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The PACE (Producing Algae for Co-Products and Energy) consortium was comprised of scientists from national laboratories (Los Alamos National Laboratory, Pacific Northwest National Laboratory), research institutions (New Mexico Consortium), academic institutions (Arizona State University, Colorado School of Mines, Colorado State University, Washington State University) and private companies (Reliance Industries, PanPacific, Genifuel and Sonosop) dedicated to making process improvements in algal biotechnology, with an emphasis on renewable fuels and co-products from biomass. The scope of work was focused on improving algal cultivation and processing to achieve an overall energy return on investment (EROI) >
3, a carbon index less than 55 grams carbon dioxide per megajoule (gCO2/MJ) and a nearly two-fold reduction in fuel cost to ?$5 per gallon of gasoline equivalent (gge). <
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The PACE project was originally focused on using two strains of Chlorella sorokiniana (Cs1412 and Cs1230), but later grew to encompass marine strains of Nannochloropsis and algal production strains from Reliance Industries Limited (RIL). A major emphasis of the project involved using genetic engineering to improve biomass yields, facilitate crop protection and enable co-product synthesis. Several notable successes in strain engineering were realized including: i) overexpression of a sugar signaling pathway regulator SnRK (Snf1-Related protein Kinase) in Chlorella sorokiniana that resulted in increased biomass and carbohydrate content, particularly when running simulated fall scripts in the laboratory
ii) the overexpression of a cyanobacterial fusion protein (fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase) that increased overall biomass accumulation of Nannochloropsis gaditana cultures in laboratory cultures, putatively by accelerating rate-limiting reactions in the Calvin cycle
iii) the expression of phosphite oxidase in Chlorella sorokiniana, which enabled this alga to use phosphite (instead of phosphate) as its sole P source, providing a novel crop protection strategy
and iv) the develop of genetically modified Chlorella sorokiniana capable of biosynthesizing phenylethanol (PEA) and/or phenylethanol glucoside (PEA-Glc) as value-added co-product(s), which were successfully attained by expressing three targets, phenylacetaldehyde synthase, phenylacetaldehyde reductase and, in some cases, UDP-glucosyltransferase. To test genetically modified (GM) algae outdoors, the PACE team in collaboration with Arizona State University pioneered establishing the process for gaining approval from the Environmental Protection Agency for TSCA Environmental Release Application (TERA) for the open release of GM algae field-trials and tested an SnRK overexpression cell line outdoors. <
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The PACE team was given access to the world-class algal culturing facilities at Reliance Industries (RIL) in Gagva, India. Critical insights were provided into the productivities and process inputs that allowed this facility to attain seasonal average productivities of ~23 g/m2/d during the PACE project. This automated facility is capable of rapid strain screening, media optimization, harvesting and conversion to algal oil. Operational details from this facility were used for some aspects of the TEA/LCA analyses. RIL also provided the PACE team with 20 liters of algal oil from hydrothermal processing (HTP) that was upgraded to a diesel blend for engine testing. A two-stage HTP system was established that allowed the carbohydrate stream to be removed from algal biomass for co-product isolation and processing. The remaining biomass was then treated in a second HTP step that resulted in high-quality biocrude. Importantly, we demonstrated that undistilled, hydrotreated HTP fuel produced from algal biomass can be blended at levels of up to 5% with petroleum fuel without negatively affecting emissions and performance in a modern compression ignition engine.<
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Using productivities attained from the RIL facility and modeling co-product production, Table 1 summarizes the LCA/TEA results against the PACE key targets for the PACE process used to produce biofuels and co-products, in this case, PEA and xanthan gum.<
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Table 1. LCA/TEA (SOPO 2018) results against PACE key targets.<
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PACE target<
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Biocrude No offset $/gge<
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Biocrude With offset <
$5/gge<
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EROI (biogas internal use) >
3<
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gCO2/MJ biooil <
55<
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TEA/LCA Results<
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6.81<
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4.79<
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2.9<
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59.95<
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These LCA/TEA results show that the biocrude cost with no offset is $\$6.81/gge$ and with offset is reduced to $\$4.79/gge$. The EROI and carbon utilization goals fall just short of the targets. Continued improvements in productivity should not only reduce biocrude costs, but also enable higher co-product offsets against biocrude. The overall results for the co-product evaluation show the need for further investigations to identify suitable co-products for the specific process designs. They also highlight the need to optimize energy use in co-product extraction processes to improve outcomes for the EROI and carbon index.<
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Significant lessons learned included: i) the importance of thoroughly testing and establishing the ability of algal species selected for study to compete and thrive in outdoor culturing testbeds, many highly promising laboratory strains are simply not competitive in outdoor scale-up testing
and ii) algal strain engineering can be a complex process that requires careful and highly reproducible protocols for the successful transfer of methodologies to new laboratories and ?research hands?. In summary, the PACE project was able to i) advance genetic engineering approaches in algae to enable biomass improvements, potential crop protection, and co-product accumulation, ii) demonstrate a two-stage HTP prototype for carbohydrate removal, and co-product isolation in the first phase, followed by transformation of the remaining solids to high-quality biocrude in the second phase, iii) hydrotreat biocrude that could be effectively blended with petroleum diesel without prior fractionation, and iv) provide a roadmap toward less expensive and more efficient renewable fuels and co-products from algal biomass.<
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