外文原文-Electro-peroxone 法处理二号橙印染废水.pdf

Electro peroxone treatment of Orange II dye wastewater Belal Bakheet a Shi Yuana Zhaoxin Lia Huijiao Wanga Jiane Zuoa Sridhar Komarneni b Yujue Wanga aState Key Joint Laboratory of Environmental Simulation and Pollution Control School of Environment Tsinghua University Beijing 100084 China bDepartment of Ecosystem Science and Management and Material Research Institute 205 MRL Building The Pennsylvania State University University Park PA 16802 USA a r t i c l e i n f o Article history Received 29 April 2013 Received in revised form 24 July 2013 Accepted 26 July 2013 Available online 6 August 2013 Keywords Synthetic dye Decolorization Mineralization Ozone Hydrogen peroxide a b s t r a c t Degradation of a synthetic azo dye Orange II by electro peroxone E peroxone treatment was investigated During the E peroxone process ozone generator effl uent O2and O3gas mixture was continuously sparged into an electrolysis reactor which was equipped with a carbon polytetrafl uorethylene carbon PTFE cathode to electrochemically convert the sparged O2to H2O2 The in situ generated H2O2then reacted with the sparged O3to produce OH which can oxidize ozone refractory organic pollutants effectively Thus by simply combining conventional ozonation and electrolysis processes and using a cathode that can effectively convert O2to H2O2 the E peroxone process degraded Orange II much more effectively than the two processes individually Complete decolorization and 95 7 total organic carbon TOC mineralization were obtained after 4 and 45 min of the E peroxone treatment respectively In comparison only 55 6 and 15 3 TOC were mineralized after 90 min of the individual ozonation and electrolysis treatments respectively In addition to its high effi ciency the E peroxone process was effective over a wide range of pH 3e10 and did not produce any secondary pollutants The E peroxone process can thus provide an effective and environmentally friendly alternative for wastewater treatment 2013 Elsevier Ltd All rights reserved 1 Introduction Synthetic dyes are used extensively in many industries such as textile printing leather tanning and paper production industries Martinez Huitle and Brillas 2009 Nidheesh and Gandhimathi 2012 Some of the dyes however are dis charged in industrial wastewaters and can cause serious aesthetic and environmental damage to receiving water bodies Most synthetic dyes are refractory to degradation in natural water e g by sunlight or microbial attack and can impart undesirable colors to water bodies even at very low concentrations Martinez Huitle and Brillas 2009 In addition to aesthetic pollution colors can decrease sunlight penetra tion through the water and thus disturb the natural growth activity of aquatic organisms Nidheesh and Gandhimathi 2012 Moreover somedyesandtheirdegradationin termediatesaretoxicandcarcinogenic andcanpose considerable hazards to aquatic life and humanbeings Brown and Devito 1993 Hammami et al 2008 Silva et al 2009 Wastewaters containing synthetic dyes should therefore be adequatelytreatedbeforebeingdischargedintothe environment Corresponding author Tel 86 10 62772914 fax 86 10 62785687 E mail address wangyujue Y Wang Available online at journal homepage water research 47 2013 6234e6243 0043 1354 e see front matter 2013 Elsevier Ltd All rights reserved http dx doi org 10 1016 j watres 2013 07 042 Decolorization and pollutant degradation are two major tasks in dye wastewater treatment Martinez Huitle and Brillas 2009 Because of the strong decolorization ability of ozone it has been widely used in dye wastewater treatment Ozone has a high selectivity in attacking conjugated double bonds e g N N C N and C C that are often the chro mophores of dye molecules and can thus decolorize dye wastewater rapidly Wu et al 2008 Tehrani Bagha et al 2010 However ozone usually has limited oxidation ability to mineralize refractory synthetic dyes effectively to CO2and H2 O Consequently ozonation effl uents can still contain considerable amounts of degradation intermediates some of which e g aromatic amines from azo dye degradation can actuallyhavehighertoxicitythantheoriginaldyes Silva et al 2009 Tehrani Bagha et al 2010 Hsing et al 2007 Liakou et al 1997a 1997b To minimize the threat associated with degradation intermediates high degrees of pollutant miner alization are therefore desired in synthetic dye wastewater treatment Martinez Huitle and Brillas 2009 Nidheesh and Gandhimathi 2012 To improve pollutant mineralization effi ciency ozone is often used in combination with other technologies such as H2O2 UV and TiO2in dye wastewater treatment Hsing et al 2007 Shu 2006 Lopez et al 2004 Particularly the use of O3 and H2O2together i e the so called peroxone process has a signifi cant synergistic effect on organic mineralization This synergy is mainly because O3can react with H2O2to form hydroxyl radicals OH Eq 1 Staehelin and Hoigne 1982 which are a very powerful oxidant and can oxidize most organic solutes at very high rates that can approach diffusion control limits von Gunten 2003 The addition of H2O2in ozonation processes can therefore usually increase pollutant mineralization effi ciencies considerably Pocostales et al 2010 In addition H2O2and O3do not produce secondary pollutants because they leave only H2O and O2as by products Martinez Huitle and Brillas 2009 Xu et al 2011 Peroxone processes have therefore been considered an effective and environmentally friendly advanced oxidation AO technol ogy for wastewater treatment Pocostales et al 2010 Rice 1997 H2O2 O3 OH O 2 O2 1 However conventional peroxone processes require addi tion of external H2O2 which is unsafe to transport store and handle due to its high reactivity It is therefore desirable that H2O2be generated in situ at controllable rates in peroxone systems To this end we have developed an electro peroxone E peroxone process that can drive the peroxone reaction using in situ electro generated H2O2 Yuan et al 2013 In the E peroxone process O3is produced from O2using an ozone generator which is the same as in conventional ozone and peroxone processes The ozone generator effl uent O3and O2 gas mixture is then sparged into a reactor that has a carbon polytetrafl uorethylene carbon PTFE cathode whichcan electrochemically convert O2to H2O2in acid solution Eq 2 andHO 2 conjugatedbase of H2O2 in base Eq 3 Wanget al 2012 Brillas et al 1995 The in situ generated H2O2 HO 2 then reacts with the sparged O3to produce OH which in turn oxidize organic pollutants Thus by using the O2that would otherwise be wasted in conventional ozonation or peroxone processes to electrochemically produce H2O2in situ the E peroxone process can drive the peroxone reaction electro chemically for pollutant degradation without the addition of external H2O2 O2 2H 2e H2O2 2 O2 H2O 2e HO 2 OH 3 The E peroxone process represents a simple combination of conventional ozonation and electrolysis processes but can achieve much better pollutant mineralization than the two processes individually Yuan et al 2013 In a preliminary study we compared the mineralization of methylene blue by ozonation electrolysis and E peroxone treatment Up to 93 of total organic carbon TOC in the wastewater was degraded in E peroxone processes In contrast only 22 and 15 TOC were degraded in ozonation and electrolysis processes respectively Yuan et al 2013 The results indicate that E peroxone process is very effective at mineralizing ozone refractory organics and may thus provide an attractive way to treat synthetic dye wastewater The main objective of this work was therefore to further investigate E peroxone treatment of synthetic dye waste water Orange II C I Acid Orange 7 which is a widely used synthetic azo dye see Supplementary Data for details was used as the model compound in this study The OH produc tion in the E peroxone process was evaluated using a ter ephthalic acid TA trapping technique which has been used to quantify OH in various AO processes Hua and Hoffmann 1997 Milan Segovia et al 2007 Decolorization and mineral ization of Orange II in the E peroxone treatment were inves tigated and compared with conventional ozonation and electrolysis processes The effects of the main operating pa rameters e g current ozone concentration electrolyte and solution pH on E peroxone performance were evaluated systematically 2 Experimental 2 1 Chemicals and reagents Analytical grade OrangeII and potassiumtitanium IV oxalate were purchased from Sinopharm Chemical Reagent Co Ltd China H2O2 3 wt and hydroxyterephthalic acid HTA 97 were from SigmaeAldrich Terephthalic acid TA 99 was from Alfa Aesar Other chemicals e g Na2SO4 NaOH and H2SO4 were analytical grade and purchased from Beijing chemical Works Co China All solutions were prepared using deionized water 2 2 Ozonation electrolysis and E peroxone treatment of Orange II solution Ozonation electrolysis and E peroxone treatment of 400 mL OrangeII initial concentration of 200 mg L were conducted in an undivided acrylic column reactor Forozonation treatment an ozone generator Tonglin Technology Co China was used water research 47 2013 6234e62436235 to produce O3from pure O2gas 99 9 The O3concentration in the ozone generator effl uent O2and O3gas mixture can be adjusted by changing the ozone generator power The ozone generator effl uent was then sparged into the bottom of the reactor using a fi ne bubble diffuser at a constant fl ow rate of 0 4 L min Both the electrolysis and E peroxone treatment were conducted under galvanostatic conditions using a DC power supply DJS 292 Leici Co Shanghai China The anode was a 1 cm2Pt plate and the cathode was a 10 cm2 2 cm 5 cm carbon PTFE electrode The carbon PTFE elec trode was prepared with Vulcan XC 72 carbon powder Cabot Corp USA PTFEdispersion andanhydrousalcohol following the procedure described elsewhere Wang et al 2012 The supporting electrolyte was a 0 05 M Na2SO4solu tion unless otherwise specifi ed The electrolysis treatment was initiated by turning on the DC power supply while the ozone generator was off For E peroxone treatment the DC power supply and the ozone generator were turned on simultaneously The O2and O3mixture from the ozone generator was bubbled into the reactor at 0 4 L min which is the same as in ozonation treatment The ozonation electrol ysis and E peroxone treatment were conducted for 90 min 2 3 Analytical methods The gas phase O3concentration at the gas inlet and outlet of the reactor was monitored using an ozone analyzer UV 300 Sumsun EP Hi Tech Co Beijing during the E peroxone pro cess The H2O2concentration in the solution was measured using the potassium titanium IV oxalate method Sellers 1980 The OH concentration was analyzed using a tereph thalic acid TA trapping protocol Hua and Hoffmann 1997 Milan Segovia et al 2007 Briefl y TA 50 mM was added into the electrolyte in the reactor before the commencement of E peroxone The E peroxone system was then turned on to generate OH in the electrolyte A proportion of the OH that were continuously generated during the E peroxone process were then trapped by the non fl uorescent TA to form highly fl uorescent HTA The concentration of HTA was determined using a fl uorescence spectrophotometer Hitachi F 7000 and can be taken as a cumulative measurement of the OH pro duced during the operation time see Supplementary Data for more discussion on OH measurement Xu et al 2011 Hua and Hoffmann 1997 Milan Segovia et al 2007 During Orange II treatment an aliquot of solution sample was collected from the reactor at various time intervals TOC was measured using a TOC VCPH analyzer Shimadzu Co Japan to evaluate the mineralization of Orange II during the treatment The absorbance at 484 nm was analyzed by a UVevisible spectrophotometer Hach DR 5000 to evaluate the decolorization effi ciency The UVevisible spectral changes of OrangeIIweremonitoredusingaUV 2401PCUVeVis Recording spectrophotometer Shimadzu Co Japan The acute toxicity of ozonation and E peroxone effl uent was determined by Microtox bioassays Hammami et al 2008 After 15 min of exposure the decrease in bioluminescence of Vibrio fi sheri was measured using the LUMIStox system Dr Lange GmbH Germany The toxicity is expressed as the percent of the inhibition of bioluminescence relative to reference 3 Results and discussion 3 1 H2O2and OH production in E peroxone process Fig 1 shows that when pure O2was sparged into the reactor during electrolysis while the ozone generator was off the H2O2concentration increased almost linearly with reaction time In contrast almost no HTA were detected in the solu tion The result indicates that H2O2was continuously pro duced from the sparged O2at the carbon PTFE cathode However the in situ generated H2O2was not further con verted to OH which would otherwise have been trapped by TA to form HTA when no O3was sparged Conversely when the ozone generator was turned on and thus the O2and O3gas mixture was sparged into the reactor no H2O2accumulation was observed Fig 1 The O3concen tration at the gas outlet w47 mg L was considerably lower than at the inlet w74 mg L see Fig S2 in Supplementary Data indicating that a substantial amount of O3was consumed in the system On the other hand the concentra tion of HTA increased signifi cantly within the fi rst 30 min of reaction time These trends demonstrate that the sparged O3 and in situ generated H2O2were consumed in the E peroxone process to produce OH continuously which were then trap ped by TA to form HTA The HTA concentration then decreased gradually after 30 min of reaction time This can be attributed to the fact that HTA can be further degraded by OH and O3 Hua and Hoffmann 1997 Thiruvenkatachari et al 2007 The above results show that considerable amounts of OH can be produced from sparged O3and in situ generated H2O2 in the E peroxone process We therefore expected that E peroxonecandegradeOrangeII effectively whichisevaluated in the following sections Fig 1 e H2O2and OH production during electrolysis with O2sparging and E peroxone process current of 400 mA inlet O3 concentration of 74 mg L gas fl ow rate of 0 4 L min water research 47 2013 6234e62436236 3 2 Comparison of electrolysis ozonation and E peroxone treatment of Orange II Decolorization of Orange II solution by electrolysis ozonation and E peroxone treatment was evaluated by monitoring the solution s absorbance at l 484 nm which is the maximum absorbance of Orange II in the range of visible wavelengths Fig 2 a Electrolysis removed approximately 60 color after 90 min treatment fi gure shown for 30 min In contrast ozonation and E peroxone processes achieved almost com plete decolorization within the fi rst 2 and 4 min of treatment respectively These results are consistent with the general observation that ozone based processes are very effective at decolorizing azo dyes because O3can selectively attack the chromosphere i e the azo bond and the reactions occur rapidly in bulk solutions Silva et al 2009 Tehrani Bagha et al 2010 Liakou et al 1997b Lopez et al 2004 In contrast decolorization by electrolysis is limited by the mass transfer of dye molecules to the anode surface where they are degraded by OH produced from H2O oxidation Brillas et al 2005 Ozcan et al 2009 Electrolysis thus usually requires a long time to decolorize dye wastewaters Martinez Huitle and Brillas 2009 Hastie et al 2006 It was noticed that E peroxone treatment removed the color of Orange II slightly slower than ozonation Fig 2 a Similarly other researchers reported that adding H2O2in ozonationprocess i e conventionalperoxoneprocess decreased the decolorization rates of Orange II slightly Lopez et al 2004 This decrease is mainly because some of the sparged O3is consumed in the reaction with H2O2to produce OH Although OH are a much stronger oxidant than O3 they are less selective in attacking the dye chromophores because they oxidize dyes and their degradation intermediates non selectively Tehrani Bagha et al 2010 Lopez et al 2004 Compared with decolorization mineralization of the dye took a much longer time Fig 2 b Only 15 3 and 55 6 TOC wasremovedfromthe solution after 90minof electrolysis and ozonation treatment respectively However TOC removal was dramatically improved when these two processes were combined in the E peroxone treatment whereby more than 95 TOC was removed after 45 min of treatment It is noted that oxidation of Orange II may produce some volatile in termediates e g carboxylic acids that can be released with the gas stream To measure the amounts of volatile organics released with the gas stream the gas effl uent from the reactor was passed through an absorber containing 400 mL NaOH solution 0 01 M The concentration of TOC in the absorbing solution was then analyzed The result shows that only w3 3 of the initial TOC of the Orange II wastewater was released with the gas stream during E peroxone treatment see Fig S3 in Supplementary Data This indicates that TOC removal by gas stripping is negligible and the pollutants are removed mainly by mineralization during E peroxone treatment of Orange II wastewater The above results show that electrolysis and ozonation alone were not very effective at mineralizing Orange II and its degradation intermediates However when they are com bined in the E peroxone process they have a signifi cant syn ergistic effect on pollutant mineralization mainly due to the considerable amounts of OH that are produced from the sparged O3and in situ electro generated H2O2 see Fig 1 Further because the OH are produced in the bulk solution they can oxidize pollutants more effi ciently than the OH produced from electrolysis which are largely adsorbed on the anode surface Ozcan et al 2009 Borras et al 2011 As dis cussed previously the rate of pollutant degradation in elec trolysis can be limited by the mass transfer of pollutant to the anode surface and this limitation becomes increasingly se vere as the pollutant concentrations decrease Brillas et a