Phytoremediation Of Heavy Metals From Urban Waste Biology Essay

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Phytoremediation is a developing technology that can potentially address the problems of polluted areas affected by urban or industrial activities. The aim of this study was to investigate the phytoremediation of heavy metals from municipal waste leachate by Typha domingensis according to randomized complete block design (with three replications). Every Typha domingensis was transplanted in pots containing 6 liter of mixed urban waste leachate and water (mixed 75 percentage waste leachate with 25 percentage water; V:V), and aeration was done. The samples were taken for testing, after 24, 48 and 72 hours. The concentrations of extractable Fe, Mn, Zn, Cu, Pb, Ni and Cd (ppm) in leachate were 45.211, 8.999, 9.231, 1.970, 1.100, 0.539, and 0.434, they (ppm) were 28.388, 5.821, 5.832, 1.061, 0.732, 0.335, 0.293, and they (ppm) were 14.172, 3.296, 3.667, 0.680, 0.492, 0.275 and 0.216, after 24, 48 and 72 hours phytoremediation, respectively. The evidences provided by this experiment indicated that the most metals removal from waste leachate by Typha domingensis was after 72 hours. These results also showed that the Typha domingensis was able to remove heavy metals from urban waste leachate.

Key word: Heavy metals, Phytoremediation, Typha domingensis, Waste leachate

Introduction

Landfill leachates are reflected one of the kinds of wastewater with the utmost environmental influence. The most serious features of leachate are connected of the high concentrations of some contaminants such as heavy metals (Mojiri, 2011a). The heavy metals commonly found in landfill leachate contain Cr, Cd, Pb, Hg, Ni, Cu, Zn, Fe and Se. The actual number and concentration of heavy metals in the leachate varies from one landfill to another (Amirossadat, 2012).

A rising method for polluted area remediation is phytoextraction (Ok and Kim, 2007). Phytoremediation is one of the suitable ways that can be anticipated capable to deal with like heavy metal contamination problems (Subroto et al., 2007).

Phytoextraction is the uptake of pollutants by plant roots and translocation within the plants. Pollutants are generally removed by harvesting the plants. It is the best approach to remove pollutants from soil, sediment and sludge (Singh et al., 2011).

The use of plants for remediation of soils and waters polluted with heavy metals, has gained acceptance in the past ten years as a cost effective and non-invasive method. This approach is emerging as an innovative tool with greater potential that is most useful when pollutants are within the root zone of the plants (top three to six feet). Further, phytoremediation is energy efficient, cost-effective, aesthetically pleasing technique of remediating sites with low to moderate levels of contamination. The method of phytoremediation exploits the use of either naturally occurring metal hyper accumulator plants or genetically engineered plants (Setia et al., 2008).

Phytoremediation is defined as the use of plants and their associated microbes to remove, reduce, degrade, or immobilize environmental contaminants from soil and water, thus restoring polluted sites to a relatively clean, nontoxic environment. Phytoremediation contains various strategies, and all of them are promising, cost-effective, and environmentally friendly technologies. A variety of polluted waters can be phytoremediated, counting sewage and municipal wastewater, agricultural runoff/drainage water, industrial wastewater, coal pile runoff, landfill leachate, mine drainage, and groundwater plumes (Olguín and Galván, 2010).

Plants may play a vital role in metal removal through absorption, cation exchange, filtration, and chemical changes through root. There is evidence that wetland plants such as Typhalatifolia, Cyperus malaccensis and, etc. can accumulate heavy metals in their tissues (Yadav and Chandra, 2011).

Typha is often found close to water, in lakes, lagoons and riverine areas of numerous regions of the world, America, Europe and Asia (Esteves et al., 2008). Typha is a highly-flood tolerant species with the capacity for internal pressurized gas flow to rhizomes through a well-developed aerenchyma system that provides oxygen for root growth in anaerobic substrates (Li et al., 2010). Typha domingensis is highly salt- tolerant and considered as the potential source of pulp and fiber (Khider et al., 2012).

Aziz et al. (2011) reported that the reed bed plant was capable of remove zinc and chromium from leachate. Dipu et al. (2012) was conducted a study to determine the efficiency of an emergent wetland plant species Typha sp. and floating wetland macrophytes such as Pistia sp., Azolla sp., Lemna sp., Salvinia sp., and Eichhornia sp. in phytoremediation of various heavy metals with addition of a chelating agent such as EDTA. EDTA addition to the treatment systems increased the uptake of heavy metals by plants, which was much pronounced with lead and copper. However, the pattern of uptake by plants was similar as that of heavy metals without EDTA amendments.

The phytoremediation of heavy metals from urban waste leachate offers a low cost method so the aim of the study was to investigate the phytoremediation of heavy metals from urban waste leachate by Typha domingensis.

Materials and Methods

Sample preparation

Every Typha domingensis was transplanted in pots containing 6 liter of mixed urban waste leachate and water (mixed 75 percentage waste leachate with 25 percentage water; V:V), and aeration was done in 2011. The samples were taken for testing, after 24, 48 and 72 hours.

Laboratory Analysis

The plant tissues were prepared for laboratory analysis by Wet Digestion method (Campbell and Plank, 1998). Extractable iron (Fe), manganese (Mn), copper (Cu), lead (Pb), nickel (Ni) and cadmium (Cd) in waste leachate and plant tissues were carried out in accordance the Standard Methods (APHA, 2005). Waste leachate and water properties are shown in Table 1.

Statistical Analysis

Descriptive statistical analysis, including mean comparison using Duncan's Multiple Range Test (DMRT), was conducted using SPSS software.

Table 1. Waste leachate and water properties

pH

EC

(dS m-1)

N

(ppm)

BOD5

(ppm)

Fe

(ppm)

Mn

(ppm)

Cu

(ppm)

Zn

(ppm)

Pb

(ppm)

Ni

(ppm)

Cd

(ppm)

Water

7.00

0.23

0.00

_

0.00

0.00

0.00

0.00

0.00

0.00

0.00

Urban Waste leachate

5.84

28.72

0.71

27.18

80.013

16.011

3.142

17.11

1.918

0.992

0.725

75 Percentage Waste leachate with 25 Percentage Water

6.14

21.60

0.53

20.38

60.00

12.00

2.357

12.83

1.440

0.744

0.503

Results and discussion

The comparing the heavy metals in urban waste leachate after 24, 48 and 72 hours can be seen in Table 2 and Figure 1. Data on the extractable concentration of heavy metals in Typha domingensis in the applied treatments can be seen in Table 3.

Table 2. Comparing the heavy metals in waste leachate after 24, 48 and 72 hours

Fe

(ppm)

Mn

(ppm)

Cu

(ppm)

Zn

(ppm)

Pb

(ppm)

Ni

(ppm)

Cd

(ppm)

Waste leachate after 24 hours

45.211a

8.999a

1.970a

9.231a

1.970a

0.539a

0.434a

Waste leachate after 48 hours

28.388b

5.821b

1.061b

5.832b

1.061b

0.335b

0.293b

Waste leachate after 72 hours

14.172c

3.296c

0.680c

3.667c

0.492c

0.275c

0.216c

+ Numbers followed by same letters in each column are not significantly (P<0.05) different according to the DMR test

Figure 1. Comparing the heavy metals in waste leachate after 0 (without phytoremediation; 75 Percentage Waste leachate with 25 Percentage Water), 24, 48 and 72 hours

Uptake of Heavy Metals by Plant

Soluble metals can enter into the root symplast by crossing the plasma membrane of the root endodermal cells, or they can enter the root apoplast through the space between cells. While it is possible for solutes to travel up through the plant by apoplastic flow, the more efficient method of moving up the plant is through the vasculature of the plant, called the xylem. To enter the xylem, solutes must cross the Casparian strip, a waxy coating, which is impermeable to solutes, unless they pass through the cells of the endodermis. Therefore, to enter the xylem, metals must cross a membrane, probably through the action of a membrane pump or channel. Once loaded into the xylem, the flow of the xylem sap will transport the metal to the leaves, where it must be loaded into the cells of the leaf, again crossing a membrane. The cell types where the metals are deposited vary between hyper-accumulator species (Peer et al., 2005).

Metal accumulating plant species can concentrate heavy metals like Cd, Zn, Co, Mn, Ni, and Pb up to 100 or 1000 times those taken up by non-accumulator (excluder) plants. There are several factors, which can affect the uptake mechanism of heavy metals, as shown in Figure 2. By having knowledge about these factors, the uptake performance by plant can be greatly improved (Tangahu et al., 2011).

Fig. 2. Factors which are affecting the uptake mechanisms of heavy metals (Tangahu et al., 2011)

Uptake of Iron by Typha domingensis

The concentration of iron (ppm) was 60.00 in the pots with 6 litre of mixed urban waste leachate with water and it was 45.211, 28.388, and 14.172 after 24, 48, and 72 hours phytoremediation, respectively. It is clear that the highest reduction of iron is after 72 hours.

The concentrations of iron (ppm) in roots of Typha domingensis were 3.991, 6.809, and 9.011 and in shoots of Typha domingensis were 2.037, 3.642, and 4.934, after 24, 48, and 72 hours, respectively. Hegazy et al. (2011) reported that Typha domingensis was able to remove iron from industrial wastewater.

Uptake of Manganese by Typha domingensis

The concentration of manganese (ppm) was 12.0 in the pots with 6 litre of mixed urban waste leachate with water and it was 8.999, 5.821, and 3.296 after 24, 48, and 72 hours phytoremediation, respectively. It is clear that the highest reduction of manganese is after 72 hours.

The concentrations of manganese (ppm) in roots of Typha domingensis were 1.819, 3.009, and 4.993 and in shoots of Typha domingensis were 0.861, 1.991, and 2.974, after 24, 48, and 72 hours, respectively. Mojiri (2012) reported that Typha domingensis was able to remove manganese form municipal wastewater.

Table 3. Comparing the heavy metals in Typha domingensis after 24, 48 and 72 hours

Fe

(ppm)

Mn

(ppm)

Cu

(ppm)

Zn

(ppm)

Pb

(ppm)

Ni

(ppm)

Cd

(ppm)

Typha domingensisin pots containing 6 liter of water (after 24 hours)

Root

1.197a

0.510a

0.196a

0.442a

0.000a

0.003a

0.001a

Shoot

0.769b

0.189b

0.069b

0.167b

0.000b

0.000b

0.000b

Typha domingensisin pots containing 6 liter of water (after 48 hours)

Root

1.242a

0.521a

0.200a

0.441a

0.000a

0.003a

0.001a

Shoot

0.781b

0.194b

0.071b

0.167b

0.000b

0.000b

0.000b

Typha domingensisin pots containing 6 liter of water (after 72 hours)

Root

1.249a

0.528

0.204a

0.447a

0.001a

0.003a

0.001a

Shoot

0.792b

0.195b

0.074b

0.166b

0.000b

0.000b

0.000b

Typha domingensisin pots containing 6 liter of mixed waste leachate with water (after 24 hours)

Root

3.991c

1.819c

0.701c

1.467

0.310c

0.199c

0.109c

Shoot

2.037d

0.861d

0.152d

0.798

0.023d

0.019d

0.016d

Typha domingensisin pots containing 6 liter of mixed waste leachate with water (after 48 hours)

Root

6.809e

3.009e

1.991e

2.639

0.541e

0.294e

0.198e

Shoot

3.642f

1.991f

1.001f

1.779

0.039f

0.039f

0.030f

Typha domingensisin pots containing 6 liter of mixed waste leachate with water (after 72 hours)

Root

9.011g

4.993g

2.976g

4.867

0.724g

0.402g

0.330g

Shoot

4.934h

2.974h

1.879h

1.807

0.070h

0.059h

0.051h

+ Numbers followed by same letters in each column are not significantly (P<0.05) different according to the DMR test

Uptake of Copper by Typha domingensis

The concentration of copper (ppm) was 2.357 in the pots with 6 litre of mixed urban waste leachate with water and it was 1.970, 1.061, and 0.680 after 24, 48, and 72 hours phytoremediation, respectively. It is clear that the highest reduction of copper is after 72 hours.

The concentrations of copper (ppm) in roots of Typha domingensis were 0.701, 1.991, and 2.976 and in shoots of Typha domingensis were 0.152, 1.001, and 1.879, after 24, 48, and 72 hours, respectively. Dipu et al. (2012) reported that Typha sp. was able to remove copper.

Uptake of Zinc by Typha domingensis

The concentration of zinc (ppm) was 12.83 in the pots with 6 litre of mixed urban waste leachate with water and it was 9.231, 5.832, and 3.667 after 24, 48, and 72 hours phytoremediation, respectively. It is clear that the highest reduction of zinc is after 72 hours.

The concentrations of zinc (ppm) in roots of Typha domingensis were 1.467, 2.639, and 4.867 and in shoots of Typha domingensis were 0.798, 1.779, and 1.807, after 24, 48, and 72 hours, respectively. Mojiri (2012) reported that Typha domingensis was capable to remove zinc from wastewater.

Uptake of Lead by Typha domingensis

The concentration of lead (ppm) was 1.440 in the pots with 6 litre of mixed urban waste leachate with water and it was 1.10, 0.732, and 0.492 after 24, 48, and 72 hours phytoremediation, respectively. It is clear that the highest reduction of lead is after 72 hours. The concentrations of lead (ppm) in roots of Typha domingensis were 0.310, 0.541, and 0.724 and in shoots of Typha domingensis were 0.023, 0.039, and 0.70, after 24, 48, and 72 hours, respectively.

The lead is not necessary for plant growth and considered as contaminated at the concentration of 30-300 μg g-1 in plant tissues (El-Shenawy et al., 2010). Chen et al. (2000) reported that Typha latifolia has been known to have strong resistance to phytotoxicity from lead contamination.

Uptake of Nickel by Typha domingensis

The concentration of nickel (ppm) was 0.744 in the pots with 6 litre of mixed urban waste leachate with water and it was 0.539, 0.335, and 0.275 after 24, 48, and 72 hours phytoremediation, respectively. It is clear that the highest reduction of nickel is after 72 hours.

The concentrations of nickel (ppm) in roots of Typha domingensis were 0.199, 0.294, and 0.402 and in shoots of Typha domingensis were 0.019, 0.039, and 0.059, after 24, 48, and 72 hours, respectively. Mojiri (2012) reported that Typha domingensis was capable to remove nickel from municipal wastewater.

Uptake of Cadmium by Typha domingensis

The concentration of cadmium (ppm) was 0.503 in the pots with 6 litre of mixed urban waste leachate with water and it was 0.434, 0.293, and 0.216 after 24, 48, and 72 hours phytoremediation, respectively. It is clear that the highest reduction of cadmium is after 72 hours.

The concentrations of cadmium (ppm) in roots of Typha domingensis were 0.109, 0.198, and 0.330 and in shoots of Typha domingensis were 0.016, 0.030, and 0.051, after 24, 48, and 72 hours, respectively. Mojiri (2012) reported that Typha domingensis was capable to remove cadmium from municipal wastewater.

According to Table 2, the most efficiency reduction of heavy metals from waste leachate was in the order of Fe (76%), Mn (72.53%), Zn (71.40%), Cu (71.14%), Pb (65.83%), Ni (63.03%), and Cd (57.05%) after 72 hours phytoremediation. According to Table 3, it is clear that among accumulation of heavy metals in plant, the highest amount is related to Fe absorption. Heavy metals are accumulated in both of the shoots and the roots in hyper-accumulator species (AL-Farraj and Al-Wabel, 2007). This result also showed accumulation of heavy metals in roots was important in shoots. In many investigations accumulation of heavy metals in roots was more important than in shoots (Mojiri and Amirossadat, 2011). This result is line with findings of Dipu et al. (2012), Kiayee et al. (2012), Mojiri (2012), and Mojiri (2011b).

Conclusion

The use of plants for the removal of heavy metals from spillage sites, sewage waters, sludge and contaminated areas has become a vital experimental and practical approach. In this study, the most efficiency reduction of heavy metals from waste leachate was in the order of Fe (76%), Mn (72.53%), Zn (71.40%), Cu (71.14%), Pb (65.83%), Ni (63.03%), and Cd (57.05) after 72 hours phytoremediation.The concentrations in the root and shoot tissues were found in the order of Fe>Mn>Zn>Cu>Pb>Ni>Cd. Accumulation of heavy metals in roots was more than in shoots.

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