The Improvement of Rice Straw Anaerobic Co-Digestion with Swine Wastewater by Solar/Fe(II)/PS Pretreatment
Round 1
Reviewer 1 Report
The following comments address some questions to be considered by the authors.
1.- The abstract should be rewritten in order to avoid the use of abbreviations without previous definition (R2, CK). Moreover, authors should avoid the use of abbreviations in abstract.
2.- It is typical to indicate that direct incineration causes environmental pollution but it is not true because a pollution control system is coupled to incineration system. Then, I recommend to the authors that present the treatment (Co-digestion after pretreatment) as a more sustainable alternative.
3.- The authors should quantify C/N too high or too low (a range of values is required). Which is the C/N of RS?
4.- What kind of swine wastewater is interesting for the process? What is an appropriate C/N ratio? Could the authors provide values of swine wastewater generated by year?
5.- An exhaustive characterization of RS and SW is required. Moreover, the PrS should be characterized in order to know the N concentration added to R2 experiment versus R1. Is the pre-treatment carried out at ambient conditions?
6.- More information of inoculum is required (source).
7.- What is the colour of the solution in which sugar content is determined? Could be any interference in the measurement using DNS method?
8.- Can the authors explain how is determined de RS degradation by gravimetric method?
9.- In the description of VFAs determination information of the CG-method and column used is required.
10.- Equation 1 is obvious.
11.- The authors indicate that “In this study, prolonging the activation time of PS by Solar/Fe(II) will not only increase the removal rate of lignin, but also increase the degra-dation of reducing sugar in the PrS by free radicals, and reduce the production of reducing sugar”, but these date are not shown in the manuscript. The evaluation of the pretreatment time is interesting to justify the selected time.
12.- In repetitive sentences the authors comment that “the process is energy-saving and environment-friendly”, but a justification is required to add value to the manuscript.
13.- The study about the pH is vague. I see differences in the results obtained at pH 7 or pH 9. The authors should justify the selection of pH.
14.- Regarding SEM micrographs the authors indicate that “the RS surface porosity is increased by the treatment”, how can the authors appreciate the porosity in the micrograph? Is there any measurement of porosity?
15.- The Figure 4 should improve including the “functional groups” in the graph. How is the transmittance measured?
16.- The sCOD is higher in R2 than in R1 or CK, but how the authors know that it is because the solubilization of sugars, acetic acid or phenolic compounds? A determination (CG-MS) is required. Why have the authors selected a volume of 0.4 L of PrS to add in R2 experiments?
17.- In order to say that R1 sCOD is higher than CK sCOD in the 6th day, the error of the determination should be included in the figure.
18.- In page 6 the authors indicate “This indicates that pretreatment of RS with Solar/Fe (II)/PS is not only beneficial for methane production in AD process, but also for subsequent treatment of AD effluent”, but the results about methane production have not been commented yet.
19.- Why do R1 and R2 TAN present the same value?
20.- Regarding Figure 5, can the authors support that CK suffer AD inhibition?
21.- Figure 6: to indicate that the lines represent the pH value.
22.- The role of Fe of R2 in the production of VFAs should be explained. Which is the concentration of Fe in the experiment? How is the Fe concentration determined?
General comments:
In the text, the author should use a certain number of significant figures
Typos:
Page 3: The co-AD “were”….
Page 3: “solor”
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript is written well and has valuable results. The format of figures is good. I think it can be published. Some minor revisions are required:
Reference must be used to interpret the results. Some interpretations are without references.
The results should be compared with other studies.
Conclusion must be improved.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The text that is the subject of this review is devoted to the study of the pretreatment of rice straw with the swine slurry for conditioning of plant biomass for anaerobic fermentation bacteria. This process is of great practical importance, as it not only allows the management of unnecessary and even harmful waste but also its use for energy purposes. It is vital for environmental protection and sustainable development. That is why the topic could be considered as very important, current both from the scientific point of view, but above all, from the practical point of view.
The material presented in the text is valuable and exciting. However, while reading the text, it is possible to find some imperfections that must be corrected and supplemented.
1. On page 3, chap. 2.2.1 describes the solar treatment procedure - there is no information about the intensity of sunlight radiation and the conditions of this irradiation. The time of sunlight exposure only is not enough. Different sun irradiation conditions will be held in different seasons of the year, at different external temperatures, and at different angles of radiation incidence (latitude). So there is a need to use a more accurate way of determining the intensity of sunlight exposure.
2. The title's content is slightly surprising because it is a declarative sentence in the personal form. The titles of technical, scientific papers are rather not in the form of declarative sentences. Consider using the impersonal form, e.g. "The improvement of rice straw anaerobic co-digestion with swine wastewater after its Solar/Fe(II)/PS pretreatment".
3. At the end of chapter 1, the purpose of the research is very shortly mentioned in two sentences. Perhaps it would be worthwhile to indicate the presented research's purpose explicitly and in a more extensive form.
4. On page 4, in line 8 from the bottom, the reaction equation should be moved close to the place of citation - after line 5 from the top.
5. The graph in Figure 4 has no value on the Y-axis (transmittance) - it should be supplemented.
6. Chapter 5 (conclusion) is too perfunctory and lapidar. The results should be more widely discussed and maybe generalized to other materials (straw and/or slurry).
Regardless of the remarks, the text has excellent cognitive value, which may be used in future research in this process, which is very important from a practical point of view.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have removed controversial information and have explained the required aspects.
