Investigation on Characteristics of Microwave Treatment of Organic Matter in Municipal Dewatered Sludge
Round 1
Reviewer 1 Report
Dear authors/editors,
I have reviewed the manuscript entitled “Investigation on Characteristics of Microwave treatment of Organic Matter in Municipal Dewatered Sludge” wherein the authors describe the optimization of microwave solvent, nanomaterial assistant, microwave absorbing agent, and activating agent on the degradation efficiency of the organic matter in municipal dewatered sludge. The manuscript shows a clear set of values that come out from the optimization process and maximize degradation efficiency. However, there are minor technical issues and major formatting and referencing issues that must be addressed.
General:
-Author affiliation numbers are not well ordered in my opinion, 3 appears before 2.
-I am not an English speaker so I will not be strict with the writing. However, English should be polished in my opinion. The text is well understood, but some sentences, along the whole manuscript, are not grammatically correct although they are understandable. You can feel that it is not written or corrected by a native English speaker.
-Referencing should be reconsidered. There are a total of 5 references in between the introduction and materials and methods sections. Not enough background for this manuscript in my opinion.
Introduction:
-The introduction does not fundamentally covers anaerobic digestion or sludge topics, and goes directly deeper into the paper objective. I appreciate this option as I like short specific introductions rather than large general ones.
-The introduction is clear but poorly referenced; only 5 references are present on it and I would expect around double. For instance, statements like “Common sludge organic matter with high molecular weight and boiling point often contains twigs, sawdust, small cloth, bacteria, insect eggs and other components” or “high-frequency electromagnetic wave of microwave radiation can penetrate the extraction medium and reach the vascular bundle and adenocyte system.” should be referenced.
Materials and methods:
-To my knowledge, the experimental methodology is not well covered in this section. Most of it is understood while you read the results and discussion section, please give further explanations here.
-Please provide brand and model of equipment like the microwave oven or the furnace.
-The plastic type used for the cup used as mixing vessel should be specified to ensure that is cannot influence the sample or be degraded in the presence of any of the mixture compounds.
-Math signs “=” are in yellow in the equations, fix it.
Results and discussion:
-I consider the second paragraph, in which the characteristics of dimethyl carbonate are covered, as introduction, not results or discussion of this work. Please rearrange it.
-In the third paragraph, I consider the added mass ratio of dimethyl carbonate and the microwave conditions as materials and methods, not results or discussion of this work. Please rearrange it.
-Only 6300W and 2 min has been used as microwave conditions. I feel that different times and/or powers could give a different optimum for the rest of parameters. Please try one different scenario, at least to know if the tendencies are the same or not.
-The tendency graphs are very clear for all the parameters, ending in a final optimized group of parameters from a technical point of view. However, I miss a certain economical discussion which can be relevant to exactly define the operational optimum of this process. I am aware that a full economical study could be too much for this manuscript and could even give birth to a second paper, but I think an economical discussion paragraph at the end of the section could improve the manuscript quality.
-Fig.6 shows a parameter that is constant for different dosing and even no dosing. Therefore I think this figure can only be used to conclude that no liquid sodium silicate should be used. However, this compound seems to play a role in solidification and compressive strength that should be discussed
Conclusions:
-The addition of liquid water glass is not well discussed previously; therefore it is difficult to use it as a conclusion. The manuscript does not even give an optimum value for it, being an optimization study. Please discuss it better and be more precise in the conclusion.
-The manuscript concludes that a balance between treatment cost and ecological benefit is made, but I miss a discussion around that topic in the results and discussion section.
Author Response
Dear reviewer:
Thank you very much for your kind consideration for the constructive comments concerning our manuscript entitled “Investigation on Characteristics of Microwave Treatment of Organic Matter in Municipal Dewatered Sludge”. (Manuscript ID: applsci-454992).
The comments are very valuable and helpful for revising and improving our article. We have carefully revised the manuscript according to your valuable feedback. The revised portions are marked in red in the article. The responses to the comments are as follows:
Reviewer 1:
I have reviewed the manuscript entitled “Investigation on Characteristics of Microwave treatment of Organic Matter in Municipal Dewatered Sludge” wherein the authors describe the optimization of microwave solvent, nanomaterial assistant, microwave absorbing agent, and activating agent on the degradation efficiency of the organic matter in municipal dewatered sludge. The manuscript shows a clear set of values that come out from the optimization process and maximize degradation efficiency. However, there are minor technical issues and major formatting and referencing issues that must be addressed.
1. Author affiliation numbers are not well ordered in my opinion, 3 appears before 2.
Response: Thank you very much for your careful reviewing. The author affiliation number is ordered according to the contributions of the authors. I think the current order of author affiliation is reasonable.
2. I am not an English speaker so I will not be strict with the writing. However, English should be polished in my opinion. The text is well understood, but some sentences, along the whole manuscript, are not grammatically correct although they are understandable. You can feel that it is not written or corrected by a native English speaker.
Response: Thanks a lot for your suggestions. We have improved English and modified several grammar mistakes in the article.
3. Referencing should be reconsidered. There are a total of 5 references in between the introduction and materials and methods sections. Not enough background for this manuscript in my opinion.
Response: Thank you for your kind suggestion. We added more references to support the introduction and materials and methods.
4. The introduction does not fundamentally covers anaerobic digestion or sludge topics, and goes directly deeper into the paper objective. I appreciate this option as I like short specific introductions rather than large general ones.
Response: Thank you very much.
5. The introduction is clear but poorly referenced; only 5 references are present on it and I would expect around double. For instance, statements like “Common sludge organic matter with high molecular weight and boiling point often contains twigs, sawdust, small cloth, bacteria, insect eggs and other components” or “high-frequency electromagnetic wave of microwave radiation can penetrate the extraction medium and reach the vascular bundle and adenocyte system.” should be referenced.
Response: Thank you very much for your kind suggestion. We have added relevant references in the introduction.
6. To my knowledge, the experimental methodology is not well covered in this section. Most of it is understood while you read the results and discussion section, please give further explanations here.
Response: Thank you for your kind suggestion. We added a further explanation in the experiment and method section.
We conducted the single factor experiment to confirm the optimized addition of microwave solvent, nanomaterial assistants, microwave absorbing agents, and activating agents.
We designed an orthogonal experiment to analyze the influence of activating agents, determining the most suitable content of addition.
7. Please provide brand and model of equipment like the microwave oven or the furnace.
Response: Thank you for your kind suggestion. We added a detailed description of the equipment in the article.
The used microwave oven was self-designed and manufactured by Guangzhou Diwei Microwave Equipment Co., LTD, and the output power of microwave ranged from 900 to 6300 W.
8. The plastic type used for the cup used as mixing vessel should be specified to ensure that is cannot influence the sample or be degraded in the presence of any of the mixture compounds.
Response: Thank you for your kind suggestion. We added the description of cup material, which was used in the experiment.
The plastic cups are made of polystyrene with the thermal decomposition temperature of over 300 oC, which is higher than the treated temperature of 212 oC. Thus, the cup material has no influence on the experimental results.
9. Math signs “=” are in yellow in the equations, fix it.
Response: We have corrected it in the article.
10. I consider the second paragraph, in which the characteristics of dimethyl carbonate are covered, as introduction, not results or discussion of this work. Please rearrange it.
Response: Thank you for your kind suggestion. We rewrote the sentences in this paragraph.
Owing to the advantages of dimethyl carbonate for safety, convenience, less pollution, and diverse dissolution to organic compounds [14, 15], in this work, it was used as an extraction agent to investigate the effect on the reduction rate of the organic matters under the microwave irradiation.
11. In the third paragraph, I consider the added mass ratio of dimethyl carbonate and the microwave conditions as materials and methods, not results or discussion of this work. Please rearrange it.
Response: Thank you for your kind suggestion. We described the detailed experimental conditions in each single factor experiment in order to guarantee the clear understanding of the readers.
12. Only 6300 W and 2 min have been used as microwave conditions. I feel that different times and/or powers could give a different optimum for the rest of parameters. Please try one different scenario, at least to know if the tendencies are the same or not.
Response: 6300 W and 2 min are the optimized factors in this experiment. The microwave power of 6300 W brings the fastest degradation of the organic matters. If the treated time is further extended, the generated large energy would result in the burning of the sludge.
13. The tendency graphs are very clear for all the parameters, ending in a final optimized group of parameters from a technical point of view. However, I miss a certain economical discussion which can be relevant to exactly define the operational optimum of this process. I am aware that a full economical study could be too much for this manuscript and could even give birth to a second paper, but I think an economical discussion paragraph at the end of the section could improve the manuscript quality.
Response: Thanks a lot for your kind suggestion. In this work, we always put the cost into the consideration. The total addition of microwave solvent and nanomaterial assistants is 2.2 wt%. The usage of dry municipal dewatered sludge as the microwave absorbing agent can further reduce the cost. The activating agents are the industrial by-products. By calculation, if one ton of sludge is treated, the cost of power consumption is 56 RMB. The price of added microwave solvent, nanomaterial assistants and liquid sodium silicate is totally 168 RMB. After microwave treatment, 0.6 ton of light aggregate is produced, which is worth 300 RMB. Thus, we can obtain profit of 76 RMB at last.
14. Fig.6 shows a parameter that is constant for different dosing and even no dosing. Therefore I think this figure can only be used to conclude that no liquid sodium silicate should be used. However, this compound seems to play a role in solidification and compressive strength that should be discussed.
Response: The liquid sodium silicate cannot play a significant role in promoting the degradation. However, it can solidify the residual organic matters and sodium silicate in the sludge mixture to produce the light aggregates, and the compressive strength is remarkably enhanced over 2 MPa.
15. The addition of liquid water glass is not well discussed previously; therefore it is difficult to use it as a conclusion. The manuscript does not even give an optimum value for it, being an optimization study. Please discuss it better and be more precise in the conclusion.
Response: Thank you for your kind suggestion. The discussion about the effects of liquid sodium silicate has been added in the article.
16. The manuscript concludes that a balance between treatment cost and ecological benefit is made, but I miss a discussion around that topic in the results and discussion section.
Response: We have added the discussion in the last paragraph. By calculation, if one ton of sludge is treated, the cost of power consumption is 56 RMB. The price of added microwave solvent, nanomaterial assistants and liquid sodium silicate is totally 168 RMB. After microwave treatment, 0.6 ton of light aggregate is produced, which is worth 300 RMB. Thus, we can obtain profit of 76 RMB at last.
Thank you very much for the excellent and professional review of our manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript can be accepted for publication after revisions. Please address the following comments:
1. The manuscript requires major editorial changes.
2. The results and discussion section should be strengthened. The section includes only experimental outcomes; there is very minimum discussion on the results.
3. Statistical analysis of data is not included. There is no discussion on hypothesis testing (e.g., for orthogonal experiment), replication, interaction effects, estimate of errors, etc.
4. Description of the microwave heating equipment should be included. Was the plastic cup an open heating container or a closed system? How is it possible to reach 212 degree C in an open cup with a material having initial moisture content of ~83%.
5. Providing an input energy of 6300 W to 20 g of material is extremely energy intensive. Justify.
6. Details of actual values of initial and final dry matter content (or moisture%) and organic content (COD) should be clearly mentioned for the best conditions. Also, these values should be compared to that of control (microwave heating only without any additives).
7. The last sentence on “balance between the treatment cost and the ecological benefit” should be discussed further or removed from the conclusion. It is misleading as it is.
Author Response
Dear reviewer:
Thank you very much for your kind consideration for the constructive comments concerning our manuscript entitled “Investigation on Characteristics of Microwave Treatment of Organic Matter in Municipal Dewatered Sludge”. (Manuscript ID: applsci-454992).
The comments are very valuable and helpful for revising and improving our article. We have carefully revised the manuscript according to your valuable feedback. The revised portions are marked in red in the article. The responses to the comments are as follows:
Reviewer 2:
The manuscript can be accepted for publication after revisions. Please address the following comments:
1. The manuscript requires major editorial changes.
Response: Thanks a lot for your kind suggestion. We have carefully edited the article according the journal format, and improved English.
2. The results and discussion section should be strengthened. The section includes only experimental outcomes; there is very minimum discussion on the results.
Response: Thank you very much for your kind suggestion. We have added discussion in this section.
3. Statistical analysis of data is not included. There is no discussion on hypothesis testing (e.g., for orthogonal experiment), replication, interaction effects, estimate of errors, etc.
Response: Thank you very much for your kind suggestion. In this work, we designed an orthogonal experiment to analyze the influence of activating agents, determining the most suitable content of addition. As is well known, orthogonal experimental design is a common strategy to investigate the effects of multiple factors. Based on the orthogonality, the representative points are selected from total experiment points. Thus, it is an efficient, rapid and economical experimental design method.
4. Description of the microwave heating equipment should be included. Was the plastic cup an open heating container or a closed system? How is it possible to reach 212 degree C in an open cup with a material having initial moisture content of ~83%.
Response: Thank you very much for your kind suggestion. The used microwave oven was self-designed and manufactured by Guangzhou Diwei Microwave Equipment Co., LTD, and the output power of microwave ranged from 900 to 6300 W. The plastic cup was an open heating container. In the microwave treatment, there are activating agents added into the sludge, thus the generated temperature of the sludge can achieve 212 oC.
5. Providing an input energy of 6300 W to 20 g of material is extremely energy intensive. Justify.
Response: 6300 W and 2 min are the optimized factors in this experiment. The microwave power of 6300 W brings the fastest degradation rate of the organic matters. If the treated time is further extended, the generated large energy would result in the burning of the sludge.
6. Details of actual values of initial and final dry matter content (or moisture%) and organic content (COD) should be clearly mentioned for the best conditions. Also, these values should be compared to that of control (microwave heating only without any additives).
Response: Thank you very much for your kind suggestion. In this work, the research object is dewatered sludge, thus the COD value is not considered. Through optimizing the experimental factors, it was confirmed that 0.1 wt% TiO2, 0.1 wt% ZnO, 2 wt% dimethyl carbonate, 10 wt% sludge-based biological carbon, 7.5 wt% Ca(OH)2, 0.5 wt% MgCl2 and 6 wt% Na2SO4 were the most appropriate addition amounts in the municipal dewatered sludge to make the organic matter decrease from 42.17% to 22.45%, and the moisture content reduce from 82.98% to 0.48% after the microwave treatment. By comparison, the organic matter degradation is almost zero, and the moisture content decreases to 8.69% without any additives.
7. The last sentence on “balance between the treatment cost and the ecological benefit” should be discussed further or removed from the conclusion. It is misleading as it is.
Response: Thanks a lot for your kind suggestion. In this work, we always put the cost into the consideration. The total addition of microwave solvent and nanomaterial assistants is 2.2 wt%. The usage of dry municipal dewatered sludge as the microwave absorbing agent can further reduce the cost. The activating agents are the industrial by-products. By calculation, if one ton of sludge is treated, the cost of power consumption is 56 RMB. The price of added microwave solvent, nanomaterial assistants and liquid sodium silicate is totally 168 RMB. After microwave treatment, 0.6 ton of light aggregate is produced, which is worth 300 RMB. Thus, we can obtain profit per ton of 76 RMB at last. We added the discussion in the last paragraph.
Thank you very much for the excellent and professional review of our manuscript.
Author Response File: Author Response.pdf
