Despite the allegations it has received over the years, the countless counterarguments have succeeded to clear Arundo’s name from the list of dangerous invasive species – thereby concluding the debate: is Arundo invasive? Whilst the official ruling on the giant reed by the Environmental Protection Agency dates back to 2013, it is yet to become public knowledge. Many still brand Arundo as an uncontrollable and useless perennial, and the US authorities’ judgement has not been popularised.
Is Arundo invasive? Purpose of the EPA’s action
In the final rule, EPA has permitted a pathway for production of renewable fuel from giant reed (Arundo donax) and napier grass (Pennisetum purpureum) as feedstock for the purposes of the RFS program – taking a positive standpoint on the Arundo invasive question. EPA has determined that renewable fuel made from napier grass and giant reed meet the lifecycle greenhouse gas (GHG) reduction requirements for cellulosic biofuel under the requirements of the RFS program.
EPA is also adopting additional registration, record-keeping, and reporting requirements to minimize the potential spread outside of the intended planting areas of giant reed or napier grass that was planted for the purpose of producing renewable fuels. These additional requirements are necessary to minimize the potential that the feedstock will spread to areas outside the intended planting area, which is the reason why many categorised Arundo invasive. Such unintended growth could result in additional GHG emissions from activities needed to control and remove the plants. Does the crop have aggressively growing rhizomes? Is Arundo invasive? The safety precautions have been done, however, Arundo is yet to be proved as an uncontrollably growing crop
Approving the new fuel pathways according to the provisions of this rule will provide biofuel producers opportunities to increase the volume of advanced, low-GHG cellulosic biofuels under the RFS program. EPA’s comprehensive lifecycle analyses in the January 5, 2012 proposal show significant lifecycle GHG emission reductions from fuels produced from giant reed and napier grass, as compared to the baseline (petroleum-based) gasoline or diesel fuel that they replace.
Feedstock production and distribution – impact of the Arundo invasive question
For the purposes of the rulemaking, Giant reed refers to the perennial grass Arundo donax of the Poaceae family. Giant reed thrives in subtropical and warm-temperate areas and is grown throughout Asia, southern Europe, Africa, the Middle East, and warmer U.S. states for multiple uses such as paper and pulp, musical instruments, rayon, particle boards, erosion control, and ornamental purposes. Based in part on discussions with industry, the EPA anticipated continued development of giant reed as an energy crop particularly in the Mediterranean region and warmer U.S. states.
For the purposes of analyzing the GHG emissions from giant reed and napier grass production, EPA examined crop yields and production inputs in relation to switchgrass to assess the relative GHG impacts. Current national yields for switchgrass are approximately 4.5 to 5 dry tons per acre. Giant reed field trials conducted in Alabama over a 9-year period showed an average yield of 15 dry tons per acre with no nitrogen fertilizer applied after the first year. Fertilized field trials have shown yields around 13 to 28 dry tons per acre in Spain, and 12 dry tons per acre in Italy (based on annual yields of 3, 14, 17, 16, and 12). High yields have been demonstrated with unimproved giant reed populations, and therefore there is potential for increased biomass productivity through improved growing methods and breeding efforts. Based on these yield assumptions, in areas with suitable growing conditions, giant reed would require less than 40% of the land area required by switchgrass to produce the same amount of biomass
Greenhouse Gas costs of various energy crops
EPA also assessed the GHG impacts associated with planting, harvesting, and transporting giant reed and napier grass feedstocks in comparison to switchgrass. Table 1 shows the assumed 2022 commercial-scale production inputs for switchgrass, average giant reed and napier grass production inputs (USDA projections and industry data) and the associated GHG emissions.
Applying the GHG emission factors used in the March 2010 RFS final rule, giant reed production results in slightly lower GHG emissions relative to switchgrass production (a decrease of approximately 2 kg CO2eq/mmbtu). Napier grass production results in slightly higher GHG emissions relative to switchgrass production (an increase of approximately 6 kg CO2 eq/mmbtu).
|Emission factors||Switchgrass||Giant Reed||Napier grass|
|Inputs (per dry ton of biomass)||Emissions (per mmBtu fuel)||Inputs (per dry ton of biomass)||Emissions (per mmBtu fuel)||Inputs (per dry ton of biomass)||Emissions (per mmBtu fuel)|
|Nitrogen Fertilizer||3,29 kgCO2e/ton of nitrogen||15.2 lbs||3.6 kgCO2 e||5 lbs||1 kgCO2 e||10 lbs||2.4 kgCO2e.|
|N2 O||N/A||N/A||7.6 kgCO2 e||N/A||4.8 kgCO2 e||N/A||7.6 kgCO2e.|
|Phosphorus Fertilizer||1,12 kgCO2e/ton of phosphate||6.1 lbs||0.5 kgCO2 e||7.4 lbs||0.6 kgCO2 e||1.1 lbs||0.1 kgCO2e.|
|Potassium Fertilizer||743 kgCO2e/ton of potassium||6.1 lbs||0.3 kgCO2 e||7.4 lbs||0.4 kgCO2 e||4.0 lbs||0.2 kgCO2e..|
|Herbicide||23,45 kgCO2e/tons of herbicide||0.002 lbs||0.003 kgCO2 e||0.02 lbs||0.03 kgCO2e||0.4 lbs||0.6 kgCO2e.|
|Insecticide (average across regions)||27,22 kgCO2e/tons of pesticide||0.025 lbs||0.04 kgCO2e||0 lbs||0 kgCO2 e||0 lbs||0 kgCO2 e.|
|Lime||408 kgCO2e/ton of lime||0 lbs||0 kgCO2 e||0 lbs||0 kgCO2 e||100 lbs||2.9 kgCO2e.|
|Diesel||97 kgCO2e/mmBtu diesel||0.4 gal||0.8 kgCO2 e||1.4 gal||2.5 kgCO2 e||1.3 gal||2.2 kgCO2e.|
|Electricity (irrigation)||220 kgCO2e/mmBtu||0 kWh||0 kgCO2 e||10 kWh||1 kgCO2 e||25 kWh||2.7 kgCO2e.|
|Total Emissions||13 kgCO2e/mmBtu||11 kgCO2e/mmBtu||19 kgCO2e/mmBtu.|
|Assumes 2022 switchgrass yield of 6.59 dry tons/acre and 92.3 gal ethanol/dry ton, 2022 giant reed yield of 18 dry tons/acre and 92.3 gal ethanol/dry ton, and 2022 napier grass yield of 20 dry tons/acre and 92.3 gal ethanol/dry ton.|
Fuel production and use
Giant reed and napier grass are suitable for the same conversion processes as other cellulosic feedstocks, such as switchgrass and corn stover. Currently available information on giant reed and napier grass composition shows that their hemicellulose, cellulose, and lignin content are comparable to other crops that qualify under the RFS regulations as feedstocks for the production of cellulosic biofuels. Based on this similar composition as well as conversion yield data provided by industry, the same production processes that were modeled for switchgrass in the March 2010 RFS final rule were applied (biochemical ethanol, thermochemical ethanol, and Fischer-Tropsch (F-T) diesel) to giant reed and napier grass.
The EPA assumed the GHG emissions associated with producing biofuels from giant reed and napier grass are similar to what we estimated for switchgrass and other cellulosic feedstocks. EPA also assumed that the distribution and use of biofuel made from giant reed and napier grass will not differ significantly from similar biofuel produced from other cellulosic sources.
Summary: is Arundo invasive?
Based on our comparison of switchgrass and the two feedstocks considered, EPA believes that cellulosic biofuel produced from the cellulose, hemicellulose and lignin portions of giant reed and napier grass has similar or better lifecycle GHG impacts than biofuel produced from the cellulosic biomass from switchgrass. The analysis suggests that the two feedstocks considered have GHG impacts associated with growing and harvesting the feedstock that are similar to switchgrass.
Emissions from growing and harvesting giant reed are approximately 2 kg CO2eq/mmBtu lower than switchgrass, and emissions from growing and harvesting napier grass are approximately 6 kg CO2eq/mmBtu higher than switchgrass. These are small changes in the overall lifecycle, representing at most a 6% change in the energy grass lifecycle impacts in comparison to the petroleum fuel baseline. Furthermore, the two feedstocks considered are expected to have similar or lower GHG emissions than switchgrass associated with other components of the biofuel lifecycle.
Regarding the question of invasiveness, the EPA is requiring that registration for producers of renewable fuel made from giant reed or napier grass would include submission by the renewable fuel producer of a Risk Mitigation Plan (RMP) that demonstrates measures are being taken to prevent the spread of these species such that the production of giant reed or napier grass will not pose a significant likelihood of spread beyond the planting area designated in the plan for the feedstock used for production of the renewable fuel.
Alternatively, the fuel producer could demonstrate that an RMP is not needed because under the circumstances giant reed or napier grass does not pose a significant likelihood of spread beyond the planting area. By requiring the fuel producer to demonstrate no significant likelihood of spread beyond the planting area EPA believes that the approval of pathways to produce renewable fuel from giant reed or napier grass is not likely to cause or promote the introduction or spread of invasive species in the United States or elsewhere.
For more information on Arundo and how it can be utilised for bioethanol, visit our website at: www.arundobioenergy.com/bioethanol.
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