Anaerobic digestion: Bio-energy for our future - Renewable Energy ...

Anaerobic digestion, biogas-energyfrom crops : potential andcomparison with ethanolSerge R. GuiotEnvironmental Bioengineering GroupBiotechnology Research Institute

Anaerobic digestion⇒ AD science and engineering have welladvanced over the three past decades⇒ plain and relatively simple technology withlittle limiting factors for implementation andnot requiring pure or defined cultures⇒ AD commonly applied at real scale, througha broad variety of technologies, from smalltovery large-scale, from rustic to sophisticated(high-rate and high-cost) designs⇒ low energy requirement⇒ broad range of organics⇒ biogas distillates off by itself⇒ fuel produced (CH 4 ) offers differentpossible usesGTM07 - 2/14

A bottleneck = bioconversionefficiency⇒ adapting /applyingpretreatment ⇒ to extendfeedstock biodegradabilitySolubilization ofthe crops as afunction of the pretreatmentPre-treatments tested :• high temperature(90ºC for 3 hours)• temperature and pressure(autoclave)• alkalinization (NaOH 7 g/L)at 35 and 55ºC• combined alkalinizationand temperature-pressure• sonication• microwave• enzymatic (peroxidase)Substrate Parameter Pre-treatmentUntreated NaOH, 35°C NaOH+autoclaveSwitchgrass sCOD 8.0 22.0 41.0VSS 97.0 89.0 80.0NaOH, 35°C SonicationCorn kernels sCOD 63.2 257.2 133.9VSS 111.0 108.3 119.7Autoclave NaOH+autoclaveCorn silage sCOD 64.0 163.8 148.2VSS 76.3 76.3 72.8NaOH, 35°C SonicationPotatoes sCOD 45.9 58.0 48.2VSS 109.7 87.0 117.6Display of best results obtained.VSS: volatile suspended solids; sCOD: soluble chemical oxygen demand;all values in g/LGTM07 - 3/14

Methane potentialfrom crops:literature dataFeedstockMethane yield range(m 3 STP / dry kg) Energy yield range(MJ/ dry kg) aRef.Corn grain 0.27-0.37 10.3-14.1 1Switchgrass 0.18-0.34 6.9-13 2, 3, 4Potato 0.23 8.7 5ausing a calorific value of 38 MJ/m 3 STP CH 4References(1) Amon T et al. Proc. 10th World Congress - Anaerobic Digestion 2004, vol 3, 1716-1719.(2) Chynoweth DP, Owens JM, and Legrand RL. 2001. Renewable Energy, 22, 1-8.(3) Pettigrew M. 2000. http://www.esru.strath.ac.uk/(4) Samson R. Journée CRAAQ Québec, 2006. http://www.craaq.qc.ca(5) Parawira W et al. Proc. 10th World Congress - Anaerobic Digestion 2004, vol 3, 1800-1804.GTM07 - 4/14

Methane potential fromcrops: experimentsCorn500= 83% conversionMethane potential from raw andpre-treated corn kernelsSlightly higher yield than inliterature: effect of pre-treatment11%9% 4%2%

Methane potential fromcrops: experiments= 30% conversionSwitchgrass160Methane potential from raw andpre-treated switchgrassLower yield than in literature:effect of dry storage, asopposed to ensiled storage orfresh feeding4%4%6%19%6%26%35%StarchCelluloseHemicelluloseProteinsLipidsOthersLigninAshCumulative methane generated(mL/gTS added)14012010080604020Untreated switchgrassNaOH pre-treatment0Thermal-NaOH pre-treatment0 5 10 15 20 25 30 35Incubation time (days)GTM07 - 6/14

Cost-effectivenessbasic analysisInput : revenue ($/d.ton)Methane potentialDegradation efficiency : 80-95%Methane yield: 0.5 m 3 STP CH 4/kg d.ton degr.Energy value:10.5 kWh or 0.038 GJ/m 3 STP methaneEnergy conversion efficiency :Electricity: 30% (at a cost of 0.8 ¢/kWh), sale to grid @ 5-20 ¢/kWhCogeneration : 1.2 thermal kWh/1 kWh electricity, 80% valor. @ 0.33 ¢/kWhAlternative : Natural gas : 92% (at a biogas purification cost of 4 ¢/m 3 STP )GHG credit : 1.96 t eCO 2/1000 m 3 STP CH 4 fossil displaced, @ 15$/t eCO 2Output : AD unit cost ($/d.ton)based on real case (German technology, EnviTec Biogas), capacity 38 000 t/yrcapital [10 yr, 6%, 1€=1.5$] + operation [1€=1$] ⇒ 84 $/d.tonGTM07 - 7/14

Cost-effectivenessbasic analysis250Profit ($/dry ton)20015010050CornMarket value ofcorn grainAlt. Nat.Gas95% conv. + GHG cred.95% conv.80% conv.05 10 15 20Electricity sale (cent/kWh)GTM07 - 8/14

Cost-effectivenessbasic analysisCorn vs switchgrass / ha5000revenue2000Corn grain SwitchgrassCrop yield (d.ton/ha)8.5 12.5Anaer. Conv. (%)95 75Methane (m 3 STP /ha)40003000200010000corn switchgrass corn switchgrassCropprofitC&Op+25%150010005000Revenue/benefit ($/ha)GTM07 - 9/14

Cost-effectivenessbasic analysisCorn vs switchgrass / ha5000revenue2000Methane (m 3 STP /ha)4000300020001000profit15001000500Revenue/benefit ($/ha)20CornSwitchgrass0corn switchgrass corn switchgrassCropwith switchgrassprofit to as forrage cropcost to 0Corn demand (kg/ton)151050Water (kg/kg) Fertilizer (g N/kg) Herbicide (kg/kg)GTM07 - 10/14

For comparison,ethanol yieldFeedstockEthanol yieldrange (L/dry kg)Energy yield range(MJ/dry kg) aRef.Difference withAD energyyield (%)Corn grain 0.37-0.47 8.6-11 1, 2, 3 –20 to –28Switchgrass 0.37-0.4 8.6-9.3 2, 3Potato 0.23 5.4 419 to –40–61CH 411%9% 4%2%

For comparison,ethanol yieldFeedstockEthanol yieldrange (L/dry kg)Energy yield range(MJ/dry kg) aRef.Difference withAD energyyield (%)Corn grain 0.37-0.47 8.6-11 1, 2, 3 –20 to –28Switchgrass 0.37-0.4 8.6-9.3 2, 3Potato 0.23 5.4 419 to –40–61CH 46%19% 35%4%4%6% 26%EtOHa using a calorific value of 23.34 MJ/L EtOHReferences(1) Patzek T. Critical Rev in Plant Sci 23(6):519-567 (2004)(2) Seungdo K and al. ISAF XV Int Symposia of AlcoholFuels, San-Diego, CA (2005)(3) Pimentel D & Patzek T. Natural Res Research,14(1): 65-76 (2005)(4) Klijnsma X. Sustainable Mobility Conf, Leeuwarden,Netherlands (2006)GTM07 - 12/14

Thank you !Questions ?GTM07 - 14/14