The Removal of Cr(VI) from Aqueous Solutions with Corn Stalk Biochar
Round 1
Reviewer 1 Report
In general, the article is written clearly, in correct language, the substantive issues are clearly presented.
However, it is accepted custom and an editorial requirement that figures be preceded by a reference to them.
The literature review includes 22 items, including those from recent years. It should be considered sufficient.
The BBD method should be described in more detail. Its basic assumptions, scope of applicability and organics should be given.
My suggestion is to introduce a few words in the conclusion section about the practical implementation of the results obtained.
In addition, the first paragraph of introduction seems too popular science, and in this light, unnecessary. I suggest a richer graphic part, supplemented with photographs of measuring equipment.
Author Response
Point 1: In general, the article is written clearly, in correct language, the substantive issues are clearly presented.
Response 1: Thank you very much for reviewing our manuscript and giving us the opportunity to revise, and thank you for approving our article.
Point 2: However, it is accepted custom and an editorial requirement that figures be preceded by a reference to them.
Response 2: Thank you very much for reviewing our manuscript and giving us the opportunity to revise. We adjusted the order of figures and descriptions.
Point 3: The literature review includes 22 items, including those from recent years. It should be considered sufficient.
Response 3: Thank you very much for reviewing our manuscript and giving us the opportunity to revise, and thank you for approving our article.
Point 4: The BBD method should be described in more detail. Its basic assumptions, scope of applicability and organics should be given.
Response 4: Thank you very much for reviewing our manuscript and giving us the opportunity to revise. We added the content about the BBD method. See line 74-82.
Point 5: My suggestion is to introduce a few words in the conclusion section about the practical implementation of the results obtained.
Response 5: Thank you very much for reviewing our manuscript and giving us the opportunity to revise. We added some results in the conclusion. See line 322-324.
Point 6: In addition, the first paragraph of introduction seems too popular science, and in this light, unnecessary. I suggest a richer graphic part, supplemented with photographs of measuring equipment.
Response 6: Thank you very much for reviewing our manuscript and giving us the opportunity to revise. We simplified the content of the first paragraph in the introduction and added the schematic illustration of adsorption experiments. See line 29-31 and Figure 1.
Reviewer 2 Report
Dear authors, the motivation of your study does not seem convincing since you are claiming “without the need for further treatment or activation.” It is generally known that the activation process will produce a better adsorbent with at least 100 times larger of surface area for adsorption. Also, the overall novelty is weak. Following are some of my comments for future consideration:
1. Since the experimental design involves “The Box-Behnken design (BBD)”, relevant literatures should be presented in the introduction, explaining why this method was used instead of central composite design (CCD).
2. How the “low level” and “high level” in the Table 1 being determined? Did the author referring to any literature to derive this? Or did the author perform any preliminary study to determine this?
3. “The total pore volume and specific surface area of bio-135 char were 1.71×10-2 cm3/g and 3.36 m2/g, respectively.” The biochar has low surface area. What makes the authors think that without further pretreatment (e.g. activation to produce activated carbon that has at least 100 times better of surface area for adsorption) is a better idea? From your findings, I’m not convince, please justify.
Author Response
Point 1: Since the experimental design involves “The Box-Behnken design (BBD)”, relevant literatures should be presented in the introduction, explaining why this method was used instead of central composite design (CCD).
Response 1: Thank you very much for reviewing our manuscript and giving us the opportunity to revise. We added the content about the BBD method and the relevant literatures about BBD have been presented in the introduction. Box-Behnken design（BBD）is one of the commonly response surface analysis, which is mainly applied to the optimization of process variables with less than 5 factors and 3 levels. Moreover, the BBD has the advantages of being able to evaluate the nonlinear influence of factors, and requiring fewer tests than the central composite design (CCD) when the number of factors is the same. In the experiment, the removal efficiency (%) of Cr(VI) by biochar was used as the evaluation index, and four factors, the Cr(VI) concentration (40 mg/L, 60 mg/L, and 80 mg/L), pH (2, 4, and 6), biochar concentration (2 g/L, 4 g/L, and 6 g/L) and contact time (120 min, 240 min, and 360 min) were established. Each factor had three levels. So we selected the BBD response surface method to obtain the optimal conditions for Cr(VI) removal by corn straw biochar.
Point 2: referring to any literature to derive this? Or did the author perform any preliminary study to determine this?
Response 2: Thank you very much for reviewing our manuscript and giving us the opportunity to revise. I am very sorry that we may have misunderstood our meaning due to our unclear statement. Taking untreated corn stalk biochar as adsorbent, the paper investigated the effects of pH, biochar concentration, Cr(VI) concentration and contact time on Cr(VI) removal, and evaluated the interaction of factors and analyzed the optimal process conditions for Cr(VI) removal by the untreated corn stalk biochar. It does not mean that the biochar can achieve better effects without the need for activation or treatment. We have corrected the mistake in the abstract and introduction.
Point 3: and 3.36 m2/g, respectively.” The biochar has low surface area. What makes the authors think that without further pretreatment (e.g. activation to produce activated carbon that has at least 100 times better of surface area for adsorption) is a better idea? From your findings, I’m not convince, please justify.
Response 3: Thank you very much for reviewing our manuscript and giving us the opportunity to revise. I am very sorry about our unclear statement. We took the untreated corn stalk biochar as adsorbent to study its adsorption effect on Cr(VI) removal. It does not mean that the biochar can achieve better effects without the need for activation or treatment. We have corrected the mistake in the abstract and introduction.
Round 2
Reviewer 2 Report
Accept in current revised form
