CHAPTER 3 MATERIALS AND METHODS - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/14691/8/08_chapter 3.pdf · CHAPTER 3 MATERIALS AND METHODS 3.1 GENERAL Studies were conducted

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CHAPTER 3

MATERIALS AND METHODS

3.1 GENERAL

Studies were conducted for the degradation and dechlorination of

three chlorophenols. The methodology for the degradation studies by ferrate,

ferrous and zero valent iron are explained in detail along with the

experimental set up diagrams. The different methods and instruments

involved in the analysis of the samples are also described. All the glassware

including sample tubes were washed with grade 1 detergent and was rinsed

thoroughly with distilled water. The glassware was then dried in hot air oven

at 105°C to remove residual moisture.

3.2 MATERIALS AND METHODS

All the chemicals which were used in the research were of

analytical reagent grade.

3.2.1 Chlorophenol stock solution

4-Chlorophenol (CP), 2,4-dichlorophenol (DCP) and 2,4,6-

trichlorophenol (TCP) were purchased from CDH, India. As the chemicals

were of analytical grade, they were used as such without any further

purification. Stock solutions of 10,000 mg/L of chlorophenols were prepared

by dissolving 5 g of the chlorophenol along with 4 to 5 pellets of sodium

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hydroxide (for the dissolution of chlorophenols in water) in 500 mL distilled

water. The stock solution was stored in a clean amber colored bottle.

3.2.2 Preparation of potassium ferrate

Potassium ferrate (K2FeO4) is an amethyst coloured solid in which

the oxidation state of iron is +6. It was synthesized by direct electrochemical

process through sacrificial anodic electrolysis with iron rod as anode, Ti/Pt

mesh type electrode as cathode and 200 mg/L of KOH and 200 mg/L of

NaOH as electrolyte (Lapicque and Valentin 2002). The electrodes were

purchased from M/s. Titanium equipment and anode manufacturing company

limited, Chennai, India. The area of the cathode was 10 × 5 cm and its

effective surface area was 27.7 cm2. The area of the anode was 10 × 5 cm and

its effective surface area was 50 cm2. The reactor was made up of glass,

having two compartments in H shape divided in between with porous Teflon

disc which allows only the diffusion of ions. The concentration of the ferrate

in aqueous phase was estimated by titrimetric method using alkaline chromite

solution (Schreyer et al 1950). The concentration of ferrate produced ranged

from 1.9 g/L to 4.8 g/L. The basic principle behind the preparation of ferrate

is the redox reaction given below.

Fe + 8 OH-

(FeO4)2-

+ 4 H2O + 6 e-

(3.1)

Figure 3.1 shows the photographs of set up for the preparation of

aqueous ferrate solution.

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Figure 3.1 Photographs showing electrochemical production of ferrate

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3.2.3 Preparation of ferrous alginate beads

Instead of preparing iron immobilized by exchanging calcium with

ferrous of calcium alginate beads (Rocher et al 2010, Kim et al 2010) which

requires treatment with ethanol, in this study ferrous alginate beads itself was

prepared by a very simple procedure. Saturated solution (10 mL) of ferrous

sulphate was mixed thoroughly with sodium alginate (1 g) to make a semi

solid paste. This paste was introduced drop wise with the help of a dropper

into a beaker containing distilled water adjusted to pH 2 with concentrated

sulphuric acid. Within 5 min, the drops of ferrous alginate in the presence of

acidic medium solidified into tiny pear shaped light green solids. The size of

the beads varied from 1-3 mm. Figure 3.2 shows the freshly prepared ferrous

alginate.

Figure 3.2 Photograph showing freshly prepared ferrous alginate beads

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3.2.4 Preparation of zero valent iron (ZVI) immobilized silica

The preparation was carried out by simple liquid - phase reduction.

About 1 g of silica was first washed with water. The wash water was decanted

and the silica was soaked in saturated FeSO4.7H2O solution ( 6.5 g in 25 mL

with 2 drops of Conc. H2SO4), for half an hour. After that, the soaked silica

along with the saturated FeSO4.7H2O solution was sonicated in an ultrasonic

bath (Bandeline, Sonorex RK 52 H) for half an hour. During sonication, the

silica gets broken down to small pieces (1-3 mm). After sonication, the silica

was washed thoroughly with distilled water. To the washed silica, 10 mL of

0.1M NaBH4 was added slowly at ambient temperature, pressure and

atmosphere. The ferrous ion immobilized into the silica was reduced to ZVI

as per the following equation.

Fe2+

+ 2BH4-

Fe0 + 2 B

3+ + H2 (3.2)

When the evolution of hydrogen gas ceased, the water was

decanted and the silica was washed again quadruple time with distilled water

to remove residual ferrous and unattached ZVI. The iron containing silica was

dried and stored in a container without any preservative or controlled

atmosphere. Figure 3.3 shows the photograph of freshly prepared ZVI

immobilized silica.

Another experiment was carried out to impregnate ZVI on silica

without sonication. The protocol mentioned above was followed as it is,

except sonication. As soon as the hydrogen evolution ceased, the silica was

washed with distilled water. Almost all the black patches covering the silica

came off with wash water whereas in case of sonication the ZVI impregnation

was firm.

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Figure 3.3 Photograph showing freshly prepared ZVI immobilized silica

3.3 EXPERIMENTAL SET UP

All the experiments were carried out in triplicates and the

efficiency of the system with respect to chlorophenol concentration, COD and

TOC had standard deviation of 5%.

3.3.1 Degradation by ferrate and sono ferrate method

A 600 mL beaker was used as a reactor vessel for ferrate method.

The experimental set up for sono ferrate method is shown in the Figure 3.4.

Ultrasonic bath (Bandelin sonorex RK 52) of fixed frequency (35 kHz) was

used as source of ultrasound. The input power of the sonicator is 140 W. The

dimension of the bath was 18 cm x 21 cm x 16 cm and that of the tub was 15

cm x 11 cm x 10 cm. The liquid depth in the tub was maintained at 2/3rd

of its

total depth. A 1L standard flask was used as a reactor vessel. The vessel was

immersed into the bath in such a way that the reactant solution was

completely immersed into the aqueous bath media. The reactor volume for

both ferrate and sono ferrate was taken as 500 mL. At regular intervals, the

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samples were drawn out and ultracentrifuged at 5000 rpm for 10 min and then

the chlorophenol concentration, COD and TOC were measured.

Figure 3.4 Experimental setup for sono ferrate method

3.3.2 Degradation by heterogeneous and sono heterogeneous Fenton

method using ferrous alginate

The experimental set up is similar to that of ferrate and sono ferrate

for heterogeneous and sono heterogeneous Fenton respectively. A known

quantity of hydrogen peroxide and ferrous alginate were added into the

chlorophenol solution. At regular intervals, the samples were drawn out and

then the chlorophenol concentration, COD and TOC were measured.

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3.3.3 Dechlorination by ZVI immobilized silica

Experiments were conducted out to transform chlorophenols in

continuous column mode in which 500 mL of initial volume of CPs were

recirculated using flow rate controllable peristaltic pump (Microlins, PP10

EX). Figure 3.5 shows the experimental set up. The total length of the column

was 47 cm, outer diameter and inner diameter were 1.10 and 0.85 cm

respectively. For the initial study, ZVI silica packed column height was taken

as 10 cm and the flow rate was 1L/h. The pH of the solution was adjusted

with concentrated sulphuric acid/ sodium hydroxide (1M). The initial

concentration of the chlorophenols and the reactant volume was taken as 100

mg/L and 500 mL. As ZVI is known for dechlorination only, the samples

drawn out at regular interval was analyzed for chloride ions by Ion

chromatography.

3.4 ANALYTICAL METHODS

3.4.1 pH

The pH of the solution was measured using Elico pH meter model

L1 120. The initial pH of the solution was set appropriately using dilute

sodium hydroxide or sulphuric acid. The instrument was calibrated using

buffer solutions pH 4.0 and 9.2.

3.4.2 Chlorophenol concentration

The chlorophenol concentration was determined

spectrophotometrically by 4- amino antipyrine method (Method No. 5530D,

APHA 2005). Chlorophenol reacts with 4- amino antipyrine in the presence of

an oxidizing agent (potassium ferricyanide) at pH 8 to form a colored

antipyrine dye. The absorbance was measured at 500 nm in Spectronic 20

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Genesys spectrophotometer. The detectable limit was found to be 0.30 mg/L,

0.25 mg/L and 0.58 mg/L for CP, DCP and TCP respectively

Figure 3.5 Photograph showing experimental set up for dechlorination

of chlorophenols by ZVI immobilized silica

3.4.3 Electrical Conductivity

The electrical conductivity of the sample was measured using a

conductivity meter (WTW LF 197). Standard solutions of 0.1N and 0.01N

KCl were used for calibrating the instrument.

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3.4.4 Total Dissolved Solids

The TDS content was determined by evaporation method detailed

in Standard Methods (APHA 2005). A known volume of sample was filtered

through Whatmann filter paper (0.45 m) and the filtrate was evaporated in a

water bath. The increase in the weight denoted the TDS content.

3.4.5 Chloride by titrimetric method

Argentometric titration was performed to estimate the chloride

content in the effluent as in method No. 4500 Cl-B (APHA 2005). The

chloride ion was titrated against standardized silver nitrate solution using

potassium chromate as indicator. The end point is the appearance of persistent

reddish brown tinge.

3.4.6 Chloride by Ion chromatograph

The expected end product of dechlorination study (chloride ions)

were analysed by Ion Chromatograph, Dionex DX-120 provided with Ion

pack AS-4 Column, a pre guard column, auto suppression and a conductivity

detector. The eluent used was 3.5 mM Na2CO3 + 1.0 mM NaHCO3 at a flow

rate of 1.0 mL/min. The samples were filtered through Gelman 0.2 µ acrodisc.

The retention time for chloride was 4.20 ± 0.50 min.

3.4.7 Chloride by chloride ion selective electrode

The chloride ion selective electrode (Type-ECl) was used to

identify the chloride ions present in the solution during the adsorption study

for ferrate method. A double junction reference electrode (PPC models ER -

74 & ER – 75) was used. It was connected with Elico pH meter model

L1 120.

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3.4.8 Ferrous/ferric ion

Ferrous / ferric ion present in the samples were determined

spectrophotometrically by 1,10-phenanthroline method as per the procedures

described in method no. 3500 Fe-D (APHA 2005). Ferrous ion reacts with

1,10 phenanthroline solution at pH 3-4 to form a red color complex Ferroin.

The intensity of the color was measured at 510 nm using 1cm cell. Total iron

was found by reducing the ferric present in the sample with hydroxylamine

hydrochloride. The difference in ferrous and total iron gives the concentration

of ferric ion.

3.4.9 Chemical Oxygen Demand

Chemical Oxygen Demand (COD) were determined by open reflux,

dichromate titrimetric method as described in Standard Methods (APHA

2005). To known volume of sample, a known amount of potassium

dichromate was added, mercuric sulfate was added to remove chloride ion

interference and the mixture was open refluxed with concentrated sulfuric

acid - silver sulfate reagent for 2 h. The amount of unreacted dichromate was

determined by titration against a standard ferrous ammonium sulfate solution

using ferroin as the indicator. The difference between the dichromate

originally added and the dichromate remaining unreacted gives the amount of

dichromate used for the oxidation of organic compound.

3.4.10 Estimation of potassium ferrate

The alakline chromite method was developed by Schreyer et al

1950. It is based on oxidation of chromite in strongly alkaline medium with

ferrate ion as shown in equation below.

Cr(OH)4- + FeO4

2- + 3H2O Fe(OH)3 (H2O)3 + CrO4

2-+ OH

-(3.3)

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This method is applicable for the analysis of low concentration of

ferrate. 150 mL of distilled water was added to alkaline chromite solution

containing 0.15 to 0.20g of potassium ferrate. This mixture was acidified with

60-70mL of 1:5 sulphuric acid and 15 mL of sulphuric acid-phosphoric acid

mixture. Near about 5 – 6 drops of sodium diphenylamine indicator was

added and titrated immediately against standard dichromate solution. The end

point is change in colour from purple to light green.

3.4.11 Total Organic Carbon

Total organic carbon (TOC) of the initial and electrolyzed solution

was determined using TOC analyzer micro N/C model 1997 manufactured by

Analytika Jena (Germany). After the collection of the sample, the pH was

adjusted to 2.0 using dilute ortho phosphoric acid (10 %). Then the sample

was stored at 4 C until analysis. The inorganic carbon present in the form of

carbonate or bicarbonate was removed by purging oxygen for 1 min before

analyzing TOC. The sample aliquot was catalytically combusted at high

temperature in an oxygen stream. The organic constituents were converted

into carbon dioxide. The carbon dioxide thus generated was measured in a

Non Dispersive Infra Red (NDIR) analyzer after condensation and drying of

the combustion products. The instrument was operated at 680 C temperature,

200 L sample injection with oxygen flow rate of 12 mL/minute and 3 min

strip time.

3.4.12 EDX-HRSEM Analysis

The morphology and chemical analysis of the ferrous alginate

beads were determined by Energy Dispersive X-Ray analysis (EDX)

combined with High Resolution Scanning Electron Microscope (HR-SEM)

from Hitachi (Model No. S- 3400 N). Gold coating was given with the help of

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Ion Sputter coater with gold target E1010. It has IRCC D camera for chamber

viewing. The EDX detector system was LN2 free and peltier cooled (139 eV).

3.4.13 GC/MS Analysis

Intermediate product identification was carried out by GC/MS.

Agilent 6890 N plus GC and Agilent 5973 N (Palo Alto, USA) mass

spectrophotometer with a quadrupole analyser was used for identification of

intermediate products. Fused capillary column used was DB 1701 with a

length of 30 m, diameter of 0.25 mm and inner diameter of 0.25µm and it was

coated with chemically bonded 14% cyanopropyl-phenyl-methyl siloxane.

The column temperature was programmed from 80°C held for 3 min to 300°C

held for 7 min at a rate of 15°C/min. carrier gas was helium (99.999%), the

flow rate was 1.2 mL/min and the scan range was 50 – 600 amu. The samples

were extracted twice with 50 mL ethylacetate. The extract was passed through

a column packed with anhydrous sodium suphate to remove trace water

(Hong et al 2003).

3.4.14 Adsorbable Organic Halide Analyzer

Thermo Total Chloride Analyzer which has an automatic sampler

introduction device was used to conduct AOX analysis. With the ThEuS

software the injection speed and – time can be set. The automatic sampler

introduction device has plunger pusher system to perform a constant

introduction rate. The furnace has two individual controlled temperature

zones with a maximum of 1250°C. The furnace is provided with a quartz

combustion tube extra oxygen to assure total combustion. Analyzer uses

argon as carrier gas and oxygen for combustion. It has a compact and

temperature controlled scrubber unit. Scrubber is filled with concentrated

sulfuric acid to remove all interfering substances and cools down the gasses.

A peltier cooled temperature controlled compartment for the titration cell. The

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unique designed chlorine titration cell, including massive silver electrodes.

The titration cell has a 35 ml capacity, thus capable of analyzing up to 60

samples without any maintenance.

3.4.15 X-Ray Diffractometer

The presence of ZVI in the ZVI immobilized silica was confirmed

by X-Ray diffraction (XRD) analysis. ET 816 X-Ray diffractometer with Cu

radiation = 1.5405A having scintillation counter detector was used for

XRD analysis

3.4.16 ICP-AES Analyzer

Apart from EDX-HRSEM, the amount of iron immobilized on the

silica was cross checked with Inductively Coupled Plasma Atomic Emission

Spectroscopy, Thermo electron corporation, UK. The iron was leached out of

the silica with sulphuric acid (0.5 M) and then iron was analysed

(Wavelength = 259.9 nm).

3.5 CALCULATIONS

3.5.1 Degradation efficiency

The degradation efficiency (DE) with respect to decrease in

chlorophenol concentration by ferrate, sono ferrate, heterogeneous Fenton and

sono heterogeneous Fenton methods was calculated by the following

expression:

.

DE (%) =Initial chlorophenol conc. Final chlorophenol conc.

x 100Initial chlorophenol conc.

(3.4)

.

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3.5.2 COD removal efficiency

The COD removal efficiency for the foresaid methods were

calculated by

COD RE (%) =Initial COD conc. Final COD conc.

x 100Initial COD conc.

(3.5)

3.5.3 TOC removal efficiency

The TOC removal efficiency which denotes the change in TOC

concentrations was calculated using the following expressions

TOC RE (%) =Initial TOC conc. Final TOC conc.

x 100Initial TOC conc.

(3.6)

3.5.4 Power dissipated

Power dissipated (Pdiss) is the actual power dissipated in the

reaction mixture by the ultrasonicator. It is calculated by calorimetric method,

using the equation formulated by Hagenson and Doraiswamy (1998).

vdiss solvent p,solvent ws w vessel p,Vessel

t 0 t 0

dTdTP m C A x C

dt dt (3.7)

dT

dt Rise in temp. of the Mixture at time t

vdT

dt Rise in temp. of the vessel at time t

Aws = Area of the wetter surface of the vessel

xw = Thickness of the inner wall

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msow = Mass of the solvent

Cpsolvent/vessel = Heat capacity of the solvent . vessel

3.5.5 Power consumption

The power consumed by electrical equipment during the

degradation study was calculated by the following equation.

Voltage (V) x Current (A) x Time (h)PC (kWh / L)

1000 x Volume of sample treated (L) (3.8)

3.5.6 Dechlorination percentage

The percentage of dechlorination was calculated by the following

formula,

Theoretical amount ofchlorine present in chlorophenol

Amount of chlorine liberatedDP% x100

Theoretical amount of chlorine present in the chlorophenol (3.9)