Pilot-scale anaerobic co-digestion of municipal biomass waste: Focusing on biogas production and GHG reduction

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    Municipal biomass wasteAnaerobic co-digestion

    diges antion

    opmenre face

    China has increased from 60 million tons to 125 million tons whichhas resulted in the rapid increase of sewage sludge and the disposalof sewage sludge has also been a big problem in almost all the cities

    ties have captured themajor market of waste treatment in the EU inthe last decade, and will certainly continue developing in thefuture. AD is expected to become global utilised because of itsenvironmental contribution, and energy benets [4e6]. Co-digestion of different types of MBW has been discussed in manyreferences due to its potential of increasing biogas output andimproving stability of anaerobic system [4,7e10]. Co-digestion alsomeans more feedstock supply, which is especially needed by large-

    * Corresponding author. Tel.: 86 1062772814; fax: 86 1062782910.E-mail addresses: liuxiaothu@gmail.com, liuxiao07@mails.tsinghua.edu.cn

    Contents lists available at


    .e ls

    Renewable Energy 44 (2012) 463e468(X. Liu).municipal solid waste (MSW) disposal. In 2009, a total of 157.4million tons of MSW was collected and transported nationwide. Ofthese, 89.0, 20.2, and 1.8 million tons were treated by landll,incineration, and composting, respectively [1]. With increasingquantity, 50e60% of the MSW was biomass waste characterized byhigh water and biodegradable organic content. The municipalbiomass waste (MBW) has led to serious adverse effects in tradi-tional MSW treatment systems (i.e. landll and incineration). Thehigh water content may cause abundant production of leachate forlandll, and may cause unstable burning conditions and dioxinrelease from incineration. Also the high biodegradable organiccontent may cause the production and emission of greenhouse gas(GHG). From 2005 to 2010, the wastewater treatment capacity in

    climate change, eutrophication, and the diminishing resources offossil energy and raw materials.

    Anaerobic digestion (AD) is considered as a sustainable optionfor the management of biomass wastes because the production ofrenewable energy and the recycling of nutrients [2]. Additionally,MBW separated from MSW and treated with AD can signicantlyreduce the load of traditional disposal facilities, and subsequentlyprolong their service life. It also decreases the secondary pollutantsoriginated from the biodegradation of organic wastes duringlandll, incineration and composting. AD has been employed inWestern Europe since the 1980s, while up to 2010 one-hundredand ninety-ve facilities have been constructed with a total annualcapacity of 5.9 million tons [3]. De Baere concluded that AD facili-Biogas productionGHG reduction

    1. Introduction

    With the rapid economic develChina, almost all of its megacities a0960-1481/$ e see front matter 2012 Elsevier Ltd.doi:10.1016/j.renene.2012.01.092content was benecial to the biogas production of the feedstock without inhibition to anaerobicdigestion. Compared with the landll baseline, GHG reduction is an important environmental benetfrom MBW digestion. Therefore, anaerobic co-digestion is a promising alternative solution for MBWbecause it contributes signicantly to the sound management of municipal solid waste in China.

    2012 Elsevier Ltd. All rights reserved.

    t and urbanization ofd with the problem of

    in China. In some cities, the sewage sludge is simply deposited ontothe wasteland without any treatment, which has caused seriouspollution. Efcient MBW management technology is increasinglyrequired due to environmental and economical concerns, such asKeywords:

    production. Stable operation was achieved with a high biogas production rate of 4.25 m3 (m3 d)1 atorganic loading rate of 6.0 kgVS (m3 d)1 and hydraulic retention time of 20 d. A total of 16.5% of lipidsAvailable online 16 February 2012 and dewatered sewage sludge were co-digested in a continuous stirred-tank reactor for biogasTechnical note

    Pilot-scale anaerobic co-digestion of muproduction and GHG reduction

    Xiao Liu a,*, Xingbao Gao a,b, Wei Wang a, Lei Zhenga School of Environment, Tsinghua University, Beijing 100084, ChinabChinese Research Academy of Environmental Sciences, Beijing 100012, ChinacDepartment of Urban and Environmental Engineering, Graduate School of Engineeringd School of Chemistry and Environment, Beihang University, Beijing 100191, China

    a r t i c l e i n f o

    Article history:Received 12 April 2011Accepted 24 January 2012

    a b s t r a c t

    A pilot-scale anaerobic co-anaerobic digestion (AD) afocusing on biogas produc

    journal homepage: wwwAll rights reserved.ipal biomass waste: Focusing on biogas

    Yingjun Zhou c, Yifei Sun d

    oto University, Katsura, Nisikyo-ku, Kyoto 615-8540, Japan

    stion research study is presented to elucidate the feasibility of developingeffective disposal method for municipal biomass waste (MBW) in China,and greenhouse gas (GHG) reduction. Food waste, fruitevegetable waste,

    SciVerse ScienceDirect


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  • sludge was treated by AD. A 1.6 m3 volume of digested sludge wascollected and pumped into the reactor. The TS, SS, VS, and VSScontents of the inoculums were 27.0, 25.0, 10.4, and 9.7 g L1,respectively.

    The reactor was operated under mesophilic condition at35 2 C by a water jacket. The reactors were constantly mixedusing mechanical stirrers (100 rpm) with an agitation time of 15min per two hours, and were fed once a day using a screw pump.

    2.3. Analytical techniques

    The analysis of TS, VS, SS and VSS were based on the StandardAnalytic Methods promulgated by the National EnvironmentalProtection Agency of China (1989). The measurement of crude berand protein were according to ISO 6865:2000 and ISO1871:2009,respectively. Lipids content was determined using soxhlet extrac-tion method according to ISO 6492:1999. The samples were lteredthrough 0.45 mm lters before the measurement of volatile fatty

    Enescale plants where large quantities of MBW are required. Mata-Alvarez et al. summarized several cases of co-digestion of MBW,in both research and practical use [11].

    Given that traditional technologies may cause severe environ-mental pollution for treating MBW, alternative environment-friendly treatment technologies of MBW are much needed inChina. Meanwhile, renewable energy recovered from the biomasswaste has become a global concern, and bioenergy has been listedin the Chinese New Energy Promotion Plan [12]. The AD of MBWcan reduce the GHG emission in two respects: reduction ascompared with the baseline management, and reduction throughproviding alternative resources in terms of non-renewable fossilenergy andmaterials. In 2009, 79% of treatedMSWwas contributedby the landll, and landll is considered as one of the main GHGemission sources in current China [1]. The development of AD canrestructure the traditional MBW treatment and disposal system inChina, and in turn achieve the reduction of GHG emissions. Alongwith other advantages mentioned earlier, AD has attracted muchattention of both government and enterprises in recent years, and itcan be expected that AD will be widely used in the near future inChina.

    At present, the support policy from the central government hasmade every megacity receptive to building large-scale AD facilitiesin China. However, due to the differences of geographic locality anddietary habit, MBWs especially food waste in China has the typicalcharacteristics of high water content (>85%) and high lipidscontent (>20% of dry basis) which is different from other countries,and few reports have discussed the AD of Chinese MBWs. There-fore, whether the Chinese MBWs t for AD, and what is the suitableoperation condition, these questions need to be answered beforethe construction and operation of the large-scale AD projects inChina. Thus, a systematic research of AD of Chinese MBWs isurgently needed to provide fundamental technology parametersand promote the commercialization of AD technology. Finally, asthe second biggest producer of carbon dioxide, China is facing greatpressure in reducing GHG emissions, so the specic GHG reductionwhich can be achieved during AD ofMBW is gaining interesting andneeds to be quantied. In this study, a pilot-scale anaerobic co-digestion research is presented to elucidate the feasibility ofdeveloping AD in China as an effective disposal method for MBW,focusing on the system performance and biogas production, andthen GHG reduction of AD was analyzed compared with landll.

    2. Methods

    2.1. Raw materials

    MBWused in this experiment comprised food waste (FW), fruit-vegetable waste (FVW), and dewatered sewage sludge (DSS). FWwas collected from a student canteen (capacity, over 1000 studentsfor a seated dinner) at Tsinghua University, FVW from a wholesalemarket, and DSS from a municipal wastewater treatment plant(WWTP) in Beijing (Qinghe WWTP; Northern Beijing; capacity,400,000 m3 d1). The inert materials in FW and FVW were manu-ally separated (e.g., plastic, bone, wood, and others). FW and FVWwere crushed to less than 3 mm size rstly by a food wastepulverizer, and thenmixed with DSS at the ratio of 2:1:1. Themixedfeedstock was kept at 4 C before use. During the experiment,a maximum of 80 kg d1 mixture was fed to the AD reactor.

    The characterization of raw materials is shown in Table 1 interms of solid content, organic composition, and elementalcomposition. Volatile solid (VS), standing for organic content,accounts for 65e90% of the total solid (TS). VS can be divided intovolatile dissolved solid (VDS) and volatile suspended solid (VSS).

    X. Liu et al. / Renewable464VSS/VS, representing the organic solid ratio in organic fraction,accounts for 46.2%, 58.3% and 96.6% for FW, FVW, and DSS,respectively, indicating that organic solid plays an important role inthe AD process, which has been proven to be the essential rate-limiting factor [13,14]. The organic compositions of the three rawmaterials differ signicantly. For FW, the lipids content is thehighest because of the Chinese traditional cooking style, whereasfor FVW, the crude ber is most abundant because of the cellulosecontent in fruits and vegetables. For DSS, the protein content is thehighest compared with KW and VFR because of the high content ofmicroorganisms. The C/N ratio of FW and FVW is suitable for AD;however, the C/N ratio of DSS is too low for AD. In the traditional ADof sewage sludge, slow degradation (>20 days), loworganic loadingrate, and the relatively low VS removal (30e40%) are often thedisadvantages of the process because the digesters are operatedwith too low C/N ratios. Hence, in this study, DSS was co-digestedwith FW and FVW of higher C/N ratios to cover the adverseeffects caused by its low C/N ratio.

    2.2. Pilot-scale reactor start-up and operation

    Continuous stirred-tank reactor (CSTR) was used in the research.The reactor had a volume of 2 m3 (effective volume, 1.6 m3; height,2.7 m; and diameter, 1.0 m). The feedstock of the reactor wasa mixture of 50% of FW, 25% of FVW and 25% of DSS in thepercentage of weight.

    Inoculums (digested sewage sludge) were collected fromanother municipal wastewater treatment plant (XiaohongmenWWTP, located in southern Beijing), where the excess sewage

    Table 1Characterization of raw materials.

    FW FVW DSS Mixture (2:1:1)

    Water content/% 83.4 93.8 84.5 88.7Total solid/g L1 166.3 26.7 62.2 16.0 154.9 18.1 142.1 9.3Volatile solid/g L1 149.0 24.3 50.8 11.2 101.9 10.8 117.3 7.8Suspended solid/g L1 72.8 14.3 35.7 14.2 151.7 21.4 91.7 15.0Volatile suspended

    solid/g L168.8 12.0 29.6 11.2 98.5 12.8 74.0 12.2

    VS/TS/% 89.6 81.6 65.8 82.5VSS/VS/% 46.2 58.3 96.6 63.1Lipids/%TS 21.8 2.9 10.3 16.5Protein/%TS 16.8 13.2 34.3 20.8Crude ber/%TS 5.6 15.3 7.1 6.4C/% 48.2 42.0 37.2 45.4H/% 7.3 6.1 5.5 6.6N/% 2.8 2.4 5.9 3.5C/N 17.4 17.4 6.3 12.9

    rgy 44 (2012) 463e468acids (VFAs) using gas chromatography (SHIMADZU GC-2010) with

  • study. Decomposable degradable organic carbon (DDOC) can be

    digestion, according to the mature technologies and productmarkets. From the experimental results, the methane production ofthe digested MBW was 46.6 m3 t1. For BNG recovery, a pressureswing adsorption system was considered. The power consumptionfor the purication of biogas is a signicant GHG source. Thecapacity of an AD facility is set at 500 t d1 as a case study; thus, themethane production is 21,000 m3 d1 (875 m3 h1); this amountwas used to evaluate the power consumption. The default GHGemission factors for power generation are based on a governmentreport concerning low-carbon technologies with fossil fuel, whichwas released by the Department of Climate Change, NationalReform and Development Commission (NDRC) of China in 2009[19]. The GHG emission associated with power consumption forlandll and AD operations varies with the technological and oper-ational conditions, and has a large uncertainty, so the ideal condi-tion of no GHG emission of power consumption was sat in thisstudy. Hence, the boundary of this evaluation included the direct

    methane yield showed that the OLR increasing procedure did not

    Energy 44 (2012) 463e468 465calculated from the results of anaerobic digestion as 0.0376 for themixed feedstock. Hence, the averagemethane production in landllfor the raw materials was calculated as 19.3 m3 t1 according tofollowing equation.

    DDOCm DDOC DOCfCm 22:412

    0:0376 0:5 0:55 22:412 103 19:3 m

    3 t1

    where DDOCm is the methane production of DDOC, m3 t1; Cm,methane concentration of biogas, using the default value of 55%.

    Power generation and BNG recovery are considered as availablea ame ionization detector and GDX-102 column (inlet, 200 C;oven, 170 C; and detector, 220 C). The various VFAs includedacetic, propionic, iso-butyric, butyric, iso-valeric, and valeric acids.The biogas volume was measured with a wet-test gas ow meter,and the composition of the biogas was monitored by gas chroma-tography (SHIMADZU GC-2010) with a thermal conductivitydetector and RT-Qplot column (column, 30 m 0.53 mm; ameionization detector, 200 C; oven, 50 C; inlet, 200 C; carrier gas,hydrogen 10 mlmin1; split ratio, 35:1, and injection volume,100 ml). The C, H, and N were analyzed by an elemental analyzer(EAI CE-440).

    2.4. Calculation of the GHG reduction

    The GHG emission of MBW treatment was evaluated using theanalytical method of carbon footprint following the Guideline toPAS 2050 [15]. In this study, the carbon footprint of three scenarioswas assessed which were baseline scenario (scenario 1), AD withpower generation (scenario 2), and AD with bio natural gas (BNG)recovery (scenario 3).

    In China more than 70% of treated MSW was disposed bylandll, therefore, the baseline scenario was set as MBW landll.The collection rate of landll gas (LFG) is generally less than 60% inthe developed countries, whereas to achieve a 20% gas recovery inChina appears to be difcult [16]. In this study, an average LFGcollection rate of 50% was set as the ideal condition resulting fromthe strict standards and laws concerning with the national energysaving and emission reduction strategy. Analyses of currentlyoperating LFG-to-electricity...


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