Chapter 1The Problem and Its Scope

Rationale

Industrialization proves itself to be both a boon and a bane to the society and

to the environment where it thrives. The rise of different industries and the onset of

large-scale manufacturing have contributed much to the ease at which people operate.

However, this advancement may have also brought with it some detrimental effects--

one such concern is the increasing environmental pollution from industrial wastewater

particularly in developing countries. One of the major classes of water pollutants are the

heavy metals which are of particular concern as they bring harmful effects to

humans.1Their intentional or accidental dispersal to the environment also poses a

threat to other living systems especially the to the aquatic biota. Notable sources of

heavy metal-contaminated water are the different kinds of industries such as metal

plating facilities, mining operations, and tanneries.2

Due to their mobility in aquatic ecosystems and their toxicity to higher life

forms, heavy metals in surface and ground water supplies have been prioritized asmajor

inorganic contaminants in the environment.3 The need to exert efforts in removing heavy

metals from aqueous solutions is now being addressed using conventional methods

which involve the isolation of the said contaminants. These processes include:

coagulation, flocculation, chemical oxidation and reduction, ion exchange, physical

adsorption, filtration, electrochemical treatment, and evaporation. However, these

procedures have significant fallbacks as they are prone to incomplete removal, high

energy requirement, and toxic sludge production, and are very expensive.2 Thus,

1

alternative methods for metal separation from aqueous solutions were developed, and

one such alternative is Bioadsorption.

Bioadsorption refers to the removal of metal or metalloid species, compounds,

and particulates from a solution by a biological material.4 Agricultural waste products

and microorganisms are usually used as the sorbents. The use of lobster

(Panulirusversicolor)shells as Bioadsorbents has been suggested because of their

adsorptive capacity ascribed to the presence of chitosan. It is produced by alkaline N-

deacetylation of chitin, which is widely found in the exoskeleton of shellfish and

crustaceans. The adsorption behavior of chitosan for heavy metal removal is attributed

to: (1) its high hydrophilicitydue to a large number of hydroxyl groups, (2) large number

of primary amino groups with high activity, and (3) the flexible structure of its polymer

chain, making suitable configuration for adsorption of metal ions.1

Aside from being natural adsorbents, lobster shells are used owing to the fact

that they are of less significance to the community as they are mainly considered as

food left over and generally thrown as wastes. Furthermore, several crustacean

biomasses had also been investigated for heavy-metal ion binding potential such as

shrimp and crab shells. However, very few, if any, studies have been conducted on

lobster biomass. These premises led the researcher to study the capacity of lobster

(Panulirusversicolor) shells as Bioadsorbent for Lead, a useful but toxic metal. It is well

established that lead is toxic to humans at high dosages, and that levels of exposure

encountered by at least some of the population are high enough to constitute a hazard

to health.4 The fact that Lead ions are widely found in industrial wastewater aggravates

2

the threat that society is facing. One significant characteristic of lead which made the

researcher choose this metal as the contaminant is that Lead (II) can form more stable

metal-adsorbent complexes than Copper, Nickel, Zinc, and Cadmium can.5 Simply put,

this study aims to highlight the feasible uses of an alternative and affordable adsorption

method in separating hazardous species such as Lead from aqueous environments

though the utilization of biomass such as Panulirusversicolor shells as adsorbents.

Significance of the Study

Lead, a useful but toxic metal is an integral part of the economy. Its uses span

from the production of lead-acid batteries, ballast keels of sailboats, electrodes in

electrolytic devices, fusible alloys, and solders for electronic devices to high-rise

building construction. 5 However, one fallback of this metal is that a considerable

amount of its input is not used for production purposes; a significant portion will be

discharged as waste, which will then pollute aquatic systems. Along with the beneficial

purposes come the environmental and health hazards brought by this metal, especially

when it is not disposed properly. For instance, the Australian Lead Education

Abatement Design Group Inc. reports an incident that happened in the Philippines in

1996 where the Marilao River in Bulacan, Philippines turned black with toxic waste

water discharged by a nearby industrial plant. Water samples from the river were found

out to have severe lead contamination, which reached about 1900 times Australian

allowable standards. Moreover, blood lead levels from the resident children were

examined and were found out to be three times higher than the Australian standard of

10 micrograms Pb per deciliter of blood. 7

3

The incident serves as a reminder about the dangers of water pollution though

heavy metal contamination as its adverse effects not only deteriorate the environment,

but also put people’s health at high risks. This study is conducted to determine the

feasibility of using Panulirusversicolor shells to bind and isolate lead in aqueous

solutions so as to provide an alternative means of water purification.

This study will thus benefit prospective researchers as it will provide insights

about using throw-away organic species as adsorbent materials. The information that

will be generated by this study could also be a significant addition to the existing body of

knowledge which posits that certain waste biological wastes can be used to alleviate an

environmental problem.

This study will also give insights to those working in the water purification and

treatment industry about a new alternative way of treating heavily contaminated water to

make it into a potable one. With the use of the bioadsorption process, these facilities will

be prompted to utilize less costly and equally effective means of treating contaminated

water.

The findings of this study may also give an idea to the local residents living near

bodies of water about a method which they could use in purifying water, making it free

of heavy metal contaminants. They may also use this as a springboard in experimenting

with other Bioadsorbents’ ability to purify water.

4

According to the World Health Organization (2011), one of the population groups,

which are at the highest risks of Lead exposure are the children. A recent report

suggests that even a blood level of 10 micrograms per deciliter can have harmful effects

on children's learning and behavior (CDC, 2011)8. As such, this research may also

benefit local civilians. They may use the knowledge generated by the study to remediate

environmental contingencies which may prove harmful to everyone’s health, especially

children.

Background of the Study

In this section, the causes, effects, and concept of water pollution are discussed.

Information on heavy metals, with Lead being the highlight, are presented. A discussion

of the two processes by which this study has its grounds on-- adsorption and

Bioadsorption-- follows. After which, properties of ideal Bioadsorbents and the

characteristics of Panulirusversicolorshell which made it suitable to be used in the study

are cited. This section also talks about the process of determining Lead concentration in

aqueous solutions using atomic absorption spectroscopy. Lastly, this section discusses

the possible isotherms by which lead adsorption through lobster shells could be

described.

Water Pollution

One thing that distinguishes the Earth from the other planets in the solar system

is the presence of water in its liquid form. Liquid water is in no way less unique as it can

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naturally renew and cleanse itself by allowing pollutants to settle out (through the

process of sedimentation), or break down by diluting the pollutants to a point where they

are no longer in harmful concentrations.9 However, this capability of water diminishes as

an increasing number of pollutants are incorporated into it. It also involves a

considerable amount of time for the pollutants to degrade. This poses an alarming form

of environmental contamination called water pollution. Water pollution occurs when

energy and other materials are released; thereby degrading the quality of water…also

includes all other materials which cannot naturally be broken down by water. 9

Water pollution is classified into two according to where the pollutants come

from. These classifications are point sources which include factories, waste water

treatment facilities, septic systems and other sources that are clearly discharging

pollutants into water sources; and non-point sources which include run-off sediments,

fertilizers, chemicals and animal wastes from farms, fields, construction sites, and

mines.9 Significant examples of water pollutants from either point or non-point sources

are the trace elements and heavy metals, like Lead, which are very toxic and harmful to

the environment, to humans, and to other biotic components upon reaching certain

concentration levels.

Heavy Metals

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Heavy metals are a subset of elements that exhibit metallic properties,

particularly the transition metals and the representative elements. They are potentially

toxic even at very low concentrations.

Heavy metals have tremendous affinity for sulfur and disrupt enzyme function

by forming sulfur groups. They can precipitate phosphate biocompounds and catalyze

their decomposition. Due to these toxic properties, heavy metals have been considered

as one of the most harmful elemental pollutants which have significant effects on human

health, aquatic biota, and water toxicity. 1

Moreover, heavy metals are not biodegradable and they tend to accumulate in

living organisms10 that results in the deterioration of their health. This process, called

“Bioaccumulation”, can lead to poisoning and other hazards especially when their

concentrations exceed the trace amounts required by the body. They enter the human

body system through food chain, drinking water, and air absorption to the skin.10 Heavy

metals become toxic when these metals are not metabolized by the body and they

accumulate in soft tissues. (See Figure 3.1)

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Figure 3.1 Scheme of heavy metal cycle. The heavy metals are moving from the

environment (pollution) to the human body through the food chain.

Although heavy metals are natural components of the Earth’s crust, their

concentrations in aquatic environments have increased due to mining and industrial

activities and geochemical processes. They can make their way to water sources by the

following contingencies: discrete discharge of industrial and consumer wastes,

percolation of contaminated soil, leaching of wastes from landfills, naturally---since for

some heavy metals, toxic levels can be just above the background concentrations found

in nature, acidic rain breaking down soils and releasing heavy metals into streams,

lakes, rivers, and groundwater.10

Lead

Lead is a chemical element in the Carbon group with the symbol Pb from the

Latin word Plumbum. It is the most common of the heavy elements, accounting for 13

mg/ kg of the Earth’s crust.11 It is a soft and malleable metal, which is also regarded as

a heavy metal. Metallic Lead has a bluish white color after being freshly cut but it soon

tarnishes into dull gray after being exposed to air. It has a melting point of 327 degrees

Celsius. Because of its widespread availability, this metal has commonly been used for

thousands of years even reaching as far as the Bronze Age where it was used with

Arsenic and Antimony. Several stable isotopes are found in nature, which include 208Pb,

206Pb, 207Pb and 204Pb.

8

Lead is used in the production of lead acid batteries, solder, alloys, cable

sheathing, pigments, and other industrial purposes. Lead pipes were also used in older

water distribution systems and plumbing. Polyvinyl Chloride (PVC) pipes contain some

Lead compounds which can be leached from them and thus contaminate it. This can be

remediated by the addition of lime and the adjustment of the pH to <7, 8-9. It can also

be released from flaking lead carbonate from lead pipes.

Lead is a metal with no known benefit to humans. Too much of it can damage

various systems of the body including the nervous, reproductive, and renal systems.11 It

can also cause high blood pressure and anemia. Lead accumulates in the bones. Lead

poisoning may be diagnosed from a blue line around the gums. Moreover, Lead is

harmful to the developing brains of fetuses and young children. Exposure to it also puts

pregnant women in danger. Lead interferes with the metabolism of calcium and Vitamin

D. High blood Lead levels in children can cause irreversible learning disabilities,

behavioral problems, and mental retardation. At very high levels, high blood Lead

concentration can cause convulsions, comatose, and even death.11Due to its toxicity,

the World Health Organization (2011) established the maximum permissible amounts of

lead to be at 5 to 10 micrograms per liter of drinking water.26 However, this limit is often

times exceeded to a significant amount as in the case of the Marilao River Lead

Contamination incident (1996) in Bulacan, Philippines.

Adsorption

Adsorption refers to the accumulation or binding of molecules at the interface

between two phases. It must be distinguished from absorption which refers to the

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process in which a substance penetrates into the actual interior of crystals, of blocks of

amorphous solids, or of liquids. Sometimes, the word sorption is used to indicate the

process of the taking up of a gas or liquid without specifying whether the process

involved is adsorption or absorption.

Adsorption can either be physical or chemical in nature. Physical adsorption

resembles the condensation of gases to liquids and depends on the physical, or Van

der Waals, force of attraction between the solid adsorbent and the absorbate molecules.

No chemical specificity is involved in physical adsorption, contrary to chemical

adsorption where adsorbates are held to the adsorbent, which is usually solid, by

chemical forces. Chemical adsorption frequently involves energy of activation.

Parameters taken into consideration when choosing an appropriate adsorbent

are mainly the sorption capability, regeneration ability, kinetic parameters, price and

market availability.13 Maximum sorption capability is the most important parameter that

characterizes each sorbent. It is the maximum amount of the adsorbed substance

available for the uptake per sorbent unit mass or unit volume (usually in mg/g or meq/g).

The sorption capability is determined experimentally at constant temperature, and the

results are presented as isotherms.

Adsorption plays a critical role in the transport, bioavailability, and fate of

contaminants and naturally occurring trace compounds in both natural and engineered

aquatic systems.12 It provides the most efficient means of removing contaminants from

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solutions to extremely low levels.12 This study on the Pb2+ adsorption using lobster shells

does not indicate specific adsorbing mechanism.

Bioadsorption

One such environmental concern which demands necessary attention is the

contamination of aquatic systems with toxic heavy metal ions. Since all heavy metal

ions are non-biodegradable, there is a need for them to be removed from polluted

bodies of water like streams and rivers so that environmental quality standards will be

satisfactorily met.13

Numerous physiochemical methods of removing heavy metals from aqueous

systems were developed: coagulation, flocculation, chemical oxidation and reduction,

ion exchange, physical adsorption, filtration, electrochemical treatment, and

evaporation.2 However, these methods have significant disadvantages as they are

prone to high-operating costs, incomplete removal, and production of large quantities of

wastes. As an alternative to these methods, a promising and less costly way of

addressing heavy-metal contamination evolved: Bioadsorption.

Bioadsorption is a promising technology for the treatment of heavy-metal

contaminated aqueous systems which is primarily based on metal-biomaterial

interactions. The Bioadsorption process has two phases: the biomaterial as the solid

phase, and the solvent water with dissolved metal ions in it as the liquid phase.14

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Bioadsorption is the capability of active sites on the surface of biomaterials to

bind and concentrate heavy metals from even the most dilute aqueous solutions. The

process of metal ion binding is comprised of many physicochemical processes like ion

exchange, complexation, microprecipitation, and electrostatic interactions.13

The advantages of this process include low-cost and ease of operation, and

selectivity against the alkaline materials when compared to the conventional methods of

heavy-metal removal. In Bioadsorption, agricultural by-products are utilized as the

adsorbents which exhibit the capability to uptake water contaminants brought by human

activities.

This study utilizes the mechanisms governing Bioadsorption and the effectiveness

it entails in removing lead ions found in aqueous environments.

Bioadsorbents

Adsorbents that come from biological materials are known as Bioadsorbents,

examples of which are non-living microorganisms such as bacteria, fungi, yeast, and

algae. Extra-cellular polysaccharides secreted by microorganisms are also

recommended as surface active agents for heavy metal removal.13Other examples of

Bioadsorbents are tobacco dust, coconut shell powder, chitin-rich wastes, activated

charcoal, and nutshells.

12

Plant biomaterials can also serve as Bioadsorbents. Residual products of wheat,

corn, rice plant and other farm crops may serve such purpose. The plant origin

biomaterials contain hemicellulose, lignins, extractives, lipids, proteins, simple sugars,

water hydrocarbons, and starch whose functional groups participate in heavy metal

removal through the mechanism of complexation. Those functional groups include

carbonyl, carboxylic, amine, and hydroxyl groups which may also uptake metal

adsorbates by ion-exchange processes.

Biomolecules found in Bioadsorbents contain ionizable functional groups such

as carboxyl, phosphate, and sulfate groups. Lead ion-adsorption may involve different

binding mechanisms. One possibility is metal-ion exchange where the Pb2+ ions will bind

to the functional groups via cationic binding. This study of Pb2+ Bioadsorption using

chitosan-containing lobster shells are based on the premise of Pb2+ cationic nature and

the presence of organic functional groups in the Bioadsorbent.

Spiny Lobster (Panulirusversicolor)

Spiny lobsters, also known as langouste or rock lobsters, constitute the family

Panulirudae of the class Malacostraca, subphylum Crustacea, under the phylum

Arthropoda. Although they superficially resemble true lobsters in terms of overall shape

and having a hard carapace and exoskeleton, the two groups are not closely related.

Spiny lobsters can be easily distinguished from true lobsters by their very long, thick,

spiny antennae, by the lack of chelae or claws on the first four pairs of walking legs,

13

although the females of most species have a small claw on the fifth pair,  and by a

particularly specialized larval phase called phyllosoma. True lobsters have much

smaller antennae and claws on the first three pairs of legs, with the first being

particularly enlarged.

Panulirus versicolor is a species of spiny lobster that lives in tropical reefs. Other

names include painted rock lobster, blue lobster, and blue spiny lobster. In the

Philippines, it is called Banagan. Reaching as long as 30 cm in body length and

weighing 950 g ,this species has a cylindrical carapace armed with blackish spines of

various sizes. Its supra-orbital spine is stronger and more curved than in other species

of the same genus. The frontal plate is armed with two pairs of spines, the anterior

slightly larger. Its ground color on carapace is dark blue, decorated with irregular white

lines. Its dorsal surface of abdomen is colored with a central white band and a marginal

dark blue on the posterior margin of each segment. The peduncles of first antenna,

walking legs and swimmerets have longitudinal white lines. The tail fans are bluish

fringed with white lines. This species is mostly found in rocky areas and sheltered edges

of protected reefs washed by strong currents of clear water.25

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Figure 3.2 Spiny Lobsters (Panulirusversicolor)

Chitosan

Chitin and its deacetylated form, chitosan, are two biopolymers that come from

crustacean shells such as shrimp, lobsters, and crabs which have the ability to fix a

great variety of heavy metals. In this study, chitin and chitosan are the active sites of

bioadsorption. The strong affinity of metal ions for these sorbents is explained by the

relatively high proportion of nitrogen sites. Chitin and chitosan are nitrogenous

polysaccharides that are made up of acetylglucosamine and glucosamine units. In fact,

these two polymers have exactly the same basic chemical structure: (1 4)-2-

acetamido-2-deoxy-β-D-glucan and (1 4)-2-amino-2-deoxy-β-D-glucan,

respectively. (See Figure 3.3)

Figure 3.3 Scheme of chemical deacetylation of chitin to produce chitosan

Chitosan is produced at an industrial level by chemical deacetylation of chitin

using sodium hydroxide (see Figure 2.1), but chitosan can also be produced by

enzymatic deacetylation of chitin using lysozyme, snailase, neutral protease, and chitin

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deacetylase. Due to the free amino groups in chitosan, this polymer chelates five to six

times greater amounts of metals than chitin. It does not take up alkali and alkali earth

metal ions but it collects transition and post-transition metal ions from the aqueous

solution. These sorption properties have been used for environmental purposes (uptake

of heavy metals), separation processes (recovery of valuable metals), and analytical

purposes.10

Atomic Absorption Spectroscopy

This study utilizes the process known as spectrophotometric method in analyzing

the samples. In this kind of method, the radiant energy of a very narrow wavelength

range is selected form a source and passed though the sample solution contained in a

quartz cell. The amount of radiation absorbed at certain wavelength is proportional to

the concentration of the light-absorbing chemical in a sample. It is a technique

characterized by simplicity and selectivity which makes it quite adequate for the

determination of metal ions in aqueous samples.

Among the spectrophotometric methods used to determine metal concentrations,

Flame Atomic Absorption Spectroscopy is particularly useful to perform water analysis.

Flame Atomic-Absorption (AA) spectroscopy uses the absorption of light to measure the

concentration of gas-phase atoms. Since samples are usually liquids or solids, the

analyte atoms or ions must be vaporized in a flame or graphite furnace. The atoms

absorb ultraviolet or visible light and make transitions to higher electronic energy levels.

The analyte concentration is determined from the amount of absorption. Applying

the Beer-Lambert law directly in AA spectroscopy is difficult due to variations in the

atomization efficiency from the sample matrix, and non-uniformity of concentration and

16

path length of analyte atoms (in graphite furnace AA). Concentration measurements are

usually determined from a working curve after calibrating the instrument with standards

of known concentration.

To determine whether adsorption of Pb 2+ ions has occurred, there must be a

difference between the initial and final Pb2+ concentrations after treating the sample with

the Bioadsorbent. This can be analyzed by employing the method above. Flame Atomic

Absorption Spectroscopy provides a sensitive means of determining 60 to 70 elements.

The detection limit of this method for Pb2+ is 5 ng/ mL.1

Adsorption Isotherms

Adsorption is usually described by isotherms, which show how much solute can

beadsorbed by the adsorbent at a given temperature. An adsorption isotherm “...relates

the concentration of solute on the surface of the adsorbent to the concentration of the

solute in the fluid with which the adsorbent is in contact…” 19 These values are usually

determined experimentally, but there are also models to predict them, both for single

metal adsorption and multi-component adsorption. The best known adsorption

isotherms are the Langmuir and Freundlich isotherm models.

The Langmuir isotherm has three assumptions to describe adsorption: (1) The

adsorbent surface is in contact with the solution containing an adsorbate and a strong

attraction exists between the adsorbent surface and the adsorbates. (2) The solute

molecules (adsorbate) can be adsorbed to a particular number of adsorbent sites. (3) In

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the adsorption process, there is only one layer of adsorbate molecules to the adsorbent

surface.22

Figure 3.4 The Langmuir adsorption process. Scheme of the simplest adsorption of

molecules on a homogeneous adsorbent.

The Langmuir isotherm is given by the following equation:

C/qe = 1/b Qo + c/ Qo

Where Qo and b are the Langmuir model parameters, c is the equilibrium solution in

mg/L of Pb2+, and qe is the equilibrium amount of Pb2+ adsorbed into the adsorbent

which is also expressed as mg Pb (II)/ g absorbent. The shape of the Langmuir

isotherm is a gradual positive curve that flattens to a constant value. The values of

qe,max and b can be determined by linearization of this equation, followed by linear

regression or by non-linear fitting using the original form of the isotherm equation.

The Freundlich equation is one of the earliest empirical equations used to

describe equilibrium data. This model can be applied to non-ideal sorption. It often

represents an initial surface adsorption followed by a condensation effect resulting from

extremely strong solute-solute interactions. The Freundlich equation does not consider

all sites on the adsorbent surface to be equal. Furthermore, it is assumed that, once the

surface is covered, additional adsorbed species can still be accommodated. In other

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words, multilayer adsorption is predicted by this equation. The Freundlich isotherm is

expressed by the equation:

Log (q) = log (k) + (1/n) log (Ce)

Where q refers to the amount of solute adsorbed per unit weight (mg/g) of the adsorbent

used. Ce is the equilibrium solute concentration in the solution (mg/L), k and n are the

constants representing the adsorption capacity (mg/g) and the intensity of the adsorbent

respectively. In a plot log (q) versus log (Ce), the values of k and n can be obtained

from the slope and the intercept. The higher the k and 1/n, the higher the adsorption

capacity.

Review of Related Studies

Numerous studies about the different means of remediating water pollution had

been conducted by various researchers. This section presents a few of such

studies,which are also the grounds from which the idea of this research is based.

Mustafiz, et al., (2007) conducted a study on lead metal adsorption in a multi-

component solution consisting of Lead and arsenic using Atlantic cod fish scales upon

varying the pH of the solution. It was found out that the utility of fish scales as

19

Bioadsorbents associated with high Lead uptake. Elemental analysis of the scales was

also part of the their study where they were able to determine the functional groups

present in the scales and even quantify the number of sites possible for cation

exchange. The adsorptive behavior of the cod fish scales were attributed to the

predominant carbonyl and amide groups found in them.6

Kamari A., and Wang Ngah, W.S (2008) ascertained the adsorption of Lead and

Copper ions onto a sulfuric acid- modified chitosan. The chitosan they used was

isolated from shrimp scales. The pH of zero point charge, the pH at which a solid has no

net charge when submerged into an electrolytic solution, of natural chitosan and

modified chitosan are 4.15 and 3.37 respectively. They cited that varying values of the

pH of zero point charge varies according to the sources of chitosan. In their

conclusions, they have chosen the pH 6.00 and pH 5.00 as the optimum pHs for Lead

and Copper adsorption systems in order to avoid the formation of lead and copper

hydroxides which will affect the adsorbing capacity of the modified chitosan. 18

In the study of Kumar and Gayathri (2009), Bael tree leaf powder was used as

bioadsorbent for lead.The experiments showed that highest removal rate was 84.93% at

a solution with pH 5, setting the contact time at 60 min and initial concentration of 50

mg/L. The effect of contact time was also investigated and it was found out that the

maximum percent lead removal was attained after about 60 min of shaking time at

different initial concentrations. The increasing contact time increased the Pb2+

adsorption and it remained constant after equilibrium reached in 30 min for different

20

initial concentrations. 24 This study became the basis of the researcher that the time of

immersion has a significant effect on the lead uptake.

Bamgmose, J.T., Adewuyi S., et al. (2010), carried out an experiment to evaluate

the kinetics and capacity of chitosan to trap lead and cadmium ions in aqueous

solutions a 25 degrees Celsius. Their results show that the adsorption process is

concentration-driven withhigh capacity of chitosan for the adsorption of these metal

ions. The lead and cadmium adsorption kinetic behavior could not be described

usingthe Langmuir isotherm over the whole concentration range but Freundlich isotherm

conforms to theexperimental data. The sorption of the metal ions wasexamined at time

intervals under conditions of vigorous agitation.Contact time was varied between 2 to 12

h. The sorption kineticswas done at pH 4.5.23

A study conducted by Futalan, Kan, et al (2011) showed that the adsorption

data of Copper and Lead in binary systems best fit the Freundlich isotherm while data

for the adsorption of Nickel follows the Langmuir isotherm. The experiment in binary

systems showed Lead having the highest preference for adsorption to the adsorbent,

Chitosan on Bentonite (CHB), followed by Copper, then Nickel. 16

A study conducted by Sibel Tunali Akar, Asli Gorgulub, Burcu Anilanb (2011),

et al, showed that Bioadsorption of lead(II)onto S. albusbiomass has a pH-dependent

profile and lead(II) Bioadsorption was higher when pH ortemperature was increased. As

much as 88.5% removal of lead(II) is also possible in the multi-metal mixture containing

21

zinc and cadmium.The Langmuir isotherm better fits the Bioadsorption data and the

monolayer Bioadsorption capacity was3.00×10−4 mol g−1 at 45 degrees Celsius.17

Yan-Hui Li,Qiuju,Du Xianjia Peng, et al (2011), conducted a study which showed

that at pH greater than 4.4, the adsorption capacity of E. prolifera, a sea anemone,

increases rapidly with increment as a result of the ionization of the Bioadsorbent’s

COOH- groups. However, at pH greater than 6.00, hydroxides of lead already start to

precipitate. The study concludes that the optimum pH at which the Bioadsorbent

uptakes Pb (II) is at 5.0. They also found out that that a decrease in the particle size

(lesser than 89 nm) of the Bioadsorbent would lead to a larger surface area, thus

increasing adsorptive capacity. In the study,after a rapid increase in the removal

percentage of Pb2+ with increasing adsorbent dosage from 0.02 to0.08 g, it only has a

slight change as the adsorbent dosage increases from 0.08 to 0.17 g. The minute rise in

the Pb2+removal percentagemay be attributed to the attainment of equilibrium between

adsorbate and adsorbent under the experimental conditions.19

Liu L., Hongping L., et al (2011) used sesame leaf as bioadsorbent for Lead ions

in aqueous solutions. It was found out in the experiments that the adsorptive behavior

was significantly affected by initial pH, where the optimum pH for maximum Lead

adsorption to occur was pH 5. The immersion time needed for equilibrium to occur was

180 minutes. The monolayer saturation adsorption capacities of lead ions were 279.86,

283.01, and 298.76 mg Lead/ gram adsorbent at temperatures 293, 303, and 313 K

respectively.26

22

Bioadsorption studies have also been conducted in the Philippines. Fabio, J.F.

and Varquez, M.F ( unpublished, 2009) studied the lead-binding capacity of Bangus

(Chanoschanos) fish scales whose maximum binding capacity amounted to 99.7 mg

Pb/ g adsorbent at 100 ppm Pb2+ concentration with 0.1 g adsorbent. The optimum pH

was determined to be pH 4. The data best fitted with the Freundlich equation.27

Arcillas J.R., and Comaingking J. (unpublished, 2013) conducted a study on the

bioadsorption of hexavalent chromium onto Napier grass (Pennisetum purpureum).

Results showed that an initial concentration of 25 ppm showed the highest percentage

removal after treatment of 2.0000 grams of bioadsorbent. The agitation time which

yielded the highest percentage removal was 120 minutes. The adsorprtion of Cr (VI)

onto napier grass did not conform to both Langmuir and Freundlich isotherms.28

The above studies serve as the bases on which this investigation on the Lead-

binding potential of spiny lobster shells has its grounds. As posited by the previous

researches, it is inferred by the experimenter that the pH which shall optimally be

maintained in the course of this study is between ph 4-5 and temperature should be

held constant at 25 degrees Celsius. The researcher has also used the basic premises

of the previous studies in conducting this investigation.

Statement of the Problem

The study aims to investigate the Lead (II) adsorption potential of powdered spiny

lobster shells specifically with the following parameters:

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1. The effect of initial Pb2+ concentration on lead uptake at constant pH temperature,

agitation time, and mass of bioadsorbent.

2. The effect of the mass of bioadsorbent on lead uptake at constant pH, temperature,

initial Pb2+ concentration, and agitation time.

Methodology

An experimental design on the use of spiny lobster shells as an adsorbent of

Pb2+ was in this study. In the Pb2+ adsorption experiment, two parameters were

varied--- bioadsorbent mass and initial Pb2+ concentration. The schematic diagram that

follows illustrates the flow of the whole experiment.

Schematic Diagram

24

Preparation of Adsorbent Material

Figure 4.1 Experimental Flow Materials and Equipment

The following materials were utilized in the course of the experiment: powdered

spiny lobster( Panulirus versicolor) shells, rotary sieve shaker, pH- meter, analytical

grade Pb (OAc)2.3H2O, Erlenmeyer flasks, distilled water, evaporating dish, rotary

shaker, 1.0 MHCl solution dessicator, Flame Atomic Absorption Spectrometer, 1.0 M

NaOH solution, analytical balance, timer, 500 mL beaker, stirring rod, weigh boats,

volumetric flasks, acid buret, iron stand with clamp, wash bottle, and filter papers.

Sample Description and Preparation of Bioadsorbent

25

Preparation of Stock Solution

Pb2+ Adsorption Experiment

Spectrophotometric Analysis

Data Collection

Variation of initial Pb2+

Concentration

Variation of Bioadsorbent Mass

Testing of Bioadsorbent for Lead Contamination

Pilot Testing with 30 ppm Pb2+

initial concentration

Percent Chitin and Moisture Content Determination

The lobster (Panulirus versicolor) shells were taken from Inday Pina’s Sutukil, a

seafood restaurant located in Mactan, Lapulapu City, Cebu. The selection poses a

limitation to this study as the size, age and gender of the spiny lobsters were strictly

taken into account. Only the shells of the spiny lobster were used as bioadsobent

species.

The spiny lobster shells, cut into small pieces, were thoroughly washed with

water so as to remove any water-soluble impurities. After which, they were air- dried for

one week to remove moisture. This step was also important in order to have a more

precise weight of the adsorbent. The bioadsorbent’s moisture was further eliminated by

oven-drying them at 50 degrees Celsius until the weight of the shells became constant.

The oven temperature must be set at 50 degrees Celsius, since the sample involved is

a biological one. This temperature ensures that the organic matrix found in the shell will

not deteriorate. After a constant mass is achieved through oven-drying, the dry mass of

lobster shells was ground using a milling machine and sieved using a rotary sieved

shaker with 850 micrometers mesh size. The smallest possible size of ground lobster

shells was needed so that the surface area of the adsorbent will be maximized, allowing

a higher rate of adsorption. The powdered spiny lobster shells were preserved in

evaporating dishes inside a dessicator.

Preparation of stock Lead (II) Solutions

26

With 1.830 grams of analytical grade Pb (OAc) 2.3H2O inside, a 1-L volumetric

flask was filled with distilled water up to the mark in order to make a 1000 ppm

Pb2+stock solution. See Appendix C for computation

Determination of Moisture Content and Percent Chitin

The moisture content of the ground lobster shells was determined by obtaining

triplicate samples of 5.00-gram lobster shells and placing them on evaporating dishes of

constant mass. The samples were then oven-dried at 110 degrees Celsius, a

temperature higher than the boiling point of water so as to remove essential water from

the samples. Once constant weight is achieved, the masses of the samples were

measured using the analytical balance.

In order to correlate the metal-binding capacity of the spiny lobster shells to the

presence of chitin, an isolation of the said polymer was done first. The procedure will

yield a measurement of how much chitin is there for a given amount of powdered spiny

lobster shell. The European Chitin Society (1997) details how chitin can be isolated from

crustacean shells and this method was adopted in this study.29The steps are as follows:

Coarse purification entailed washing the adsorbent thoroughly; air-drying and

oven- drying it. This step was done in the preparation stage of the bioadsorbent in this

study.

27

The second step involved protein removal. Five grams of the powdered lobster

shells were prepared then added with 50 ml of 2% sodium hydroxide solution. The

mixture was heated at 60-70°C for half an hour. The shells were filtered off with a

strainer and the process was repeated. The filtrate should almost be clear and

colorless. Then the shells were washed with demineralized water.

The last step involved calcium carbonate removal where 50 mL of 7%HCl were

added to the deproteinated lobster shells. The mixture was stirred at room temperature

until no carbon dioxide gas escapes anymore. The mixture was filtered off and the

product, chitin, will be oven-dried until constant weight is achieved.

Pb2+ Adsorption Experiment

Prior to experimenting with the variations, a negative control group was tested. In

this case the negative control group consisted of 2.00 grams of the powdered adsorbent

mixed with 50 mL of distilled water. The solution’s pH was adjusted to pH 5 using 1.0 M

HCl. The mixture was subjected to agitation using the rotary shaker at 360 rpm for 2

hours enough for dynamic equilibrium to occur. The mixture inside the flask was filtered

through suction-filtration. Any trace of Pb2+ concentration in the filtrate was then

analyzed using the atomic absorption spectrometer.

28

Pilot-Testing

Duplicate samples of 30 ppm Pb2+ solutions were placed in individual

Erlenmeyer flasks. This concentration will be obtained by diluting 30 mL of the stock

solution with distilled water and 1.0 M HCl to come up with 1000 mL solutions with pH 5.

Fifty mL aliquots were prepared from this concentration. Two grams of the adsorbent

were added to each of the solutions and were agitated using the rotary shaker at 360

rpm for 2 hours enough for dynamic equilibrium to occur. The mixtures inside the flask

were separated using a strainer and was subjected to suction filtration to separate the

adsorbent from the solution. The Pb2+ concentration of the filtrates was individually

analyzed using the atomic absorption spectrometer. The absorbance was referred to

the calibration curve and the Pb2+ concentration of the filtrates will be determined.

A.Variation of Initial Pb 2+ Concentration

Duplicate samples of 40, 80, and 120, 170 and 220 ppm Pb 2+ solutions were

placed in individual Erlenmeyer flasks. These solutions of different concentrations were

obtained by diluting 40.00, 80.00, and 120.00, 170.00, 220.00 mL of the stock solution

respectively with distilled water and 1.0 M HCl to come up with 1000 mL solutions with

pH 5. This pH is the one posited by the related studies to be the optimum and will thus

be maintained to deter the formation of lead hydroxides.

Two grams of the adsorbent were added to each of the solutions and were

agitated using the rotary shaker at 360 rpm for 2 hours enough for dynamic equilibrium

to occur. The mixtures inside the flask were separated using a strainer and then

29

underwent suction filtration to separate the adsorbent from the solution. The

Pb2+concentration of the filtrate were individually analyzed using the atomic absorption

spectrometer. The absorbance was referred to the calibration curve and the Pb 2+

concentration of the filtrates was determined.

B. Variation of Adsorbent Mass

Duplicate samples of adsorbents weighing 0.50, 1.00, and 1.50 grams were

obtained using a digital balance and placed in individual Erlenmeyer flasks. Each flask

was added with 50 mL of Pb2+ solution having a pH 5. The concentration of Pb2+will

depend on which concentration in procedure A showed the highest absorbance of Pb2+.

The samples were agitated with a rotary shaker with a speed of 360 rpm at room

temperature for 2 hours also. The mixtures underwent suction filtration after being

strained and the Pb2+ concentrations of the filtrates were analyzed using the atomic

absorption spectrometer. The absorbance will be referred to the calibration curve and

the Pb2+ concentrations of the filtrates were determined.

C. Concentration Analysis of Filtrates

Standard Pb2+ solutions with concentrations of 0.05, 0.10, 0.30, 0.50, 1.00, and

3.00 ppm and pH 5 were analyzed for their absorbance. Using distilled water as blank

and the standard solutions, the maximum wavelength was identified. A calibration curve

was drawn from their absorbance and will serve as reference to determine the Pb 2+

concentrations of the filtrates. In the same manner, the absorbances of the filtrate

30

samples were determined. Their absorbance values were based on the calibration

curve.

CHAPTER 2

PRESENTATION, ANALYSIS, AND INTERPRETATION OF DATA

Data gathered from the preceding experimental procedures are presented in this

section along with their corresponding analyses and interpretation. This section

discusses the results obtained from the determination of the moisture content and

percent chitin of the spiny lobster shells. The effect of varying the initial concentration

and bioadsorbent mass on the lead-uptake of the adsorbent are presented in the form

of tables and graphs. Analyses and interpretations of the results are furnished with

accompanying literature for the purpose of clarity and conciseness.

Moisture Content Determination

The moisture content of the bioadsorbent was analyzed for reproducibility

purposes. Triplicate samples of 5.00 g spiny lobster shells were placed on evaporating

dishes having constant mass and were oven-dried at 110 degrees Celsius until constant

weight was achieved. The temperature was such in order to remove any essential water

which are chemically bonded to the structure of the adsorbent material. The percent

31

moisture with respect to the mass before oven-drying was found out to be 8.5856 %.

See Table 2.1

Table 2.1 Moisture Content Determination

Initial

Bioadsorbent Weight (g)

Final

Bioadsorbent Weight (g)

Percent Moisture (%)

5.0001 4.5718 8.5658

5.0030 4.5705 8.6448

5.0093 4.5812 8.5461

AVERAGE 8.5856 %

The percent moisture obtained can be accounted by the fact that the

bioadsorbent material had already been air-dried for two months before oven-drying in

the course of its preparation.

Percent Chitin Determination

This part of the study seeks to find any correlation between the amount of chitin

present in the boadsorbent material and its lead-uptake capacity. Chitin in the spiny

lobster shell acts as an active site for bioadsorption though it may not be the only

species involved. After coarse purification, the lobster shells underwent deproteination

and demineralization by immersion in 2% NaOH and 7% HCl respectively under chitin

was obtained. The immersion was followed with the addition of I2 in KI solution where no

discoloration of the IKI occurred, implying a positive result that chitin, not chitosan, was

32

obtained. Chitosan would have rendered the I2 in KI solution colorless upon contact.

The spiny lobster shell was found out to be composed of 21.7775 % chitin. See Table

2.2

Table 2.2 Percent Chitin in the Spiny Lobster Shells

Weight of Lobster Shells

before Treatment (g)

Weight of Chitin Obtained

after Treatment (g)

Percent Chitin (%)

5.0138 1.2019 23.9718

5.0528 1.0171 201294

5.0440 1.0709 21.2312

Average 21.7775 %

Curita, as cited by Lee30 provided a list of selected crustaceans with the

corresponding percentage of chitin and CaCO3in their structures. Apparently, there was

no entry for any lobster species. However, crab shells, which more or less have the

same structure as that of lobsters shells, were found out to have 15- 30 % chitin and 40-

50 % CaCO3. The study further emphasized that the chitin percentage varies from

species to species.

The moisture content and chitin determination are just some of the ways by

which this study characterized the bioadsorbent material. One limitation of this study is

its inability to provide the complete physico-chemical parameters like ash content and

mineral content of the spiny lobster shells.

33

Pb2+ Adsorption Experiment

Prior to proceeding with the variations, the spiny lobster shells were examined

first for any lead contamination. Results of the Atomic Absorption Spectroscopy analysis

on the negative controls indicated that there was no lead contamination on the

bioadsorbent sample as no lead ions were detected. A significant limitation on this part

of the experiment is the lack of financial resources which would have allowed the

researcher to carry out his sampling in triplicates. As such, the samples were prepared

only in duplicates.

A pilot test was also conducted in order to find the appropriate starting

conditions. Duplicate samples of 30 ppm Pb2+ solutions were analyzed using AAS after

treatment of 2.00 grams of bioadsorbent. The idea behind was to treat the solution

having the least concentration with the highest dosage of bioadsorbent in order to

ensure a reasonable range for the variation of initial concentration. Apparently, the

lead-ions were almost completely adsorbed by the bioadsorbent during the pilot test,

leaving only 0.07 ppm of lead ions after treatment. That made the researcher increase

the first denomination in the variation of initial concentrations to 40 ppm to ensure that a

notable difference can be obtained from the initial and final concentrations in the sample

variations.

Effect of the Initial Concentration on Pb2+ adsorption

34

The effect of varying the initial lead concentrations on lead-uptake by the

bioadsorbent was studied by preparing lead solutions of different concentrations ( 30,

40, 80, and 120 ppm). These were treated with 2.0000 grams of bioadsorbent, agitated

with a speed of 360 rpm, and under a pH of 5.00. Agitation time was set at two hours.

Table 2.3 summarizes the results.

Table 2.3 Effect of varying initial Concentration

Initial Concetration (ppm) Final Concetration (ppm) Percentage Removal (%)mg Pb

adsorbedLead uptake

(Qe)33.5 0.07 99.79 1.67 0.83543.5 0.12 99.72 1.99 0.99783.5 0.17 99.80 3.99 1.995

123.5 1.1 99.11 5.94 2.972174 7.3 95.80 8.13 4.067223 20.3 90.90 9.90 4.950

The table shows that the concentration with the highest percentage removal was

83.5 ppm (99.80 %) with a final concentration of 0.17 ppm lead after treatment with 2.00

grams of spiny lobster shells. The values show that there was a gradual increase in

percentage removal as the initial concentration increased from 33.5 to 83.5 ppm and

there was a gradual drop when it reached the 123.5 ppm concentration onwards. This

drop in percentage removal maybe attributed to the saturation of active coordination

sites of the bioadsorbent, as posited in the study of Rao in 2007.31 in that study, a

decrease in the percentage removal of chromium from 94.6 % to 78.6 % when initial

concentration was increased from 25 ppm to 125 ppm. In the given initial

concentrations, an increasing number of coordination sites that are utilized as the

system approaches equilibrium, thereby diminishing the final concentrations. Arcillas

35

and Comaingking28 further quote Ghoulipour in explaining that a specific amount of

bioadsorbent offers a finite amount of active sites which can accommodate a certain

amount of heavy metal adsorbate, any excess will remain in the solution once the

saturation point was reached. Figure 2.1 shows the percentage removal plotted against

the initial concentration,

0 50 100 150 200 25086

88

90

92

94

96

98

100

102

f(x) = − 0.000386725420235488 x² + 0.0525689708267184 x + 98.2951768323781R² = 0.998226308745329

Percentage Removal v.s. Initial Concentration

Percentage RemovalPolynomial (Percentage Removal)

Initial Concentration

Percentage Rmeoval (%)

Figure 2.1 Percentage Removal vs. Initial Concentration

However, a gradual increase can also be observed in the amount of lead ions

adsorbed as the initial concentration increased. The highest amount of lead adsorbed

can be attributed to the 223.5 ppm concentration. Figure 2.2 shows the linear

relationship between the increase of initial concentration and the lead-uptake (mg Pb

adsorbed per gram of the bioadsorbent).

36

0 50 100 150 200 2500

1

2

3

4

5

6

f(x) = 0.0222201749521475 x + 0.11167680959792R² = 0.997040677544868

Lead uptake v.s Initial Concetrtion

Lead uptakeLinear (Lead uptake)

Initial Concentration

Lead uptake (mg Pb/ g adsrobent)

Figure 2.2 Lead-uptake vs. Initial Concentration

The reason for the very high adsorption may be attributed to the combined

action of the chitin and CaCO3 in the structure of the bioadsorbent material. Lee, et al 32

conducted a study on the lead uptake of crab shells and asserted that the high

adsorptive capacity was due to the microprecipitation mechanism that happens to lead

once it comes into contact with the crab shell particles. In their study, the equilibrium

isotherm showed that at optimum pH 5.5, the crab shells were able to have an uptake of

1300 mg Pb per gram of adsorbent. Their results confirmed that the N-acetyl and

calcium carbonate groups of the crab shells were mainly responsible for the adsorption.

Furthermore, the removal of lead occurred mainly through dissolution of CaCO3

followed by the precipitation of Pb3(CO3)2(OH)2 and PbCO3 on the crab shell surface.

These microprecitipates were then adsorbed by the chitin. The same mechanism could

37

have had happened in this study as posited by the grayish-white coloration of the

powdered lobster shells after the solutions were filtered.

Effect of Mass of Bioadsorbent on Adsorption

Variation on the adsorbent dosage was done and its effect on lead-uptake was

studied. Samples containing 0.5000, 1.0000, and 1.5000 of spiny lobster shells were

mixed with 123.5 ppm lead solutions at pH 5, agitated at 360 rpm and 2 hours agitation

time. Table 2.4 presents the results.

Adsorbent Mass (g) Final Concentration (ppm) Percent Removal (%)

mg Pb adsorbed

Binding Capacity (Qe)

0.5002 14.5 88.3 5.45 10.91.0004 7.5 93.2 5.8 5.80

1.5 6.1 95.1 5.87 3.91

Table 2.4 Effect of Mass of Bioadsorbent at 120 ppm initial concentration

The highest percentage removal was after treatment with 1.5000 grams of

bioadsorbent (95.1%). The values show that as the amount of bioadsorbent increased,

an increase in the lead adsorbed can also be noticed. This can be primarily attributed to

the number of active sites participating in the biaodsorptive process. As the number

active sites increase, so does the number of lead being adsorbed. Figure 2.3 presents a

linear proportionality of this parameter of the lead uptake employing the line of best fit.

38

0.4 0.6 0.8 1 1.2 1.4 1.684

86

88

90

92

94

96f(x) = 6.80226781876465 x + 85.6130383943383R² = 0.870869555239743

Percent Removal v.s. Adsorbent Mass

Percent RemovalLinear (Percent Removal)Linear (Percent Removal)

Adsorbent mass (g)

Percentage Removal

Figure 2.3 Percent Removal vs. Adsorbent Mass

Similar trends can be observed in other studies concerning bioadsorption such

as those conducted by Fabio27, Wang3 and many others. Any increase in the adsorbent

dosage gives way to an increase in heavy-metal uptake due to the presence of more

active sites relative to the prior dosages.

Adsorption Isotherms

The Pb2+ binding capacity of the spiny lobster shells was investigated whether it

will fit the Langmuir and/ or Freundlich isotherms, which give an idea on how these ions

are adsorbed onto the bioadsorbent material. The initial concentration which was

considered was 120 ppm since the 170 and 220 ppm concentrations were only

conducted as a check towards the behavior of the percentage removal with further

increase in initial concentration.

39

The Langmuir adsorption isotherm describes the formation of a monolayer

adsorbate on the outer surface of the bioadsorbent, and after which, no more adsorption

occurs. This isotherm represents the equilibrium distribution of metal ions between solid

and liquid phases and is valid for monolayer adsorption onto a surface containing a

finite number of identical sites. It is represented by the following equation:

Qe= Qo KL Ce

1+ KL Ce

The Langmuir isotherm parameters are determined by transforming the equation

into linear form:

1/ Qe= 1/Qo + 1/ ( Qo * KL * Ce)

Where Ce= equilibrium concentration of adosrbate ( mg Pb/ L)

Qe= metal uptake ( mg Pb/ g adsorbent)

Qo= maximum monolayer coverage capacity (mg Pb/ g)

KL= Langmuir isotherm constant

The linearized Langmuir isotherm is plotted by graphing 1/ Qe v.s. 1/ Ce. The

values of Qo and KL can be computed from the slope and y- intercept of the graph

respectively. See Figure 2.4

40

Biodorbent

Mass

Equilibrium

Conc. (Ce)

1/ Ce Lead Uptake

(Qe)

1/ Qe

0.5002 14.5 0.068965517 10.9 0.094

1.0004 7.5 0.133333333 5.80 0.178

1.5 6.1 0.163934426 3.91 0.263

Table 2.5 Bioadsorbent Mass, Ce, 1/Ce, Qe, and 1/ Qe values

The table above shows the necessary values needed in order for a linear graph

to be drawn. The resulting graph is shown in Figure 2.4

Figure 2.4 Langmuir Adsorption Isotherm in Linear Form

0.06 0.08 0.1 0.12 0.14 0.16 0.180

0.05

0.1

0.15

0.2

0.25

0.3

f(x) = 1.65178044238745 x − 0.0283792539752346R² = 0.956235783805946

Langmuir Model

1/ QeLinear (1/ Qe)Linear (1/ Qe)

1/Ce

1/Qe

The values of Qo and KL parameters were computed to be -35.71 mg Pb/ L

and -0.0165 respectively from the equation. The figure above shows that the

bioadsorption behavior of the spiny lobster shells as bioadsorbent mass is increased

41

somehow conforms to the Langmuir isotherm as indicated by an R2 value of 0.956 of

the line of best fit.

The Freundlich adsorption isotherm is used to describe the adsorption processes

of heterogeneous surfaces.It is described by the equation

Qe= Kf Ce1/n

and its linear form is

logQe= log Kf + 1/n log Ce

Where Kf= Freundlich isotherm adsorption constant (mg/g)

Ce= equilibrium concentration of adsorbate (mg/L)

Qe= lead uptake (mg Pb/ g adsorbent)

The Freundlich isotherm is drawn by plotting log Qev.s. log Ce. See

corresponding table and graph.

Biodorbent

Mass

Equilibrium

Conc. (Ce)

Log Ce Lead Uptake

(Qe)

Log Qe

0.5002 14.5 1.161368002 5.275 1.0372528151.0004 7.5 0.875061263 5.625 0.763254311

1.5 6.1 0.785329835 5.695 0.592546842

Table 2.6 Bioadsorbent mass, Ce, log Ce, Qe, an log Qe

42

Figure 2.5 Freundlich Adsorption Isotherm in Linear form

0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.20

0.2

0.4

0.6

0.8

1

1.2

f(x) = 1.12774549051525 x − 0.263057377828557R² = 0.974676348516328

Freundlich Model

Log QeLinear (Log Qe)

Log Ce

Log Qe

From the equation of the line, the constants Kf and n, which are parameters of

the sorbent-sorbate system, are determined. Kf is an approximate indicator of

adsorption capacity. From the graph above, it was computed to be 0.53 mg Pb/ g

adsorbent. 1/n is a function of the strength of adsorption in the adsorption process. If n=

1, then the partition between the two phases are independent of the concentration. If 1/n

is below one, it indicates normal adsorption. A 1/n value greater than 1 indicates

cooperative adsorption25. In this case the 1/n value is 1.124, which means that the

adsorptive behavior is cooperative in nature. The adsorption data also fits the

Freundlich model with a relatively higher R2 value of 0.974 compared to that of the

Langmuir isotherm.

The resulting analysis may have yielded adsorption data which show conformity

to the Freundlich isotherm than to the Langmuir model. However, it is important to point

out that the adsorbent-adsorbate systems have not yet reached equilibrium state as

43

evidenced by the high percentage removal (> 90%) even at concentrations 170 ppm

and 220 ppm of Pb (II). It cannot be claimed whether the adsorption behavior can be

modeled by either of the two isotherms because of the possibility that there may be

more free active coordination sites compared to the number of adsorbate species which

impedes the system from attaining equilibrium.

Chapter 3

Summary, Conclusions, and Recommendations

Summary

This study entails the determination of some physico-chemical properties of

spiny lobster ( Panulirusversicolor) shells which make it a suitable bioadsorbent for

lead, and more importantly highlights the effects of initial adsorbate concentration and

adsorbent mass on such bioadsorptive activity. Furthermore, the favorability of the

adsorption process was examined using the Langmuir and Freundlich adsorption

isotherm models.

Spiny lobster (Panulirusversicolor) shells were air-dried for 8 weeks and were

further oven-dried at 50 degrees Celsius. These samples were then powdered. Moisture

analysis was conducted. Determination of percent chitin of the bioadsorbent material

was done through coarse purification, deproteination, and demineralization. A liter of

1000 ppm lead stock solution was prepared using 1.840 g analytical grade Pb

(OAc)2.3H2O and distilled water. Serial dilution was done to the stock solution in order to

come up with 30 (pilot test), 40, 80, and 120, 170, and 220 ppm working lead solutions.

44

Two grams of the bioadsorbent were added to these working solutions, and with the pH

set to 5, these were agitated at 360 rpm for two hours. The best concentration was

chosen to be used in the next step involving variation of bioadsorbent mass. 0.5000,

1.0000, and 1.5000 g of bioadsorbent were added to 50 mL of the lead solution with 120

ppm concentration. The final concentration for each variation was determined through

Atomic Absorption Spectroscopy with maximum wavelength at 283 nm. The percentage

removal, amount of lead ions adsorbed, and binding capacity of the bioadsorbent were

calculated and their relationship with the varied parameters was analyzed.

Findings

The powdered spiny lobster shells were found out to have 8.59 % moisture and

21.78 % chitin. In the variation of initial concentration, the 80 ppm solution has the

highest percentage removal at 99.80% and the trend truned to a gradual drop starting at

120 ppm with 99.08% removal attributed to the increasing number of coordination sites

involved which are in equilibrium with the lead ions. There is a direct relationship

between the initial concentration and the lead uptake of the bioadsorbent species. As

the initial concentration increased, so did the lead uptake. However, a nonlinear

relationship can be observed in the plot of percentage removal v.s. initial concentration.

In the variation of the bioadsorbent mass while keeping all other parameters

constant, the dosage 1.50 g showed the highest percentage removal at 95.10 %.

Increasing the adsorbent mass also increased the lead-uptake activity of the

bioadsorbent.

45

The adsorption mechanism cannot be determined whether it can be modeled by

either Langmuir or Freundlich isotherms because the system has not yet reached

equilibrium even at 170 ppm and 220 ppm Pb (II) concentrations.

Conclusions

Increasing the initial concentration and bioadsorbent mass results in an increase

in the lead-binding capacity of the bioadsorbent. At 120 ppm lead concetration, a

gradual drop in percentage removal can be observed. Adsorptive behavior of the spiny

lobster shells can be ascribed to the combined action of chitin and calcium carbonate

found in its structures. Microprecipitation of lead ions into Pb3(CO3)2(OH)2 and PbCO3

and its adherence to the chitin’s N-acetyl groups may be accountable for the high

percentage removal.. The mechanism governing lead adsorption onto spiny lobster

shells cannot be modeled by either the Freundlich or Langmuir isotherm due to the

inability of the adsorbent-adsorbate systems to reach equilibrium.

Recommendations

The researcher recommends the following to further improve this study and/ or

use this study as a springboard for future ones related to this:

Determine the other physic-chemical parameters of the bioadsorbent such as

ash content, protein content, and mineral content.

46

Investigate the effect of other parameters excluded in this research such as pH,

agitation speed, time of immersion, particle size, and temperature

Investigate the adsorption capacity of spiny lobster shells with other heavy

metals

Study the desorption capacity of the bioadsorbent

Conduct the experiment in triplicate amounts

Use large scale initial concentrations to ensure equilibrium attainment.

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47

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APPENDIX

53

Moisture Content Analysis

%Moisture= [ (Wo+Dish )− (Wf +Dish ) ][(Wo+Dish )−Wt Dish ]

∗100

TRIAL 1 TRIAL 2 TRIAL 3 AVERAGE

DISH Weight (g) Weight (g) Weight (g) Weight (g)

1 51.1236 51.122 51.122 51.122533

2 49.1016 49.1001 49.1002 49.100633

3 45.812 45.8112 45.8108 45.811333

SAMPLE Wo + Dish Wf + Dish wt. Dish Wf sample % Moisture AVERAGE

1 56.123 55.6938 51.1225 4.5713 8.5658

8.5856

2 54.1036 53.6707 49.100633 4.570067 8.6448

3 50.8203 50.3922 45.8113 4.5809 8.5461

Percent Chitin Determination

%Chitin= Wt .ChitinWt .Sample

∗100

TRIAL 1 TRIAL 2 TRIAL 3 TRIAL 4 AVERAGE

DISH Weight (g) Weight (g) Weight (g) Weight (g) Weight (g)

1 51.1394 51.1371 51.1316 51.1312 51.134825

2 44.3278 44.3253 44.3217 44.3215 44.324075

3 44.3236 44.3207 44.3169 44.3173 44.319625

Sample Wt. Sample Dish + Chitin Wt. Chitin % Chitin Avergae

54

1 5.0138 52.3333 1.2019 23.9718

21.7775 %2 5.0528 45.3387 1.0171 20.1294

3 5.0440 45.3380 1.0709 21.2312

Preparation of Stock Solution

Weight of Pb (OAc)2 3 H2O needed:

1000 mgPbLsolution∗1

g Pb1000mgPb

∗1mol Pb

207.2g Pb∗1mol Pb (OAc )23H 2O

1mol Pb∗379.33g Pb (OAc )23H 20

1mol Pb (OAc )23H 2O∗1L=1.830g Pb (OAc )23H 20

Serial Dilution of Stock Solution to Make Working Solutions:

M1* V1 = M2*V2

V1= (M2* V2)/ M1

For 30 ppm

V1= ( 30 ppm * 1000 mL)/ 1000 ppm = 30 mL then dilute to 1000 mL

For 40 ppm

V1= ( 40 ppm * 1000 mL)/ 1000 ppm = 40 mL then dilute to 1000 mL

55

For 80 ppm

V1= ( 80 ppm * 1000 mL)/ 1000 ppm = 80 mL then dilute to 1000 mL

For 120 ppm

V1= ( 120 ppm * 1000 mL)/ 1000 ppm = 120 mL then dilute to 1000 mL

Atomic Absorption Spectroscopy Analysis

Negative Control, Pilot Testing, and Variation of Initial Concentration

Sample ID Description

1896.1

1896.2

1896.3

1896.4

1896.5

MC1311-2021-01

MC1311-2012-03

MC1311-2012-03

MC1311-2012-03

Negative Control

Pilot Test ( 30 ppm after treatment)

40 ppm Pb after treatment

80 ppm Pb after treatment

120 ppm Pb after treatment

170 ppm Pb after treatment

220 ppm Pb after treatment

170 ppm Pb before treatment

220 ppm Pb after treatment

56

Variation of Adsorbent Mass

Sample ID Description1924.1

1924.2

1924.3

At 0.5 g adsorbent dosage

At 1.5 g adsorbent dosage

At 1.5 g adsorbent dosage

57

58

59

60