Ammonium and Phosphate Recovery from Biogas Slurry: Multivariate Statistical Analysis Approach

Round 1

Reviewer 1 Report

The paper presents significant information and analysis, which I can appreciate. Additionally, the theme of the paper is within the scope of the journal and the results look secure. However, I cannot recommend its publication at this stage for the following points:

The goal of the paper is not clear. What gap does this study fill in the literature? What is main novelty ?

In study authors should mention how they evaluated data quality?

Sincerely

Author Response

Dear Editor

Sustainability

Re: No. sustainability -1680816

Enclosed is the revised manuscript entitled “Ammonium and phosphate recovery from biogas slurry: multivariate statistical analysis approach” (sustainability-1680816) by Aftab Ali Kubar, Qing Huang*, Kashif Ali Kubar, Muhammad Amjad Khan, Muhammad Sajjad, Sumaira Gul, Chen Yang, Qingqing Wang, Genmao Guo, Ghulam Mustafa Kubar, Muhammad Ibrahim Kubar and Niaz Ahmed Wahocho. The manuscript has been revised according to the reviewer suggestions. We also appreciate the reviewers for their valuable comments/corrections/changes. We are also grateful to editor for his valuable comments. Based on their kind comments, we have carefully modified the manuscript (highlighted with yellow color for reviewer one, highlighted with green color for reviewer two and highlighted with pink color for reviewer three).We wish that the revised manuscript will meet the standard for publication.  

We are looking forward to hearing from you soon

Sincerely

Dr. Huang Qing

Reviewer # 1

Thank you for your valuable comments. We have revised this manuscript according to your suggestions. I hope that the revised manuscript would meet your requirements for Publication in Sustainability. 

Comment: The goal of the paper is not clear. What gap does this study fill in the literature? What is main novelty?

Response: The main goal of this study is to define the possibilities of applying multivariate statistical analysis (principal component, regression, path analysis, and pearson correlation) for monitoring the potential for NH₄⁺ and PO₄³⁻ recovery from different biogas digester waste using struvite and biochar co-precipitation. This paper presents the assessment of the possibility of the application of PCA and other statistical techniques in the analysis and monitoring of biological treatment of wastewater by two variables: Ammonium recovery and Phosphate concentration under different biochar, pyrolysis temperature, and element concentration and removal efficiencies.

Novelty and Study Gap: This study devoted to use different multivariate statistical analysis to investigate the interrelationship of one factor to another factor. Hence, this study designed to assess significance of phosphate and ammonium recovery from biogas slurry and their interaction with diverse factors using different statistical techniques. Multivariate statistical analysis was used to comprehensively evaluate the biochar and struvite effects on recovery of ammonium and phosphate from biogas slurry. To obtain reliable result, it is essential to use multivariate statistical methods for look over significant characters in studied material.

Comment: In study authors should mention how they evaluated data quality?

Response: Thank you for valuable comments. The evaluated of data quality were analyzed via an SPSS and R software based approach aiming at the correlation between two different regimes. If asking in case of chemical analysis answer is here: The main objectives of this study were to assess the recovery of phosphate and ammonium nitrate from biogas slurry effluent via struvite co-precipitation and determine the influence of pH and Mg²⁺ and PO₄³⁻ molar ratio modification on the struvite co-precipitation. Additionally, the study examined the effects of different variables, such as pH, PO₄³⁻, NO₃⁻, Fe²⁺, Fe³⁺, CO₃²⁻,HCO₃₋, Zn²⁺, K⁺, and Cu²⁺, on the phosphorous and ammonium recovery capacity of biochar and their availability to plants. However, chemical comparison part of this study has been already published. This part mainly concern on the use of multivariate statistical analysis to compare or correlate parameters each other. 

Author Response File: Author Response.pdf

Reviewer 2 Report

ournal Title: Sustainability 

Journal Name: Ammonium and Phosphate Recovery from Biogas Slurry in Relation to Multivariate Statistical Analysis

In the current research article, the authors have studied the ammonium and phosphate recovery from the biogas slurry.  
The article is very nicely written and I suggest minor revision. 
Minor concern 
    1. How different transition metal concentrations (Fe, Zn, Cu) will affect the phosphate ammonium recovery. 
    2. Why biochar effectively reuses N and phosphate from biogas slurry authors need to explain in brief 
    3. Abstract can be improved by including the obtained results
    4. Citation should be added for the R software
    5. The height and length of the Fig 3 subfigures have to be improved
    6. Full details of the linear regression equations should be mentioned (for Fig. 3) 
    7. Conclusion can be further improved
          

Author Response

Dear Editor

Sustainability

Re: No. sustainability-1680816

Enclosed is the revised manuscript entitled “Ammonium and phosphate recovery from biogas slurry: multivariate statistical analysis approach” (sustainability-1680816) by Aftab Ali Kubar, Qing Huang*, Kashif Ali Kubar, Muhammad Amjad Khan, Muhammad Sajjad, Sumaira Gul, Chen Yang, Qingqing Wang, Genmao Guo, Ghulam Mustafa Kubar, Muhammad Ibrahim Kubar and Niaz Ahmed Wahocho. The manuscript has been revised according to the reviewer suggestions. We also appreciate the reviewers for their valuable comments/corrections/changes. We are also grateful to editor for his valuable comments. Based on their kind comments, we have carefully modified the manuscript (highlighted with yellow color for reviewer one, highlighted with green color for reviewer two and highlighted with pink color for reviewer three). We wish that the revised manuscript will meet the standard for publication.

We are looking forward to hearing from you soon

Sincerely

Dr. Huang Qing

Reviewer 2

Thank you for your valuable comments. We have revised this manuscript according to your suggestions. I hope that the revised manuscript would meet your requirements for Publication in Sustainability. 

Comment:  How different transition metal concentrations (Fe, Zn, Cu) will affect the phosphate ammonium recovery. 

Response: The essential principle of the struvite precipitation method is to add a certain magnesium resource to the solution, so that the NH₄⁺, Mg²⁺, and PO₄³⁻ in the solution are greater than the solubility product constant (Ksp). Cao et al., [14] suggested that struvite precipitation could remove ammonia, phosphate, and chemical oxygen demand (COD) substances from digested wastewater more efficiently and for a lower cost. Additionally, the recovery of heavy metals during rock phosphate processing as well as the extraction of other associated elements of value, such as ammonium and magnesium, is particularly significant considering resource efficiency and the sustainable use of biowaste materials. Heavy metals recovered during phosphate fertilizer production are not dissipated onto agricultural soils from where they may leach into ground water. Common non- crystalline ions in biogas slurry, such as Ca²⁺, Zn²⁺, Na⁺, K⁺, and CO₃²⁻, have different effects on the struvite precipitation reaction. Yuanyao et al., reported that Ca²⁺, Na⁺, and K⁺ in wastewater considerably inhibited the recovery of ammonia nitrogen, while Ca²⁺ and K⁺ significantly promoted the efficient total recovery of phosphorus.

Comment: Why biochar effectively reuses N and phosphate from biogas slurry authors need to explain in brief. 

Response: Thanks for suitable comment. Biochar has a great capacity for adsorbing cations and anions from a solution containing a variety of organic compounds. Using biochar to recover surplus nutrients from biogas slurry effluents and then utilizing the nutrient-enriched biochar for soil alteration offers an eco-friendly solution to multiple issues. The accessibility of the adsorption positions is ruled by the adsorbent dose.

Comment: Abstract can be improved by including the obtained results.

Response: Thank you for valuable comments. Obtained results has been included in the abstract.

Comment: Citation should be added for the R software.

Response: It’s done according to your suggestions. Now citation of R software were added.

Comment: The height and length of the Fig 3 subfigures have to be improved.

Response: It’s done according to your suggestions. See revised manuscript.

Comment: Full details of the linear regression equations should be mentioned (for Fig.3).

Response: It’s done according to your suggestions. Full details of the linear regression equations has been incorporated in fig 2.

Comment: Conclusion can be further improved.

Response: It’s done according to your suggestions. Conclusions has been improved according to your suggestion.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments to Author:

Review of the manuscript entitled: “Ammonium and Phosphate Recovery from Biogas Slurry in Relation to Multivariate Statistical Analysis”. This study designed to assess significance of phosphate and ammonium recovery from biogas slurry and their interaction with diverse factors using different statistical techniques. This study has certain value and significance. However, due to the lack of some key contents of this paper and the poor writing level, the current manuscript is far from the publication standard.

Comments:

1.The experimental design of this paper is not clearly introduced. How many treatments are there? How exactly does each process work? What materials are used, how much is used and so on. For example, what kind of material biochar is fired at what degree, the amount and usage of biochar, etc. The absence of this part seriously affects our reading and understanding of this paper.

2.The quality and clarity of the pictures in this article are poor that it is almost impossible to see the details. At the same time, when displaying the group of pictures, each small picture is not marked “a/b/c/d”, which has a great impact on the understanding of the content. In addition, in general, the numbers of pictures and tables start from 1, but in this paper, the numbers of pictures and tables start from 3.1, which is not appropriate.

3.The author takes multivariate statistical analysis method as a main content of this paper and writes it in the title, which I personally think is not appropriate. The whole paper should have an exit. What do so many analytical methods mean? What was the final conclusion? The author needs to comb through and answer these questions. At the same time, the theme needs to be clear, that is, what is the story to be told? Once you've identified a theme, you need to clarify the storyline, and the rest of the content needs to serve that storyline.

4.The introduction describes the recovery of ammonium and phosphorus in a large part, but it does not put forward scientific hypotheses, which is a failure for the writing of scientific papers.

Author Response

Dear Editor

Sustainability

Re: No. sustainability-1680816

Enclosed is the revised manuscript entitled “Ammonium and phosphate recovery from biogas slurry: multivariate statistical analysis approach” (sustainability-1680816) by Aftab Ali Kubar, Qing Huang*, Kashif Ali Kubar, Muhammad Amjad Khan, Muhammad Sajjad, Sumaira Gul, Chen Yang, Qingqing Wang, Genmao Guo, Ghulam Mustafa Kubar, Muhammad Ibrahim Kubar and Niaz Ahmed Wahocho. The manuscript has been revised according to the reviewer suggestions. We also appreciate the reviewers for their valuable comments/corrections/changes. We are also grateful to editor for his valuable comments. Based on their kind comments, we have carefully modified the manuscript (highlighted with yellow color for reviewer one, highlighted with green color for reviewer two and highlighted with pink color for reviewer three). We wish that the revised manuscript will meet the standard for publication.

We are looking forward to hearing from you soon

Sincerely

Dr. Huang Qing

Reviewer 3

Thank you for your valuable comments. We have revised this manuscript according to your suggestions. I hope that the revised manuscript would meet your requirements for Publication in Sustainability. 

Comment: The experimental design of this paper is not clearly introduced. How many treatments are there? How exactly does each process work? What materials are used, how much is used and so on. For example, what kind of material biochar is fired at what degree, the amount and usage of biochar, etc. The absence of this part seriously affects our reading and understanding of this paper.

Response: Thanks for your valuable comments and suggestion. Now experimental design has been clarified. Please see the revised manuscript.

Comment: The quality and clarity of the pictures in this article are poor that it is almost impossible to see the details. At the same time, when displaying the group of pictures, each small picture is not marked “a/b/c/d”, which has a great impact on the understanding of the content. In addition, in general, the numbers of pictures and tables start from 1, but in this paper, the numbers of pictures and tables start from 3.1, which is not appropriate.

Response: Thanks for suitable comment. Now it’s done according to your suggestion quality and clarity of the pictures improved as per suggestions. We have formatted the numbering of the tables starting from 1.

Comment: The author takes multivariate statistical analysis method as a main content of this paper and writes it in the title, which I personally think is not appropriate. The whole paper should have an exit. What do so many analytical methods mean? What was the final conclusion? The author needs to comb through and answer these questions. At the same time, the theme needs to be clear, that is, what is the story to be told? Once you've identified a theme, you need to clarify the storyline, and the rest of the content needs to serve that storyline.

Response: Use of multi analysis (Correlation, simple linear regression, path, and principal component analyze) were used to investigate the relationships between PO₄^3- concentration and the PO₄^3-removal efficiency under the biochar, pyrolysis temperature etc effect. For example PO₄^3- concentration Increase, the PO₄^3-removal efficiency was also increased under biochar effect and graph was lagged after sometime.  The relationship between the two variables can be quantified as NH₄⁺ concentration and NH₄⁺ removal efficiency under pyrolysis temperature are the variables. This also define the possibilities of applying multivariate statistical analysis (principal component, regression, path analysis, and pearson correlation) for monitoring the potential for NH₄⁺ and PO₄³⁻ recovery from different biogas digester waste using struvite and biochar co-precipitation.  

This study concluded that temperature, biochar type, and varying levels of components such as K⁺, Zn²⁺, Fe³⁺, Fe²⁺, Cu²⁺, CO₃^2-, and HCO₃^- all had a substantial impact on P and NH₄⁺ recovery. PCA is best technique to find out the relationship of one factor to another. Multivariate statics is best approach to display complex relationships among many objects.

Many studies has conducted to use multivariate statistical analysis approach in diverse fields see few examples

1. Adam, A.M.A.; Eltayeb, M.A.H. Multivariate statistical analysis of radioactive variables in two phosphate ores from Sudan. Journal of environmental radioactivity. 2012, 107, 23-43.
2. Wąsik, E.; Chmielowski, K.; Cupak, A.; Kaczor, G. Stability Monitoring of the Nitrification Process: Multivariate Statistical Analysis. Polish Journal of Environmental Studies, 2018, 5,
3. Arzu, K.O.S.E.; Onder, O.; Bilir, O.; Kosar, F. Application of multivariate statistical analysis for breeding strategies of spring safflower (Carthamustinctorius L). Turkish Journal of Field Crops, 2018, 1, 12-19.

Comment: The introduction describes the recovery of ammonium and phosphorus in a large part, but it does not put forward scientific hypotheses, which is a failure for the writing of scientific papers.

Response: Thanks for your suggestions. The recovery of ammonium and phosphorus is describes in introduction because it is the base of the study from where we has collected date correlated each other. Basic Hypothesis was that could multivariate statistical approach is useful to correlate the scientific study.  I hope you understand the basic theme of the study.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

This revised version is a great improvement over the first version of the manuscript. In particular, the author introduced more details of the experiment and clarified the scientific hypothesis, which greatly improved the logicality and readability of the manuscript. However, there are still several issues with the current version.

1. The definition and quality of pictures are too low for readers to quickly get effective information from pictures, which seriously affects the reading experience. Especially for Fig. 1 and Fig. 3, the author only added annotations to the picture, but the quality of the picture did not improve, it is still in a fuzzy state. It is suggested that the author re-draw to ensure the clarity and quality of the picture. In addition, please unify the format of several sub-figures in Fig. 2.
2. These content (L176-210) are more experimental details, whereas “2.2 Details of experiments” are more statistical analysis details. It is recommended that “2.3. Preparation of biochars, 2.4. Preparation of simulated biogas slurry, 2.5. Preparation of stock solution, 2.6. Analytical methods” be placed in “2.2. Details of experiments” and that the content of the statistical analysis in “2.2 Details of experiments” was put into “2.8. Statistical analysis”.
3. Some detailed errors in the manuscript need to be corrected, such as 0.5 mol L^-1 in L192 and L201. Note that “-1” requires a superscript.

Author Response

Dear Editor

Sustainability

Re: No. sustainability-1680816

Enclosed is the revised manuscript entitled “Ammonium and phosphate recovery from biogas slurry: multivariate statistical analysis approach”(sustainability-1680816) by Aftab Ali Kubar, Qing Huang*, Kashif Ali Kubar, Muhammad Amjad Khan, Muhammad Sajjad, Sumaira Gul, Chen Yang, Qingqing Wang, GenmaoGuo, Ghulam Mustafa Kubar, Muhammad Ibrahim Kubarand Niaz Ahmed Wahocho. The manuscript has been revised according to the reviewer suggestions. We also appreciate the reviewers for their valuable comments/corrections/changes. We are also grateful to editor for his valuable comments. Based on their kind comments, we have carefully modified the manuscript (highlighted with pink color for reviewer three round two). We wish that the revised manuscript will meet the standard for publication.

We are looking forward to hearing from you soon

Sincerely

Dr. Huang Qing

Reviewer 3 round 2

Thank you for your valuable comments. We have revised this manuscript according to your suggestions. I hope that the revised manuscript would meet your requirements for Publication in Sustainability. 

Comment: The definition and quality of pictures are too low for readers to quickly get effective information from pictures, which seriously affect the reading experience. Especially for Fig. 1 and Fig. 3, the author only added annotations to the picture, but the quality of the picture did not improve, it is still in a fuzzy state. It is suggested that the author re-draw to ensure the clarity and quality of the picture. In addition, please unify the format of several sub-figures in Fig. 2.

Response:Thanks for suitable comment. Now it’s done according to your suggestion we have re-draw the figures to improve the quality and clarity of the Fig. 1 and Fig. 3as per suggestions and also unify the format of sub-figures in Fig. 2. We have tried to make these figures clear for the readers and I hope now it looks better than first one. 

Comment: These content (L176-210) are more experimental details, whereas “2.2 Details of experiments” are more statistical analysis details. It is recommended that “2.3. Preparation of biochar, 2.4. Preparation of simulated biogas slurry, 2.5. Preparation of stock solution, 2.6. Analytical methods” be placed in “2.2. Details of experiments” and that the content of the statistical analysis in “2.2 Details of experiments” was put into “2.8. Statistical analysis”.

Response:Thanks for your valuable suggestion and comments. Now it’s done according to your suggestion.See revised version of the manuscript.

Comment:Some detailed errors in the manuscript need to be corrected, such as 0.5 mol L^-1 in L192 and L201. Note that “-1” requires a superscript.

Response:Thanks for your comments. Now it’s done according to your suggestion and most of the minor errors also has been furnished to improve the quality of the paper

Author Response File: Author Response.pdf