The Selectivity of Different Sized Catalysts on DOM Fractional Removal during the Catalytic Ozonation of Municipal Sewage
Round 1
Reviewer 1 Report
The manuscript describes the oxidation of organic matter as it occurs as pollutant in water. Oxidative decomposition of organic material by ozonolysis was investigated using fluorescence spectroscopy. With gamma-Al2O3 as a catalyst, more organic matter decomposed than without catalyst. The authors found that the particle size of the catalyst has an impact on the efficiency of the catalyst system; the smaller the particle size, the more organic matter is oxidatively destroyed in most cases. Decomposition products were analyzed based on the hydrophilicity. The toxicity of the treated wastewater remained more or less the same.
In general, the research touches an important topic. Waste water can contain organic pollutants, and their oxidative removal improves water quality. Simple catalyst systems for the inexpensive removal of pollutants from wastewater are an important goal to achieve. It is a bit disappointing that in the study provided by the authors, after ozonolysis the toxicity of the water did not significantly change. However, the results may inspire other researchers to find improved catalyst systems for the treatment of wastewater with ozone.
As such, the research is publishable. However, I find the paper, in its current version, very difficult to read, and the scholarly presentation deserves improvement.
It is not clear to me, how the EEM analyses in Figure 1 translate to catalyst efficiency. First, the authors need to clarify what spectra (A), (B) and so on are. Which are the non-catalytic and the catalytic runs? I assume the color coding says something about the intensity, but the authors need to state how. At the moment, I cannot see how the spectra in Figure 1 provide information about the efficiency of the ozonolysis. Same holds true for Figure 2. In Figure 3, it may be a little easier to see that there is obviously a decrease in intensity, but the authors still should state which bar refers to what type of reaction. The legend in Figure 3 says “Ozone”, “C9+Ozone” and so on, but C9 is not defined until the experimental. It is very difficult for the readers to follow.
How often were the experiments in Figure 3, Figure 4, Figure 6, Figure 7 and Figure 10 repeated? Are there error bars available? The bars and curves show trends, but the differences may be small and perhaps too small to make a clear statement about catalyst efficiency.
Also, the authors should state where the water samples came from. Currently, it is just stated that these were “biological effluents”.
Terms like SUVA or COD should be defined the first time they appear in the manuscript. It would be helpful to the readers if the authors could explain in one or two sentences what the corresponding methods are and what type of information they provide.
The authors should at least comment on the informative value of the study with respect to pollutants that are not fluorescent-active. Not all pollutants are fluorescent active, and may not be “seen” by the analytic methods the authors are using.
The English language may need some improvement. I cannot go in detail, but a sentence like “In the present work, the typical catalyst γ- Al2O3 was used for DOM removal under suitable for industrial ozonation processes. Meanwhile, the effect of catalysts with different sizes on the catalytic performance of municipal sewage was investigated by COD and UV254” (line 62/63) should be better “In the present work, the common catalyst γ- Al2O3 was used for DOM removal under conditions suitable for industrial ozonation processes. The effect of the γ- Al2O3 particle size on the catalytic performance of municipal sewage was investigated by COD and UV254”? As mentioned, COD should be defined.
Author Response
Point 1: It is not clear to me, how the EEM analyses in Figure 1 translate to catalyst efficiency. First, the authors need to clarify what spectra (A), (B) and so on are. Which are the non-catalytic and the catalytic runs? I assume the color coding says something about the intensity, but the authors need to state how. At the moment, I cannot see how the spectra in Figure 1 provide information about the efficiency of the ozonolysis. Same holds true for Figure 2. In Figure 3, it may be a little easier to see that there is obviously a decrease in intensity, but the authors still should state which bar refers to what type of reaction. The legend in Figure 3 says “Ozone”, “C9+Ozone” and so on, but C9 is not defined until the experimental. It is very difficult for the readers to follow.
Response 1: Thanks for the reviewer’s careful work. As mentioned in the manuscript, three-dimensional fluorescence spectra for water quality determination can reveal the organic pollutants of classification and information content, and it also can be used on multiple complex systems in overlapping fluorescence spectra of object spectrum identification and characterization. In the three-dimensional fluorescence spectra (Fig.1 and Fig.2), the fluorescence types can be divided into four parts: tyrosine, tryptophan, fulvic acid and humic acid. T1, T2, T3 and T4 respectively represent the maximum fluorescence intensity of these four different types of substances, namely tyrosine, tryptophan, fulvic acid and humic acid. Fig.3 and Fig.4 represent the changes in the maximum fluorescence intensity of these four substances under ozone and ozone-catalytic conditions, thus obtaining the degradation efficiency of ozone and ozone-catalytic fluorescence substances. T1 represents the change in tyrosine, T2 represents the change in tryptophan, T3 represents the change in fulvic acid and T4 represents the change in humic acid. Corresponding supplementary content have been explained and explained in the manuscript. “Commercial γ-Al2O3 was smashed into different sizes of particles by mechanical broken, and the particles were passed through screen mesh with different pore sizes so that they were divided into about 0.9 mm, 0.5 mm, 0.3 mm and 0.1 mm, which were named C9, C5, C3 and C1, respectively.” This statement has been included in the results and discussion section.
Point 2: How often were the experiments in Figure 3, Figure 4, Figure 6, Figure 7 and Figure 10 repeated? Are there error bars available? The bars and curves show trends, but the differences may be small and perhaps too small to make a clear statement about catalyst efficiency.
Response 2: Thanks for the reviewer’s kind advice. We repeated the experiment of each water sample for 5 times, and the data in the graph is the average of 5 experiments. Since the error in the experiment did not exceed ±5%, we did not label the error line. If necessary, we can provide the data of 5 experiments in the supplementary materials.
Point 3: Also, the authors should state where the water samples came from. Currently, it is just stated that these were “biological effluents”.
Response 3: Thanks for the reviewer’s suggestion. Corresponding supplementary content have been explained and explained in the manuscript: “sample A was taken from donggang sewage treatment plant (Wuxi) and sample B was taken from wulongkou sewage treatment plant (Zhengzhou)”.
Point 4: Terms like SUVA or COD should be defined the first time they appear in the manuscript. It would be helpful to the readers if the authors could explain in one or two sentences what the corresponding methods are and what type of information they provide.
Response 4: Thanks for the reviewer’s careful work. Corresponding supplementary content have been explained and explained in the manuscript: “SUVA (specific ultraviolet absorbance, it is the ratio of UV254 to dissolved-organic-carbon, which can indirectly represent the hydrophilic and hydrophobic characteristics of organic compounds in water)”; “COD (chemical oxygen demand, a chemical method is used to measure the amount of reducing substances to be oxidized in a water sample, and reflects the degree to which water is polluted by reducing substances)”
Point 5: The authors should at least comment on the informative value of the study with respect to pollutants that are not fluorescent-active. Not all pollutants are fluorescent active, and may not be “seen” by the analytic methods the authors are using.
Response 5: Thanks for the reviewer’s kind advice. DOM in the biological effluents is a typical kind of the pollutants with complex composition. At present, its effective methods for analysis are 3d fluorescence spectrum, hydrophilic/hydrophobic, and molecular weight. Substances with no fluorescence activity may be classified as hydrophilic/hydrophobic or of different molecular weight. Just as the conclusion is drawn in the manuscript, “the use of catalyst in ozonation increased the removal of hydrophilics and the decrease of the catalyst particle size increase the removal of hydrophilics.” Hydrophilic/hydrophobic substances also contain substances with or without fluorescence activity.
Point 6: The English language may need some improvement. I cannot go in detail, but a sentence like “In the present work, the typical catalyst γ- Al2O3 was used for DOM removal under suitable for industrial ozonation processes. Meanwhile, the effect of catalysts with different sizes on the catalytic performance of municipal sewage was investigated by COD and UV254” (line 62/63) should be better “In the present work, the common catalyst γ- Al2O3 was used for DOM removal under conditions suitable for industrial ozonation processes. The effect of the γ- Al2O3 particle size on the catalytic performance of municipal sewage was investigated by COD and UV254”? As mentioned, COD should be defined.
Response 6: Thanks for the reviewer’s careful work. We have revised the WHOLE manuscript carefully and tried to avoid any grammar or syntax error. Also, we have asked several colleagues who are skilled authors of English language papers to check the English. We believe that the language is now acceptable for the review process. Specific modifications have been highlighted in blue in the manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The development of more efficient techniques for removing dissolved organic pollutants in residual waters is a very interesting topic in environmental chemistry. The use of catalysts that favour the oxidation of these residues is a very attractive opportunity to achieve an optimal treatment of the waste water. This article present very interesting results based on the utilization of gamma-alumina with high specific surface area and high concentration of surface hydroxyls that facilitates the generation of hydroxyl radical species. Furthermore, the authors studied the influence of the particle size of catalyst considering the diffusional phenomena. The research topic is within the scope of “Catalysts” and this work could be published in the journal. However, the manuscript must be considerably modified and some aspects should be clarified.
Comments:
- The text is difficult to read and some English mistakes have to be revised.
- The results of EEM in Figure 2 are hardly distinguishable. The discussion of these results must be modified and clarified.
Author Response
Point 1: The text is difficult to read and some English mistakes have to be revised.
Response 1: Thanks for the reviewer’s careful work. We have revised the WHOLE manuscript carefully and tried to avoid any grammar or syntax error. Also, we have asked several colleagues who are skilled authors of English language papers to check the English. We believe that the language is now acceptable for the review process. Specific modifications have been highlighted in blue in the manuscript.
Point 2: The results of EEM in Figure 2 are hardly distinguishable. The discussion of these results must be modified and clarified.
Response 2: Thanks for the reviewer’s careful work. As mentioned in the manuscript, three-dimensional fluorescence spectra for water quality determination can reveal the organic pollutants of classification and information content, and it also can be used on multiple complex system in overlapping fluorescence spectra of object spectrum identification and characterization. In the three-dimensional fluorescence spectra (Fig.1 and Fig.2), the fluorescence types can be divided into four parts: tyrosine, tryptophan, fulvic acid and humic acid. T1, T2, T3 and T4 respectively represent the maximum fluorescence intensity of these four different types of substances, namely tyrosine, tryptophan, fulvic acid and humic acid. Fig.3 and Fig.4 represent the changes in the maximum fluorescence intensity of these four substances under ozone and ozone-catalytic conditions, thus obtaining the degradation efficiency of ozone and ozone-catalytic fluorescence substances. T1 represents the change in tyrosine, T2 represents the change in tryptophan, T3 represents the change in fulvic acid and T4 represents the change in humic acid. Corresponding supplementary content have been explained and explained in the manuscript. In addition, “Commercial γ-Al2O3 was smashed into different sizes of particles by mechanical broken, and the particles were passed through screen mesh with different pore sizes so that they were divided into about 0.9 mm, 0.5 mm, 0.3 mm and 0.1 mm, which were named C9, C5, C3 and C1, respectively.” This statement has been included in the results and discussion section.
have been highlighted in blue in the manuscript.
Author Response File: Author Response.pdf
