Literature Review of Biogenic CO2 Emissions From Industrial Processes Associated with Annual Crops
July 21, 2020 Dr. Seungdo Kim Prepared for the Biogenic CO2 Coalition
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Introduction I have been asked by the Biogenic CO2 Coalition to review peer-reviewed scientific
articles that address biogenic carbon dioxide emissions from annual crop-based product systems and their potential impact on atmospheric greenhouse gases, with a particular focus on how biogenic CO2 emissions from stationary sources are calculated in greenhouse gas (GHG) accounting schemes. Relevant scientific articles published from 2010 to present were selected for review from the Web of Sciences database using the Boolean search terms below. About 100 articles have been deemed suitable for review, and the majority of articles reviewed here are concerning biofuel or bioenergy. (biogenic OR CO2 OR "greenhouse gas" or GHG) AND ("carbon accounting" or "greenhouse gas
accounting" or "GHG accounting" or LCA or "life cycle analysis" or "carbon footprint") AND (corn or soybean or cotton or "annual crop") NOT (wood or tree or "woody material" or forest
or animal or dairy or manure or "anaerobic")
Biogenic CO2 emission sources associated with the annual crop-based product system are: (1) carbon stock loss due to direct land conversion from forest/grassland to cropland, (2) carbon stock loss by indirect land use change (ILUC) (3) soil organic carbon loss, (4) stationary sources (e.g., fermentation, etc.), and (5) combustion of biomass and biofuel. The first three emission sources are out of the scope of this literature review since the focus is on biogenic CO2 released from stationary sources. Therefore, this review focuses on the last two emission sources.
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There are three main approaches to dealing with the biogenic carbon dioxide emissions in GHG accounting: (1) Neutrality, (2) Input-output and (3) Additionality. Neutrality
In the Neutrality approach, biogenic CO2 emissions from stationary and mobile sources associated with annual crops are carbon neutral. The biogenic carbon released as CO2 from any stationary/mobile sources (e.g., fermentation, combustion of annual crop, etc.) does not affect climate change. This is a steady state condition because all biogenic CO2 released into the atmosphere is absorbed by biomass growth over a short period of time. Therefore, biogenic CO2 emissions are excluded from GHG accounting. Most of articles reviewed here (83 out of 108 articles) use this Neutrality approach in their GHG accounting without including biogenic CO2 emissions. Furthermore, the Neutrality approach has been widely used in regulation (EPA, 2010) and international guidelines (UNFCCC, 2006; IPCC 2006). Input-output
In the input-output approach, carbon flux taken up by biomass and biogenic carbon releases are taken into account in the GHG calculations. Some LCA studies reviewed here (14 articles) use this approach and show that carbon uptake by crops completely offsets biogenic CO2 emissions associated with annual crops. Articles from Argonne National Laboratory (Wang et al., 2012, Dunn et al., 2012, Cai et al. 2013) also use the input-output approach. These articles subtract the biogenic carbon credit from combustion of biofuel, but do not include biogenic CO2 emissions from fermentation in their GHG calculations. van der Voet et al. (2010) found that exclusion of biogenic carbon generates the same results when co-products are not
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produced in the biofuel system. However, for biofuel systems with co-products, excluding biogenic carbon produces different results due to the allocation method. It is clear that the magnitude of carbon uptake by biomass allocated to biofuel is not always the same as the magnitude of biogenic carbon emissions from biofuel, because allocation is usually done by physical (e.g., mass, energy, etc.) or economic properties, not molecular weight. Before the allocation, carbon uptake by biomass is the same as biogenic carbon emissions. Therefore, this is an allocation issue, not a carbon neutrality issue.
Additionality
Currently, several studies (Searchinger, 2010; Haberl et al., 2012; DeCicco, 2015; DeCicco et al., 2016; DeCicco, 2018) have questioned the carbon neutrality of biogenic CO2 emissions, especially biogenic CO2 emissions in the bioenergy/biofuel system. "Additional biomass (or additional carbon uptake on cropland)" is the key concept in those studies. They claimed that if no bioenergy were produced, plants for bioenergy would not be harvested and would continue to absorb carbon, helping to reduce CO2 in the air. In global projections of atmospheric carbon, treating biogenic CO2 emissions released in the bioenergy system as carbon neutral is a "double-counting error". Atmospheric carbon is absorbed by plants regardless of bioenergy. Therefore, biogenic CO2 emissions should be offset by additional carbon uptake on cropland. DeCicco et al. (2016) claimed that only 37% of the biogenic CO2 emissions in corn-based ethanol fuel production systems should be offset by carbon uptake by additional corn production, so only 37% of biogenic CO2 emissions are carbon neutral.
However, this analysis struggles with uncertainties related to inconsistent system boundaries, selection of periods for evaluation, economic conditions and weather dependence
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(De Kleine et al., 2016; De Kleine et al., 2017; Khanna et al., 2020). De Kleine et al. (2017) pointed out that biogenic carbon in corn grain is released into the atmosphere in a short time, even when used as biofuel or food/feed. As a result, there is no substantial change in net carbon emissions to the atmosphere. Wang et al. (2015) raised two questions about the additional biomass:
"Would farmers/growers continue to grow biomass if there were no demand for biomass due to bioenergy production? In particular, if there were no cellulosic biofuel industry demanding cellulosic biomass, can one assume that farmers/growers would grow cellulosic biomass anyway?"
"When bioenergy production results in managed biomass growth, how does the growth rate differ from that of natural biomass growth?" The additional biomass (or additional carbon uptake on cropland) relies heavily on
value-choice and scenario-based modeling. Similar to ILUC, the additionality approach assigns to biofuel/bioenergy all the changes in the crop system in spite of many inter-related factors that also contribute to changes in the crop system. These inter-related factors include local and global economic conditions, weather, national policy, international trade, dietary preferences, biofuel/bioenergy, technology improvements, etc. In other words, the "additionality approach" is oversimplified. Other approaches
Cherubini et al. (2011) quantified global warming potentials (GWP) for biogenic CO2 emissions, taking into account the timing of biogenic CO2 emissions and uptake by biomass
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regrowth (at the end of the rotation period). Therefore, the modified GWP for biogenic CO2 emissions depends on the biomass rotation period, as seen in Table 1. The modified GWP for biogenic CO2 emissions released form one-year rotation biomass (e.g., annual crop, grass, etc.) is zero, implying that biogenic CO2 emissions associated with one-year rotation biomass have no negative impact on the climate per unit of biogenic CO2 emitted from stationary/mobile sources associated with annual crops.
Downie et al. (2014) investigated three different GHG accounting methods: 1) the biogenic method, which includes biogenic CO2 emissions, even though they may be neutral over the timeframe; (2) the stock method, which excludes biogenic CO2 emissions, but includes credit for biogenic carbon not released for a long-term C cycle (e.g., biochar, etc.); and (3) the simplified method, in which the net biogenic CO2 flux is neutral over the timeframe. The biogenic method is corrected if the term for carbon uptake by biomass is added. The stock method is the most accurate method to forecast the net change in atmospheric GHG for activities that involve biogenic carbon. When all biogenic carbon is released over a short time of period, results from the simplified method are equal to those from the stock method.
Table 1 Modified GWPs for biogenic CO2 emissions (Cherubini et al., 2011).
Rotation period (years)
1 10 20 50 70 100
Modified GWP for biogenic CO2 emission
(time horizon = 100 years) 0.00 0.04 0.08 0.21 0.30 0.43
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Discussion
Brandao et al. (2013) pointed out that biogenic carbon management differs from fossilfuel carbon management in that biomass can sequester and release carbon into the atmosphere. They were also concerned about the time differences between uptake and release of CO2, even though CO2 release is balanced by carbon uptake by biomass. The time lag between uptake and release of CO2 will lead to different trajectories of atmospheric CO2 concentrations and thus different cumulative radiative forcing, which have different impacts on climate change. In annual crop-based systems, uptake and release of CO2 occur within one year. As seen in Cherubini et al (2011), the effects of the time lag in the annual crop-based systems can be negligible. Thus, the time lag issues are not relevant in the annual crop systems.
Table A in the Appendix A lists articles, their feedstock types and the biogenic CO2 accounting approach. For clarity, the text of each article on biogenic carbon is also quoted in the table if available. Biogenic CO2 emissions associated with annual crops, perennials and other biomass in 104 articles out of 108 are regarded as carbon neutral regardless of the biogenic carbon accounting approaches (i.e., Neutrality, Input-out approaches and Modified GWP). Note that some articles do not mention biogenic carbon in their text at all, suggesting that biogenic carbon is not taken into account. The 104 articles reviewed here show that biogenic CO2 emissions from stationary/mobile sources associated with annual crops are completely balanced by biomass regrowth over a short period of time; i.e., carbon neutral.
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Scacchi CCO, Gonzalez-Garcia S, Caserini S, Rigamonti L. Greenhouse gases emissions and energy use of wheat grain-based bioethanol fuel blends. Science of the Total Environment. 2010;408(21):5010-8. Schumacher B, Oechsner H, Senn T, Jungbluth T. Life cycle assessment of the conversion of Zea mays and x Triticosecale into biogas and bioethanol. Engineering in Life Sciences. 2010;10(6):577-84. Searchinger, T. D., Biofuels and the need for additional carbon. Environmental Research Letters 2010, 5 (2). Semba T, Sakai Y, Sakanishi T, Inaba A. Greenhouse gas emissions of 100% bio-derived polyethylene terephthalate on its life cycle compared with petroleum-derived polyethylene terephthalate. Journal of Cleaner Production. 2018;195:932-8. Sharara MA, Sahoo K, Reddy AD, Kim S, Zhang XS, Dale B, et al. Sustainable feedstock for bioethanol production: Impact of spatial resolution on the design of a sustainable biomass supply-chain. Bioresource Technology. 2020;302. Shuai W, Chen N, Li B, Zhou D, Gao J. Life cycle assessment of common reed (Phragmites australis (Cav) Trin. ex Steud) cellulosic bioethanol in Jiangsu Province, China. Biomass & Bioenergy. 2016;92:40-7. Smullen E, Finnan J, Dowling D, Mulcahy P. The environmental performance of pretreatment technologies for the bioconversion of lignocellulosic biomass to ethanol. Renewable Energy. 2019;142:527-34.
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Song S, Liu P, Xu J, Chong C, Huang X, Ma L, et al. Life cycle assessment and economic evaluation of pellet fuel from corn straw in China: A case study in Jilin Province. Energy. 2017;130:373-81. Souza SP, Seabra JEA. Integrated production of sugarcane ethanol and soybean biodiesel: Environmental and economic implications of fossil diesel displacement. Energy Conversion and Management. 2014;87:1170-9. Staples MD, Malina R, Suresh P, Hileman JI, Barrett SRH. Aviation CO2 emissions reductions from the use of alternative jet fuels. Energy Policy. 2018;114:342-54. Su M, Huang C, Lin W, Tso C, Lur H. A Multi-Years Analysis of the Energy Balance, Green Gas Emissions, and Production Costs of First and Second Generation Bioethanol. International Journal of Green Energy. 2015;12(2):168-84. Tabatabaie SMH, Tahami H, Murthy GS. A regional life cycle assessment and economic analysis of camelina biodiesel production in the Pacific Northwestern US. Journal of Cleaner Production. 2018;172:2389-400. Tsang M, Fox-Lent C, Wallace S, Welp T, Bates M, Linkov I. Life-cycle impacts of soybean and algae biodiesel: Case study of US marine vessels. Biofuels Bioproducts & Biorefining-Biofpr. 2015;9(5):567-80. Ukaew S, Shi R, Lee JH, Archer DW, Pearlson M, Lewis KC, et al. Full Chain Life Cycle Assessment of Greenhouse Gases and Energy Demand for Canola-Derived Jet Fuel in North Dakota, United States. Acs Sustainable Chemistry & Engineering. 2016;4(5):2771-9.
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UNFCCC (United Nations Framework Convention on Climate Change) 2006, Updated UNFCCC reporting guidelines on annual inventories following incorporation of the provisions of decision. 14/CE.11. FCCC/SBSTA/2006/9, Aug. 18. Valli L, Rossi L, Fabbri C, Sibilla F, Gattoni P, Dale BE, et al. Greenhouse gas emissions of electricity and biomethane produced using the Biogasdoneright system: four case studies from Italy. Biofuels Bioproducts & Biorefining-Biofpr. 2017;11(5):847-60. van der Voet, E.; Lifset, R. J.; Luo, L., Life-cycle assessment of biofuels, convergence and divergence. Biofuels-Uk 2010, 1 (3), 435-449. Vargas-Ramirez JM, Wiesenborn DP, Ripplinger DG, Pryor SW. Carbon footprint of industrialbeet sugars stored as raw thick juice for use as a fermentation feedstock. Journal of Cleaner Production. 2017;162:1418-29. Viskovic M, Djatkov D, Martinov M. Corn stover collection prior to biogas production Evaluation of greenhouse gas emissions. Journal of Cleaner Production. 2018;199:383-90. Voet Evd, Lifset RJ, Luo L. Life-cycle assessment of biofuels, convergence and divergence. Biofuels. 2010;1(3):435-49. Wang C, Chang Y, Zhang L, Chen Y, Pang M. Quantifying uncertainties in greenhouse gas accounting of biomass power generation in China: System boundary and parameters. Energy. 2018;158:121-7. Wang M, Han J, Dunn JB, Cai H, Elgowainy A. Well-to-wheels energy use and greenhouse gas emissions of ethanol from corn, sugarcane and cellulosic biomass for US use. Environmental Research Letters. 2012;7(4).
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Wang MQ, Tyler WE, Williams D, Dunn JB (2015) Comments on and discussion of 'the liquid carbon challenge: evolving views on transportation fuels and climate.' Manuscript, March 30. Argonne National Laboratory, https://greet.es.anl.gov/publication-comments-liquid-carbon. Weinberg J, Kaltschmitt M. Greenhouse gas emissions from first generation ethanol derived from wheat and sugar beet in Germany - Analysis and comparison of advanced by-product utilization pathways. Applied Energy. 2013;102:131-9. Yan X, Boies AM. Quantifying the uncertainties in life cycle greenhouse gas emissions for UK wheat ethanol. Environmental Research Letters. 2013;8(1). Yang Y, Ni J-Q, Bao W, Zhao L, Xie GH. Potential Reductions in Greenhouse Gas and Fine Particulate Matter Emissions Using Corn Stover for Ethanol Production in China. Energies. 2019;12(19). Yang Y, Suh S. Marginal yield, technological advances, and emissions timing in corn ethanol's carbon payback time. International Journal of Life Cycle Assessment. 2015;20(2):226-32. Zamboni A, Murphy RJ, Woods J, Bezzo F, Shah N. Biofuels carbon footprints: Whole-systems optimisation for GHG emissions reduction. Bioresource Technology. 2011;102(16):7457-65. Zhang X, Witte J, Schildhauer T, Bauer C. Life cycle assessment of power-to-gas with biogas as the carbon source. Sustainable Energy & Fuels. 2020;4(3):1427-36. Zhang Y, Kendall A. Life Cycle Performance of Cellulosic Ethanol and Corn Ethanol from a Retrofitted Dry Mill Corn Ethanol Plant. Bioenergy Research. 2017;10(1):183-98.
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Zhao L, Ou X, Chang S. Life-cycle greenhouse gas emission and energy use of bioethanol produced from corn stover in China: Current perspectives and future prospectives. Energy. 2016;115:303-13.
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Appendix A. Table A. List of articles
Approach
Zhang X, Witte J, Schildhauer T, Bauer C. (2020)
Neutrality
Sharara MA, Sahoo K, Reddy AD, Kim S, Zhang XS, Dale B, et al. (2020)
Neutrality
Pecanha Esteves VP, Vaz Morgado CdR, Fernandes Araujo OdQ. (2020)
Neutrality
Oliveira MdCTBE, Rosentrater KA. (2020)
Neutrality
Moreno J, Iglesias J, Blanco J, Montero M, Morales G, Melero JA. (2020)
Neutrality
Biomass
anaerobic digestion of sewage sludge and green waste
Quotation/Remark
,'Biogenic CO2 emissions are not accountedfor assuming a closed carbon circle."
corn stover
not explicitly mentioned
soybean and livestock not explicitly mentioned
corn corn
not explicitly mentioned
"... sorbitol production starting from corn starch has been evaluated using a cradle-to-gate life cycle assessment (LCA) approach
including biogenic carbon for calculations makes that CO2 fixed during corn cultivation almost compensates the emissions of the rest of the process steps, highlighting the importance of using autotrophic biomass as raw materials."
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Approach
Mahmud N, Rosentrater KA. (2020)
Neutrality
Khanna M, Wang W, Wang M. (2020) Additionality
Bartocci P, Zampilli M, Liberti F, Pistolesi V, Massoli S, Bidini G, et al. (2020)
Neutrality
Akmalina R, Pawitra MG. (2020)
Neutrality
Biomass
oil palm frond
corn food waste empty fruit bunch
Quotation/Remark
"According to the IPCC, only non-biogenic CO2 emissions should be considered as greenhouse gas (GHG) emissions, which eventually contribute towards an increase in global warming potential (GWP). The biogenic CO2 is not considered as GHG emission, because, throughout plants' life, they are conducting a photosynthesis process by taking CO2 from the atmosphere (49). The biogenic CO2 emissions fractions in most of the simulated models were higher than that of non-biogenic, because of the large fraction of CO2 generated during the fermentation process and the waste fibers burning in the CHP generation system."
Criticize uncertainty associate with selecting time frame for evaluation, economic conditions, and weather dependency
not explicitly mentioned
"Carbon dioxide releasedfrom the biomass-based process can be considered as biogenic carbon. It is the carbon contained in biomass during plant growth, involving photosynthetic process. In other words, this substance is possibly to be removed from the atmosphere through a carbon cycle."
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Approach
Biomass
Yang Y, Ni J-Q, Bao W, Zhao L, Xie GH. (2019)
Neutrality
corn stover
Smullen E, Finnan J, Dowling D, Mulcahy P. (2019)
Prieler M, Lindorfer J, Steinmueller H. (2019)
Neutrality Neutrality
switchgrass grass silage
Obnamia JA, Dias GM, MacLean HL, Saville BA. (2019)
Neutrality
corn stove
Lienhardt T, Black K, Saget S, Costa MP, Chadwick D, Rees RM, et al. (2019)
Neutrality
Knoope MMJ, Balzer CH, Worrell E. (2019)
Neutrality
pea and wheat soybean
Quotation/Remark
"It was assumed that carbon in the form of CO2 from vehicular ethanol combustion originatedfrom biogenic carbon that was derivedfrom corn stover because more than 96% of all carbon in the process entered as biomass feed, with only small amounts of additional carbon coming from glucose (for enzyme production) andfermentation nutrients such as corn steep liquor 33). Thus, CO2 emissions from ethanol in the vehicle-use stage were negligible in this study."
not explicitly mentioned
"The GWP excludes biogenic carbon so the bound carbon in the grass silage is not included."
"The LCA software packages apply this approach by determining total emissions in the fuel use stage and then subtracting CO2 emissions traceable to the fuel's biogenic carbon component. This leads to net zero GWP for CO2 from the fuel's biogenic carbon content (i.e., biofuelfraction) while CO2 from the fuel's fossil carbon fraction and all other non-CO2 GHGs emitted in the fuel use stage are still accounted for."
not explicitly mentioned
not explicitly mentioned
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Approach
Kim S, Dale BE, Zhang XS, Jones CD, Reddy AD, Izaurralde RC. (2019)
Neutrality
Kim S, Dale BE, Jin M, Thelen KD, Zhang Neutrality X, Meier P, et al. (2019)
Han D, Yang X, Li R, Wu Y. (2019)
Input-output
Guzman-Soria D, Taboada-Gonzalez P, Aguilar-Virgen Q, Baltierra-Trejo E, Marquez-Benavides L. (2019)
Bicalho T, Sauer I, Patino-Echeverri D. (2019)
Neutrality Neutrality
Abraha M, Gelfand I, Hamilton SK, Chen Neutrality J, Robertson GP. (2019)
Approach
Biomass corn stover corn stover corn stover
corn
Quotation/Remark
"Biogenic carbon dioxide emissions releasedfrom combusting ethanolfuel are not included as GHG emissions."
not explicitly mentioned
"For GWPs, the percentage of absorption of carbon in the biomass production is higher than its release in the production process; thus, the net GWP is negative, and that the entire life cycle is absorbing GHGs."
not explicitly mentioned
sugarcane and corn
switchgrass, restored prairie, and corn
Biomass
not explicitly mentioned
"We present a whole-system LCA of the global warming impact (GWI) of all convertedfields over eight years by measuring GHGfluxes (CO2, N2O and CH4), farming operations, agronomic inputs and a fossilfuel offset credit that include co-products.
A fossilfuel offset creditfor ethanol was computed from the dry mass yield (kg rn-2 yr-1), its ethanol production potential (L kg-1), and its ethanol energy content (MJ L-1) compared to the equivalent energy and CO2 emissions for the gasoline use the ethanol would offset (table S6).
Quotation/Remark
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Wang C, Chang Y, Zhang L, Chen Y, Pang Neutrality M. (2018)
Viskovic M, Djatkov D, Martinov M. (2018)
Neutrality
Tabatabaie SMH, Tahami H, Murthy GS. Neutrality (2018)
Staples MD, Malina R, Suresh P, Hileman JI, Barrett SRH. (2018)
Neutrality
corn stover corn stover
"The GHG emissions of the CSPGS were categorized into two parts: 1) onsite emissions, including N2O emission from the nitrification and denitrification processes in the soil, CO2 emission from the soil tilling and erosion processes, CH4 and N2O emitted by biomass burning, and GHG emitted by fossil energy combustion; and 2) supply-chain emissions derivedfrom material (building materials, fertilizers, pesticides, and water) production, powerplant equipment manufacturing, services provision (including transport, installation, and repair services), andfossil energy production and supply."
"Global warming potential (GWP 100 years) excluding biogenic carbon."
camelina
not explicitly mentioned
soybean, rapeseed, jatropha and oil palm; maize grain, sorghum grain and cassava; sugarcane and sugar beet; switchgrass, miscanthus and reed canary grass
not explicitly mentioned
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Approach
Biomass
Semba T, Sakai Y, Sakanishi T, Inaba A. (2018)
Neutrality
sugarcane and corn
Rathnayake, M.; Chaireongsirikul, T.; Svangariyaskul, A.; Lawtrakul, L.; Toochinda, P. (2018)
Neutrality
cassava, cane molasses, and rice straw
Michailos, S. (2018)
Input-output
sugarcane
Liu H, Ou X, Yuan J, Yan X. (2018)
Neutrality
Liu C, Huang Y, Wang X, Tai Y, Liu L, Liu H. (2018)
Input-output
corn stover corn stover
Liptow, C.; Janssen, M.; Tillman, A.-M., (2018)
Modified global warming potential
wood; sugarcane
Quotation/Remark
"It was assumed that PET was incinerated at the disposal stage and that biomass derived GHG emissions were carbon neutral. CO2 emissions from biomass were assumed to be carbon neutral."
" The carbon neutral rule is appliedfor biogenic CO2 emissions (Neamhom et al., 2016)."
"the amount of CO2 absorbed by photosynthesis during the sugarcane growth is subtractedfrom the total emissions of the system. The equivalent amount of CO2 stored in the sugarcane is estimated using the stoichiometric relationship of CO2 to carbon of 3.66 kg/kg 38."
not explicitly mentioned
Carbon uptake (CO2 absorption): 0.12 kg/MJ) Biogenic CO2 emissions: 0.07 kg/MJ But before allocation, carbon uptake equals to biogenic CO2 emissions
"In the case of boreal wood, this re-growth takes around 100 years, causing an impact of 3-4 t CO2,eq/t PE using the GWPbio and the WF methods. In contrast, the sugarcane grows very fast, leading to an almost instantaneous uptake of emissions and hence an impact close to 0 t CO2,eq/t PE."
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Kim S, Zhang XS, Dale BE, Reddy AD, Jones CD, Izaurralde RC. (2018)
Kim S, Zhang XS, Dale B, Reddy AD, Jones CD, Cronin K, et al. (2018).
Approach Neutrality Neutrality
Biomass corn stover corn stover
Khoshnevisan B, Rafiee S, Tabatabaei M, Ghanavati H, Mohtasebi SS, Rahimi V, et al. (2018)
Neutrality
castor
Heng L, Zhang H, Xiao J, Xiao R.(2018) Neutrality
corn stover
Quotation/Remark
not explicitly mentioned
not explicitly mentioned
"The origin of biomass, i.e., plants, absorbs atmospheric CO2 during photosynthesis. This CO2 is approximately equal to the amount of CO2 released during their subsequent conversion and combustion (Naik et al. Osamu and Carl 1989). Therefore, biofuels not only can alleviate world's dependence on fossil-basedfuels but also can simultaneously reduce global CO2 production. ... the CO2 releasedfrom castor biodiesel was considered to be completely biogenic as the ethanol and methanol usedfor biodiesel production were assumed to be of biomass origin (ethanol was completely supplied internally by the biorefinery)."
"The reduction in GHG emissions is mainly attributed to the biogenic CO2 credit from the uptake of atmospheric CO2 during growth of biomass. The biogenic CO2 credit can offset the biogenic carbon emissions from biomass pyrolysis, bio-oil upgrading, biofuel consumption, and the disposal of carbonaceous organics in wastewater. Obviously, if the atmospheric CO2 absorbed by biomass is returned to the atmosphere, the net greenhouse effect is nearly zero."
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Approach
Heng L, Xiao R, Zhang H. (2018)
Neutrality
DeCicco JM. (2018). Chen R, Qin Z, Han J, Wang M, Taheripour F, Tyner W, et al. (2018)
Buchspies B, Kaltschmitt M. (2018)
Additionality Input-output Neutrality
Zhang Y, Kendall A. (2017)
Neutrality
Vargas-Ramirez JM, Wiesenborn DP, Ripplinger DG, Pryor SW. (2017)
Neutrality
Valli L, Rossi L, Fabbri C, Sibilla F, Gattoni P, Dale BE, et al. (2017)
Neutrality
Biomass
corn stover
corn soybean
wheat straw
corn grain and corn stover
Sugar beet
cattle slurry, potato scraps, cereal byproducts, corn silage, poultry droppings, sorghum silage, triticale silage, citrus pulp, olive and whey
Quotation/Remark "The corn stover plays a role of carbon fixation via the uptake of atmospheric CO2 during its growth. The biogenic carbon credit from CO2 uptake can cancel out all the biogenic CO2 emission from various unit processes including the disposal of carbonaceous organics in waste water." Additional carbon uptake accounting biodiesel combustion and biogenic carbon credit of the same scale "Emissions originating from the combustion of biofuels are considered to be carbon neutral due to the biogenic origin of carbon."
not explicitly mentioned
"Carbon dioxide emitted during ethanol combustion was excludedfrom this analysis because it is biogenic and does not contribute to global warming potential (Munoz et al., 2013)."
not explicitly mentioned
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Approach
Song S, Liu P, Xu J, Chong C, Huang X, Ma L, et al. (2017)
Neutrality
Biomass corn stover
Pellegrino Cerri CE, You X, Cherubin MR, Moreira CS, Raucci GS, Castigioni BdA, et al. (2017).
Neutrality
De Kleine, R. D.; Anderson, J. E.; Kim, H. C.; Wallington, T. J., (2017)
Additionality
Adom FK, Dunn JB. (2017)
Input-output
soybean corn corn stover
Zhao L, Ou X, Chang S. (2016)
Ukaew S, Shi R, Lee JH, Archer DW, Pearlson M, Lewis KC, et al. (2016)
Neutrality Neutrality
Shuai W, Chen N, Li B, Zhou D, Gao J. (2016)
Neutrality
corn stover canola common reed
Quotation/Remark
"we first assume that biomass utilization is carbon neutral, which means that the CO2 fixed by photosynthesis in the biomass equals the CO2 emissions from burning the biomass."
"Our study did not mention the emissions from the final stage (i .e ., combustion) of the life cycle, because the combustion of soybean biodiesel emits biogenic CO2, which is covered in the agriculture stage, and was considered as zero in this study."
Criticize inconsistent system boundary
Biogenic carbon was treated as stored within the bioproduct in cradle-to-gate analyses. acconting CO2 uptake during feedstock growth and CO2 release upon degradation of the same scale
Subtracting biogenic CO2 from overall CO2 emissions associated with E10 fuel
"The CO2 emission from HEFA fuel combustion is considered as carbon neutral; therefore, this emission is not counted in the GHG analysis."
"Because biogenic GHG emission was climate neutral, only GHG emissions from fossilfuel and other non-renewable resources were counted in calculation."
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Pourhashem G, Adler PR, Spatari S. (2016)
Kim S, Dale BE. (2016)
Approach Neutrality Neutrality
Hums ME, Cairncross RA, Spatari S. (2016)
Neutrality
DeCicco JM, Liu DY, Heo J, Krishnan R, Kurthen A, Wang L. (2016)
Additionality
Daylan B, Ciliz N. (2016)
Neutrality
Carvalho M, da Silva ES, Andersen SLF, Abrahao R. (2016)
Neutrality
Canter CE, Dunn JB, Han J, Wang Z, Wang M. (2016)
Neutrality
Yang Y, Suh S. (2015)
Neutrality
Biomass residue of corn, wheat and barley corn stover
grease trap waste
Quotation/Remark
"Biogenic carbon released by biofuel production and combustion is assumed to be captured again by annual cropping."
not explicitly mentioned
"The CO2 credit for biodiesel was represented in the fuel's combustion. The CO2 producedfrom biogenic sources was considered zero because of the recent sequestration of carbon from the atmosphere."
corn
Additional carbon uptake
corn stover
"Biofuels have a large reduction potentialfor CO2 emissions throughout their life cycle, since the vehicle combustion of biofuels does not contribute to net emissions of CO2, which is absorbed by the biomass feedstock through photosynthesis."
soybean
not explicitly mentioned
corn and corn stover corn
"We treat CO2 emissions from ethanol combustion during vehicle operation as offset by carbon uptake during feedstock growth, which in the case of corn grain and corn stover occurred in the recent past."
not explicitly mentioned
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Approach Tsang M, Fox-Lent C, Wallace S, Welp T, Neutrality Bates M, Linkov I. (2015)
Su M, Huang C, Lin W, Tso C, Lur H. (2015)
Neutrality
Sastre CM, Gonzalez-Arechavala Y, Santos AM. (2015)
Neutrality
Murphy CW, Kendall A. (2015)
Neutrality
Kim S, Dale BE. (2015a)
Neutrality
Biomass
Quotation/Remark
soybean and algae
"The burning of biodiesel is a closed loop carbon system, meaning that the carbon dioxide emissions during fuel combustion originate from carbon consumedfrom the atmosphere during growth of the feedstock. Such carbon is considered biogenic and their resulting release into the atmosphere during combustion does not add to the global greenhouse gas burden."
corn, rice straw, switchgrass, sweet potato, sweet sorghum and sugarcane
Not including biogenic CO2 emissions
wheat straw
"The emissions of carbon dioxide from straw combustion have not been accounted because CO2 was previously fixedfrom the air by the crop no more than one year before being burned."
corn stover and switchgrass
"All CO2 emittedfrom combusting process byproducts is biogenic and assumed to not to contribute to changing atmospheric CO2 and, in accordance with widely accepted carbon accounting methods, is not included in calculations."
barley straw, corn stover, oat straw, sorghum stubble, wheat straw, energy sorghum, switchgrass and willow
not explicitly mentioned
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Kim S, Dale BE. (2015b)
Approach Neutrality
Jeswani HK, Falano T, Azapagic A. (2015)
Neutrality
Daystar J, Treasure T, Reeb C, Venditti R, Gonzalez R, Kelley S. (2015)
Input-output
Borjesson P, Prade T, Lantz M, Bjornsson L. (2015)
Neutrality
Belboom S, Bodson B, Leonard A. (2015)
Neutrality
Biomass
Quotation/Remark
corn stover
"Biogenic carbon dioxide emissions are released from the fermentation and the cogeneration facilities."
wheat straw, poplar, miscanthus and forest residue
"As per standard LCA practice, biogenic CO2 emissions are excludedfrom the GWP as they are part of the natural carbon cycle. Similarly, biogenic carbon storage in the products is not considered as this carbon will be released during the use of ethanol in vehicles
for ethanol the biogenic CO2 emitted during its use is not taken into account as that is equivalent to the amount of CO2 sequesteredfrom the atmosphere by the feedstocks during their growth."
pine, eucalyptus, natural hardwood, switchgrass, and sweet sorghum
Carbon uptake and biogenic CO2 emissions are accounted.
hemp; sugar beet; maize; triticale; ley crops; wheat (grain)
"The calculation oflife cycle emissions of GHGs includes carbon dioxide (CO2) offossil origin and based on changes in soil organic carbon (SOC) content, methane (CH4) and nitrous oxide (N2O).,,
wheat
"During crop cultivation, carbon dioxide from atmosphere is converted by the plant into biomass. In this study, we do not take this benefit into account as recommended by the Annex V of the RED (3) neither the emissions of biogenic CO2 released during combustion phase."
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Approach
Aguirre-Villegas HA, Larson R, Reinemann DJ. (2015)
Neutrality
Souza SP, Seabra JEA. (2014)
Neutrality
Sanscartier D, Dias G, Deen B, Dadfar H, Neutrality
McDonald I, MacLean HL. (2014)
Olukoya IA, Ramachandriya KD, Wilkins MR, Aichele CP. (2014)
Neutrality
Nguyen L, Lafferty KG, Searcy EM, Spatari S. (2014)
Input-output
Munoz I, Flury K, Jungbluth N, Rigarlsford G, Canals LMI, King H. (2014)
Neutrality
Moller F, Slento E, Frederiksen P. (2014)
Neutrality
Biomass
Quotation/Remark
manure, corn stover and switchgrass
"...to account for the CO2(b) recycling process that takes place during plant growth as it is assumed that the carbon contained in biomass has been previously captured as CO2"
sugarcane and soybean not explicitly mentioned
corn cobs
".. . biogenic CO2 emitted during the combustion of the pellets is not counted in calculations as it does not have a net contribution to the global warming effect."
red cedar
not explicitly mentioned
corn stover
maize corn stover sugarcane wheat and sugar beet
rapeseed
Carbon uptake by biomass and Biogenic CO2 emission are accounted.
Biogenic carbon uptake: -234 gCO2/MJ Fermentative CO2: 34 gCO2/MJ
Boiler: 122 gCO2/MJ Ethanol combustion: 71gCO2/MJ
"... global warming potentials (GWP) from carbon dioxide (CO2) and methane were used as proposed by Mulioz et al. (2013) fora 100-year period, accounting for methane oxidation in the atmosphere and considering biogenic CO2 emissions as neutral, with the exception of those resulting from land use change (LUC)."
"RME consists of100% renewable carbon and therefore its CO2 emissions are considered neutral."
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Approach
Martinez-Hernandez E, Campbell GM, Sadhukhan J. (2014)
Neutrality
Garba NA, Duckers U, Hall WJ. (2014) Neutrality
Downie A, Lau D, Cowie A, Munroe P. (2014)
Neutrality, Inputoutput
Yan X, Boies AM. (2013)
Neutrality
Weinberg J, Kaltschmitt M. (2013)
Neutrality
Patrizi N, Caro D, Pulselli FM, Bjerre AB, Neutrality Bastianoni S. (2013)
Martinez-Hernandez E, Ibrahim MH, Leach M, Sinclair P, Campbell GM, Sadhukhan J. (2013)
Neutrality
Biomass jatropha seeds
corn and soybean
wheat straw, animal manures, forestry residue wheat wheat and sugar beet wheat, barley and oat straw
wheat
Quotation/Remark
"CO2 emissions from the processing and end use (e.g. combustion) were considered as balanced as they originate from the carbon contained in Jatropha seeds."
"Biofuels are considered 'carbon neutral' because they are produced within the short-term carbon cycle, and their combustion only returns as much CO2 to the atmosphere as that is captured during plant growth.
biogenic method (input-output); stock method (neutrality); simplified method (neutrality)
"we assume complete combustion whereby the CO2 emitted is initially absorbedfrom the atmosphere during wheat growing."
not explicitly mentioned
"The combustion of bioethanol by transportation is considered "carbon neutral", since the combustion of biomass releases the same amount of CO2 as was captured by the straw during its growth."
"The biogenic carbon capture is not affected by these parameters and therefore CO2 binding and carbon emissions from end use ofproducts are not changed."
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Approach
Biomass
Hajjaji N, Pons M-N, Renaudin V, Houas Neutrality A. (2013)
wheat and cattle manure
Grau B, Bernat E, Rita P, Jordi-Roger R, Antoni R. (2013)
Neutrality
rapeseed
Eranki PL, Manowitz DH, Bals BD, Izaurralde RC, Kim S, Dale BE. (2013)
Cai H, Dunn JB, Wang ZC, Han JW, Wang MQ. (2013)
Neutrality
corn stover
Input-output for combustion of biomass and biofuel (not for CO2 emissions from fermentation)
sorghum
Han J, Elgowainy A, Dunn JB, Wang MQ. Input-output (2013)
corn stover and forest residue
Quotation/Remark
"The biological CH4 reforming systems contribute less to the global warming potential impact. CO2 emissions from biogenic sources (biomethane and bioethanol reforming processes) are not included in this paper."
"CO2 emissions for SVO (straight vegetable oil) have been considered null because they are compensated by the amount of this gas absorbed during the growth of the rapeseed plant (CO2 neutral balance)
not explicitly mentioned
"WTW GHG emissions are separated into WTP, PTW, and biogenic CO2 (i.e., carbon in bioethanol) emissions. Combustion emissions are the largest GHG emission source for allfuel pathways. However, in the bioethanol cases, the uptake
of CO2 during feedstock production almost entirely offsets ethanol combustion GHG emissions."
"The large observed reduction in WTW GHG emissions for all pyrolysis pathways are mainly due to the biogenic CO2 credit (CO2 absorbed during growth ofbiomass that is converted into fuel) that cancels out the GHG emissions from the vehicle's operation. Note that pyrolysis, stabilization and upgrading generate large biogenic carbon emissions (CO2, CO, VOC and CH4). These emissions are offset, however, by the uptake of atmospheric carbon during feedstock growth."
38
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Wang M, Han J, Dunn JB, Cai H, Elgowainy A. (2012)
Dunn JB, Mueller S, Wang M, Han J. (2012)
Roy P, Tokuyasu K, Orikasa T, Nakamura N, Shiina T. (2012)
Kumar D, Murthy GS. (2012)
Krohn BJ, Fripp M. (2012)
Approach
Biomass
Quotation/Remark
Input-output for combustion of biomass and biofuel (not for CO2 emissions from fermentation)
corn, sugarcane, corn stover, switchgrass and miscanthus
"...biogenic CO2 in ethanol offsets ethanol combustion GHG emissions almost entirely."
Input-output for combustion of biomass and biofuel (not for CO2 emissions from fermentation)
corn, corn stover and switchgrass
"...biogenic CO2 emissions from the cellulosic ethanol plant are not included."
Neutrality
corn stover
"Biomass combustions are assumed to be carbon neutral."
Neutrality
grass straw
"The CO2 released during ethanolfermentation and lignin burning was sequesteredfrom environment by photosynthesis process during grass straw production. Hence, CO2 emissions produced during fermentation process and lignin residue burning were not accounted into calculations."
Neutrality
soybean and canola
not explicitly mentioned
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ED_017426_00003026-00040
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Approach
Biomass
Eerhart AJJE, Faaij APC, Patel MK. Neutrality corn (2012)
Acquaye AA, Sherwen T, Genovese A, Kuylenstierna J, Koh SCL, McQueenMason S. (2012)
Input-output
rapeseed, corn, soybean, and sugarcane
Zamboni A, Murphy RJ, Woods J, Bezzo F, Shah N. (2011)
Neutrality
corn and soybean
Quotation/Remark
"When comparing PEF with PET, it is important to distinguish between fossil and biogenic GHG emissions. For petrochemical products, such as PET, the methodfor determining GHG emissions is broadly accepted. Accounting for CO2 emissions arising from biobased products is more complex as there are two concepts which can be considered, i.e. carbon neutrality or carbon storage***. However, these two methods yield the same result for the system cradle-to-grave which has been chosen in this paper; therefore, we do not discuss here possible further implications and instead refer the reader to Pawelzik and Patel."
"The carbon released through combustion of biofuels is biogenic CO2; this was captured in the process LCA ecoinvent data (39). It was calculated using the principle of carbon balance (input of carbon=output of carbon); that is, the uptake of carbon during plant growth plus all inputs of biogenic carbon with all pre-products minus biogenic carbon emissions should equal the biogenic carbon content of the biofuel or the product after all allocations have been done."
not explicitly mentioned
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ED_017426_00003026-00041
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Reinhard J, Zah R. (2011)
Approach Neutrality
Melamu R, von Blottnitz H. (2011)
Neutrality
Kauffman N, Hayes D, Brown R. (2011) Neutrality
Kaliyan N, Morey RV, Tiffany DG. (2011) Neutrality
Fazio S, Monti A. (2011)
Neutrality
CHERUBINI, F.; PETERS, G. P.; BERNTSEN, T.; STROMMAN, A. H.; HERTWICH, E., (2011)
Modified global warming potential
Biomass
Quotation/Remark
rapeseed
"We have not considered the biogenic CO2 uptake of the biofuels. Thus, we did not take account of its release but rather added the combustion of diesel in the baseline scenario in order to account for the full differences in the emissions of the analysed systems."
sugarcane bagasse
"... biogenic carbon dioxide emissions from burning bagasse are taken not to contribute to global warming."
"Given that bio-oil is composed of biogenic carbon,
corn
there are thus no GHG emissions associated with
hydroprocessing."
"Combustion emissions of CO2 are not includedfor corn biomass fuels because the CO2 released by biomass
fuel was removedfrom the atmosphere during photosynthesis."
miscanthus, giant reed, switchgrass, cynara, fibre sorghum , maize, wheat, rapeseed, and sunflower
"The amount of emitted CO2 during combustion of biomass crops was considered equal to that absorbed by crops through photosynthesis."
GWPb,O = 0 for annual crop
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Approach
Voet Evd, Lifset RJ, Luo L. (2010)
Input-output
Schumacher B, Oechsner H, Senn T, Jungbluth T. (2010)
Neutrality
Scacchi CCO, Gonzalez-Garcia S, Caserini S, Rigamonti L. (2010)
Neutrality
Kusiima JM, Powers SE. (2010)
Neutrality
Kaufman AS, Meier PJ, Sinistore JC, Reinemann DJ. (2010)
Neutrality
Biomass
Quotation/Remark
"In chains where coproducts are not important, exclusion of biogenic carbon generates the same results. However, Luo and colleagues show that, in cases of chains with coproducts, it does make a difference. Allocation may put the credits for extracted CO2 in a different part of the multiproduct chain than the debits for emitted CO2, while ignoring biogenic CO2 would not have this effect."
corn and triticale
not explicitly mentioned
wheat
corn, corn stover, switchgrass and forest residue
corn-grain and cornstover
"... the amount of carbon dioxide released in the combustion step is the same as the amount stored during the growing phase of the wheat. Therefore the carbon dioxide emissions counted come from the combustion of only the fossilfraction contained in the fuel."
"The CO2 released during lignin combustion is considered biogenic carbon that was sequestered during feedstock growth. This biogenic carbon is treated as an additional credit. Biogenic carbon credits could also be assignedfor the combustion of ethanol in an automobile."
"The CO2 released during stover combustion is negated by the CO2 captured during plant growth, resulting in no net CO2 impact."
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ED_017426_00003026-00043
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Approach
Iriarte A, Rieradevall J, Gabarrell X. (2010)
Neutrality
Gonzalez-Garcia S, Teresa Moreira M, Feijoo G. (2010).
Neutrality
Feng H, Rubin OD, Babcock BA. (2010) Neutrality
Biomass
rapeseed
alfalfa stems, flax shives, hemp hurds, poplar and ethiopian mustard corn
Quotation/Remark
"... The flows of CO2 associated with the capture of atmospheric carbon in photosynthesis during crop growth and its release by oxidation are considered neutral. As a result, these flows are not included in the analysis of greenhouse gases, in agreement with the standard approach related to the carbon cycle in agriculture ..."
"... the carbon released as CO2 from combustion and production of the fuel would be incorporated into the re-growth of the plant."
"The emissions from the burning of ethanol are cancelled by the absorption of carbon as corn grows and therefore are not considered."
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ED_017426_00003026-00044
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ED_017426_00003026-00045
SC_EVERSPLIT0001768