Revista Mexicana de Ingeniería Química

ISSN: 1665-2738

amidiq@xanum.uam.mx

Universidad Autónoma Metropolitana Unidad

Iztapalapa

México

Gan, J.; Montaño, G.; Fajardo, C.; Meraz, M.; Castilla, P.

ANAEROBIC CO-TREATMENT OF LEACHATES PRODUCED IN A BIODEGRADABLE URBAN

SOLID WASTE COMPOSTING PLANT IN MEXICO CITY

Revista Mexicana de Ingeniería Química, vol. 12, núm. 3, diciembre, 2013, pp. 541-551

Universidad Autónoma Metropolitana Unidad Iztapalapa

Distrito Federal, México

Available in: http://www.redalyc.org/articulo.oa?id=62029966016

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Revista Mexicana de Ingeniería Química

Vol. 12, No. 3 (2013) 541-551

ANAEROBIC CO-TREATMENT OF LEACHATES PRODUCED IN ABIODEGRADABLE URBAN SOLID WASTE COMPOSTING PLANT IN MEXICO

CITY

CO-TRATAMIENTO ANAEROBIO DE LIXIVIADOS PRODUCIDOS EN UNAPLANTA DE COMPOSTEO DE DESECHOS SÓLIDOS URBANOS

BIODEGRADABLES EN LA CIUDAD DE MÉXICO

J. Gan l, G. Montaño l

, C. Fajardo l, M. Meraz h and P. Castilla2

1Departmento de Biotecnología, Universidad Autónoma Metropolitana-Iztapalapa. Av. San Rafael Atlixco 186,Col. Vicemina, lztapalapa, México, 09340.

2Departmento El Hombre y su Ambiente, Universidad Autónoma Metropolitana-Xochimilco. Calzo del Hueso1100, Col. Villa Quietud, Coyoacán, México, 04960.

Received May 13,2013; Accepted August 7,2013

AbstraetIn this work the anaerobic co-treatment of the leachates produced during urban solid biodegradable wastescomposting diluted with municipal wastewater, was investigated. Leachates produced during the first 30 days ofgarbage composting contained 102.1 g COD L-1, 20 g VFA L-1, acid pH and 0.64 g NHt -N L-l. Instead, leachatesthat remained for 3 months the composting plant after being produced contained 15.8 g COD L-1,2.35 g VFA L-1,

a pH near neutrality and 5.36 g NHt -N L-l. An anaerobic zeolite packed filter reactor was used for the biologicaltreatment and was operated at a constant HRT of 1.5 d. Leachates were diluted with municipal wastewater (0.4 gCOD L-1) to obtain feedings with organic matter concentrations ranging from 1.8 to 13.1 g COD L-1 and organicloading rates from 1.2 to 8.7 g COD L-1 d- I . Removal efficiencies attained increased from 79.5 to 91.5% andmethane productivity from 0.23 to 1.84 L L-1 d-I , rendering 0.48 L CH4 per g consumed COD, equivalent to 118kJ L-1 of fed infiuent.

Keywords: anaerobic filter reactor, biodegradable solid waste, compost leachate, co-treatment, methane.

ResumenEn este trabajo se investigó el co-tratamiento anaerobio de los lixiviados producidos durante el composteo dedesechos sólidos urbanos biodegradables, diluidos con agua residual municipal. Los lixiviados producidos durantelos primeros 30 días de composteo de la basura, contenían en promedio 102.1 g DQO L-1, 20 g AGV L-\ , pH ácidoy 0.64 g NHt -N L-\. En contraste, los lixiviados que permanecieron 3 meses en la planta de composteo después dehaber sido producidos, presentaron 15.8 g DQOL-1,2.35 g AGV L-1, pH cercano a la neutralidad y 5.36 g NHt-NL-l. Para el tratamiento biológico se utilizó un reactor de filtro empacado con zeolita que se operó a un tiempo deretención hidráulica de 1.5 d. Los lixiviados fueron diluidos con agua residual municipal (0.4 g DQO L-1) para unaconcentración en la alimentación de 1.8 a 13.1 g DQO L-1 Yvelocidades de carga orgánica de 1.2 a 8.7 g DQO L- I

d- I . Las eficiencias de remoción alcanzadas se incrementaron de 79.5 a 91.5% y la productividad de metano de 0.23a 1.84 L L-1 d- I , obteniendo 0.48 L CH4 por g DQO consumido, equivalente a 118 kJ L-1 de infiuente alimentado.

Palabras clave: reactor de filtro anaerobio, desechos sólidos biodegradables, lixiviado de composteo, co­tratamiento, metano.

• Corresponding author. E-mail: meraz@xanum.uam.mx

Te!. +52555804 4723. Fax: +525558046406

Publicado por la Academia Mexicana de Investigación y Docencia en Ingeniería Química A.c. 541

Gan el al./ Revisla Mexicana de Ingeniería Química Vol. 12, No. 3 (2013) 541-551

1 Introduction

Nowadays around 13,000 melric lons of urbansalid wastes are generated in Mexico City everyday, and 1,500 lo 3,000 metric lons correspondlo biodegradable wasles lhal are separaled al lhesource (Solid Wasles Invenlory of Mexico Cily,2010), and are slabilized for 30-40 days in openwindrow composting piles of around 300 cubic meters.The static piles are not aerated and are tumedupside down to homogenize contents every otherday and the stabilized waste is reused afterwards aspeal substitute in parks and avenues (Solid WaslesInlegraled Managemenl Program for Mexico Cily,2010).

The composting process produces liquid effiuentsor leachales wilh such a high dissolved and suspendedorganic matter content that cannot be c1assifiedas waslewalers (Graja and Wilderer, 2001). Theamounl produced depends on lhe inherenl garbagewater content and the rainwater percolated throughlhe composting piles. It has been reporled lhalaround 27 lo 53% of lhe inilial moislure of lhecomposting pile can be released as leachate equivalentlo 0.2 lo 0.4 cubic melers per cubic Ion ofurban solid biodegradable wasles (Krogmarm andWoyczechowski, 2000). An eslimation of around 120cubic meters of these effiuents can be produced everyday in Mexico City, which remain untreated in unlinedponds excavated near the composting pile.

Problems on designing adequale handlingprocedures for these wastes arise since the generatianof food and other biodegradable wastes increasesconstantIy. In tum, waste accumulation lead tohazards for population and to the environment. Infacl, il has been calculaled lhal lhe biggesl landfill andcomposling planl sile in Mexico Cily may produce1.2 Mlons per year of carbon clioxide due lo lhebiodegradation process during garbage stabilization(Inventory of Oreen House Effect Emissions inMexico Cily, 2008), lhe contribution of lhe leachalesproduced in this site to these emissions is unknown.AIso, the main interest in the adequate treatment oflhe urban solid biodegradable wasles is lhal mayrender important amounts of biofuels as methane,and supplement energetic requirements in compostingplanls (Flores el al., 2008).

Compared lo landfill leachales, composl leachaleshandling and lrealmenl has been rarely addressed.The biological anaerobic lrealmenl in UASB, EGSB,or hybrid anaerobic reactors reduced significantIy theamount of carbonaceous organic matter and produced

significanl amounls of melhane (Han and Shin, 2004;Han el al. 2005; Slabnikova el al. 2008; Liu el

al. 2010; Rajabi and Vafajoo, 2012). The anaerobic­aerobic treatment of compost leachates in a full­scale planl has been also reported by Mokhlaraniel al. (2012), whom utilized an anaerobic hybridreaclor packed wilh clay blocks as filtering media.Other mineral supports such as zeolite, have beenused as filtering, packing and support material inseveral anaerobic reactor prototypes, to favor biomassimmobilization and to improve methanogenesisthrough ammoniurn/ammonia removal by cationicinterchange with Mg2+, Ca2+ and Na+, that constitutelhe zeolile slruclure (Milán el al., 2001; Tada el al.,2005; Femández el al., 2007; Wang el al., 2011;Monlalvo el al., 2012).

Given lhe composl leachales high organicmatter content, to facilitate biological treatmentand guarantee reactor stability, it is advisable todilute these effiuents with municipal wastewater thatgenerally has a low organic matter concentration asCaslilla el al. (2009) and Mokhlarani el al. (2012)have proposed. The aim of lhis work was lo sludy lheco-treatment of compost leachates produced duringurban solid biodegradable wasles slabilizalion diluledwith municipal wastewater. An anaerobic filter reactorpacked with Mexican zeolite was used to promote gas­liquid-solid-separation, anaerobic biofilm formationand enhance methane production from this waste.

2 Materials and methods

2.1 Composition of eompost leaehates andmunicipal wastewater (MWW)

Composl leachales were collecled al a full-scalecomposting planl in Mexico Cily lhal received urbansolid biodegradable wasles al a rale of 1000 lo 3000Ion per day. Those collecled afler 30 days of beingproduced were considered as fresh leachales (FE) andlhose lhal were collecled afler 3 monlhs of beingproduced were considered as depleled leachales (DE).The basis for the c1assification was the high organicmatter and acetic acid content and low ammoniumconcentration found in the fresh effiuents. At theconlrary, lhe low organic maller and volatile fally acids(VFA) contents and high ammonium concentrationfound in lhe depleled ones. Two fresh balches werecollecled by May 2009 (FE1) and January 2010 (FE2)and one depleled balch was collecled by November2009 (DE). MWW used for dilution was oblained

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from the wastewater treatment plant located at theUniversity campus. Collected leachates and MWWbatches were characterized through total and dissolvedCOD content, suspended solids content, VFA contentand composition, ammonium concentration and pH.

2.2 Methanogenic reactor

An anaerobic filter reactor (AFR) was selected tocarry on the biological treatment and to allow solid­gas-liquid-separation. Comprised a column of 13.7L nominal volume (Fig. 1) packed with zeolitepebbles from San Luis Potosí, Mexico, with a meandiameter of 1.6 cm. The reactor was inoculatedwith 260 mL of sludge from a malting factory toattain a concentration of 12.1 g SV and operated atenvironmental temperature of 21±4°C and constanthydraulic retention time (HRT) of 1.5 d. Leachateswere diluted with MWW at increasing total organicmatter concentrations ranging from 1.8 g COD L-1

for start-up (15 days) to 3.2, 7.1, 10.5 and 13.1g COD L-1 during full operation for 113 days.The criteria for increase feeding concentration was,initially to duplicate COD concentration after start-up,and afterwards step increases in 3.0 g COD L-1 foreach stage, to adapt the sludge to increasing organicloading rates (OLR), that varied from 1.2 to 8.7 g CODL-1 d-1. The performance of the AFR was followed upthrough infiuent and effiuent analysis.

andsludge

•

2.3 Analytical methods

Samples from leachates and MWW batches and fromthe AFR infiuent and effiuent, were filtered using fiberglass filters of 0.45 flm pore size (Millipore, USA)for dissolved COD, ammonium and VFA content andcomposition determinations. Total COD, aIkalinityand solids content were determined in non filteredsamples. Total and dissolved COD contents weredetermined by closed refiux colorimetric method.Total and suspended solids (TS, TVS, TSS and VSS)were determined through gravimetric determinations.The pH was measured with a potentiometer (Hanna255) and aIkalinity content expressed as CaC03

concentration by potentiometric titration to pH 5.75with H2S04 0.05 N. Alkalinity ratio was determinedtitrating at pH 5.75 and at pH 4.3 with H2S04

0.5 N; the quotient of both expended volumes isthe ratio between produced alkalinity and titrableVFA and indicated the conversion capacity of themethanogenic process. Ammonium was determinedwith a selective electrode (Orion 93). VFAcontent and composition were determined by FID­Gas Chromatography (HP 5890) using an Altech­1000 capillary column. Biogas production rate wasmeasured in a device with two constant volumechambers for gas accumulation, and compositionwas determined by TCD-Gas Chromatography (GowMac 580) using a Carbosphere 80/100 column. Alldeterminations were made according to StandardMethods for the Analysis of Water and Wastewater(2005). The data set obtained fram the analysisof all samples and parameters detennined, wereanalyzed statistically obtaining the average value andthe standard deviation with a confidence interval of95%.

3 Results alld discussioll

3.1 Composition of compost leachates andMWW

Fig. 1. Schematic diagram of the zeolite packedanaerobic filter reactor.

Influent

Feedingpump

RecITculationpump

Leachates and MWW composition is shown in Table1. In this work it was found that depending uponthe composting pile stabilization time, leachates haddifferent COD, VFA and ammonium contents. Ascan be seen, fresh leachates FE1 and FE2 had hightotal and dissolved COD content, while the depletedbatch (DE) had a fraction of the COD of freshbatches indicating that went through further naturaldegradation in situ.

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Table 1. Physicochemical characterization of compost leachates and municipal wastewaterutilized lo feed lhe AFR.

Parameler (g L-1 ) FEl FE2 DE MWW

Tolal CaD 120.0 84.35 15.8 0.402Dissolved caD 118.0 75.13 14.9 0.278

TS 135.0 79.7 16.2 n.d.TVS 128.0 76.1 15.8 n.d.TSS 15.7 5.62 1.38 0.137VSS 13.0 4.0 0.94 0.115

Acetic acid 11.1 7.2 1.48 0.082Propionic acid 2.8 3.3 0.19 0.016n-Butyric acid 2.4 6.3 0.48 0.007n-Valeric acid 0.69 4.2 0.29 0.002

Ammonium (g NH;-N L-1) 0.55 0.74 5.36 0.049pH 4.50 4.83 6.55 8.10

FE: Fresh leachate. DE: Depleted leachate. MWW: Municipal wastewater

The total COD concentratian contained in freshbatches, was found to be within the range reportedby Liu el al. (2010), Rajabi and Vafajoo (2012) andMokhlarani el al. (2012) from 42 lo 109 g CaD L-l.

Coincidenl findings may arise from lhe facl lhal lheseauthors investigated compost leachates produced infull scale composting planls in China and !ran, similarin capacity to those found in Mexico City.

On lhe olher hand, TS values found were higherlhan lhose reported before by Rajabi and Vafajoo(2012) and Maleki el al. (2009). TSS and VSSconcentration were lower as compared to previouslyreported values of 15.9 lo 33.6 g TSS L-1 by Liuel al. (2010) and Rajabi and Vafajoo (2012), whileMokhlarani el al. (2012) found a range belween2.9 lo 17 g TSS L-1 In lhis work, lhe VSSconlenl in lhe FE samples represenled 82.8 and 70.4%of lhe TSS, indicaling high organic maller conlen!.Leachales suspended solids conlenl probably dependson the composting pile stabilization stage; as thewastes are stabilized the suspended solids releasedlo lhe leachales diminishes, and probably also lhenatural organic marter degradatian in the leachate mayproduce lhe dissolution of suspended solids.

The acid pH in fresh leachales was due lo lhe VFAconlenl found of 17.0 g L-1 for FEl and 21.0 g L-1 forFE2, lhal are several limes higher lhan lhose reporledby Slabnikova el al. (2008) and Shin el al. (2001).Brinlon (1988) reporled lhal lhe highesl degradationand VFA production in the composting process wasobserved during lhe firsl 200 hours, and lhal lhesecompounds are responsible for lhe lypical rejeclableodor of these wastes. Regarding VFA composition,acetic acid represenled 65.6% and 34.2% for FEl and

FE2 respectively, indicating lhal lhese balches werecollected during a still active fermentation stage oflhe composting process (Brinlon, 1988; Han and Shin,2004). It is also noliceable lhal acelic acid, whichis the main methane precursor, predominated aooveolher VFA in fresh leachales balches collecled; ascan be seen in Table 1, indicating the freslmess ofthe leachate accumulated near the composting pile.AIso propionic, butyric and valeric acids were found inlesser concentration, and varied between both batchesand did nol show a pallem relaled lo lhe leachale timeof production.

Fresh leachates attained an ammoniumconcentralion less lhan 1.0 g NH;-N L-1 lhal iscomparable lo values reported by Krogmarm andWoyczechowski (2000), Liu el al. (2010) and Zhou el

al. (2010), ranging from 0.23 a 0.82 g NH;-N L-l.

In conlrasl wilh FE balches, DE presenled acharacteristic dark brown color, that was not removedduring lrealmenl, CaD and VFA concenlration of 15.8and 2.35 g L-1, suspended solids conlenl of 1.38g TSS L-1 and 0.94 g VSS L-1, while ammoniumconcentration was as high as 5.6 g NH; -N L-1,

consequentIy pH was near neutrality. Krogmann andWoyczechowski (2000) found lhal composl leachalesproduced in a 200 hours period had acid pH and lowammonium concentration, and that pH increased alongwith ammonium content during composting time; thehighest ammonium concentration was found in foodwasles leachales afler of 7 weeks. Brinlon (1988)found oul lhal VFA climinished al a rale of 1000 ppmeach 10 days in relalion lo lhe leachale age. All DEcharacteristics can be attributed to the elapsed timebefore its collection.

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The diíferences found between the datareported by other authors and those found in thiswork, are probably due to urban biodegradablewastes composition in diíferent countries, handlingprocedures in the composting facilities, the timeelapsed between leachates formation and collectionand the season of the year when samples werecollected.

In comparison, MWW presented aIkaline pH andlow total and dissolved CaD content, suspendedsolids, VFA and ammonium concentration (Table 1),that are typical of these effiuents (Cervantes el al.,2011).

3.2 Methanogenic AFR performance

For performance evaluation, the AFR was fed withcaD increasing concentrations in five stages (Figure2). aperation parameters, removal efficiency andmethane productivity corresponding to these stages areshown in Table 2.

The reactor was started-up with the mixture ofFE1 and MWW at a concentration of 1.8 g CaD L-1,

attaining 79.5% removal efficiency that increased to88.0% when the organic matter concentration in thefeeding was increased to 3.2 g CaD L-1 in stage1 (day 16 to 36). AIkalinity ratio increased from0.82 during start-up to 0.84 in stage 1 and producedalkalinity as bicarbonate increased slight1y, while

methane productivity duplicated from 0.23 to 0.46 LCH4 L -1 d- l . In this stages, ammonium concentrationfed was 70 mg NH1-N L -1 while 146 mg NH1-N L- l

during start-up and 175 mg NH1-N L -1 in stage 1werefound in the effiuent, indicating that around 76 to 105mg L -1 were formed.

During stage II (day 37 to 50), 7.1 g CaD L- l

were fed, removal efficiency attained 91.5 % andmethane productivity increased to 1.0 L L -1 d- l , whilealkalinity ratio diminished to 0.75, indicating that thereactor was slightly aífected by the increase in loadingrateo Additionally, ammonium concentration in theeffiuent increased to 223 mg NH1-N L -1 along withan increase in organic matter of 0.49 g CaD L-l.

In stage III (day 51 to 98), the concentration fedwas increased to 10.5 g caD L-1, organic matter in theeffiuent increased to 2.0 g L-l and removal efficiencydiminished to 81.2%. The amount of organic matterfound was probably due to the saturation of the AFRby the solids retained during operation that weredischarged in this stage. Produced alkalinity increasedslightly but alkalinity ratio remained in 0.74, whileno eífect on methane productivity was noticed whichincreased to 1.3 L L-1 d- l (Table 2). At the end ofstage III (day 83), the mixture of DE and MWW wasfed and yielded a mean ammonium concentration of675 mg NH1-N L-1 while 703 mg NH1-N L-1 weredetermined in the effiuent, indicating no ammoniumremoval by zeolite.

1 II III IV16 100

14 ~~

ª:s 8012 o

OJ) <'-' 10 ::»~ 60 -(1)

O 8 S1U 40 ()- 6 ....C'á 9....

4 ~oE--< 20 ~

2 :!2.o'-'

O O

O 10 20 30 40 50 60 70 80 90 100 110

Time(d)

-e- Influent ~Effluent -<>- Removal Efficiency

Fig. 2. Total CaD fed and removal efficiency pattem of the AFR.

www.rmiq.org 545

Table 2. AFR performance and methane productivity based in total CaD.

Stage (d) EffluentCaD

(g L-1)

0.37 ±0.260.39 ± 0.090.49 ± 0.152.02 ± 0.991.67 ±0.57

0.23 ± 0.040.46 ± 0.061.04 ±0.091.36 ± 0.221.84 ± 0.15

Methaneproductivity

(L CH4 L- 1 d- 1)

Alkalinityratio

0.82±0.080.84±0.040.75±0.040.74±0.070.79±0.08

1.2±0.921.3±0.132.1±0.152.6±0.362.6±0.24

1.8 ± 0.13 1.21 ± 0.09 79.5±14.13.2 ± 0.41 2.16 ± 0.28 88.0±2.97.1 ± 0.49 4.72 ± 0.53 91.5±1.910.5 ±2.02 7.0 ± 1.09 81.2±7.913.1 ± 0.52 8.73 ± 0.34 87.2±4.7

Batch Influent OLR Removal AlkalinityCaD (g L-1 d- 1) efficiency (g CaC03 L-1)

(gL-1) (%)

FElFElFEl

FEl, DEDE, FE2

1-1516-3637-5051-98

99-113

Start-up1IIIIIN

Gan el al./ Revista Mexicana de Ingeniería Química Vol. 12, No. 3 (2013) 541-551

At the beginning of stage IV (day 99 to 106) themixture of DE and MWW was still being fed and CaDconcentration was increased to 13.1g L-l. Removalefficiency increased to 87.2% and alkalinity ratio to0.79; organic matter in the effiuent diminished slighUywhile methane productivity increased to1.8 L L-1 d-l .A mean ammonium concentration of 911 mg NH;­N L-1 was fed during the first 7 days of this stagewhich diminished gradually to 415 mg L-1, for anammonium removal attributed to zeolite of 54.4%,improving methane productivity, as other authors hasreported before (Milán el al., 2001; Tada el al., 2005;Wang el al., 2011).

Also zeolite has been reported as a suitable supportfor microorganisms immobilization (Femández el al.,2007; Weill el al., 2011). In this investigation, thebiomass immobilized on the packing of the AFRprobably hindered a rapid ionic interchange that wouldlead to ammonium diminution since the moment whena high concentration was fed.

At the end of stage IV (day 107), the feedingwith FE2 reduced the ammonium concentration to93 mg NH; -N L-1 and in the effiuent 127 mg L-l

were found and ammonium removal by zeolite wasnot detectable. CaD removal efficiency and alkalinityratio increase was observed, although a high organicmatter concentration was still being detected in theeffiuent.

Liu el al. (2010) found that ammonium producedduring anaerobic treatment, from 350 to 900 mg NH;­N L-1 helped to buffer the system when high CaDconcentrations were fed. No buffering was found inthe AFR when ammonium concentrations similar tothose reported by Liu el al. (2010) were fed, due tothe zeolite ammonium removal.

As can be seen in Figure 3a, the highest removalefficiency attained in the AFR was around 90% atan organic loading rate of 4.7 g CaD L-Id-l. After80 days of operation (stage III), an important amount

of organic matter was detected in the effiuent andconsequenUy removal efficiency diminished, probablydue to the saturation of the filtering packing media bythe solids retained in the reactor, that were draggedout at this time. Also the dragging of small solidparticles by biogas production was observed whichmay contribute to the organic matter amount detectedin the effiuent.

Along with the increase in organic loading rate,methane productivity increased from 0.46 to 1.84 LL-1 d-l , as can be seen in Figure 3b. The high methaneproductivity equivalent to production rates of 6.0 to25.2 L CH4 d-l , indicated the biodegradability of thediluted leachate rendering 0.48 L CH4 produced perg consumed CaD (at 0.77 atm and 21°C in MexicoCity), that is higher than the theoretical value. Thehigh methane productivity is in agreement with theresults obtained by Milán el al. (2001) and WeiB el al.(2011), who found that zeolite may enhance methaneproduction by ammonium removal and by providingessential micronutrients for methanogenic archaea.Interestingly, the energetic capacity estimated for amethane production rate of 25.2 L d- l is of 717 kJ d- l

equivalent to 118 kJ L-1 of infiuent fed, indicating thesuitability of compost leachates to obtain an altemativeenergy source.

The results obtained in this work are similar tothose presented by Han and Shin (2004) and by Han el

al. (2005) that operated UASB reactors at pilot scaletreating urban food waste leachates at HRT from 3.8to 0.18 days and attained CaD removal efficienciesbetween 56-96%, with methane productivities of 0.4a 4.1 LVI d- l . Also are similar to those found byLiu el al. (2010), whom reported that the treatmentof compost leachates in an expanded granular sludgebed (EGSB) reactor at HRT of 31 hours, attainedremoval efficiencies from 90 to 97% and methaneproductivities from 0.7 to 7.1 m3 m-3 d- l , at dissolvedCaD concentrations of 4.0 to 38.0 g L-l.

b)~ 2.0-o;..¡ 1.6¿Lo

1.2.¡;.;::

(.)

.g 0.8::o."c: 0.4.,

-5"~ 0.0

0.0 2.0 4.0 6.0 8.0 10.0

OLR (g COD fed L-1d- 1)

o Total• Dissolved

100

~ 90;>,(.)

"" 80.¡:;

S"-¡;¡ 70>oa

60"~50

0.0 2.0 4.0 6.0 8.0 10.0

OLR(gCOD fedL-1d-1)

Fig. 3. Removal efficiency pattem (a) and methane productivity (b) vs. organic loading rates applied to the AFR.

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Gan el al./ Revista Mexicana de Ingeniería Química Vol. 12, No. 3 (2013) 541-551

0.0 +---+--+---+--+----+--+-----10.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Total COD red (g L-!)

0.0 +---+--+----+--+--t-----+-------j0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Total COD red (g L-!)

1.21.2

a) +Influentb)

+Influent1.0 1.0

-:>Effiuent

~ 0.8 :::' 0.8

Z< ~0Jl

.::9 0.6 ~ 0.6

'" '"'" '"f-< 0.4 > 0.4

0.2 0.2

Fig. 4. Total (a) and volatile (b) suspended solids removal pattern during the AFR operation.

In contrast the hybrid anaerobic system (HASL)proposed by Stabnikova el al. (2008) attained CaDremoval efficiencies higher than 90% at HRT of 2.1d and 8.7 g caD L-1 d-1, although the estimatedmethane produced from biogas was 2.1 L CH4 d-1

in the methanogenic section of the system. A fullscale plant reported by Mokhtarani el al. (2012)consisting of hybrid anaerobic reactors and an aerobicpostreatment, attained a CaD removal efficiency of91 % at 4.5 kg caD m-3 d- l , although no methaneproductivity was reported.

These findings indicate that anaerobic digestionis the suitable treatment for liquid effiuents formedduring the composting of urban biodegradable wastesto produce a biofuel such as methane.

Start-up I 11 III IV4.0

~ 3.5 OVa DBt opr I!JAc-~ 3.0~--o 2.5~

2.0

~ 1.5I 1.0Q

O 0.5U

0.0

1.5 2.4 6.0 8.9 12.2

Dissolved COD fed (g L'1)

Fig. 5. VFA composition in the AFR fed at differentstages: acetic acid (Ac); propionic acid (Pr); butyricacid (Et); valeric acid (Va).

3.3 Suspended solids removal efficíency

TSS infiuent concentration increased gradually from0.27 to 0.81 g L-1 along with the total CaD beingfed (Figure 4a), and removal efficiencies increasedfrom 34.5% to 69.0% during start-up and stage I anddecreased to 50.2% and 29.2% during stage 11 and IIIwith a slight recovery to 47.0% in stage IV. As can beseen in Figure 4b, VSS presented a similar increasingconcentration pattern in the feeding from 0.19 to 0.54g L-l. Removal efficiency increased after start-up to70.7% and decreased in stage III to 31.3%, due tosolids output found in the effiuent. A slight recoveryto 45.9% during the last stage was found.

In spite of the high organic matter removalefficiencies found, the suspended solids removal wasnot as high as expected in the anaerobic filter asreported before by Castilla el al. (2009), that attained80% removal. As explained before, two operationaldrawbacks may have been responsible for the variablesolids removal efficiency found: the saturation of

the filter and solids dragging to the effiuent due tobiogas production during stages III and IV, as shownin Table 2. Also, TSS fed contained an importantbiodegradable fraction and after being retained anddegraded in the filter, probably contributed in sorneextent to the biogas production, which may explain thehigh methane yield obtained.

3.4 VFA conversion

The VFA content in the fed varied according to theincrease in dissolved CaD (Table 3 and Figure 5) andrepresented from 45 to 79% in the stages fed with freshleachates and diminished to 25% when the DE batchwas fed. VFA varied in the feeding in the proportionshown in Figure 5, being acetic, propionic and butyricacids the predominant compounds while valeric acidwas found in a smaller concentration. During stagesI and 11, no VFA were detected in the effiuent, andattained 0.1 and 0.2 g CaD L-1 during stages III and

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Table 3. COD-VFA content based in dissolved CaD.

Influent Effiuent

Stage (d) CaD COD-VFA CaD COD-VFA Removal(g L-1) (g L-1) (g L-1) (g L-1) Efficiency (%)

Start-up 1-15 1.5±0.17 0.7±0.04 0.3±0.28 0.3±0.06 81.0±17.51 16-36 2.4±0.22 1.9±0.19 0.2±0.13 0.01±0.0 89.1±5.7II 37-50 6.0±0.23 2.7±0.32 0.4±0.41 O.O±O.O 91.9±6.7III 51-98 8.9±0.64 2.2±0.10 1.4±0.59 0.1±0.03 83.8±6.1IV 99-113 12.2±0.31 3.6±0.32 1.4±0.49 0.2±0.05 88.3±3.9

IV (Table 3), which along with the stability foundin produced alkalinity, indicated that the AFR couldtolerate higher loading rates without acidificatian.

It is important to notice that fresh leachates withhigh acetic acid content are suitable for the anaerobictreatment because acetic acid is the main methaneprecursor.

Conclusions

Compost leachate characterization showed that thecomposting pile maturation stage and the time elapsedsince leachates were produced had an important eífecton the type and concentration of organic mattercontent, such as CaD, VFA, ammonium and pH.

The AFR used for the co-treatment of compostleachates diluted with municipal wastewater,represented a feasible strategy for CaD removaland its conversion to methane. The biodegradabilityof the mixture used in the anaerobic treatment wasdemonstrated since the methane prcxiuction framthe consumed CaD was higher lhan the lheoreticalyield value. High ammonium concentration presentin depleted leachates was removed in 50% byzeolite, improving removal efficiency and methaneproductivity. Nevertheless, it is advisable to carryout fresh leachates treatment, because of the natureof leachates, the organic maller content is highlybicx:legradable and can be recovered as an altemativeenergy source, avoiding emissions to the atmosphere.

Suspended solids removal efficiency has to beoptimized and a nitrogen removal postreatment has tobe implemented to obtain a high quality effiuent.

Acknowledgements

This research was supported by the Institute forScience and Technology of Mexico City throughproject PICSO 11-55. Compost leachate samples

were provided by the Recycling Sub Direction of lheGeneral Direction of Urban Services of Mexico City.

References

Brinton, w.F. (1988). Volatile organic acidsin compost production and odorant aspects.Compost Science and Utilization 6, 75-82.

Castilla, P., Aguilar, L., Escamilla, M., Silva,B., Milán, Z., Momoy, O., Meraz, M.(2009). Biological degradation of a mixtureof municipal wastewater and organic garbageleachate in expanded bed anaerobic reactors anda zeolite filler. Water Science and Technology59, 723-728.

Cervantes-Zepeda, A.I., Cruz-Colín, M.R., Aguilar­Corona, R., Castilla-Hemández, P. and Meraz­Rodríguez, M. (2011). Physicochemicaland microbial characterization of the treatedwastewater in a pilot scale UASB reactor.Revista Mexicana de Ingeniería Química 10,67-77.

Femández, N., Montalvo, S., Femández-Polanco, F.,Guerrero, L., Cortés, 1., Borj a, R., S ánchez,E. and Travieso, 1.. (2007). Real evidenceal:x:mt zeolite as microorganisms immobilizerin anaerobic fiuidized bed reactors. ProcessBiochemistry 42,721-728.

Flores, R., Mufloz-Ledo, R., Flores, B.B. and Cano,K.1. (2008). Power generation from biomassestimation for projects of the clean developmentmechanism programo Revista Mexicana deIngeniería Química 7, 35-39.

Graja, S. and Wilderer, P.A. (2001). Characterizationand treatment of the liquid effiuents from lhe

www.rmiq.org 549

Gan et al./ Revista Mexicana de Ingeniería Química Vol. 12, No. 3 (2013) 541-551

anaerobic digestion of biogenic salid waste.Water Science and Technology 43,265-274.

Oreen House Effect Emissions Inventory of MexicoCity (2008). Secretariat of !he Environment­Mexico City Government. Available in:http://www.sma.df.gob.mx/inventario_emisionesjindex.php?op~gei [Accesed: September 6,2012].

Han, S.K., Kim, S.H., Shin, H.S. (2005). UASBtreatment of wastewater with VFA and alcoholgenerated during hydrogen fermentation of foodwaste. Process Biochemistry 40,2897-2905.

Han, S.K. and Shin, H.S. (2004). Performance ofan innovative two-stage process converting foadwaste to hydrogen and methane. Air & WasteManagement Association 54, 242-249.

Krogmann, U. and Woyczechowski, H. (2000).Selected characteristics of leachate, condensateand leachate released during composting ofbiogenic waste. Waste Management andResearch 18, 235-248.

Liu, J., Zhong, J., Wang, Y, Liu, Q., Qian, G., Zhong,L., Guo, R., Zhang, P. and Xu, Z.P. (2010)Effective bio-treatment of fresh leachate frampretreated municipal salid waste in an expandedgranular sludge bed bioreactor. BioresourceTechnology 101,1447-1452.

Maleki, A., Zazouli, M.A., Izanloo, H. andRezaee, R. (2009). Composting plant leachatetreatment by coagulation-fiocculation process.American-Eurasian Journal Di Agricultural &

Environmental Sciences 5, 638-643.

Milán, Z., Sánchez, E., Weiland, P., Borja, R.,Martín, A. and Ilangovan, K. (2001). Influenceof natural zeolite concentratian on the anaerobicdigestion of piggery wastes. BioresourceTechnology 80,37-43.

Mokhtarani, N., Bayatfard, A. and Mokhtarani, B.(2012). Full scale performance of compost'sleachate treatment by biological anaerobicreactors. Waste Management and Research 30,524-529.

Montalvo, S., Guerrero, L., Borja, R., Sánchez, E.,Milán, Z., Cortés, l., de la Rubia, M.A. (2012).Application of natural zeolites in anaerobicdigestion processes: A review. Applied ClayScience 58, 125-133.

Rajabi, S. and Vafajoo, L. (2012). Investigatingthe treatability of a compost leachate in ahybrid anaerobic reactor: An experimentalstudy. World Academy oj Science, Engineeringand Technology 61,1175-1177.

Shin, H.S., Han, S.K., Song, yc. and Lee, c.y(2001). Performance of UASB reactor treatingleachate from acidogenic fermenter in the two­phase anaerobic digestion of food waste. WaterResearch 35,3441-3447.

Solid Wastes Integrated Management Program forMexico City (2010). Official GovemmentJoumal of Mexico City No. 925. Available in:http://www.semamat.gob.mx/temas/residuos/solidosjDocumentsjpepgirjPPGIR %20Distrito%20Federal.pdf [Accessed: November 11,2012].

Solid Wastes Inventory of Mexico City(2010). Secretariat of the Environment­Mexico City Government. Available in:http://www.sma.df.gob.mxjsmajlinks/download/bibliotecajinventarioJesiduos_solidos_201O.pdf[Accessed: January 10, 2013].

Stabnikova, O., Liu X-Y and Wang, J-Y (2008).Anaerobic digestion of food waste in ahybrid anaerobic solid-liquid system withleachate recirculation in an acidogenic reactor.Biochemical Engineering Journal41, 198-201.

Standard Methods for the Examination of Waterand Wastewater (2005). Edited by !heAmerican Public Hea1th Association/AmericanWater Works Association/Water EnvironmentFederation, 21th ed., Washington DC, USA.

Tada, C., Yang, Y., Hanaoka, T., Sonoda, A., Ooi, K.,Sawuayama, S. (2005). Elfect of natural zeoliteon methane production for anaerobic digestionof ammonium rich organic sludge. BioresourceTechnology 96, 459-464.

Wang, Q., Yang, Y., Yu, c., Huang, H., Kim, M.,Feng, C. and Zhang, Z. (2011). Study on afixed zeolite bioreactor for anaerobic digestionof ammonium-rich swine wastes. BioresourceTechnology 102,7064-7068.

WeiB, S., Zankel, A., Lebuhn, M., Petrak, S.,Somitsch, W. and Guebitz, G.M. (2011).Investigation of mircroorganisms colonisingactivated zeolites during anaerobic biogas

550 www.rmiq.org

Gan et al./ Revista Mexicana de Ingeniería Química Vol. 12, No. 3 (2013) 541-551

production fram grass silage. BioresourceTechnology 102, 4353-4359.

Zhou, c., Wang, R. and Zhang, y. (2010).Fertilizer efficiency and environmental risk ofirrigating Impatiens with composting leachate indecentralized salid waste management. WasteManagement 30, 1000-1005.

www.rmiq.org 551