Effects of spiked metals on the MSW anaerobic digestion

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  • http://wmr.sagepub.com/Waste Management & Research

    http://wmr.sagepub.com/content/30/1/32The online version of this article can be found at:

    DOI: 10.1177/0734242X10383079 2012 30: 32 originally published online 29 September 2010Waste Manag Res

    Banks, CY Lin, WF Liu, PH Chen, CK Chen, HY Chiu, HY Wu, TW Chao, YR Chen, DW Liou and FC LoHM Lo, CF Chiang, HC Tsao, TY Pai, MH Liu, TA Kurniawan, KP Chao, CT Liou, KC Lin, CY Chang, SC Wang, CJ

    Effects of spiked metals on the MSW anaerobic digestion

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  • Research Article

    Effects of spiked metals on the MSWanaerobic digestion

    HM Lo1, CF Chiang2, HC Tsao3, TY Pai1, MH Liu1, TA Kurniawan4,KP Chao5, CT Liou6, KC Lin7, CY Chang8, SC Wang1, CJ Banks9,CY Lin10, WF Liu11, PH Chen1, CK Chen1, HY Chiu1, HY Wu1,TW Chao1, YR Chen1, DW Liou1, and FC Lo5

    AbstractThis study aimed to investigate the effects of eight metals on the anaerobic digestion of the organic fraction of munici-

    pal solid waste (OFMSW) in bioreactors. Anaerobic bioreactors containing 200mL MSW mixed completely with 200mL

    sludge seeding. Ca and K (0, 1000, 2000 and 6000mgL1) and Cr, Ni, Zn, Co, Mo and W (0, 5, 50 and 100mgL1)of various dose were added to anaerobic bioreactors to examine their anaerobic digestion performance. Results showed that

    except K and Zn, Ca (;728 to ;1461mgL1), Cr (;0.0022 to ;0.0212mgL1), Ni (;0.801 to ;5.362mgL1), Co(;0.148 to ;0.580mgL1), Mo (;0.044 to ;52.94mgL1) and W (;0.658 to ;40.39mgL1) had the potential toenhance the biogas production. On the other hand, except Mo and W, inhibitory concentrations IC50 of Ca, K, Cr, Ni,

    Zn and Co were found to be ;3252, ;2097, ;0.124, ;7.239, ;0.482, ;8.625mgL1, respectively. Eight spiked metalsshowed that they were adsorbed by MSW to a different extent resulting in different liquid metals levels and potential

    stimulation and inhibition on MSW anaerobic digestion. These results were discussed and compared to results from

    literature.

    KeywordsMetals, municipal solid waste, anaerobic digestion, IC50, biogas

    Date received: 6 February 2010; accepted: 8 August 2010

    Introduction

    Municipal solid waste (MSW) has been found to contain

    more metals in Taiwan recently. MSW may be recycled or

    be treated with incineration, composting, pyrolysis, gasica-

    tion, anaerobic digestion or landlling. Among them, anaer-

    obic digestion was reported to have the potential for energy

    recovery, digestate utilization and greenhouse gas mitigation

    (Mller et al., 2009; Gohlke, 2009; Young et al., 2010). As it

    is treated with anaerobic digestion, various metals present in

    the MSW may have the potential to aect the microbial

    activity, causing eects on biological treatments to a certain

    extent, thus resulting in a varying anaerobic process perfor-

    mance. Several researchers have reported that organic

    1Department of Environmental Engineering and Management,Chaoyang University of Technology, Wufong Township, TaichungCounty, Taiwan, ROC.2Institute of Environmental Health, China Medical University,Taichung, Taiwan, ROC.3Department of Business Administration, Asia University, Wufeng,Taichung, Taiwan, ROC.4Laboratory of Applied Environmental Chemistry (LAEC), Departmentof Environmental Sciences and Forestry, University of EasternFinland, Mikkeli, Finland.5Department of Occupational Safety and Health, China MedicalUniversity, Taichung, Taiwan, ROC.6Department of Safety, Health and Environmental Engineering,Hungkuang University, Sha Lu, Taichung, Taiwan, ROC.

    7Department of Occupational Safety and Health, Chung Shan MedicalUniversity, Taichung, Taiwan, ROC.8General Education Center, National Taitung Junior College, TaitungCity, Taiwan, ROC.9Department of Civil Engineering and the Environment, SouthamptonUniversity, Southampton, UK.10Department of Soil and Water Conservation, National Chung HsingUniversity, Taichung, Taiwan, ROC.11Department of Electrical Engineering, Feng Chia University,Taichung, Taiwan, ROC.

    Corresponding author: HM Lo, Department of EnvironmentalEngineering and Management, Chaoyang University of Technology,168, Gifong E. Rd., Wufong Township, Taichung County 41349,Taiwan, ROC.Email: hmlo@cyut.edu.tw; huangmu@yahoo.com

    Waste Management & Research

    30(1) 3248

    The Author(s) 2012Reprints and permissions:

    sagepub.co.uk/journalsPermissions.nav

    DOI: 10.1177/0734242X10383079

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  • matters and metals could aect the anaerobic process (Kuo

    and Genthner, 1996; Kida et al., 2001; Ren and Frymer,

    2003; Gikas, 2007; Li and Fang, 2007; Yue et al., 2007;

    Chen et al., 2008; Lin and Shei, 2008; Altas, 2009; Fermoso

    et al., 2009; Tan et al., 2009; Ma et al., 2009; Worm et al.,

    2009; Yuan et al., 2010). These substances included ammo-

    nia, sulde, chlorophenols, halogenated aliphatics, N-substi-

    tuted aromatics, long chain fatty acids, lignins and lignins

    related compounds, light metal ions and heavy metals.

    These mentioned literatures indicated that dierent sub-

    strate, various metals levels and recalcitrant organic com-

    pounds might aect the microbial diversity and bioreactor

    performance. Furthermore, the anaerobic biodegradation

    rate would be aected by metals uptake (Gurgel et al.,

    2008), substrate compositions, microbial community and

    operational conditions. Other investigations focusing on the

    synergistic/antagonistic eects or mechanisms of heavy

    metals on anaerobic digestion or fermentation process has

    also been reported by several researchers (Takashima and

    Speece, 1990; Peier et al., 1994; Espinosa et al., 1995;

    Wang 1995; Artola et al., 1997; Becker and Peier, 1997;

    Lin et al., 1998; Zhang et al., 2003; Malik, 2004). However,

    adverse or benecial eects of metals on MSW anaerobic

    digestion are not many and are not systematically investi-

    gated (Banks and Lo, 2003; Lo, 2005; Lo and Liao, 2007;

    Yue et al., 2007; Chen et al., 2008; Lo et al., 2009a, b). Due to

    the potential existence of metals in MSW and as it is treated

    with anaerobic digestion, it is therefore necessary to assess

    their potential eects on MSW anaerobic digestion.

    This study aims to investigate the eects of selected metals

    on the MSW anaerobic digestion. Selected metals include

    alkali metals of Ca and K, heavy metals of Cr, Ni and Zn,

    and trace metals of Co, Mo and W. The results of the present

    studies are evaluated and compared with those of other

    investigations. The ndings reported in this study are

    expected to provide the baseline data and useful information

    for the anaerobic digestion of MSW and/or anaerobic

    co-digestion of MSW/sludge containing metals.

    Materials and methods

    Municipal solid waste substrate

    To minimize possible interferences with selected metals on

    MSW digestion, MSW that contained ;6% total solids

    (TS) and ;5% volatile solids (VS) was prepared according

    to previous studies (Banks and Lo, 2003; Lo, 2005; Lo and

    Liao, 2007; Lo et al., 2009a, b). Based on the weight propor-

    tion, the MSW was comprised of oce paper (30%), news-

    paper (30%), yard waste (35%) and food waste (5%). This

    composition proportionally represents typical organic frac-

    tions of MSW. In addition, the chemical constituents of C,

    H, O, N and others of MSW were determined to be around

    46, 6, 41, 1.4 and 5.6%, respectively. The carbon/nitrogen

    (C/N) ratio of this synthetic MSW (32.86) was also similar

    to that of typical MSW in Taiwan (39.86). A C/N ratio

    ranging from 25 to 50 has been reported to be suitable

    for the composting and anaerobic digestion of MSW

    (Lo et al., 2009a, b). The food/micro-organisms (F/M)

    ratio is important for the biological treatment process.

    Generally, 0.51 kgBOD (m3 day)1 of volume loading and0.20.4 kgBOD (kgMLSS (Mixed liquor suspended solids)

    day)1 of sludge loading were thought suitable for wastewa-ter biological treatment. In this study, F/M ratio was thought

    to be the initial MSW/initial sludge seeding (200mL

    (;5%VS MSW)/200mL (;2.5% VS sludge seeding)) equal

    to 10 gVS MSW/5 gVS sludge. The experiment was done in

    batch mode. In the MSW anaerobic digestion, a C/N ratio of

    25 was suitable for anaerobic digestion and composting. This

    C/N ratio of 25 was close to that of 32.6 in this study. The C/

    N ratio and F/M ratio and anaerobic bacterial community

    were important factors that will aect the anaerobic diges-

    tion process. The MSW samples were stored in a refrigerated

    storage chamber at 4 8C to minimize any further changes that

    might occur in their physico-chemical properties prior to the

    experiments.

    Anaerobic sludge seeding

    To initiate the MSW anaerobic digestion, 200mL of anaer-

    obic sludge (;TS 3%, ;VS ;2.5%) was added into tested

    batch bioreactors containing 200mL MSW substrate

    (TS;6%;12 g, VS;5%;10 g). The sludge wasobtained from Fu-Tien municipal wastewater treatment

    plant located at Taichung City in central Taiwan. The

    plant collects ;50 00055 000m3 day1 sewage and adoptsaerobic activated sludge process (hydraulic retention time

    (HRT), 6 h). The sludge from the rst (HRT, 1.5 hrs) and

    the second sedimentation tank (HRT, 4 hrs) is processed to

    a gravity thickener (solid retention time (SRT), > 12 h) and

    then sent to the anaerobic digesters (SRT, > 30 days) for

    anaerobic digestion. The anaerobic sludge was taken from

    anaerobic digester and their metal contents and basic param-

    eters such as pH, TS and VS, etc. have been reported in

    previous studies (Lo and Liao, 2007, Lo et al., 2009b). The

    metals content of the sludge used for seeding and the MSW

    are presented in Table 1.

    Experimental

    About 200mL MSW substrate and 200mL sludge seeding

    and the designate spiked metal amounts were mixed comple-

    tely in 500mL anaerobic bioreactors (plastic bottles). The

    bioreactors with working volume of 400mL were operated

    to test the toxicity and response of eight selected metals on

    MSW anaerobic digestion. Bioreactors were maintained at

    35 8C oven which was suitable for anaerobic digestion. The

    anaerobic bioreactors had an exit for biogas collection using

    the water replacement method. Initial pHs were ;66.5 and

    Lo et al. 33

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  • the initial VS of the MSW and sludge used for seeding were

    ;5% and ;2.5%, respectively. Tested metal compounds

    were CaCl2, K2SO4, CrCl66H2O, NiSO46H2O,ZnSO47H2O, CoSO47H2O, Na2MoO42H2O, andNa2WO42H2O which were purchased from Merck Co. TheCaCl2 and K2SO4 were weighted and spiked directly into the

    batch bioreactors according to the Ca and K of the desig-

    nated added amounts of 1000, 2000 and 6000mgL1, respec-tively. For example, Ca 1000mgL1 was prepared by adding1107.59mgCaCl2 into the batch bioreactors. 1107.59mg (X)

    was calculated by X3 (Ca/CaCl2)/0.4 L 1000mgL1, thatis, X3 (40.08/110.98)/0.4 L 1000mgL1. Similarly, theCrCl66H2O, NiSO46H2O, ZnSO47H2O, CoSO47H2O,Na2MoO42H2O and Na2WO42H2O were spiked accordingto the Cr, Ni, Zn, Co, Mo and W of the designated added

    amounts of 5, 50 and 100mgL1, respectively. Controlbioreactors without metals addition (0mgL1) wereemployed for comparison.

    Forty-four bioreactors for each metal of three various

    spiked amounts and control were used. They were used for

    biogas measurement and 100mL mixture (MSW and sludge

    seeding) were taken one by one (on day 1, 5, 8, 15, 19, 29, 33,

    36, 43, 47 and 50) for each individual metal and parameter

    analysis over the whole digestion period. The required total

    bioreactors for each metal including control and three dier-

    ent added amounts (0, 1000, 2000 and 6000mgL1 or 0, 5, 50and 100mgL1) were 113 4 44 and the total bioreactorsfor the eight metals were 443 8 352. The bioreactors weremaintained within a homeostatic oven with a constant tem-

    perature around 358C. Anaerobic digestion of 200mL MSW

    (VS ;5%;10 g VS) nearly reached the biochemical meth-ane potential (BMP) after 50 days. The biogas production

    was around 455mL (;455mL/10 gVS;45.5mLg1 VS).During the digestion period, biogas production in each

    bioreactor was recorded daily by biogas collectors using the

    water replacement method. A sample of 100mL of MSW

    substrate and sludge seeding mixture was collected in each

    sacriced bioreactor and was ltered through a 0.45mm mem-

    brane for metal and parameter analysis on day 1, 5, 8, 15, 19,

    29, 33, 36, 43, 47 and 50, respectively. The metal concentration

    in each bioreactor was measured by ICP-OES (Inductively

    Coupled Plasma Optical Emission Spectrometry, IRIS

    Intrepid II, Thermal Electron Corporation). The analytical

    method followed the manual of the manufacturer. Briey

    speaking, the ICP-OES equipment was set at the required oper-

    ational conditions. Incident energy was 1100W and reective

    energy was

  • Results and discussion

    Biogas production and anaerobic parameters

    Theotal biogas production measured using the water replace-

    ment method is presented in Figure 1. The composition

    of biogas production was normally comprised of CH4(;5070%), CO2 (;3050%), H2S (

  • and dosed metals minus the metals concentration in the

    liquid phase. The mass balance of the metals in the liquid

    and solid phase can be found in Table 2.

    From Figures 2 and 3 and Table 3, it was shown that

    Ca (;728 to ;1461mgL1, average ;1035mgL1),Cr (;0.0022 to ;0.0212mgL1, average ;0.0148mgL1),Ni (;0.801 to ;5.362mgL1, average ;1.842mgL1), Co(;0.148 to ;0.580mgL1, average ;0.307mgL1),Mo (;0.044 to ;52.94mgL1) and W (;0.658 to;40.39mgL1) had the potential to enhance the biogasproduction. By dividing the highest levels to the lowest

    ones, Mo and W showed wider stimulation ranges whereas

    Ca, Cr, Ni and Co showed narrower stimulation ranges in

    comparison to those of Mo and W. The IC50 concentrations

    showed the order of Ca>K>Co>Ni>Zn>Cr. Typical

    metal levels in the biogas plant will vary with the dierent

    digested substrate, metals adsorption and operating condi-

    tions. Typical metal levels in the organic fraction of MSW

    (OFMSW) anaerobic digestion or waste compost can be

    found in Lo et al. (2010), Iglesias et al. (2000) or Farrell

    and Jones (2009) (Table 4). On the other hand, inhibitory

    concentrations (IC50) of Ca, K, Cr, Ni, Zn and Co were

    found to be ;3252, ;2097, ;0.124, ;7.239, ;0.482,

    ;8.625mgL1, respectively. The Mo and W that wasdosed under 100mgL1 showed stimulatory results ratherthan inhibitory eects (Figure. 3 (E-a) and (F-a)). The

    alkali metals Ca and K showed higher IC50 values than

    those of the heavy metals Cr, Ni and Zn and trace metal Co.

    The initial VS and TS of MSW were ;5% and ;6%,

    respectively. TOC in leachate and VS and TS of MSW at

    the end of the digestion were thought to decrease as the

    MSW anaerobic digestion was progressed. Bioreactors that

    have higher biogas production will lead to lower VS at the

    end of digestion process. The total organic carbon (TOC)

    [chemical oxygen demand (COD)] has been found to

    decrease as the anaerobic digestion process progressed (Lo

    et al., 2009b, 2010). The pH was thought to have the poten-

    tial eects on organic refuse degradation (Kong, 2010). The

    pH values in all bioreactors were found to range between ;5

    and ;8.5, which was suitable for anaerobic digestion as can

    be seen in Figure 4.

    Inhibitory or stimulatory effects of metals

    With the exception of K and Zn, suitable soluble levels of Ca,

    Cr, Ni, Co, Mo and W were found to improve the MSW

    digestion performance and enhance the biogas production

    (Table 3). Metals levels higher than threshold values would

    result in adverse eects, leading to the inhibition of biogas

    production. The ndings in that study were similar to those

    of Fermoso et al. (2009) that the anaerobic digestion might

    be limited or inhibited if metals such as Cu, Co, Fe, Mn, Mo,

    Ni, Se, W, Zn and V were not optimally added or overdosed.

    In addition, the reported inhibitory concentrations of Co, Ni

    and Zn (Gikas, 2007; Li and Fang, 2007; Lin and Shei, 2008;

    Altas, 2009; Fermoso et al., 2009) exceeded the IC50 levels

    investigated in this study (Table 3).

    The Ca concentration of 100400mgL-1 reported by

    Chen et al. (2008) and Yuan et al. (2010) was optimum,

    which could improve the operational stability of the diges-

    tion. However, at a concentration higher than 400mgL1,Ca was reported to be detrimental to the anaerobic process

    Ca initial dose of 0, 1000, 2000 and 6000 (mg L1)

    0

    Ca s

    olub

    le c

    once

    ntra

    tion

    (mg L

    1 )

    0

    1000

    2000

    3000

    4000

    y=16.48+0.02044x; R2=0.680IC50=~3252 mg L

    1

    SC=~1035 mg L1 average(~728 ~1461 mg L1)

    Ca ave. soluble concentration (mg L1)0

    500 1000

    1500

    2000

    2500 300

    0

    Tota

    l bio

    gas

    inhi

    bitio

    n (%

    )

    40

    20

    0

    20

    40

    60

    80

    100

    K initial dose of 0, 1000, 2000 and 6000 (mg L1)

    K so

    lubl

    e co

    ncen

    tratio

    n (m

    g L

    1 )

    0

    500

    1000

    1500

    2000

    2500

    3000

    3500

    4000

    IC50=~2097 mg L1

    K ave.soluble concentration (mg L1)0

    Tota

    l bio

    gas

    inhi

    bitio

    n (%

    )

    0

    20

    40

    60

    80

    100(a)

    (a)(a)

    (b)(b)

    (b)

    1000 2000 6000 0 1000 2000 6000

    500 1000 1500 2000 2500 3000 3500

    y=10.9+0.01865x; R2=0.800

    Figure 2. (a) Total biogas inhibition VS average Ca soluble concentration (A-a) and Ca soluble concentrations variation (A-b) inthe three various Ca dosed and control bioreactors (: Ca 0; *: Ca 1000; H: Ca 2000; : Ca 6000); (b): Total biogas inhibition VSaverage K soluble concentration (B-a) and K soluble concentrations variation (B-b) in the three various K dosed and controlbioreactors (: K 0; *: K 1000; H: K 2000; : K 6000).

    36 Waste Management & Research 30(1)

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  • Cr initial dose of 0, 5, 50 and 100 (mg L1)0

    Cr s

    olub

    le c

    once

    ntra

    tion

    (mg L

    1 )

    0.00

    0.05

    0.10

    0.15

    0.20

    0.25

    0.30

    Cr ave. soluble concentration (mg L1)0.0

    00.0

    20.0

    40.0

    60.0

    80.1

    00.1

    20.1

    4

    Tota

    l bio

    gas

    inhi

    bitio

    n (%

    )

    40

    20

    0

    20

    40

    60

    80

    100

    Ni initial dose of 0, 5, 50 and 100 (mg L1)

    Ni s

    olub

    le c

    once

    ntra

    tion

    (mg L

    1 )

    0

    2

    4

    6

    8

    10

    12

    14

    Ni ave. soluble concentration (mg L1)1

    0

    Tota

    l bio

    gas

    inhi

    bitio

    n (%

    )

    60

    40

    20

    0

    20

    40

    60

    80

    100

    Zn initial dose of 0, 5, 50 and 100 (mg L1)

    Zn s

    olub

    le c

    once

    ntra

    tion

    (mg L

    1 )

    0.00

    0.01

    0.02

    0.03

    0.200.40

    0.60

    0.80

    1.00

    1.20

    Zn ave. soluble concentration (mg L1)

    Tota

    l bio

    gas

    inhi

    bitio

    n (%

    )

    20

    0

    20

    40

    60

    80

    100

    Co initial dose of 0, 5, 50 and 100 (mg L1)

    Co s

    olub

    le c

    once

    ntra

    tion

    (mg L

    1 )

    0

    1

    2

    5

    10

    15

    20

    Co ave. soluble concentration (mg L1)0

    Tota

    l bio

    gas

    inhi

    bitio

    n (%

    )40

    20

    0

    20

    40

    60

    80

    100

    Mo initial dose of 0, 5, 50 and 100 (mg L1)

    Mo

    solu

    ble

    conc

    entra

    tion

    (mg L

    1 )

    0.0

    0.1

    0.2

    20.0

    40.0

    60.0

    80.0

    100.0

    Mo ave. soluble concentration (mg L1)0

    Tota

    l bio

    gas

    inhi

    bitio

    n (%

    )

    50

    40

    30

    20

    10

    0

    W initial dose of 0, 5, 50 and 100 (mg L1)

    W s

    olub

    le c

    once

    ntra

    tion

    (mg L

    1 )

    0.0

    0.5

    1.0

    1.5

    10.0

    20.0

    30.0

    40.0

    Wave. soluble concentration (mg L1)0

    Tota

    l bio

    gas

    inhi

    bitio

    n (%

    )

    1816141210

    86420

    (a) (b)

    (a)

    (b)

    (a)

    (b)

    (c) (d)

    (e) (f)

    (a)

    (b)

    (a)

    (b)

    (a) (a)

    (b) (b)

    5 50 100

    0 5 50 100

    0 5 50 100

    0 5 50 100

    0 5 50 100

    0 5 50 100

    1 2 3 4 5 6 7

    0.00

    0.05

    0.10

    0.15

    0.20

    0.25

    0.30

    10 20 30 40 50

    2 4 6 8

    5 10 15 20 25 30

    Figure 3. (a) Total biogas inhibition VS average Cr soluble concentration (A-a) and Cr soluble concentrations variation (A-b) inthe three various Cr dosed and control bioreactors (: Cr 0; *: Cr 5; H: Cr 50; : Cr 100); (b): Total biogas inhibition VS averageNi soluble concentration (B-a) and Ni soluble concentrations variation (B-b) in the three various Ni dosed and control biore-actors (: Ni 0; *: Ni 5; H: Ni 50; : Ni 100); (c): Total biogas inhibition VS average Zn soluble concentration (C-a) and Zn solubleconcentrations variation (C-b) in the three various Zn dosed and control bioreactors (: Zn 0; *: Zn 5; H: Zn 50; : Zn 100); (d):Total biogas inhibition VS average Co soluble concentration (D-a) and Co soluble concentrations variation (D-b) in the threevarious Co dosed and control bioreactors (: Co 0; *: Co 5; H: Co 50; : Co 100); (e): Total biogas inhibition VS average Mosoluble concentration (E-a) and Mo soluble concentrations variation (E-b) in the three various Mo dosed and control bioreactors(: Mo 0; *: Mo 5; H: Mo 50; : Mo 100); (f): Total biogas inhibition VS average W soluble concentration (F-a) and W solubleconcentrations variation (F-b) in the three various W dosed and control bioreactors (: W 0; *: W 5; H: W 50; : W 100).

    Lo et al. 37

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  • (Chen et al., 2008; Tan et al., 2009). The optimal result was

    dierent from the stimulatory concentrations of ;728 to

    ;1461mgL1 found in the present investigation (Table 3).It is further noted that moderately inhibitory levels (Chen

    et al., 2008) of Ca (25004000mgL1) was close to the nd-ings of IC50 (;3252mgL

    1) in that study as can be seen inTable 3.

    Potassium concentration of less than 400mgL1 has beenreported to enhance the anaerobic performance, whereas at a

    higher concentration it had inhibitory eects (Chen et al.,

    2008). The two reported values of IC50 (0.15mol L1,

    ;5865mgL1 and 0.74molL1, ;28934mgL1) of K con-centrations (Chen et al., 2008) were found to be substantially

    higher than the IC50 of K levels (;2352mgL1) in this study.

    With respect to heavy metals, toxicity was reported to

    have the order of Cr>Ni>Cu>Zn (Chen et al., 2008)

    which was similar to the present study in which Cr had the

    highest toxicity. However, some investigations have reported

    Table 2. Metals balance in liquid and solid phase of the bioreactors at the end of anaerobic digestion process (assuming thegaseous metals were trace amount compared to liquid and solid phase)

    Category,variousmetalsdosed andcontrolbioreactors

    Final(experimental)liquid phaseconcentration(mg L-1) atthe end point

    Final(experimental)liquid phasecontent (mg)at theend point

    Initial solidphase content(sum of initialMSW metalsand initialsludge seedingmetals, mg)

    Dosedmetalsconcentration(mg L-1)

    Dosedmetals(mg)

    Initial solidphase content(sum of initialdosed metals,initial MSWmetals andinitial sludgeseedingmetals, mg)

    Finalsolid phasecontent inthe mixtureof MSWand sludgeseeding (mg)

    Ca 0 261.318 104.527 207.22 0.00 0.00 207.22 102.69

    Ca 1000 490.751 196.301 207.22 1000.00 400.00 607.22 410.92

    Ca 2000 728.073 291.229 207.22 2000.00 800.00 1007.22 715.99

    Ca 6000 1559.246 623.698 207.22 6000.00 2400.00 2607.22 1983.52

    K 0 188.164 75.265 85.48 0.00 0.00 85.48 10.21

    K 1000 490.482 196.193 85.48 1000.00 400.00 485.48 289.29

    K 2000 1181.082 472.433 85.48 2000.00 800.00 885.48 413.05

    K 6000 2313.446 925.378 85.48 6000.00 2400.00 2485.48 1560.10

    Cr 0 0.000 0.000 0.70 0.00 0.00 0.70 0.70

    Cr 5 0.014 0.006 0.70 5.00 2.00 2.70 2.70

    Cr 50 0.053 0.021 0.70 50.00 20.00 20.70 20.68

    Cr 100 0.074 0.029 0.70 100.00 40.00 40.70 40.67

    Ni 0 0.058 0.023 0.38 0.00 0.00 0.38 0.36

    Ni 5 0.680 0.272 0.38 5.00 2.00 2.38 2.11

    Ni 50 0.801 0.321 0.38 50.00 20.00 20.38 20.06

    Ni 100 2.847 1.139 0.38 100.00 40.00 40.38 39.24

    Zn 0 0.019 0.008 8.46 0.00 0.00 8.46 8.45

    Zn 5 0.015 0.006 8.46 5.00 2.00 10.46 10.45

    Zn 50 0.067 0.027 8.46 50.00 20.00 28.46 28.43

    Zn 100 0.113 0.045 8.46 100.00 40.00 48.46 48.41

    Co 0 0.020 0.008 0.07 0.00 0.00 0.07 0.06

    Co 5 0.148 0.059 0.07 5.00 2.00 2.07 2.01

    Co 50 0.569 0.228 0.07 50.00 20.00 20.07 19.84

    Co 100 2.757 1.103 0.07 100.00 40.00 40.07 38.96

    Mo 0 0.002 0.001 0.03 0.00 0.00 0.03 0.03

    Mo 5 0.105 0.042 0.03 5.00 2.00 2.03 1.99

    Mo 50 5.153 2.061 0.03 50.00 20.00 20.03 17.97

    Mo 100 17.845 7.138 0.03 100.00 40.00 40.03 32.89

    W 0 1.104 0.441 ND 0.00 0.00 0.00 0.00

    W 5 0.782 0.313 ND 5.00 2.00 44.44 44.13

    W 50 13.148 5.259 ND 50.00 20.00 444.44 439.19

    W 100 30.689 12.275 ND 100.00 40.00 888.89 876.61

    38 Waste Management & Research 30(1)

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  • Table 3. Comparison of inhibitory or stimulatory concentration of anaerobic process in this study and literatures

    Element Comparative data from literature Data in present study

    Inhibitoryconcentration(IC50)

    Stimulatoryconcentration(SC)

    Inhibitoryconcentration (IC50)from regressionanalysis

    Stimulatoryconcentration(SC)

    Ca [2]>300mgL1 [2]25004000mgL1

    (moderately) [2]8000mgL1 (strongly)

    [2]200mgL1 [2]

  • dierent toxicity results. Altas (2009) demonstrated the

    IC50 order of Zn (7.5mgL1)>Cr (27mgL1)>Ni

    (35mgL1);Cd (36mgL1) on methane producing anaer-obic granular sludge. Li and Fangs (2007) ndings of the

    IC50 of individual heavy metals were Cu (30mgL1)>

    Ni;Zn (1600mgL1)>Cr (3000mgL1)>Cd(3500mgL1)>Pb (5000mgL1). Lin and Shei (2008) indi-cated that the IC50 of Zn, Cu and Cr was in the order of Zn

    (4.5mgL1)>Cu (6.5mgL1)>Cr (60mgL1). However,Cu 3mgL1 and Cr 15mgL1 in the sucrose fermentationprocess were found to lead to the 1020% hydrogen produc-

    tion stimulation. Yue et al. (2007) reported the IC50 of Cd

    (4.4mgL1)>Cu (6.4mgL1)>Cr (18mgL1). In addition,stimulatory concentrations were also reported to be Cd

    (1.6mgL1), Cu (2.4mgL1), and Cr (4.0mgL1), respec-tively. Kuo and Genthner (1996) found that the addition of

    Cr(VI) at 0.01mgL1 could increase the biodegradationrates of phenol (177%) and benzoate (169%), while Cd(II)

    and Cu(II) at 0.01mgL1 enhanced the biodegradation ratesof benzoate (185%) and 2-chlorophenol (168%), respec-

    tively. The ndings reported in the above-stated studies

    showed a dierent toxicity order in comparison with that

    produced by the present study; however, it supported the

    fact that suitable concentrations of Cr and other heavy

    metals could enhance the biogas production, which has

    been conrmed by this study.

    Gikas (2007) reported that a Ni concentration less than

    27mgL1 (maximal stimulation, 10mgL1) and a Co

    concentration less than 19mgL1 (maximal stimulation,5mgL1) could enhance the degradation stimulation ofsludge. These stimulatory levels were higher than the result

    of this study [Ni, stimulatory concentration (SC): ;0.801 to

    ;5.362mgL1, Co, SC:;0.148 to;0.580mgL1) (Table 3).The ndings in this study were in agreement with the result

    concluded by Kida et al. (2001) who reported that the

    Ni concentration of 0.5mgL1and Co concentrationof 0.2mgL1 were required to facilitate the methanebiotransformation through increases of coenzymes F430 and

    corrinoids. Ma et al. (2009) summarized that the stimulatory

    micronutrients of Co, Cu, Fe, Mo, Ni, Se and Zn for carbon

    monoxide dehydrogenase (CODH), superoxide dismutase

    (SODM), formate dehydrogenase (FDH) and sulfate-

    reducing bacteria (SRB) were 1001000, 5650, 5008500,

    65300, 1013 500, 20600 and 101250mg g1 COD,respectively. The above-stated varying stimulatory

    or inhibitory levels were thought to be due to the varying treat-

    ment substrate, microbial community and dierent operating

    conditions. In this study, the toxicity order of metals in

    terms of the average IC50 was found to be Cr

    (;0.124mgL1)>Zn (;0.482mgL1)>Ni (;7.239mgL1)>Co (;8.625mgL1)>K (;2097mgL1>Ca(;3252mgL1).

    Mo and W could increase the degrading activity of

    microbes in a UASB reactor (Worm et al., 2009) by adding

    Mo (0.5mmolL1, 21mgL1) and W (0.5mmolL1,37mgL1). This same phenomenon was observed in the

    Table 3. Continued

    Element Comparative data from literature Data in present study

    Inhibitoryconcentration(IC50)

    Stimulatoryconcentration(SC)

    Inhibitoryconcentration (IC50)from regressionanalysis

    Stimulatoryconcentration(SC)

    Co [1]Up to 35400mgL1(no detectableinhibition)

    10]

  • Table

    4.Metals

    levels

    inMSW

    anaerobic

    digestersleach

    ate

    andwastecompost

    inthis

    studyandcomparative

    data

    inanaerobic

    digestionorferm

    entationprocess

    from

    literatures

    Element

    Comparative

    data

    from

    literature

    asnotedbelow

    Data

    inthis

    study

    Metals

    levels

    inleach

    ate

    of

    MSW

    anaerobic

    digester

    (mgL1)orin

    MSW

    compost

    (mgkg-1)from

    literatures

    Inhibitory

    concentration

    (IC50)

    Stimulatory

    concentration(SC)

    Inhibitory

    concentration

    (IC50)from

    regression

    analysis

    Stimulatory

    concentration(SC)

    Metallevels

    (mgL1)in

    controlanddose

    d

    bioreactors

    Soluble

    metal

    concentration(m

    gL1)or

    metalcontent(m

    gkg1)

    Al

    [2] 1000mgL1Al(OH) 3(IC50for

    methanogens;

    IC72for

    acetogens)

    [2] 2500mgL1Al+3tolerance

    afteracclimation

    [14] ND1.05mgL1

    Ca

    [2] >

    300mgL1

    [2] 2500-4000mgL1

    (moderately)

    [2] 8000mgL1(strongly)

    [2] 200mgL1

    [2] 550mgL1(IC50)

    [5] 150mgL1(IC50)

    [5] 3300mgL1(IC50)

    [5] 170mgL1(IC50)

    [5] 7.7mgL1(IC50)

    [6] 3300mgL1(IC50)

    [6] 170mgL1(IC50)

    [6] 330mgL1(IC50)

    [6] 3400mgL1(IC50)

    [6] 110mgL1(IC50)

    [6] 180mgL1(IC50)

    [14] ND1.31mgL1

    [15] ND

    0.3060.08mgL1

    (continued)

    Lo et al. 41

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  • Table

    4.Continued

    Element

    Comparative

    data

    from

    literature

    asnotedbelow

    Data

    inthis

    study

    Metals

    levels

    inleach

    ate

    of

    MSW

    anaerobic

    digester

    (mgL1)orin

    MSW

    compost

    (mgkg-1)from

    literatures

    Inhibitory

    concentration

    (IC50)

    Stimulatory

    concentration(SC)

    Inhibitory

    concentration

    (IC50)from

    regression

    analysis

    Stimulatory

    concentration(SC)

    Metallevels

    (mgL1)in

    controlanddose

    d

    bioreactors

    Soluble

    metal

    concentration(m

    gL1)or

    metalcontent(m

    gkg1)

    [6] 2800mgL1(IC50)

    [6] >550mgL1(IC50)

    [6] 150mgL1(IC50)

    [8] 4.47.1mgL1

    [8] 1.6mgL1

    [14] ND1.31mgL1

    [15] ND

    0.3060.08mgL1

    Cr

    [5] 27mgL1(IC50)

    [5] 250mgL1(IC50)

    [5

    ] 630mgL1(IC50)

    [5] 210mgL1(IC50)

    [5] 3000mgL1(IC50)

    [5] 72mgL1(IC50)

    [6] 3000mgL1L(IC50)

    [6] 72mgL1(IC50)

    [6] 250mgL1(IC50)

    [6] 2500mgL1(IC50)

    [6] 42mgL1(IC50)

    [6] 140mgL1(IC50)

    [6] 2200mgL1(IC50)

    [6] 630mgL1(IC50)

    [6] 210mgL1(IC50)

    [7] 60mgL1(IC50,Hydrogenesis)

    [7] 17mgL1(IC50,Acidogenesis)

    [7] 14.7mgL1(IC50,

    Methanogenesis)

    [8] 1827.5mgL1(IC50)

    [5] 2mgL1

    [7] 15mgL1

    [8] 4mgL1

    [9] 0.01mgL1

    IC

    50:;0.124mgL1

    SC:;0.0022;0.0212mgL1

    (average;0.0148mgL1)

    Cr0:ND0.008mgL1

    Cr5:0.0020.0212mgL1

    Cr50:0.04120.1031mgL1

    Cr100:0.07350.2502mgL1

    [14] ND0.01mgL1

    Cu

    [5] 130mgL1(IC50)

    [5] 158mgL1(IC50)

    [5] 175mgL1(IC50)

    [5] 30mgL1(IC50)

    [5] 350mgL1(IC50)

    [5] 65mgL1(IC50)

    [5] 12.5mgL1(IC50)

    [6] 30mgL1(IC50)

    [6] 350mgL1(IC50)

    [6] 65mgL1(IC50)

    [6] 130mgL1(IC50)

    [6] 30mgL1(IC50)

    [6] 37mgL1(IC50)

    [6] 130mgL1(IC50)

    [6] 10mgL1(IC50)

    [6] 158mgL1(IC50)

    [6] 175mgL1(IC50)

    [7] 6.5mgL1(IC50,

    Hydrogenesis)

    [7] 3mgL1

    [8] 2.4mgL1

    [12] 5650mgg1COD

    [13]0.5mmolL

    1,31.77mgL1

    (0.03177mgL1)

    [14] ND0.05mgL1

    [15] 0.0660.05

    0.2160.23mgL1

    [16] ;

    130;350mgkg1

    (continued)

    42 Waste Management & Research 30(1)

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  • Table

    4.Continued

    Element

    Comparative

    data

    from

    literature

    asnotedbelow

    Data

    inthis

    study

    Metals

    levels

    inleach

    ate

    of

    MSW

    anaerobic

    digester

    (mgL1)orin

    MSW

    compost

    (mgkg-1)from

    literatures

    Inhibitory

    concentration

    (IC50)

    Stimulatory

    concentration(SC)

    Inhibitory

    concentration

    (IC50)from

    regression

    analysis

    Stimulatory

    concentration(SC)

    Metallevels

    (mgL1)in

    controlanddose

    d

    bioreactors

    Soluble

    metal

    concentration(m

    gL1)or

    metalcontent(m

    gkg1)

    [7] 350mgL1(IC50,

    Hydrogenesis)

    [7] 0.9mgL1(IC50,Acidogenesis)

    [7] 28mgL1(IC50,

    Acidogenesis)

    [7] 364mgL1(IC50,

    Acidogenesis)

    [7] 12.5mgL1(IC50,

    Methanogenesis)

    [8] 6.47.4mgL1

    [7] 3mgL1

    [8] 2.4mgL1

    [12] 5650mgg1COD

    [13]0.5mmolL

    1,31.77mgL1

    (0.03177mgL1)

    [14] ND0.05mgL1

    [15] 0.0660.05

    0.2160.23mgL1

    [16] ;

    130;350mgkg1

    Ni

    [1] 81mgL1(50%

    inhibitionof

    VFAdegradation)

    [1] 440mgL1(50%

    inhibitionof

    VFAdegradation)

    [1] 118mgL1(IC50or50%

    inhibitionofSMA)

    [1] 81mgL1(50%

    inhibition,bed

    ludge)

    [1] 78mgL1(50%

    inhibition,

    blanketsludge)

    [1] 118mgL1(IC50)

    [5] 35mgL1(IC50)

    [5] 1600mgL1(IC50)

    [5] 118mgL1(IC50)

    [5] 100mgL1(IC50)

    [5] 1300mgL1(IC50)

    [6] 1300mgL1(IC50)

    [6] 1600mgL1(IC50)

    [6] 1600mgL1(IC50)

    [6] 1400mgL1(IC50)

    [6] 118mgL1(IC50)

    [6] 100mgL1(IC50)

    [10];160;320mgL1(100%

    inhibition)

    [5] 4mgL1

    [10] 5000mgL1(IC50)

    [5] 67.2mgL1(IC50)

    [6] >5000mgL1(IC50)

    [6] 8000mgL1(IC50)

    [6] 3200mgL1(IC50)

    [4] 1mmolL

    1,0.207mgL1

    [14] ND0.76mgL1

    [15] 0.0460.04

    0.7560.30mgL1

    [16] ;

    180680mgkg1

    (continued)

    Lo et al. 43

    at UNIV OF SOUTHERN CALIFORNIA on April 9, 2014wmr.sagepub.comDownloaded from

  • Table

    4.Continued

    Element

    Comparative

    data

    from

    literature

    asnotedbelow

    Data

    inthis

    study

    Metals

    levels

    inleach

    ate

    of

    MSW

    anaerobic

    digester

    (mgL1)orin

    MSW

    compost

    (mgkg-1)from

    literatures

    Inhibitory

    concentration

    (IC50)

    Stimulatory

    concentration(SC)

    Inhibitory

    concentration

    (IC50)from

    regression

    analysis

    Stimulatory

    concentration(SC)

    Metallevels

    (mgL1)in

    controlanddose

    d

    bioreactors

    Soluble

    metal

    concentration(m

    gL1)or

    metalcontent(m

    gkg1)

    Zn

    [1] 690mgL1(50%

    inhibitionof

    methanogenic

    activitywith

    sludgeoperatedatHRT1day)

    [1] 270mgL1(50%

    inhibitionof

    methanogenic

    activitywith

    sludgeoperatedatHRT2day)

    [1] 96mgL1(50%

    inhibitionof

    methanogenic

    activity)

    [5] 7.5mgL1(IC50)

    [5] 270mgL1(IC50)

    [5] 97mgL1(IC50)

    [5] 110mgL1(IC50)

    [5] 1500mgL1(IC50)

    [5] >500mgL1(IC50)

    [5] 120mgL1(IC50)

    [5] 16mgL1(IC50)

    [6] 1500mgL1(IC50)

    [6] >500mgL1(IC50)

    [6] 120mgL1(IC50)

    [6] 270mgL1(IC50)

    [6] 135mgL1(IC50)

    [6] 200mgL1(IC50)

    [6] 1200mgL1(IC50)

    [6] 97mgL1(IC50)

    [6] 110mgL1(IC50)

    [7] 4.5mgL1(IC50,

    Hydrogenesis)

    [7] >350mgL1(IC50,

    Hydrogenesis)

    [7] 3.5mgL1(IC50,Acidogenesis)

    [7] 718mgL1(IC50,

    Acidogenesis)

    [7] >364mgL1(IC50,

    Acidogenesis)

    [7] 16mgL1(IC50,

    Methanogenesis)

    [5] 2mgL1

    [12] 101250mgg1COD

    [13]0.5mmolL

    1,32.70mgL1

    (0.0327mgL1)

    IC

    50:;0.482mgL1

    Zn0:0.010.0246mgL1

    Zn5:0.01010.0151mgL1

    Zn50:0.06720.6295mgL1

    Zn100:0.11271.1132mgL1

    [15] 0.07860.074

    1.2861.31mgL1

    [16] ;

    150;300mgkg1

    Fe

    [12] 5008500mgg1COD

    [14] 0.0170.346mgL1

    [13]5mmolL

    1,279.25mgL1

    (0.27925mgL1)

    [15] 3.5460.33

    192.2656.0mgL1

    (continued)

    44 Waste Management & Research 30(1)

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  • Table

    4.Continued

    Element

    Comparative

    data

    from

    literature

    asnotedbelow

    Data

    inthis

    study

    Metals

    levels

    inleach

    ate

    of

    MSW

    anaerobic

    digester

    (mgL1)orin

    MSW

    compost

    (mgkg-1)from

    literatures

    Inhibitory

    concentration

    (IC50)

    Stimulatory

    concentration(SC)

    Inhibitory

    concentration

    (IC50)from

    regression

    analysis

    Stimulatory

    concentration(SC)

    Metallevels

    (mgL1)in

    controlanddose

    d

    bioreactors

    Soluble

    metal

    concentration(m

    gL1)or

    metalcontent(m

    gkg1)

    Co

    [1] Upto

    35400mgL1(no

    detectable

    inhibition)

    [1] 600800mgL1(717%

    inhibition)

    [1] 950mgL1(100%

    inhibition)

    [1] 120mgg1dry

    matter

    [10];160;320mgL1(100%

    inhibition)

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