duckweed group - research paper

7/29/2019 Duckweed Group - Research Paper

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THE EFFECT OF PH AND AGITATION TIME ON LEAD BIOSORPTION

EFFICIENCY FROM AQUEOUS SOLUTION BY DUCKWEED (Lemna sp.)

__________

A Research Paper

Presented to the

School of Technology

University of the Philippines Visayas

Miag-ao, Iloilo

__________

In Partial Fulfilment

of the Requirements in

ChE 198

__________

By

Juniper V. Magallanes, Jerome T. Magdato and Alyssa Jean C. Sala

October 2011


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ABSTRACT

Different technologies have been developed with the growing concern for

environmental protection. Phytotechnology, the use of plant in combatting environmental

issues, have been the focus of some studies for the past years. Duckweeds (Lemna sp.)

collected from UPV Facultative Pond were used in the experiment as biosorbent in the

removal of lead (Pb) from aqueous solution. The experiment was performed using

different pH levels (4.0, 6.0, 7.0, 8.0 and 10.0) with 45-minute and 90-minute agitation

times. The result showed the highest percent removal for the pH value of 10.0, 79.7% and

79.9%, at 45 minute and 90 minute agitation time, respectively. The 90- minute agitation

time gave higher% removalof lead compared to the 45-minute agitation time at the same

pH level. As can be clearly seen in the result, the basicity or acidity of the solution affects

the amount of lead removed from it. Generally, the amount of lead removed from the

solution increases as the pH level of the solution increases. The result shows a great

potential of duckweed as biosorbent material in the removal of heavy metals in

wastewater.

Keywords: Duckweed, lead removal, biosorption, pH level, agitation time.


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ACKNOWLEDGEMENT

"The acomodadoror giving-up point: there is always an event in our lives that is

responsible for us failing to progress: a trauma, a particularly bitter defeat, a

disappointment in love, even a victory that we did not quite understand, can make

cowards of us and prevent us from moving on."Paulo Coelho, The Zahir

In accomplishing our study, we had not only been through one but many giving

up points. Sometimes, it made us stop and think twice about whether we had made the

right choices. Other times, it had almost led us to stray from the right track we're

supposed to take. However, looking back, we realized that unlike most people, we have

reached, got over through ouracomodadors, and turned each into another spark of hope.

With strong will, eager minds and unconditional support from every good soul we know,

we have survived each point.

To our parents, for their undying support and endless love even when our

biddings often leave their pockets empty, thank you and we surely love you more.

To our classmates, for brightening up our grumpy moods by cracking the corniest

jokes on earth, for almost five years of happy days and chismisan sessions, and for letting

us know we're never alone, our deepest gratitude and big bear hugs, at last friends, we did

it!

To all our friends, for putting up with our stress-provoked-monster attitudes, for

never hesitating to lend their shoulders and ears whenever we have troubles and most

importantly for sharing with us a wonderful friendship even at times when we least

deserve it, we couldn't be more lucky to have you! We know we can never thank you

enough.

To our advisers, for sharing all the knowledge we need, for the time, patience and

effort, and for simply believing that we can, thank you Sir and Ma'ams. You being with

us every step of the way made it all easier to take.

And lastly, but most importantly, to God, our Creator, for this awesome life and

for giving us these awesome people, thank you! All our success we offer to you and only

you Lord.

Japs, Juni and Alyssa


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TABLE OF CONTENTS

Page

Title Page .....

Abstract

Acknowledgement ...

Table of Contents .

List of Figures ..

List of Tables ...

List of Appendices ...

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ii

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CHAPTER

1

2

THE PROBLEM AND ITS SCOPE

INTRODUCTION .

Background of the Study

Objectives of the Study ..

Hypotheses .

Significance of the Study ...

Scope and Limitations of the Study ...

Definition of Terms

REVIEW OF RELATED LITERATURE

Lead

Removal of Heavy Metal in Contaminated Water .

Phytotechnology .

The Duckweeds ..

Species Identification .

Duckweed Composition .

Heavy Metal Accumulation by Duckweeds ...

Biosorption of Duckweeds .

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MATERIALS AND METHODS

Collection and Preparation of Research Materials

and Equipment .

Research Procedure/Experimental Design .

Gathering of Data ...

Treatment of Data ...

Ways of Proper Disposal

RESULTS AND DISCUSSIONS

Findings ..

CONCLUSION AND RECOMMENDATIONS ...

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APPENDICES ..

REFERENCES .

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LIST OF FIGURES

Figure Page

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The flow of processes on the determination of the effect of pH

and agitation time on lead biosorption efficiency on aqueous

solution by duckweed (Lemna sp.)..

The UPV Facultative pond covered with duckweeds (Lemna sp.)

Collection of samples using a long-handed mesh sampler ........

Collected duckweed samples with impurities .

Washing of collected samples ....

Clean duckweed samples ....

Air-drying of samples .

Air-drying of samples .

Cabinet-drying of samples ..

Dried duckweeds

Weighing of dried duckweeds ....

Preparation of Lead solution ..

Prepared Lead solution ...

pH adjustment .

Moisture analysis ....

The experimental setup ...

Filtration of mixture ...

Bottled filtrate sample .

Packed filtrate samples ready for analysis ..

ApHvs. % Removalplot for 45-minute agitation time .....

ApHvs. % Removalplot for the 90-minute agitation time ...

A combinedpHvs. % Removalplots of the 45and 90-minute agitation time . .

Plots ofAgitation Time vs. % Removalfor different pH levels .

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LIST OF TABLES

Table Page

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Specifications of treatments used in the study ...

Summary of results on the effect of variations in pH and

agitation time on lead biosorption efficiency from aqueous

solution by duckweed (Lemna sp.).

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LIST OF APPENDICES

Appendix Page

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The Research Paradigm on the Effect of pH and Agitation Time

on Lead Biosorption Efficiency on Aqueous Solution

by Duckweed (Lemna sp.) ..

Lead Solution Preparation (Serial Dilution) .

Storage and Preservation of Samples

Certificate of Analysis from the Department of Science and Technology

Regional Office No. 7 (DOST VII) .

Calculations for% Removalof Lead

Raw Data for Moisture Content Analysis . ..

Letter to the Chancellor for Permission to have Access to the

UPV Facultative Pond

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CHAPTER 1

INTRODUCTION

Background of the Study

With the growing awareness on environmental issues, global interest nowadays is

on the development of the cost effective and environment friendly technologies for the

remediation of soils and wastewaters polluted with toxic substances including heavy

metals. Occurrence of toxic metals in bodies of water affects the lives of people within its

locality because of their dependence upon these water sources for their daily

requirements (Rai et al., 2002). Aquatic food contaminated with toxic metals may be

consumed through its introduction in the food chain and may cause serious health

hazards. Among all metals, the public is at greater risk from lead than any other metal

(Scott, 1995).

In the tropical region of Asia, environmental pollution is of a greater threat due to

lack of wastewater treatment facilities as it is mostly occupied by low to middle income

countries with rapid industrial and urban development, and most wastewater treatment

technologies, like chemical precipitation and coagulation, are known to be costly for

municipalities and small scale polluting industries (Trihadiningrum, Verheyen and De

Pauw, 1997).

In the Philippines for example, despite the improving household garbage

collection, still 90 percent of the sewage is not treated and disposed in an

environmentally sound manner. Only 10 percent of the countrys total population is

connected to sewers and others rarely maintain adequate on-site sanitation. The increase

in water pollution which is caused primarily by fragmented water management, weak

enforcement of regulations, and poor planning are preventing adequate responses, isdegrading the countrys groundwater, rivers, lakes, and coastal areas and the quality of

pollution is estimated to be at US$1.3 billion, including health costs, losses in fisheries

production, and impact on tourism (World Bank, 2011).

The good thing however is that tropical regions are characterized by whole year

of solar energy resource which proves to be beneficial for supporting plant based


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wastewater treatment technology. Technologies that are of this type is known as cost-

effective and publicly accepted.

One example of these said technologies which already receives increasing

appraisal nowadays is phytotechnology. Phytotechnology is the application of science

and engineering in resolving environmental issues with the use of plants. This implies a

wider understanding of the importance of plants and their beneficial role in the society

and in natural systems (Mangkoedihardjo, 2007).

Phytotechnology is not only known as cost-effective but it as well offers

aesthetics and supports wild life habitat (USEPA, 1993).

Biosorption is a new cost-effective phytotechnology that is of significant use

today. It is a process that involves a solid phase (sorbent or biosorbent) and a liquid phase

(solvent, usually water). The mechanism of metal biosorption is a complicated process

which would either involve a living or a non-living biomass (Das, R., & Karthika, 2007).

Plants such as algae and other macrophytes are known to be good biosorbents for

biosorption as they tend to concentrate metals to exceptionally high levels and may

therefore help in reclamation of effluents containing heavy metals. Duckweeds are widely

used macrophyte for this purpose as they have a wide range of temperature tolerance, are

easily harvested and are capable of rapid growth. Duckweeds can tolerate and accumulate

high concentrations of heavy metals and organic compounds (Ornon et al., 1984).

Various studies abroad had also been conducted to show that duckweeds can be an

effective medium to clean waste water contaminated with heavy metals.


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Objectives of the Study

The study aimed to determine the effect of variations in conditions in the

biosorption efficiency of duckweed (Lemna sp.) in lead removal. Specifically, the study

1. determined the effect of pH2. and agitation time

on the efficiency of duckweed (Lemna sp.) as bioadsorbent in terms of% removalof lead

from the aqueous solution.

Hypotheses of the Study

The following hypotheses were put forward:

1. There exists no relationship between the % removal of lead by duckweed(Lemna sp.) and pH.

2. There exists no relationship between the % removal of lead by duckweed(Lemna sp.) and agitation time.

Significance of the Study

Heavy metal pollution is a pressing problem the world faces today. As compared

to most organic materials, heavy metals cannot be transformed by organisms, resulting to

their accumulation in water, soil, bottom sediments and living organisms. These

pollutants usually result from sewage works, industrial processing and irrigation run-off.

Most of the heavy metals are toxic or carcinogenic in nature and pose a threat to human

health and the environment especially our waters. In view of the fact that theres an

undeniable need for water purification and reuse, duckweeds potential in removing

heavy metals is a promising solution. In addition to that, duckweeds can be used as

indicator species as their content of heavy metals can be used to indicate potentialpollution levels of waters.

In the Philippines, there are limited studies on the use of duckweeds as biological

means of removing heavy metals from waste water. Most of the literatures available were

conducted outside the country. Therefore, the study will be significant for future

researches about duckweeds because of its local setting. The result of the study on the


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efficiency of biosorption of duckweed can be used as basis for industrial waste water

treatment plant with heavy metal effluents.

Scope and Limitations of the Study

This study focused only on the investigation of the effect of pH and agitation time

on the efficiency of duckweed (to be harvested from UPV Facultative Pond) in lead

removal from aqueous solution through biosorption. It was conducted at the Laboratory

of the School of Technology, Miag-ao, Iloilo during the First Semester of Academic Year

2011-2012.

The variable evaluated was the biosorption efficiency of duckweed in terms of%

removalof lead. Also, the effect of agitation time and the pH of the solution were given

specific attention.

Definition of Terms

Biosorption. Removal of heavy metals on polluted water by non-living, inactive

biomass.

Blank. A portion of the prepared lead solution.

Digestion. Use of acid and heat to break organo-metallic bonds and free ions foranalysis.

Duckweed. One of the smallest, free-floating aquatic macrophytes that take up

metals in water.

Lead. A toxic heavy metal usually present in industrial effluents.

Percent Removal. The initial concentration of lead minus the final concentration

over the initial concentration in the aqueous solution multiplied to 100%.

Biosorption Efficiency. The efficiency of the biosorption process in removal of

lead.


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CHAPTER 2

REVIEW OF RELATED LITERATURE

Technological advancement has given an increasing problem of heavy metals

which are listed as priority pollutants by the US Environmental Protection Agency

(Rai,P.K,2007). Soil and water pollution by heavy metals is a serious environmental

problem worldwide. Unlike organic pollutants, they cannot be degraded by

microorganisms. Heavy metals can make its way to the food chain and be consumed by

people. Different metals have wide range of applications. Even though a metal doesnt

have a role in the manufacturing process, we can still be exposed to it. Considering levels

of exposure and levels necessary to produce toxic effects, the public is at greater riskfrom lead than any other metal (Scott, 1995).

Lead

Lead is used in storage batteries. Lead alloyed with antimony and tin is used as a

sheath to pigments, in solders and in ammunition. Before, leaded gasoline was used as an

anti-knock additive. But because of its environmental impact, it was changed to unleaded.

The toxic effects of lead on the body are varied but greatly affect the nervous system.Lead poisoning symptoms include convulsions, hallucinations, coma, weakness and

tremors. It can also lead to anemia and kidney damage. Once exposed to lead, it is

incorporated into the bones and is released very slowly (Scott, 1995).

Removal of Heavy Metal in Contaminated Water

The removal of heavy metals from industrial wastewater has been the focus of

some studies. To reduce the heavy metals concentration in water, conventional methods

such as chemical precipitation, ion exchange, reverse osmosis, and adsorption have been

proposed. These processes either have low efficiencies or extremely expensive. Some

studies examine the potential of natural materials in removing heavy metals. Natural

materials that are available in large quantities or certain waste from agricultural processes


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may have the potential to be used in the removal. In addition, they represent unused

resources, widely available and are environmentally friendly (Afkhami et al., 2008).

Phytotechnology

Phytotechnology describes the application of science and engineering in

examining environmental problems with the use of plants. In phytotechnology, the plants

used serve as pump and treat system as they take up water soluble contaminants through

their roots and transport them through various plant tissues, where they can be

metabolized or volatilized (Doty et al., 2007).

Terrestrial and aquatic plants have the ability to acquire and accumulate metal

ions such as Pb, Cu, Mn and Zn. Some metal ions are essential for plant growth and

development. Thus, these plants can be used to remove the heavy metals from

contaminated sites. Because of their ability to grow under polluted conditions, some

aquatic plants have been investigated for their potential to remove the heavy metals and

improve the quality of the wastewater (Reiner et al., 1993). These freshwater vascular

plants when combined with macroscopic algae are collectively known as macrophytes.

According to Outridge and Noller (1991), heavy metal uptake and retention by the

macrophytes are controlled by the sediment geochemistry, water physicochemistry, plant

physiology and genotypic differences. Sediment geochemistry and water

physicochemistry control metal speciation in sediments and water. Plant physiology and

genotypic differences control the ability of plants to accumulate plant- available forms of

the metal.

Freshwater vascular plants exhibit several advantages when compared to algae.

These plants have longer life cycles. They have a higher degree of tolerance to most

heavy metal that are causing pollution. Availability of a large sample for analysis is

possible because of larger biomass compared to algae (Brooks and Robinson).Remediation of polluted water by these plants may be achieved in two ways. The

first uses the monospecific pond cultures of free-floating plants. Free floating

macrophytes are generally restricted to sheltered habitats and slow-flowing waters. Their

nutrient absorption is completely from the water, and most of these macrophytes are

found in water bodies rich in dissolved salts. The plants accumulate the pollutants until


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an equilibrium condition is achieved. Then they are removed from the pond. Problems

that can be encountered in this method are the proper disposal of the plant contaminated

with heavy metals after they are removed from the pond. Also, unwanted pathogens may

destroy the whole of a monospecific culture. Then, there is also the need for continuous

harvesting that requires specialized equipment second method involves growing rooted

emergent in trickling bed filters. Rhizophore microbes are responsible for the uptake of

trace elements in these systems (Brooks and Robinson).

Aquatic plants, such as water hyacinth (Eichhorniacrassipes), pennywort

(Hydrocotyle umbellate), small water fern (Azolla sp.), water lettuce (Pistia sp.) and

duckweeds are known to be effective in single pass wastewater treatment processes

(Mishra,Tripathi, 2009).

The Duckweeds

Attention given on the duckweed has been due to its wide range of applications or

possible ways it can be utilized. El-Shafai et al, in 2006 studied the uptake of nutrients

and mineral contaminants from wastewater effluent. Duckweed can also be used as

animal feed (Cheng and Stomp, 2009). Iqbal in 1999 studied the potential of duckweed as

compost. Recent studies utilize duckweed in bio-energy production (Fedler et al, 2007;

Cheng and Stomp, 2009).

Duckweed is one of the smallest macrophytes, free-floating aquatic plants found

distributed worldwide. They are monocotyledons belonging to the family Lemnaceae.

Duckweeds belong to five genera; Lemna, Landolita, Spirodela, Wolfia and Wolffiella.

About 40 species are known worldwide. Duckweeds have flattened minute, leaf-like oval

to round fronds from about 1 mm to less than 1cm across. The bulk of the frond is

composed of chlorenchymatous cells separated by large intracellular spaces that are filled

with air or other gases which provides buoyancy to the plant.

Species Identification

In open water, some species develop root-like structures to stabilize the plant or

to help in obtaining nutrients in dilute concentrations. The fronds of Spirodela and


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Lemnaare flat, oval and leaf like. On each frond of the Spirodela species, two or more

thread-like roots are present while Lemna has only one. Wolfia fronds are usually sickle

shaped. Wolffiella is boat shaped Wolffiellaand Wolfia are thalloid and have no roots.

They are also much smaller compared to Spirodela orLemna.

Species of the genus Spirodela have the largest fronds measuring to about 20 mm

across. The size of the fronds ofLemna species typically average between 6-8 inches

while those of the Wolffia species are about 2 mm or less in diameter.

In all genera, each mother frond produces a considerable number of daughter

fronds during its lifetime. It can produce as many as 20 daughter fronds during its

lifetime, which lasts for a period of 10 days to several weeks. The daughter fronds are

produced alternatively and in a pattern. In Spirodela andLemna, daughter fronds appear

in a pattern from two pockets which is close to where the roots arise in each side of the

mature frond. In Wolffiella and Wolfiaonly one pocket exists.

Some cells of Lemna and Spirodela have needle like raphides which are

presumably composed of calcium oxalate. The upper epidermis in the Lemna is highly

cutinized and is unwettable. Stomata are on the upper side in all the genera. Roots in both

Spirodela andLemna are adventitious.

The plant reproduces both vegetatively and sexually. The flowering occurs

sporadically and unpredictably.

Turion is a starchy survival frond formed by many species of duckweeds to

survive at low temperature. In cold weather, it sunk at the bottom of the pond where it

remains dormant until warm water triggers the resumption of normal growth.

Duckweed Composition

Duckweed is composed of water, mineral elements, and organic matter. The

composition of the duckweeds varies per species. It has been reported on a study byCross in 2006 that the freshwater duckweed fronds water content ranges from 87% to

97% depending on the species. Chemical analyses shows varying composition of crude

protein, ash, fibre and water content, fat and mineral content depending on the species,

the harvest location and the water source. The crude protein content of duckweeds

depends mostly on the nitrogen content of the water upon which they grow. Cheng and


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Stomp (2009) reported starch content values ranging from 3- 75% of the dry weight

depending on the species of duckweeds. Accumulation of starch in the plant biomass is

possible during periods of dormancy which can be achieved by varying growth

conditions like pH, nutrient concentration, and temperature (Cheng and Stomp, 2009).

Heavy Metal Accumulation by Duckweeds

All members of the duckweed family can tolerate and accumulate high

concentrations of heavy metals and organic compounds from sources. Many reports are

available on the uptake of metal ions by duckweeds and the numerous interactions that

occur. Duckweeds will uptake and concentrate Cd, N, Cr, Zn, Sr, Co, Fe, Mn, Cu, Pb, Al

and even Au.

Biosorption of Duckweeds

Biosorption is a wastewater remediation approach in which removal of heavy

metals from aqueous solutions by non-live, inactive biomass. The non-live biomass used

is called biosorbent. Some biosorbent show high heavy metal binding capacity. There are

various types of biomass, such as leaves, wood or agricultural residues. Jameel M.

Dhabab in January 2011 studied the removal of some heavy metal ions from their

aqueous solutions by duckweeds using biosorption technique. The result showed that

removal percentage was 94% for Pb2+, 72% for Zn2+, 65% for Cu2+, and 50% for Fe2+.

The efficiency of adsorption depends on pH value; it increases with the increase of pH

value at 2 to 8 in range time between 60 to 90 min. The most percentage of removal in

the main way of loading weigh was 1.5 grams and 50 ml mixed metal ions solution at 50

ppm concentration of each metal. The duckweed is found to be a promising adsorbent for

the removal of metal cations from mixed metal ions solution, representing an effective

and environmentally clean waste matter.


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CHAPTER 3

MATERIALS AND METHODS

The flow of processes on the determination of the effect of pH and agitation time

on lead biosorption efficiency on aqueous solution by duckweed (Lemna sp.) is shown in

Figure 1, the Schematic Diagram.

Collection and Preparation of Research Materials and Equipment

Preparation of Duckweed Samples. The researchers collected about two (2)

kilograms of fresh duckweeds (Lemna sp.) from the surface of waste water pond (UPV

Facultative Pond) (see Figures 2 and 3) using a long-handed mesh sampler. The samples

then were brought to the School of Technology Laboratory, UPV, Miag-ao, Iloilo.

The gathered samples (see Figure 4) were washed with tap water to partially clean

the plant surface (see Figure 5). Foreign materials from the pond that mixed up with the

samples upon gathering were removed manually. To ensure the removal of other

impurities, distilled water was used for rinsing the material. Then, the clean samples (see

Figure 6) were air-dried for twenty-four (24) hours (see Figures 7 and 8) and cabinet-

dried for three (3) hours at fifty (50) to sixty (60) C (see Figure 9). Dried duckweed

sample (see Figure 10) was placed in clean plastic bag and weighed (see Figure 11). Final

moisture contents before and after cabinet-drying were monitored (see Figure 15).

Preparation of Lead Solution. Six (6) L of about fifty (50) mg/L (ppm) lead

solution was prepared from Lead Nitrate (Pb(NO3)2) salt using distilled water as the

diluent (see Figures 12 and 13, also see Appendix 3). The final concentration of the

prepared solution was determined by subjecting a sample of the solution to lead analysis

using Atomic Absorption Spectrometer (AAS).

Five hundred (500) mL of the solution was used for six (6) treatments. The pH

levels were varied for each treatment. The pH adjustment was carried out using 0.1 M

Hydrochloric Acid (HCl) or 0.1 M Sodium Hydroxide (NaOH) (see Figure 14). Two (2)


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sets of samples were prepared making twelve (12) in total (see Table 1. Specifications of

treatments used in the study).

Preparation of Sample Containers. Unused five hundred (500) mL Polyethylene

(PET) bottles were prepared as sample containers prior to the experiment. The bottles

were ensured to be clean before use.

Research Procedure/Experimental Design

Moisture Content Analysis. One (1) gram of duckweed sample was analysed for

moisture content using a moisture analyser (see Figure 14).

Biosorption Experiment. The experiment was carried out in one (1) L glass

beakers containing five hundred (500) mL of the prepared lead solution of known pH.

For each treatment, seven (7) grams of the duckweeds (wet basis) samples was

introduced into the solution. To maximize the contact of the plant material with the

solution, Phipps and Bird Mechanical Stirrer was used to agitate the system at one

hundred forty (140) rotations per minute (rpm) were used in the study. The first set of

samples was subjected to forty-five (45) minute agitation. The sample procedure was

repeated on the other set of treatments agitated for ninety (90) minutes (see Figure 16).

The mixtures were filtered through a filter paper (see Figure 17). Four hundred

(400) mL of the filtrate were stored in clean sample containers and sealed prior to sample

digestion and analysis (see Figures 18 and 19).

The specification of the treatments used in the study is shown in Table 1.


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Table 1. Specifications of treatments used in the study.

Treatments pHMass of Dried

DuckweedsInitial Lead

Concentration

45-minute Agitation

TA,45 4.0

7.0 g~50 mg/L

TB,45 6.0

TC,45 7.0

TD,45 8.0

TE,45 10.0

Blank Unaltered (5.0) 0.0 g

90-minute Agitation

TA,90 4.0

7.0 g~50 mg/L

TB,90 6.0

TC,90 7.0

TD,90 8.0

TE,90 10.0

Blank Unaltered (5.0) 0.0 g

Table 1 shows the specification of treatments used in the study. The lead solutions

for Treatments A to E were adjusted to pH values of 4.0, 6.0, 7.0, 8.0 and 10.0respectively; with Treatment C at pH 7.0 as the control; as it is neither acidic nor basic.

pH values were chosen in a way that with enough number of treatments, it would

produce a clear result of how acidity or basicity affects the adsorption capacity of

duckweed.

All the treatments were then subjected to forty-five (45) and ninety (90) minutes

agitation along with the blanks having no duckweed content.


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Gathering of Data

Moisture Content Analysis. The analyses were repeated until three trials (%

moisture) are obtained that pass the Q-test.

Lead Analysis. The samples were brought to the Department of Science (DOST)

and Technology Regional Office No. 7 Regional Standards and Testing Laboratory

(Laboratory No. 11-09-154-03) for the analysis using Atomic Absorption Spectrometer.

Samples were digested using Nitric acid (HNO3) and diluted to volume prior to the

analysis.


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Figure 1. The flow of processes on the determination of the effect of pH and agitationtime on lead biosorption efficiency on aqueous solution by duckweed (Lemna sp.)

TA TB TC TD TE

Moisture ContentAnalysis

Moisture Content

Duckweeds Harvesting

Cleaning/Washing

Air Drying

Cabinet Drying

Weighing

Distilled Water

Pb2+

pH Adjustment

Blank

Pb Analysis by AAS

% Pb Removal

Pb Content

Sample Digestion

Packing/Storing

Filtration

90 minutes45 minutes

Stirring


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Figure 2. The UPV Facultative pond covered with duckweeds (Lemna sp.).

Figure 3. Collection of samples using a long-handed mesh sampler.

THE EFFECT OF PH AND AGITATION TIME ON LEAD BIOSORPTION EFFICIENCYFROM AQUEOUS SOLUTION BY DUCKWEED (Lemna sp.)



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Figure 4. Collected duckweed samples with impurities.

Figure 5. Washing of collected samples.

THE EFFECT OF PH AND AGITATION TIME ON LEAD BIOSORPTION EFFICIENCYFROM A UEOUS SOLUTION BY DUCKWEED Lemna s .



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Figure 6. Clean duckweed samples.

Figure 7. Air-drying of samples.




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Figure 8. Air-drying of samples.

Figure 9. Cabinet-drying of samples.




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Figure 10. Dried duckweeds.

Figure 11. Weighing of dried duckweeds.




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Figure 12. Preparation of Lead solution.

Figure 13. Prepared Lead solution.




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Figure 14. pH adjustment.

Figure 15. Moisture analysis of dried duckweeds.




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Figure 16. The experimental setup.

Figure 17. Filtration of mixture.




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Figure 18. Bottled filtrate samples.

Figure 19. Packed filtrate samples ready for analysis.




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Treatment of Data

Average Moisture Content (AMC). The data (% moisture) at different trials were

averaged.

Lead Concentration. The lead concentrations for each treatment as analysed was

plotted against pH and agitation the time and interpreted.

Percent Removal. The efficiency of biosorption was assessed in terms % removal

of lead from the aqueous solution. % removal by duckweed was calculated using the

following equation:

Where and were the initial and final concentration (ppm) of lead in the

solution respectively. The percent efficiencies were plotted against pH.

Ways of Proper Disposal

The remaining solutions containing lead were contained in reagent bottles. The

duckweeds residue exposed to lead were sealed in bottles and were disposed in a specific

area in the UPV dumpsite reserved for waste chemicals.


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CHAPTER 4

RESULTS AND DISCUSSIONS

Findings

Cabinet-drying of duckweeds resulted to reduction of moisture from 87.65 % to

47.35 % (see Appendix 6).

The final concentration of the prepared lead solution as determined by AAS was

found to be forty-eight (48.0) ppm (see Appendix 4). This concentration served as the

initial concentration (Ca) forall treatments.

The results of the experimentations on the determination of the effect of pH and

agitation time on lead biosorption efficiency on aqueous solution by duckweed (Lemna

sp.) are summarized in Table 2.

Table 2. Summary of results on the effect of variations in pH and agitation time on leadbiosorption efficiency from aqueous solution by duckweed (Lemna sp.).

Treatments pH45-minute Agitation 90-minute Agitation

Cfa

(ppm) % removalb

Cfa

(ppm) % removalb

A 4.0 48.0 0.0 45.8 4.58

B 6.0 45.9 4.38 44.7 6.88

C 7.0 42.1 12.3 42.7 11.04

D 8.0 21.4 55.4 16.1 66.5

E 10.0 9.76 79.7 9.64 79.9

Blank 5.0* 45.3 5.63 43.0 10.4

Note: a - see Appendix 4; b - see Appendix 5; * - unaltered

Given the initial and final lead concentrations of the treatments, the percentage of

removal of lead from the aqueous solution was calculated and tabulated in Table 2. Thecalculated percentage of removal illustrates the efficiency of duckweed in removing lead

from the solution.

As can be observed in Table 2, the combined effect of increasing the pH and

agitation time produced a corresponding increase in the removal of lead.


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The positive results for the removal of lead rendered by two blank samples imply

the possibility of the effect of agitation alone on the removal of lead. However, the

factors that can be attributed to these results are no longer within the scope of this study.

Giving specific attention for each agitation time, the plot ofpHvs. % removalfor

the 45-minute agitation as shown in Figure 20, illustrates clearly that as pH increases, the

amount of lead removed from the solution also increases. Same observation can be

deduced for the 90-minute agitation time as shown in Figure 21.

Figure 20. ApHvs. % Removalplot for 45-minute agitation time.

Figure 21. ApHvs. % Removalplot for 90-minute agitation time.

0

10

20

30

40

5060

70

80

90

0 2 4 6 8 10 12

%

Removal

pH

0

10

20

30

40

50

60

70

80

90

0 2 4 6 8 10 12

%

Removal

pH


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Figure 22. A combinedpHvs. % Removalplots of the 45 and 90-minute agitation time.

As can be seen in Figure 22, the 90-minute agitation time exceeds the 45-minute

agitation time in terms of% removal. Although there is an overlap in the pH value 7.0 for

both 45 and 90-minute agitation, in general, 90-minute agitation time has higher %

removal. This is because, as the agitation time increases, there is an increased possibility

of more contact between the duckweed and the solution. So there is more chance that the

duckweed can increase its uptake of lead.

0

10

20

30

40

50

60

70

80

90

0 2 4 6 8 10 12

%

Removal

pH

45

90


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Figure 23. Plots ofAgitation Time vs. % Removalfor different pH levels.

For Figure 23, at pH 4.0 and 45-minute agitation time, there was no lead removal.

This is because the contact between the duckweed and the solution is not yet enough for

removal to take place but for 90-minute agitation, some amount of lead was already

removed from the solution.

The % removalwas higher for both 45 and 90-minute agitation time at pH 10.0.In low pH values, binding sites are generally protonated or positively charged by the

hydronium ions present. Thus, repulsion occurs between the metal cation (Pb2+) and the

adsorbent. At a higher pH values, binding sites start deprotonating, hydroxide ions

prevail, and makes different function groups available for metal binding. In general,

cation binding increases as pH increases (Forsner and Wittman, 1981; Esposito et al.,

2002).

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100

%

Removal

Agitation Time

pH 4

pH 6

pH 7

pH 8

pH 10


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CHAPTER 5

CONCLUSION AND RECOMMENDATIONS

Conclusion

The outcome of the study has generally shown the great potential of duckweed in

removing heavy metals specifically lead and that varying conditions of the process could

significantly magnify the results.

Based on the results obtained after the experiment, there exist a relationship

between the percentage of removal of lead from aqueous solution by duckweed and both

varying pH and agitation time. As it has been shown, increasing pH value and agitation

time produces a greater yield of lead removed from the solution. The pH value of 10.0 at

90-minute agitation gave the highest amount of lead removed.

Recommendations

In view of the results and the conclusion, the researchers recommend that further

study must be made on the effect of varying the process conditions (i.e. concentration of

solution, pH, agitation time, mechanical stirring etc.) on the heavy metal biosorption

efficiency of duckweed. It is recommended as well that further studies must be conducted

to determine the optimum condition that would give optimum yield of removal. Also,

particular attention must be given to the adsorption isothermal studies of duckweed.

In addition to that, the researchers also suggest that thorough investigation must

be done regarding the efficiency of duckweed to remove other heavy metals like

chromium, zinc and iron and the kinetics behind it.


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APPENDICES


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Appendix 1. The Research Paradigm on the Effect of pH and Agitation Time on LeadBiosorption Efficiency on Aqueous Solution by Duckweed (Lemna sp.)

Dependent VariableIndependent Variables

% Removal

Treatment C (Control)pH 7.0, 7.0 g dried

duckweed, ~50 ppm Lead,

45 and 90-minute agitation

Treatment B

pH 6.0, 7.0 g driedduckweed, ~50 ppm Lead,


Treatment DpH 8.0, 7.0 g dried



Treatment ApH 4.0, 7.0 g dried



Treatment EpH 10.0, 7.0 g dried



BlankpH 5.0, 0.0 g dried




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Appendix 2. Lead Solution Preparation (Serial Dilution)

The Lead solution was prepared as followed,

1. 1.6135 grams Lead Nitrate (Pb(NO3)2) salt was weighed in an analytical balance.2. The salt was dissolved with 50 mL distilled water in a 100 mL beaker.3. The solution was decanted into a 1000 mL volumetric flask.4. The beaker was washed thrice with distilled water pouring the washings into the

flask.

5. The flask was filled up to mark with distilled water.6. 600 mL aliquot of the prepared solution was transferred into a larger container

container and diluted with 5.4 L distilled water.


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Appendix 3. Storage and Preservation of Samples

Samples were stored in clean polyethylene (PET) bottles away from any

potentially contaminating source prior to analysis.

Since the analysis was not done immediately, the samples were refrigerated in

order to minimize microbial activity. An additional advantage of refrigeration as a

preservation method is that it neither affects the sample composition nor interferes with

any analytical method. (Nollet, 2007).


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Appendix 4. Certificate of Analysis from the Department of Science and TechnologyRegional Office No. 7 (DOST VII) Regional Standards and Testing Laboratory


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Appendix 5. Calculations for% Removalof Lead

Sample calculations:

For TA (4.0 pH, 45-minute agitation):

For TA (4.0 pH, 90-minute agitation):

Summary of the results of% Removalcalculation of each treatment for both agitationtimes.

Treatments pH% Removal

45-minute Agitation 90-minute Agitation

A 4.0 0.0 4.58

B 6.0 4.38 6.88

C 7.0 12.3 11.04

D 8.0 55.4 66.5

E 10.0 79.7 79.9

BL 5.0 5.63 10.4


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Appendix 6. Raw Data for Moisture Content Analysis

Moisture Content(%)

Trials

1 2 3

Air-driedDuckweeds

87.34 86.40 89.21

Cabinet-driedDuckweeds

50.40 46.97 44.69

Q-test:

||

; if , the suspected value is accepted. At 90% degrees

of freedom, Qtab = 0.941

Moisture Content (%) Qcal Result

87.34| |

| | Accept

86.40| |

| | Accept

89.21| |

| |

Accept

Average Moisture Content of air-dried duckweeds: 87.65 %

Moisture Content (%) Qcal Result

50.4| |

| | Accept

46.97| |

| | Accept

44.69| |

| | Accept

Average Moisture Content of cabinet-dried duckweeds: 47.3533 %


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Appendix 7. . Letter to the Chancellor for Permission to have Access to the UPVFacultative Pond


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