Fenton法中的物化和氧化去除垃圾渗沥水的有机物 毕业论文外文翻译.doc

Fenton法中的物化和氧化去除垃圾渗沥水的有机物 毕业论文外文翻译.doc Fenton法中的物化和化去除渗沥水的有机物氧垃圾 Yang Deng Department of Civil, Architectural and Environmental Engineering, University of Miami, McArthur Building Room 325, 1251 Memorial Dr., Coral Gables, FL 33124-0630, USA Received 22 August 2006; received in revised form 10 December 2006; accepted 12 December 2006 Available online 15 December 2006 摘要,市政渗沥水～尤其是沥沥久置沥酵的渗沥水～影中等沥模的以活性沥泥法沥沥理垃圾会响 方法的沥水沥理的行～且不利于生物前置沥理。近期～厂运并Fenton法用于渗沥水的化垃圾学沥沥理中。本沥文中～沥沥沥果沥明了在Fenton法中～化和混凝在少渗沥水中的有机氧减垃圾 物中所起到的作用～沥沥了COD的化及混凝效率～同沥～在不同的操作件下～通沥氧条将 氧化和混凝分沥去除COD的去除率沥行比沥。考沥了低初始pH沥～适的相沥及沥沥当Fenton使用量～通沥～逐步增加化添加沥～通沥化除去学氧COD～以及化混凝的重要性比沥。在曝氧与 气会断氧碳的沥程中逐步加沥～由于沥程中生成酸性中沥沥物和沥沥不通入二化～在沥理沥无需初始pH沥成酸性。一方面～高另COD氧化效率和和低沥沥含量抑制了混凝沥理中COD的去除。在高化效率下～由于低混凝效率沥致氧会COD沥量下降。在最佳件下;初始条pH沥沥 2+3～[H O ]/[Fe ] = 3, [H O ] = 240 mM～六次定量加沥,～COD的去除率沥61%～化去氧2222 除率,混凝去除率沥0.75。沥果明了在渗沥水垃圾Fenton沥理方法中～化和混凝沥合使用氧 的重要以及在混凝中去除COD中化所起到的控制作用。氧 沥沥字,Fenton法～渗沥水～化～混凝～有机沥染物垃圾氧 1.介沥 目前～在美甚至全世界～埋被沥沥是最沥沥最考沥沥境容量的固沥沥物沥理方国垃圾填体弃 法～但是～其中沥生的渗沥水是一沥高沥染的沥水～要是直接排到沥水沥理中腐沥抽垃圾厂会 水沥沥～沥以沥持出水余沥的不沥～以及沥泥膨沥和淀物沥沥。生化沥理能沥用于新沥的渗沥水;少沉 于2年,～一般沥沥的渗沥水的BOD/COD大于0.6～含有高沥度低分子量的有机物。然而～沥5 些方法不适用于久置的渗沥水;沥存沥沥超沥并垃圾5~10年,～因沥此沥BOD/ COD小于0.3且5 有机物的分子大又沥降解～因此～物化沥理就沥用于此沥渗沥水的沥沥理和主沥理中。 在久置渗沥水的物化沥理方法中～近年出沥了垃圾几Fenton法～据分析Fenton法是最沥沥有效的沥理方法之一。有机沥染物的去除效率有沥于行,反沥几个运参数pH沥～Fenton沥沥加入量～通沥曝～混凝气pH～沥外添加沥～度～紫外沥照射～混凝沥的温pH沥整～有沥沥些件条的沥沥沥沥沥沥沥。典型的Fenton法沥理沥水包括四步沥,化～个氧中和～混凝/凝沥～固液分。因离此～有机物的去除需要化和混凝步操作。化是通沥溶液中的沥基沥沥的～一有效的氧两氧个 且无沥沥性化沥～然～也有其他物沥可以作沥沥沥化沥。氧当氧 有沥三价沥子在溶液中沥化沥二价沥～管沥化的量沥比二价沥沥化沥三价沥低好。离会尽数几个 溶液中生成的二价沥子可能沥沥化沥反沥以提供更多的沥基～在中和部分～由于沥离会与氧 氧会研响几个响化沥的析出沥致絮凝～但是～以前的究更注重影沥有机物去除率的影因素～沥些因素是沥化和混凝沥程的～在不同件下沥理沥水化和混凝是否好地沥合起沥了怎氧条氧很来～而且沥些沥沥沥渗沥水的沥理沥依然是沥有限的～垃圾来极Yoon et al指出在沥理前期中～沥于有机物的除去起到作用的是混凝～沥沥沥是通沥沥察个Fenton法和沥沥的混凝沥理高分子有机沥染物得到的。Wang和Lau沥沥沥～在具有生化沥定性 的渗沥水的垃圾COD的去除中～化和混凝氧的作用分沥占沥20%和80%。Kang和Hwang沥沥～pH和Fenton沥沥加入量在化和混凝沥合沥理氧 垃圾渗沥水中沥COD的去除有着巨大的影～且混凝沥期的响并pH会响影混凝效率。然而～就去除效率而言化和混凝的沥系沥有待于沥一步沥沥。氧 2.沥沥 本文指出了沥的COD去除效率和在不同件下沥理久置渗沥水～化和混凝沥条垃圾氧 COD的去除。通沥化去除的氧COD和通沥混凝去除的COD,沥者的比例是衡量究竟沥在沥理两 中起主沥作用一重要的沥准～其次～化和混凝操作涉及到的初始个很氧pH沥～摩沥比～Fenton沥沥加入量～通沥曝以及沥外添加沥的逐步加入～本文也有沥明。外～也沥述了混凝气另 和化在沥理中的配合～最后～通沥曝和沥外添加沥的配合作用也有提到。氧气 表1 垃圾渗沥水的基本沥成 垃圾来渗沥水自于Polk County North Central Landfill～平均BOD/COD小于0.05～很5 沥然沥是久置的渗沥水～存沥在无盖子中～一般沥沥前的度都保持在垃圾瓶温4沥氏度。其成分在表1中沥出。 所有化沥品均沥分析沥～如无特沥沥明按沥明沥指示使用～未沥沥理的渗沥水先沥沥沥沥沥沥以除学 去大沥粒物沥～且保持所有沥品的一致性。沥沥的每沥操作都在室和常沥下沥行。用沥硫酸沥沥并温 使初始pH沥到沥期沥～在达1L沥杯中加入200mL沥沥沥的渗沥水～沥磁力沥拌沥沥拌。沥通沥后～垃圾 用小型的抽机注入空～气气(20L/h)。沥水面至沥杯沥沥的距防止沥水在反沥除器因沥沥桌离会湿 生泡沫而溢出～沥了究通沥和研Fenton沥沥的逐步加入～本沥沥中～其化沥程沥沥沥氧9h～沥沥量随着沥外沥沥的延沥而增加～在其他沥沥中～Fenton氧化沥程的沥沥沥2h～添加沥沥按下文沥行,首先～加入沥粒硫酸沥沥;七水硫酸沥沥,～接着加入沥化沥溶液～在化沥段沥束后～状氧氧将NaOH加入到沥快速沥拌后的溶液中～使pH达到6.5～然后逐滴加入液沥沥碱pH至8～然后渗沥水将在Phipps & Bird沥拌器下沥拌20min～沥持沥速沥20沥/分。沥COD去除量以及化和混凝去除的氧 COD量是将Kang和Hwang的方法沥行了稍加改沥沥得的～相沥地～100mL等分的均溶液移匀至璃杯中在玻50沥氏度水浴中加沥30min以去除溶液中多余的沥化沥～溶液氧将温冷却至室～静沉置降90min～然后～沥沥沥沥泥量～将清上液中的COD和沥泥沥沥分沥沥行沥定～前者表示沥理沥程后的COD～后者表示沥混凝后得到的固相中的COD沥～沥化去除的氧COD不同于整沥程个中去除的COD和沥混凝除去的固相的COD～pH沥由pH沥沥得。COD由比色而得～沥差由沥准差表示(n=3)。 3.沥果沥沥与 3.1初始pH沥。 初始pH沥沥COD去除率的影如下沥响1(a)～沥化沥沥度沥氧23.5Mm～沥沥子沥度沥离14mM沥～最佳pH沥2.5~3.5～此沥沥COD去除率沥50%～沥些沥果与Kang&Hwang沥得的一致～当pH沥小于2.5沥～COD去除效率大大降低～沥主要是因沥沥沥水合子和沥化沥的反沥速率降低～由离氧 于沥子的增加中和了部分沥离氧离离会离氧根子～同沥沥子也抑制三价沥子和沥化沥的反沥～ 沥化沥自沥分解的能力提高了～沥氧离另当一方面～pH大于5沥～效率也下降了～沥是因沥～ 子沥沥沥的沥化合物的能力降低了～沥氧氧离会碳碳减根子的增加沥致酸沥和重酸沥的少～以及沥氧离氧根子的化沥沥也降低了～因此～各沥COD的去除率初始与ph有大的沥系。很 初始pH沥沥化和混凝去除氧COD的比例的影沥沥响1(b)～沥比例沥在Fenton沥理中是衡量有机物化降解重要性的一沥沥而有效的表示～如沥所示～氧个pH=3沥～出沥峰沥0.43～故此沥沥氧化沥段的最佳pH沥～相反～当pH>6沥～化去除的氧COD相沥于去除的沥COD沥的比例沥0.10～沥表面在沥些件下～混凝沥个条COD的去除占主沥地位～因此～初始pH沥沥化和混凝氧的沥更有主沥作用有大的影。很响 沥1 初始pH沥(a)COD去除率的影响～(b)氧化去除的COD相沥于去除的沥COD沥的比例的影;此沥件响条 2+沥Fe = 14 mM; HO = 23.5 mM; mean initial COD = 1166 mg/L,22 3.2 Fenton沥沥用量。 2+[HO]/[Fe]的摩沥比沥COD去除率的影沥沥响2～此沥沥化沥用量固定沥氧180mM～初始22 pH=3.0.当[H2O2]/[Fe2+]=3沥～出沥最大的化去除效率氧27%～摩沥比增加至当12沥～氧化效率沥下降至最大沥的一会氧会半～原因沥因于沥化沥沥沥基的去除在摩沥比增大沥增强～如反沥式(3), • •H O +OH ?H O +HO (3) 2222 当摩沥比小于3沥～比率也下降～因沥沥子会离会消耗沥基。如反沥式(4) 2+3+? (4)OH + Fe?Fe + OH 2+沥2 [H O ]/[Fe ]沥COD的去除率的影和响φ沥的影;件是,初始响条pH沥3～[H O ] = 180 mM～初始2222 COD1133mg/L, 2+在化沥程中～沥果表示最佳氧[HO]/[Fe]摩沥比大沥是3.0～一方面～摩沥比沥另当22 2~12～沥化沥加入量沥氧180mm沥～沥混凝去除的COD由34%降至22%～沥主要是因沥沥沥子离含量的增加～沥些沥沥子沥沥中和和混凝最沥沥沥沥沥化三沥～下降了离会氧83%。因此沥沥子大离会大影混凝效率～沥化和混凝沥合起去除的响氧来COD中的55%在摩沥比沥2~3沥是沥定的～摩沥比沥3~12沥下降至会34%～外～另φ沥也摩沥比有沥～一般最大沥跟φ沥沥1.0～此沥摩沥比沥3.0。 沥COD去除量～沥化和混凝去除的氧COD量～以及φ沥与Fenton沥沥的加入量之沥的沥系沥沥 2+3(a)-(c)～在任意特定的[Fe]沥度下～沥COD去除量着沥化沥的增加而增加～随氧 2+2+2+;pH=3.0[Fe]=30mM, [HO]>90mM;[Fe]=60mM,[HO]>180; [Fe] = 90mM, 2222 [HO]>270,沥不明沥～此外～沥并COD去除量着沥沥子沥度增加而增加;限定沥度在随离22 30~60mM,～但60~90mM沥增加不明沥～沥表明最佳沥子加入量沥沥离60mM。 在Fenton法中～化和混凝之沥的沥系特性由沥氧3(b)表示～第一～由于沥化沥量和化氧氧期沥的效率增加～混凝沥期的COD去除量逐步降低～沥暗示化沥程中氧副沥物不利于混凝沥程～沥沥沥沥个与Fenton法在化和混凝中首先去除高分子有机沥染物是氧当氧吻合的～第二～沥沥化沥量沥多沥～沥沥子含量离越多～沥混凝的去除效率越大～沥是因沥沥中和后三价沥絮凝沥沥度增大了～ 然而～沥化沥量沥少沥～化效果不明沥～当氧氧个离那沥沥效率也就不明沥了。故沥沥子的含量也是混凝沥程中COD去除效率的一重要影因素～前提是化效率高～化效率不高沥～个响氧当氧 沥沥沥也不成个很氧会响氧会立～因此明沥化效率影混凝效率～高化效率可能沥致低混凝效率。 2+如沥3(c)所示～沥在任意沥度的[Fe]下着随[HO]的增加而增大～当[HO]>90mM沥～2222φ随离当着沥子含量的增加而降低～但[HO]<90mM沥～沥不出沥沥沥会况当情。摩沥比沥10沥～22 沥到最大达2.10。 沥3 不同Fenton沥沥加入量沥沥理沥果的影,响(a)COD沥去除率～(b)由化和混凝分沥去除氧COD的效率～(c) 比率φ沥;件,初始条pH=3～初始COD=1133mg/L, 3.3 通沥和逐步增加Fenton沥沥量。 只通沥～只逐步增加Fenton沥沥量以及二者沥合起沥将来COD去除的影沥沥响4～九次逐步增加Fenton沥沥量使化去除氧COD的效率有了小幅度的提高～从18%升至24%～使沥COD去除效率由46%增至56%～只通沥的沥～是化去除会氧COD的效率增至22%～但是不会来会氧提高沥去除效率～二者沥合起使化去除效率增至32%～使沥去除效率增至55%。 沥些基沥可能成沥出沥～可能不沥出沥而会会称从会与离形成相沥沥定的化合物～或者沥沥子反沥～沥些有机中沥沥物沥沥沥沥基会与&氧气沥生反沥～沥致分解甚至沥化。 沥4 通沥和逐步加入沥沥沥各沥COD去除率的影～;响pH=3～沥反沥沥沥=9h～初始COD=1295mg/L～H O] = 22 2+240 mM; 摩沥比[HO]/[Fe]= 3,22 将来会响氧氧当氧二者沥合起影化沥程～沥有～逐步加入沥化沥也有利于沥理～沥沥因于沥沥化沥沥度大沥沥生自沥分解而沥致沥沥基的除能力降低。通沥沥～水中含有很会清氧足沥的溶解～抑制了沥化沥的分解～而氧从氧避免了沥化沥的浪沥。 2H O ? 2H O + O (5) 2222 另氧气会与外～水中的R-基沥生反沥～形成沥基和有机化合物～如反沥式(7)•+R+O?R(H)+HO (6) 22• ••R O?ROO?RO(7)2• 逐步添加沥沥沥COD沥去除率～通沥化和混凝去除的氧COD,以及φ的影如沥响5～分九步增加沥沥量～沥化去除的氧COD由22%至32%～φ沥由0.90增至1.33～分六步添加～COD去除率比九步要高～此沥化效率最大～氧φ沥也最大～可能是因沥低分子的化氧副沥物有利于混凝～如沥所示～COD去除效率到最大沥达61%沥～此沥初始pH=3～摩沥比沥3～[HO] = 240 mM～22且沥沥添加步沥沥6～此沥φ沥沥0.75。 沥5 逐步增加沥沥量沥去除效率和φ沥的影响 沥通沥件下分步添加沥沥的条Fenton法沥理渗沥水～沥些沥沥究了初始垃圾研pH沥和沥化沥氧量的相互沥系如沥6(a)和(b)～如沥a～就沥COD的去除沥～着沥化沥沥量的增加～沥酸化来随氧 的要求沥要降低。特沥的是～在指定的pH范沥～沥化沥沥内当氧从0增至80mM沥～沥COD去除量大大增加～但沥化沥量多的沥当氧条候～增加沥相沥小了。如沥示～在沥沥的沥件下～相沥于初始pH～沥化沥量更多地是影化沥程中氧响氧COD的去除而不是沥的COD去除～同沥的～比率也呈沥沥沥的沥沥～如沥b～沥沥影在分步添加沥沥沥沥的更明沥～例如～使初始响体即pH沥8沥～在沥沥 逐沥加入沥～渗沥水的pH会氧慢慢降低～所以一般化沥程都是在低pH状当氧沥沥沥行的～沥沥化沥量沥80mM沥～最沥的pH会来由原的8降到2.523～而初始pH沥3沥也不沥降低至2.312。pH在化沥段降低的氧两个氧碳原因可沥沥～一是分解沥形成了有机酸中沥沥物～二是通入二化形成了酸。碳 沥6 将氧通沥及逐步添加沥沥作沥沥化沥量和pH的函数～a是去COD去除率的影～响b是沥φ沥的影响4. 沥沥。 本沥沥究了沥沥研Fenton法沥理久置的渗沥水～初始垃圾pH沥低～Fenton沥沥的相沥加入量和沥沥加入量～通沥～逐步加入沥沥～沥些都使COD的去除率得以提高～不沥是化沥程的沥是混氧凝沥段的～但通沥件和逐步加入沥沥沥合起沥～初始条来pH的影就响会削弱了～因沥生成酸性有机中沥沥物加上通入二化～氧碳pH会另自然降低～一方面～可以得到混凝沥程的去除效 率主要是受氧离氧残化沥程的去除效率和沥子的含量。化效率高沥暗示了有机留物中可能 包含沥多小分子物沥～沥些小分子大多是高分子物沥的化沥物且有利于混凝沥程。沥得注氧意的 是～化效率高的沥降低氧会COD的沥去除量～因沥混凝效率降低。因此～沥然会来氧看起化 在沥水沥理中;例如COD 的去除～以及沥混凝沥程的影,响个很极扮演了一沥沥的角色～此外～ 高沥度的沥子由于离氧形成大絮沥而使混凝的效率提高～前提是化效率也要高～不然就无 2+从条即沥起～在最佳件下;初始pH=3～[HO]/[Fe] = 3, [HO] = 240 mM～分六步添加沥2222 沥,61%的COD都得以去除～且并φ沥0.75～沥揭示了化在混凝沥程中氧COD去除所起到的 重要作用。 参献考文, [1] Kreith (Eds.), P.R. O’leary, G. Tchobanoglous, Landfilling, in: G. Tchobanoglous, F.Handbook of Solid Waste Management, McGraw-Hill,2002. [2] H. Ehrig, R. Stegmann, Biological processes, in: T.H. Christensen, R.Cossu, R. Stegmann (Eds.), Landfilling of Waste: Leachate, firsted., Elsevier Applied Science, London and New York, 1992. [3] A. Amokrane, C. Comel, J. Veron, Landfill leachates pretreatment bycoagulation- flocculation, Water Res. 31 (1997) 297-336. [4] L.C. Chiang, J.E. Chang, C.T. Chung, Electrochemical oxidation combined with of refractory landfill leachate, J. physical-chemical pretreatment processes for the reatment Environ. Eng. Sci. 18(2001) 369-379. [5] W.M. Copa, J.A. Meidl, Powdered carbon effectively treats toxic leachate, Pollut. Eng. 18 (1986) 32-34. [6] S. Ho, W.C. Boyle, R.K. Ham, Chemical treatment of leachate from sanitary landfills, J. Water Pollut. Control Fed. 46 (1974) 1776-1791. [7] N.H. Ince, Light-enhanced chemical oxidation for tertiary treatment of municipal landfill leachate, Water Environ. Res. 70 (1998) 1161-1169. [8] K. Ushikoshi, T. Kobayashi, K. Uematsu, A. Toji, A. Kojima, K. Matsumoto, Leachate treatment by the reverse osmosis system, Desalination 150 (2002)121-129. [9] S.H. Gau, F.S. Chang, Improved Fenton method to remove the recalcitrant organics in landfill leachate, Water Sci. Technol. 34 (part 4) (1996) 455-462. [10] H. Gulsen, M. Turan, Treatment of sanitary landfill leachate using a combined anaerobic fluidized bed reactor and Fenton’s oxidation, J. Environ.Eng. Sci. 21 (2004) 627-636.[11] Y.K. Kim, I.R. Huh, Enhancing biological treatability of landfill leachate by chemical oxidation, J. Environ. Eng. Sci. 14 (1997) 73-79. [12] I.W.C. Lau, P. Wang, S.S.T. Chiu, H.H.P. Fang, Photoassisted Fenton oxidation of refractory organics in UASB-pretreated leachate, J. Environ. Sci.14 (2002)388-392. [13] S.H. Lin, C.C. Chang, Treatment of landfill leachate by combined electroFenton (2000)4243-4249.oxidation and sequencing batch reactor method, Water Res. 34 mature landfill [14] A. Lopez, M. Pagano, A. Volpe, A. Di Pinto, Fenton’s pretreatment of leachate, Chemosphere 54 (2004) 1000-1005. [15] A. Pala, G. Erden, Chemical pretreatment of landfill leachate discharged into municipal biological treatment systems, J. Environ. Eng. Sci. 21 (2004)549-557. [16] R.M. Roddy, H.J. Choi, Research project using the Fenton process to treat landfill leachate: problems encountered during scale up from laboratory to pilot plant, in: Proceedings of the International Conference on Solid Waste Technology and Management, 654-657, Philadelphia, PA, USA, 1999. [17] Z.P. Wang, Z. Zhang, Y.J. Lin, N.S. Deng, T. Tao, K. Zhuo, Landfill leachate treatment by a coagulation-photooxidation process, J. Hazard. Mater. 95 (2002)153-159. [18] J.D. Englehardt, Y. Deng, D. Meeroff, Y. Legrenzi, J. Mognol, J. Polar, Options for managing municipal landfill leachate: year 1 development of iron-mediated treatment processes, Technical Report, Florida Center for Solid and Hazardous Waste Management, 2006. [19] Y. Deng, J.D. Englehardt, Treatment of landfill leachate by the Fenton process, Water Res. 40 (2006) 3683-3694. [20] R.J. Bigda, Consider Fenton’s chemistry for wastewater treatment, Chem. Eng. Prog. 91 (1995) 62-66. [21] P.R. Gogate, A.B. Pandit, A review of imperative technologies for wastewater treatment I: oxidation technologies at ambient conditions, Adv. Environ.Res. 8 (2004) 501-551. [22] S. Rahhal, H.W. Richter, Reduction of hydrogen peroxide by the ferrous iron chelate ′′ ′′ ′of diethylenetriamine N,N,N ,N ,Npentaacetate, J. Am.Chem. Soc. 110 (1988) 3126-3133. [23] J.D. Rush, W.H. Koppenol, Reactions of iron(II) nitrilotriacetate and iron(II) ′ethylenediamine-N,N -diacetate complexes with hydrogen peroxide, J. Am. Chem. Soc. 110 (1988) 4957-4963. [24] J. Yoon, S. Cho, Y. Cho, S. Kim, The characteristics of coagulation of Fenton reaction Technol. 38 (1988) 209-214.in the removal of landfill leachate organics, Water Sci. [25] P. Wang, I.W.C. Lau, H.H.P. Fang, D. Zhou, Landfill leachate treatment with combined UASB and Fenton coagulation, J. Environ. Sci. Health A35 (2000)1981-1988. [26] I.W.C. Lau, P. Wang, H.H.P. Fang, Organic removal of anaerobically treated leachate by Fenton coagulation, J. Environ. Eng. 27 (2001) 666-669. [27] Y.W. Kang, K.Y. Hwang, Effects of reaction conditions on the oxidation efficiency in the Fenton process, Water Res. 34 (2000) 2786-2790. [28] H. Gallard, J. De Laat, B. Legube, Effect of pH on the oxidation rate of organic compounds by Fe-II/H O , mechanisms and simulation, New J.Chem. 22 (1998) 263-268.22 [29] W.Z. Tang, C.P. Huang, 2,4-Dichlorophenol oxidation kinetics by Fenton’sreagent, Environ. Technol. 17 (1996) 1371-1378. 3+[30] J.J. Pignatello, Dark and photoassisted Fe -catalyzed degradation of chlorophenoxy herbicides by hydrogen-peroxide, Environ. Sci. Technol.26 (1992)944-951. [31] E.S.K. Chian, F.B. DeWalle, Sanitary landfill leachates and their treatment,J. Environ. Eng. 2 (1976) 411-431. [32] C.S. Slater, C.G. Uchrin, R.C. Ahlert, Ultrafiltration processes for the characterization and separation of landfill leachates, J. Environ. Sci. Health, PartA 20 (1985) 97-111.[33] F.J. Rivas, F. Beltran, O. Gimeno, F. Carvalho, Fenton-like oxidation of landfill leachate, J. Environ. Sci. Health, Part A 38(2003) 371-379. [34] H. Zhang, H.J. Choi, C.P. Huang, Optimization of Fenton process for the treatment of landfill leachate, J. Hazard. Mater. 125 (2005) 166-174. [35] J. Pignatello, E. Oliveros, A. MacKay, Advanced oxidation processes for organic contaminant destruction based on the Fenton reaction and related chemistry, Crit. Rev. Env. Sci. Technol. 36 (2006) 1-84. 英文原稿, Abstract Municipal landfill leachate, especially mature leachate, may disrupt the performance of moderately-sized municipal activated sludge wastewater treatment plants, and likewise tend to be recalcitrant to biological pretreatment. Recently, Fenton methods have been investigated for chemical treatment or pre-treatment of mature leachate. In this paper, the results of laboratory tests to determine the roles of oxidation and coagulation in reducing the organic content of mature leachate during Fenton treatment are presented. The efficiencies of chemical oxygen demand (COD) oxidation and coagulation were tested, and the ratio of COD removal by oxidation to that by coagulation was assessed, under various operating conditions. Low initial pH, appropriate relative and absolute Fenton reagent dosages, aeration, and stepwise addition of reagents increased COD removal by oxidation and the importance of oxidation relative to coagulation. Simultaneous aeration and stepwise reagent addition allowed comparable treatment without initial acidification pH, due to the generation of acidic organic intermediates and the continuous input of CO . On the other hand, high COD oxidation efficiency and low 2 ferrous dosage inhibited COD removal by coagulation. At significantly high oxidation efficiency, overall COD reduction decrease slightly due to low coagulation efficiency. Under the 2+most favorable conditions (initial pH 3, molar ratio [H O ]/[Fe ] = 3, [H O ] = 240 mM, and 2222 six dosing steps), 61% of the initial COD was removed, and the ratio of COD removal oxidation to coagulation was 0.75. Results highlighted the synergistic roles of oxidation and coagulation in Fenton treatment of mature leachate, and the role of oxidation in controlling the efficiency of removal of COD by coagulation. ? 2006 Elsevier B.V. All rights reserved. Keywords: Fenton treatment; Landfill leachate; Oxidation; Coagulation; Organic contaminants 1. Introduction nomical and environmentally Sanitary landfills have been suggested to be the most eco acceptable method for disposal of municipal solid wastes, in the United States and out the world [1]. However, leachate produced from landfills is a high strength organic through wastewater which, when discharged directly to a municipal wastewater treatment plant, may cause corrosion of the pump station, difficulty in maintaining constant effluent chlorine residual, and sludge bulking and settling problems. Biological methods are typically applied for of young leachates (e.g., from landfills of less than 1-2 years age), characterized by treatment high 5-day biochemical oxygen demand (BOD)/chemical oxygen demand (COD) ratios (>0.6) 5 and high concentrations of low molecular weight organics [2]. However,such methods are not effective for treatment of mature leachates (e.g., from landfills of more than 5-10 years age), due to their low BOD/COD ratios (<0.3) and high fraction of high molecular weight, refractory 5 organics. Hence, several physicochemical processes have been studied or used for treatment of mature leachate [3-8].pretreatment or full Among potential physicochemical technologies for leachate treatment, the Fenton process has been extensively studied in recent years [9-17], and analyses indicate Fenton process to be cation [18]. Organic removal one of the most cost-effective alternatives for this appli efficiency depends upon several operating parameters, including reaction pH, dosages of Fenton reagents, aeration, coagulation pH, mode of reagent addition, temperature, UV irradiation, and subsequent pH adjustment for coagulation. A detailed discussion on the effects of these operational factors is available somewhere [19]. The typical Fenton wastewater treatment process includes four stages: oxidation, neutralization, coagulation/flocculation, and solid-liquid sepa ration [20,21]. Hence, organics are removed by both oxidation and coagulation. The •oxidation is generally ascribed to generation of hydroxyl radical (OH) according to Eq. (1), a strong and indiscriminant oxidant. However, other species including ferryl moieties are also candidate oxidants [22,23]. 2+3+ •? Fe + H O ? Fe +OH + OH22 (1) 3+2+Some of Fe produced can be reduced to Fe through Eq. (2), although the rate is several 2+3+orders of magnitude slower than that of Fe to Fe conversion through Eq. (1). 3+2+ •+Fe + H O ? Fe +HO + H222 (2) 2+ •The Fe generated in Eq. (2) may react with HO to produce moreOH through Eq. (1). 22 precipitation of ferric-oxyhydroxides after the neutralization Coagulation is then due to stage. However, most previous investigations focused primarly on the effects of operating parameters on overall organics removal efficiencies; how these parameters impact oxidation and coagulation and whether oxidation or coagulation predominates in terms of treatment well recognized, and such understanding as pertains to under various conditions are not ment of landfill leachate is still more limited. Yoon et al. [24] concluded that treat removal of organics from leachate, based only coagulation played a primary role in Fenton on the observation that both Fenton treatment and simple coagulation removed high molecular organics more readily and selectively. Wang etal. [25] and Lau et al. [26] reported that oxidation and coagulation were responsible for approximately 20 and 80% of overall COD removal, respectively, in Fenton treatment of a biologi-cally stabilized leachate. Kang and Hwang [27] found that pH and absolute dosages of Fenton reagents significantly affected the removal of COD from leachate by oxidation and coagulation, and that coagulation pH influenced the efficiency of coagulation. However, more required relationships particularly between oxidation and coagulation in terms of removal efficiency have not been clear.In this paper, overall COD removal efficiency, and COD reduction by oxidation and by coagulation under various operating conditions are reported for a mature leachate. The ratio of COD removal by oxidation to that by coagulation was used to determine whether dominating role under the tested conditions. oxidation or coagulation played a pre Specifically, the effects of initial pH, molar ratio and absolute dosages of Fenton reagents, oxidation and coagulation are described. aeration, and mode of stepwise reagent addition on In addition, the interaction between oxidation and coagulation in terms of treatment efficiency is characterized. Finally, the interactive effects of aeration and stepwise addition of reagents on both oxidation and coagulation are described. Landfill leachate was collected from the Polk County NorthCentral Landfill collection tank (Winter Haven, FL, USA). The mean BOD/COD was less than 0.05, typical for mature 5 leachate. The collected leachate was stored in a zero headspace plastic bottle in refrigerator at 4 ?C until use. The average composition of the tested landfill leachate is listed in Table 1. All chemicals were at least analytical grade and were used as received, except as noted. The filtered through a glass filter paper (934-AH, Whatman, Cifton, raw landfill leachate was pre VA, USA) to remove large particles and debris, and maintain uniformity of tested samples. All runs were conducted at room temperature and atmospheric pressure. Initial leachate pH was adjusted to the desired value with concentrated sulfuric acid (HSO, 96%, FishChemical, 24 quently, 200 mL of prefiltered leachate was dispensed to a 1-L Fair Lawn, NJ, USA). Subse beaker. The leachate was stirred thoroughly with a magnetic stirrer. In the aerated Fenton tests, injected air was supplied by a small air pump (20 L/h, Tetratec, China). The height from the overflow due to foaming leachate table to the beaker brim adequately avoided the tion under aeration. In the experiments to investigate effects occurring at initial stage of reac of aeration and stepwise feeding of Fenton reagents, Fenton oxidation proceeded for 9 h, and the total reagent dose was added incrementally at each designated addition time. In other experiments, Fenton oxidation proceeded for 2 h. Reagents addition was as follows. First, ?7HO, heptahydrate, FishChemical, Fair Lawn, NJ, USA) was granular ferrous sulfate (FeSO42 added. Subsequently hydrogen peroxide solution (HO, 30% w/w, VWR, West Chester, PA, 22 USA) was added. After the designated oxidation time, NaOH pellets were added to the rapidly stirred solution, to increase the pH to approximately 6.5. A solution of 10 M NaOH solution was then added dropwise, to a pH of 8.0. The beaker with leachate was transferred to a Phipps & Bird Stirrer (Model 7790, Richmond, VA, USA) for a period of 20 min flocculation at 20 rpm. Overall COD removal, and COD removal by oxidation and by coagulation were measured by a slight modification of the method of Kang and Hwang [27]. Accordingly, 100 mL aliquot of uniformly mixed solution was immediately dispensed to a glass cylinder ?and heated in a 50C water bath (8851, Cole Parmer, Chicago, IL, USA) for 30 min to remove any residual HO in solution, and the sample was brought to the room temperature for a 90 22 min sedimentation period. Then, the volume of the settled iron sludge was recorded. After that, the COD values of the supernatant and the settled sludge samples were measured separately. The former indicated COD in the effluent after the overall process, and the latter indicated the COD of the solid phase that was contributed from these organics coagulated. COD removal by oxidation was the difference between COD reduction by the overall process and the COD coagulated to the solid phase. Sample pH was measured by pHmeter. COD was measured colorimetrically following digestion (20-1500 mg/L range, HACH, Loveland, CO, USA). Error bar in the figures represent one standard deviation (n = 3). 3. Results and discussion 3.1. Initial pH The effect of initial pH on COD removal efficiency is shown in Fig. 1(a). At a HO22 2+ concentration of 23.5 mM and Feconcentration of 14 mM, maximum COD removal efficiencies by oxidation and coagulation occurred at pH 2.5-3.5, such that overall COD removal efficiency peaked above 50%. These observations are consistent with those of Kang and Hwang [27]. At extremely low pH (<2.5), COD oxidation efficiency and over-all COD removal 2+efficiency decreased sharply, due principally to the lower reaction rate of [Fe(HO)] and 2 •+HO [28], the increased scavenging ofOH by H [29], and the increased inhibit on the 22 3++reaction between Fe and HO due to H [30]. On the other hand, COD removal dropped 22 increasing pH (>5.0), due to the increasing rate of autodecomposition of HO, significantly with 22 deactivation of iron ion into iron oxyhydroxides, the increased scavenging effect of carbonate and • •bicarbonate on OH, and the decreased oxidation potential ofOH. Therefore, COD removal by depended strongly on initial pH.oxidation, coagulation, and overall process The effect of initial pH on the ratio of COD removal by ?oxidation to that by coagulation is shown in Fig. 1(b). This is ?proposed as a simple but useful indicator to evaluate the relative importance of oxidative degradation of organics in Fenton treat- ment. As shown, the ratio peaked around 0.43 at pH 3.0, thus suggesting an optimal initial pH for oxidative Fenton treatment. In contrast, at pH ? 6.0, the ratio of removal by oxidation to overall COD removal was less than 0.10, indicating that coagula- tion predominated in Fenton treatment of mature leachate under these conditions. Hence, initial pH also significantly influenced importance of oxidation relative to coagulation。 3.2. Dosages of Fenton reagents 2+The effect of molar [HO]/[Fe] ratio on COD removal efficiencies at a fixed HO2222 dosage of 180 mM at initial pH=3.0 is shown in Fig. 2. The maximum oxidative COD removal 2+efficiency of 27% occurred at a molar ratio [HO]/[Fe] = 3. Oxidation efficiency dropped 22 2+sharply to one half of the maximum when the molar [HO]/[Fe] ratio increased to 12. This 22 on hydroxyl radicals, which result is attributed to the scavenging effect of peroxide 2+presumably became stronger as the relative ratio [HO]/[Fe] rapidly increased, as shown in 22 Eq.(3). • •H O +OH ? H O +HO(3)2222 2+Oxidation efficiency also dropped a little at a molar ratio [HO]/[Fe] < 3, due to the 22 2+Fe on hydroxyl radicals, shown in Eq. (4).increasing scavenging effect of •2+3+? OH + Fe ? Fe + OH(4) 2+Results indicated the optimal molar ratio [HO]/[Fe] to be approximately 3.0, for 22 2+the other hand, from molar ratios [HO]/[Fe] of 2 to 12 oxidation of this leachate. On 22 under a fixed HO dosage of 180 mM, COD removal by coagulation decreased slightly 22 from 34 to 22%, primarily because the content of ferrous ion added, which was eventually transferred to ferric-oxyhydroxides as the coagulant after neutralization, decreased by 83%. 2+Thus, Fe dosage strongly nfluenced the treatment efficiency of coagulation. Overall COD removal of ca. 55% resulting from the interaction between oxidation and coagulation was 2+[HO]/[Fe] = 2-3, gradually decreasing to 34% at molar ratio almost constant at molar ratio 22 2+2+[HO]/[Fe] = 3-12. Additionally, the ratio was related to molar ratio [HO]/[Fe]. The 2222 2+maximum ? 1.0 occurred at ?[HO]/[Fe] = 3.0. Overall COD removal, COD removal by 22 oxidation and coagulation, and the ratio versus dosages of Fenton reagents are ?shown in 2+for any particular [Fe], overall COD Fig.3(a)-(c), respectively.As shown in Fig.3(a), removal increased with increasing peroxide dosage, though the increase was insignif-icant at 2+2+2+molar ratio [HO]/[Fe] > 3.0 (for [Fe] = 30 mM, [HO] > 90 mM; for [Fe] = 60 mM, 2222 2+[HO] > 180; and for [Fe] = 90 mM, [HO] > 270). Furthermore, overall COD removal 2222 2+increased with increasing Fe concentration over the interval 30-60 mM, but did not increase 2+significantly over the interval 60-90 mM, indicating that the optimal Fe dosage for overall COD reduction was near 60 mM. Two characteristics of the interaction between oxidation and coagulation during Fenton treatment can be noted in Fig.3(b). First, as peroxide dosage increased, COD coagulation decreased gradually, implying that and oxidation efficiency remaining oxidative by-products were not as amenable to coagulation. This explanation would coincide with the observation that Fenton oxidation and coagulation both remove high molecular weight organics preferentially [31,32,24]. Second, at high peroxide dosages, 2+ dosage led to higher efficiency of coagulation due to higher concentrations of higher Fe ferric coagulant after neutralization; however, this effect was not obvious at low peroxide ciency occurred. That is, ferrous dosage greatly dosages where low oxidation effi influenced COD removal by coagulation at high oxidation efficiency, but not at low oxidation efficiency. Therefore, oxidation effi-ciency apparently controls coagulation efficiency, such that high oxidation efficiency may cause relatively low coagulation efficiency. As shown in Fig. 3(c), the ratio increased with increasing ?[HO] for any particular 22 2+[Fe].At[HO] > 90 mM, higher ferrous dosage apparently resulted in a lower ratio, though 22 the phenomena was not observed at [HO] < 90 mM. The ratio was increased to ca. 2.10? 22 2+only at an extremely high molar ratio [HO]/[Fe] = 10.22 3.3. Aeration and stepwise addition of Fenton reagents The effects of aeration alone, stepwise addition alone, and the combination of the two on gated, as shown in Fig. 4. The addition of reagents in nine steps COD removal were investi increased COD removal by oxidation slightly, from 18 to 24%, and increased overall COD removal from 46 to 56%. Aeration alone similarly increased COD oxidation to 22%, but did obviously improve overall COD removal. The combination of aeration and stepwise not addition further improved COD oxidation to 32%, with an overall COD removal of 55%. Stepwise addition and aeration showed a clear synergistic effect on COD oxidation. The positive effect of stepwise addition of HO may be due to a reduction in the autodecomposition of high-22 localized HO concentrations at the point of injection, and to reduced scavenging of hydroxyl 22 may decrease ineffective consumption of radicals by hydrogen peroxide [33,34]. Aeration HO by maintain-ing high concentration of O in water and then inhibiting the 222 autodecomposition of HO through Eq. (5).22 2H O ? 2H O + O(5)2222 Additionally, O in water may rapidly and usually irreversibly react with carbon-centered 2 •radicals (R), formed in the reaction of hydroxyl radicals and organic compounds, through Eqs. (6) and (7). •+R + O ? R( H) + HO(6)22 • ••R + O ? ROO ? RO (7)2 •••These radicals R, ROO, and RO may couple or disproportionate to form relatively stable molecules, or react with iron ions [35]. The organic intermediates produced may continue to react with hydroxyl radicals and O, thus leading to further decomposition and perhaps 2 mineralization. The effect of the number of dosing steps on overall COD reduction, COD removal by oxidation, and the ratio , is shown ?in Fig. 5. As the number of dosing steps increased from one to nine, COD removal by oxidation increased from 22 to 32%, and the ratio increased? observed overall COD removal was higher for six steps than gradually from 0.90 to 1.33. The for nine, where the maximum oxidation efficiency and the highest ratio occurred, perhaps? again because low molecular weight oxidative byproducts were less amenable to coagulation. shown, the maximum overall COD removal of approximately 61% was achieved at initial As 2+pH 3, molar ratio [HO]/[Fe] = 3, [HO] = 240 mM, and six reagent addition steps, in 2222 which case the ratio of removal by oxidation to coagulation ?was 0.75. A set of experiments was conducted to investigate the inter action between initial pH and peroxide dosage on aerated Fenton treatment of leachate with stepwise addition of reagents(Fig. 6(a) and (b)). As shown in Fig. 6(a), in terms of overall COD removal, the need for acidification could be overcome to some degree with increasing peroxide dosage. In particular, overall COD removal increased sharply for hydrogen peroxide addi-tion rates increasing from 0 to 80 mM over the tested pH range, where the increase was minor or absent at higher hydrogen peroxide dosage. As shown, under the conditions tested, hydrogen peroxide dosage was even more dominant in terms of COD oxidation than was observed for overall removal, relative to initial pH. A similar trend was also observed in terms of the ratio , as shown in Fig. 6(b). This effect may have been enhanced by the stepwise addition of reagents. For example, even at an initial pH of 8, leachate pH during Fenton treatment decreased gradually with dosing steps, such that most of the Fenton oxidative treatment actually occurred at low pH; at hydrogen peroxide dosage equal to 80 mM, the final pH of the group with initial pH 8 was 2.523, approximately equal to final pH 2.312 of the group with initial pH 3. Reasons for this pH decrease during Fenton oxida-tion may be (a) the formation of organic acids as decomposition intermediates, and (b) the introduction of CO that generates HCO。223 4. Conclusions In this study of the traditional Fenton treatment of mature leachate, low initial pH, appropriate relative and absolute dosages of Fenton reagents, aeration, and stepwise addition of reagents all increased COD removal by oxidation as well as the oxidation/coagulation, ratio. When aeration was combined with stepwise addition of reagents, the effect of initial pH COD removal became minor, due to the gradual decrease in leachate pH with the on ates and continuous input of CO. On the other hand, generation of acidic organic intermedi2 removal efficiency by coagulation was principally influenced by oxidation efficiency COD and ferrous dosage. High COD oxidation efficiency meant that residual organics probably contained high fraction of low molecular weight organics, most of which were oxidation originally in the mature leachate, and were not products of high molecular weight organics amenable to coagulation treatment. Significantly, high oxidation efficiency even might decrease overall COD reduction due to greatly decreased removal efficiency of coagulation. Hence, oxidation seemed to play a more active role in Fenton treatment, which itself contributed to COD reduction, and controlled the treatment behavior of coagulation. Moreover, high ferrous treatment efficiency by coagulation due to high concentration of dosage increased the coagulant, while the effect was not obvious at low oxidation efficiency. Under the most 2+favorable conditions (initial pH 3, molar ratio [HO]/[Fe] = 3, [HO] = 240 mM, and six 2222 dosing steps), 61% of the initial COD was removed, and the ratio of COD removal by oxidation to by coagulation was 0.75. Results highlighted the synergistic roles of oxidation and coagulation in Fenton treatment of mature leachate, and the role of oxidation in controlling the efficiency of removal of COD by coagulation。