Anaerobic Co-Digestion of Cassava Pulp and Pig Manure: Effects of ...

Anaerobic Co-Digestion ofCassava Pulp and Pig Manure:Effects of Waste Ratio andInoculum-Substrate RatioPornpan Panichnumsin, Annop Nopharatana,Birgitte Ahring and Pawinee Chaiprasert

Why? Anaerobic Co-Digestion• Treatment of at least two waste types• Help improvement– methane yield– process stability• Economically more favorable system• Share common facility of different wastestreams• Successful application to several typeof agricultural and industrial wastes

Background: Potential wastesCassava Pulp• 3.5 Million tons generated annually• Contributes to environmental impacts;methane emission, soil and ground-watercontamination by leachate, odour problem• Comprises of 56% starch, 5.3% proteins,0.1% lipids, 2.7% ash and 35.9% fiber• Potential substrate for biogas production

BackgroundPig Manure• generated approximately 2 billions kg drymatter/year• Comprises of 52% carbohydrate, 23% proteins,13% lipids, 7% VFA and 5% lignin• could contribute to future renewable energy(biogas) up to about 2,828 TJ/year

CO-DIGESTION OF CASSAVA PULPWITH PIG MANURECASSAVA PULP• Carbohydrate - rich• High C/N ratio• Low alkalinity• Lack of macro/micronutrientsPIG MANURE• Low C/N ratio• High alkalinity• Rich in macro/micronutrientsImprove C/N ratio, buffering capacityand more biodegradable substrateHigh process stability and better biodegradabilityand methane yield

Objective• To study effect of waste ratio and inoculumsubstrateratio (ISR) on anaerobic co-digestion ofcassava pulp and pig manureCassava pulpPig manureCharacterizationCo-digestionISRWaste ratioMethane production rateLag phase periodMethane production potentialMethodology & AnalysisEvaluation

Experimental Set-up• Substrates:• cassava pulp from cassava starch factory• pig manure from medium scale pig farm• Inoculum: digested pig manure taken fromanaerobic plug flow reactor• Batch experiment: using serum vial techniquegVS of Inoculum ( Fixed)ISR == 0.5,1.0,1.5gVS of Substrate ( Varied)Cassava pulpWaste Ratio = % = C : M RatioPig manure• C:M Ratios = 0:100, 20:80, 40:60, 50:50, 60:40, 80:20 &100:0based on VS conc.

AnalysisParameters Methods ReferencesBiogas Displacement method APHA, 1995productionBiogascomposition(CH 4 , CO 2 , Air)GC-TCD Shimudzu GC-9A,column SUS, porapack NTS Dried at 105°C APHA, 1995VS TS loss after ignited at 550°Cfor 3 hr.pHElectrometric method, pHmeterVFA GC-FID Shimudzu GC- 14B,column carbowax B-DAAPHA, 1995APHA, 1995

Evaluation• Ultimate methane production• Modified Gompertz equation:Rm × eM = P × exp{ − exp[ ( λ − t)+ 1]}P• Rm = Max. specific methane production rate(mlCH4/gVS-inoculum.d)• λ = Lag phase time (day)• P = Methane potential (ml)• SOLVER tool of Excel TM

Results & DiscussionUltimate methane yield(ml/g VSadded)4003503002502001501005000 0.5 1 1.5ISR0:100 20:80 40:60 50:50 60:40 80:20 100:0ISR C:M Max.Yield0.5 0:100 3931 50:50 3671.5 100:0 318Both ISR and wasteratio have strongeffect on methaneyieldUltimate methane yield vs ISR and waste ratio

Pattern of accumulative methane production(A) ISR-1.5(B ) IS R -1100200Methane (ml)50Methane (ml)1501005000 50 100Time (day)Methane (ml)400350300250200150100500(C ) IS R -0 .50 5 0 1 0 0Tim e (day)00 50 100Time (day)0:100, •20:80,40:60,50:50,60:40, •80:20and +100:0

Effects of ISR & waste ratio on calculated Rm, λ and PC:MRatio0:100Rm (ml/gVS.day) λ (days) P (ml)ISR-0.559ISR-119ISR-1.58ISR-0.50ISR-10ISR-1.50ISR-0.5355ISR-1165ISR-1.56620:805023120003501766540:60 17 25 14 4.56 0 0376 180 6550:5014261710.94004161836860:4012131930.09004381706680:20-1126-8.250-18071100:0 -933-38.560- 17181λ occurred at low ISR and high %CassavaP increased with increasing ISR and % Cassava

Accumulation of high VFA at low pH inhibited themethanogenesis at low ISR and high %Cassava50008Total VFA(mg/l as acetic acid)450040003500300025002000150010005007654321pH valueVFA-ISR-0.5VFA-ISR-1VFA-ISR-1.5pH-ISR-0.5pH-ISR-1pH-ISR-1.5000:10020:8040:6050:5060:4080:20100:0C:M RatiosTotal VFA and pH values at day 7th

Methanogenesis was inhibited when high conc. ofAA, PA and BA accumulatedC:MratiosAcetic acid Propionic acid n-Butyric acidISR0.5ISR1ISR0.5ISR1ISR0.5ISR10:100 0 0 0 0 21 020:80 0 0 63 0 68 040:60 38 0 1568 0 814 050:50 1662 0 1412 0 1106 060:40 1730 110 1567 318 1238 10480:20 2082 1925 2112 215 1469 1168100:0 2429 2017 1539 84 2103 1768

Conclusions• Both ISR and waste ratio directly have stronginfluence on co-digestion of cassava pulp andpig manure in terms of methane production rate,methane yield and process stability.• Co-digesting the two wastes has been provedbeneficial in this study.• The examined ISR and waste ratio could beused to specify appropriate substrate input andinoculum concentrations for further optimizationin order to maximize methane production andavoid acid inhibition during a start-up period.

Acknowledgement• The Joint Graduate School of Energy andEnvironment• The Royal Jubilee Ph.D Program• National Research Council of Thailand• Nunsurakit’s Tapioca Flour Ltd., Part•K P Farm• Excellent Center of Waste Utilization andManagement (ECo Waste) at KMUTT

Thank you for your attention

Waste CharacteristicsCompositional analysis of fresh cassava pulp and pig manureComposition Unit Cassava pulp Pig manureTS g kg -1 fresh waste 305±2 253±4VS g kg -1 TS 984±1 716±10Ash g kg -1 TS 16±1 284±10TKN g kg -1 TS 1.7±0.0 31.7±0.8NH 4+-N g kg -1 TS n.d. 4.5±0.5COD g kg -1 VS 1050±50 1400±200Starch g kg -1 VS 655.1±4.7 n.d.Crude fiber g kg -1 VS 312±3 312±5Protein g kg -1 VS 10.8±0.3 276.8±4.5Values are the mean ± S.D. of 3 determinations, n.d. = not determine

Methodology10 ml Distilled water20 ml Substrate15 mlDigested pig manureCO 2 /N 2 (30:70%)120 ml Vial 120 ml VialSampleWorking vol. 45 mlIncubated at 37°Cfor 120 daysControl

C:MRatiosRm (ml/gVS.day)ISR-0.5 ISR-1 ISR-1.50:1005919820:8050231240:6017251450:5014261760:4012131980:20-1126100:0-933

λ occurred at low ISR and high %CassavaP increased with increasing ISR and % CassavaC:MRatiosλ (days)P (ml)ISR-0.5 ISR-1 ISR-1.5 ISR-0.5 ISR-1 ISR-1.50:100 0 0 0 355 165 6620:80 0 0 0 350 176 6540:60 4.56 0 0 376 180 6550:50 10.94 0 0 416 183 6860:40 30.09 0 0 438 170 6680:20 - 8.25 0 - 180 71100:0 - 38.56 0 - 171 81

Maximum specificmethane production rate(mlCH4/g VS.d)60504030201000:100 20:80 40:60 50:50 60:40 80:20 100:0C:M Ratios0.5 1 1.5Max. methane production rate of different wasteratios at ISR 0.5, 1, 1.5

Evaluation• Ultimate methane production• Modified Gompertz equation:MRm × e= P × exp{ − exp[ ( λ − t)+ 1]}P• Max. specific methane production rate (Rm)• Lag phase time (λ)• Methane potential (P)• SOLVER tool of Excel TM• Effluent characteristics after 120 days ofdigestion

9080706050403020100Effluent characteristics after 120 days of digestion(A) VS0:10020:8040:6050:5060:4080:20100:0C:M RatiosISR-0.5ISR-1ISR-1.59080706050403020100(B) Total COD0:10020:8040:6050:5060:4080:20100:0C:M RatiosISR-0.5ISR-1ISR-1.5VS Reduction (%)Total COD Reduction (%)(C) Soluble COD1086420ISR-0.5ISR-1ISR-1.5Soluble CODConcentration (g/l)0:10020:8040:6050:5060:4080:20100:0C:M Ratios

Methanogenesis was inhibited when high conc. ofAA, PA and BA accumulated300025002000150010005000(A) ISR-1Specific VFAConcentration (mg/l)0:10020:8040:6050:5060:4080:20100:0C:M Ratios300025002000150010005000(B) ISR-0.5Specific VFA Concentration(mg/l)0:10020:8040:6050:5060:4080:20100:0C:M RatiosAcetic acid Propionic acid Butyric acidAcetic acid Propionic acid Butyric acidSpecific VFAs at day 7 th

Many investigations reported high conc. of VFA(AA, PA, BA) are associated with inhibitory effectGebauer and Eikebrokk (2006): The retardation of anaerobic processwas due to high concentration of acetate.Ahring and Westermann (1988): Acetate accumulation inhibiteddegradation of propionate and butyrate.Raposo et al. (2006):The degradation of longer chain VFAs was inhibitedwhen the acetic acid concentration was greater than 1600 mg/l.Kaspar and Wuhrmann (1978): propionic acid inhibited the methaneformation.Mechichi and Sayadi (2005) : Butyrate, isobutyrate and valerateaccumulated when acetate and propionate concentration reached highconcentration.