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Abstract The performance of different solar-driven advancedoxidation processes (AOPs), such as TiO2/UV, TiO2/H2O2/UV,and Fe2+/H2O2/UV–visible in the treatment of a real textileeffluent using a pilot plant with compound parabolic collectors(CPCs), was investigated. The influence of the main photo-Fenton reaction variables such as iron concentration (20–100 mg Fe2+L−1), pH (2.4–4.5), temperature (10–50 °C),and irradiance (22–68 WUVm−2) was evaluated in a lab-scaleprototype using artificial solar radiation. The real textile waste-water presented a beige color, with a maximum absorbancepeak at 641 nm, alkaline pH (8.1), moderate organic content(dissolved organic carbon (DOC)=129 mg C L−1andchemical oxygen demand (COD)=496 mg O2 L−1), andhigh conductivity mainly associated to the high concentra-tion of chloride (1.1 g Cl−L−1), sulfate (0.4 g SO42−L−1),andsodium(1.2gNa+L−1) ions. Although all the pro-cesses tested contributed to complete decolorization andeffective mineralization, the most efficient process was the solar photo-Fenton with an optimum catalyst concen-tration of 60 mg Fe2+L−1, leading to 70 % mineralization(DOCfinal=41 mg C L−1;CODfinal<150 mg O2 L−1)atpH3.6, requiring a UV energy dose of 3.5 kJUVL−1(t30 W=22.4 min; T¼ 30 C; UV G;n ¼ 44 Wm−2) and consum-ing18.5mMofH2O2.Keywords Text ile dyeing wastewater . Solar advancedoxidation processes . Solar photo-Fenton . SUNTESTsimulator . 33630
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Pilot plant with CPCsIntroductionWater is an essential and important natural resource for keep-ing the life in the world; as it gradually has become a scarceresource in many countries, many populations are sufferingwith the shortage of water and clean drinking water. Textileindustry is one of the largest consumers of freshwater, requir-ing around 3–308 L kg−1fabrics, throughout several process-ing steps. According to the US Environmental ProtectionAgency, the main textile-processing steps include desizing(3–9Lkg−1), scouring (26–43 L kg−1), bleaching (3–124 L kg−1), mercerizing (232–308 L kg−1), dyeing, andprinting (8–300 L kg−1), for the treatment of different typesof synthetic or natural fibers, such as cotton, denim, polyester,silk, linen, wool, and viscose (dos Santos et al. 2007;EPA1997). In addition, different type of dyes (acid, basic, direct,dispersed, reactive, azoic, and sulfurous) are widely applied indyeing and printing processes, in order to assign commercialcharacteristics and finishing to fabrics.Textile wastewater composition depends mainly on thetype of organic and inorganic compounds used, such as dyes,waxes, oils, fats, surfactants, salts, etc., to process different fabrics throughout several industrial steps (dos Santos et al.2007; ul Islam et al. 2013)(Table 1).When untreated textile wastewaters containing dyes, char-acterized by having complex organic structures and showingintense specific color, are discharged into freshwater bodies,undesirable effects on the water quality are expected such asreducing the penetration of sunlight and, consequently, affect-ing the photosynthesis and aquatic plant growth, as well aslimiting the developing of invertebrates, and other life formsof aquatic biota (Torrades et al. 2004), requiring thus the use ofdifferent treatment methods for dye removal.Conventional biological processes have been applied withineffectively results on the organic pollutant removal fromtextile wastewaters, due mainly to its low biodegradability(Sarayu and Sandhya 2012). In that view, alternative textilewastewater treatment methods based on bacteria-polymer cells(Pearce et al. 2003), adsorption on activated carbon (Ahmadand Hameed 2010; Foo and Hameed 2010;Syedaetal. 2012),coagulation/flocculation (Harrelkas et al. 2009;Qianetal.2013), electrochemical processes (Palácio et al. 2009;Yuet al. 2013), and membrane filtration processes (nanofiltration,ultrafiltration, reverse osmosis) (Ellouze et al. 2012;Lorenaet al. 2011;Wangetal. 2012), have been proposed for theremoval of dyes from aqueous solutions. In spite of removingorganic pollutants, high amounts of sludge ended up as finalproduct, retaining still the environmental concern in the finaldestination of solid wastes. In this context, advanced oxidationprocesses (AOPs) have been recognized as an effective tech-nology to obtain a full degradation of organic compounds andtheir intermediates, based on the active action of powerfuloxidant species, such as hydroxyl radical (HO•). Dye moleculesunder the action of such radicals can be easily degraded andreach a complete mineralization, as summarized in Table 2.Despite the potential for this clean technology for textilewastewater treatment, it has not reached a mature level, beingnecessary a big effort in getting pilot plant data using real textilewastewaters, in order to provide better operating conditions inaccordance with the characteristic of a real textile wastewaterfor a suitable applicability of this technology in industrial scale.Therefore, the main goal of this work is to evaluate theefficiency of different AOPs, TiO2/UV, TiO2/H2O2/UV, andFe2+/H2O2/UV–visible, in the treatment of a real textile waste-water in a pilot scale unit with compound parabolic collector(CPCs), under natural radiation, and evaluate the influence ofthe main photocatalytic reaction variables of the most efficientAOP, in a lab-scale prototype under controlled conditionsusing artificial solar radiation.Materials and methodsTable 1 Characteristics of different textile-processing wastewatersTextile-processingmatrixMain characteristics ReferenceDyeing–cotton andpolyester–industrialwastepH=9.1Abs. at 455 nm=0.754COD=1,505 mg O2 L−1BOD5=91 mg O2 L−1Sulfate=1.2 mg SO42−L−1Surfactants=30.7 mg L−1Somensi et al.(2010)Mixed–industrialwastepH=7.2Abs. at 503 nm=0.92COD=1,065 mg O2 L−1TDC=354 mg C L−1Merzouk et al.(2011)Dyeing–cotton–industrial wastepH=10.8COD=1,020 mg O2 L−1DOC=382 mg C L−1BOD5=110 mg O2 L−1TDN=32.4 mg N L−1Chloride=4,578 mg Cl−L−1Sulfate=265 mg SO42−L−1Vilar et al.(2011)Dyeing–fibers–industrial wastepH=7.6Abs. at 503 nm=0.97COD=1,357 mg O2 L−1TDC=369 mg C L−1Merzouk et al.(2011)Printing–industrialwastepH=8.2Abs. at 426, 558, and660 nm=0.141, 0.090, 0.064COD=503 mg O2 L−1BOD5=51 mg O2 L−1TSS=60.1 mg TSS L−1TDN=105.9 mg N L−1TDP=11.3 mg P-PO4 L−1Surfactants=30.7 mg L−1Lotito et al.(2012)Dyeing and scouring–denim–industrialwastepH=12.5COD=1,636 mg O2 L−1TDC=638 mg C L−1Color=5.1 g Pt-Co L−1Turbidity=310 NTUMódeneset al.(2012)Mixed–fabric–industrial wastepH=7.3Abs. at 254 nm=3.534COD=2,100 mg O2 L−1TDC=465 mg C L−1TSS=52 mg TSS L−1Turbidity=75 NTUBlanco et al.(2012)Dyeing and scouring–cotton–industrialwastepH=8.2Abs. at 641 nm=0.198COD=684 mg O2 L−1TSS=193 mg TSS L−1TDC=460 mg C L−1TDN=117 mg N L−1VSS=171 mg VSS L−1Ammonia=79 mg N‐NH4+L−1Chloride=105 mg Cl−L−1Sodium=405 mg Na+L−1Sulfate=35 mg SO2−L−1Soares et al.(2014) treatment and was preserved according to the standard meth-odologies described in standard methods (Clesceri et al.2005).All chemicals used were of analytical reagent grade. AOPexperiments were performed employing titanium dioxide(Degussa, P25, 80 % anatase and 20 % rutile), hydrogenperoxide (Quimitécnica S.A., 50 % (w/v), 1.10 g/cm3),iron(II) sulfate heptahydrate (Panreac), sulfuric acid(Pronolab, 96 %, 1.84 g/cm3), and sodium hydroxide(Merck) for pH adjustment. Ultrapure and deionized waterwas produced by aMillipore® system (Direct-Q model) and areverse osmosis system (Panice®), respectively.RB5 Reactive Black 5, RB19 Reactive Blue 19 (Remazol Brilliant Blue R-A)aAcid Blue 193 (a chromium complex disazo dye; AB193) and Reactive Black 39 (a disazo dye; RB39)bAcid red 151, Acid orange 7 and Acid blue 113cSolophenyl orange TGL, Solophenyl blue 71, Solophenyl scarlet BNLE, Solophenyl yellow ARL, Solophenyl black FR and Navy Blue 98.3RemazolRed RR and Remazol Blue RRdRemazol Red RR and Remazol Blue RReIn these works, authors reported the solar photo-Fenton reaction as the best process between the AOPs studied Analytical determinationspH, temperature, and conductivity were measured using aHANNA HI 4522 pH meter. The chemical oxygen demand(COD) was determined using Merck Spectroquant kits (ref.1.14541.0001). The dissolved organic carbon (DOC) concen-tration was measured by NDIR spectrometry in a TC-TOC-TN analyzer equipped with an ASI-V auto sampler(Shimadzu, model TOC-VCSN) and calibrated with standardsolutions of potassiumhydrogen phthalate (total carbon) and amixture of sodium hydrogen carbonate/sodium carbonate (in-organic carbon). Total dissolved nitrogen was measured in thesame TC-TOC-TN analyzer coupled with a TNM-1 unit(Shimadzu, model TOC-VCSN) by thermal decomposition,and NO was detected by a chemiluminescence method cali-brated with standard solutions of potassium nitrate. Theamount of H2O2 was spectrophotometrically determinedthrough the measurement of peroxovanadium cations formedfrom the reaction of H2O2 with NH4VO3 in acidic medium(Nogueira et al. 2005).