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International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol: 11 No: 05 73

115005-2424 IJCEE-IJENS October 2011 IJENS I J E N S

Abstract Heavy metals were present at relatively highconcentrations in the landfill leachate. Therefore, the exposure of

heavy metals into the environment is great concern due to their

serious effects on food chain and furthermore on animal and

human health. This study focussed on comparing the efficiency of

horizontal and vertical subsurface flow (SSF) constructed

wetland in the removal of heavy metals (Fe and Mn) in landfillleachate. Where, it also determines the amount of heavy metals

uptake by Limnocharis flava and the amount of heavy metals

retained in the soil media. A laboratory-scale study was

conducted on SSF constructed wetland systems operated in

vertical and horizontal mode. Each system comprises of one

planted and one control system. The planted systems namely HP

and VP were planted with Limnocharis fl ava, while the control

systems namely HC and VC were left unplanted. The systems

operated identically at a flow rate of 0.029 m3/dand HRT of 24.1

hours and 19.7 hours in HSSF and VSSF systems, respectively.

The results shows both system performed well in the removal of

heavy metals from landfill leachate with the overall removal

efficiency ranging from 91.5 - 99.2% and 94.7 - 99.8% for Fe and

Mn, respectively. This research also publicized the suitability of

Limnocharis flava to be used in constructed wetland to treat

landfill leachate.

I ndex Term Landfill leachate, Constructed wetland, Heavy

metals removal, Plant uptake, Soil media

I.

INTRODUCTION

Alandfill, also known as a dump, is a site for the disposal of

waste materials by burial and is the oldest form of waste

treatment. The main purpose of landfill is to stabilize the waste

and to make it hygienic through the use of natural metabolic

pathways [1]. Landfill leachate produced from these areas are

toxicity, classified as problematic wastewaters and represent a

This work was supported by Ministry of Higher Education, Malaysia

under Fundamental Research Grant Scheme (FRGS).

K. Ain Nihla is with School of Environmental Engineering, Universiti

Malaysia Perlis, 02600 Jejawi, Perlis, Malaysia (Phone: 604-9798968; Fax:

6049798636; Email: [email protected]).

A. A. Roslaili is with School of Environmental Engineering, Universiti

Malaysia Perlis, 02600 Jejawi, Perlis, Malaysia.

A. J. Mohd. Faizal is with Perlis State Department of Environment, 2nd

Floor, KWSP Building, Jalan Bukit Lagi, 01000 Kangar, Perlis, Malaysia.

dangerous source of pollution for the environment due to its

fertilizing and toxic effects [2]. Landfill leachate mainly

consists of heavy metals, organics with different

biodegradation and inorganic matters such as ammonia,

sulphate and cationic metals [3]. However, landfill leachate

characteristics were varying depending on the operation typeand the age of the landfill. Health problems and environmental

pollution are often related to inadequate landfill leachate

treatment. Proper collection, treatment and disposal of landfill

leachate are necessary to promote better environment and

healthful condition.

Therefore, the treatment of landfill leachate by natural

systems seems to be environmentally sustainable for treatment

of many constituents. Constructed wetlands have proven very

effective method for the treatment of variety of wastewaters.

The environmental benefit treatment of landfill leachate in a

constructed wetland includes; decreased energy consumption

by using natural processes rather than conventional; efficiently

removed many pollutants from wastewater and also enhance

the environment by providing a habitat for vegetation, fish and

other wildlife [4]. Studies of the long-term use of wetlands for

landfill leachate treatment have demonstrated significant

economic advantages, mainly through lowered construction,

transportation and operation costs [5].

Reference [5] also reported the removal of several metals in

treatment wetlands, including aluminium, arsenic, cadmium,

copper, iron, manganese, mercury, nickel, silver and zinc.

Metals are removed in treatment wetlands by three major

mechanisms; binding to soils, sediments, particulates, and

soluble organics by cation exchange and chelation;

precipitation as insoluble salts, principally sulfides andoxyhydroxides and uptake by plants, including algae and by

bacteria. Removals of heavy metal occur mainly through

adsorption and precipitation and to a minor extent through

plant uptake for some metals. Metals are retained in the soil

profile or the sediments or substratum. Metals can precipitate

out as sulfides and carbonates, or get taken up by plants [6].

Several studies have demonstrated that constructed wetland

systems were very effective to remove and immobilize metals

Removal of Heavy Metals from Landfill

Leachate Using Horizontal and Vertical

Subsurface Flow Constructed Wetland Planted

withLimnocharis flava

Ain Nihla Kamarudzaman, Roslaili Abdul Aziz, and Mohd Faizal Ab Jalil

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contained in landfill leachate. Reference [7] reported the

percentage of Mn removal using free water surface (FWS)

constructed wetland planted with Eichhornia crassipes was

achieved more than 60% removal. In this study, reference [7]

was also remarked that Eichhornia crassipes had shown

capability to absorb heavy metals in leachate. It shows that

wetland plant plays an outstanding role as a heavy metal

decontaminator. Reference [8] reported high heavy metals (Fe

and Mn) removal by using vertical subsurface flow (VSSF)

planted with S.sumatrensis and S.mucronatus. The reason

might be because the effect on using two types of plants such

as S.sumatrensisand S.mucronatusin one constructed wetland

system which is can increased the removal of heavy metals in

landfill leachate.

The main objective of this study is to compare the efficiency

of horizontal subsurface flow (HSSF) with vertical subsurface

flow (VSSF) constructed wetland systems in the removal of

heavy metals (Iron (Fe) and Manganese (Mn)) from landfill

leachate planted with Limnocharis flava. This study also

examines the accumulation of heavy metals in plant tissues and

the amount of heavy metals retained in the soil sediments.

II.

METHODOLOGY

A. Leachate Collection and Preparation

In this study, the leachate used as feeding substrate was

taken from the municipal solid waste landfill (MSWLF) site

located at Kampung Padang Siding, Ulu Pauh, Perlis,

Malaysia (62651.45N, 1001815.93E). The Padang

Siding MSWLF area is about 20 hectares, where its received

abundance amount of municipal solid waste from the whole

Perlis state with a loading approximately 300 tonnes/day. The

landfill leachate was collected at the leachate collection pond

and stored in a high density polyethylene (HDPE) bottle. The

collected landfill leachate was later diluted with tap water to

achieve 25% concentrations, in order to provide an acceptable

condition for plant growth.

B.

Experimental Set up

In this study, four laboratory scale constructed wetland

systems have been constructed, which consist of two vertical

subsurface flows (VSSF) and two horizontal subsurface flows

(HSSF) constructed wetland systems. Each system comprises

of one planted system and one control system. The planted

systems namely VP and HP were planted with Limnocharis

flava, while the control systems namely VC and HC were leftunplanted. Each of the VSSF and HSSF system consists of a

feeding tank, a wetland reactor and settling tank. The wetland

reactor and operation characteristics are summarized in Table

I. The wetland reactors were constructed using acrylic with the

dimension of 0.58 m length, 0.31 m wide, and 0.33 m depth.

Both HP and VP reactors were planted with Limnocharis

flavawith density of 15 peduncles (stem) per reactor, which

transferred from a ditch near paddy field in Kampung Sungai

Bakau, Perlis, Malaysia.TheLimnocharis flava was chosen in

this study because of its availability, where it can be

commonly found throughout the state of Perlis, Malaysia. It

was also chosen due to the fact that it has long fibrous roots

that can provide oxygen supply to the media and promote

uptake of contaminants. After the transplantation, the wetland

reactors (HP and VP) were loaded with tap water to establish

the emergent plant. The duration takes 7 days for theacclimatization process, where the readiness of the plant for

the actual experimental procedure was illustrated by the

healthy leaves and stem and also by the growth of new leaves

and inflorescence.

The influent flow across the wetland reactors and effluent

was collected in a settling tank and manually transferred back

into the feeding tank to be re-circulated to the wetland reactors

on a daily basis for the whole treatment period. A 20 mm PVC

pipe and a 20 mm valve were used to regulate flow. The inlet

feeding pipe and perforated holes in each wetland reactors

were installed at 0.08 m below the surface of the substrate. The

experiments were continuously monitored throughout the

whole treatment period. Fig. 1 shows the experimental set up

for horizontal and vertical subsurface flow constructed wetland

system.

C. Analysis of Plant Tissues

Analysis of the plant tissue was conducted initially before

the treatment procedure begin and after the termination of the

experiment. This analysis was conducted to determine the

uptake of heavy metals by the plant. The method used for the

analysis of the plant tissue was Dry Ashing Method [9], where

two replicate samples from the planted (HP and VP) reactors

were selected and harvested. The plants were cleaned by

washing them with tap water followed by distilled water andsorted into leaf, stem (peduncles) and root component.

The plants samples were then placed in a porcelain crucible

and ashed by heating it overnight in a muffle furnace at 500C.

The ash residue was then cooled and 1 g of each samples (leaf,

stem, and root) were weighted and dissolved in 5 mL of 20%

hydrochloric acid (HCl) for digestion. The solutions were then

shaken for four hours with orbital shaker. It was later filtered

through an acid-washed filter paper into a 50 mL

TABLEI

REACTORCHARACTERISTICS

Total reactor height 0.33 m

Total surface area 0.178 m2

Total planting area 0.141 m2

Weight of gravel used per reactor 35.6 kg

Weight of soil per reactor 27.45 kg

Average gravel size 10-25 mm

Average void volume per reactor 0.016 m3

Flow rate 0.029 m3/d

Hydraulic Retention Time (HRT) per

cycle

HRTHSSF

HRTVSSF

24.1 hours

19.7 hours

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volumetric flask. The solutions were then diluted to volume

with deionised water and mixed well. The solution was

analyzed for heavy metals according to United State

Environmental Protection Agency (USEPA) approved

methods, by using HACH DR 2800 spectrophotometer. Fig. 2

shows plant digestion for analysis of heavy metals in plant

tissues.

D.

Analysis of Soil Composition

The analysis on the soil composition was conducted to

identify the initial and final composition of the soil used in

both HSSF and VSSF constructed wetland system. Only one

sample was used for the initial characteristic, while three

replicate soil samples were collected at different depth

(surface, mid depth, and bottom) of each reactors (HC, HP,

VC, and VP) for the final characterization study. The samples

were analysed using X-Ray Fluorescence (XRF) Spectrometer.

Prior to the XRF analysis, the soil samples were oven dried at

105C overnight, grinded and sieved to obtain soil samples

size of less than 70 m and pressed into pellet by using

hydraulic Pellet Press Model PP 25. The preparation of the

soil samples as shown in Fig. 3.

III.

RESULT AND DISCUSSION

A. Heavy metals Removal

The initial leachate characterization study was conducted to

determine the most significant heavy metals that will be the

parameter of interest. The results of initial leachate

characterization study are summarized in Table II. By referringto Table II, it can be clearly observed that the leachate sample

was exhibited significant value of heavy metals content, among

which the highest concentration was recorded for Fe and Mn

with 11.6 mg/L and 10.6 mg/L, respectively.

Fig. 1. Initial experimental set up

Fig. 2. Samples preparation for plant analysis

(a) Leaf sample; (b) root sample; (c) stem sample; (d) orbital shaker

Fig. 3. Preparation for soil analysis. (a) soil sample after oven dried; (b) soil

sample after sieved; (c) soil pellet; (d) XRF spectrometer unit

TABLEII

RESULTOFINITIALLEACHATECHARACTERISTICS

Parameter Unit Value

Manganese (Mn) mg/ L 10.6

Nickel (Ni) mg/ L 0.587

Calcium (Ca) mg/ L ND

Magnesium (Mg) mg/ L 0.437

Zinc (Zn) mg/ L ND

Iron (Fe) mg/ L 11.6

Copper (Cu) mg/ L ND

Chromium (Cr) mg/ L ND

Cadmium (Cd) mg/ L ND

Aluminium (Al) mg/ L 0.978

Plumbum (Pb) mg/ L 0.653

Note: ND = Not detected

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In this study it can be clearly observed that the influent

concentration of Fe in the leachate sample was subsequently

reduced to a significantly low concentration throughout the

treatment period as shown in Fig. 4. The final effluent

concentration of Fe was significantly reduced and varies

among all four wetland microcosm, with 0.985 mg/L, 0.250

mg/L, 0.653 mg/L and 0.093 mg/L for reactor VC, VP, HC,

and HP, respectively. The optimum removal percentage of the

planted systems (VP and HP) was recorded on the day 3 of the

treatment period with 15.5% and 17.2% for VP and HP,

respectively. While, for the unplanted system (VC and HC) the

optimum removal was only achieved on the day 21 of the

treatment period with 32.8% for VC and 24.1% for HC

reactor.

However, it was observed the overall treatment efficiency

for all reactors does not varies greatly between each other,

with the most efficient system in the removal of Fe from

landfill leachate was reactor HP with 99.2%, while the least

efficient system was reactor VC with removal of 91.5%. This

finding was higher than those reported by [10]; [11] and [12],

which proved the effectiveness of constructed wetland in theremoval of Fe from wastewater and concurrent with the

findings by [13] and [14].

In this study, both VP and HP reactors were effective in

reducing the high level of Mn from landfill leachate. As it been

demonstrated in Fig. 5, the final concentration of Mn was

reduced to a significant value of 0.561 mg/L, 0.042 mg/L,

0.323 mg/L and 0.027 mg/L for VC, VP, HC, and HP reactors,

respectively. The highest treatment efficiency was recorded for

reactor HP with 99.8% removal and the least was reactor VC

with 94.7% removal at the end of treatment period. The

optimum removal of Mn for the planted systems was recorded

on day 3 of the treatment period with 18.9% and 20.8% for VPand HP respectively, while the optimum removal of the

unplanted system (VC and HC) was only achieved on day 12

and day 15 of the treatment period with 17.0% for VC and

25.7% for HC reactor.

In this study it can be clearly observed that all reactors

managed to subsequently reduce the concentration of Fe and

Mn to significantly low concentrations after 45 days of

treatment period. The control system (unplanted) also

demonstrated high reduction of heavy metals which is more

than 90% removal. The reduction of heavy metals in the SFF

wetland system maybe was due to settling and sedimentation,

uptake by algae and bacteria, precipitation as insoluble salts,

and binding to soil, sediments and particulate [5]; [15].

However, the reduction of Fe and Mn in control system still

showed lower removal if compared to the planted system.

Plants species have variety of capacity in accumulating and

removing heavy metals. Several processes are envisioned as

being effective in pollutant reduction; for example metals are

taken up by plants, and in many cases stored preferentially in

the roots and rhizomes [16].

B.

Heavy Metals in Plants Tissue

The analysis of plant tissues were conducted to study the

extents of phytoaccumulation or phytoextraction of heavy

metals (Fe and Mn) in the plant tissues which was segregated

into three main components which is leaves, stems, and roots.

The results of the plant tissue analysis as shown in Fig. 6

shows that there was an accumulation of heavy metals in the

tissue of Limnocharis flava planted in both HP and VPsubsurface flow system. The accumulations of heavy metals

shows that the contribution of macrophytes in the sense of the

uptake of pollutants are significant in this study, apart from

providing a large surface area for attached microbial growth,

supplying reduced carbon through root exudates and micro-

aerobic environment and a via root oxygen release in the

rhizosphere, and stabilizing the surface of the bed [17]; [18];

[19]; [20].

The ability ofLimnocharis flavato uptake heavy metals was

also proven in this study. Where, the highest amount of heavy

metals were determined in the root for both VSSF and HSSF,

with 0.728 mg/g (VSSF) and 1.117 mg/g (HSSF) for Fe and

0.223 mg/g (VSSF) and 0.362 mg/g (HSSF) for Mn,

respectively. In which it was consistent with the findings by

reference [21] and [22]. These roots have been reported to be

the most beneficial for phytostabilisation of the metal

contaminants. As depicted previously in Fig. 6, the result

shows that Mn uptake by plants was less than Fe. Study by

references [23], [24] and [25] also reported that the amount of

Fe uptake by plants was higher compared to Mn in the plant

tissues. Fe2+was the micronutrient for plants that was required

in higher concentration than Mn2+ [26]. Additionally, plants

require a small amount of Mn, high level of Mn interfere with

enzyme structure and nutrient consumption. As it can be

noticed in Fig. 6, HSSF systems exhibited a higher uptake ofheavy metals as compared to VSSF system due to the higher

HRT for HSSF system. These findings have shown the

significant and positive effect of macrophytes on pollutants

removal [19]. Whereby, the roles of macrophytes as an

essential component of constructed wetland have been well

established [17]; [27].

C.

Heavy Metals in Soil Media

The wetland media is one of the important components of

constructed wetland, as it provides a viable condition for

maximum removal of pollutant, since the reduction is said to

be accomplished by diverse treatment mechanisms including

sedimentation, filtration, chemical precipitation and

adsorption, microbial interactions and uptake by vegetation

which governed by the accurate selection of media type [28].

Therefore in this study, soil analysis was conducted to

determine the suitability of the media beds used, as it is

indicated by the accumulation of the heavy metals within the

soil media.

Fig. 7 and Fig. 8 shows concentration of Fe and Mn in the

soil media collected at different depth of four reactors (VC,

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VP, HC and HP). The unplanted control systems (VC and HC)

exhibited a higher concentration of Fe and Mn in the soil

samples collected at the bottom of the reactors, with an

increase of 5.2% (VC) and 7.7% (HC) for Fe and 0.2% (VC)

and 0.3% (HC) for Mn. While, the reactors planted with

Limnocharis flavaexhibited a higher concentration of Fe and

Mn in the soil samples collected at mid-depth of the reactors,

with an increase of 3.9% (VC) and 6.6% (HP) for Fe and 0.2%

(VP) and 0.3% (HP) for Mn, respectively.

Fig. 4. Concentration of Fe in landfill leachate effluent

throughout treatment period

Fig. 5. Concentration of Mn in landfill leachate effluent

throughout treatment period

Fig. 6. Accumulation of heavy metals in plant tissues after 45 days

of treatment period

Fig. 7. Concentration of Fe in soil at different depth Fig. 8. Concentration of Mn in soil at different depth

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The increased concentration of heavy metals (Fe and Mn) in

the soil samples collected at the bottom of unplanted control

reactors (VC and HC) indicates that the heavy metals were

actually precipitated towards the bottom of the reactors [12].

While, the higher concentration of Fe and Mn at the middle of

the planted reactors was due to the rhizofiltrations of these

heavy metal in the rhizosphere since precipitation and

rhizofiltration are the main mechanism in the removal of heavy

metals in constructed wetland [12].

IV. CONCLUSION

Based on the above results and discussions, it can be

summarized that HSSF system has higher removal efficiency

compared to VSSF system for the removal of heavy metals.

The higher removal of HSSF system was due to the higher

HRT value for this system, which also indicates the

importance of HRT that affects the removal efficiency of

heavy metals in the constructed wetland system. Also, its so

obvious that by comparing the planted and control system,

both systems were achieved high percentage of heavy metals

removal at the end of treatment. The greater heavy metalsremoval in the control system maybe was due to clogging of

the substrate in the soil media. So it can be concluded that,

reduction of heavy metals concentration in the planted and

control system were most likely due to chemical precipitation

and sorption on sediment, and aided by the macrophytes. This

is also shows the shorter treatment period is required in

achieving optimum removal for planted system as compared to

unplanted system. However, for a longer treatment period

there were only slender differences in the effluent

concentration of pollutants between the planted and control

system. To further enhance the result obtained in this study,

the following areas of investigation are recommended: (1)degradation by microorganism is among the important

mechanisms in the removal of pollutants. However, this study

does not quantify the development of microorganism within

the wetland reactor. If the microorganism formation and

development within the reactor could be measured, it surely

will enhance the findings in this study and (2) further studies

should vary the flow rates, retention time, types of plant and

size of constructed wetlands system in order to determine the

efficient of pollutants removal.

ACKNOWLEDGMENT

We are grateful for the university resources provided by

Universiti Malaysia Perlis (UniMAP), Malaysia. Special

acknowledge to the Ministry of Higher Education (MOHE),

Malaysia for granting us financial support under the

Fundamental Research Grant Scheme (FRGS) (900300289).

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