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Chemical Engineering and Processing 47 (2008) 169–176

Photocatalytic decolourisation of synthetic and real textilewastewater containing benzidine-based azo dyes

Erick R. Bandala ∗, Miguel A. Pelaez, A. Javier Garcıa-Lopez,Maria de J. Salgado, Gabriela Moeller

Instituto Mexicano de Tecnologıa del Agua, Paseo Cuauhnahuac 8532, Jiutepec, Morelos 62550 Mexico

Received 5 September 2006; received in revised form 19 January 2007; accepted 9 February 2007Available online 25 February 2007

bstract

Decolourisation of synthetic and real textile wastewater containing benzidine-based azo dyes was carried out using dark Fenton reaction and solarriven photo-Fenton process. Experimental runs with synthetic wastewater were used to identify the best conditions to perform real wastewaterecolourisation. It was found that, using solar energy to promote the advanced oxidation process (AOP) proposed, the reaction kinetic is increasedy almost twice, compared with dark Fenton reaction. With solar driven photo-Fenton, decolourisation of 90% was achieved using 1 mM of Fe2+

nd 50 mM of H2O2 with only 12 kJ/L. When these conditions were tested for real wastewater, 56% of colour removal was obtained and 62.6%f the organic matter found initially in the effluent (measured as chemical oxygen demand, COD) was eliminated after 16 kJ/L. The collectorrea per mass (ACM), a figure-of-merit proposed by the International Union of Pure and Applied Chemistry (IUPAC) was calculated as scaling-uparameter in order to find out the actual solar collecting area required to treat 100 L of wastewater under the proposed conditions. Depending on the

astewater type and effluent application after the photoassisted process, it was found that effluents with the characteristics of synthetic wastewater

ested in this work can be completely decoloured using 4 m2 in 1 h of solar irradiation. For the case of real wastewater, if coupling the photoassistedrocess to a biological method, treatment of 100 L can be carried out using 7 m2 of solar collectors.

2007 Elsevier B.V. All rights reserved.

hoto-

Taembucadwp

eywords: Wastewater; Water detoxification; Advanced oxidation processes; P

. Introduction

Azo dyes are used by a wide number of industries, textileills predominantly, but they can also be found in the food,

harmaceutical, paper and printing, leather and cosmetic indus-ries. It is not surprising that these compounds have become a

ajor environmental concern. Many of these dyes find their waynto the environment via wastewater facilities. These compoundsetain colour and structural integrity under exposure to sunlight,oil, bacteria and sweat. They also exhibit a high resistance toicrobial degradation in wastewater treatment systems.There is a continual demand to develop longer lasting, more

pplicable dyes. Azo dyes are second only to polymers in termsf the number of new compounds submitted for registration inhe US under the Toxic Substance Control Act (TSCA) [1].

∗ Corresponding author. Tel.: +52 7773293664; fax: +52 7773293664.E-mail address: ebandala@tlaloc.imta.mx (E.R. Bandala).

cydippi

255-2701/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.cep.2007.02.010

Fenton; Decolourisation; Benzidine-based azo dyes

he development of synthetic fibers such as nylon, lycra, rayonnd polyester has required the production of new dyes that canffectively bond to these materials. The US Department of Com-erce has predicted a 3.5-fold increase in textile manufacturing

etween 1975 and 2020 [2,3]. Azo dyes must be continuallypdated to produce colours that reflect the trend dictated byhanging social ideas and styles. Brighter, longer lasting coloursre often necessary to satisfy this demand. It have been wellocumented [12,13] that benzidine (BZ)-based azo dyes areidely used in the dye manufacturing, textile, dyeing, colouraper printing and leather industries.

In Mexico, only in 1995, the total production of dyes andolourants was 15,651 t and the apparent consumption in thisear was 18,038 t with a continuous trend to increase [4]. Pro-uction of coloured wastewater in our country had become a very

mportant environmental issue. For example, the main water sup-ly source for this economic activity is underground water whichrovide near to 97% of the total supply [11]. Nevertheless, Mex-can legislation does not include colour as a control parameter

1 eering and Processing 47 (2008) 169–176

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2

2

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1cciWcdiwas carried out using a 2N solution of H2SO4 (reactive grade,Backer). For each experiment, an initial sample (10 mL, t = 0)was taken immediately after the DB38–water mixture. The nec-essary quantity of Fe2+ to get the desired concentration was then

Table 1Experimental conditions tested for colour removal using dark Fenton reaction

Experiment no. [Fe2+] (mM) [H2O2] (mM) pH Colourremoval (%)

1 0.0072 10 3 522 0.0216 10 3 66.53 0.036 10 3 66.24 0.051 10 3 655 0.0612 10 3 906 0.072 10 3 917 0.14 10 3 998 0.216 10 3 98.59 0.36 10 3 98.7

10 0.43 10 3 98.411 0.14 7 3 9912 0.14 10 3 9913 0.14 14 3 9914 0.14 10 2 9815 0.14 10 3 98.9

70 E.R. Bandala et al. / Chemical Engin

or wastewater monitoring analysis [5]. Effective and economicreatment of a diversity of effluent containing BZ-based azoyes has become a problem because no single treatment systems adequate for degrading the various dye structure. Currently,esearch has been focused on chemical and physically degrad-ng of these compounds in wastewater. These methods includehemical oxidation, which uses strong oxidizers such as chlorineioxide, activated carbon adsorption or coagulation/flocculation6]. Many of these technologies are cost prohibitive, and there-ore are not viable options for treating large waste streams.

BZ-based azo dyes are considered to be mutagenic and car-inogenic by the US National Institute for Occupational Safetynd Health due to their transformation to BZ [14,15]. Due toheir recalcitrant nature, this kind of dyes often pass throughctivated sludge facilities with little or no reduction in colour7–9]. Although some researchers have observed slight coloureduction, their findings are largely outweighed by those whoave not [10].

Advanced oxidation processes (AOPs) are described asromising option to remove persistent pollutants from contam-nated water when conventional water treatment processes areot efficient enough [20]. One of the most widely used AOP forastewater treatment is the Fenton process. Fenton’s reactionses hydrogen peroxide and ferrous salt to generate hydroxyladicals (HO•). The hydroxyl radicals possess inherent prop-rties that enable it to attack organic pollutants in water tobtain a complete mineralization into CO2, water and mineralcids [16–19]. When the process uses ultraviolet (UV) radia-ion, visible light or both it is known as photo-Fenton process.hoto-Fenton process possesses several advantages, mainly the

ncrease of reaction rate and the possibility of use a cheap,on-contaminant and widely distributed energy source; solaradiation.

Despite several papers published recently dealing with thepplication of AOPs to dye degradation [21–29], relatively feworks have reported the use of solar energy as promoting sourcef the process and even fewer deals with the treatment of realastewater from textile industry for colour removal using this

lternative methodology [30]. The aim of this study is to showhe results from the application of solar driven photo-Fentonrocess to decolourisation of synthetic and real textile wastewa-er contaminated with the benzidine-based azo dyes direct black8.

. Experimental

.1. Reagents

The chemicals used in the experiments, FeSO4·7H2O (Baker)nd H2O2 (50% stabilized, Baker) were used as received. Directlack 38 (disodium-4-amino-3-((4′((2,4-diaminophenyl)azo)--hydroxy-6-(phenylazo)-2,7-naphthalene disulphonate, DB38,ee Fig. 1 for chemical structure) industrial grade was supplied

y Orion Co. (Cuernavaca, Morelos). Real textile wastewater20 L) was obtained from the effluent of the treatment plantf a textile industry in Tepeji del Rıo, Hidalgo. An aliquot ofhe real wastewater sample was analyzed for determination of

1111

Fig. 1. Chemical structure of direct black 38.

hemical oxygen demand (COD), biochemical oxygen demandBOD), total suspended solids (TSS), volatile suspended solidsVSS), settable solids (SS), electric conductivity (EC), pH, nitro-en (organic, Norg; ammonia, N–NH3), oil and grease (O&G)nd colour using standard methodologies [31]. The sample wassed as received except for the pH adjustment prior to Fentonnd photo-Fenton processes.

.2. Non-irradiated experiments

Experiments for the water decolourisation in the absencef solar radiation were performed at laboratory scale using a00 mL pyrex glass baker as reactor under continue magnetictirring. The reactor was covered with aluminium foil to avoidhe incidence of diffuse light in the laboratory and maintainednder controlled environmental temperature at 20 ± 1 ◦C.

Synthetic wastewater samples were prepared by dissolving00 mg/L (0.128 mM) of DB38 in tap water. This colourant con-entration was used because in additional solubility tests of theolourant (data not shown) we found that, after 100 mg/L anmportant precipitation is observed in the colourant solution.

e assumed then that 100 mg/L will be the maximal colourantoncentration could be found even in real wastewater. Manyifferent Fe2+ and H2O2 concentrations were tested as well asnitial pH values as depicted in Table 1. Initial pH adjustment

6 0.14 10 4 98.17 0.14 10 5 98.48 0.14 10 6 639 0.14 10 7 8.3

eering

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ampi

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cgL2ewttdutrwe

Q

wasa

3

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ttbtfvTutant variable with direct effect on the Fenton reaction efficiencyas it has been previously reported [34].

Fig. 2 shows the results of decolourisation using a singlerepresentative Fenton reaction conditions from the whole set of

Table 2Reaction rate constants for the selected radiated and non-radiated Fenton pro-cesses showed in Fig. 2

−1

E.R. Bandala et al. / Chemical Engin

dded to the system and the reaction mixture was homogenizedor 10 min. After this time, enough H2O2 was added to achievehe desired concentration. The moment of H2O2 addition wasonsidered the start of the Fenton reaction. Sampling was per-ormed at 5, 10, 15, 30, 45 and 60 min. No further additional

2O2 was added to the system during the experiments.

.3. Photoreactor

Solar photocatalytic experiments were performed in a benchcale system consisting of one compound parabolic concentratorCPC) with a total collection surface of 0.1 m2 described else-here [30,32]. The CPC system was facing the sun on a platform

lopped 19◦ (equal to local latitude). The photocatalytic reactionas carried out in a pyrex glass tube having 100 cm in length

nd 2.54 cm of internal diameter, located in the focus of the CPCollector. The total volume of the system was 3 L.

.4. Irradiated experiments

.4.1. Experiments with synthetic samplesSynthetic wastewater samples were prepared by dissolving

00 mg/L (0.128 mM) of DB38 in tap water. From dark Fentonxperiments, two Fe2+ concentrations were chosen to be tested,.1 and 1 mM while the H2O2 concentrations used were 5, 10nd 50 mM. The initial pH in synthetic samples was adjusted tousing a 2N solution of H2SO4 (reactive grade, Backer).For each experiment, an initial sample (10 mL, t = 0) was

aken immediately after the DB38–water mixture. The Fe2+ washen added to the system and the reaction mixture was homoge-ized for 10 min with the solar collector covered. After this time,he H2O2 was added and the cover was removed. Sampling waserformed at 5, 10, 15, 30, 45 and 60 min. For high reagent con-entration, after 15 min of reaction, additional H2O2 (equal tonitial concentration) was added to the system.

.4.2. Experiments with real wastewater samplesExperiments with real wastewater (Table 4 shows the results

f their initial chemical characterization) were carried out usinghe same experimental procedure described above. In this case,nly one Fe2+/H2O2 condition was tested, identified as theore reliable to perform wastewater decolourisation. The actual

nitial reagent concentrations used were [Fe2+] = 1 mM andH2O2] = 25 mM. For the case of experiments with real wastewa-er, an equal quantity of H2O2 was added after 10 min of reaction.

.5. Sample handling

Colour in the synthetic was determined using a diode arrayP-8452A UV/Vis at 470 nm (the maximal absorption wave-

ength for DB38). For real samples, colour was also determinedsing the spectrometric procedure proposed in the Standard

ethods [31]. The total absorptive spectrum for each sampleas also determined in the UV/Vis equipment by scanning from90 to 820 nm. The chemical oxygen demand (COD) was alsoetermined at the beginning and end of the experimental runs

E

D[[

and Processing 47 (2008) 169–176 171

gree with Standard Methods Procedure [31] using the volu-etric titration methodology because we have found that this

rocedure provide more accurate results and minimize H2O2nterference.

.6. Evaluation of solar radiation

All the experiments were performed under the same solaronditions between 11:00 and 14:00 in April 2006. The incidentlobal radiation on the CPC collector was determined using ai-Cor pyranometer (LI-200SA) in a wavelength range between80 and 2800 nm. Radiation measurements were performedvery 5 min. The pyranometer used for radiation measurementsas tilted in the same angle than the solar collector in order

o avoid tilt angle adjustments. Since the photo-Fenton reac-ion allows the use of wavelengths from 300 to 650 nm for solarriven processes, the actual incoming irradiation was estimatedsing as reference an AM1.5 standard, from which a 0.35 fac-or was obtained for the radiation included in this wavelengthange as proposed by Chacon et al. [11]. Accumulated energyas computed using the relation previously reported by Goslich

t al. [33]:

n = Qn−1 + �tGn

(A

V

), �t = tn − tn−1 (1)

here �t is the time between radiation measurements, Qn theccumulated energy and Gn the adjusted global radiation mea-ured in the pyranometer in each experiment, A the module areand V is the total system volume.

. Results and discussion

.1. Comparison between dark and irradiated Fentonrocesses

As shown in Table 1, several dark Fenton conditions wereested with a wide variety of results depending on the varia-ion of Fenton reagent’s concentration. It is noticeable that theest results of decolourisation were found for Fe2+ concentra-ions around 0.1 mM after 120 min of reaction. As expected,urther increases or decreases in the iron salt concentration pro-ided similar and lower decolourisation results, respectively.he effect of H2O2 concentration during dark experiments wasndetectable at the conditions tested and pH was a very impor-

xperimental conditions k (min )

ark H2O2 0Fe2+] = 0.1 mM; [H2O2] = 5 mM; pH < 3, no radiation 0.007Fe2+] = 0.1 mM; [H2O2] = 5 mM; pH < 3, solar radiation 0.013

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72 E.R. Bandala et al. / Chemical Engin

xperiments described in Table 1 and, in a comparative way,esults of the application of photo-Fenton reactions at similareagent concentrations. The figure depicts also colour behaviourhen hydrogen peroxide is used alone in the dark. As seen, theresence of H2O2 (50 mM) in dark conditions did not produceny changes in water colour after 60 min of reaction time. These of Fe2+ in the reaction mixture allowed to increase reac-ion rate as shown also in Fig. 2. When the colourant was in theresence of Fenton reagent ([Fe2+] = 0.1 mM; [H2O2] = 5 mM),otal decolourisation achieved was 47% in 60 min of reac-ion. Nevertheless, when solar energy was included in therocess (photo-Fenton reaction) the reaction kinetics improveubstantially. For this last case and using the same conditionsested in dark experiments described earlier, the decolourisationbtained was 77% for the same reaction time (average radiation,00 W/m2).

In order to have a better comparison between both processes,ata in Fig. 2 were fitted by using a pseudo-first order kineticssee Table 2). Kinetic constant value for non-irradiated hydro-en peroxide process was zero, dark Fenton reaction kineticonstant was 0.007 min−1 whereas photo-Fenton process gen-rated a k value of 0.013 min−1; almost twice as the value of darkrocess. These results agree with previous reports dealing witholar driven photo-Fenton processes for degradation of severalollutants. Chacon et al. [11] reported the improvement of acidrange 24 degradation process by the use of solar energy in Fen-on reaction. Bandala et al. [34] demonstrated that, despite theigh effect of temperature on Fenton reaction, UV and visibleart of the solar spectrum improves effectively the degradationrocess. In this latter case, similar increase in reaction rate con-tants as reported here was observed for pesticide degradationhen solar energy was involved in the process.

.2. Solar driven Fenton reaction

Once stated the improvement of the Fenton process by these of solar energy as driven force, additional experimental runsere carried out in order to find the most effective conditions forecolourisation process. Because solar energy incoming is not

ig. 2. Direct black 38 decolourisation using non-irradiated and irradiatedenton process. Reaction condition in both experiments was [Fe2+] = 0.1 mM;H2O2] = 5 mM.

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and Processing 47 (2008) 169–176

onstant in time and its value depends on weather conditions (i.e.louds average, suspended particles), the use of reaction time asndependent variable for solar driven experiments is not alwaysseful. In order to get a better comparative variable, accumulatednergy have been proposed [33] for solar irradiated experiments.ig. 3 shows the results of the experiments as a function of accu-ulated energy in order to a better comparison among different

olar incoming conditions.As shown in Fig. 3, the use of solar radiation alone for

olour removal (photolysis) did not produced any change inhe concentration after 16 kJ/L. In the same way, no signifi-ant colour removal (∼20%) was determined when using Fe2+

alts alone in the presence of solar irradiation (accumulatednergy 16 kJ/L). A different picture was obtained when hydrogeneroxide (50 mM) was used alone in the presence of solar radia-ion, 88% of colour removal was obtained in around 16 kJ/L.he use of mild photo-Fenton conditions ([Fe2+] = 0.1 mM;

H2O2] = 5 mM) shows an spectacular decrease in colour justew moments after the experiment starts (65% of colour removalfter 2.5 kJ/L of accumulated energy) and an overall colouremoval of 77% in 16 kJ/L. The increase of hydrogen perox-de concentration affected reaction kinetics depending on thechedule of H2O2 delivery. When hydrogen peroxide concen-ration was increased from 5 to 10 mM since the beginning ofhe experiment (data not shown), final colour removal and kineticehaviour was the same as described earlier for 5 mM of H2O2.evertheless, when the additional oxidant agent (5 mM) waselivered after 15 min of the start of the process (see Fig. 3), theeaction rate increased again to achieve 80% of colour removaln 13 kJ/L. Increasing Fe2+ concentration one magnitude order1 mM) and hydrogen peroxide up to 50 mM (25 mM fromhe start of the experiment and 25 mM after 10 min), colouremoval in the process achieved 90% in 12 kJ/L of accumu-ated energy. This result agreed with previously reported [11]or colour removal using the same methodology and similar con-itions for the acid orange 24, a chemically simpler dye. Theyound close colour removals (around 90%) with ca. 75 kJ/L forFe2+] = 0.143 mM and [H2O2] = 7.8 mM.

For a better comparison between the different solar drivenrocesses, the kinetic approach proposed by Chacon et al. [11]as used to fit experimental data showed in Fig. 3. They pro-osed that, for dye degradation using solar radiation, reactionate can be explained by a first order kinetic with respect tohe substrate as function of incoming energy instead of reactionime. By this way colour removal can be expressed as

ln

(C

C0

)= KQn (2)

here C and C0 are the dye concentration corresponding to Qn

nd Q0, respectively, and k is the reaction rate constant. Table 3hows the k values obtained with this approach.

Values for k from Table 3 show the effect of hydrogen per-

xide concentration and dosage as explained earlier. The lowestvalue was obtained for the experiment using irradiated Fe2+

lone (k = 0.003 L/kJ) followed by the experiment using hydro-en peroxide alone under irradiation with a k value of 0.032 L/kJ,

E.R. Bandala et al. / Chemical Engineering and Processing 47 (2008) 169–176 173

F ted energy. White arrows shown the time of addition of second doses of H2O2 to ther

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Table 4Results of real wastewater characterization

Parameter Value (mg/L) Parameter Value

COD 975 pH 8.3BOD 98 EC 5.7 mS/cmTSS 130 Colour 10,000 Pt–CoUVN

patuSsr

ig. 3. Colour removal in synthetic and real wastewater as function of accumulaeaction mixture (10 and 15 min).

magnitude order higher. For the experiment using Fentoneagents at [Fe2+] = 0.1 mM and H2O2 concentration of 5 mM, kalue was 0.081 L/kJ, whereas delivering additional 5 mM after5 min, k went to 0.13 L/kJ, almost twice the value. Furtherncrease in the H2O2 concentration did not show the expectednhanced in the reaction rate, as observed for experiment 6 whereinetic constant increased only from 0.13 to 0.15 L/kJ. Earliereports [35] have concluded that this behaviour is due to thexcess of H2O2 in the reaction mixture that can react scaveng-ng hydroxyl radicals, decreasing HO• concentration and colouremoval ratio.

.3. Application to real wastewater

Application of the photo-Fenton process to coloured realastewater is shown in Fig. 3 and Table 3. From Fig. 3 isorth to note that, despite the reagent conditions used were

he highest tested in this work, colour removal was only 56%fter 16 kJ/L. Reaction kinetic constant for the decolourisationeaction of real wastewater (see Table 3) was low (0.056 L/kJ)ainly because the use of real wastewater involves a more com-

able 3eaction kinetic constant values obtained for the different experiments of colour

emoval using photo-Fenton reaction

xperimento.

Wastewatertype

[Fe2+](mM)

[H2O2](mM)

k (L/kJ) ACM (m2/g)

Synthetic 0 0 0 –Synthetic 1.0 0 0.003 1.307Synthetic 0 50 0.032 0.436Synthetic 0.1 5 0.081 0.409Synthetic 0.1 10 0.130 0.364Synthetic 1.0 50 0.150 0.364Real 1.0 50 0.056 0.560

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SS 100 N–NH3 40.6 mg/L

org 47 SS 0.1 mg/LO&G 17 mg/L

lex matrix compared to synthetic wastewater. Table 4 shows thectual physico-chemical characteristics of the real wastewater. Inhis case, additional to colour, many others organic compoundssually considered only as organic matter (OM) are present.ince AOPs, and specifically photo-Fenton process, are non-pecific oxidative processes, produced hydroxyl radicals willeact with any kind of OM included in the reaction mixture withhe probable effect of decreasing the reaction with target pollu-ants. Nevertheless, when the total content of organic matter isonsidered, the advantages of use the photo-Fenton process cane better determined. Initial concentration of COD in the realastewater was determined as high as 975 mg/L, after 16 kJ/L of

ccumulated energy, equivalent to 1 h of solar irradiation, underhe tested conditions. Final COD concentration was 363.8 mg/L,decrease of 62.6% in the total concentration of organic matter.his result agrees with found by Kang et al. [36], they observed

hat COD of a textile wastewater stream inhibits colour removal.ark et al. [37] found COD removals up to 59% and colouremoval of 18% in pigment wastewater.

.4. Estimation of scaling-up parameters

Full-scale commercialization of AOPs is a desirable tech-ological approach which have been successfully developed in

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74 E.R. Bandala et al. / Chemical Engin

ome specific processes, mostly for electric energy driven AOPs.he use of solar energy to detoxify water contaminated withrganic pollutants has gained considerable interest in last decade38,39,50]. For this reason, identification of scaling-up param-ters which allows to define solar detoxification for its possibleommercial application is an interesting issue to explore. To pro-ide comparative scaling-up parameters of the proposed AOPs,figure-of-merit recommended by the Photochemistry Com-ission of International Union of Pure and Applied Chemistry

IUPAC) was used [40]. This figure-of-merit, a collector areaer mass (ACM) is defined as the “area required to bring abouthe degradation of a unit mass (e.g. 1 kg or 1 g) of a contaminantn polluted water in a time t0 (1 h) when the incident solar irra-iance is 1000 W/m2 [40]”. ACM (m2/g) in a batch reactor, forass concentration in mg/L, is calculated from the expression

40]:

CM = AEst1000

E0s t0V (ci − cf)

(3)

here A (m2) is the actual collector area, V (L) the volumereated, Es(W m−2) the average solar irradiance over the periodof the treatment, and ci and cf are the influent and efflu-

nt concentration (mg/L). E0s is the standardized irradiance

1000 W m−2 based on the AM1.5 standard solar spectrum on aorizontal surface [41]) and t0 is the reference time (1 h) [40].onsidering Eq. (3), ACM values for the different experimentalonditions tested in this work where determined and are alsoisplayed in Table 3. As seen, collector area per mass for theilder conditions tested in this work (experiment 2, Table 3)

s 0.409 m2/g which means that 100 L of water containing dyeoncentrations equivalent to those tested here for syntheticastewater (100 mg/L of DB38) could be treated using 4.09 m2

f solar collectors. By using the highest photo-Fenton reactiveoncentration (experiment 4, Table 3) ACM value is 0.364 m2/g,n the case of synthetic wastewater, and 0.56 m2/g for the realastewater (see also Table 3). In the latter case, the result becomeery interesting considering that real wastewater has the char-cteristics shown in Table 3. For a matrix as described, usingolar driven photo-Fenton under the reaction conditions tested,00 L of these wastewater can be treated (until complete removalf COD) using 14 m2 of solar collectors considering 4 h ofrradiation. If considering AOPs coupling to, for example, bio-ogical treatment this results may become more interesting. Inecent years, coupled systems (photoassisted AOPs-biological)ave been proposed to treat various types of industrial wastew-ter with advantages for water treatment [42–45]. According toifferent biodegradability tests using Zahn–Wellens procedurendicated in these previous works, solutions become biocompat-ble after elimination of around 45% of the initial organic matter46]. Considering the last statement and the possibility of furtheriological treatment of the effluent after photoassisted Fentonrocess, solar collection area necessary to achieve the required

emoval become 7 m2. AOPs are considered emerging as theost widely used treatment technology for water contaminatedith organic pollutants in the near future and, as proposed, cou-ling of photocatalytic technologies in tandem processes with,

and Processing 47 (2008) 169–176

or example, biological treatment is probably the technologicalorizon mainly if considering that development of pilot-plantnd full-scale implementation of this technology are nowadaysreality [47–50].

. Conclusions

Decolourisation of water contaminated with a benzidine-ased azo dye was achieved using solar driven photo-Fentonrocess. Almost complete decolourisation was obtained usingmM of Fe2+ and 50 mM of H2O2 in 60 min of irradiation

ime when synthetic wastewater was used. For the case of realoloured wastewater containing DB38 and high organic matteroncentration, decolourisation decreased to 56% under the sameeaction conditions and a COD removal up to almost 63% waschieved.

Application of a previously reported kinetic approachllowed to a more accurate analysis of the process and the dif-erences between all of them. This model lead to establish thatot only concentration of the chemical reagents (hydrogen per-xide and ferrous sulphate) showed important influence on theeaction kinetic but also the schedule of delivery of these (i.e.,ydrogen peroxide addition in different reaction times duringxperimental runs).

The application of the figure-of-merit proposed by the IUPACas of great help in the determination of scaling-up parametersepending on the wastewater composition and the applica-ion that wastewater will have after AOP treatment. It wasetermined that, when sequential treatment processes are con-idered, the actual solar collection surface can be effectivelyecreased raising reasonable values. These scaling-up param-ters are currently being used to application in a pilot plantnd the results from this experiment are under collection at thisime.

cknowledgements

This work was supported by the National Council ofcience and Technology (CONACyT Mexico, grants HGO-005-C01-2 and CNA-2000-C01-70). Authors gratefully thankilis Moreno-Anorve and Manuel Sanchez Zarza for theirelp in the performance of the physico-chemical determina-ions and their discussion of the experimental part of thisork.

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[6] P. Cooper, Removing colour from dyehouse waste waters—a criticalreview of technology available, J. Soc. Dyers Colour. 109 (3) (1993) 97–100.

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