutions with time may be due to biochemical
variation within the aquatic plant system. Though aquatic plants with similar weight were
taken for different concentrations, this does not indicate homogeneous physiology and
biochemistry of the plant samples.

TABLE II !
Percentage removal of lead and zinc from feed solutions of different concentrations by Salvinia in
August-November '90

Days
Treatment 2 4 6 8 10 12 14

Lead
(single group)
1 PPM 88.0 86.0 81.0 73.0 63.0 60.0 58.0
2 PPM 91.0 86.5 85.0 78.5 74.5 62.5 59.0
4 PPM 86.2 82.0 78.5 75.7 73.0 71.5 70.2
8 PPM 83.3 81.8 79.8 77.5 72.0 70.8 69.6
Zinc
(single group)
1 PPM 93.0 88.0 81.0 75.0 71.0 68.0 65.0
2 PPM 92.0 87.5 84.5 82.0 79.0 72.0 68.5
4 PPM 89.5 85.2 83.7 80.5 76.7 71.7 70.2
8 PPM 85.8 84.2 83.1 81.6 68.0 67.1 63.2
Lead
(mixed group)
Pb+Zn
1 PPM 80.0 74.0 68.0 61.0 57.0 52.0 48.0
2 PPM 82.5 76.5 74.0 70.5 66.5 60.0 52.5
4 PPM 82.0 79.5 78.5 76.0 70.2 69.2 64.0
8 PPM 77.8 73.0 69.6 67.8 66.6 64.7 64.1
Zinc
(mixed group)
Pb+Zn
1 PPM _ — _ - - - -
2 PPM 84.5 79.0 72.0 66.0 62.0 58.5 52.0
4 PPM 83.2 81.2 79.5 77.5 76.0 70.7 , 69.5
8 PPM 79.1 77.8 76.7 73.1 59.3 55.5 55.0
 HEAVY METAL REMOVAL 47

TABLE III
Percentage removal of lead and zinc from feed solutions of different concentrations by Spirodela in
August-November '90

Days
Treatment 2 4 6 8 10 12 14

Lead
(single group)
1 PPM 87.0 85.0 81.0 77.0 70.0 66.0 63.0
2 PPM 76.0 74.0 67.0 65.5 63.5 62.0 61.5
4 PPM 79.5 76.0 72.0 67.0 60.5 59.5 54.5
8 PPM 73.6 71.8 68.7 67.2 63.6 60.2 59.5
Zinc
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(single group)
1 PPM 75.0 69.0 68.0 63.0 58.0 57.0 52.0
2 PPM 81.0 73.5 75.0 71.0 68.5 67.5 66.0
4 PPM 79.5 77.5 76.5 72.5 71.5 69.7 68.2
8 PPM 70.2 69.7 68.3 66.6 64.7 63.1 60.7
Lead
(mixed group)
Pb+Zn
1 PPM 80.0 77.0 65.0 57.0 52.0 48.0 46.0
2 PPM 73.5 72.5 67.0 65.0 63.0 60.0 52.0
4 PPM 70.2 68.5 65.7 61.7 58.0 56.0 54.7
8 PPM 69.5 66.8 64.3 63.5 58.0 42.7 40.7
Zinc
(mixed group)
Pb+Zn
1 PPM 76.0 73.0 69.0 63.0 56.0 52.0 48.0
2 PPM 63.5 57.5 53.5 51.0 43.5 39.5 37.5
4 PPM 73.5 71.0 68.2 64.7 62.0 61.2 58.2
8 PPM 52.8 48.2 47.7 43.6 41.2 39.3 35.6

3. Lead and Zinc Content in Aquatic Plants

The concentrations of lead and zinc ions in the aquatic plants after 14 days of contact
time are shown in Table VI. The total amount of both metal ions taken up during multiple
exposure increases as the metal concentration in feed solution increases. Both aquatic
plants treated with a mixed group of lead and zinc tend to absorb less than the single
group of metal ion in both seasons, indicating the influence of the other ion. Similar
results have also been reported.2'314

4. Metal Concentration Factor

A given weight of plant for metal ion removal is seen in terms of the Metal Concentration
Factor (MCF), defined as the ratio of metal concentration in the plants to the initial
concentration of metal in the feed solutions. MCF is a useful parameter to evaluate the
potential of the accumulating metals and this value was calculated on a dry weight basis
(Table VII). The MCF value of Spirodela was higher when compared with Salvinia in
above group of metal ions; a higher value of MCF indicates that Spirodela is more
effective than Salvinia for the removal of lead and zinc. In the mixed group the MCF
 48 R. K. SRIVASTAV ET AL.

TABLE IV
Percentage removal of lead and zinc from feed solutions of different concentrations by Salvinia in
April-July '91

Days
Treatment 2 4 6 8 10 12 14

Lead
(single group)
1 PPM 92.0 88.0 82.0 75.0 65.0 57.0 55.0
2 PPM 90.5 87.0 83.0 76.5 68.0 61.5 57.5
4 PPM 87.0 82.0 79.2 75.7 73.5 71.5 70.7
8 PPM 84.2 82.2 80.6 78.5 72.7 71.1 68.0
Zinc
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(single group)
1 PPM 89.0 86.0 79.0 73^0 65.0 62.0 57.0
2 PPM 91.0 86.0 83.0 81.0 75.0 71.0 66.0
4 PPM 88.0 84.2 82.7 78.7 76.2 69.5 68.2
8 PPM 85.3 83.2 80.8 78.5 69.2 66.8 63.5
Lead
(mixed group)
Pb+Zn
1 PPM 85.0 76.0 71.0 57.0 47.0 42.0 37.0
2 PPM 79.5 76.5 72.0 66.5 63.0 57.0 45.0
4 PPM 79.7 78.2 77.0 71.7 68.7 66.2 60.5
8 PPM 76.0 73.2 70.3 66.8 65.3 63.3 60.5
Zinc
(mixed group)
Pb+Zn
1 PPM 81.0 75.0 71.0 64.0 57.0 51.0 40.0
2 PPM 82.5 79.5 74.0 67.0 62.5 59.0 52.0
4 PPM 82.0 78.7 76.0 73.7 71.5 68.2 66.5
8 PPM 76.0 73.1 69.2 67.8 57.1 54.7 52.3

value was lower than in the single group of metal ions, indicating the influence of other
ions in the case of both plants.

CONCLUSIONS

The Salvinia and Spirodela plants are able to remove lead and zinc effectively even at a
8.0 ppm concentration. The removal rate was higher by Spirodela than Salvinia for both
metal ions. Wastewater containing these metals at low concentration can be treated by
using these plants by continuously passing polluted water through a suitable batch type of
treatment.

ACKNOWLEDGEMENT

R. K. Srivastav is grateful to University Grant Commission (UGC), New Delhi, India for
providing financial assistance during the study.
 HEAVY METAL REMOVAL 49

TABLE V
Percentage removal of lead and zinc from feed solutions of different concentrations by Spirodela in
April-July '91

Days
Treatment 2 4 6 8 10 12 14

Lead
(single group)
1 PPM 91.0 88.0 86.0 81.0 79.0 74.0 73.0
2 PPM 76.5 75.0 73.0 71.0 69.0 67.5 66.0
4 PPM 78.7 77.0 75.7 73.7 62.2 58.7 57.5
8 PPM 76.0 76.7 73.1 70.1 70.3 68.2 64.5
Zinc
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(single group)
1 PPM 80.0 76.0 72.0 67.0 63.0 61.0 60.0
2 PPM 79.0 73.5 72.0 72.0 66.5 65.0 64.5
4 PPM 81.2 80.0 78.7 76.7 73.2 70.7 67.0
8 PPM 74.3 72.6 70.5 69.0 66.2 65.8 60.3
Lead
(mixed group)
Pb+Zn
1 PPM 87.0 76.0 75.0 66.0 62.0 59.0 53.0
2 PPM 69.0 66.0 64.0 58.5 56.0 40.0 37.5
4 PPM 70.2 68.0 66.0 64.7 62.5 58.5 54.0
8 PPM 67.2 66.1 65.1 63.8 56.7 43.5 41.2
Zinc
(mixed group)
Pb+Zn
1 PPM 84.0 80.0 77.0 67.0 58.0 53.0 52.0
2 PPM 62.0 59.5 57.0 54.0 47.0 41.5 39.5
4 PPM 71.7 69.5 67.0 63.5 59.2 57.0 54.5
8 PPM 50.8 47.2 42.1 41.6 39.0 33.1 31.1

TABLE VI
Concentration of lead and zinc in aquatic plants (ug/g dry weight basis) after 14 days of experiments in
different concentration of solutions

August—November' '90 April-July '91

Salvinia Spirodela Salvinia Spirodela
Single Mixed Single Mixed Single Mixed Single Mixed
group group group group group group group group
(Pb+Zn) (Pb+Zn) (Pb+Zn) (Pb+Zn)

Treatment
Lead
1 PPM 794 685 967 798 820 695 932 921
2 PPM 1605 1493 1628 1487 1673 1434 1867 1414
4 PPM 3398 3284 3518 3280 3445 3197 3723 3465
8 PPM 6765 6077 6924 4660 6872 6090 7028 4585
Control 1.20 - 1.32 - 1.26 - 1.36 -
Zinc
1 PPM 805 712 824 813 815 718 1023 943
2 PPM 1784 1465 1826 1295 1773 1523 1843 1428
4 PPM 3465 3376 3819 3395 3504 3285 3784 3492
8 PPM 6695 5956 6895 4884 6745 5760 7029 5048
Control 76.0 - 83.0 - 70.5 - 91.0 -
 50 R.K.SRIVASTAVE7-AL.

TABLE VII
Metal Concentration Factor for lead and zinc removal by aquatic plants in different concentrations of solutions

August-November' '90 April-July •91

Salvinia Spirodela Salvinia Spirodela
Single Mixed Single Mixed Single Mixed Single Mixed
group group group group group group group group
(Pb+Zn) (Pb+Zn) (Pb+Zn) (Pb+Zn)

Treatment
Lead
1 PPM 794 685 967 798 820 695 932 921
2 PPM 802 746 814 743 836 111 933 707
4 PPM 849 821 879 820 861 799 930 866
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8 PPM 845 759 865 582 859 761 878 573

Zinc
1 PPM 805 712 824 813 815 718 1023 943
2 PPM 892 732 913 647 886 761 921 714
4 PPM 866 844 954 848 876 821 946 873
8 PPM 836 744 861 610 843 720 878 631

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