Review Reports
- Jung Eun Park,
- Sang Eun Lee and
- Seokhwi Kim*
Reviewer 1: Qing Jin Reviewer 2: Mentore Vaccari Reviewer 3: Anonymous
Round 1
Reviewer 1 Report
I have reviewed ‘a comparative study on washing methods to remove sodium chloride in oyster shells waste’. The study is simple and easy to follow, however, the language is poor and needs significant improvement (better checked with a native speaker) before further consideration. Some other comments:
1. Why using tap water? Tap water contains different types of minerals including NaCl, which may affect the results.
2. Please add several sentences of how the shells were pretreated such as grinding method.
3. Why using agitation time of 1 min? Is there a reference support? Does this time sufficient?
4. Freshwater not freshwaters.
5. In the leaching test, what elution solution is used? Please be specific. Also please add reference for the conditions used in the leaching test.
6. Grammar issue of the sentence ‘to confirmation of washing water required…’
7. Please add the replication in the manuscript. In addition, add error bar/standard deviation in all figures and tables.
8. Section 3.1, 1.22%+3? Please double check this number.
9. Many grammar issues in the manuscript, please check throughout the manuscript.
Author Response
Comment #1: Why using tap water? Tap water contains different types of minerals including NaCl, which may affect the results.
Response: We appreciate reviewer’s kind comments. Generally, the experimenal values can be derived using D.I. water in a lab scale, but these experiment results will be used for 2ton/day plant so this experiment condition was conducted to apply them to field using tap water. Also, we measured the conductivity of tap water and corrected and calcuated based on the calculation formula. Therefore, we are absoutely sure that the results fo this study will not be different.
Comment #2: Please add several sentences of how the shells were pretreated such as grinding method.
Response: We appreciate reviewe’s kind comments. The shell we receive does not preprocess additionally in the field. However, the crushing was not intentionally carried out, but physically carried out in the process of separating the luggage rope, and information on the samples obtained in the field was added to the revised manuscript as follow.
On page 2, “The shell separates the luggage rope using a cylindrical centrifuge, and in this process, some of the shell is crushed. The speed of the centrifuge is about 250 rpm, and the size of the crushed shell is about 5 cm or less.”
Comment #3: Why using agitation time of 1 min? Is there a reference support? Does this time sufficient?
Response: We appreciate reviewer’s kind comments. In previous studies, we compared the effect of the washing time such as 1 minute, 2 minute, 3 minute, 4 minute, 5 minute, 6 minute, 7 minute, and 8 minute for the batch type, and the dissolution rate was the most common in 1 minute including error range. Therefore, we suggested the continuous washing time was conducted based on one minute and we judged that the factor for washing could be sufficiently confirmed even with one minute stirring.
Figure. NaCl elution concentration vs elapsed time on B-OWR1 and B-OWR6
Comment #4: Freshwater not freshwaters.
Response: We appreciate reviewer’s kind comments. As a reviewer point out, we changed freshwaster to tap waste in the experiment part and waster in the text in revised manucript as follow.
On page 3, “The batch experiment was conducted with 500 g of shells in a container by washing them with tap water by varying the ratio of the volume of tap water from one to six times the weight of the shells; 1:1, 1:3, 1:4, 1:5, and 1:6, the different ratios were denoted as B-OWR1 to B-OWR6 (B-OWR, batch-oyster shell to tap water ratio). Each of the oyster shell sample was agitated with the corresponding volume of tap water at 100 rpm at room temperature.”
On page 3, “In the continuous washing process, oyster shells were washed once, and the tap water used for elution of NaCl from the shells was removed, followed by the addition of tap water. The ratios of tap water used for the washing steps were maintained the same as those used for batch washing; the different ratios were denoted as C-OWR1 to C-OWR6 (C-OWR, continuous-oyster shell to tap water ratio).”
On page 3, “Considering that the oyster shells have not been washed with tap water during shucking, the concentrations of leached dissolved ions from the shell could be associated with those of seawater components. The NaCl content of the tap water eluted after batch or continuous washing was estimated indirectly using electrical conductivity.”
On page 4, “Since washing efficiencies could be attributed to the physical properties of the oyster shells, the washing method was tested based on the volume of water used, washing dura-tion, and mixing speeds.”
On page 4, “As previously mentioned, NaCl is highly soluble in water; therefore, its leaching would depend on the volume of water used in the washing step. Figure 2 illustrates the leaching properties of NaCl from the shells with elapsed time depending on the volume of water.”
On page 6, “OWRs were chosen at 2, 3, and 4 times of tap water volumes. The washing steps were repeated 10 times sequentially as shown in Figure 5a.”
Comment #5: In the leaching test, what elution solution is used? Please be specific. Also please add reference for the conditions used in the leaching test.
Response: We appreciate reviewer’s kind comments. The leaching test in this paper, we meant the NaCl was dissolved in the process of washing using tap water. Therefore, the solution was tap water and no other solution was used.
Comment #6: Grammar issue of the sentence ‘to confirmation of washing water required…’
Response: We appreciate reviewer’s kind comments. We revised the manuscript based on the reviewer’s valuable comments. Also, as a reviewer point it out, we checked the English and it was also revised by “Editage”.
Comment #7: Please add the replication in the manuscript. In addition, add error bar/standard deviation in all figures and tables.
Response: We appreciate reviewer’s kind comments. We revised the manuscript based on the reviewer’s valuable comments. Also, as a reviewer point it out, we added the error bar/standard deviation in all figure and tables in revised manuscript as follows.
Comment #8: Section 3.1, 1.22%+3? Please double check this number.
Response: We appreciate reviewer’s kind comments. As a reviewer point out, we changed this sentence in revised manuscript as follows.
On page 3, “The moisture content of sampled shells was measured as 1.22%±0.03 on average.“
Comment #9: Many grammar issues in the manuscript, please check throughout the manuscript.
Response: We appreciate reviewer’s kind comments. We revised the manuscript based on the reviewer’s valuable comments. Also, as a reviewer point it out, we checked the English and it was also revised by “Editage”.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
A breif summary: The aim of the article is clear which is assessing the potential usage of waste oyster shells as a resource. The main problem involved with waste oyster shells is NaCl content in it which can be removed by washing it with water. Assessing the physical properties that can affect the washing efficiency can be identified as a strength of the study.
Article: The clarity of the article is a little poor due to poor word usage and wordy sentences. It is very hard to track the flow of the research due to the same reason. Please check the English, and use appropriate vocabulory to strengthen the arguments brought up. I also encountered repetions in the last parts and typos in many places. Some references were not cited appropriately and need improvements. Methodology part has lost it's clarity and hard to understand the steps. It's better if batch and continuouse experiment steps explained seperately under the method using short sentences. Leaching part is clear enough to understand. However, usage of correct unit symbols for size of the particles is a must.
Review: Why only physical properties were analysed through the study? Cite any references that justify the claim "Since washing efficiencies are closely related to the physical properties, the washing method was reviewed to the volume of water used, washing duration, and mixing speeds". Justify why is the effect of chemical properties (temperature, conductivity, pH of the water and other additives) were not studied in this research. How the heavy metal analysis was done? have you used any instrument for this such like ICP? How is the batch test and continuous tests are different in this study? It's not clear.
Author Response
Comment #1: Why only physical properties were analysed through the study? Cite any references that justify the claim "Since washing efficiencies are closely related to the physical properties, the washing method was reviewed to the volume of water used, washing duration, and mixing speeds". Justify why is the effect of chemical properties (temperature, conductivity, pH of the water and other additives) were not studied in this research.
Response: We appreciate reviewer’s kind comments. In this paper, these results will be used for 2ton/day plant so this experiment condition was conducted to apply them to field using tap water and physcial properties. Considering chemical factors, cleaning efficiency will be higher than physical factors. However, if this is scaled up, the process will become enlarged, and additional problems will need to be solved in terms of energy and environment.
The use of neglected oyster shell is stronger in order to solve environmental problems than for economic benefits. Therefore, a physical cleaning method that can minimize economic damage was studied, and based on this result, a facility capable of cleaning 2ton/day shells was constructed.
Comment #2: How the heavy metal analysis was done? have you used any instrument for this such like ICP?
Response: We appreciate reviewer’s kind comments. In this paper, we analyzed the contents of NaCl and heavy metals using X-ray fluorescence (XRF) and can be measured the semi-quantitative. The XRF analysis method was introduced in Experiment 2.3 in manuscript. The composition of heavy metal such as Al2O3, SiO2, Fe2O3 were contained in small particles and it was confirmed that selecting the particle size was very important factor to increase the washing efficiency, as shown in Figure 6 and Table 4.
On page 3, “Chemical compositions of the shells before and after washing were identified using X-ray fluorescence spectroscopy (XRF-1800, Shimadzu, Japan), and an X-ray diffractometer (XRD-6100, Shimadzu, Japan) was used to analyze the mineral phases.”
Comment #3: How is the batch test and continuous tests are different in this study? It's not clear.
Response: We appreciate reviewer’s kind comments. In this paper, the final NaCl concentrationis same in batch system or continuous system. However, the concentration of NaCl in the middle where the NaCl is dissolved is different.
In this study attempted to reduce waste water by minimizing washing water, and to reduce the treatment size of washing facilities by continuously performing washing.
In batch system, only the amount of water ratio and time can be physically compared. To facilitate washing at once in batch system, a large amount of washing water should be used.
In our previous research, it doesn't take long for the NaCl to elute as shown in Figure S1. As shown in Figure 1, we compared the effect of the washing time such as 1 minute, 2 minute, 3 minute, 4 minute, 5 minute, 6 minute, 7 minute, and 8 minute for the batch type, and the dissolution rate was the most common in 1 minute including error range. Therefore, we suggested the continuous washing time was conducted based on one minute and we judged that the factor for washing could be sufficiently confirmed even with one minute stirring.
Figure 1. NaCl elution concentration vs elapsed time on B-OWR1 and B-OWR6.
Also, we describe the experiment methods of batch system and continuous system as shown in Figure 2.
Figure 2. The experiemt methods of batch system and continuous system.
Author Response File: Author Response.pdf
Reviewer 3 Report
The study discussed the viability of the oyster shell which is a valuable material for calcium resources, but they have higher contents of NaCl. The results show that the batch system removed NaCl when washed for >24 hours over the shell-to-water ratio = 1:5. The batch experiments confirmed that washing twice could completely remove NaCl from the shells on a like-for-like basis. Moreover, the efficiency of washing sequentially was also evaluated in terms of the number of washing cycles. Compared to batch experiments, it is enough only 10 min to wash out NaCl at the shell-to-water ratio = 1:4. Regardless of washing methods, the volume of washing water plays a key role in enhancing the NaCl removal efficiency. Consequently, increasing the washing water and properly sorting fine particles is a way to advance calcium purities as an alternative Ca-resource of the oyster shell.
The study is well written and achieved its stated objective; however, the following comments will improve the manuscript structure, i.e.,
1) Equations (1) and (2) should be placed in section 2: Method
2) discuss the research objectives in line with the research questions.
3) Research hypotheses can be added to clarify the literature's soundness, and
4) conclusions section should be engaged with subsequent policy implications.
Author Response
Comment #1: Equations (1) and (2) should be placed in section 2: Method
Response: We appreciate reviewer’s kind comments and thank you for kind suggestion. However, thes two equation (1) and (2) are generally prepared the equation (1) which shell is used and the equation (2) that can occur when salt in shell is present. Therefore, it is judged that these two equations are suitable to be located in introduction as they correspond to the results of previous studies.
Comment #2: discuss the research objectives in line with the research questions.
Response: We appreciate reviewer’s kind comments and thank you for kind suggestion. This study mentioned that shell cannot be used as a resource unless shell is washed. The problem of this study is how to clean the shell, and a method for physically cleaning the shell is suggested. In this paper, these results will be used for 2ton/day plant so this experiment condition was conducted to apply them to field using tap water and physcial properties.
Comment #3: Research hypotheses can be added to clarify the literature's soundness, and
Response: We appreciate reviewer’s kind comments and thank you for kind suggestion. In factor, there are few previous studies on the washing neglected oyster shells. Most of previous resarch, they alrealy use the well washed oyster shell for use it as a raw materals for high value-added materials. Therefore, it is hard to compared the previous research and added research hypothese.
Comment #4: conclusions section should be engaged with subsequent policy implications.
Response: We appreciate reviewer’s kind comments. In order to utilize the shell as a resource, the standard value of the wash shell as a resource, not waste, is currently being discussed with related ministries. Therefore, these findings are in progress following this paper and are being written with greenhouse gases. Therefore, in the results of this study, I would like to mention the policy part as you suggested, but I did not write it to be more faithful to the results of subsequent studies. The main factor in this study is to derive washing physical factor using neglected oyster shells and apply them to the pilot plant. In particular, the use of neglected oyster shell is stronger in order to solve environmental problems than for economic benefits. Therefore, a physical cleaning method that can minimize economic damage was studied, and based on this result, a facility capable of cleaning 2ton/day shells was constructed.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
All my comments have been well addressed.
Author Response
We thank the valuable comments and suggestions from both you and the referees, which are very helpful to improve the quality of our manuscript. This paper strongly mentioned that the reason why the Neglected-oyster shells needs to be washed and the washing conditions were studied. The manuscript has been rechecked and the necessary changes have been made in accordance with the reviewer’s suggestions. This paper revised by “Editage” and we are also planning to add English Pre Editing service in MDPI.
Author Response File: 
Author Response.docx