外文翻译--Overview of Some Colour removal Technologies in the Textile wastewater

Overview of Some Colour removal Technologies in the Textile wastewater(a)Aamr Alalewi (b)Prof.Cuiling Jiang a Aamr Alalewi:PhD candidate in the Department of water resource and hydrology,Hohai University,China,Nanjing,2009 E-mail: b Prof.Cuiling Jiang:State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering,Hohai University,AbstractDyes are natural compounds that make the world more beautiful through coloured substances.However,the release of coloured wastewaters represents a serious environmental problem and a public health concern.Colour removal,especially from textile wastewaters,has been a big challenge over the last decades,and up to now there is no single and economically attractive treatment that can effectively decolourise dyes.In the passed years,notable achievements were made in the use of biotechnological applications to textile wastewaters not only for colour removal but also for the complete mineralization of dyes.Different microorganisms such as aerobic and anaerobic bacteria,fungi and actinomycetes have been found to catalyse dye decolourisation.Moreover,promising results were obtained in accelerating dye decolourisation by adding mediating compounds and/or changing process conditions to high temperatures.This paper provides a critical review on the current technologies available for decolourisation of textile wastewaters and it suggests effective and economically attractive alternatives.Keywords:Dyes;decolourisation;textile;anaerobic;Biological;1.INTRODUCTION With the increased demand for textile products,the textile industry and its wastewaters have been increasing proportionally,making it one of the main sources of severe pollution problems worldwide.In particular,the release of coloured effluents into the environment is undesirable,not only because of their colour,but also because many dyes from wastewater and their breakdown products are toxic and/or mutagenic to life.Without adequate treatment these dyes are stable and can remain in the environment for an extended period of time.For instance,the half-life of hydrolysed Reactive Blue 19(RB19)is about 46 years at pH 7 and 25.In addition to the environmental problem,the textile industry consumes large amounts of potable water.In many countries where potable water is scarce,this large water consumption has become intolerable and wastewater recycling has been recommended in order to decrease the water requirements.Textile wastewaters are characterized by extreme fluctuations in many parameters such as chemical oxygen demand(COD),biochemical oxygen demand(BOD),pH,colour and salinity.The wastewater composition will depend on the different organic-base compounds,chemicals and dyes used in the industrial dry and wet-processing steps.The most common textile-processing set-up consists of desizing,scouring,bleaching,mercerising and dyeing processes(1).2.DYE CHARACTERISTICS AND CLASSIFICTION It is important to note that all colored substances are not necessarily dyes.A dye is a colored substance that can be applied in solution or dispersion to a substrate(e.g.,a textile 978-1-4244-4713-8/10/$25.00 2010 IEEEfiber,paper,or foodstuff),thus giving it a colored appearance.The substrate has a natural affinity for appropriate dyes and readily absorbs them from solutions or aqueous dispersion.Concentrations of dyes,temperature,and pH are important factors in controlling the dyeing process.A common example of an azo dye can be seen in Figure 1.Figure 1:Example of an azo dye structure 3.DECOLOURISATION PROCESSES 3.1 Biological and chemical reductive decolourisation The reductive decolourisation of azo dyes under anaerobic conditions is a combination of both biological and chemical mechanisms.The biological contribution can be divided in specialised enzymes called azo reductases,which are present in bacteria that are able to grow using only azo dye as a carbon and energy source.However,up to date there is no clear evidence of anaerobic azo reductase;or non-specific enzymes that catalyse the reduction of a wide range of electron-withdrawing contaminants,including azo dyes(9).Thus,a co-metabolic reaction is probably the main mechanism of dye reduction,in which the reducing equivalents or reduced cofactors like NADH,NAD(P)H,FMNH2 and FADH2 acting as secondary electron donor,channel electrons to cleave the azo bond(8).The chemical contribution to the reductive decolourisation of azo dyes under anaerobic conditions may involve biogenic reductants like sulphide,cysteine,ascorbate or Fe2+(12;13).Particularly for sulphide,it can be formed by sulphate reduction in anaerobic bioreactors.Therefore,there will be a competition between sulphate and dye to become the terminal electron acceptor of the reducing equivalents.(13)Observed that different sulphate concentrations did not have an adverse effect on the reduction of RR2 in either batch assays or reactor experiments.The authors concluded that sulphate,even present at concentrations up to 60 mM,did not obstruct the transfer of electron to the azo dye.In another investigation on colour removal,(14)used an anaerobicaerobic sequencing batch reactor fed with sulphate(0.35 mM).The results indicated that the decolourisation capacity was not improved while testing the dye Acid Orange 7,even though a sulphate reducing microbial population was established.Therefore,for a real perspective application,the contribution of sulphide generated by sulphate reduction seems to be negligible,and therefore the colour removal is mainly due to biological processes.Fig.2 shows the electron flow preference in the presence of different redox couples involved in biological processes Thus,oxygen is a more effective electron acceptor than azo dyes,which justify the low decolourisation rates(1030%)under aerobic conditions.Nevertheless,either by using pure cultures or granular sludge under anaerobic conditions,literature reports poor reductive decolourisation with specific dyes(19;20;18).Furthermore,the rates are extremely dependent on the type of dye,in which the azo dyes generally present the highest rates of decolourisation.On the other hand,anthraquinone and phthalocyanine dyes are shown to be rather recalcitrant(18;21;22).Another drawback is that some dyes are quite toxic to the anaerobic microorganisms,which in some cases,may lead to a permanent loss of the methanogenic activity even for low dye concentrations(23;24;5;25;22).Thus,oxygen is a more effective electron acceptor than azo dyes,which justify the low decolourisation rates(1030%)under aerobic conditions.Nevertheless,either by using pure cultures or granular sludge under anaerobic conditions,literature reports poor reductive decolourisation with specific dyes(19;20;18).Furthermore,the rates are extremely dependent on the type of dye,in which the azo dyes generally present the highest rates of decolourisation.On the other hand,anthraquinone and phthalocyanine dyes are shown to be rather recalcitrant(18;21;22).Another drawback is Fig.2.Electron flow preference as a function of the different electron couples(adapted from 15;16;17;18).RM and RMreduc are the oxidized and the reduced form of the redox mediator,respectively that some dyes are quite toxic to the anaerobic microorganisms,which in some cases,may lead to a permanent loss of the methanogenic activity even for low dye concentrations(23;24;5;25;22).4.NON-BIOLOGICAL COLOUR REMOVAL 4.1 Chemical methods:Chemical oxidation typically involves the use of an oxidizing agent such as ozone(O3),hydrogen peroxide(H2O2)and permanganate(MnO4)to change the chemical composition of a compound or a group of compounds,e.g.dyes(26).Among these oxidants,ozone is the most widely used because of its high reactivity with many dyes,usually providing good colour removal efficiencies(27).Actually disperse dyes and those insoluble in water represent a drawback for the process,as well as the high cost of ozone(28;29).Table 3 gives an indication of the oxidative power of the hydroxyl radical based on the electrochemical oxidation potential(EOP)capacity compared with other oxidants.At present,many different combinations of these AOP have been investigated for colour removal,all of which are capable of producing the free hydroxyl radical(HO)The first example is a reaction called the Fenton reaction,in which hydrogen peroxide is added in an acid solution(pH 23)containing Fe2+ions:Fe2+H2O2Fe3+HO+HO (1)In comparison with ozonation,this method is relatively cheap and also presents high COD removal and decolourisation efficiencies(30).The main process drawbacks are the high sludge generation due to the flocculation of reagents and dye molecules(31),as well as the need for decreasing the bulk pH to acidic conditions(28).Table 3:Oxidation capacity of different oxidants in terms of electrochemical oxidation potential(EOP)(adapted from(26)Oxidizing agent EOP(V)Fluorine 3.06 Hydroxyl radical 2.80 Oxygen(atomic)2.42 Ozone 2.08 Hydrogen peroxide 1.78 Hypochlorite 1.49 Chlorine 1.36 Chlorine dioxide 1.27 Oxygen(molecular)1.23 In H2O2/UV process HO radicals are formed when water-containing H2O2 is exposed to UV light,normally in the range of 200280 nm(26).The H2O2 photolysis follows the reaction:H2O2+UV(orhv,k200280 nm)HO+HO(2)This process is the most widely used AOP technology for the treatment of hazardous and refractory pollutants present in wastewaters,mainly because no sludge is formed and a high COD removal in a short retention time is achieved(3)5.CONCLUSIONS All the decolourisation methods described in this review have advantages and drawbacks,and their selection will depend on the wastewater characteristics like class and concentration of dye,pH,salinity and toxic compounds.seems to be a very attractive technology.Moreover,the use of redox mediators and/or thermophilic treatment to accelerate decolourisation rates in bioreactors is very promising,while ways to immobilize redox mediators in bioreactors or their recovery when continuously dosed,still represents a challenge.Efficient post-treatment methods,e.g.aerobic biological post-treatment,ozone and fenton reagents,for the complete mineralization of the aromatic amines,which are formed in the anaerobic step,must be utilized.Therefore,the treatment of textile wastewater either to guarantee the emission requirements or to close the water cycle should be composed of a sequence of treatments,and eachscenario should be analysed individually REFERENCES 1 Dos Santos,A.B.,2001.Tratamento de aguas residuarias texteis pelo sistema de lodos ativados em batelada.Departamento de Engenharia Hidraulica e Ambiental,Universidade Federal do Ceara,Fortaleza,p.111 Crit.Rev.Env.Sci.Technol.30,449505.5 Fontenot,E.J.,Lee,Y.H.,Matthews,R.D.,Zhu,G.,Pavlostathis,S.G.,2003.Reductive decolorization of a textile reactive dyebath under methanogenic conditions.Appl.Biochem.Biotechnol.109,207225 8 Gingell,R.,Walker,R.,1971.Mechanism of azo reduction by Streptococcus faecalis II.The role of soluble flavins.Xenobiotica 1,231239.12 Yoo,E.S.,2002.Chemical decolorization of the azo dye CI Reactive Orange 96 by various organic/inorganic compounds.J.Chem.Technol.Biotechnol.77,481485.13 Van der Zee,F.P.,Bisschops,I.A.E.,Blanchard,V.G.,Bouwman,R.H.M.,Lettinga,G.,Field,J.A.,2003.The contribution of biotic and abiotic processes during azo dye reduction in anaerobic sludge.Water Res.37,30983109 14 Albuquerque,M.G.E.,Lopes,A.T.,Serralheiro,M.L.,Novais,J.M.,Pinheiro,H.M.,2005.Biological sulphate reduction and redox mediator effects on azo dye decolourisation in anaerobicaerobic sequencing batch reactors.Enzyme Microbiol.Technol.36,790799 15 Dubin,P.,Wright,K.L.,1975.Reduction of azo food dyes in cultures of Proteus vulgaris.Xenobiotica 5,563571.16 Cervantes,F.J.,2002.Quinones as Electron Acceptors and Redox Mediators for the Anaerobic Biotransformation of Priority Pollutants.Agrotechnology and Food Sciences,Sub-department of Environmental Technology,Wageningen University,Wageningen,The Netherlands,p.166 17 Madigan,M.T.,Martinko,J.M.,Parker,J.,2003.Brock Biology of Microorganisms,10th ed.Prentice-Hall Inc.,Simon&Schuster/A Viacom Company,Upper Saddle River,New Jersey,USA.18 Dos Santos,A.B.,2005.Reductive Decolourisation of Dyes by Thermophilic Anaerobic Granular Sludge.Sub-department of Environmental Technology,Wageningen University,Wageningen,p.176 19 Brown,M.A.,DeVito,S.C.,1993.Predicting azo dye toxicity.Crit.Rev.Env.Sci.Technol.23,249324.20 Van der Zee,F.P.,Lettinga,G.,Field,J.A.,2001b.Azo dye decolourisation by anaerobic granular sludge.Chemosphere 44,11691176.21 Lee,Y.H.,Pavlostathis,S.G.,2004.Reuse of textile reactive azo dyebaths following biological decolorization.Water Environ.Res.76,5666 22 Lee,Y.H.,Matthews,R.D.,Pavlostathis,S.G.,2005.Anaerobic biodecolorization of textile reactive anthraquinone and phthalocyanine dyebaths under hypersaline conditions.Water Sci.Technol.52,377383.23 Brown,D.,Laboureur,P.,1983a.The aerobic biodegradability of primary aromatic amines.Chemosphere 12,405414.24 Van der Zee,F.P.,Bouwman,R.H.M.,Strik,D.P.B.T.B.,Lettinga,G.,Field,J.A.,2001a.Application of redox mediators to accelerate the transformation of reactive azo dyes in anaerobic bioreactors.Biotechnol.Bioeng.75,691701.25 Van der Zee,F.P.,Villaverde,S.,2005.Combined anaerobicaerobic treatment of azo dyes a short review of bioreactor studies.WaterRes.39,14251440.40 Metcalf and Eddy,2003.Wastewater Engineering:Treatment and Reuse,4th ed.McGraw-Hill,New York,USA.27 Alaton,I.A.,Balcioglu,I.A.,Bahnemann,D.W.,2002.Advanced oxidation of a reactive dyebath effluent:comparison of O3,H2O2/UV-C andTiO2/UV-A processes.Water Res.36,11431154.28 Hassan,M.M.,Hawkyard,C.J.,2002.Decolourisation of aqueous dyes by sequential oxidation treatment with ozone and Fentons reagent.J.Chem.Technol.Biotechnol.77,834841.29 Anjaneyulu,Y.,Sreedhara Chary,N.,Raj,D.S.S.,2005.Decolourization of industrial effluents available methods and emerging technologies a review.Rev.Environ.Sci.Bio/Technol.4,245273.30 Van der Zee,F.,2002.Anaerobic azo dye reduction.Environmental Technology.Wageningen University,Wageningen,The Netherlands.32 Safarzadeh,A.A.,Bolton,J.R.,Cater,S.R.,1997.Ferrioxalate-mediated photodegradation of organic pollutants in contaminated water.Water Res.31,787798