Enhancing Thermophilic High-Solid Anaerobic Digestion of Swine Manure Using Ammonia-Stripped Biogas Slurry Reflux Amended with Waste Iron Powder and Biochar
Waris Khan
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
Overall Impression
This study addresses biogas sludge recycling, a significant waste management issue in large-scale biogas plants. The authors investigate the inhibitory effects of ammonia-stripped biogas sludge (ASBS) on the anaerobic digestion (AD) of high-solids pig manure and evaluate the use of waste iron powder (WIP) and rice husk biochar (RHB) to mitigate this inhibition. The study is valuable for focusing on a practical problem, evaluating waste materials as additives, and presenting comprehensive experimental analyses (SEM, FTIR). However, the article needs improvements in clarity, data presentation, and interpretation of some results.
Weaknesses and Areas for Improvement
Language and Expression: While the article's English is understandable, some sentences lack fluency and contain minor grammatical errors. Professional editing would significantly improve the quality of the article.
Example: "This finding allows us to combine WIP and RHB as composite additives which cannot only mitigate AD inhibition, but also improve soil quality." (The "cannot" in this sentence is likely an incorrect use of the construction "can not only" or "not only... but also").
Presentation of Statistical Analysis: Results are presented as "mean ± standard deviation" and indicate that ANOVA was used. However, it is important to indicate statistically significant differences (p<0.05) more clearly in figures and tables (e.g., with different letter notations) to facilitate comparisons for the reader.
Deepening the Discussion on Free Ammonia (FAN): The study shows that the addition of WIP and RHB significantly increases FAN concentration by increasing pH (Figure 5). This is a significant finding. The authors should further discuss why no inhibition of methanogenesis was observed despite this increase (perhaps due to adaptation in the microbial community or other positive effects prevailing). A comment should be added regarding whether this poses a risk in long-term, continuous reactor operation.
Figure and Table Quality:
Figures 1, 2, and 3 are followed by Figure 1 again. This should be Figure 4.
The title and axis labels of Figure 4 are unclear. It should be more clearly stated which panels (a, b, c, d) represent what.
The bar chart for panel (c) (TS degradation rate) in Figure 6 lacks statistical significance indicators.
The abbreviations in Table 3 (MBY, MBP, MMP) should be clearly defined immediately below the table or in a footnote.
The scientific content, methodology, and findings of the study are above acceptable levels, considering the Processes journal's impact factor of 2.8, and constitute a valuable contribution to the literature. However, addressing the points detailed above, such as improving language quality, clarifying statistical presentation, more in-depth discussion of critical findings such as increased FAN, and improving figures/graphics, would significantly enhance the scientific impact and readability of the article. Once these changes are made, the article will be eligible for acceptance.
Minor Recommendations to Authors (For Revision)
The entire article should be reviewed for grammar, spelling, and fluency by a native English speaker or a professional language editor.
In all figures and tables, statistically significant differences (p < 0.05) should be indicated with appropriate notations (e.g., letters a, b, c).
The Results and Discussion section should provide a more comprehensive discussion of why no inhibition was observed despite WIP and RHB supplementation increasing FAN concentrations, and the potential risks of this situation.
The axis labels and legends of Figures 4 and 6 should be clarified.
The abbreviations for all abbreviations in Table 3 should be added below the table.
A revision based on these suggestions will enhance the scientific quality and communicative power of the article.
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsManuscript entitled “Enhancing Thermophilic High-Solid Anaerobic Digestion of Swine Manure Using Ammonia-Stripped Biogas Slurry Reflux Amended with Waste Iron Powder and Biochar” mainly investigates recycling effect of slurry amended with WIP and RHB.
The manuscript presents valuable findings, however there is some major problems that need to be addressed.
- Methane yield is one of the major results for AD systems please provide cum CH4 graph (and discussion) . daily and cumulative combined graph can be more illustrative.
- Please combine fig 1 a and b, add error bars to fig 1 b
- L310 is there any mechanism like adsorption?
- L321 that would be Figure 4. Please indicate that with bar graph.
- Please make sure that all values are consistent L27-L254 L423
- L282 Combining the WIP and RHB stated as highest production, however, sole WIP addition seems to have a higher production rate (fig 3.) please clarify.
- The central premise is to "mitigate the inhibition that arises when biogas slurry is recycled", which is strongly implied to be ammonia-related. However, the data in Section 3.3.2 and Figure 5 show that while TAN is reduced, the pH increases, leading to a significant increase in toxic Free Ammonia (FAN) concentration. Please deeply discuss this phenomena.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
Comments and Suggestions for AuthorsThe article “Enhancing Thermophilic High-Solid Anaerobic Digestion of Swine Manure Using Ammonia-Stripped Biogas Slurry Reflux Amended with Waste Iron Powder and Biochar” addresses an interesting strategy for improving AD performance by mitigating ammonia toxicity in ASBS via biochar and iron. However, there are several areas that require revisions, once the below points are addressed, the manuscript should be suitable for acceptance.
Line 24: The terms “RBS “and “C0” please clearfiy their meaning upon first use.
Line 27: “C1” also without explanation, define all abbreviation upon first use.
Line 29: “TAN” also not defined
Line 33: The phrase “mitigate the inhibition” is general. Specify the particular inhibition that could be mitigated.
Line 42: “slurry.[3].” Correct it and also review the entire manuscript for such errors, like consistent lack of spaces before reference number at sentence end.
Line 108: “iron pow-107 der(WIP)” correct the spacing, there are several typo mistakes, a thorough proofreading is needed.
The objectives of this work are not clearly stated, please clearly describe the research objective in introduction.
Line 111-112: The statement “The results of this research will give an important reference to the sus-111 tainable development of large-scale biogas plants.” is too general, make this more specific relating the contribution of your findings.
Line 193: Reference insertion spacing issue
Line 117: Specify the type of air used (is it ambient air or specific gas mixture)
Table 1. for VS%, TS%, and pH, consider appropriate number of significant digits.
Line 131-132 The manuscript mentioned that WIP and RHB were exposed to UV light, please explain the purpose of this treatment with reference and also discuss the potential effect of UV exposure effect on organic matter composition in the sample.
Line 136: indicate whether “water” refer to tap, distilled, or DI water ?
Line 141; please justify the selection of 3 to 9 g/L concentrations for RHB and WIP.
Line 188, 189, 190: Values such as 230.2, 222.9, 212.9 ml/g-VSS, should be round to appropriate significant digits for consistency. Like also consider revising other values e.g., 1,653.10 mg/L and 1,126.75 mg/L in line 203, the pH values, line 219 28.24% and so on. Unless such precision is scientifically necessary, I recommend round values accordingly throughout the manuscript.
195; The term “certain inhibitory” is vahue. please described the specific mechanism involved.
Figure 1: correct the Y-axis title spacing.
Figure 1c and Figure 2. The Y-axis lable units should be given in parentheses (_)
Figure 3C. The grap bar lables are unclear due to overlapping with errors bars.
Line 238-239: This statement should be supported by a reference, if possible.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsCouldn't be better
Reviewer 3 Report
Comments and Suggestions for AuthorsI recommend this manuscript for publication, as the authors have comprehensively addressed all the major concerns.
