treatment of paper pulp and paper mill wastewater by

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


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


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.


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.


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


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


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-


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.

References

[1] S. Lacorte, A. Latorre, D. Barcelo, A. Rigol, A. Malmqvist, T. Welander,Trends Anal. Chem. 22 (10) (2003) 725737.

[2] D. Pokhrel, T. Viraraghavan, Sci. Total Environ. 333 (2004) 3758.[3] C.V. Srivastava, I.D. Mall, I. Mishra, Coll. Surf. A 260 (2005) 1728.[4] S.S. Wong, T.T. Teng, A.L. Ahmad, A. Zuhairi, G. Najafpour, J. Hazard.

Mater. B 135 (2006) 378388.[5] G. Thompson, J. Swain, M. Kay, C.F. Forster, Bioresour. Technol. 77 (2001)

275286.[6] J.L. Morais, C. Sirtori, P.G. Peralta-Zamora, Qum. Nova 29 (1) (2006)

2023.[7] E. Chamarro, A. Marco, S. Esplugas, Water Res. 35 (4) (2001) 10471051.[8] R.J. Stephenson, S.J.B. Duff, Water Res. 30 (4) (1996) 781792.[9] S. Delgado, F. Diaz, D. Garcia, N. Otero, Filtr. Sep. Sep. (2003) 4346.

[10] J. Duan, J. Gregory, Adv. Coll. Interf. 100 (102) (2003) 475502.[11] A. Pinotti, A. Bevilacqua, N. Zaritzky, J. Food Eng. 32 (1997) 6981.[12] R. Divakaran, V.N.S. Pillai, Water Res. 35 (16) (2001) 39043908.[13] S. Bratskaya, S. Schwarz, D. Chervonetsky, Water Res. 38 (2004)

295529[14] H. Li, Y

(2004) 2[15] R. Divak[16] A. Pinot[17] R. Divak[18] J. Rouss

324732[19] S.P. Stra

[20] R. Andreozzi, V. Caprio, A. Insola, R. Marotta, Catal. Today 53 (1999)5159.

[21] A. Cuzzola, M. Bernini, P. Salvadori, Appl. Catal. B: Environ. 36 (2002)231237.

[22] M. Pera-Titus, V. Garca-Molina, M.A. Banos, J. Gimeneza, S. Esplugas,Appl. Catal. B: Environ. 47 (2004) 219256.

[23] P.R. Gogate, A.B. Pandit, Adv. Environ. Res. 8 (2004) 501551.[24] N. Daneshvar, D. Salari, A.R. Khataee, J. Photochem. Photobiol. A: Chem.

157 (2003) 111116.[25] M. Faisal, A.M. Tariq, M. Muneer, Dyes Pigments 72 (2007) 233239.[26] C.C. Chen, J. Mol. Catal. A: Chem. 264 (2007) 8292.[27] Y. Wang, C. Hong, Water Res. 33 (9) (1999) 20312036.[28] N.M. Mahmoodi, M. Arami, N.Y. Limaee, N.S. Tabrizi, J. Coll. Interf. Sci.

295 (2006) 159164.[29] A.E.H. Machado, J.A. Miranda, R.F. Freitas, E.T.F.M. Duarte, L.F. Ferreira,

Y.D.T. Albuquerque, R. Ruggiero, C. Sattler, L. Oliveira, J. Photochem.Photobiol. A: Chem. 155 (2003) 231241.

[30] Y. Wang, C.S. Hong, F. Fang, Environ. Eng. Sci. 16 (1999) 433440.[31] P.A. Pekakis, N.P. Xekoukoulotakis, D. Mantzavinos, Water Res. 40 (2006)

12761286.[32] C. Hachem, F. Bocquillon, O. Zahraa, M. Bouchy, Dyes Pigments 49 (2001)

117125.[33] W. Chu, C.C. Wong, Water Res. 38 (2004) 10371043.[34] L.S. Clesceri, A.E. Greenberg, A.D. Eaton, Standard Methods for the

Examination of Water and Wastewater, 20th ed., American Public HealthAssociation, Washington, DC, USA, 1998.

[35] M.O.S.A. Silva, Analises fsico-qumicas para controle de estacoes de trata-mento de esgotos, Companhia de Saneamento Ambiental CETESB, SaoPaulo, Brazil, 1977.

[36] M.R.A. Silva, M.C. Oliveira, R.F.P. Nogueira, Ecletica Qum. 29 (2004)1926.

indsaCastri07) 1Favil06) 1. Me

LaugY.A. Mcke, J61.. Du, Y. Xua, H. Zhanb, J.F. Kennedyc, Carbohydr. Polym. 5805214.aran, V.N.S. Pillai, Water Res. 38 (2004) 21352143.ti, N. Zaritzky, Waste Manage. 21 (2001) 535542.aran, V.N.S. Pillai, Water Res. 36 (2002) 24142418.y, M.V. Vooren, D.A. Brian, E. Guibal, Water Res. 39 (2005)58.nd, T. Nordengen, K. stgaard, Water Res. 36 (2002) 47454752.

[37] J. L[38] J.

(20[39] M.

(20[40] B.N

Mc[41] M.

Coy, J.S. Metcalf, G.A. Codd, Toxicon 48 (2006) 9951001.tsi-Catharios, N. Bourdaniotis, G. Persoone, Chemosphere 671271132.la, L. Macchia, A. Gallo, C. Altomare, Food Chem. Toxicol. 449221931.yer, N.R. Ferrigini, J.E. Putnan, L.B. Jacobsen, D.E. Nichols, J.L.hlin, Planta Medica 45 (1982) 31.

ollah, P. Morkovsky, J.A.G. Gomes, M. Kesmez, J. Parga, D.L.. Hazard. Mater. B 114 (2004) 199210.

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

treatment of paper pulp and paper mill wastewater by

Documents