Inhibitory Effects of Appropriate Addition of Zero-Valent Iron on NH3 and H2S Emissions during Sewage Sludge Composting
Round 1
Reviewer 1 Report
Overall a well written article albeit I do think we could do with a bit more justification on why this is interesting as there is a vast amount of literature on odour and the impacts thereof.
On specific comments:
L73 I’d like a bit more information about the ‘automatic control device’ – is it a commercially available product?
L88 how were they calibrated?
L112 saying 5,6,6 and 7 as a list is difficult to relate to first part of sentence
L114 for readers who don’t really know what this standard is can you say what the requirement is
L149 chemical factors such as?
L159 ‘occurred’ as ‘actually happened’ is a bit colloquial
L174 replace ‘bad odours’ with undesirable or similar
L177/78 I think it’s confusing to put the percentage additions and then days sequentially and hard to read
L184 define SRB
L229 I am just wondering as it does not say whether water was added at all to the process during composting, or whether it was outside and hence might have experienced precipitation?
L264 can you reference all these things that are ‘generally accepted’?
Overall – I cannot see any quoted p-values and whether the changes highlighted are actually statistically significant?
Author Response
Dear editors and the reviewers,
We would like to express our appreciation to you and the reviewers for your suggestions on how to improve our manuscript titled “Inhibitory Effects of Appropriate Addition of Zero-valent Iron on NH3 and H2S Emissions during Sewage Sludge Composting" (ID: agriculture-2015668). Those comments were valuable and very helpful for revising and improving our paper, as well as providing important guiding significance for our study. We have studied the comments carefully and made corrections that we hope will meet with your approval. The revised portions are visible which marked in red in the paper. The main corrections to the paper and the responses to the editors and the reviewer’s comments appear below.
Overall a well written article albeit I do think we could do with a bit more justification on why this is interesting as there is a vast amount of literature on odour and the impacts thereof.
Author’s response:
Thank you for your recognition of our study.
On specific comments:
L73 I’d like a bit more information about the ‘automatic control device’ – is it a commercially available product?
Author’s response:
We would be glad to answer your questions. The so-called "automatic control devices" are already commercially available for small-scale composting.
Revised text:
L75-76:
The composting process was conducted using a small aerobic composting auto-matic control device as shown in Figure 1.
L88 how were they calibrated?
Author’s response:
We will be glad to answer your questions and make corrections in the manuscript.
Revised text:
L93:
The concentrations of NH3 and H2S were detected using a portable NH3 detector
L112 saying 5,6,6 and 7 as a list is difficult to relate to first part of sentence
Author’s response:
Thank you for your suggestion, we have made changes.
Revised text:
L117-122:
Their high-temperature stages were 4, 6, 6, and 7 days, respectively, all of which met the requirement of at least 3 days for the high-temperature stage of sludge composting according to the Standard for Stabilization of Municipal Wastewater Treatment Plant Sludge (CJ/T 510-2017). Compared to the control group, the piles with the addition of ZVI all demonstrated an increase in peak temperature and a prolongation of the high-temperature phase.
L114 for readers who don’t really know what this standard is can you say what the requirement is
Author’s response:
Thank you for your suggestion, we have made changes.
Revised text:
L117-122:
Their high-temperature stages were 4, 6, 6, and 7 days, respectively, all of which met the requirement of at least 3 days for the high-temperature stage of sludge composting according to the Standard for Stabilization of Municipal Wastewater Treatment Plant Sludge (CJ/T 510-2017). Compared to the control group, the piles with the addition of ZVI all demonstrated an increase in peak temperature and a prolongation of the high-temperature phase.
L149 chemical factors such as?
Author’s response:
Thank you for your suggestion, we have made changes. The chemical factors are mainly the NH4+ concentration and the pH value. Other factors also have an influence, such as PO43- and the concentration of Mg2+ and Ca2+. This is because Mg2+ and Ca2+ bind to NH4+ through the action of (H2PO4)-, forming garnet crystals or other stable compounds that inhibit the conversion of NH4+ to NH3. (Cao et al., 2019)
Cao Y, Wang X, Bai Z, Chadwick D, Misselbrook T, G. Sommer S, et al. Mitigation of ammonia, nitrous oxide and methane emissions during solid waste composting with different additives: A meta-analysis. J. Clean. Prod. 2019; 235: 626-635. https://doi.org/10.1016/j.jclepro.2019.06.288.
Revised text:
L156-157:
In addition, the emission of NH3 is not only related to biological influences but also influenced by chemical factors [31], such as NH4+ concentration and pH value.
L159 ‘occurred’ as ‘actually happened’ is a bit colloquial
Author’s response:
Thank you for your suggestion, we have made changes.
Revised text:
L148-151:
In the control group, as well as the groups with 1%, 2%, and 3% ZVI additions, the peak time of NH3 emission was observed on days 4, 2, 7, and 5, with peak concentrations of 827.0, 936.8, 1408.4, and 653.7 mg·m−3, respectively.
L174 replace ‘bad odours’ with undesirable or similar
Author’s response:
Thank you for your suggestion, we have made changes.
Revised text:
L181-184:
The trend in H2S concentrations was similar, with peak concentrations at the beginning of the composting period and H2S emissions almost ceasing after 3 days. In the control group, the peak H2S emission occurred on day 1 with a concentration of 105.3 mg·m−3. In the group treated with 1% ZVI, the peak H2S emission occurred on day 2 with a concentration of 98.7 mg·m−3.
L177/78 I think it’s confusing to put the percentage additions and then days sequentially and hard to read
Author’s response:
Thank you for your suggestion, we have made changes.
Revised text:
L185-190:
In the group treated with 2% ZVI, the peak H2S emission occurred on day 1 with a concentration of 79.0 mg·m−3. In the group treated with 3% ZVI, the peak H2S emission occurred on day 1 with a concentration of 227.8 mg·m−3. Compared to the control group, the peak H2S……
L184 define SRB
Author’s response:
Thank you for your suggestion, we have made changes.
Revised text:
L197:
Sulfate-reducing bacteria (SRB) play a key role in this process, and their activity is influenced by the substrate (SO42−) concentration
L229 I am just wondering as it does not say whether water was added at all to the process during composting, or whether it was outside and hence might have experienced precipitation?
Author’s response:
I'd be glad to answer that question for you. During the composting process, no water was added and it was not affected by the rainfall.
L264 can you reference all these things that are ‘generally accepted’?
Author’s response:
Thank you for your suggestion, we have made changes.
Revised text:
L274-275:
Relevant research and industry standards suggest that a mature compost product should have a pH between 8 and 9 [51].
Overall – I cannot see any quoted p-values and whether the changes highlighted are actually statistically significant?
Author’s response:
We apologize for this absence, we have made it clear where appropriate
Revised text:
L107-109:
The results were tallied by paired Student's t-test when appropriate. Results are expressed as means, and differences of P<0.05 were considered significant.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The article was written according to the editorial guidelines. However, I have a few minor comments.
Please expand the topic of sewage sludge in the introduction. This is a broad subject and a few more examples should be added.
One can argue whether the chapter of research results and discussion should be written together. Of course, the guidelines do not prohibit this, but it is better to read and analyze if there are two separate chapters.
The results are presented clearly and legibly. However, please provide more examples of similar research findings from the literature.
Sufficient conclusions.
Author Response
Dear editors and the reviewers,
We would like to express our appreciation to you and the reviewers for your suggestions on how to improve our manuscript titled “Inhibitory Effects of Appropriate Addition of Zero-valent Iron on NH3 and H2S Emissions during Sewage Sludge Composting" (ID: agriculture-2015668). Those comments were valuable and very helpful for revising and improving our paper, as well as providing important guiding significance for our study. We have studied the comments carefully and made corrections that we hope will meet with your approval. The revised portions are visible which marked in red in the paper. The main corrections to the paper and the responses to the editors and the reviewer’s comments appear below.
The article was written according to the editorial guidelines. However, I have a few minor comments.
Author’s response:
Thank you very much.
Please expand the topic of sewage sludge in the introduction. This is a broad subject and a few more examples should be added.
Author’s response:
Thank you for your suggestion, we have made changes according to your comments.
Revised text:
L26-28:
With the rapid development of urbanization, the amount of urban wastewater treatment is increasing, and the amount of sewage sludge is also increasing year by year.
One can argue whether the chapter of research results and discussion should be written together. Of course, the guidelines do not prohibit this, but it is better to read and analyze if there are two separate chapters.
Author’s response:
Thanks for your advice. We tried to write the results separately from the discussion, but the overall reading experience was not good. We revised the original manuscript to form the present one.
The results are presented clearly and legibly. However, please provide more examples of similar research findings from the literature.
Author’s response:
Thank you for your suggestion and we have made the changes according to your comments. However, we still want to state that we do not seem to see the use of ZVI powder to control the odor of compost in the studies published so far.
Revised text:
L193-195:
In other studies [37], nitrates were used to reduce the release of hydrogen sul-fide from sewage sludge composts, with the effect of reducing it by 20%.
Sufficient conclusions.
Author’s response:
Thank you for your comments, we have condensed and rewritten the conclusion section.
Revised text:
L290-297:
Furthermore, the addition of ZVI increased the available sulfur content of the compost product, reduced the loss of total sulfur, and promoted the maturation and dewatering of the compost. Under the ZVI addition conditions designed for this experiment, no negative effects of the ZVI addition on the composting process were observed. The experimental results showed that a greater addition of ZVI led to more favorable dewatering and decomposition in the aerobic composting process.
Author Response File: Author Response.docx
Reviewer 3 Report
The reviewed text concerns the problem of finding a way to reduce odour emissions (NH3 and H2S) during the composting of sewage sludge. This problem is very interesting from the point of view of science and has great practical significance. Hence the subject matter should be considered important and well-chosen.
Both the research and the text are designed and performed correctly. However, reading the text prompts the formulation of the following comments and questions:
- The article lacks a clearly and explicitly formulated research goal.
- The research shows (as stated in the Conclusions) that the 3% addition of ZVI is the most favourable for reducing ammonia emissions. It is also the highest value of the iron supplement used in the research. Should not another series of tests be performed for ZVI additives higher than 3%?
- Figure 1 shows four temperature sensors in a model composter. The authors use one temperature value for a single experiment in the text. How was this value determined? Is it an average value?
- Wouldn't it be worth analysing the concentration of Fe2+ and Fe3+ in the filtrate (water extract)?
- Is using a few percent by weight of iron dust (ZVI) not an overly expensive method of reducing odour emissions (including ammonia and hydrogen sulphide) from sewage sludge composting?
- The summary and conclusions are overly obvious, and there is no shown broad coverage of the results, especially regarding the practical application and the possible costs of such a process.
The text needs some corrections. Please take account of the indicated comments. In particular, formulate the explicit purpose of the work and expand the conclusions.
Author Response
Dear editors and the reviewers,
We would like to express our appreciation to you and the reviewers for your suggestions on how to improve our manuscript titled “Inhibitory Effects of Appropriate Addition of Zero-valent Iron on NH3 and H2S Emissions during Sewage Sludge Composting" (ID: agriculture-2015668). Those comments were valuable and very helpful for revising and improving our paper, as well as providing important guiding significance for our study. We have studied the comments carefully and made corrections that we hope will meet with your approval. The revised portions are visible which marked in red in the paper. The main corrections to the paper and the responses to the editors and the reviewer’s comments appear below.
The reviewed text concerns the problem of finding a way to reduce odour emissions (NH3 and H2S) during the composting of sewage sludge. This problem is very interesting from the point of view of science and has great practical significance. Hence the subject matter should be considered important and well-chosen.
Author’s response:
Thank you for your recognition of our research!
Both the research and the text are designed and performed correctly. However, reading the text prompts the formulation of the following comments and questions:
The article lacks a clearly and explicitly formulated research goal.
Author’s response:
We are very sorry to cause you such trouble. We have made clear clarification in the appropriate position.
Revised text:
L61-65:
According to the relevant studies, we explored the addition of ZVI and analyzed its effects on NH3 and H2S emissions during the sewage sludge composting process, and we investigated its effect on the nutrient content of the compost, dewatering effectiveness, and product maturation. The results of the study can provide a new approach to control odor pollution and improve product quality in actual sewage sludge composting.
The research shows (as stated in the Conclusions) that the 3% addition of ZVI is the most favourable for reducing ammonia emissions. It is also the highest value of the iron supplement used in the research. Should not another series of tests be performed for ZVI additives higher than 3%?
Author’s response:
As you said in your other comments, a larger zero-valent iron addition would impose additional costs and not be conducive to practical application. Therefore, based on the economic considerations of practical applications, we did not design a larger number of additional experiments.
Figure 1 shows four temperature sensors in a model composter. The authors use one temperature value for a single experiment in the text. How was this value determined? Is it an average value?
Author’s response:
We are sorry to have caused you such a problem. Because of the wide variation in temperature inside the composting system, we use the average of the 4 temperature sensor readings to represent the actual temperature inside the composting system. We have redone this in the article to make it clear.
Revised text:
L76-77:
In order to accurately describe the temperature of the composting process, the composting device was equipped with four temperature sensors at different depths.
Wouldn't it be worth analysing the concentration of Fe2+ and Fe3+ in the filtrate (water extract)?
Author’s response:
Thank you for your comments, this indicator was indeed omitted in our experiments and we apologize for this oversight. In future experiments, we will definitely take all cases into account in order to explain the results in a more detailed and specific way.
Is using a few percent by weight of iron dust (ZVI) not an overly expensive method of reducing odour emissions (including ammonia and hydrogen sulphide) from sewage sludge composting?
Author’s response:
We'd be happy to answer your questions. Odor pollution is already a major issue in compost plant operations, so adding a small amount of ZVI is worthwhile. And adding zero-valent iron increases the iron content of the compost, allowing for better utilization of the compost product.
The summary and conclusions are overly obvious, and there is no shown broad coverage of the results, especially regarding the practical application and the possible costs of such a process.
Author’s response:
Thank you for your comments, we have condensed and rewritten the conclusion section.
Revised text:
L290-297:
Furthermore, the addition of ZVI increased the available sulfur content of the compost product, reduced the loss of total sulfur, and promoted the maturation and dewatering of the compost. Under the ZVI addition conditions designed for this experiment, no negative effects of the ZVI addition on the composting process were observed. The experimental results showed that a greater addition of ZVI led to more favorable dewatering and decomposition in the aerobic composting process.
The text needs some corrections. Please take account of the indicated comments. In particular, formulate the explicit purpose of the work and expand the conclusions.
Author’s response:
Thanks to your comments, we have recondensed our experimental aims and organized our conclusions accordingly.
Revised text:
L61-65:
According to the relevant studies, we explored the addition of ZVI and analyzed its effects on NH3 and H2S emissions during the sewage sludge composting process, and we investigated its effect on the nutrient content of the compost, dewatering effectiveness, and product maturation. The results of the study can provide a new approach to control odor pollution and improve product quality in actual sewage sludge composting.
L290-297:
Furthermore, the addition of ZVI increased the available sulfur content of the compost product, reduced the loss of total sulfur, and promoted the maturation and dewatering of the compost. Under the ZVI addition conditions designed for this experiment, no negative effects of the ZVI addition on the composting process were observed. The ex-perimental results showed that a greater addition of ZVI led to more favorable de-watering and decomposition in the aerobic composting process.
Author Response File: Author Response.docx
