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Removal of aqueous solution of an organic dye DRIMARZEN BLACK-PS SG by H2O2 + UV-C, Fenton, Fenton +...
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Transcript of Removal of aqueous solution of an organic dye DRIMARZEN BLACK-PS SG by H2O2 + UV-C, Fenton, Fenton +...
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Removal of aqueous solution of an organic dye DRIMARZEN BLACK-PSSG by H2O2 + UV-C, Fenton, Fenton + UV-A and Fenton + UV-C processesand their comparison
Lakshmi Priya*, G. Swaminathan, P.V.S GiribabuDepartment of Civil Engineering, National Institute of Technology, Tiruchirappalli, India, Tel. +918220298170; email: [email protected] (Lakshmi Priya); email: [email protected] (G. Swaminathan);email: [email protected] (P.V.S Giribabu)
ABSTRACT
The process of degradation of a commercial organic dye DRIMARZEN BLACK-PS SG,
obtained from a dying industry in Tamil Nadu in India was studied using various
Advanced Oxidation Processes (AOPs) such as H2O2 + UV-C, Fenton, Fenton + UV-A
and Fenton + UV-C. Effects of various parameters like dosage of Ferrous Sulphate(II),
concentration of H2O2 and pH were studied. On increasing the Fe(II) dosage, the
degradation efficiencies of Fenton process, Fenton + UV-A process (using UV light of
356nm wavelength) and Fenton + UV-C process (using UV light of 254nm wavelength)
increase linearly and a minor decrease was observed in degradation efficiency after a
limiting value. Fe(II) dosage was found to be optimum at 15mg/l, 20mg/l and 30mg/l for
Fenton, Fenton + UV-A and Fenton + UV-C processes respectively. Concentration of
H2O2 showed an optimum value of 10mM and pH showed an optimum value of 3.5 for all
the processes. The dye degradation efficiencies were found to be 33%, 41%, 46% and
63% for H2O2 + UV-C, Fenton, Fenton + UV-A and Fenton + UV-C processes
respectively.
Keywords: Fenton; H2O2 + UV-C; Fenton + UV-A; Fenton + UV-C
C0 C
Fe (2) HOO H H 2O2 F
1. Introduction
Industrial effluents being dischargedinto land and water bodies withoutadequate treatment
deteriorate theenvironment and the textile industry isalso no exception, which releases varietyof chemicals and untreated effluentscausing major threat by
virtue ofpossessing more chemicals. They create adeficiency of oxygen, which proves to befatal for living organisms. Presence ofthese chemicals in effluents creates adifficulty for light penetration throughwater. Conventionally, treatment of textile
*Corresponding author
effluents is done by physical and chemicalmethods. Nonetheless, these methodshave a shortcoming that they do notconvert the pollutants into inert ones;instead they just transform its phase andnecessitate further treatment. These days,biological treatment methods are alsodone for dye effluent treatment. But theyalso suffer limitations. An organic dyeDRIMARZEN BLACK-PS SG obtainedfrom a textile dying industry in TamilNadu, India was used for the studies.Since the effluents are discharged into thewater and land environment, a detailedstudy is required on degradation of this
dye. Very few numbers of studies havebeen reportedin degradation ofDRIMARZEN BLACK-PS SG.
The mechanism of Fenton reaction isgiven below:Fe
2 H 2O2 Fe 3 HO OH
(1)3 2
Oxidative radicals are formed in the abovereaction by the reactions of hydrogenperoxide and ferrous ions.
The mechanism of Photo Fenton
reaction is given below:
HO H(4)
2
spectrophotometer and degradation ratewas measured by equation Eq. (6).Degradation rate 100 (6)
CoThe experiments were carried with initialdye concentration (IDC) of 10m
g/l withdifferent processes. 10mg/l was taken asthe dye concentration, since the dyeconcentration in the streams near theindustries was found to be 10mg/l. It maybe noted that the experiments were donein steady state and repeated for manytrials for concordance.
H 2O2 h HO HO (3)Fe3 H 2O h
Fe
2
The mechanism of H2O2 + UV-C isthat when UV light of wavelength lessthan 400nm falls on hydrogen peroxide,its cleavage occurs and two OH radicalsare formed [1].H 2O2 h 2HO
2. Materials and Method
(5)
2.1. Dye
An organic dye was obtained from atextile dying industry in Erode, a districtin Tamil Nadu in India. The chemicalformula of dye was not available.
2.2. Experimental Setup
The experiments were carried out in awooden box of 60cm x 60cm x 60cmdimensions to guarantee maximum use ofradiation and to avoid external radiation.UV-A lamp of 356nm wavelength andUV-C lamp of 254nm wavelength wereused. Dye solution was taken in a beaker
and stirred continuously using a magneticstirrer. The experimental setup is shown inFig. 1. The absorbance of the sample wasmeasuredat intervals
using a UV
Fig. 1. Experimental setup of the batch reactor
3. Results and discussion
3.1. Effect of variation of Ferrous
Sulphate(II) dosage on organic dyedegradation
The consequence of addition ofFerrous Sulphate(II) has been studied.Ferrous Sulphate(II) plays an importantrole in degradation of the dye
by Fentonand Photo Fenton processes. Fe2+ helps increating HO• radicals on getting mixedwith H2O2. It was observed that as theFe(II) dosage was increased in Fentonprocess, the degradation rate alsoincreased up to an optimum dosage of15mg/l as shown in Fig. 2. This could bedue to the increase in production of OH
radicals [2]. However, on further increaseof Fe(II) dosage beyond the critical value,degradation rate of dye was found todecrease. This could be attributed toscavenging [2].
3
produced reacts with H2O2 to formFe(OH)2+, that has high absorption and asa consequence the power of UV lampdecreases [3]. The optimum dosages ofFe(II) in Fenton + UV-A and Fenton +UV-C processes are 20mg/l and 30mg/lrespectively.
Fig. 2. Effect of variation of Fe(II) dosage inFenton process; IDC = 10mg/l, [H2O2] = 10mM,pH = 3.5
Fig. 3. Effect of variation of Fe(II) dosage inFenton + UV-A process; IDC = 10mg/l, [H2O2] =10mM, pH = 3.5
For Fenton + UV-A and Fenton + UV-Cprocesses, a similar trend as in Fentonprocess was observed as shown in Fig. 3and Fig. 4 respectively. On increasing theFe(II) dosage beyond a critical value, thedegradation rate decreased. This may bedue to increase in Fe3+ production as theFe2+ dosage is increased [9, 10]. The Fe3+
Fig. 4. Effect of variation of Fe(II) dosage inFenton + UV-C process; IDC = 10mg/l, [H2O2] =10mM, pH = 3.5
3.2. Effect of variation of H2O2 onorganic dye degradation
H2O2 performs the role of anoxidizing agent in the AOP process. InH2O2 + UV-C process, from Fig. 5, whenH2O2 concentration was increased from6mM to 10mM, the degradation efficiencyalso increased.
Fig. 5. Effect of variation of H2O2 in
H2O2 + UV-Cprocess; IDC = 10mg/l, pH = 3.5
4
In Fenton + UV-A and Fenton + UV-Cprocesses, 10mM was found to be criticalas shown in Fig. 7 and Fig. 8 respectively.In the presence of UV light, more OHradicals are produced and as a result,degradation rate was found to be more [7].
Fig. 6. Effect of variation of H2O2 in Fentonprocess; IDC=10mg/l, Fe(II) = 15mg/l, pH = 3.5
The increase in efficiency may be due tothe increase in production of hydroxylradicals with increase
in H2O2concentration [4, 6]. With increase inH2O2 concentration beyond 10mM, thedegradation efficiency decreased. Thiscould be due to the scavenging action ofOH radicals [4-6]. In Fenton process,from Fig. 6, a similar trend as given byH2O2 + UV-C was observed.
Thedegradation efficiency increased till acritical H2O2 concentration of 10mM,which could be due to the catalytic actionof Fe(II) [8]. On increasing the H2O2concentration beyond the critical value,the degradation efficiency decreased.
Fig. 7. Effect of variation of H2O2 in
Fenton + UV-A process; IDC = 10mg/l, Fe(II) = 20mg/l, pH =3.5
Fig. 8. Effect of variation of H2O2 in Fenton + UV-C process; IDC = 10mg/l, Fe(II) = 30mg/l, pH =3.5
3.3. Effect of variation of pH on organicdye degradation
The pH significantly contributes todye degradation. In all the processes, theeffects of pH variation were studied. ThepH was varied by using decinormalsolutions of H2SO4 and NaOH solution. InH2O2 + UV process, from Fig. 9, whe
n pHwas increased from 2.5 to 3.5, degradationefficiency increased. The increase indegradation rate may be due to increasedproduction of OH radicals [3, 4]. WhenpH value is less than 2.0, dye degradationis reduced. This occurs since the hydrogenions begin to work as OH radicalscavengers [6]. When pH was increasedbeyond 3.5, the degradation efficiencydecreased. This could be due to thedecomposition of hydrogen peroxide intomolecular oxygen and not into OHradicals at higher pH.
5
Fig. 9. Effect of variation of pH in H2O2 + UV-Cprocess; IDC = 10mg/l, [H2O2] = 10mM
Fig. 11. Effect of variation of pH in Fenton + UV-A process; IDC = 10mg/l, Fe(II) = 20mg/l, [H2O2]= 10mM
Fig. 10. Effect of variation of pH in Fentonprocess; IDC = 10mg/l, Fe(II) = 15mg/l, [H2O2] =10mM
In Fenton process from Fig. 10, thecritical value of pH was 3.5. On increaseof pH beyond 3.5, degradation ratedecreased, which might be due to theproduction of complex compounds of ironwhich hinders degradation. In Fenton +UV-A and Fenton + UV-C processes, thedegradation efficiency increased when pHwas increased up to 3.5 and on furtherincrease, the degradation efficiency gotreduced as shown in Fig. 11 and Fig. 12respectively.
Fig. 12. Effect of variation of pH in Fenton + UV-C process; IDC = 10 mg/l, Fe(II) = 30 mg/l,[H2O2] = 10 mM
4. Comparison of various processes
After performing all the fourprocesses, the degradation efficiency wasthe maximum for Fenton + UV-C. Thedegradation efficiencies shown in Fig. 13for H2O2 + UV-C, Fenton, Fenton + UV-Aand Fenton + UV-C were 33%, 41%, 46%and 63% respectively at 30 minutes. FromFig. 13, it was found that Fenton + UV-Cprocess is having the highest degradationrate.
Fig. 13. Comparison of degradation efficiencies ofall processes (1-Fenton, 2-Fenton
+ UV-A, 3-Fenton + UV-C, 4-H2O2 + UV-C)
5. Conclusions
Four methods were used for dye
degradation studies; H2O2 + UV-
C, Fenton, Fenton + UV-A and
Fenton + UV-C. The influenceof
variousparameters like effects
of variationof pH, H2O2 concen
tration andFerrous Sulphate(II)
dosage wasstudied.
The optimum conditions for H2O2
+ UV-C are pH of 3.5 and H2O2
concentration of 10mM. H2O2 +
UV-C showed a degradationefficiency of 33%.
The optimum conditionsforFenton process are Fe2+ do
sage of15mg/l, pH of 3.5
and H2O2concentration of 10mM.
Fentonprocess showed a
degradationefficiency of 41%.
The optimum conditionsforFenton + UV-A process
areoptimum Fe2+ dosage of
20mg/l,pH of 3.5 and H2O2 concent
rationof 10mM. It showed a degra
dationefficiency of 46%.
The optimum conditionsforFenton + UV-C process
are Fe2+
6
dosage of 30mg/l, pH of 3.5 and
H2O2 concentration of 10mM. It
showed a degradation efficiency
of 63%. H2O2 + UV-C process was
havingleast degradation which
could bedue to the absence
of Fe(II)catalyst, which enhancesproduction of OH radicals.
Fenton + UV-A and Fenton + UV-
C processes had more degradation
rate than Fenton process which
might be due to the presence of
UV light, which helps in larger
production of OH radicals. The difference in degr
adation ratebetween Fenton + U
V-A andFenton + UV-C processes
is duethe difference in the
UV lampsused.
Nomenclature
t - time (s)C0 - Concentration at t = 0 (mg/l)C - Concentration at t =‘t’ (mg/l)
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