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Available online at www.sciencedirect.com
Journal of Photochemistry and Photobiology A: Chemistry 194
(2008) 110
Treatment of paper pulp and papercoagulationflocculation
followed by hete
ki,i,omboJune007
Abstract
In this work is investigated the combined treatment of
post-bleaching effluent from a cellulose and paper industry. The
biodegradability indexdeterminedlittle biodegcoagulationobtained
frowere chosenof TiO2 andwithout chit10 FTU of iN-ammonia90% at the
wchitosan forUV/H2O2 wfor aliphaticSO42 was fmethod (coatreated
wateshowed thatout in associ 2007 Else
Keywords: W
1. Introdu
The cellwater [13which contion. The lmay produ
CorresponE-mail ad
In memo
1010-6030/$doi:10.1016/jby the biochemical oxygen demand
(BOD)/chemical oxygen demand (COD) ratio of in natura sample was
0.11, which impliesradability and that it may not be discharged to
the environment without previous treatment. First, the effluent was
submitted to theflocculation treatment applying FeCl3 as the
coagulating agent and chitosan as an auxiliary. In sequence, the
aqueous soluble phase
m the first treatment was submitted to a UV/TiO2/H2O2 system
using mercury lamps. The optimized coagulation experimental
conditions: pH 6.0, 80 mg L1 of FeCl36H2O, and 50 mg L1 of
chitosan. The optimized photocatalysis conditions were: pH 3.0 in
0.50 g L110 mmol L1 of H2O2. COD values for the in natura sample
was 1303 mg L1 and after the optimized conditions of
coagulation
osan and in chitosan presence were 545 and 516 mg L1,
respectively. Effluent turbidity decreased sharply after
coagulations (fromn natura samples to 2.5 FTU without chitosan and
1.1 FTU with chitosan). Similarly, a decrease was observed for
concentrations ofc, N-organic, nitrate, nitrite, phosphate, and
sulfate ions after coagulation. Additionally, it was observed an
absorbance reduction of
avelength of 500 nm and of 7080% in regions corresponding to
aliphatic and aromatic groups (254, 280, and 310 nm). The use
ofquantitative purposes was not so efficient; however, it improves
sedimentation and compaction. COD results of photolyzed samples
byere 344 mg L1, UV/TiO2 326 mg L1, and UV/TiO2/H2O2 246 mg L1. The
reduction in absorbance intensity was approximately 98%and aromatic
chromophores, and 100% for chromophores absorbing at 500 nm with
color disappearance. During photodegradation,ormed (340 mg L1 for
the coagulated sample to 525 mg L1) suggesting again the
mineralization of the pollutant. The combinedgulation followed by
photocatalysis) resulted in a biodegradability index of 0.71,
transparency, and absence of color and odor in ther, suggesting
again good water quality. This result is reinforced by the toxicity
studies employing Artemia salina bioassay, whichan expressive
decrease in toxic pollutants in effluents after treatment, mainly
by combined processes. The wastewater treatment carriedation at
optimized experimental conditions provided good results.vier B.V.
All rights reserved.
astewater; Coagulation; FeCl3; Photocatalysis; TiO2
ction
ulose and paper industry employs large amounts of], and produce
equally large amounts of wastewater,stitutes one of the major
sources of aquatic pollu-ignin and its derivatives contained in
this residuece highly toxic and refractory compounds, some
ding author. Tel.: +55 44 3261 3656.dress: [email protected] (N.
Hioka).riam.
potentially mutagenic [4]. The largest volume of pollutants
areproduced in the cellulose pulp bleaching step, which
generatesseveral chlorinated compounds via chlorination, and others
toxicorganic compounds, including lignin-derived refractory
ones.This pulp and paper mill wastewater is little
biodegradable,with BOD/COD ratio (biochemical oxygen demand divided
bychemical oxygen demand) values usually around 0.020.07
[5].Research [6] reports that samples with biodegradability
indexsmaller than 0.3 are not appropriate for biological
degradation.According to Chamarro et al. [7], for complete
biodegradation,the effluent must present a biodegradability index
of at least0.40.
see front matter 2007 Elsevier B.V. All rights
reserved..jphotochem.2007.07.007Angela Claudia Rodrigues, Marcela
BorosJuliana Carla Garcia, Jorge Nozak
Departamento de Qumica, Universidade Estadual de Maringa, Av.
ColReceived 12 March 2007; received in revised form 26
Available online 12 July 2mill wastewater byrogeneous
photocatalysisNatalia Sueme Shimada,Noboru Hioka , 5790, CEP
87020-900 Maringa, PR, Brazil2007; accepted 7 July 2007
-
2 A.C. Rodrigues et al. / Journal of Photochemistry and
Photobiology A: Chemistry 194 (2008) 110
Coagulationflocculation is one of the most used watereffluent
treatments. It employees a cationic metal as a coag-ulant
agenformationent chargesthe formatiinteract wior adsorptilowed by
sdepend onstrength, asresidues inpolyelectrothus enhanrobust andand
compatoxic biodecharges inand neutraling their remas a
coagul[11,13,17
A moredation propollutantsalization [2radical oxiO3
(ozonatirradiationUV/{Fe(II)ozonation)because itas
photodeaccordingcatalysis, Csuspendedthe same tiface (adsorthat
reachetive for waprocedurematerials fiment.
UV/hetetors like Tcatalyst macatalyst surtory
speciephotocatalycost techniemployed ibilized [28range of
pHadequate foimportant plates the caadsorption
The photocatalytic reaction occurs when the semiconductoris
activated by light. The light radiation energy should be equal
or
thand gaelented fducti
h
equeundstheyundsan re
)) atl is cor ththe
ls (Els (Ents
+ H2+ HO
O2
H+
+ eC+ O2itioydrogani
withe dve inourc
tem,32,3he plationd tonalysitioh prwas
erim
ater
niumrea,t that usually promotes water hydrolysis and theof
hydrophobic hydroxide compounds with differ-, depending on the
solution pH. It may also lead toon of polymeric compounds. The
coagulant agentsth colloidal materials by either charge
neutralizationon, leading to coagulationflocculation usually
fol-edimentation [8]. Coagulation effectiveness and costcoagulant
type and concentration, solution pH, ionicwell as both
concentration and nature of the organiceffluent [9,10].
Additionally, natural and artificial
lytes can be employed as flocculation auxiliaries,cing the
processes due to their ability to generatedense flocks, which in
turn may easily form stablect sediments [4]. Chitosan, a natural
[11,12] non-gradable polyelectrolyte [1315], presents positive
acid medium due to its glucosamin units that interactize
negatively charged surface particles, thus allow-
oval [16]. Several researchers have applied chitosanant alone or
associated with iron and aluminum salts19].
complex effluent treatment is the advanced oxi-cess (AOP)
involving the conversion of organicto short species and even to
their complete miner-0] through the generation of highly reactive
free
dants [21]. Some AOP techniques [22] are: H2O2,ion),
Fe(II)/Fe(III) with H2O2 (Fenton reaction), UV(direct photolysis),
UV/H2O2, UV/catalyst/H2O2,/Fe(III) + H2O2} (Photo-Fenton), UV/O3
(photo-
, and others. Photocatalysis is an important alternativecan
eliminate refractory residues (also known
gradation and photo-oxidation methods). However,to Gogate and
Pandit [23], for successful photo-OD values must be lower than 800
mg L1 as highmaterial content leads to light scattering effects.
Atme, organic matter tends to recover the catalyst sur-ption),
which could diminish the amount of photonss photo-reactive sites on
TiO2 [24,25]. One alterna-stewater treatment is to apply a
physicalchemicalsuch as coagulation to eliminate most of the
organicrst, followed by photocatalysis as the second treat-
rogeneous treatment using metal oxide semiconduc-iO2, ZnO, CeO2,
CdS, ZnS, and others [23] as ay generates large amounts of free
radicals on theface leading to the fast degradation of many
refrac-s, usually in larger amounts than by homogeneoussis. In
addition, the heterogeneous system is a lowque [23,26]. Titanium
dioxide is a catalyst widelyn photocatalysis either in suspension
[27] or immo-]. It has low cost, is non-toxic, photo stable in a
wide
[29], recoverable after wastewater treatment, andr industrial
scale [23]. The solution/effluent pH is anarameter in heterogeneous
photocatalysis. It modu-
talyst charge and consequently affects both pollutantand
particle aggregation [30].
higherthe banat wavpromoto con
TiO2 +In s
compowherecompohVB+ c(Eq. (4radicatem. Freduceradicaradica
Polluta
hVB+
hVB+
eCB +
O2 +2HO2
H2O2
H2O2
Addform hThe ormainlyever, teffectiquate sthe sys[27,29
In tfloccuappliewere a
compofor botsalina
2. Exp
2.1. M
TitaBET athose necessary to generate the band gap. For TiO2,p
energy is 3.2 eV, which corresponds to absorptiongths shorter than
ca. 390 nm [29]. One electron isrom valence band (producing
positive holes, hVB+)on band (eCB), as describes Eq. (1) [22]: TiO2
(eCB) + TiO2 (hVB+) (1)nce there are some possibilities evolving
adsorbedat the catalyst surface by reaction with the roles hVB+
are oxidized. The hVB+ can oxidize adsorbed organicdirectly
leading them to degradation (Eq. (2)); the
acts with adsorbed water (Eq. (3)) and hydroxide ionsthe surface
producing hydroxyl radicals (HO). Thisonsidered the main oxidant
specie formed in the sys-e other hand, simultaneously the electron
(eCB) canadsorbed oxygen (Eq. (5)) producing hydroperoxylq. (6)),
hydrogen peroxide (Eq. (7)), more hydroxylqs. (8) and (9)), and
others [22,31]:+ hVB+ oxidized products (2)O HO + H+ (3) HO (4) O2
(5) HO2 (6)H2O2 + O2 (7)
B HO + HO (8)
HO + HO + O2 (9)nally, hydrogen peroxide can absorb light and
directlyxyl radicals even in the absence of semiconductor.
c compounds (pollutants) present in the medium reacth both
hydroxyl and hydroperoxyl radicals; how-egradation by hydroxyl
radical is cited as the most
these systems. As hydrogen peroxide is an ade-e of hydroxyl
radicals, the addition of this reagent toenhances the efficacy of
the photocatalysis process3].resent work, a combined treatment of
coagulation
followed by heterogeneous photocatalysis iscellulose and paper
industry effluents. All sampleszed before and after each step.
Optimal chemicalns and experimental conditions were
investigatedocesses. A bioassay using micro-crustacean
Artemiaperformed to certify water purity.
ental procedures
ials
dioxide (TiO2 P25, ca. 80% anatase, 20% rutile;ca. 50 m2 g1) was
kindly supplied by Degussa Co.
-
A.C. Rodrigues et al. / Journal of Photochemistry and
Photobiology A: Chemistry 194 (2008) 110 3
(Brazil). The catalyst was used as received. All of the
reagentsused in this work were analytical grade and were used
withoutany further
Effluenting. Analyeffluent anof
Examindeterminedincubationdescribed [try after diacid mediawas also
oVarian-Cartion of absquartz cuvelengths repcorrespondmatic
groukind of efflrings; 500 n(Tecnal-3Mwere alsostudied in j
2.2. Coagu
Coagulacoagulant ations of 0.dissolved inin jar test ufor 30 s
fo30 min, floaqueous phand FeCl3process. InFeCl3 alon
2.3. Photo
The phoUV/H2O2,samples froin optimizefridge. Thecatalysis trby a
250 W(Empalux)effluent wa(3) useda wooden mtop side 15sured by
aModel 183amounts ofthe concen
stirred during irradiation (magnetic stirrer). Four fans fit on
thebox side walls were used to reduce the heat caused by the
lamps.
atalyitherromnicf degundsl pe
a etpHt pHd 0.
L1m Hadiaol Ldiedes inl). Inon (a
par
iotox
toxicribe1)
8 h,repatest tuce4 h,d. Atrol
ults
oagu
Optifirst,
witalityidityr chrd. Thordity awas
st promounds
-
4 A.C. Rodrigues et al. / Journal of Photochemistry and
Photobiology A: Chemistry 194 (2008) 110
Fig. 1. pH influence on the coagulation of pulp and paper mill
effluent: (A) turbidity values () and concentration () of COD. (B)
Percent reduction of absorbanceintensity at several wavelengths.
Coagulation performed at 80.0 mg L1 of FeCl36H2O.
can neutralize negative charge density materials like
organicsubstances and suspended particles [24]. On the other
hand,Fe(OH)3, a hydrophobic compound, can adsorb
contaminantsparticles byto polymerare presentand precipi
3.1.2. OptChosen
was determpresented i
The datity and COvery similaboth paramand CODtration
incrFeCl36H2coagulant aan efficacymance decrthat the redshown)
andwhose valuwas raised.
From thwith 80 mgThus, this c
Even though the use of high FeCl3 quantities does not
enhanceprocess efficiency, therefore it allows coagulant
saving.
Optdiesondume a
uateres
se in50 m
L1ant aor w, wh
he mas tcom
, aftethe a
le 1.con
1).ODis n
or corada
conc
suita
Fig. 2. Effectabsorbance insurface interactions, which in some
cases can leadic entities [41]. At the chosen pH 6.0, both
compounds(mainly Fe(OH)2+), leading to pollutant
aggregationtation.
imization of FeCl3 concentrationthe adequate pH (pH 6.0), the
best coagulant quantityined. Analytical data for the coagulated
samples aren Fig. 2.a in Fig. 2(A) show that both the residual
turbid-D values against coagulant concentration exhibit ar profile,
similarly to that observed in Fig. 1(A) foreters. The profile for
these two parameters, turbidityvalues, shows a decrease as the
coagulant concen-eases, exhibiting the highest effect for 80 mg L1
ofO (Fig. 2(A)) as attested by Tukey test. For highermounts,
turbidity remained constant, meaning thatlimit was reached; while
for COD values, the perfor-eases slightly. Similarly, the results
in Fig. 2(B) showuction of absorbents species at 254, 280, 310
(not500 nm reached the highest removal at 80 mg L1,
es became constant as the coagulant concentration
ese results it is clear that at pH 6.0, the assaysL1 of
FeCl36H2O presented the best performance.oncentration was applied
for the others experiments.
3.1.3.Stu
were c
The sato eval
Thedecrea25 and50 mgcoagullevel fgroupswere tchosen
Fornatura6.0) inin Tab
For(TableBOD/Csampleover, fbiodegCODis nots of FeCl3
concentrations on final wastewater sample treated by coagulation at
pHtensity at several wavelengths.imization of polyelectrolyte
loadingof chitosan as an auxiliary polyelectrolyte coagulantcted
with 80.0 mg L1 of FeCl36H2O and pH 6.0.nalytical parameters
previously used were employedtreated effluent (Fig. 3).
ults illustrated in Fig. 3(A) indicate that the largestturbidity
occurred in experiments carried out withg L1 of chitosan, while for
COD reduction, it tookof chitosan. Absorbent reduction data showed
thatmounts of 50, 60, and 75 mg L1 neared bleachingavelengths
corresponding to aliphatic and aromaticile at 500 nm, coagulant
amounts of 25 and 50 mg L1ost efficient. Thus, 50 mg L1 of
polyelectrolyte washe optimized condition.parison sake, the
analytical results of samples in
r coagulationflocculation treatments (FeCl3 and pHbsence and in
the presence of chitosan are presented
venience, in natura effluent data are also presentedThe
calculated experimental biodegradability (ratio) is 0.11. For
indexes below 0.3, it is known that theot appropriate for
biological degradation [6]. More-mplete biodegradation, the
effluent must present a
bility index of at least 0.40 [7]. At the same time, aentration
of 1303 mg L1 indicates that the effluentble for photocatalysis
treatment as the first method,6.0: (A) turbidity () and COD (). (B)
Percent reduction of
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A.C. Rodrigues et al. / Journal of Photochemistry and
Photobiology A: Chemistry 194 (2008) 110 5
Fig. 3. Influence of chitosan concentration on coagulation: (A)
turbidity () and COD () values. (B) Percent reduction of absorbance
intensity at several wavelengths(calculated taking experimental
value without chitosan as reference). All experiments were
performed at 80.0 mg L1 of FeCl36H2O and pH 6.0.
which requires a COD value lower than 800 mg L1 for success-ful
treatment [23]. As previously discussed, the turbidity andCOD
values decrease sharply after coagulation (Table 1). Thesame
pattern is observed for all ions analyzed. The major anion inin
natura wIts concent
The stachitosan, T(values wiDespite it, tauxiliary coever in
indmay be intion and bflocks.
The opt6.0 and 80 minitial methThe aqueouphotocataly
3.2. Photo
The lighmercury lamat the samapproxima
3.2.1. pH optimizationThe effect of pH on photocatalysis
efficiency was investi-
gated employing TiO2 in in natura effluent (diluted 1:1,
v/v).The results are shown in Fig. 4.
The major percent reduction in absorbance and the lowestt
ofcien3.0.poi
O2.hanide i
s (Eqc suby chperaniorboxore,alyst
Optieffl
adatities (showficie
Table 1Analytical cha and ppH 6.0 and 50
Parameter
pHTurbidity (F.TCODa (mg LBODa (mg LN-ammoniacaN-organica
(mNitratea (g LNitritea (g LPhosphatea (Sulfatea (mg LDifferent
lette
a n = 3 sampastewater is sulfate, resulting from Kraft
technology.ration fell by almost 50% after coagulation.tistical
treatment on the data for the system withable 1, showed effluent
purification improvement
th different letters in the same line are different).he chitosan
performance is only moderate so that thisagulant was not used in
the next experiments. How-
ustrial scale applications, the use of polyelectrolytesteresting
because they promote faster coagula-etter sedimentation, producing
compact pollutant
imized coagulationflocculation conditions are pHg L1 of
FeCl36H2O. This process was used as the
od to treat cellulose and paper industry wastewater.s phase
obtained was submitted to a second step, thesis process.
catalysis studies
t source power inside the photo-reactor (3 250 W,ps) was
measured with the light meter probe placed
e position of the sample resulting in irradiance oftely 8.9 mW
cm2.
amoun
est effiat pHchargefor Tilower thydroxspecieorganiface band
padue togen, caTherefthe cat
3.2.2.The
todegrquanti
Ascess ef
racteristics of effluents in natura, after coagulation (80.0 mg
L1 of FeCl36H2O.0 mg L1 chitosan)In natura After co
9.8 4.3.U.) 10 2.51) 1303 25a 545 11) 148 5 Not me(mg L1) 1.68
0.00 NDg L1) 1.1 ND1) 168.5 13.5a 16.3 1) 44.8 0.3 NDg L1) 871.6
2.3a 14.4 1) 677.6 7.3a 341.1 rs in the same line imply values
statistically different (P < 0.05 by Tukey test). ND, nles
analyzed.remaining COD, parameters that indicate the high-cy, were
obtained in the experiment photocatalyzedThis result could be
explained considering the zeront of the catalyst (pHpcz), which
occurs at pH 6.25As the surface is positively charged at pH
values6.25 (TiOH2+), it allows the adsorption of water andons,
generating hydroxyl radicals and other oxidizings. (3)(9)). As the
same time there are adsorption ofstances and suspended materials on
TiOH2+ sur-
arge and surface intermolecular interactions. Pulpmill effluent
particles have negative charge densitynic suspended materials and
the presence of oxy-yl, and other negative groups in organic
molecules.the pollutants react with radical species formed
onsurface.
mization of TiO2 concentrationuent coagulated in the first step
was used in the pho-on process at pH 3.0 in presence of different
TiO2Fig. 5).n in Fig. 5, TiO2 increased the photo-reaction pro-ncy,
which can be noted by the increase in percent
H 6.0) and in the presence of chitosan (80.0 mg L1
FeCl36H2O,agulation After coagulation chitosan
4.21.1
8b 516 9casured Not measured
NDND
0.4b 7.0 0.5cND
0.5b 10.4 0.6c4.6b 271.0 9.2cot detectedbelow detection
limits.
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6 A.C. Rodrigues et al. / Journal of Photochemistry and
Photobiology A: Chemistry 194 (2008) 110
Fig. 4. Effect of pH on TiO2 photocatalysis: (A) percent
reduction of absorbance intensity at several wavelengths. (B) COD
concentrations. Sample in natura diluted1:1 (v/v), irradiated for
360 min in 0.50 g L1 of TiO2.
Fig. 5. Photo at sevcombined trea 60 mi
absorbance0.50 g L1than that fopercent remconcentratiincreases
pnot necessasome regiodition is nTiO2 can cof light thrlight
scatteshould bebecause decentration
tion,. Inctory
Fig. 6. EffectEffluent submcatalysis of coagulated samples: (A)
percent reduction of absorbance intensitytments. Step 1: 80 mg L1
of FeCl36H2O and pH 6.0; step 2: irradiation for 3
removal and the decrease in COD values. Forof catalyst,
purification efficacy was slightly lowerr 0.75 g L1; however,
Tukeys test proved that theoval absorbance and COD values for these
two TiO2
generaditionssatisfaons are similar. Although the presence of
the catalysthoto-oxidation yield, a high TiO2 concentration
doesrily imply a high reaction performance, at least inns with
excess catalyst. The last experimental con-ot convenient for
photodegradation because excessause strong turbidity effects, which
make the passageoughout the heterogeneous solution difficult due
toring effects [22,23]. Therefore, TiO2 concentrationoptimized for
each effluent and system employed,gradation efficiency depends on
the nature and con-of pollutants as well as on the level of free
radicals
3.2.3. OptThe coa
mum conce
The optimitodegradatiare illustra
At the mpercent abs93 to 99ever, this pand 75 mm
of H2O2 concentration on photodegradation efficiency: (A)
percent reduction of absitted to combined treatments. Step 1: 80 mg
L1 of FeCl36H2O and pH 6.0; step 2:eral wavelengths. (B) COD
concentrations. Effluent submitted ton and pH 3.0.
which is related to the photo-reactor operating con-the present
case, 0.50 g L1 of TiO2 and pH 3.0 were.imization of H2O2
concentrationgulated water sample was used to determine the
opti-ntration of H2O2 to be employed in photocatalysis.zation
studies were developed with 360 min of pho-on time, 0.50 g L1 of
TiO2, and pH 3.0. The resultsted in Fig. 6.onitored wavelengths
(except in visible region), theorbance removal undergoes a small
increase (from%) with the addition of 10 mmol L1 of H2O2. How-
arameter remains constant for further increases to 50ol L1 of
H2O2 (Fig. 6(A)). The values of remaining
orbance intensity at several wavelengths. (B) COD
concentration.irradiation for 360 min, 0.50 g L1 of TiO2 and pH
3.0.
-
A.C. Rodrigues et al. / Journal of Photochemistry and
Photobiology A: Chemistry 194 (2008) 110 7
Fig. 7. Effectitored at 280 nphotocatalysi0.50 g L1 TiO
COD (Fig.cacy); howwere much75 mmol Lues are not(5075 mmin some
cirerogeneousdiminishinpart of theverting it toby other
hyproductionhigh amoun
The H2O10 mmol Lresidual pe40 min of irresidues in
3.2.4. ComFig. 7 s
optimized qtocatalysisin the preseabsorbanceand aromat
As canpromotedphoto-excireaction islow absorpments carriof
irradiati(not shownthat hydrooxidation.
Table 2UV-photolysis data of COD and percent COD removal
calculated by comparisonto coagulated and in natura samples
2O2O22O2 +
on at pthe s
samp
O2/Hancecompso e
sorbsencal vele 2egrarisonnd 1s. Ir).CO
utaner: Uith2 o), an
nm;emo
espeto hC (ts of TiO2 and H2O2 on photo-reaction. Residual
absorbance mon-m as a function of irradiation time. Sample:
effluent coagulated;
s at pH 3.0 with: () 10 mmol L1 H2O2 (without TiO2); ()2
(without H2O2); () 0.50 g L1 TiO2 and 10 mmol L1 H2O2.
6(B)) decreased in the presence of H2O2 (higher effi-ever, at
10, 25, and 50 mmol L1 H2O2, the results
similar (COD 247 mg L1), with a change for1 H2O2, COD 205 mg L1.
However, these val-proportional to the increase in H2O2
concentrationol L1, 50% increment). Some authors [33] state
thatcumstances hydrogen peroxide may prejudices het-photocatalysis
by direct H2O2 absorption light, thus
g TiO2 photo-excitation. Another possibility is thathydroxyl
radical is annihilated by excess H2O2, con-
hydroperoxyl radical (HO2), which is suppresseddroxyl radical
producing H2O + O2. Therefore, theof hydroxyl radical decreases as
consequence of thet of H2O2 in solution.2 concentration adopted in
the next experiments was
1 at 0.50 g L1 of TiO2 and pH 3.0. Analysis of theroxide during
the reaction indicated its clearance afterradiation, which is very
important, because peroxidewastewater are hazardous to the
environment.
UVUV + HUV + TiUV + H
Irradiatiletters intests).
a n = 3
UV/Tiabsorbwhenis notilar abthe abremov
Tabphotodcompa545 asystemulation
Theto pollthe ordagree wof H2Oto 55%at 280COD r
In rmittedat 55 parison of photo-reaction conditionshows the
results for photocatalysis carried out withuantities of TiO2/H2O2,
and pH, as well as the pho-results obtained in the presence of the
H2O2 andnce of TiO2. Treatment efficiency was analyzed byin the 280
nm region, which is related to aliphatic
ic groups, including phenols.be observed in Fig. 7, even the
UV/H2O2 systemphotodegradation, which occurred by direct H2O2tation
followed by oxidation. Direct H2O2 photo-
limited by the need of light at 254 nm and thetion coefficient
of H2O2 at this wavelength. Experi-ed out only with UV light showed
that after 360 minon, the remaining absorbance at 280 nm was 32%),
while for UV/H2O2, it was 20%, which impliesgen peroxide improves
the homogeneous photo-However, the data (Fig. 7) show that while
both
thermal realiterature [2
3.2.5. KineThe ab
UV/TiO2 awavelengthkinetics mexperimentkinetic lawexperiment
The obstime (t1/2) f
The k anshowing thprocess ovealmost the sin the UV rCODa(mg
L1)
COD removal(calculated againstcoagulated) (%)
COD removal(calculated againstin natura) (%)
441a 14 19 66344b 2 37 74326c 4 40 75
TiO2 246d 1 55 81
H 3.0 and 0.50 g L1 of TiO2 and 10 mmol L1 of H2O2. Differentame
column imply values statistically different (P < 0.05 by
Tukey
les analyzed.
2O2 and UV/TiO2 systems lead to almost completeremoval after 360
min irradiation (a 94% decreaseared to coagulated effluent), the
UV/H2O2 system
fficient. Although the UV/TiO2 system shows sim-ance removal
values at 280 nm in presence and ine of H2O2, H2O2 clearly
increases the absorbancelocity.contains COD determinations for
experiments afterdation and percent COD reductions calculated
by
to after-coagulation and in natura sample values,303 mg L1,
respectively, for different photolysisradiated samples were
previously treated by coag-
D results in Table 2 show that all photosystems leadt
degradation. The efficiency improvement followsV < UV/H2O2 <
UV/TiO2 < UV/TiO2/H2O2, which
absorbance reduction results. However, the presencen TiO2
improved degradation reasonably (from 40
effect not observed on the decrease in absorbancepart of the
organic matter degradation, expressed byval, may form products
absorbing at this wavelength.ct to possible degradation reactions
in samples sub-igh temperatures in the dark, it was observed thathe
averaged temperature in the photo-reactor), thection did not occur.
This result is similar with the3].
tic studies of photodegradationsorption intensities during the
irradiation of the
nd UV/TiO2/H2O2 systems monitored at severals, such as at 280
nm, Fig. 7, were submitted toathematical treatment. Despite the low
number ofal points, the data reasonable obeyed the first-order(Fig.
8) and showed no order changes for differental conditions, which
agrees with the literature [32].erved first-order kinetic constants
(k) and the half-lifeor both systems were exhibited in Table 3.d
t1/2 values reinforced previous qualitative results,
at hydrogen peroxide accelerates the photo-oxidationr twofold.
The photo-reaction of each system showedame kinetic parameters at
all wavelengths monitored
egion. However, for both photolysis systems, the data
-
8 A.C. Rodrigues et al. / Journal of Photochemistry and
Photobiology A: Chemistry 194 (2008) 110
Fig. 8. Applic ce of:of H2O2.
Table 3Correlation co iO2/H
254 nm 280 nm 310 nm
CC 0.999 0.999 0.981k ( 102 min 2.7 2.8 3.3t1/2 (min) 26 25
21
obtained atat UV regi500 nm wadensity
ofgation/resosusceptibleThe absorprelated to arestrict congroups
whireaction vekinetic studinformationall the combe better
tocomplete ifor both, kiexperiment
In Fig. 9COD decastep producthe first 60of absorban
3.3. Combphotocatal
A summthe coagulthe samplephoto-oxidabsorbanceexperimenttion
with 80ation of first-order kinetic law to photodegradation data at
pH 3.0 in the presen
efficients values (CC), k and t1/2 for effluent irradiated at pH
3.0 in TiO2 and TTiO2 (0.50 g L1)254 nm 280 nm 310 nm 500 nm
0.994 0.994 0.993 0.9851) 1.1 1.1 1.1 1.8
63 63 63 39
500 nm show faster reaction than the ones monitoredon; for the
UV/TiO2/H2O2 system, the kinetics ats too fast to be followed.
Probably, the high electronicthe chromophore unit (aromatic rings
in high conju-nance) that absorbs light in visible regions is
moreto fast attack by the photo-generated free radicals.tion at
254, 280 and 310 nm, wavelengths which isliphatic region, aromatic
ring (phenol groups) andjugated aromatic ring, respectively,
correspond toch present lower electronic density, leading to
photo-locity slower than that one at 500 nm. However theies
performed by absorbance measurements can giveonly for determined
wavelengths that do not coverpounds present in the solution.
Therefore it woulduse TOC measurements that permit to obtain
more
nformation about complete organic mineralizationnetic and
photodegradation yielding (not performeds).it is presented data on
the sulfate ions formation and
y during irradiation. Sulfate ion appearance, at thised by
organic matter decomposition, is very fast inmin. The COD variation
profile was similar to thatce decay.
ined treatment (coagulationocculation andysis): efuent
quality
ary of the quality of in natura effluent
sample,ationflocculation treated (FeCl3) sample, and of
treated by combination coagulation followed byation
(UV/TiO2/H2O2) is analyzed as a function of
intensity, and COD and ion concentrations. Thes were conducted
in optimized conditions (coagula-mg L1 of FeCl36H2O at pH 6.0 and
photocatalysis
Fig. 9. Coag10 mmol L1appearance of
with 0.50 g360 min ofremaining
As can btially remathe final tre7080% ingroups (254removal
waent. The COcoagulationtreatment iand PO43no
significapreviously(A) 0.50 g L1 of TiO2; (B) 0.50 g L1 of TiO2 and
10 mmol L1
2O2 systems
TiO2 (0.50 g L1) + H2O2 (10 mmol L1)ulated effluent submitted to
irradiation in 0.50 g L1 of TiO2,of H2O2 and pH 3.0: () COD
concentrations decrease; ()SO42.
L1 of TiO2, 10 mmol L1 of H2O2, pH 3.0 atirradiation). The
photographs in Fig. 10 show the
samples color.e seen, the brown color of the in natura effluent
par-ined in the coagulated sample and was clarified inated water.
Coagulation reduced absorbance aroundwavelengths associated to
aromatic and aliphatic, 280, and 310 nm), while in the combined
treatment,s over 98% when compared to that of in natura efflu-D
value of in natura effluent was 1303 mg L1; after, it decreased to
545 mg L1 and after the combinedt fell to 246 mg L1. The
concentrations of NO3in effluent before and after photodegradation
showednt changes (16 and 14g L1, respectively). Asinformed, NH3 and
NO2 were eliminated by the
-
A.C. Rodrigues et al. / Journal of Photochemistry and
Photobiology A: Chemistry 194 (2008) 110 9
Fig. 10. Photocoagulation; (
coagulationproduced dfate ions ch(coagulatedof the sulfaing
sulfatedindicatingin ionic sothe mineramineralizatthe inorganand/or
degr
Additioby the coagditions. Vashown in T
The samin COD (ar(higher thacomplete bple, 514 minfer the suof
coagulatability indepositive, cofrom wastemay result
These rremoving mof pollutan
Table 4Chemical and
Sample
In naturaAfter coagulaAfter 2 h photAfter 4 h phot
a n = 3 samp
Percebined
s wereith a
atalyous twer
assacondepenity dentsegratly omplewa
tocat
seotodmillova
nclu
bes. Thegraph of samples analyzed: (a) after combined treatment;
(b) afterc) in natura.
flocculation process (step 1). These ions are noturing
photocatalysis. However, the quantity of sul-anged from 678 mg L1
(in natura) to 341 mg L1sample) to 525 mg L1 (after
photocatalysis). Part
te ions is removed by coagulation and the remain-organic
molecules are degraded during irradiation,
the mineralization process. Similarly, the increaselution
conductivity after photo-reaction reinforcedlization direction
(data not shown). Although totalion did not take place, these data
pointed out thatic compounds and organic pollutants were
removedaded to simpler compounds.
nally, another in natura effluent sample was treatedulation
followed by photocatalysis in optimized con-lues of COD, BOD and
biodegradability results areable 4.ple treated by coagulation
showed a strong decreaseound 56%) and a biodegradability index
equal 0.50n 0.40), which means that the effluent can
undergoiodegradation [7]. The COD of the coagulated sam-g L1, is
lower than 800 mg L1, which allowed toccess of the photocatalysis
process. The associationion with 2 and 4 h of photocatalysis lead
to biodegrad-x of 0.63 and 0.71, respectively. These results are
very
Fig. 11.and comsolutiondiluted w
photochazardiments
Biomized
IndmortaltreatmPhotodpendenan exa
samplein phoindex.
Thetion/phpaperthe rem
4. Co
Thecessesnfirming the high level of elimination of
pollutantswater and that biological treatment in the next stepin
complete organic mater degradation.esults indicate that the water
quality is improvedaterials by coagulation followed by the
conversion
ts to simpler and biodegradable compounds applying
biochemical oxygen demand values and biodegradability index
COD (mg L1)a BOD (mg L1)a BOD/COD1162 3 172 1 0.14
tion 514 14 257 3 0.50ocatalysis 204 7 129 2 0.63ocatalysis 205
6 145 2 0.71les analyzed.
FeCl3 as awater efficwhich mayof turbiditycoagulant
dabsorbanceand compa
The adddid not enincreased tefficient th
The cothe inorgaresults. Thcoagulationthat the finant death
ofArtemia salina for samples: in natura, after
coagulation,coagulation-photodegradation for several irradiations
time. Allneutralized to pH 7 before bioassay. The untreated
effluent was
queous NaCl, 3.8 g L1 (v/v).
sis. However, some of the residues formed may beo aquatic
environment. Therefore, biotoxicity exper-e carried out.y results
of all effluents (in natura and treated in opti-itions) using A.
salina are illustrated in Fig. 11.dently of effluent concentration,
the index ofA. salinaecreased after effluent coagulation for all
sampleand was improved by photocatalysis purification.dation
efficacy showed to be almost the same, inde-f irradiation time,
being 1 h seemingly sufficient. As, at 83% effluent, the mortality
index in in natura
s 97%, while in coagulated effluent, it was 50% andalyzed water,
it was around 25%, the highest survival
results demonstrate that the combined coagula-egradation method
investigated to treat pulp andeffluents may be used to reduce water
toxicity byl and/or degradation of pollutants.
sion
t experimental conditions were obtained for both pro-first
treatment step, coagulationflocculation usingcoagulant agent,
eliminated several impurities fromiently, allowing the replacement
of aluminum salts,be hazardous health [8,17]). Although the
reductionin chitosan presence was observed, this auxiliary
id not contribute significantly to decrease COD and. However
chitosan improves sedimentation velocityction.ition of hydrogen
peroxide to the UV/TiO2 systemhance degradation yields
substantially; however ithe photo-process velocity. UV/TiO2/H2O2
was morean UV/TiO2, UV/H2O2 and UV were.mbined method reduced the
organic charge andnic pollutant species in effluent with goode
biodegradability index for effluent submitted toflocculation
followed by photocatalysis showedl sample is suitable for complete
biological degrada-
-
10 A.C. Rodrigues et al. / Journal of Photochemistry and
Photobiology A: Chemistry 194 (2008) 110
tion. The experimental application of the combined treatmentsto
cellulose and paper industry effluents exhibited
promisinglarge-scale perspectives.
Acknowledgements
The authors wish to thank Dr. Edivaldo Egea Garcia forhelping in
manuscript preparation. This work was sponsoredby Brazilian
agencies Fundacao Araucaria, CNPq, and CAPES.
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Treatment of paper pulp and paper mill wastewater by
coagulation-flocculation followed by heterogeneous
photocatalysisIntroductionExperimental
proceduresMaterialsCoagulation-flocculation processPhoto-oxidation
processBiotoxicity method
Results and discussionCoagulation-flocculation
studiesOptimization of pHOptimization of FeCl3
concentrationOptimization of polyelectrolyte loading
Photocatalysis studiespH optimizationOptimization of TiO2
concentrationOptimization of H2O2 concentrationComparison of
photo-reaction conditionsKinetic studies of photodegradation
Combined treatment (coagulation-flocculation and
photocatalysis): effluent quality
ConclusionAcknowledgementsReferences