Characterization of refuse landfill leachates of three different stages in landfill stabilization pr

Available online at www.sciencedirect.comJOURNAL OFENVIRONMENTALScienceDirectSCIENCESISSN 1001-0742. CN 1-2629/XJESJoumal of Eovironmental Sciences 21(20090) 1309-1314www.jesc.sc.cnLLLCharacterization of refuse landfill leachates of three diferent stagesin landfll stabilization processLou Ziyangl.2, DONG Bin', CHAI Xiaoli2, SONG Yu2,ZHAO Youcaiz.*, ZHU Nanwen'(riomenmal Sine and Egineringe Shanghaitong University, Shanghai 200240, China. E-mail: lonworld12@ sjau.edu.cn2. The State Key Laboratory of Pollution Control and Resource Reuse, School of Envionmental Science and Engineering,Tongji Universit, Shanghai 200 ChinaReceived 23 November 2008; revised 02 January 2009; acepted 12 February 2009AbstractLandfill leachates with diferent ages (mature leachate, 11 years; semi-mature leachate, 5 years; fresh leachate, under operation)were collected from Laogang Refuse Landill, Shanghai to characterize the colloid size distribution and variations of leachate. Theseleachates were separated using micro filtration and ultra filtration into specific size fractions, i.e., suspended particles (SP)(> 1.2 pum),coarse clloids (CC) (1.2-0.45 um), fine cllids (FC) (0.45 um, 5 kDa/1 kDa molecular weight (MW), and dissolved organic matters(DM, < 5 kDa/1 kDa MW). The specific colloids in each size fraction were quantified and characterized through chemical oxygendemands (COD), total solid (TS), pH, NH4+*-N, total organic catbon (TOC) and fixed solid (FS). It was found that COD, NH4+*-N andTS in leachate decreased signifcantly over ages, while pH increased. The dissolved fractions (< 5 kDa/l kDa) dominated (over 50%)in three leachates in terms of COD, and the organic matter content in dissolved fraction of leachates decreased and the inorganic matterincreased as the disposal time extended, with the TOC/COD ratio 30% -7%. Dissolved fractions decreased from 82% to 40% in termsofTOC as the disposal time extended, suggested that the organic matter remained in leachate would form into middle molecular weightsubstances during the degradation process.Key words: characterization; landfill leachate; different ages; size-distributionDOI: 10.1016/S1001-0742(08)62400-6Introductionmg/L (Jensen et al, 1999; Caron et al, 1996), in com-parison with the COD of 1000- -55000 mg/L in leachatesLandills are adopted as a dominated way in waste (Christensen er al, 2001; Lou et al, 2007). The molecularmanagement system (Chian, 1977; Trebovet et al., 2001).weight dstribution in aged raw leachate had been reportedMillions of landills are under operation, especially in by several publications (Calace et al, 2001; Vasllos etdeveloping countries.al, 1993; Wang et al, 2006), whereas the particle sizeThe major concem with the landfill is the fate of thedistribution, percentages of colloidal and dissolved mattersconstituents in leachate. It has been known that leachatein leachate from diferent landfill stabilization time periodscomposition would vary significantly as the disposal time in East Asia, where the refuse contains high contents ofextended (Kjeldsen et al, 2002; Renou et al, 2008). It has food wastes, are still unknown. Hence, it is importantbeen concluded that landfill leachate management is one ofto characterize the main components of leachate withthe complex tasks according to the practical experiencesdiferent ages, including molecular weight and particle size(Lou et al., 2007), and only 12% of leachate treatment distributions.process could meet the Class II in Standard for PollutionIn this work, leachate samples with three diferent agesControl on the Landfill Site of Municipal Solid Waste (GBwere separated sequentally using a series of micro- and16889-1997) in China.ultra-membranes with different porosities, to evaluate theIt is clear that leachate treatment process would per-variation of leachate compositions as disposal time ex-form better if it is designed according to the leachatetended. This investigation confirmed the existence and thecharacteristics, especially for the track of the variation ofdiffer中国煤化工nolecules substancesleachate compositions in the entire time horizon of landfll. and Corovided fundamentalHowever, only small parts of organic matter could be data ai YHC N M H Gters in leachate fromdetermined, for example, a tolal equivalent COD of 10 -20 landill with high content of food waste.●Corresponding author. E mail: Zhaoyoucai@tongji.edu.cn1310LOU Ziyang et al.1 Materials and methodsrespectively. Chemical oxygen demand (COD), NH4*-N,turbidity, color were determined according to the standard1.1 Samplingmethods recommended by USEPA.Potassium was determined using an atomic absorptionLaogang Refuse Landill in Shanghai was constructedspectrometer (AA-6501F, Shimadzu, Japan) after digestionin 1989 along the shore of the East China Sea. The landby microwave-assisted acid digestion method with com-was formed by the sedimentation of silt carried by Yangtzebined acid (HNO3:H2O2:HCI, 6:0.25:3 (mL). ContentsRiver and put into operation at the end of 1991. The matureof heavy metals were determined by inductively coupledleachate sampled from the cell compartment closed inplasma atomic emission spectrometer (ICP-AES) (Optima1991, and semi -mature leachate and fresh leachate were2100DV, PerkinElmer, USA) after digestion.collected from the cell compartment closed in 1997 and thecell compartment under placement operation, respectively.2 ResultsThe samples were collected using a bucket (with thevolume 2 L) made of stainless steel for several times2.1 Fundamental chemical characteristics of leachatesand immediately transferred into a 10-L polyethylenecontainers, which were rinsed twice with deionized waterGeneral characteristics of leachate with different agesand conditioned two times with sample before collecting.are summarized in Table 1. The great decrease of TOC1.2 Ultra-filtration apparatusfrom 9870 mg/L in fresh leachate to 182 mg/L in matureleachate was due to the degradation of the majority ofThe ultra filration apparatus used in this study is shownorganic matter. The concentrations of NH4 +-N and Ortho-in Fig. 1. It consists of a methyl-methacrylate glass holderphosphate were reduced from 4632 to 1388 mg/L and fromwith a volume of 300 mL and the efective membrane area20.20to 0.36 mg/L, respectively as disposal time extended.is 0.02 m2. The samples were pressed through the filtersIt was found that fresh leachate contained amounts of blackby a pressure applied at the top of the barrel with the aidsuspended substances with stronger odor, and semi-matureof N2. The operation pressures of micro filration processleachate seemed to be less black with strong odor, whileand ultra-fltration process were maintained at 0.1 and 0.25mature leachate was yellowy without any odor.MPa, respetively.Metal contents in three leachates are shown in Table 2.Leachate samples were treated to separate and con-Contents of Ca and Mg in fresh leachate was much highercentrate leachate colloids into size fractions, using athan that in other two leachates, meaning that Ca and Mg1.2-um membrane and subsequently 0.45-pum, 100 kDa,are lower in the methanogenic phase leachates, due to a50 kDa/30 kDa, 10 kDa, 5 kDa/1 kDa molecular weighthigh pH (enhancing sorption and precipitation) and low(MW) membranes (1 Da = 1/16 0 atomic mass unit)content of dissolved organic matter, which may complex(Shanghai Institute of Nucleus Physics, Chinese Academythe cations. Most of heavy metals could be found in allof Sciences). The micro membranes were made of mixedthree leachates samples, and their contents were below thecellulose, while the ultra-membrane was made of polyethermaximum permissible level recommended by the Chinasulfone (PES). .Environmental Protection Agency (GHZB 1-1999), except1.3 Analytical methodsCr in fresh leachate and Pb in all leachates.Total organic carbon (TOC) was measured by TOC-VTable 1 Elemental analysis of leachate with dfferent ages at LaogangRefuse Landill, ShanghaiCPH/CPN (Shimadzu, Japan). Total solid (TS) and fixedsolid (FS) in each fraction were measured by weighingTOC NH4*-N PO。3- pHTsthe residues after 20 mL of each fraction was dried in(mg/L) (mg/L) (mg/L)(mg/Lporcelain crucibles at 105°C for 24 h and at 600°C for1 h,Fresh leachate9870463220.20 7.71 28400Semi-mature leachate80921971.718.38 13205Mature leachate18213880.368.60 6700了一10Sampling date: March 2003; around 159C. TS: total solid.Table 2 Heavy metal contents in leachate with diferent ages (mg/L)FreshSemi- matureMatureBackgroundleachatevalue3、C0.05< 0.050.348<0.050.5220.2440.4170.108PL< 0.2<0.2Ni0.0.16< 0.01< 0.00中国煤化工Fig. 1 Schematic diagram of SCM type of ulra-f1ter. (1) admiting pipe;MCYHCNMHG0.2391540883104010.1(2) sirer; (3) fixator; (4) 0-ring seal packing; (5) seat; (6) outlet; (7) slowdeflector, (8) ultra-membrane; (9) sealing plate; (10) ultrafiter cup; (11) The background value is "responding metal contents incal surfacefeed inle.water. .No.9Caracerization of reiuse landf1 lachates of thee diferet sages in lndi sbiliain poces13112.2 Effet of membrane porosity on pHwith. 1 years was sti in a high value, comparing to theThe high pH in all three leachates (Table 1)revealed thatrequirements of the Chinese NationalDischarge Standardlandil leachate in Laogang Landf11 was alkalinity (Fig. (COD < 300 mg/L, Class II of (GB 16889-1997)).2). The increase pH sequence of fresh leachate < semiCOD in leachate decreased afer gradient separation us-mature leachate < mature leachate indicated that pH ininga series of membranes with diferential pore sizes dowleachate wouldincrease up to a steady state as disposalto 5 kDa/l kDa MW (Fig. 3), with a total removal rale oftime extended. pH of the leachate would not only dependabout 48%, 34% and 27% (data not shown), respectively,on the concentration of the acid but also on the partial indicating that the dissolved matters predominated in allpressure of CO2 in. the landf11 gas which is in contactleachate samples.with the leachate,It has been demonstrated that fatty2.4 Efect of membrane porosity on NH4*-Nacid matters with low molecular weight predominated infresh leachate, and the majority matter would be someFresh leachate has a higher NH4*-N concentration thannon-degradable matters in mature leachate, such as thumicother two leachates implying that NH4* -N concentrationlike and fulvic like compounds,', which resulted in the pHin leachate would decrease over time (Fig. 4). The NH4*-increase in leachate as the time extended (Christensen etN concentrations in three leachates were in high levelal., 2001; Lou et al, 2007). The decrease in the volatile(over 1300 mg/L), while most of C from that stage wasfatty acid(VFA)concentration in leachate causes the risingrecalcirant matter (mai et al, 1995; Wang et al, 2006),of pH as the disposal time extended.Mcanwhile, CO2which result in the un-favorable ratio of CN for theconcentration in landfll gas increased from < 40% to >biological treatment.Therefore, the selection of mature70% as the disposal time extended, and the crrespondingleachate treatment process should be diferent from that ofH2CO3 would also increase, which contributes to thefresh leachate.increase of pH in leachate (George et al, 2000).2.5 Effect of membrane porosity onTSAs shown in Fig. 2. pH values in leachate fltratesAs shown in Fig. 5, Ts in fresh leachate was muchincreased slightly and then progressively level off withhigher than that in semi-mature and mature leachates,filtered sequentially by the series membranes used, whichmay resulted from the stripping of CO2 during the filtra- indicating that solid particles in leachate would decreasetion. It can be supportrtedby the previous report, in whichdramatically in the first 6 years. There are more solidCO2 concentrations (CO32-) in the leachate decreasedsoils in fresh refuses than that in aged refuses, and thesefrom the initial 6-15 mmol/L to 0.5-1.5 mmo/L duringsolid soils in refuses would be leaching out, and the cor-the size fraction operation, and the corresponding pH responding TS content in leachate would decrease as theincreased by 0.4 -1.4 pH units (Jensen et al, 1999).disposal time extended. The great diference (two times)between thS contents in leaches indicated that fresh2.3 Effect of membrane porosity on CODleachate contained amount of suspended substances andCOD in fresh leachate were higher than those in semi- dissolved matters, and semi-mature leachate contained lessmature leachate and mature leachate. lIt decreased fromsuspended matters, while there were almost no suspended36653 mg/L to 2675 mg/L during the first 6 years aftersubstances in mature leachates observed in site.disposal, and then decreased to about 1500 mg/L in theThe distribution of FS and TOC in each fraction offllowing 5 years. Meanwhile, COD in marure leachateleachates is shown in Figs. 6a and 6b, respectively. Both of9.0 [口Fresh leachate四Semimature leachate 0 Mature leachate3.8 t8.6 t8.4 t3.2 t苦8.0.8-7.6 t7.42t7.Leachatc<12 um<0.45 m<100 kDa中国煤化工<5 kDa/l kDaMembrane poYHCNMHGhem Retoahip htrte阳aod peabrne pro 50kDw30 kDa mens thu fesh lochahe and semi mture eachate were ftered by 30kDaRonamemre me mau hueee r fe by S0Da membrane 5kDVI kDa means ta fesh lachale and semi matuee lehahe wee hereeglekDa membranes,. and maure leachale was flered by 5 kDa membrne.1312LoU Ziyang et al.VoL. 2140000 [囚Fresh leachate中 Semi-mature leachate 0 Mature leachate3500030000250002000015000100005000Leachate< 1.2 um<0.45 um < 100kDa < 50 kDa/30kDa < 10kDa < 5 kDa/1 kDaMembrane porosityFig3 Relationship between COD and membrane porosity.5000 r口Fresh leachate皿Semi- mature leachate口Mature leachate450040002 3500300025002000151000500oL<1.2 pum< 0.45 pm< 100kDa < 50kDa/30kDa < I0kDa < 5 kDa/1 kDaFig 4 Relationship between NH4*-N and membrane porosity.0000因Fresh leachate @ Semi-mature leachate 0 Mature leachate己15000中国煤化工YHCNMHG<0.45 pum< 100kDa < 50kDa/30kDa < 10kDa<5kDa/1 kDaFig 5 Relationship between TS and membrane porosity.Characterization of refuse landfill leachates of three different stages in landfll stabilization process131314000 [0 Fresh leachate日 Semi-mature leachate 0 Mature leachate1200010000800总600040002000o:Leachate <1.2 um<0.45 um<100kDa <50kDa/30kDa <10kDa <5 kDa/l kDaMembrane porosity12000 nb80006000βLeachate<1.2 um<0.45μm <100kDa <50 kDa/30kDa <10kDa <5 kDa/1 kDaFig6 Relationships between FS (a) or TOC (b) and membrane porosity.FS and TOC were major components of the colloidal massmg/L would be detrimental slightly. NH4*-N would harmin all leachate samples, with the occupation percentage ofto the biological treatment process in high pH, when the55%.concentration reached 1500 mg/L, and it would inhibit thegrowth of microorganism in treatment process greatly, with3 Discussionthe value above 3000 mg/L (Lou et al., 2007). Hence,NH4+-N in leachate from Laogang Refuse Landfill shouldThe COD, NH4*-N and TS in fresh leachate were muchbe pretreated before leachate was introduced into thehigher than those in the other two leachates, indicating thatbiological treatment processes.landill would be a bioreactor with an effectiveness naturalIn addition, FS/TS in leachate increased with the dis-attenuation process. Therefore, some landfll engineeringposal age increasing, ie., the percentage of FS/TS was inpractices, such as bioreactor and leachate recirculation,the range of 35% 45% in fresh leachate, was 51% -72%could be taken into account during the landfill design.in semi- mature leachate, and was 56% -73% in matureMeanwhile, although concentrations of individual heavyleachate, indicating that the inorganic matter content inmetals in leachates were in a low level (< 1 mg/L), theleachate increased over disposal time. Meanwhile, thetotal concentrations of all heavy metals in leachate are stillpercentage of dissolved fractions decreased from 82% tohigh, and the combined toxic efect of heavy metals might40% in terms of TOC as the disposal time extended,do detrimental to micro-organism in biological treatmentsuggested that the organic matter remained in leachateprocess. Consequently, the removal of heavy metals iswould be formed as the large molecular weight substancesstill one of the important tasks for leachate pre-treatmentduring the degradation process, and could be removedprocess, with the stricter leachate discharge regulation.by中国煤化coneee was higber工-n each size fraction,The NH4*-N concentrations in all three leachate sam-thanples were in high level and were inhibitive to mostsuggqYHC N M H Gf inorganic solids co-biological treatment processes generally. As well known,existeu wIu uc urgai mauucl M urese leachate samples.the NH4+-N range of 50 -200 mg/L would be beneficialAdditionally, organic compounds were the key constituentsfor anaerobic treatment process, and the range 200 -1000in the acid phase in leachate, and then the inorganic com-1314LOU Ziyang et alVol. 21pounds were predominated in leachate from methanogenicof organic matter in landill leachate and their role in soilphase. Therefore, the biological treatment process couldsorption of heavy metals. Envronmental Pollution, 113(3):be applied in the fresh leachate after pretreatment by331-339.the removal of high concentration of NH4*-N, such asCaron F, Elchuk s, Walker Z H, 1996. High-performance liquidchromatographic characterization of dissolved organic mat-stripping stage. The physical and chemical treatment couldter from low _level radioactive waste leachates. Journal ofbe used in the mature and semi-mature leachates, dueChromatography A, 739(1-2): 281- 294.to the increase of inorganic matter in leachate, such asChian E, 1977. Stability of organic matter in landfll leachates.flocculation, coagulation and reverse osmosis.Water Research, 11: 225- 232.Christensen TH, Kjeldsen P, Bjerg P L, Jensen D L, Christensen J4 ConclusionsB, Baun A et al, 2001. Biogeochemistry of ladil leachateplumes. Applied Geochemistry, 16: 659 -718.Landill leachates contain high concentration of organicGeorge T, Hilary T, Samuel V, 2000. Integrated Solid Waste Man-matter as well as inorganic matters (including heavy met-agement: Engineering Principles and Management Issues.als) in terms of TOC and FS, and the occupation ratioUSA: McGraw-Hill. 384 -387.of inorganic matters in leachate would increase as theImai A, Onuma K, Inamori Y, Sudo R, 1995. Biodegradation andadsorption in refractory leachate treatment by the biologicaldisposal time extended.activated carbon fuidized bed process. Water Research,The dissolved fractions predominated in three leachates29(2): 687- 694.in terms of COD, whichoccupies over 50%，and someJensen D L, ChristensenT H, 1999. Colloidal and dissolved met-organic macro-molecular species in leachate could beals in leachates from four Danish landills. Water Research,isolated from leachate samples based on the membranes33(9): 2139- -2147.separation results. The organic matter content in dis-Kjeldsen P K, Barlaz M A, Rooker A P, Baun A, Ledin A, Chris-solved fraction of leachates decreased and the inorganictensen T H et al, 2002. Present and long term compositionmatter increased as the disposal time extended, with theof MSW landfll leachate: A review. Critical Reviews inTOC/COD ratio from 30% to 7%, and the correspondingEnvironmental Science and Technology, 32(4): 297- -36.leachate treatment process should be improved accordingLou Z Y, Zhao Y C, Zhang Q, 2007. Leachate Treatment andPractical Application. Bejing: Chemical Industry Press.to the characteristics of landfill leachate as the landill age124-128.extended.Renou S, Givaudan J G, Poulain S, Dirassouyan F, Moulin P,Acknowledgments2008. Landfill leachate treatment: Review and opportunity.Journal of Hazardous Materials, 150(3): 468- 493.This work was financially supported by the State KeyTrebovet D, Schlumpf J P, Jaouen P, 2001. 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