The Role of Biorefinery Co-Products, Market Proximity and Feedstock Environmental Footprint in Meeting Biofuel Policy Goals for Winter Barley-to-Ethanol

Round 1

Reviewer 1 Report

The study The importance of biorefinery location and co-products in meeting biofuel policy goals: a case study of winter barley presents the life cycle of winter barley-to-ethanol.

Positive elements of the study is that it is well written, the methodology is proven and the results are well justified.

There are though topics that needs to be improved, which are the following:

1. The title of the study is not in line with its content. There is actually not location allocation analysis in the study (see for example Biomass and Bioenergy, 84, 107-117).
2. The boundaries of the assessment is not clear, as well as the input of the inventory, especially for those parameters which are related to the energy production - the authors need to clarify.
3. The study is not a comprehensive LCA study, in accordance to ISO 14040, as the only indicator provided in the results of the study are the GHG emissions.

The authors should either revise their study based on the above comments in order to comply with its actual content.

Author Response

Reviewer 1

The study The importance of biorefinery location and co-products in meeting biofuel policy goals: a case study of winter barley presents the life cycle of winter barley-to-ethanol. Positive elements of the study is that it is well written, the methodology is proven and the results are well justified.

There are though topics that needs to be improved, which are the following:

1. The title of the study is not in line with its content. There is actually not location allocation analysis in the study (see for example Biomass and Bioenergy, 84, 107-117).

Response: The reviewers raise an important point, our finding refers not to biorefinery location but to the environmental profile of feedstock and the importance of proximity to end use markets for products and co-products, but the previous title suggests investigation of logistics. We have revised the title as follows:

The role of biorefinery co-products, market proximity and feedstock environmental footprint in meeting biofuel policy goals for winter barley-to-ethanol.

 

Also in response to Reviewer 3, we added further literature review on studies that focus on supply chains and logistics and our specific objective that examines proximity to end-use markets. See lines: 110-112.

 

2. The boundaries of the assessment is not clear, as well as the input of the inventory, especially for those parameters which are related to the energy production – the authors need to clarify.

 

Response: We have revised the Methods to more clearly articulate direct inputs that were used in the life cycle inventory. Table 1 defines the co-product scenarios in which system expansion was used to credit the life cycle of the barley-to-ethanol pathway. Scenario WB1 includes the greatest number of co-product credits, with the co-production of captured fermentative CO2 to be sold to the beverage industry and scenario WB4 has no credits applied. Table 2 shows the cradle-to-gate inputs to the biorefinery for the scenarios tested. In our previous submission, we neglected to show the electricity requirement for CO2 capture, so we have revised this important input of 3 kWh/MJ ethanol produced, where this input is only applied in scenario WB1.

In the revised Table 2, we have clarified the co-products considered in the analysis and list them as barley hulls for displacement of coal and on-site steam that would be produced from natural gas; barley protein meal, and fermentative CO₂. We have also modified the system boundary diagram (Figure 2) to show that barley hull residues are used to displace coal and on-site steam.

3. The study is not a comprehensive LCA study, in accordance to ISO 14040, as the only indicator provided in the results of the study are the GHG emissions. The authors should either revise their study based on the above comments in order to comply with its actual content.

Response: The reviewer is correct that we do not present a complete LCIA that evaluates multiple metrics; however, our goal is to examine the environmental performance of winter barley-to-ethanol using life cycle GHG emissions under uncertainty (through Monte Carlo methods) to evaluate compliance with the U.S. Renewable Fuel Standard (RFS2) for winter barley in a specific geographic region of the U.S. An important objective of the paper for understanding advanced fuel policy compliance is comparing the indirect land use change (ILUC) findings reported by the US EPA for winter barley and for ethanol produced from other small grains (feedstocks other than corn) that meet a 50% GWP reduction relative to the gasoline baseline with consideration of uncertain parameter inputs. Thus, we included discussion of our winter barley work with US EPA’s analysis of both barley and grain sorghum. See objectives statement, lines 113-116.

To clarify our rationale for not completing a full LCIA with multiple midpoint metrics, we have carefully edited the objectives of the research in the Introduction and Methods to be clear about the global warming potential (GWP) focus under uncertainty. In addition, in response to Reviewer 3’s comments, we include the cumulative energy demand (CED), but present the result in the Supporting Information file. See lines 120-124.

We agree with the reviewer that it is important to evaluate multiple LCIA metrics, but because of the reasons noted above, we limited our analysis to only GWP and CED. However, we discuss additional follow-up research in the Conclusion on winter crops that would be valuable for calculating site-specific eutrophication potential due to changes in N-fertilizer runoff if winter crops like barley are introduced to agricultural regions for biofuel production. See lines 425-428.

Reviewer 2 Report

Research is very well written.

The most interesting thing is you addressed the importance of having co-products in bio-refineries. w/o co-production bio-based sector is not yet competitive at all.

I have no particular comments just the manuscript seems too long: reading the whole text could be not so easy. Think about reducing it, by moving some parts in ESI.

Publication is recommended.

 

Author Response

Reviewer 2

Research is very well written.

The most interesting thing is you addressed the importance of having co-products in bio-refineries. w/o co-production bio-based sector is not yet competitive at all.

I have no particular comments just the manuscript seems too long: reading the whole text could be not so easy. Think about reducing it, by moving some parts in ESI.

Publication is recommended.

Response: We thank the reviewer for the feedback on our research. We have edited the paper further, aiming to reduce any redundancies and shorten the paper while also addressing all reviewer comments. In addressing the comments of Reviewers 1 and 3 to add more discussion of LCIA metrics, we have included the cumulative energy demand (CED) metric but include the table for this in the supporting information (SI) file.  

Overall, with edits to the manuscript, the manuscript text has been shortened to under 6000 words and remains at 12 pages with approximately 4 pages of references.

Reviewer 3 Report

The manuscript analyses the performances in terms of GHG emissions of using winter barley for the production of ethanol, to meet US law targets, using LCA approach. The methodology seems correct and the work has important applications on energy planning and agricultural management of the area. Overall, my opinion is positive.   

I have few comments that could improve the paper:

• The addition of a Cumulative Energy Analysis could certainly provide additional and valuable insights to the analysis. This is particularly relevant when comparing renewable vs. non-renewable sources and/or different scenarios (e.g. Gaglio et al. 2019 Resources, 8(2), 60)
• The spatial location of biorefineries is a fundamental issue for the sustainability of ethanol (and bioenergies in general) supply chain. This argument deserves to be discussed more in deep. I suggest for example: Young, et al (2011) BioResources, 6(1), 329-343. Longato et al 2019 Journal of Cleaner Production, 237, 117672.
• Did you consider allocation for co-products? if not, you need to justify it
• Did you consider any specific range of uncertainties in the montecarlo analysis? please, specify

Author Response

Reviewer 3

The manuscript analyses the performances in terms of GHG emissions of using winter barley for the production of ethanol, to meet US law targets, using LCA approach. The methodology seems correct and the work has important applications on energy planning and agricultural management of the area. Overall, my opinion is positive.  

I have few comments that could improve the paper:

The addition of a Cumulative Energy Analysis could certainly provide additional and valuable insights to the analysis. This is particularly relevant when comparing renewable vs. non-renewable sources and/or different scenarios (e.g. Gaglio et al. 2019 Resources, 8(2), 60)

Response: The reviewer raises an important point. We have added cumulative energy demand (CED), also in response to Reviewer 1’s comment, and include the following passage in the Methods as rationale for its inclusion, lines 124-124:

We focus on two LCIA metrics, the 100-year global warming potential (GWP) to examine RFS2 policy compliance and cumulative energy demand (CED), a metric that measures renewable and non-renewable energy inputs in a product life cycle and is relevant to evaluating proposed renewable fuel pathways as studied in prior bioenergy systems [38].

The spatial location of biorefineries is a fundamental issue for the sustainability of ethanol (and bioenergies in general) supply chain. This argument deserves to be discussed more in deep. I suggest for example: Young, et al (2011) BioResources, 6(1), 329-343. Longato et al 2019 Journal of Cleaner Production, 237, 117672.

Response: The reviewer raises an important point about geography in relation to the sustainability of biofuel supply chains. In responding also to Reviewer 1’s comments about location, we have edited the text to be more explicit that our analysis targets proximity to market for value-added co-products like fermentative CO₂ captured for the soft drink industry. We added discussion on the importance of prior work on feedstock logistics and supply chains in the Introduction and add that our study investigates the role of products and co-products in relation to end-use markets. See lines 110-112.

Did you consider allocation for co-products? if not, you need to justify it

Response: Our analysis applied system expansion described in ISO (2006), where credits for displacing products were assigned to the ethanol pathway. We describe the co-product allocation scenarios in Table 1 and show co-product credits for GHG emissions in Table 2 and Table S1 (CED) in the SI. We explain that we test certain scenarios where co-product credits are not included to see their effect on uncertainty. Description of the scenarios is on lines 255-256 and 263-267.

Did you consider any specific range of uncertainties in the montecarlo analysis? please, specify

 

Response: The Monte Carlo simulation focused on parametric uncertainty in geographically weighted soil N₂O emissions and change in soil organic carbon (SOC) from DayCent simulations for all of the counties included in the study (Figure 1).

Round 2

Reviewer 1 Report

Paper can be accepted

Author Response

Response: We thank the reviewer for positive feedback on our revised manuscript.

Reviewer 3 Report

The autors addressed all the the previous comments and the analysis was improved. I have only one more observation to arise: The results of CED should be discussed more in detail, which implications for the results? and how they can be justified?

This needs to be implemented in the text.

 

Author Response

Reviewer comment:

The autors addressed all the the previous comments and the analysis was improved. I have only one more observation to arise: The results of CED should be discussed more in detail, which implications for the results? and how they can be justified?

This needs to be implemented in the text.

 

Response: In our previous submission we neglected to note that we added results of the cumulative energy demand (CED) from fossil energy sources for all co-product scenarios and include a new table in the supporting information (SI Table S1) that summarizes fossil energy CED for the four alternatives. We have expanded discussion of the CED metric on lines 318-329, which we also copy below. Please see also the attached revised supporting information file with CED results in Table S1. We believe that we have now addressed the reviewer's comments.

The CED fossil energy metric (SI Table S1) follows a similar pattern for all winter barley scenarios in that the case with fermentative CO₂ capture (WB1) and full co-product crediting for displacing fossil energy with energy recovery from combusted barley hulls yields requires the least fossil energy input per unit of ethanol produced, 0.55  MJ MJ^-1. Moreover, the scenario without fermentative CO₂ capture but with energy recovery from barley hulls, (WB2), also requires less fossil energy input relative to each unit of ethanol produced 0.71 MJ MJ^-1. Scenarios WB3, with only crediting of barley protein meal (1.05 MJ MJ^-1), and WB4, with no co-product crediting (1.18 MJ MJ^-1), with the WB4 scenario approaching the fossil energy well-to-wheel performance of gasoline, 1.2 ± 0.1 MJ MJ^-1 [59]. This finding underscores the importance of co-products as noted in prior biofuel LCA studies [60] in reducing the environmental and resource demand impacts of biorefineries and it further demonstrates the importance of market proximity for the case of fermentative CO₂ capture.

Author Response File: Author Response.docx