Transcript
Page 1: Production of methane from anaerobic digestion of jatropha and pongamia oil cakes

Applied Energy 93 (2012) 148–159

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Applied Energy

journal homepage: www.elsevier .com/ locate/apenergy

Production of methane from anaerobic digestion of jatropha and pongamia oil cakes

R. Chandra a,⇑, V.K. Vijay b, P.M.V. Subbarao c, T.K. Khura a

a Department of Farm Power and Machinery, College of Agricultural Engineering and Post Harvest Technology (Central Agricultural University), Ranipool, Gangtok,Sikkim 737 135, Indiab Centre for Rural Development and Technology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, Indiac Department of Mechanical Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, India

a r t i c l e i n f o

Article history:Received 14 November 2009Received in revised form 30 July 2010Accepted 12 October 2010Available online 7 January 2011

Keywords:JatrophaPongamiaOil seed cakeAnaerobic digestionBiogasMethane

0306-2619/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.apenergy.2010.10.049

⇑ Corresponding author. Tel./fax: +91 3592 251390E-mail address: [email protected] (R. C

a b s t r a c t

The experimental study was carried out on anaerobic digestion of jatropha (Jatropha curcas) and pong-amia (Pongamia pinnata) oil seed cakes in a 20 m3/d capacity floating drum biogas plant under mesophilictemperature condition. The average specific methane production potential of jatropha oil seed cake wasobserved as 0.394 m3/kg TS and 0.422 m3/kg VS. The average content of methane and carbon dioxide inthe produced biogas over 30 days of retention time period was found as 66.6% and 31.3%, respectively.Cumulative methane yield over 30 days of retention time period was found as 131.258 m3 with a259.2 kg of input volatile solids, with an average total volatile solids mass removal efficiency of 59.6%.However, in case of pongamia oil seed cake average specific methane production was observed as0.427 m3/kg TS and 0.448 m3/kg VS. The average value of methane and carbon dioxide content in the pro-duced biogas over 30 days of retention was found as 62.5% and 33.5%, respectively. Cumulative methaneyield over 30 days of retention time period was found as 147.605 m3 with a 255.9 kg of input volatile sol-ids, with an average total volatile solids mass removal efficiency of 74.9%.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

One of the major thrust towards sustainable socio-economicdevelopment of the world in 21st century is cultivation of energyresources and technologies as the depletion of petroleum fuel isat alarming level. The associated energy experts over the worldare searching for supplementing the fossil fuel energy resourceswith cultivated bio-fuel energy resources. Development of sustain-able and commercially viable technologies for production of alco-hols, biogas, producer gas and bio-diesel are good examples onthis scenario. The commercial viability of any bio-resource energytechnology strongly depends on level of utilization of the culti-vated resources and the amount of energy consumption for pro-duction of useful fuel.

Bio-diesel has high potential as a new and renewable energysource in forthcoming future as a substitution fuel for petroleumderived diesel. Presently, more than 95% of bio-diesel of the worldis produced from edible oil, which is available at large scale fromthe agricultural industry. However, continuous and large-scaleproduction of bio-diesel from edible oil without proper planningmay cause negative impact such as depletion of food supply leadto economic imbalance. A possible solution to overcome this prob-lem is to use non-edible oil for production of bio-diesel [1].

ll rights reserved.

.handra).

India is endowed with more than 100 species of tree born non-edible oil seeds occurring in wild or cultivated sporadically to yieldoil in considerable quantities [2]. The country has a huge potentialof tree born non-edible oil seeds. Therefore, the attempts are beingmade for utilization of non-edible and under-exploited oils for bio-diesel production. A National Mission on bio-diesel in India hasbeen launched in the year 2003 under demonstration phase withthe objective to produce enough bio-diesel to meet 20% blendingof total diesel requirement using various non-edible oils by theyear 2011–2012 [3]. In this context, cultivation of jatropha andpongamia (non-edible oil seed bearing plants) on 40 million hect-are waste land has been started to meet the oil seed requirement.

However, there are critical issues, which need to be addressedto make the production of bio-diesel as a techno-economically via-ble and ecologically acceptable renewable substitute or additive todiesel. Present method of utilization of only extracted vegetable oilfrom the bio-diesel resource results in generation of huge unuti-lized biomass. In general, 50% (dry weight basis) of the collectedfruits of bio-diesel resource are seeds (kernels). Out of these seeds,at the most 35% is converted into vegetable oil and remaining 65%material is rejected as toxic oil seed cake. In short, more than 85%of cultivated bio-resource (seed’s pericoat and oil seed cake) isremaining unutilized in bio-diesel production. This toxic oil seedcake can neither be used as cattle feed nor as a bio-fertilizer forgrowing plants, due to presence of phorbol ester (a toxic com-pound). The current annual production of toxic jatropha oil seedcake alone has been estimated to be about 60,000 tonnes [4]. The

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Nomenclature

C carbonC/N carbon–nitrogen ratioCD cattle dungd daydb dry basisDR dilution ratiog gramh hourH hydrogenJC jatropha oil seed cakekg kilo gram

l litrem3 cubic metreN nitrogenOLR organic loading ratePC pongamia oil seed cakeSTP standard temperature and pressureTS total solidsTVSMRE total volatile solids mass removal efficiencyVS volatile solids

R. Chandra et al. / Applied Energy 93 (2012) 148–159 149

estimated amount of jatropha oil seed cake could be a significantsource of bio-energy production if it is utilized in a planned man-ner. Further, waste-to-energy provides a solution to waste man-agement and energy generation. An integrated anaerobic wastevalorization process is an interesting option for energy generationfrom non-edible oil seed cakes [5].

Anaerobic digestion is considered to be a sustainable bio-con-version technology as it produces biogas a renewable gaseous fueland it also stabilizes and reduces the volume of waste. As a part ofan integrated waste management system anaerobic digestion re-duces the emission of green house gases into the atmosphere.The degradation process or digestion of solids in an anaerobic di-gester takes place in three stages. The first stage is the hydrolysisof particulate and colloidal wastes to solublise the waste in theform of organic acids and alcohols. The second stage is the conver-sion of the organic acids and alcohols to acetate, carbon dioxide,and hydrogen. The third stage is the production of gases mostlymethane and new bacterial cells or sludge from acetate and hydro-gen. In an anaerobic digester a great diversity of bacteria are re-quired to perform phases of hydrolysis, acidogenesis andmethanogenesis of the input substrate feed that contains diversi-fied wastes in term of carbohydrates, fats and proteins [6].

The yield and constituents of biogas are greatly affected by car-bohydrates, fats and proteins contents of the feed material. Anaer-obic digestion of carbohydrates, fats and protein yields 886 l ofbiogas (with methane content of around 50%), 1535 l of biogas(with methane content of around 70%) and 587 l of biogas (withmethane content of around 84%) per kg of VS destroyed, respec-tively [7]. The oil seed cakes of jatropha and pongamia are rich infat and protein and therefore, are considered to be good feed mate-rial for biomethanation.

The governing factors of anaerobic digestion process such as pH,retention time (RT), total solids (TS), volatile solids (VS) and organ-ic loading rates (OLR) influence the sensitivity of bacteria, the re-sponse to toxicity and acclimatization characteristics [8].Methanogens are sensitive to both high and low pH and performwell within pH of 6.5–8.0 [9]. Long retention time increases the po-tential for acclimatization and also minimizes the severity of re-sponse to toxicity. The heavy metals at higher concentrationhave toxic effect on bacterial activity. Further, at higher OLRnon-toxic organic or inorganic substances become inhibitory tobacterial growth. The threshold toxic levels of inorganic substancesdepend on the conditions that whether these substances act aloneor in combination. Certain combinations have a synergistic effect,whereas other display an antagonistic effect [10,11]. The carbon/nitrogen (C/N) ratio of the feedstock has been found to be a usefulparameter in providing optimal nitrogen level for bacterial growth.The optimal C/N ratio is 30 [12]. The actual available C/N ratio is afunction of feedstock characteristics and digestion operational

parameters and may vary from less than 10 to above 90. Since allof the carbon and nitrogen present in the feedstock are not avail-able for digestion. Furthermore, it has been reported that at 37 �Ctemperature the amount of biogas production is reaches at maxi-mum from each category of waste material under anaerobic diges-tion process [13].

Most of the experimental studies have been performed to findout the biogas generation potential of various feedstock mixtureand its individual components of various categories of waste mate-rials like animal dung, kitchen wastes, waste flowers, etc. In theanaerobic digestion, the pre-treated substrate produce higheramount of biogas as well as considerably reduce the total and vol-atile solids content in the digester. Furthermore, the chemical anal-ysis of substrates indicates an improvement in nitrogen contentafter anaerobic digestion [14]. The potential biogas productionfrom municipal garbage under batch anaerobic digestion at roomtemperature conditions (26 ± 4 �C) for 240 days of retention timewas reported 0.661 m3 kg–1 of volatile solids. Total biogas yieldfrom municipal garbage per kg dry matter was observed 0.50 m3

with an average methane content of the biogas of 70% by volume[15].

Anaerobic digestion of olive oil mill wastewater (OMW) mixedwith diluted poultry manure (DPM) in pilot plant reactor of 100 l,containing 40% volatile solids produces biogas at a rate of 1.53 l/d per unit volume of reactor with a methane content of 65% by vol-ume. Co-digestion of wastewater together with local agriculturalresidues is a sustainable and environmentally attractive methodto treat wastes and convert to useful resources. The biogas pro-duced can be used for the generation of heat or electricity; apartfrom this energy co-digestion results in liquid and solid effluentsthat are also valuable as they retain all their nutrient constituents(nitrogen, phosphorus, trace elements, etc.). Thus, it can be used asbio-fertilizers and soil organic matter improvers [16].

The review of the literature showed that no study has been re-ported on anaerobic digestion of jatropha and pongamia oil seedcakes. Although, the production of these two oil seed cakes is ex-pected to be very high in India. These feed materials could be a po-tential source of biogas production which would be used tosupplement the petroleum demand in substantial amount.

2. Analysis of feed materials and experimental details ofanaerobic digestion process

2.1. Proximate and ultimate analysis of feed material

The proximate and ultimate analysis of jatropha and pongamiaoil seed cakes were carried out as per standard procedure de-scribed below.

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150 R. Chandra et al. / Applied Energy 93 (2012) 148–159

2.1.1. Proximate analysis2.1.1.1. Moisture content. The moisture content of the feed materialwas determined as follows: the initial weight of the samples of50 g biomass with pre-weighed moisture boxes were taken byusing an electronic balance with least count of 0.001 g. The sam-ples were first heated at 60 �C for 24 h and then at 103 �C for 3 husing a hot air oven. The final weight or dried samples weight withpre-weighed moisture boxes were recorded. The percentage mois-ture content of the sample was then calculated by using:

MC ¼ Ww �Wd

Ww

� �� 100 ð1Þ

where MC is the moisture content, % (wet basis); Ww is the weightof wet sample, g; and Wd is the weight of oven dried sample, g.

2.1.1.2. Oil content. The oil content of the mechanically expelled oilseed cakes of jatropha and pongamia were determined by Soxhletextraction method. The samples of 200 g of jatropha and pongamiaoil seed cakes were crushed using mechanical blender. The crushedsamples of oil seed cake were packed in a thimble and the oil wasextracted with the solvent n-hexane. The solvent n-hexane was fi-nally removed by rotary evaporator (Laborta 4000-HeidolphInstruments, Germany) to recover the oil.

2.1.1.3. Total solids content. The total solids content of feed materi-als were determined as per the standard method [17]. The initialweight of the samples of 50 g biomass with pre-weighed porcelainboxes were taken by using an electronic balance with least count of0.001 g. The samples were first heated at 60 �C for 24 h and then at103 �C for 3 h using a hot air oven. The final weight or dried sam-ples weight with pre-weighed porcelain boxes were recorded. Thepercentage total solids content of the sample was then calculatedby using:

TS ¼ Wd

Ww

� �� 100 ð2Þ

where TS is the total solids, %; Wd is the weight of oven dried sam-ple, g; and Ww is the weight of wet sample, g.

2.1.1.4. Volatile solids content and non-volatile solids content. Thevolatile solids content and non-volatile solids content of feedmaterials were determined as per the standard method [17]. Theoven dried samples used for determination total solids contentwere further dried at 550 �C ± 50 �C temperature for 1 h in a mufflefurnace and allowed to ignite completely. The dishes were thentransferred to a desiccator for final cooling. The weight of thecooled porcelain dishes with ash were taken by the electronic bal-ance. The volatile solids content and non-volatile solids content ofthe sample were calculated using:

VS ¼ ðWd �WaÞWd

� �� 100 ð3Þ

NVS ¼ Wa

Wd

� �� 100 ð4Þ

where VS is the volatile solids in dry sample, %; NVS is the non-vol-atile solids in dry sample, %; Wd is the weight of oven dried sample,g; Wa is the weight of dry ash left after igniting the sample in a muf-fle furnace, g.

2.1.2. Ultimate analysisCarbon, hydrogen and nitrogen contents in feed materials (cat-

tle dung, jatropha oil seed cake and pongamia oil seed cake) weredetermined using fully automatic instrument ‘Vario EL’ elementalanalyzer (Perkin Elmer, USA Made) which enables speedy andaccurate quantitative analysis of CHN in the sample. The instru-

ment works on the principle of thermal conductivity detector(TCD).

2.2. Start up of anaerobic digester

The major challenge in anaerobic digestion of jatropha andpongamia oil seed cakes is lack of inherent bacteria like in cattledung. Apart from the existing bacteria in a digester, fresh cattledung continuously adds more bacteria to the digestion systemand stabilizes the anaerobic digestion process. However, lack ofthe inherent bacteria, demands a special attention for operationof digester with non-edible oil seed cakes. Another major draw-back of oil seed cake is the presence of long chain free fatty acids,which can destroy the population of bacteria in the digester. More-over, an appropriate amount of cattle dung with oil seed cake maystabilize the bacterial population.

The time between initial digester feed sludge and stable opera-tion of digester should be as short as possible for smooth start-upof the anaerobic digestion process. The steady-state condition forefficient operation of the digester is normally achieved approxi-mately in one month. This condition is reflected by the productionof burnable biogas and a stable volatile acid-to-alkalinity ratio [6].The start-up is generally considered the most critical step in theoperation of anaerobic digesters. Once an anaerobic digester hasbeen started up successfully, it is expected to run without muchattention as long as operating conditions are not significantly al-tered. The source of micro-organisms, the size of the inoculumand the initial mode of operation are important factors duringstart-up. Usually, the inoculum volume is at least 10% of the newdigester volume and consists of an undefined mixed culture froman equivalent system that is actively digesting a similar feedstock[18].

2.3. Preparation of efficient inoculum

In the present study, a running 20 m3/d capacity floating drumtype biogas plant with cattle dung substrate was selected as anenvironment. The feeding of cattle dung was stopped for threemonths to make sure that there is no unprocessed cattle dungpresent in the digester (no volatile matter) prior to feeding ofnon-edible oil seed cakes. Thereafter, feeding of pongamia oil seedcake with a dilution ratio of 3:1 (water:oil seed cake on weight ba-sis) was carried as per following schedule.

Schedule 1. 8 kg of oil seed cake substrate (2 kg pongamia oil seedcake with 6 kg water) with a dilution ratio of 3:1 for 5 days.

The position of gas holder drum was remain unchanged for first2 days of the experiment. However, addition of oil seed cake sub-strate was continued. On third day of the experiment a small rise(approximately 10 cm) of gas holder drum was recorded which isequivalent to 0.90 m3 volume of biogas. The same feeding patternwas continued for two more days and a rapid rise in gas holderdrum was observed. This showed encouraging results in biogasproduction from pongamia oil seed cake.

Schedule 2. 20 kg of oil seed cake substrate (5 kg pongamia oilseed cake with 15 kg water) with a dilution ratio of 3:1 for next10 days:

For the first 2 days of increased loading, a drop in gas produc-tion was observed as compared to fifth day of the experiment.The feeding was continued for few more days and positive resultswere observed on third day with rapid upward movement of gasholder drum. The gas holder drum reached at its highest position(30 cm) on fifth day and remained almost at the same level up totenth day during the experiment.

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R. Chandra et al. / Applied Energy 93 (2012) 148–159 151

This pattern of biogas production from pongamia oil seed cakeshowed the adaptation of bacteria to the changed environment of-fered by the new substrate possibly by developing a suitable strain.This acclimatization is due to the fact that, when the concentra-tions of inhibitory or toxic materials are slowly increased withinthe environment many micro-organisms rearrange their metabolicresources, and overcoming the metabolic block produced by theinhibitory or toxic materials. However, sufficient time must beavailable to the bacteria for the rearrangement of metabolic re-sources under sudden change in environment [19].

The slurry of the biogas plant fed with pongamia oil seed cakewas used as inoculum for anaerobic digestion of jatropha andpongamia oil seed cakes substrates. The new micro-organismspresent in the inoculum could act comfortably with jatropha andpongamia oil seed cake substrates. The above study lead to a setof important developments namely, an effective inoculum as a poolof new micro-organisms, an optimal size of the inoculum and amode of operation of the anaerobic digester [18].

2.4. Experimental biogas plant and parameters of anaerobic digestionprocess

Anaerobic digestion of jatropha and pongamia oil seed cakesubstrates were carried out in a floating drum biogas plant of20 m3/d capacity by continuous (daily) feeding of substrates for30 days. Fig. 1a and b shows the schematic and pictorial view ofexperimental biogas plant. Table 1 shows daily feeding levelof jatropha and pongamia oil seed cake substrates. Measurementof ambient temperature and substrate temperature (�C) was car-ried by using K-type thermocouple. Substrate temperature wasmeasured by inserting a thermocouple into the digester of the bio-gas plant at a depth of 1.0 m. The daily biogas production (m3) atstandard temperature and pressure (STP) was measured. Themethane and carbon dioxide content in the produced biogas wasmeasured by using a Biogas Analyzer (Model No. MG-609u) madeby Chemtron Science Limited, Mumbai, India. This biogas analyzerwas specially built for compositional analysis of biogas constitu-ents (CH4 and CO2). The infrared sensors for methane and carbondioxide have measurement range of 0–100%. The cumulative bio-gas, methane and carbon dioxide production over the study period

F

A

B1C

DD

30 30

15 T

hick

Par

tion

Wal

l

Cen

tral

Gui

de F

ram

e

Flan

ge P

late

s

30

15

7.5235.7 32All dimensions in centimetres

10 D

iam

ter

ASB

/CE

M P

ipe

10 D

iam

ter

ASB

/CE

M P

ipe

CC

Fou

ndat

ion

(1:3

:6)

Ear

th F

illin

g

Ground Level

Gas Holder Supporting Structure(a)

Fig. 1. (a and b) A view of biogas plant (20 m3/d) f

was calculated by adding daily biogas, methane and carbon dioxideproduction, respectively. Specific biogas production (m3/kg TS &m3/kg VS), specific methane production (m3/kg TS & m3/kg VS)and total volatile solids removal efficiency (%) were determinedby using standard formulae.

2.4.1. Theoretical calculationObserved daily biogas production was corrected at standard

temperature and pressure (STP) condition using Eq. (5). STP refersto 0 �C (273 K) temperature and one atmospheric pressure.

BVo ¼ 273� BV273þ T

� �ð5Þ

where BVo is the volume of daily produced biogas at STP (at 0 �C), lor m3; BV is the volume of daily produced biogas at temperature T, lor m3; T is the observed biogas temperature, �C.

The daily production of methane and carbon dioxide in pro-duced biogas were determined by:

CH4Yield ¼CH4 Conc:

100� BVo ð6Þ

where CH4Yield is the daily methane yield at STP, l or m3 CH4 Conc. isthe methane concentration in biogas, %

CO2Yield ¼CO2 Conc:

100� BVo ð7Þ

where CO2Yield is the carbon dioxide yield at STP, l or m3; CO2 Conc.is the carbon dioxide concentration in biogas, %.

The specific biogas production (per unit TS and VS) were calcu-lated using:

BVoSpecificTS ¼BVo

DMF� TS

� �ð8Þ

BVoSpecificVS ¼BVo

DMF� VS

� �ð9Þ

where BVoSpecificTS is the specific biogas production, m3/kg TS;BVoSpecificVS is specific biogas production, m3/kg VS; DMF is the dailymass of feed, kg; TS is the total solids content, decimal; VS is thevolatile solids content, decimal.

B

(b)

ed with jatropha and pongamia oil seed cakes.

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Table 1Total solids and volatile solids concentration in the substrates.

Treatment Substrate concentration of the daily feed material

Total solids Volatile solids

kg/d % kg/d %

Jatropha oil seed cake substrate 9.25 18.5 8.64 17.3Pongamia oil seed cake substrate 8.95 19.9 8.53 19.0

Table 3Carbon, hydrogen, nitrogen contents and carbon–nitrogen ratio of the feed materials.

Sl. no. Feed material C (%) H (%) N (%) C/N ratio

s1 Cattle dung 35.20 4.60 1.55 22.72 Jatropha oil seed cake 48.80 6.20 3.85 12.73 Pongamia oil seed cake 47.80 6.50 5.50 8.7

152 R. Chandra et al. / Applied Energy 93 (2012) 148–159

The specific methane production (per unit TS and VS) wasdetermined using:

MVoSpecificTS ¼CH4Yield

DMF� TS

� �ð10Þ

MVoSpecificVS ¼CH4Yield

DMF� VS

� �ð11Þ

where MVoSpecificTS is the specific methane production, m3/kg TS;MVoSpecificVS is the specific methane production, m3/kg VS.

The loss of volatile solids during anaerobic digestion process oc-curs due to conversion of the volatile solids primarily into biogas.Thus, the total volatile solids mass removal efficiency was esti-mated based on biogas production rate. In this estimation method,it was assumed that the organic mass converted into biogas isequal to the mass of dry biogas produced. The methane and carbondioxide content in the biogas was determined for every operatingday during the entire period of operation. An assumption wasmade that biogas behaves as an ideal gas.

The total volatile solids mass removed was then assumed to beequal to mass of methane and carbon dioxide produced as given in:

TVS mass removed ¼Mass of CH4 þMass of CO2 ð12Þ

The requirement of above approach is that the biogas volumeand its contents should be accurately measured. The molecularweight of methane and carbon dioxide as well as dry biogas volumewere then correlated to obtain total volatile solids mass removed.The following relationship (Eq. (13)) was used to obtain the totalvolatile solids mass removed in the anaerobic digestion process:

TVSMR ¼½ð16�CH4 Conc:Þ�

100 þ ½ð44�CO2 Conc:Þ�100

22:413� BVo� DBF ð13Þ

where TVSMR is the total volatile solids mass removed, kg; BVo isthe daily biogas volume at STP (at 0 �C), m3; DBF is the dry biogasfactor.

The constants 16 and 44 represent the molecular weight ofmethane and carbon dioxide, respectively. The volume of one moleof ideal gas at STP was taken as 22.413 l in the above equation.Thetotal volatile solids mass removal efficiency of the anaerobic diges-tion process is expressed as the % removal of initial total volatilesolids. The total volatile solids mass removal efficiency (TVSMRE)was calculated using the following relationship given in:

TVSMRE ¼ ðTotal VS mass removed=Initial total VS mass fedÞ� 100

ð14Þ

Table 2Physiochemical properties of basic feed materials.

Feed material Physiochemical properties

Moisture content (%) Oil content (%)

Cattle dung 81.6 (442.5 db) –Jatropha oil seed cake 7.5 (8.1 db) 8.3Pongamia oil seed cake 10.5 (11.7 db) 7.2

Thus, for estimation of total volatile solids mass removal effi-ciency the Eq. (14) becomes:

TVSMRE ¼½ð16�CH4 Conc:Þ�

100 þ ½ð44�CO2 Conc:Þ�100

22:413� TVSM� BVo� DBF� 100 ð15Þ

where TVSMRE is the total volatile solids mass removal efficiency,%; TVSM is the total volatile solids input mass, kg.

3. Results and discussion

3.1. Properties of feed materials

Tables 2 and 3 show the proximate and ultimate analysis of feedmaterials. The proximate analysis of jatropha and pongamia oilseed cakes showed the volatile solids content of these oil seedcakes was more than six times higher than that of cattle dung. Ta-ble 2 shows that the non-volatile solids content of both oil seedcakes was very low in comparison to cattle dung. This is due tonon presence of lingo-cellulosic materials in oil seed cake. Table3 clearly shows that the carbon and hydrogen contents in the oilseed cakes were also higher than that of cattle dung.

3.2. Parameters of anaerobic digestion process

3.2.1. pH of input substrateThe average pH of input substrate for the jatropha oil seed cake

substrate, JC (4.0 DR, 0% CD) was found as 6.8. Similarly, the aver-age pH of input substrate for pongamia oil seed cake substrate, PC(3.5 DR, 0% CD) was found as 6.1. It has been reported that, mostanaerobic bacteria including methane-forming bacteria performwell within a pH ranges from 6.8 to 7.2. The pH in an anaerobic di-gester initially decreases due to the production of volatile acids.However, as methane-forming bacteria consume the volatile acidsand alkalinity is produced, the pH of the digester increases andthen stabilizes. At hydraulic retention time more than 5 days themethane-forming bacteria begin to rapidly consume the volatileacids. In a properly operating anaerobic digester the pH is main-tained between 6.8 and 7.2 as volatile acids are converted into

Total solids (%) Volatile solids (%) Non-volatile solids (%)

18.4 14.4 (78.8 db) 21.292.5 86.4 (93.0 db) 7.089.5 85.3 (94.8 db) 5.2

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Fig. 2. Daily biogas production rate from jatropha oil seed cake substrate.

R. Chandra et al. / Applied Energy 93 (2012) 148–159 153

methane and carbon dioxide. The pH of an anaerobic system is sig-nificantly affected by the carbon dioxide content of the biogas [6].

3.2.2. Daily biogas productionFig. 2 shows the relationship between the daily biogas produc-

tion yield and substrate temperature with respect to retentiontime for jatropha oil seed cake substrate, JC (4.0 DR, 0% CD) at feed-ing rate of 9.25 kg TS/d. The average daily biogas production during

Fig. 3. Daily biogas production rate from

30 days retention time period was observed as 6.541 m3/d. Simi-larly, daily biogas production yield at feeding rate of 8.95 kg TS/dand substrate temperature with respect to retention time for pong-amia oil seed cake substrate (PC (3.5 DR, 0% CD)) is depicted inFig. 3. Average daily biogas production over a period of 30 dayswas found as 7.791 m3/d. It was observed that biogas productionrate became stable after eighth day of digestion process. Figs. 2and 3 depicted that the biogas production rate during initial days

pongamia oil seed cake substrate.

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154 R. Chandra et al. / Applied Energy 93 (2012) 148–159

(1–7 days) was very low as compared to than later days of reten-tion time. It has been reported that when the hydraulic retentiontime is more than 5 days, the methane-forming bacteria begin torapidly consume the volatile acids, and thereby more biogas pro-duction occurs [6].

The substrate temperature during anaerobic digestion of jatro-pha oil seed cake and pongamia oil seed cake were observed inthe range of 26.3–34.5 �C and 33.7–35.2 �C, respectively. The ob-served substrate temperature indicates that the digester was oper-ating in mesophilic temperature range. It has been reported that

Fig. 4. Variation of methane and carbon dioxide content in

Fig. 5. Variation of methane and carbon dioxide content in p

mesophilic methanogens come into play in the temperature rangeof 20–45 �C and the biogas production reaches the maximum whenthe process temperature is maintained around 35 �C [20]. Further-more, it has also been reported that most of the methane-formingbacteria are active in mesophilic range from 30 to 35 �C [21].

3.2.3. Methane and carbon dioxide content of produced biogasFig. 4 shows the variation of methane and carbon dioxide con-

tent in the produced biogas from jatropha oil seed cake substrate.The maximum and minimum values of methane and carbon

produced biogas from jatropha oil seed cake substrate.

roduced biogas from pongamia oil seed cake substrate.

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R. Chandra et al. / Applied Energy 93 (2012) 148–159 155

dioxide were found to vary from 68.0% to 60.7% and 32.7% to 29.0%,respectively starting from first day to thirtieth day of retentiontime. The average methane and carbon dioxide content over30 days were found as 66.6% and 31.3%, respectively. Similarly,the variation of methane and carbon dioxide content of biogas pro-duced from pongamia oil seed cake substrate is shown in Fig. 5.The maximum and minimum values of methane and carbon diox-ide were found to vary from 65.3% to 56.0% and 38.3% to 31.7%,

Fig. 6. Cumulative biogas, methane and carbon diox

Fig. 7. Cumulative biogas, methane and carbon dioxi

respectively. The average value of methane and carbon dioxidecontent over 30 days of retention time period were found as62.5% and 33.5%, respectively.

The observed values of methane concentration in the producedbiogas from jatropha and pongamia oil seed cake substrates haveshowed a significantly higher methane percentage than the pro-duced biogas from cattle dung. This fact is due to degradation offats and proteins give more methane content (70–84%) in the

ide yields from jatropha oil seed cake substrate.

de yields from pongamia oil seed cake substrate.

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156 R. Chandra et al. / Applied Energy 93 (2012) 148–159

biogas than 50% from carbohydrates [6]. It was also observed thatthe variation of the average methane content in the biogas pro-duced from jatropha oil seed cake substrate was marginally higherin comparison to pongamia oil seed cake substrate.

3.2.4. Cumulative biogas, methane and carbon dioxide productionFig. 6 shows cumulative biogas, methane and carbon dioxide

production over 30 days retention period for jatropha oil seed cake

Fig. 8. Variation of specific biogas yield

Fig. 9. Variation of specific biogas yield o

substrate. The cumulative biogas, methane and carbon dioxide pro-duction were found as 196.224, 131.258 and 61.271 m3, respec-tively with total 259.2 kg of input volatile solids. Fig. 7 showscumulative biogas, methane and carbon dioxide production over30 days retention period for pongamia oil seed cake substrate.The cumulative biogas, methane and carbon dioxide productionwere found as 233.725, 147.605 and 77.625 m3, respectively withtotal 255.9 kg of input volatile solids.

on jatropha oil seed cake substrate.

n pongamia oil seed cake substrate.

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R. Chandra et al. / Applied Energy 93 (2012) 148–159 157

3.2.5. Specific biogas production rateThe variation in specific biogas production yield per unit TS and

per unit VS in case of jatropha and pongamia oil seed cake sub-strates are depicted in Figs. 8 and 9, respectively. The observedrange of specific biogas production yield with jatropha oil seedcake substrate with in 30 days retention time period was observedin the range of 0.16–0.71 m3/kg TS and 0.17–0.76 m3/kg VS. Simi-

Fig. 10. Variation of specific methane yiel

Fig. 11. Variation of specific methane yield

larly, the average specific biogas production yield over 30 daysretention time period on pongamia oil seed cake substrate wasfound in the range of 0.17–0.87 m3/kg TS and 0.18–0.91 m3/kg VS.

The average specific biogas yield with jatropha oil seed cakesubstrate over the 30 days retention time period was recorded as0.598 m3/kg TS and 0.640 m3/kg VS. Similarly, the average valueof specific biogas production yield with pongamia oil seed cake

d on jatropha oil seed cake substrate.

on pongamia oil seed cake substrate.

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158 R. Chandra et al. / Applied Energy 93 (2012) 148–159

over the 30 days retention time period was observed as 0.703 m3/kg TS and 0.738 m3/kg VS.

3.2.6. Specific methane production rateThe variation in specific methane production yield per unit TS

and per unit VS in case of jatropha and pongamia oil seed cake sub-strates are shown in Figs. 10 and 11, respectively. The range of spe-cific methane production yield with jatropha oil seed cake

Fig. 12. Variation of total volatile solids mass removal efficiency of th

Fig. 13. Variation of total volatile solids mass removal efficiency of the

substrate over the 30 days retention time period was found0.097–0.473 m3/kg TS and 0.104–0.506 m3/kg VS. Similarly, thespecific methane production yield over the 30 days retention timeperiod with pongamia oil seed cake substrate was found in therange of 0.096–0.55 m3/kg TS and 0.100–0.577 m3/kg VS.

The average specific methane production yield with jatropha oilseed cake substrate over the 30 days retention time period was re-corded as 0.394 m3/kg TS and 0.422 m3/kg VS. The average specific

e anaerobic digestion process on jatropha oil seed cake substrate.

anaerobic digestion process on pongamia oil seed cake substrate.

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R. Chandra et al. / Applied Energy 93 (2012) 148–159 159

methane production yield over the 30 days retention time periodwith pongamia oil seed cake substrate was observed as 0.427 m3/kg TS and 0.448 m3/kg VS.

3.2.7. Total volatile solids mass removal efficiency of the anaerobicdigestion process

Fig. 12 shows the variation in total volatile solids mass removalefficiency of the anaerobic digestion process of jatropha oil seedcake, JC (4.0 DR, 0% CD). The total volatile solids mass removal effi-ciency of jatropha oil seed cake substrate over the 30 days reten-tion time period was found in the range of 15.7–71.8%. Similarly,Fig. 13 shows the variation in total volatile solids mass removalefficiency of the anaerobic digestion process of pongamia oil seedcake, PC (3.5 DR, 0% CD). The total volatile solid mass removal effi-ciency on pongamia oil seed cake substrate over the 30 days ofretention time period was found in the range of 16.0–97.2%.

The average total volatile solids mass removal efficiency ofjatropha oil seed cake substrate over the 30 days retention timeperiod was recorded as 59.6%. Further, the average total volatilesolids mass removal efficiency over the 30 day retention time ofpongamia oil seed cake substrate was observed as 74.9%.

The study revealed that the biogas yield per unit TS and VS wasfound higher in case of pongamia oil seed cake substrate than thatof jatropha oil seed cake substrate. This is due to lower content ofnon-volatile solids in pongamia oil seed cake (5.2%) than in jatro-pha oil seed cake (7.0%). Furthermore, it was observed that thepongamia oil seed cake has higher biodegradability than jatrophaoil seed cake, may be due to higher concentrations of long-chainfatty acid oleates and stearates in jatropha oil seed cake.

4. Conclusions

The proximate and ultimate analysis of jatropha and pongamiaoil seed cakes confirmed that they have rich proportionate of vol-atile solids content. These oil seed cakes have low non-volatile sol-ids content, higher content of hydrogen and carbon as compared tothe cattle dung. Results show that the jatropha and pongamia oilseed cakes contain more than six times higher volatile solids con-tent in comparison to that of cattle dung. Further, the anaerobicdigestion of jatropha oil seed cake, JC (4.0 DR, 0% CD) is resultedinto an average specific biogas and specific methane productionpotential of 0.640 m3/kg VS and 0.422 m3/kg VS, respectively withan average total volatile solids mass removal efficiency of 59.6%.Whereas, the anaerobic digestion of pongamia oil seed cake, PC(3.5 DR, 0% CD) yields an average specific biogas and specific meth-ane production of 0.738 m3/kg VS and 0.448 m3/kg VS, respectivelywith an average total volatile solids mass removal efficiency of74.9% over a retention time period of 30 days. The biogas producedfrom jatropha and pongamia oil seed cakes contains 15–20% moremethane than the biogas produced from the cattle dung.

Acknowledgements

Authors are highly thankful to Centre for Rural Developmentand Technology and Mechanical Engineering Department, IndianInstitute of Technology Delhi, New Delhi, India for providing neces-sary facilities, support and financial funding to conduct this re-search work. Authors are also highly thankful to Prof. S.K.Rautaray, Head Department of Farm Power and Machinery, Collegeof Agricultural Engineering and Post Harvest Technology (CentralAgricultural University), Ranipool, Gangtok, Sikkim, India for hiskind help in revision of the manuscript.

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