8/3/2019 Photo Catalytic Treatment of Paper and Pulp Industry Effluents Using TiO2 Deposited Calcium Alumino Silicate Beads
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Photo catalytic Treatment
of Paper and Pulp IndustrialEffluents using TiO2Deposited Calcium
Alumino-Silicate Beads
Research Paper ByS. Ananda, H.P. Shivaraju, Dr. K. ByrappaDepartment of Studies in Chemistry, Department ofStudies in Environmental Science,Department of Studies in Geology,University of Mysore, Manasagangothri, Mysore- 570006, India
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IntroductionThe initial interest in thephotocatalysis was started whenFujishima and Honda discovered thephotochemicalsplitting of water into hydrogen andoxygen with TiO2.The catalyst absorbs a photon of lightmore energetic than band gap of thecatalyst.Main Advantage:Because the process gradually breaksdown the contaminant organicpollutants, no residue of the original
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TiO2+ hv e- CB (TiO2) + h+CB (TiO2)
h+ + OH- OHOOO2 + e- O-2 OO-2O + H+ HOO2HOO2 + HOO2 H2O2 + O2H2O2 + O-2 O OHO + OH-H2O2 + hv 2OHOH2O2 + e- OH- + OHO
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Paper and pulp industryeffluentsIn India, pulp and paper mills are now
considered as the
nations third largest polluter and it has been
estimated that this industry is
responsible for 50% of all the waste dumped into
the nations waters.
The main
component groups of wood are cellulose and
lignin.
The ul in and bleachin ste s enerate most
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Pulping -the raw material is treated mechanically or
chemically to remove lignin in order to facilitate cellulose
fibre separation and to improve the papermaking properties
of fibres.Bleaching -process to whiten and brighten the pulp through
removal of residual lignin.
The effluents generated by the mills are associated withthe following major problems:
1. Dark brown coloration of the receiving water bodies
result in reduced penetration of light, thereby affecting
benthic growth and habitat.
2. High content of organic matter, which contributes to
the biological oxygen demand (BOD) and depletion of
dissolved oxygen in the receiving ecosystems.
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3. Significant solid wastes from pulp and paper mills
include bark; reject fibres, wastewater treatment plant
sludge, scrubber sludge and boiler and furnace ash.
4. Sludge disposal is a serious environmental problem due
to the partitioning of chlorinated organic from effluents
to solids-Harmful to the fish population.
5. The major air emissions are fine and coarse
particulates from recovery furnaces and burners, sulphur
oxides (SOx) from sulphite mills, volatile organic
compounds (VOC) from wood chip digestion, spent liquor
evaporation and bleaching, Volatile organics include carbon
disulfide, methanol, methyl ethyl ketone, phenols, terpenes,
acetone, alcohols, chloroform, chloromethane, and
trichloroethane.
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In order to increase the photocatalyticefficiency of photocatalyst, attemptsmade based on the immobilization of thephotocatalysts on various supportingmaterials.In the present work, CASB of 0.5 to 1 mmdiameter as the supporting material fordeposition of TiO2 by hydrothermaltechnique has been used.Photoreactor setupcarried out batch scale photoreactor.
photoreactor :100 ml standard borosilicatereaction vessel ke t on heatin late with
Use of caSB balls
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The effluent and suspended catalysts
continuously mixed by magnetic stirrerReactor vessel was exposed to the light
sources in a closed chamber provided
with UV light source (Sankyo Denki,
Japan, 8W) and visible light sourcePhili s 220V 15W India .
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The experimental runs were carried out for 5 h
duration.
COD was estimated for the effluent before and afterthe photochemical treatments to observe reduction
of carbon contents in the effluent.Based on the COD results the photocatalytic
degradation efficiency was calculated by usingEquation
Photocatalytic degradation efficiency() =
((initial COD final COD)/ initial COD) * 100
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Results and discussion
The photocatalytic degradation rate of organics
depends on various experimental parameters:
Photocatalyst load
Temperature
pH
concentration of organic substrate
Light sources
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Lightsource: UV
lightPaper &pulpindustrialeffluent
Irradiationtime: 5 hInitial pH: 10
100
80
60
40
20
0
0 10 20 30 40 50 60 7080 90 100
Effect of photocatalysts load on the photocatalytic
degradation efficiency.
Amount of photocatalyst load in mg
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Photocatalytic degradation efficiency was gradually
increased up to 87 % when the photocatalyst load was
increased up to the range of 60 mg/50ml and beyond 60
mg/50 ml the photocatalytic degradation efficiency slightly
decreased.It is due to the increased number of active sites available on
the surface of deposited photocatalyst for the photoreaction.
The large number of active sites in turn increases the rate ofradical formation in the aqueous solution.The photochemical reaction rate was slightly reduced
beyond the 60 mg of photocatalyst load due to the large
amount of photocatalyst load in the effluent leads to light
scattering and reduction in light penetration through the
effluent.
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Photocatalytic experiments were carried out at differentlevels of initial pH ranging from 2 to 12.
The minimum rate of photodegradation (43%) was
recorded at pH 5.5
Photocatalytic efficiency of COD removal
from the effluent increased under alkaline conditions due
to increase of hydroxyl ions, which induces more
hydroxyl radicals that can form hydrogen peroxide.
Under acidic conditions, the per-hydroxyl (HO2) radical
can form hydrogen
peroxide, which in turn gives rise to the hydroxyl
radicals.
Effect of pH
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Effect of temperatureThe photocatalytic treatment of effluent has been studied
at different temperatures in the range 293-323 K.Constant temperature (> 303 K) of the effluent was
maintained by keeping the reaction vessel on the heating
plate provided with magnetic stirrer and the low
temperature ( 293 K) was maintained by keeping thereaction vessel in the cold water bath with continuous
stirring.Photocatalytic treatment efficiency was reached up to
100 % in the temperature range of 323 K within 3 h and the
same rate of photocatalytic degradation (96%) was
achieved in the range of 313 to
318 K for 4 h irradiation time.Results obtained show the rate of photochemical reaction
increases with an increased experimental temperature, itenhanced the photocatalytic treatment efficiency of the
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Photocatalytictreatmentundersunlight, 5
hirradiationtime
PhotocatalytictreatmentunderUV light, 5 h
irradiationtime
Initial
COD inmg/l
Final
CODinmg/l
COD
removal%
Initial
COD inmg/l
Final
CODinmg/l
COD
removal%
Untreatedraweffluent
2700 459 83 2700 351 87
Conventio1040 52 95 1040 20.8 98
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Under uv lightUnder visible light
Under sunlight100
80
60
40
20 0
0 1 2 34 5
PhotocatalyticDegradation
%Irradiation timein hrs
CODin
mg/l
2500
2000
1500
1000
500 0 1 2 3
4 5Irradiation timein hrs
a) b) Under uv light
Under visible lUnder sunligh
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Scope of photocatalytictreatement
The future of this technology will depend on demand due
to current and emerging pollution issues and innovative
reactor designs that maximize the effectiveness of
photocatalysis so it can compete economically withestablished technologies like activated carbon
adsorption and biological treatment.
It offers great potential as an industrial technology for
detoxification of wastewater due to several factors:
1. The process occurs under ambient conditions very
slowly; direct UV light exposure increases the rate of
reaction.
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2. The formation of photocyclized intermediate products,
unlike direct photolysis techniques, is avoided.
3. Oxidation of the substrates to CO2 is complete.
4. The photocatalyst is inexpensive.
Although photocatalytic reactors have the potential to
oxidize compounds to carbon dioxide and water, the
reactor design must provide sufficient conditions
(residence time, mass transfer and UV flux) to ensure that
complete oxidation takes place.
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references
International Journal of Chemical EngineeringResearch ISSN 0975 - 6442 Volume 2, Number 2(2010), Research India Publicationshttp://www.ripublication.com/ijcher.htm (slides-2,3,7-16)
Treatment of Pulp and Paper Mill Wastes bySuresh Sumathi, Indian Institute of Technology,Bombay, India
Yung-Tse Hung, Cleveland State University,Cleveland, Ohio, U.S.A. (slide- 4, 5, 6)
Fujishima A., and Honda, K., 1972,Electrochemical photolysis of water at asemiconductor electrode, Nature., 238. ( slide-
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QUESTIONS?
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