Remediation of Aqueous Phosphate Agricultural Runoff Using Slag and Al/Mg Modified Biochar

Round 1

Reviewer 1 Report

Overall, the paper was well-written and provided valuable information on phosphate adsorption and desorption using modified biochar and slag. The authors should review the paper for spelling and grammar mistakes. 

The references in the text and in the references section are not formatted correctly. If a reference management program (Mendeley, Zotero, etc.) was used to input refs into the text, the authors should carefully check for errors. Please review Processes guide for authors for reference format. MDPI typically requires numbering of refs in text based on their first appearance. In this paper, some are numbered as superscripts and some are written out.

In addition, the formatting of figures and tables should be improved. For example, the outer border of figure 6 should be removed and the caption removed from inside a border/cell. Column colors (ex. green and tan in fig 6) should be changed to black and grey or white with black outlines. This makes figures more clear for those who are colorblind. Line graphs can be changed to different patterns rather than different colors (e.g. black dashes, lines, dots, etc.). Inside borders of tables should be removed, and only use horizontal lines that separate treatments from result data for the outermost border of the table.

There are many inconsistencies with units (e.g. sometimes the authors write out minutes and hours and other times use min and h). Sometimes the degree symbol is between the number and "C" without spaces and other times there are spaces. The same inconsistencies are there for "greater than" and "less than" symbols. pH values should include the tenths place (ex. 6.0 instead of 6). Please be consistent and consult the author guidelines.

Did the authors perform any statistical analyses on the data? Were the differences between AMOB and slag significantly different? 

Please remove the grey background on Figure 10, and make the labels "a, b, c" more prominent. Keep them consistent with other figures (uppercase, lowercase, etc.). 

Please provide line numbers in the manuscript when submitting to journals. 

Author Response

Overall, the paper was well-written and provided valuable information on phosphate adsorption and desorption using modified biochar and slag. The authors should review the paper for spelling and grammar mistakes. 

Response - Thank you for your positive comments on our work. We have extensively edited the manuscript and addressed all spelling and grammar mistakes.

The references in the text and in the references section are not formatted correctly. If a reference management program (Mendeley, Zotero, etc.) was used to input refs into the text, the authors should carefully check for errors. Please review Processes guide for authors for reference format. MDPI typically requires numbering of refs in text based on their first appearance. In this paper, some are numbered as superscripts and some are written out.

Response - The reference issues were addressed, and all the references were formatted to the MDPI template using EndNote

In addition, the formatting of figures and tables should be improved. For example, the outer border of figure 6 should be removed and the caption removed from inside a border/cell. Column colors (ex. green and tan in fig 6) should be changed to black and grey or white with black outlines. This makes figures more clear for those who are colorblind. Line graphs can be changed to different patterns rather than different colors (e.g. black dashes, lines, dots, etc.). Inside borders of tables should be removed, and only use horizontal lines that separate treatments from result data for the outermost border of the table.

Response: Figures and tables were improved as suggested by the reviewer

There are many inconsistencies with units (e.g. sometimes the authors write out minutes and hours and other times use min and h). Sometimes the degree symbol is between the number and "C" without spaces and other times there are spaces. The same inconsistencies are there for "greater than" and "less than" symbols. pH values should include the tenths place (ex. 6.0 instead of 6). Please be consistent and consult the author guidelines.

Response: All the issues related to units and formatting inconsistencies were addressed

Did the authors perform any statistical analyses on the data? AFor example, were the differences between AMOB and slag significantly different?

Response: The performance of AMOB and slag on batch kinetics studies were not dramatically different because, in a batch system, the mixing is fast; hence the adsorption kinetics are likely similar. But the fixed-bed system is more representative of the applied system, and the slag performs poorly versus the AMOB, but their mixture performs somewhat satisfactorily. Therefore, we believe that instead of AMOB or slag along, their blend can perform better with respect to 1) flow rates, 2) synergetic adsorption/precipitation, and hence 3) slow phosphate leaching.

In this study, we wanted to introduce this material and compare its performance with slag. However, no statistical comparison was performed since our system is a simulated laboratory system. Our future work (a continuation of this paper) will look into more systematic and holistic evidence on these material's capability to treat natural agricultural runoff waters and use them in slow-release fertilizer applications.

Please remove the grey background on Figure 10, and make the labels "a, b, c" more prominent. Keep them consistent with other figures (uppercase, lowercase, etc.). 

Response – This figure was improved

Please provide line numbers in the manuscript when submitting to journals. 

Response – Line numbers were added in the revised version

 

Author Response File: Author Response.docx

Reviewer 2 Report

This paper is a case study for analyzing the remediation of aqueous phosphate agricultural runoff using slag and Al/ Mg modified biochar. However, some questions have not been well addressed. Thus, my suggestion is major revision at this stage. 

 

1. Page 13: authors mentioned the historical agricultural runoff data. However, the features of this data was not found in this paper.  

 

2. I did not found any information on the changes of agricultural runoff. Authors emphasized the effects of slag and Al/ Mg biochar on runoff.  However, the results about how the slag and Al/ Mg biochar affects runoff was not deeply described. 

 

3. If we did not add the slag and Al/ Mg biochar, how agricultural runoff will change?

 

4. The reference section was not well organized. Please refer to the requirements of this Journal. 

Author Response

Reviewer 2 comments

This paper is a case study for analyzing the remediation of aqueous phosphate agricultural runoff using slag and Al/ Mg modified biochar. However, some questions have not been well addressed. Thus, my suggestion is major revision at this stage. 

Response - Thank you for your comments and views on our manuscript.

1. Page 13: authors mentioned the historical agricultural runoff data. However, the features of this data was not found in this paper.  

Response - Thank you for your comment. We have included relevant references to support this statement in the revised version. The key features of this data relevant to our work are pH and temperature, which we already have stated in section 2.2.1. The phosphate concentrations on the runoff can vary dramatically from location to location, and we used elevated phosphate concentrations i.e., 500 mg/L, to unveil the highest uptake capacities of the materials. Our future studies will be focused mainly on the background concentration of phosphate in the agricultural run-off is MS. However, this study primarily focuses on introducing the AMOB material and evaluating its phosphate uptake compared to slag.

2. I did not found any information on the changes of agricultural runoff. Authors emphasized the effects of slag and Al/ Mg biochar on runoff.  However, the results about how the slag and Al/ Mg biochar affects runoff was not deeply described. 

Response - We would like to bring reviewer’s kind attention to our adsorption experiments with simulated agricultural runoff. Typically, the agricultural run-offs contain large amounts of phosphate due to the excessive use of fertilizers. So, we simulated our solutions by spiking large amounts of phosphate. We agree that the runoff may contain other species such as nitrates, sulfates etc. However, this study is the introductory study of this materials and assessing its synergetic effects with slag.  

3. If we did not add the slag and Al/ Mg biochar, how agricultural runoff will change?

Response - Run off phopshate can typically endup in lakes and ponds and lead to eutrophication. Soil may can retain a fraction of the runoff nutrients depends on the type of soil. However, this study did not looked into such aspects. Our future studies are focused more on soil, slag and AMOB biochar on runoff treatment,

4. The reference section was not well organized. Please refer to the requirements of this Journal. 

Response - The reference issues were addressed, and all the references were formatted to MDPI template using EndNote

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The MS can be accepted at this current stage.