Development of Red Clay Ultrafiltration Membranes for Oil-Water Separation
Round 1
Reviewer 1 Report
This paper reported a work on the investigation of red clay ultrafiltration membranes for wastewater treatment. The main issue of the paper is its presentation, which is not comprehensive and clear. Therefore, this paper need major revision before it is considered to be published in the journal of “Crystals”.
The detailed comment and suggestions are listed as below.
Title
The title is suggested as “Development of red clay ultrafiltration membranes for oil-water separation”. It is not a composite membrane, as nano-activated carbon is burnt off after sintering.
Abstract
This part shall be re-phrased and add key concluding remarks on the membrane testing results of oil-water separation.
Keywords
In general, keywords shall be selected from the title and the abstract, while “extruder” is not.
- Introduction
Please explain how does CaF2 as a nucleating agent minimize the sintering temperature.
The concept of porous ultrafiltration membrane without a coating layer and the materials system used for preparing the membrane are not novel. The significance of the work comes from low-cost red clay raw materials.
- Methodology
Please remove section 2.1, as it has been mentioned in the “Introduction” part.
Please explain how does CaF2 improve the mechanical strength.
Figures 2 and 3 shall be combined in one figure. In Figure 3, what happens for the red clay paste after 500 oC? Why the weight still reduces even the temperature is over 1000 oC? How about CaF2, it is still in the materials system, or it is burnt off?
This part shall include the presentation on mechanical property testing, contact angle measurement and pore size distribution measurement.
In Equation (1), “water flux rate” shall be termed as “water flux”. In Equation (2), Cc shall be the turbidity after filtration. Equation (3) has two different parameters with same name. Please pay attention to the definitions between permeance and permeability.
- Experimental Outcome (change to Results) and Discussion
Figures 6 and 7 shall be combined in one figure.
In Figure 8, the pore size % for 96 nm is 12, what is the pore size range for the other 88%?
What is the porosity of the prepared membrane? How does the microstructure of the membrane look like? Please add a SEM image of the cross section of the membrane, with which the pore size and the porosity of the membrane could be revealed clearly.
Again, though the work can compare the properties and performance with other membranes, please do not state the drawback of the membrane with coating layer.
- Conclusions
Has the experiment of foulant removal using backwashing technology been done in this work? If not, please do not give a concluding remark on this point.
References
There exist some noncoincidence for the references between the context and the reference list. For examples, Dongwei et al. [14], Lobo et al. [15], Luo et al. [16], and so on. Please check them one by one and coincide them.
Others
There are some grammatical and other errors in the manuscript, like “Microfiltration (MF), ultrafiltration (UF) have been; 450 (without temperature unit oC); …” It is suggested that the author read throughout the entire manuscript to correct them.
Author Response
Abstract
This part shall be re-phrased and add key concluding remarks on the membrane testing results of oil-water separation.
Answer: In this study, a red clay/nano-activated carbon membrane was investigated for the removal of oil from industrial wastewater. The sintering temperature was minimized using CaF2 powder as a binder. The fabricated membrane was characterized by its mechanical properties, average pore size, and hydrophilicity. A contact angle of 67.3° and membrane spore size of 95.46 nm were obtained. The prepared membrane was tested by a cross-flow filtration process using an oil-water emulsion, and showed a promising permeate flux and oil rejection results. During the separation of oil from water, the flux increased from 191.38 to 284.99 L/m2 on increasing the applied pressure from 3 to 6 bar. In addition, high water permeability was obtained for the fabricated membrane at low operating pressure. However, the membrane flux decreased from 490.28 to 367.32 L/m2·h due to oil deposition on the membrane surface; regardless, the maximum oil rejection was 99.96% at an oil concentration of 80 NTU and a pressure of 5 bar. The fabricated membrane was negatively charged, as were the oil droplets, thereby facilitating membrane purification through backwashing. The obtained ceramic membrane functioned well as a hydrophilic membrane and showed potential for use in oil wastewater treatment.
Introduction
Please explain how does CaF2 as a nucleating agent minimize the sintering temperature.?
Answer: Sintering temperature of the ceramic membranes with and without CaF2 was performed. The membrane with CaF2 showed a lower sintering temperature of 1000 oC than the membrane without CaF2 (1150 oC).
The concept of porous ultrafiltration membrane without a coating layer and the materials system used for preparing the membrane are not novel. The significance of the work comes from low-cost red clay raw materials.
Answer: Yes, it was corrected
Methodology:
Please remove section 2.1, as it has been mentioned in the “Introduction” part.
Answer: It was removed
1)This part shall include the presentation on mechanical property testing, contact angle measurement and pore size distribution measurement.
Answer:
Characterization of ceramic membrane
2.3.1. Scanning electron microscopy (SEM)
SEM (model NNL-200, Philips, 1 nm resolution) was used for morphological characterization of the fabricated membrane.
2.3.2. Mechanical test
The mechanical properties of the ceramic membrane were determined by using the three-point bending strength technique by using the Shimadzu-Universal AGS-X (5 kN) test machine with a crosshead speed of 0.5 mm/min.
2.3.3. Apparent porosity
The apparent porosity of the ceramic structures has been determined by DIN 51056 (ISO EN 993-1) standardized for ceramic structures and refractory materials.
2.3.4. Contact angle measurements
Contact angle measurements were accomplished by using a K100 force tensiometer.
2.3.5. Pore size distribution measurements
The pore size distribution of the membrane was determined using a constant-pressure fluid-fluid porometer (IFTS advanced fluid-fluid porometer, Institut de la Filtration et des Techniques Séparatives, France).
2) explain how does CaF2 improve the mechanical strength.
Answer: Mechanical testing of the ceramic membranes with and without CaF2 was performed using the three-point bending technique with a crosshead speed of 0.5 mm/min. The membrane without CaF2 showed a lower bending strength of 49.53 MPa than the membrane with CaF2 (54.13 MPa); the stress-strain relationship of both the membranes was linear.
3)Figures 2 and 3 shall be combined in one figure. In Figure 3, what happens for the red clay paste after 500 oC? Why the weight still reduces even the temperature is over 1000 oC? How about CaF2, it is still in the materials system, or it is burnt off?
Answer:
- Figures 2 and 3 were combined in one figure.
It happened for the red clay paste after 500 oC and the weight still reduces even the temperature is over 1000 oC:
Answer: Crystal water decomposition was found to occur at 500–600 °C, and the standard decomposition or recrystallization possible during heat treatment occur at 600–1100 °C.
CaF2 is still in the materials system. The TGA data for CaF2 (Figure 2) showed that the residual weight was ~94 wt.%.
In Equation (1), “water flux rate” shall be termed as “water flux”. In Equation (2), Cc shall be the turbidity after filtration. Equation (3) has two different parameters with same name. Please pay attention to the definitions between permeance and permeability.
Answer: It was corrected.
Results and discussion:
Experimental Outcome (change to Results) and Discussion
Answer: It was changed.
Figures 6 and 7 shall be combined in one figure.
Answer: It was combined.
3)In Figure 8, the pore size % for 96 nm is 12, what is the pore size range for the other 88%?
Answer: The pore size of this membrane ranged from 40 nm to 110 nm with an average pore size of 96 nm, and 88% of the total pores were smaller than 96 nm.
4) What is the porosity of the prepared membrane? How does the microstructure of the membrane look like? Please add a SEM image of the cross section of the membrane, with which the pore size and the porosity of the membrane could be revealed clearly.
- SEM was used to determine the morphology of the fabricated membrane (Figure 6). It was noted that the absence of cracks in the fabricated membrane was indicative of its high quality and good material properties in agreement with the results of the three-point bending strength test.
-Porosity measurement was 32.56%
Cross-section
Top view,
Figure 6: SEM of the top view of the tubular ceramic membrane.
5) Again, though the work can compare the properties and performance with other membranes, please do not state the drawback of the membrane with coating layer.
Answer: It was removed the part of the drawback of the membrane with a coating layer.
The effectiveness of the fabricated membrane was similar to those of membranes described in the literature [27-31], and some comparisons are presented in Table 2. It is evident that the fabricated membrane presented favorable performance with red clay, which is locally available, and an inexpensive material. Table 2 also presents data for some expensive membrane materials, such as NaA zeolite deposited on α-Al2O3. Additionally, our tubular ceramic membrane has a higher water flux (367.32 L/m2 h) than the tubular PVDF-UF at the same operating pressure (5–6 bar, 309 L/m2 h).
Conclusions:
Has the experiment of foulant removal using backwashing technology been done in this work? If not, please do not give a concluding remark on this point.
Answer: Yes it was done as shown in Figure 11.
Refrence:
There exist some noncoincidence for the references between the context and the reference list. For examples, Dongwei et al. [14], Lobo et al. [15], Luo et al. [16], and so on. Please check them one by one and coincide them.
Answer: It was corrected.
Others
There are some grammatical and other errors in the manuscript, like “Microfiltration (MF), ultrafiltration (UF) have been; 450 (without temperature unit oC); …” It is suggested that the author read throughout the entire manuscript to correct them.
Answer: It was done.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Title: Fabrication of Ultrafiltration Composite Membrane from Metal Oxides Mixture as of Red Clay/Nano-Activated Carbon for Wastewater Treatment
Manuscript No.: crystals-1096499
In this work, a clay/nano-activated carbon membrane was investigated for the removal of oil from industrial wastewater. The idea of this work is to synthesis the membrane from nature sources. The concept of this work may meet the hot issue of economy circular and cause reader’s interest. However, there are many mistakes should be improved/revised and the effects of AC content on the membrane separation performance should be evaluated before further decision will be made.
- The membrane synthesis from clay here should be classified as ceramic membrane, please revised the title of “metal oxide” into “ceramic.”
- The crystal phase of the membrane after sintering treatment should be analyzed with XRD or other analyzer to the meet the scope of the journal of “CRYSTALS.”
- Page 3, Sec. 2.3.: What’s the dimension of extruder? Did the calcined membrane tubular or cylindrical type?
- Page 3, Sec. 2.3.: what’s the atmosphere of sintering and TGA? Under N2 or Air?
- Page 3, Sec. 2.3.: what the holding time of sintering procedure after treatment at 1000 °
- The title of Y-axis in Fig. 3 and 4 should be revised as “Weight remaining (wt. %).
- As shown in Fig. 3, the weight remaining of clay paste is ca. 85 wt.%. please check the description of Fig. 3 as shown in page 4, line 1~2. The words of “burned completely” should be rewritten.
- It is no necessary to draw the preparation procedure as shown in Fig. 4.
- Page 5, Sec. 2.4.: What's the concentration of the prepared emulsion? any surfactant was added here?
- Page 5, Sec. 2.5.1:
(a) revise the title as “ultrafiltration testing”
(b) please describe the filtration set-up more detail, including the values, pressure gauge, … etc.
(c) Did outside-in or inside-out mode used here?
(d) did the concentration of oily wastewater were measured? Or only turbidity were analyzed?
- The flux decay very quickly during 240 min testing, indicating that the oil foulant may deposited on the surface of membrane or block inside the porous structure of membrane. The authors are suggested to discuss the fouling mechanism.
- The effect of AC content should be evaluated.
Author Response
Please see the file
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The author has considered all my suggestions/comments, and I'm satisfied with reply/answers. Now this article is meet the quality of journal of Crystals and can be accepted to publish in Crystals.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The authors present a study devoted to the investigation of the fabrication of ultrafiltration composite membrane from metal oxides mixture for wastewater treatment.
In my opinion, it is highly difficult to understand the meaning behind every sentence because of poor English.
The author made disturbing mistakes like “Tatiana”, which is the female name (line 25) instead of “titanium”.
The error bars in Figures 8, 9, 10 indicate huge errors in the reported measurements, which demonstrates that the presented results are not trustworthy. Figures 5 and 6 don’t contain any graphical representations of the variability of the presented data at all. Figure 8 represents a very small dataset, which makes me question the representability of the data.
Equation 3 should be written with regard to membrane permeability, not the flux.
The term “wastewater purification” (line 17) does not exist.
Irreversible and irrecoverable fouling are not investigated in the presented study at all, therefore the authors can not claim that the tested membranes are suitable for industrial implementation.
Besides, no discussion is provided. What are the practical implications of the obtained results? What were the scientific contribution, the working hypotheses, and limitations of the presented study?
I can not call this article “scientific” in the present form.
Reviewer 2 Report
The result is not sufficient to publish.
