The Occurrence of Legacy P Soils and Potential Mitigation Practices Using Activated Biochar
, Ariel A. Szögi 1, Kenneth Pantuck 2, Don W. Watts 1 and Mark G. Johnson 3Round 1
Reviewer 1 Report
This study is interesting and novel; however, there are few concerns
- Line 34. wasters replaced by waste
- Line 54- 64 I recommend the authors need to discuss the environmental risk of long-term application of manure and potential assessment such as degree of P saturation (DPS), soil P storage capacity (SPSC) and P stability ratio (Psat) …. to predict potential P loss from the soils and Management practices that reduce agricultural losses of P.
- Line 94. Sediment replaced by soil
- In the section 2.3 line 125: 1) the technologies in the title should include more than one not only "P-sorbing materials" 2) in this section you mentioned also that "acid mine drainage treatment (AMD) residuals was found to decrease plant available P", it is known the pH decreasing increase the P availability, so you should explain the soil type and its properties in this study because the P behavior differ from soil to another one. In addition explain the nature of this sorbent material its mechanism in reducing P availability.
- In the line 157 "after pyrolysis" is contradicted with the line 22 "after pyrolysis"
- In the line 157: "biochar properties are often modified physically or chemically" I recommend to describe even briefly the physical and chemical activation processes because the paper mainly focuses on activated biochar.
- In the line 192: "The studies cited in Table 1 used a number of chemical and physical activation process on the biochars" such as what?
- Because you mention soil legacy P remediation requires further investigation: I recommend to extract more information form the studies in table 1 and also focus on the processes that led to P removal on this studies to be more focus on the review aim.
- In the line 197: the word "shoed" I think it is showed
- From line 205 to line 211 "For example, water holding capacity …… (1-2 mm) particle sizes 210 [87]." this is not related to this review and the review should emphasis more on the soil P.
- In the conclusion section you focused only on the activated biochar and in the text body didn't focus very well on it. Therefore, this part should be covered well in the main manuscript. In addition, other practices that you discussed on the review should be also extended to the conclusion.
- The recommendations and future studies should be added to the conclusion section.
Author Response
Reviewer #1:
Dear Sir,
Thank you very much for your valuable comments to our manuscript. We are grateful and appreciate your very nice comments which helped to improve our paper. We have responded to all your comments and the detail corrections are listed below line by line and we hope this edition is suitable and cover all the comments.
Line 34. Wasters replaced by waste.
Author’s response: We have replaced wasters by waste.
Line 54-64. I recommend the authors need to discuss the environment risk of long-term application of manure and potential assessment such as degree of P saturation (DPS), soil P storage capacity (SPSC) and P stability ratio (Psat) … to predict potential P loss from the soils and Management practices that reduce agricultural losses of P.
Author’s response: The following text was inserted into our manuscript:
Although agronomic soil P test extensively used for making soil fertility recommendations, the soil P storage capacity (SPSC) concept, has been proposed as a diagnostic tool to assess the potential of P movement from field environment to surface waters and to estimate of legacy P loss at excessive concentrations for soils of eastern and central United States [15]. The SPSC is based on a threshold molar ratio of extractable P/(Al+Fe), called the soil P saturation ratio (PSR), above which water-soluble P abruptly increases [94]. The research results revealed, that the degree of P saturation (DPS), which relates a measure of P already adsorbed by a soil to its adsorption capacity, could be an indicator of soil’s P release capability. Particularly, for the threshold DPS (Mehlich-1 extract) of 30% is recommended for Florida sands, values for DPS of 31 to 60% warrant caution with regard to further addition of P to a land, and DPS values of >60% suggest soils will be a contributor to water quality impairment [95]. As a result, P stability in a soil with values below the threshold value indicate that P release from the soil is minimal [96]. Kleiman and Sharpley [97] research results showed that Mehlich-3 extractable P can be effectively used to estimate P sorption saturation for over a wide range of acidic and alkaline soils as well.
Line 94. Sediment placed by soil.
Author’s response: Sediment was replaced by soil.
Line 125. In the section 2.3: 1) the technologies in the title should include more than one not only “P-sorbing materials”. 2) in this section you mentioned also that “acid mine drainage treatment (AMD) residuals was found to decrease plant available P”, it is known the pH decreasing increase the P availability, so you should explain the soil type and its properties in this study because the P behavior differ from soil to another one. In addition, explain the nature of this sorbent material its mechanism in reducing P availability.
Author’s response: The following text was inserted into a paper:
Naturally occurring and waste materials
It appears that gypsum is a valuable strategy to control P movement [98,99] as well as large potential of waste materials, such as bauxite residuals, fly-ash, wood ash, slag [47]. Pen et al. [100] observed, that using steel slag as the P sorption material in the P removal structure resulted in 25% of all dissolved P removal from rainfall and irrigation events during the first 5 months period of structure operation. The other study demonstrated that the maximum adsorption capacity of the fly-ash and bauxite residuals were respectively 29 and 25 g kg-1 [101] and P removal vary based on by-products chemical properties [102, 103]. Therefore, P mobility can be controlled by Al, Fe, or Ca depending on pH. For an example, the P removal by AMD residuals and WTRs was a result of adsorption to Al or Fe-oxides/hydroxides or precipitation of Al- or Fe-phosphates. In contrast, P removal from stormwater by slag materials used in field scale filtration structures occurred through both (Ca and Al/Fe) mechanisms [104]. The mobility of P is also highly pH dependent. Lee et al., [105] observed that a higher P adsorption rate onto WTR was obtained at low reaction media (pH 4) as compared with neutral and the lowest P adsorption rate was obtained at pH 9. As Silva [106] reported, there are two highest peaks occur in the soil pH acid range of pH 4 and 5.5, where P precipitates with Fe and Al and the third peak occurs in alkaline soils around pH 8.0 when P, is precipitated primarily by Ca.
Line 157. In the line 157 “after pyrolysis” is contradict with the line 22 “after pyrolysis”.
Author’s response: ___ ???? ________ could not find contradict in those lines.
Line 157. In the line 157 “biochar properties are often modified physically or chemically” I recommend to describe even briefly the physical and chemical activation process because the paper mainly focuses on activated biochar.
Author’s response: The following text was inserted into a paper: “Physical biochar engineering techniques include ball milling modification, gas/steam activation, magnetization, and microwave irradiation”.
And
…, which includes its activation by: different acids (HCI, HNO3, H2SO4, H3PO4 and H2O2), with different alkali (NaOH, KOH), with different other oxidizing agents (KMnO4, Fe(III) [107] and salts (MgCl2, CaCl2) [67, 71, 78]”.
Line 192. “The studies cited in Table 1 used a number of chemical and physical activation process on the biochar” such as what?
Author’s response: The following text inserted into a paper:
…”to improve biochar’s physicochemical properties and enhance its adsorption performance”.
Because you mentioned soil legacy P remediation requires further investigation, I recommend to extract more information from the studies in Table 1 and also focus on the process that led to P removal on these studies to be more focus on the review aim.
Author’s response: The following text was inserted into the manuscript:
“MgO-biochar showed better phosphate adsorption in saline soils and the maximum phosphate adsorption capacity was 1.46 folds higher than biochar [77]. Phosphates were bound to the Mg-biochar not only by electrostatic adsorption but also by covalent bonds to form magnesium phosphate crystal [77, 78]”.
In the line 197 the word “shoed” I think it is showed.
Author’s response: Yes, we fixed “shoed” to showed.
Line 205-211. For example, water holding capacity …(1-2 mm) particle sizes 210 [87] “this is not related to this review and the review should emphasis more on the soil P.
Author’s response: A few sentences here only, which show the main purpose of our work with biochars (pristine or activated) and we would like to leave it as it is. Our program has done considerable research on the positive, negative, or neutral impact of biochars on soil properties (e.g., water retention, pH increases, etc.). We wanted to emphasize this in the manuscript.
The recommendations and future studies have been added to the conclusion.
Author’s response: The following text was inserted into the manuscript:
“Furthermore, biochar can be used as a soil amendment to improve soil quality by reducing heavy metals availability in contaminated soils, as well as a slow-release fertilizer for improving the fertility of the agricultural soils. However, we suggest that further biochar research needs to adjust biochar application rates under field environment conditions. In this way, the risk of high-risk pollution is reduced from heavy metals containing in those by-products”.
Reviewer 2 Report
The manuscript is interesting, however, contains only one table and no figures. I would appreciate in this review article if you submitted at least one or two illustrative images and expanded the manuscript a bit.
The significance of this study should be more emphasize in the introduction.
See these papers which can help you a lot. https://www.mdpi.com/2571-8789/4/4/74/htm
https://www.mdpi.com/2073-4441/12/10/2847
Line 37: How 36 or 40 million tons?
Line 57: Check the units throughout the manuscript.
Line 129: Would you please specify in what proportion?
Line 137: This topic has been discussed in detail in this important paper and should be added here as a reference. https://www.sciencedirect.com/science/article/pii/S0304389420316149
Line 153: This very important paper has addressed this issue in detail, and authors are therefore encouraged to add it here as a reference to improve the introduction. https://www.sciencedirect.com/science/article/pii/S0160412021001525
Line 157: What was the pyrolysis temperature?
Line 171: Please indicate measurement deviations. Did you do parallel measurements? To be satisfied with your results.
Line 187: Specific surface area (SSA) of wheat straw is he clearly the highest, what do you attribute to him?
Line 213: The conclusion needs to be extended. Indicate the possible risks of such research. Add your recommendations for future research.
Line 243: Make sure the references are added correctly according to the journal's instructions.
As I said at the beginning, the manuscript should be expanded and adapted to the requirements of the review article.
Author Response
Reviewer #2:
Dear Sir,
Thank you very much for your valuable comments to our manuscript. We are grateful and appreciate for your very nice comments which helped to improve our paper. We have responded to all your comments and the detail corrections are listed below line by line and we hope this edition is suitable and cover all the comments.
Line 37. How 36 or 40 million tons?
Author’s response: Although, both numbers are correct, from those two numbers 36 million metric tons and 40 million short US tons, we left written the number 36 metric tons.
Line 57. Check the units throughout the manuscript.
Author’s response: The units throughout the manuscript have been checked.
Line 129. Would you please in what proportion?
Author’ response: The following text was inserted into our manuscript: “The P-sorbing materials have been applied as an soil amendments at rates of 2.5, 5.0, 7.5, 10% (w/w)”.
Line 137. This topic has been discussed in detail in this important paper and should be added here as a reference.
Author’s response: The following text was inserted into our manuscript:
“The addition of Fe/Mn-and P-modified Al-WTR to the soil reduced significantly the concentrations of Pb (up to 60% by Fe/Mn-Al-WTR and 32% by P-Al-WTR) and Cu (up to 45% by Fe/Mn-Al-WTR and 18% by P-Al-WTR) in the shoots and roots of ryegrass as compared to raw Al-WTRs and untreated soil, according to [108]”, and added the paper “Fe/Mn and P-modified drinking water treatment residuals reduced Cu and Pb phytoavailability and uptake in a mining soil” and we cited it as a reference.
Line 153. This very important paper has addressed this issue in detail, and authors are therefore encouraged to add it here as a reference to improve the introduction.
Author’s response: The following text was inserted into our manuscript:
“Kang et al., [109] observed, that biochar application improved the soil bulk density, soil organic carbon content, pH, and cation exchange capacity in the field soil, which positively affected corn and Chinese cabbage growth” and added the paper: “Exploring suitable biochar application rates with compost to improve upland field environment” and we cited it as a reference.
Line 171. What was the pyrolysis temperature?
Author’s response: The following text was inserted into our manuscript: “The pyrolysis temperature for biochar derived from: poultry litter, cattle manure, rice straw, soybean straw, and corn were 450°C [61]; peanut hull 400, 500°C, pecan shell 350, 700°C, poultry litter 350, 700°C, switchgrass 250, 500°C [58]; pine chips, poultry litter 500°C [60]; wood chips: Japanese cedar, Japanese cypress, bamboo chips, rice husks, sugarcane bagasse, poultry manure were 400, 600 and 800°C [56]”.
The recommendations and future studies, possible risks have been added to the conclusion.
Author’s response: The following text was inserted into our manuscript:
“Furthermore, biochar can be used as a soil amendment to improve soil quality by reducing heavy metals availability in contaminated soils, as well as a slow-release fertilizer for improving the fertility of the agricultural soils. However, we suggest that further biochar research needs to adjust biochar application rates under field environment conditions. In this way, the risk of high-risk pollution is reduced from heavy metals containing in those by-products”.
Round 2
Reviewer 1 Report
The authors answered all the questions and modified the manuscript significantly.
Reviewer 2 Report
Manuscript can be accepted.
