Supplemental Sewage Scum and Organic Municipal Solid Waste Addition to the Anaerobic Digestion of Thickened Waste Activated Sludge: Biomethane Potential and Microbiome Analysis
Round 1
Reviewer 1 Report
In this manuscript, the experiment about the anaerobic co-fermentation of sewage scum, organic fraction of municipal solid waste and thickened waste activated sludge were conducted. The addition of OFMSW and SS to TWAS helped improve the methane production rate. Also, the lag phase of SS was reduced by over 95% during co-digestion with TWAS and SS. Percentage VS removal did not lead to an increased methane production rate. The whole study was well-organized and presented in a logical way. It is a topic of interest to the researchers in the related areas but the paper needs very significant improvement before acceptance for publication. The following points should be taken into consideration.
1. In the abstract, the sudden mention of “trinary mixtures” was abrupt, it should be supplied which substances are together and the description of microorganisms should be a little more detailed.
2. In the introduction, in the part of explaining the background of the study, the current sludge production problem should be added to highlight the severity of the situation.
3. Line 130 in the part of Materials and Methods, please change "43days" into "43-day".
4. In the Figure 1 and Figure 2, why use hours as digestion time.
5. Please unify the tenses of the whole manuscript, i.e., line 223-231, line 266-271 and 303-318.
6. In the section 3.3.4, there are four stages in the anaerobic digestion, please be more specific and clear about the connection analysis about the experiment result and the four stages.
7. In the 3.4. Microbial analysis, the discussions about the microbial part of the fermentation experiment was not sufficient. More detailed analysis and contents are recommended for better understanding.
8. In the Figure 3, please supply legend for clearer identification of the abundance of microorganisms.
Author Response
Reviewer #1
In this manuscript, the experiment about the anaerobic co-fermentation of sewage scum, organic fraction of municipal solid waste and thickened waste activated sludge were conducted. The addition of OFMSW and SS to TWAS helped improve the methane production rate. Also, the lag phase of SS was reduced by over 95% during co-digestion with TWAS and SS. Percentage VS removal did not lead to an increased methane production rate. The whole study was well-organized and presented in a logical way. It is a topic of interest to the researchers in the related areas, but the paper needs very significant improvement before acceptance for publication. The following points should be taken into consideration.
-Thank you for your comment.
- In the abstract, the sudden mention of “trinary mixtures” was abrupt, it should be supplied which substances are together and the description of microorganisms should be a little more detailed.
-As recommended, the first appearance of the word “trinary” was eliminated and replaced by the substrates digested. Subsequent mention of “trinary” was followed by the substrates treated. Due to the 200-word limit of the abstract, a more detailed description of microbial analysis could not be done.
- In the introduction, in the part of explaining the background of the study, the current sludge production problem should be added to highlight the severity of the situation.
-This suggestion has been added to the manuscript.
- Line 130 in the part of Materials and Methods, please change "43days" into "43-day".
-As suggested, this correction was made.
- In the Figure 1 and Figure 2, why use hours as digestion time.
-Hours were used to have a more definitive time point. However, this has been changed to days. Also, Figures 1 and 2 were redone with colors for clarity and easier identification of the data points and legend.
- Please unify the tenses of the whole manuscript, i.e., line 223-231, line 266-271 and 303-318.
-As recommended, a comprehensive review of the language, tenses and style manuscript was done.
- In the section 3.3.4, there are four stages in the anaerobic digestion, please be more specific and clear about the connection analysis about the experiment result and the four stages.
-Authors thank the reviewer for this comment. As discussed in the manuscript, the VFA to Alkalinity ratio (derived from VFA and Alkalinity measurement) was used as an indication of stability at the initial stage (Hydrolysis) and the final stage (Methanogenesis). As a result, data points are not available for the acidogenic and acetogenesis stage. Since one of the objectives of the study is biogas enhancement, pH was monitored daily.
- In the 3.4. Microbial analysis, the discussions about the microbial part of the fermentation experiment was not sufficient. More detailed analysis and contents are recommended for better understanding.
-As recommended, a detailed discussion on the microbial analysis has been included.
- In the Figure 3, please supply legend for clearer identification of the abundance of microorganisms.
-The legend was replaced with a scored legend. As this is a heat map, scored legend reflects the abundance.
Reviewer 2 Report
Manuscript fermentation-2217665 entitled “Supplemental sewage scum and organic municipal solid waste addition to anaerobic digestion of thickened waste activated sludge: Biomethane potential and microbiome analysis”.
Please notice the following:
General view: The manuscript illustrated a great idea to use of SS and organic fraction of municipal solid waste (OFMSW) in anaerobic processes in wastewater treatment plants. The topic is very interesting.This problem is relevant for journal scope.
The Autors expressed their idea in moderate language and grammar. The manuscript might require copyediting and proofreading up to a little degree to provide more simplified sentences.
The introduction is easy detailed. The concept and aim are clearly defined. The presentation and discussion of the presented topicis clear and very detailed.
Suggests supplementing the "Introduction" with information bringing a new scientific contribution. Please provide a review of the literature in this area.The text can be supplemented with information on the use of organic waste in anaerobic co-digestion processes in wastewater treatment plants.
To raise the level of paper, please use the articles on the efficiency of anaerobic digestion and anaerobic co-digestion in wastewater treatment plants:
doi: 10.3390/en13226056
doi: 10.3390/en14113157
doi: 10.12912/23920629/122657
In general, the paper is well written, the results are conclusive and of interest for this topic. I have not found any important formal mistakes or typo errors. Formally, the paper is well written and easy to understand.
Please cite more papers from MDPI journals at the last 2-3 years in the similar topic of this research.
Other weaknesses to be corrected:
1. Keywords should be in alphabetical order.
2. The conclusions should be shorter and more specific. I propose to shorten the conclusions and keep the most important ones. It is best to list 3-4 critical conclusions.
The manuscript follows the formal regulations of MDPI journals.
I suggest the acceptance after minor revision
Author Response
Reviewer 2
Manuscript fermentation-2217665 entitled “Supplemental sewage scum and organic municipal solid waste addition to anaerobic digestion of thickened waste activated sludge: Biomethane potential and microbiome analysis”.
Please notice the following:
General view: The manuscript illustrated a great idea to use of SS and organic fraction of municipal solid waste (OFMSW) in anaerobic processes in wastewater treatment plants. The topic is very interesting. This problem is relevant for journal scope. The Authors expressed their idea in moderate language and grammar. The manuscript might require copyediting and proofreading up to a little degree to provide more simplified sentences. The introduction is easy detailed. The concept and aim are clearly defined. The presentation and discussion of the presented topic is clear and very detailed.
-We thank you for your kind comments
Suggests supplementing the "Introduction" with information bringing a new scientific contribution. Please provide a review of the literature in this area. The text can be supplemented with information on the use of organic waste in anaerobic co-digestion processes in wastewater treatment plants.
-On the use of organics in WWTP, kindly note that this was already included in the introduction part of the manuscript ( See lines 93-101). On the issue of new scientific contribution, authors already stated in line 101-103 “So far, the use of sewage scum (SS) as a supplemental source of FOG and energy during co-digestion of OFMSW and sewage sludge is yet to receive enough attention in the literature”. Furthermore, in lines 110-115 “Furthermore, the characterization of the microbial community during trinary co-digestion could unravel the microbial dynamics, microbial community stability, and mechanism behind methane production, especially during changes in substrate proportions in a mixture. The influence of substrate proportion on the microbial community during the addition of SS and OFMSW to sewage sludge will also provide new information”.
To raise the level of paper, please use the articles on the efficiency of anaerobic digestion and anaerobic co-digestion in wastewater treatment plants:
doi: 10.3390/en13226056
doi: 10.3390/en14113157
doi: 10.12912/23920629/122657
-We thank you for your suggestion. Two of the suggested papers have been cited and added to the references.
In general, the paper is well written, the results are conclusive and of interest for this topic. I have not found any important formal mistakes or typo errors. Formally, the paper is well written and easy to understand.
Please cite more papers from MDPI journals at the last 2-3 years in the similar topic of this research.
Other weaknesses to be corrected:
- Keywords should be in alphabetical order.
- As suggested earlier, relevant papers have been cited and referenced.
- The conclusions should be shorter and more specific. I propose to shorten the conclusions and keep the most important ones. It is best to list 3-4 critical conclusions.
-As suggested, the conclusion has been reviewed and made specific to the most important conclusions.
The manuscript follows the formal regulations of MDPI journals. I suggest the acceptance after minor revision
-We thank you for your kind comments
Round 2
Reviewer 1 Report
The authors have responded all comments from reviewers.
