Biogas Production from Two-stage Anaerobic Digestion of Jatropha curcas Seed Cake

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  • This article was downloaded by: [Erciyes University]On: 21 December 2014, At: 03:50Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

    Energy Sources, Part A: Recovery,Utilization, and Environmental EffectsPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/ueso20

    Biogas Production from Two-stageAnaerobic Digestion of Jatropha curcasSeed CakeN. Sinbuathong a b , P. Sirirote c , B. Sillapacharoenkul d , J.Munakata-Marr e & S. Chulalaksananukul fa Scientific Equipment and Research Division , Kasetsart UniversityResearch and Development Institute (KURDI), Kasetsart University ,Bangkok , Thailandb KU-Biodiesel Project, Center of Excellence for Jatropha, KasetsartUniversity , Bangkok , Thailandc Department of Microbiology, Faculty of Science , KasetsartUniversity , Bangkok , Thailandd Department of Agro-Industrial Technology, Faculty of AppliedScience , King Mongkut's University of Technology North Bangkok ,Bangkok , Thailande Civil and Environmental Engineering, Colorado School of Mines ,Golden , Colorado , USAf Department of Chemical Engineering, Faculty of Engineering ,Mahidol University, Salaya Campus , Nakornpathom , ThailandPublished online: 24 Sep 2012.

    To cite this article: N. Sinbuathong , P. Sirirote , B. Sillapacharoenkul , J. Munakata-Marr & S.Chulalaksananukul (2012) Biogas Production from Two-stage Anaerobic Digestion of Jatrophacurcas Seed Cake, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 34:22,2048-2056, DOI: 10.1080/15567036.2012.664947

    To link to this article: http://dx.doi.org/10.1080/15567036.2012.664947

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    http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditions

  • Energy Sources, Part A, 34:20482056, 2012

    Copyright Taylor & Francis Group, LLC

    ISSN: 1556-7036 print/1556-7230 online

    DOI: 10.1080/15567036.2012.664947

    Biogas Production from Two-stage Anaerobic

    Digestion of Jatropha curcas Seed Cake

    N. SINBUATHONG,1;2 P. SIRIROTE,3

    B. SILLAPACHAROENKUL,4 J. MUNAKATA-MARR,5 and

    S. CHULALAKSANANUKUL6

    1Scientific Equipment and Research Division, Kasetsart University Research

    and Development Institute (KURDI), Kasetsart University, Bangkok, Thailand2KU-Biodiesel Project, Center of Excellence for Jatropha, Kasetsart University,

    Bangkok, Thailand3Department of Microbiology, Faculty of Science, Kasetsart University,

    Bangkok, Thailand4Department of Agro-Industrial Technology, Faculty of Applied Science, King

    Mongkuts University of Technology North Bangkok, Bangkok, Thailand5Civil and Environmental Engineering, Colorado School of Mines, Golden,

    Colorado, USA6Department of Chemical Engineering, Faculty of Engineering, Mahidol

    University, Salaya Campus, Nakornpathom, Thailand

    Abstract Digestion of Jatropha curcas seed cake was investigated in two-stage (aci-dogenic and methanogenic) anaerobic bioreactors without pH adjustment. Acidogenic

    reactors were fed once daily with a slurry of 1:10 Jatropha curcas seed cake:watercontaining approximately 100 g of chemical oxygen demand/l. Organic loading rates

    were 2.5, 3.3, 5, 10, and 20 kg chemical oxygen demand/m3.day, which correspondedto hydraulic retention times of 40, 30, 20, 10, and 5 days, respectively, for each

    reactor stage. The maximum methane yield (340 l at STP/kg of chemical oxygendemand degraded) was observed at an organic loading rate of 3.3 kg chemical oxygen

    demand/m3.day (hydraulic retention times D 30 days for each stage). At this organic

    loading rate and hydraulic retention time, the chemical oxygen demand degradationefficiency was 65%. The average pH in the acidogenic and methanogenic reactors was

    4.9 and 7.4, respectively. This study demonstrates high methane yield and degradationextent of Jatropha curcas seed cake in a two-stage anaerobic process without chemicaladdition for pH adjustment.

    Keywords agricultural waste, anaerobic digestion, bioenergy, biogas, Jatropha cur-cas, methane, two-stage operation

    Introduction

    Every year in the world several million tons of agricultural wastes are disposed of through

    methods, such as incineration, land application, and land filling. This global waste has a

    high potential as a biorenewable energy resource and can be turned into high-value by-

    Address correspondence to Dr. Nusara Sinbuathong, Scientific Equipment and ResearchDivision, Kasetsart University Research and Development Institute, Kasetsart University, Bangkok10900, Thailand. E-mail: rdinrs@ku.ac.th

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  • Anaerobic Digestion of Jatropha curcas Seed Cake 2049

    products (Isci and Demirer, 2007). Jatropha curcas is a drought-resistant shrub belonging

    to the family Euphorbiaceae, which is cultivated on a large scale in Central and South

    America, Southeast Asia, India, and Africa (Schmook and Seralta, 1997). Jatropha curcas

    seed cake is one of the agricultural wastes considered as a possible energy source. The

    seed cake is a by-product of oil extraction from the seeds; the oil can be used as a

    substitute for diesel after transesterification (Singh et al., 2008). With the known high

    potential of Jatropha curcas for energy production, researchers have generally focused on

    the production of biodiesel (Achtena et al., 2008). A few studies have investigated biogas

    production from Jatropha curcas seed cake. Most of these studies were conducted using

    batch operation and single stage semi-continuous operation. In general, they conclude

    that Jatropha curcas seed cake is a good biogas source, due to the high conversion rates

    and efficiencies obtained (Staubmann et al., 1997; Singh et al., 2008; Sinbuathong et al.,

    2010, 2011).

    The solids concentration of Jatropha curcas seed cake is crucial to ensure sufficient

    gas production. However, high solids content may cause a system failure due to the acidic

    pH of the seed cake slurry (Gunaseelan, 2009; Sinbuathong et al., 2010, 2011). In the

    previous studies, the initial pH of the Jatropha curcas slurry needed to be adjusted to

    neutral during the start-up period in order to prevent system failure (Sinbuathong et al.,

    2010, 2011). For batch operation, the appropriate Jatropha curcas seed cake-to-water ratio

    for methane (CH4) production was found to be in the range of 1:20 to 1:10 (Sinbuathong

    et al., 2011). For a single-stage semi-continuous operation, the organic loading rates

    (OLRs) were found to be optimal between 1.25 and 1.67 kg chemical oxygen demand

    (COD)/m3.d (Sinbuathong et al., 2010). In the present study, higher OLRs were applied

    to the two-stage system under the assumption that phase separation may be appropriate

    for the digestion of the acidic slurry of Jatropha curcas seed cake, because acidogenic

    bacteria favor an acidic aqueous environment in the first phase as described below.

    The anaerobic biodegradation is carried out by three groups of bacteria: (1) hydrolytic

    and fermentative bacteria, which hydrolyze the long chain molecules and ferment the

    resulting monosaccharides to organic acids; (2) acetogenic bacteria, which convert these

    acids to acetate, hydrogen (H2), and carbon dioxide (CO2); and (3) methanogenic bacteria,

    which convert the end products of acetogenic reactions to methane (CH4) and carbon

    dioxide (CO2). Several studies have proposed the physical separation of these phases

    in order to increase the degradation of organic matter, improve biogas production, and

    attain better control of operating conditions (Derimelk and Yenigun, 2002; Kasapgil and

    Ince, 2000; OKeefe and Chynoweth, 2000; Yu et al., 2002). The metabolic pathways

    of the two-stage anaerobic digestion process are the same as those of conventional

    digestion; however, they are physically separated in (1) an acidogenic stage (hydrolytic

    and acetogenic stage) and (2) a methanogenic stage. The two-stage anaerobic treatment

    process has several advantages over conventional processes. First, it permits the selection

    and enrichment of different bacteria in each digester; in the first phase, acidogenic bacteria

    degrade complex pollutants into volatile fatty acids (VFAs), which are subsequently

    converted to CH4 and CO2 by acetogenic and methanogenic bacteria in the second phase.

    Second, it increases the stability of the process by controlling the acidification phase in

    order to prevent overloading and the build-up of toxic material. Third, the first stage

    may act as a metabolic buffer, preventing pH shock to the methanogenic population;

    in addition, low pH and a high OLR are all factors that favor the establishment of the

    acidogenic phase.

    This research experimentation was carried out in a semi-continuous, laboratory-

    scale, two-reactor system operated at five different OLRs. The research objectives were

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  • 2050 N. Sinbuathong et al.

    to observe the CH4 yield and the organic degradation efficiency from two-stage anaerobic

    reactors and identify a method of operation that did not require addition of any chemicals

    for pH adjustment.

    Materials and Methods

    Seed Cake Characterization

    The most important parameters affecting CH4 production are the composition of feed-

    stock. The analyses of the seed cake include moisture content, total solids (TS), total

    volatile solids (TVS), organic carbon, organic matter, nitrogen, and phosphorous. The

    moisture content of the samples was determined by oven-drying to a constant weight

    at 105C. Total solid content was calculated as 100% % moisture content. TVS was

    obtained by igniting the TS in a muffle furnace at 550C. Organic carbon in the sample

    was measured using the Walkley-Black method (Buurman et al., 1996; Walkley, 1947).

    Organic carbon was oxidized with a mixture of potassium dichromate and sulfuric acid;

    the excess potassium dichromate was titrated with ferrous sulfate. The organic matter

    content of soil was indirectly estimated through multiplication of the organic carbon

    content by 1.72 (Soil Science Society of America and American Society of Agronomy,

    1996). Nitrogen was determined by the Kjeldahl method by digesting samples to convert

    organic-N to NHC4-N and determining NHC

    4-N in the digest (Walkley, 1947). Total

    phosphorous was determined by digesting samples with sulfuric acid and analyzed by an

    ascorbic acid method (Rayment and Higginson, 1992).

    Inoculum, Feed Solution, and Test Bioreactors

    Fresh cow dung was collected and brought back to the laboratory in bags. For experi-

    ments, sufficient water was added to cow dung at a ratio of 1:1 by weight to produce a

    slurry. Then biomass (as mixed liquor volatile suspended solids; MLVSS) was measured

    in order to start each test bioreactor with the same cell mass. Jatropha curcas seed cake

    was collected from Prathumthani Province, Thailand. The seed cake was stored in a

    plastic bag at room temperature and was blended prior to use.

    Five sets of reactors were constructed with plastic bottles. Each set consisted of two

    reactors, an acidogenic and a methanogenic reactor with a working volume of five liters

    each (Figure 1). The acidogenic reactor was equipped with two outlet ports, one port for

    gas venting and the other port for digested slurry, both of which fed to the methanogenic

    reactor. The methanogenic reactor was connected to a gas collection system, which was

    based on water displacement by the exiting gases. Sulfuric acid of 0.05 molar was used

    to measure the displacement by gas in the gas collection system.

    Jatropha curcas seed cake was prepared as a slurry with tap water at a ratio of

    1:10 by weight. The initial COD and TVS content of this slurry were 100 and 110 g/l,

    respectively. The initial pH of the seed cake slurry was 5.5 and the pH was not adjusted

    during the entire period of the experiment. The conditions were 13.8 g/l MLVSS, initial

    pH 5.5, and temperature 30 1C.

    Two-Stage Operation

    Each bioreactor was filled with a liter of mixture of the culture that contained 13.8 g

    MLVSS/l. Initially, the Jatropha curcas seed cake slurry was added to the acidogenic

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  • Anaerobic Digestion of Jatropha curcas Seed Cake 2051

    Figure 1. Two-stage experiment set up; reactors I and II were acidogenic and methanogenic

    reactors, respectively. (color figure available online)

    reactor at a rate of 2 liters/day for 2 days. This acidogenic reactor was operated for 2

    days in a batch mode before feeding with the Jatropha curcas seed cake slurry semi-

    continuously in an upflow mode by feeding once per day at a feed rate of 1,000, 500,

    250, 167, and 125 ml/day in each set of reactors, giving rise to OLRs of 20, 10, 5,

    3.3, and 2.5 kg COD/m3.day and the corresponding increasing hydraulic retention times

    (HRTs) of 5, 10, 20, 30, and 40 days in both acidogenic and methanogenic reactors. The

    ambient temperature of all reactors was 30 1C and the reactors functioned without

    pH control. When the system reached steady state, the total gas production was recorded

    (at room temperature) daily and the CH4 content was determined by a Shimadzu GC-

    14B gas chromatograph equipped with a thermal conductivity detector. The CH4 volumes

    were then adjusted to standard temperature and pressure (STP). The operating period was

    approximately 100 days. The digested slurry from the methanogenic reactor was analyzed

    for COD, TVS, and pH according to t...