# Greenhouse Gas Impact of Algal Bio-Crude Production for a Range of CO2 Supply Scenarios
## 4 Conclusions  
Sourcing CO\({}_{2}\) from a biomass-based plant makes the bio-crude production process carbon negative. Delivery of CO\({}_{2}\) from an existing coal based plant (scenario 1) has a better GHG footprint (43 g CO\({}_{2}\) eq./MJ refined bio-crude) when compared to a purpose-built DAC system (49 g CO\({}_{2}\) eq./MJ refined bio-crude). This scenario, however, limits the choice of location to the vicinity of existing powerplants. Building a new natural gas-based plant (scenario 3) for supplying CO\({}_{2}\) to the biorefinery results in higher emissions compared to sourcing of CO\({}_{2}\) from existing fossil fuels plants and is not recommended. The greenhouse gas emissions are very sensitive to the grid electricity carbon footprint. A techno-economic analysis for the six scenarios would provide additional information on the trade-offs. This study highlights the importance of CO\({}_{2}\) sources for the sustainability of algal biorefineries.  
Figure 5: GHG emissions sensitivity analysis.  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/article/10.3390/app112411931/s1](https://www.mdpi.com/article/10.3390/app112411931/s1)]([https://www.mdpi.com/article/10.3390/app112411931/s1](https://www.mdpi.com/article/10.3390/app112411931/s1)). Figure S1: CO\({}_{2}\) from a coal-based power plant; Table S1: Mass balance: CO\({}_{2}\) from a coal-based power plant; Figure S2: CO\({}_{2}\) from a natural gas-based power plant; Table S2: Mass balance: CO\({}_{2}\) from a natural gas-based power plant; Figure S3: CO\({}_{2}\) from an NGCC unit with carbon capture and refrigeration; Table S3: Mass balance: CO\({}_{2}\) from an NGCC unit with carbon capture and refrigeration; Figure S4: CO\({}_{2}\) from a biomass combustion plant; Table S4: Mass balance: CO\({}_{2}\) from a biomass combustion plant; Figure S5: CO\({}_{2}\) from a biomass gasification plant; Table S5: Mass balance: CO\({}_{2}\) from a biomass gasification plant; Figure S6: CO\({}_{2}\) from DAC; Table S6: Mass balance: CO\({}_{2}\) from DAC.  
**Author Contributions:** Conceptualization, P.A., R.R.C., M.J.R., V.M.T. and Y.Y.; Investigation, P.A.; Methodology, H.H. and V.M.T.; Software, P.A. and Y.Y.; Writing--original draft, P.A.; Writing--review & editing, R.R.C., M.J.R., V.M.T. and Y.Y. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Bioenergy Technologies Office Award Number DE-EE0007690.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** A mass balance for all scenarios along with the assumptions undertaken are presented in the supplementary information.  
**Acknowledgments:** This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Bioenergy Technologies Office Award Number DE-EE0007690.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
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