chapter 3 materials and methods -...
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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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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)