Proposal for a Conceptual Biorefinery for the Conversion of Waste into Biocrude, H2 and Electricity Based on Hydrothermal Co-Liquefaction and Bioelectrochemical Systems
, Gisella Lamas-Samanamud 3 and Mateus de Souza Amaral 1,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors,
I have reviewed the manuscript "Proposal for a Conceptual Biorefinery for the Conversion of Waste Into Biocrude, H2 and Electricity Based on Hydrothermal Co-Liquefaction and Bioelectrochemical Systems" submitted to Fermentation Journal. In this article, the authors discuss an important issue regarding the potential for energy generation from solid waste commonly generated in emerging countries such as Brazil, based on a simplified schematic of a conceptual biorefinery using algal biomass co-HTL along with sugarcane bagasse, malt bagasse and sewage sludge. The review article discusses the most important issues regarding the co-HTL process.
However, I have a few comments that should be improved.
2. Consume and Energy Demand
Line 70-71. Please update the information regarding the population on earth. The year is 2024.
Line 104. Please write how much the concentration of CO2 in the atmosphere is now.
4. Sugarcane Bagasse
Line 194. Should be metric ton or Mg . Please correct.
Line 204. It would be better to write 68.8 Mg/ha.
5. Malt Bagasse
Line 219. It should be "ton". Correct throughout the text.
Line 222. It should be 3.74 Mg/ha.
9. Hydrothermal Co-Liquefaction Process and Biocrude as Product
Line 365. It should be "5-28 MPa". Please provide examples of catalysts used in the HTL process.
Author Response
Comment 1:
Line 70-71. Please update the information regarding the population on earth. The year is 2024.
Response 1: Thank you for pointing this out. The information was updated in line 70 – 71 “In 2024, the global population estimation is 8 billion people with the prospect of reaching the mark of 9.6 billion in 2050 (UN, 2022).”
Comment 2
Line 104. Please write how much the concentration of CO2 in the atmosphere is now.
Response 2: Thank you for pointing this out. The information was updated in line 105 “In 2024 CO2 concentration achieved 425.39 ppm (GML, 2024)”
Comment 3
Line 194. Should be metric ton or Mg . Please correct.
Response 3: Thank you for observation. The correction has been made in line 195. “36 million metric ton”
Comment 4.
Line 204. It would be better to write 68.8 Mg/ha.
Response 4: Thank you for observation. The correction has been made in line 205. “of 68.8 Mg/há”
Comment 5
Line 219. It should be "ton". Correct throughout the text.
Response 5: Thank you for observation. The correction has been made throughout the text
Comment 6
Line 222. It should be 3.74 Mg/ha.
Response 6: Thank you for observation. The correction has been made in line 224. “3,74 Mg/há”
Comment 7
Line 365. It should be "5-28 MPa". Please provide examples of catalysts used in the HTL process.
Response 7: Thank you for pointing this out. The revision has been made in line 367 “5-28 MPa with or without added catalyst (e.g. Fe, Zn, Pt/Al, Na2CO3, K2CO3)”
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper aims to present the potential for generating energy from solid waste commonly generated in emerging countries such as Brazil based on a simplified scheme of a conceptual biorefinery employing algal biomass co-HTL together with sugarcane bagasse, malt bagasse and sludge. But there are some comments should be addressed before publication.
1. The work comprehensively analyzes global energy consumption, proposes that biomass energy is an effective solution to environmental problems, and analyzes in detail the residual amounts of sugarcane bagasse, malt residue, and sewage sludge algae. However, the paragraphs are a bit confusing. For example, discussing the biological structure of lignocellulose separately is not conducive to logical clarity. It is recommended to combine it with sugarcane bagasse and malt residue.
2. The more details about the pictures and tables should be discussed.
3. This work focuses on biomass energy. It is not appropriate to simply focus on microbial batteries in the end. It is better to have a more macro perspective.
Comments on the Quality of English Language
Minor editing of English language required
Author Response
Comment 1
- The work comprehensively analyzes global energy consumption, proposes that biomass energy is an effective solution to environmental problems, and analyzes in detail the residual amounts of sugarcane bagasse, malt residue, and sewage sludge algae. However, the paragraphs are a bit confusing. For example, discussing the biological structure of lignocellulose separately is not conducive to logical clarity. It is recommended to combine it with sugarcane bagasse and malt residue.
Response 1: Thank you for pointing this out. The sugarcane and malt bagasse topics were combined and the lignocelluloses structure topic was incorporated (lines 187 – 258)
Comment 2
- The more details about the pictures and tables should be discussed.
Response 2: Thank you for pointing this out.
More details have been made in:
lines 287 – 292 (regarding table 1) “These information are relevant to this area of study because these factors can signifi-cantly affect HTL products. To illustrate: the feedstock characterization shown in Table 1 reveals high nitrogen content, which leads to the necessity of understanding nitrogen compounds distribution in HTL products. In this context, the presence of nitrogen heavily impacts the upgrading of biocrude products and the safe disposal of the aqueous phase (RAHMAN et al., 2021).”
Lines 342 – 345 (regarding table 2) “These information show that significant portions of algal biomass are carbohydrate and protein, which means that if utilized as added value products after reactive extraction, it could improve the process's economy (SALAM; VELASQUEZ-ORTA; HARVEY, 2016).”
Lines 575 – 579 “As shown in Figure 2, a MFC general structure comprises two compartments: the first one is and houses an anode; the second one is aerobic and contains a cathode. These electrodes are internally separated by a barrier that prevents the diffusion of oxygen gas (O2) from the cathodic chamber to the anodic one, but they are externally connected by an electrical circuit (RAHIMNEJAD et al., 2015).”
Comment 3
- This work focuses on biomass energy. It is not appropriate to simply focus on microbial batteries in the end. It is better to have a more macro perspective.
Response 3: Thank you for pointing this out. In this sense was created a new topic "9. Challenges and prospects in HTL-AP valorization technologies" (lines 576 – 617) “9. Challenges and prospects in HTL-AP valorization technologies
After analyzing various HTL-AP valorization methods, a comprehensive and macro-scopic overview can be constructed regarding the challenges and prospects associated with technologies for valorizing HTL-AP. In the realm of obtaining value-added chemi-cals from HTL-AP, a promising approach emerges. Methodologies yielding favorable re-sults include the separation and concentration of chemicals from HTL-AP via nanofiltra-tion and resin utilization. These methods exhibit potential for commercializing solvents, acids, and other chemicals. However, current research remains confined to simplified chemical compositions of HTL-AP, necessitating further exploration into applications in-volving HTL-AP with more complex compositions. Additionally, there is potential in inte-grating separation and biological conversion techniques, as organic residues produced post-separation could serve as feedstock for subsequent biological processes (LYU et al., 2015; WATSON et al., 2020).
Biomass cultivation using HTL-AP as a growth medium demonstrates effective nu-trient recovery and economic viability for fertilizer production. Still, challenges persist with high-organic-content HTL-AP, including inhibition and inefficient organic com-pound utilization. Besides, commercializing biomass produced via this method faces ob-stacles such as environmental risks from heavy metal accumulation and substantial land area requirements for cultivation (SWETHA et al., 2021). Bioelectrochemical systems offer various advantages, such as conversion of recalcitrant compounds (phenols, furan deriva-tives, and nitrogen heterocycles) and production of energy, gas, and electricity. However, there are still some limitations that must be overcome to enable their large-scale commer-cial application with economic and sustainable viability. Among the necessary advance-ments are reducing startup time, optimizing electrode materials, progressing in process scaling, and developing lower-cost proton exchange membranes (WANG et al., 2021; WATSON et al., 2020).
Recycling HTL-AP represents a promising strategy to increase biocrude oil yield while recovering energy. It is straightforward to implement, cost-effective, and requires minimal scaling effort. However, this approach may exacerbate AP toxicity and complicate the disposal of resultant waste. To mitigate these challenges, integrating this technique with complementary valorization methods presents a viable alternative. Anaerobic fer-mentation of HTL-AP is already considered a mature and well-developed technology with potential for commercial application. However, pre-treatment of HTL-AP, enrichment of functional microbes, and bio-augmentation need to be emphasized to enhance the HTL-AP anaerobic fermentation. Additionally, this method requires residual effluent to be treated using other valorization approaches. At last, the gasification approach presents the ad-vantage of being readily integrated into an HTL biorefinery to enhance the commercial po-tential of biocrude oil production technology. However, it comes with high energy and fi-nancial demands and needs to address challenges such as low efficiency and yields before it can be considered a conventional treatment technique for HTL-AP (SWETHA et al., 2021; WANG et al., 2021).”
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe issues have been modified in the revised manuscript. I recommend to publish this work.
