Enhanced Phosphorus Removal from Wastewater Using RSPRC and a Novel Reactor

Round 1

Reviewer 1 Report

The manuscript reports on the production of Residue and Soil Phosphorus Removal Composite (RSPRC) from activated clay, steel sludge and fly ash. The suitability of the obtained materials for the removal of phosphorus in simulated wastewater was also assessed by batch experiments. Experiments implementing a prototypal concentric circular diversion wall adsorption reactor were also presented. The manuscript is well arranged scientifically and contains much new information, but an improvement of some sections should be provided. The paper contains useful information in the field of water remediation by solid sorbents and for these reasons, I consider the paper suitable for publication, but before this, some revisions should be done. I suggest to improve the entire manuscript taking into account the following indications: 

Entire manuscript:

• The work plan is correct and the manuscript is easy to follow, but, anyway, I suggest a linguistic revision and a proper check for some grammar errors. Some sentences are quite unclear and need to be rewritten.
• There is a large use of acronyms (also in the title) within the text and since many of them are not the well accepted and known acronyms, I suggest to create a section of abbreviations and the first time you use an acronym in the document, the words should be written out with the short form placed in parentheses immediately after. Anyway, I suggest to avoid the use of acronym in the Title.

Introduction:

• Some aspects related to the phosphorus pollution should be improved. Which are the main sources of phosphorus release in wastewater? Which is the concentration limit allowed by national or international rules? Which are the damages related to phosphorus pollution? Are there statistical evaluations? Which is the typical concentration of phosphorus and the pH of a contaminated wastewater?
• Line 38: check the sentence starting with However,…
• Lines 50-52: please rewrite, it is quite confusing and unclear.
• Line 56: why the authors use the word arrangement to indicate the distribution of the adsorbent inside the reactor?

Experimental section:

• Section 2.1: A scheme with the reactor dimensions should be provided.
• Section 2.1, line 62: which is the difference between “a diversion wall” and “diversion walls”, are they different? If yes, please specify.
• Section 2.2: the characteristic of the foaming agent should be provided (composition, type, seller, and so on).
• Section 2.2: the acronym EPRC stays for what?
• Section 2.3: move in the section 2.2 the details about the preparation of RSPRC and the table 3
• Section 2.3: more details about the main contaminants of the polluted water used for decolorization test should be provided. Which are the main contaminants in the used wastewater?
• Section 2.3, lines 115-117: the description of the decolorization experiment should be improved? What do the authors mean with “was decolorized with vacuum”?
• Which is the reproducibility of the reported data? How many times the decolorization and the P adsorption tests have been performed?
• Have the authors tested also the cyclic use of the proposed materials?
• Did the authors perform leaching test to probe the loss of ions or components from the produced RSPRC?
• There are no details about the instruments and the experimental conditions applied to structural characterize the synthetized materials.

Results and Discussion section:

• Section 3.1: The data about the decolorization properties of RSPRCs are ancillary to the main focus of the work (P adsorption) and they are not integrated with the remaining part of the text, so a question arises: why are they included in this manuscript?
• Section 3.1: Compositional, morphological and textural details of the materials object of study are missing, why? The characterization of the materials surface chemistry and of their textural properties is very important for understanding the measured adsorption performances.
• The authors did not evaluate the pH effect on the adsorption performances of the produced materials, which is the expected pH of the real wastewater rich in phosphorus?
• Section 3.4 and Table 5: why each condition has been tested with a different effluent concentration? This does not allow a homogeneous comparison of the data.
• Section 3.5 and line 327: BF stays for what?

Author Response

Dear Editor-in-Chief Applied Sciences Journal Thank you for the time and effort spent in reviewing our manuscript entitled “Enhanced phosphorus removal from wastewater using RSPRC and a novel reactor” (ID: applsci-795494). These comments are highly valuable and very helpful for revising and improving the quality of our manuscript, as well as the important guidance for to our research work. We have studied all the comments very carefully and have made corrections with utmost care. Revised portion are marked in YELLOW color in the revised manuscript. Kindly consider our revised manuscript for further process and publication in Applied Sciences journal. With regards, Zhang Limin

1) I suggest a linguistic revision and a proper check for some grammar errors. Some sentences are quite unclear and need to be rewritten.

Response: Thank you for the kind suggestion. We checked it out and corrected some grammar errors. Some sentences you mentioned later were rewritten. I have to improve my English while doing research

2) There is a large use of acronyms (also in the title) within the text and since many of them are not the well accepted and known acronyms, I suggest to create a section of abbreviations and the first time you use an acronym in the document, the words should be written out with the short form placed in parentheses immediately after. Anyway, I suggest to avoid the use of acronym in the Title.

Response: We have made correction according to the suggestion. We have changed the title “Enhanced phosphorus removal from wastewater using RSPRC and a novel reactor” to “Enhanced phosphorus removal from wastewater using a composite and a novel reactor”.(Line 3) In the abstract, where the acronym is first used, we have written out the words with the short form placed in parentheses immediately after.(Lines 13-14)

3) Some aspects related to the phosphorus pollution should be improved. Which are the main sources of phosphorus release in wastewater? Which is the concentration limit allowed by national or international rules? Which are the damages related to phosphorus pollution? Are there statistical evaluations? Which is the typical concentration of phosphorus and the pH of a contaminated wastewater?

Response: Thanks for the kind advice. The statements of “Phosphorus is one of the core elements that cause water eutrophication. At the same time, phosphorus is an indispensable nutrient element for life. Phosphorus exists in all cells of the human body and participates in almost all physiological chemical reactions.” were replaced with “Phosphorus (P) usually originates from human and animal wastes, household detergents, food-processing effluents, commercial fertilizers, and agricultural land runoffs. Phosphorus is a major nutrient for biomass growth. However, excessive concentration of P in water bodies such as lakes, lagoons or rivers causes an abnormal growth of algae and aquatic plants resulting in the degradation of the water quality. State Environmental Protection Administration of china has recommended total P should not exceed 0.5mg/L according to the class A demands of discharge standard of pollutants for municipal wastewater treatment plant (GB18918-2002). The European Union (EU) maintains that the cut-off for total P concentration between at risk and not risk of eutrophication in lakes is < 10 µg/L to > 100 µg/L, and for rivers, total P concentration below 0.01-0.07 µg/L is considered premium waters. Therefore, the enhanced removal of phosphorus is the trend.”(Lines 24-33) The pH of a contaminated wastewater is usually from 6.5 to 7.5. Generally, the phosphorus concentration in the influent of municipal wastewater treatment is 4-7 mg/L. The average total phosphorus concentration in the effluent of the second settling tank is 0.3-0.4 mg/L. Because we studied the enhanced removal of wastewater, so we determined the concentration of phosphorus was set to 0.3, 0.4 and 0.5 mg/L. We haven’t found the statistical evaluation currently.

4) Line 38: check the sentence starting with However,…

Response: We are very sorry for our incorrect writing. The sentence has been corrected as “However, there is clearly a lack of research related to the phosphorus removal performance of activated clay.”(Lines 45-46)

5) Lines 50-52: please rewrite, it is quite confusing and unclear.

Response: Thank you for underlining this deficiency. The statements of “Therefore, residue and Soil Phosphorus Removal Composite (RSPRC) prepared in our laboratory was selected as the adsorbent and a concentric circular diversion wall adsorption reactor was developed as the adsorption device.” corrected as “Therefore, the prepared RSPRC was used as the adsorbent and a concentric circular diversion wall adsorption reactor was developed as the adsorption device.”(Lines 57-58)

6) Line 56: why the authors use the word arrangement to indicate the distribution of the adsorbent inside the reactor?

Response: We are very sorry for our negligence of the wrong use of this word “arrangement”. We have replaced it with “distribution” in the entire article. (Line 62)

7) Section 2.1: A scheme with the reactor dimensions should be provided.

Response: Thank you for the useful suggestion. “The design scheme of the concentric circular diversion wall adsorption reactor was as follows: comparing the advantages and disadvantages of the existing reactors, combined with the purpose of this research, the preliminary design scheme of the reactor type, namely the fixed bed type, was proposed. In order to realize the functions of multi-stage series adsorption and flexible distribution of adsorbents, taking the oxidation ditch for reference, the reactor adopted the shape of concentric circles and was equipped with slots and grills. Based on the preliminary design scheme, comprehensively considering the advantages and disadvantages of various types of materials, after repeated research and discussion with the manufacturer on the details of the reactor, stainless steel was chosen as the reactor material and the necessary adjustment of the reactor structure were made. Finally, the reactor dimensions were determined, such as the height-to-diameter ratio of the reactor, the size of the water inlet and outlet, and the size of the overflow port and so on.” was added in section 2.1. (Lines 68-78)

8) Section 2.1, line 62: which is the difference between “a diversion wall” and “diversion walls”, are they different? If yes, please specify.

Response: Thank you for your careful examination. We are very sorry for our incorrect writing. They are the same thing. We have corrected it and will pay more attention to the usage of words. (Line 80)

9) Section 2.2: the characteristic of the foaming agent should be provided (composition, type, seller, and so on).

Response: As you suggested that we have provided the characteristic of the foaming agent in section 2.2. The sentence “The plant-type foaming agent was bought from Shanghai Fangbao Building Material Technology Co., Ltd. The plant-type foaming agent was prepared from rosin and sodium hydroxide through saponification reaction and has the advantages of low cost and large foam production.” was added. (Lines 133-136)

10) Section 2.2: the acronym EPRC stays for what? Response: The Efficient Phosphorus Removal Composite (EPRC) is composed of steel slag and fly ash. RSPRC and EPRC are basically the same in terms of material physical properties. Therefore, we take the optimal dosage of plant-type foaming agent in EPRC for reference when preparing RSPRC. (Line 131)

11) Section 2.3: move in the section 2.2 the details about the preparation of RSPRC and the table 3.

Response: It is more appropriate as you suggested, we have moved the details about the preparation of RSPRC and Table 3 to section 2.2. (Lines 105-115)

12) Section 2.3: more details about the main contaminants of the polluted water used for decolorization test should be provided. Which are the main contaminants in the used wastewater?

Response: Thank you for your kind suggestions. As we studied the decolorization performance of RSPRC, we didn’t detect the main contaminants of the polluted water. Your suggestion is very important. We haven’t considered the details. I will learn from the advice in the future research.

13) Section 2.3, lines 115-117: the description of the decolorization experiment should be improved? What do the authors mean with “was decolorized with vacuum”?

Response: Thanks for the kind comments. We are very sorry for mistake in language e.g. “was decolorized with vacuum”. We have re-written this part according to the suggestion. We have replaced it with “250 mL wastewater was taken into the conical flasks. As shown in Table 3, 5 g adsorbents of different groups were respectively added. The colored wastewater was slowly stirred for 20 min and stood for 2 h. After that, the wastewater was filtered and the filtrate was taken to measure absorbance.” (Lines 139-142)

14) Which is the reproducibility of the reported data? How many times the decolorization and the P adsorption tests have been performed?

Response: As for the reproducibility of the reported data, we think if the methods are consistent and the materials are similar, it is possible to obtain similar conclusions. We performed three times of the decolorization and the P adsorption tests. When we did each experiment, we performed 3 times to reduce the error.

15) Have the authors tested also the cyclic use of the proposed materials? Did the authors perform leaching test to probe the loss of ions or components from the produced RSPRC?

Response: Thank you very much for your kind suggestion. It is very useful and profound. We haven’t tested also the cyclic use of RSPRC and haven’t performed leaching test to probe the loss of ions or components from the produced RSPRC. Due to your suggestion, I have found the shortcomings in my current work. I will consider these aspects and improve the scientific research level in my future work.

16) There are no details about the instruments and the experimental conditions applied to structural characterize the synthetized materials.

Response: Thank you very much for your kind suggestion. We have added details about the instruments and the experimental conditions applied to structural characterize the synthetized material in section 3.2. (Lines 225-226)

17) Section 3.1: The data about the decolorization properties of RSPRCs are ancillary to the main focus of the work (P adsorption) and they are not integrated with the remaining part of the text, so a question arises: why are they included in this manuscript?

Response: Thank you very much for valuable comments. Although the focus of the article was to study the P adsorption, the influence of the addition of activated clay on this was also studied. Since activated clay has good decolorization performance, it was investigated whether RSPRC also has good decolorization performance. The results showed it has good decolorization performance, which broadens the use of RSPRC. So we included in this manuscript.

18) Section 3.1: Compositional, morphological and textural details of the materials object of study are missing, why? The characterization of the materials surface chemistry and of their textural properties is very important for understanding the measured adsorption performances.

Response: Thank you for your kind suggestions. It is really true as you suggested. I didn’t add the details and overlooked the importance of this, because I thought its application was more important, I mistakenly thought it was unnecessary to write it. According to your suggestion, I added the characterization of the materials surface chemistry and their textural properties in section 3.2. (Lines 225-239)

19) The authors did not evaluate the pH effect on the adsorption performances of the produced materials, which is the expected pH of the real wastewater rich in phosphorus?

Response: Thank you for your kind query. We haven’t not evaluated the pH effect on the adsorption performances of RSPRC. I will consider this problem in future research according to your comment. When we conducted the experiment, the pH was adjusted to 7. Thanks for reminding, we have added the pH in section 2.3-2.7. (Lines 148,174,181,194)

20) Section 3.4 and Table 5: why each condition has been tested with a different effluent concentration? This does not allow a homogeneous comparison of the data.

Response: As shown in the Table 6, the initial P concentration was 0.5 mg/L, and the P effluent concentration was different under four different distributions of adsorbents. It was because the distribution of adsorbent had an effect on P adsorption. (Line 364)

21) Section 3.5 and line 327: BF stays for what?

Response: We quoted an article entitled “Methodological aspects of using blast furnace slag for wastewater phosphorus removal”, the research object of which is Blast Furnace (BF) slag. According to the comment, we expanded BF in section 3.6. (Line 372) Once again, we would also like to thank for you for your valuable comments and positive feedback on our research work. We tried our best to improve the manuscript quality and made some changes according to your kind suggestions and comments.

Reviewer 2 Report

This work is devoted to the development of a multi-component sorbent based on fly ash, steel slag, and activated clay. The resulting composite was studied as a sorbent for the treatment of wastewater from phosphorus, as well as their decolorization. In addition to the sorbent itself, a wastewater treatment reactor was developed. The topic of the article is relevant, and the results are new. However, some changes need to be made.

A significant part of the manuscript is devoted to the study of the effect of the additive of activated bentonite on the sorption properties of the composite. However, neither bentonite itself nor its modified sample have been sufficiently studied. It is necessary to indicate the origin of the sample, its mineral, and chemical composition. Since an increase in the porosity and specific surface area of ​​activated clay is discussed in the text of the article, it would be important to measure these parameters in natural and activated bentonite.

Other changes to the text:

Abstract - add a description of the materials and methods that were used.

103 - the origin of bentonite?

103-111 - move to section 2.2.

XRF - add a description of the technique and device

168 - expand abbreviation HRT

185 - a wrong formula

186-189 - Each specific bentonite is converted differently. The main increase in the specific surface area is not due to impurities, but due to the transformation of montmorillonite and changes in its structure.

Author Response

Dear Editor-in-Chief Applied Sciences Journal Thank you for the time and effort spent in reviewing our manuscript entitled “Enhanced phosphorus removal from wastewater using RSPRC and a novel reactor” (ID: applsci-795494). These comments are highly valuable and very helpful for revising and improving the quality of our manuscript, as well as the important guidance for to our research work. We have studied all the comments very carefully and have made corrections with utmost care. Revised portion are marked in YELLOW color in the revised manuscript. Kindly consider our revised manuscript for further process and publication in Applied Sciences journal. With regards, Zhang Limin

1) A significant part of the manuscript is devoted to the study of the effect of the additive of activated bentonite on the sorption properties of the composite. However, neither bentonite itself nor its modified sample have been sufficiently studied. It is necessary to indicate the origin of the sample, its mineral, and chemical composition. Since an increase in the porosity and specific surface area of activated clay is discussed in the text of the article, it would be important to measure these parameters in natural and activated bentonite.

Response: Thank you very much for your kind suggestions and comments. It is really true as you suggested. We are very sorry for negligence of the importance of this. According to your suggestion, I added the Characterization of RSPRC in section 3.2. (Lines 225-239) The origin of the ingredients was also be added in the article.

2) Abstract - add a description of the materials and methods that were used.

Response: Considering your kind suggestion, we checked the abstract and found we had made a short description “In order to deep dephosphorize in wastewater, two different industrial wastes (steel slag, fly ash) were blended into activated clay as adsorption substrate, supplemented with binder and foaming agent to prepare RSPRC (Residue and Soil Phosphorus Removal Composite).” in the abstract. Considering the characteristics of the abstract, we provided the details in materials and methods.

3) 103 - the origin of bentonite? Response: The bentonite was from Tangshan, Jiangning District, Nanjing. We added the origin of bentonite in section 2.2. (Lines 106-107) 4) 103-111 - move to section 2.2.

Response: It is more appropriate as you suggested. We have moved the sentences Lines 103-111 and Table 3 to section 2.2. (Lines 105-115)

5) XRF - add a description of the technique and device

Response: Thank you for your kind advice. I am deeply sorry for the lack of information about the description of XRF. Because my research is to continue the previous research of the team, I checked the previous information and asked the teacher, I learned that the chemical composition was marked on the product manual, and the material was sent to the school analysis center for testing and verification after purchase. After asking my teacher, I added this sentence “The Chemical composition of the steel slag and fly ash was analyzed by wavelength dispersive X-ray fluorescence analyzer (XRF-1800) produced by Shimadzu.” to section 2.2. (Lines 97-101)

6) 168 - expand abbreviation HRT

Response: Thank you for the suggestion. We have expanded abbreviation HRT to hydraulic retention time. (Line 194)

7) 185 - a wrong formula

Response: We are sorry for this mistake and thank you for your careful examination. Considering the suggestion, we have deleted the wrong formula. I will try to be more rigorous in the future research. (Line 194)

8) 186-189 - Each specific bentonite is converted differently. The main increase in the specific surface area is not due to impurities, but due to the transformation of montmorillonite and changes in its structure.

Response: Thanks for your kind suggestion. We are very sorry for our incorrect writing. The statements of “During the acid activation treatment, Wang et al. and Vlasova et al. found that the impurities contained in bentonite exchanged with ions to form a microporous mesh structure, which dramatically increased the porosity and specific surface area of the activated clay. Because of this, RSPRC have good adsorption and decolorization performance” were corrected as “During the acid activation treatment, Wang et al. and Vlasova et al. found that Na+, Mg2+, K+, Ca2+ and other cations between the bentonite layers can be converted into soluble salts and dissolved out, increasing the layer spacing, and forming a porous active substance with a microporous mesh structure and a large specific surface area. Additionally, the impurities distributed in the bentonite structure channels can also be removed, and the pore volume was increased, which was beneficial to the diffusion of adsorbate molecules.” (Lines 213-218) Once again, we would also like to thank for you for your valuable comments and positive feedback on our research work. We tried our best to improve the manuscript quality and made some changes according to your kind suggestions and comments.

Round 2

Reviewer 1 Report

Dear Authors, 

Thanks for your fruitful corrections, 

All the best for furture research