Research and Prevention of Harmful Gases in Special Structures of Urban Deep Drainage Systems

Round 1

Reviewer 1 Report (New Reviewer)

Comments and Suggestions for Authors

paper entitled Research and prevention of harmful gases in special structures of urban deep drainage systems is good but at some point some changes are suggested

Line 44 is unclear and in the end of introduction the gap to be studied is unclear Figure 3 and 8 are unclear

Conclusion needed to be more elaborated

Conclusion lacks in corelation with prospects of socail aspected of the outcome

results needed to be more compared and corelated with sustainability

Comments on the Quality of English Language

moderate english improvement is needed 

Author Response

Reviewer #1:

has the following comments that need to be addressed.

1. Line 44 is unclear and in the end of introduction the gap to be studied is unclear Figure 3 and 8 are unclear

Answer: Thank you for your question. I have modified the content of line 44 according to your question. The modified content is shown in the fluorescent content below.

Regarding Figure 3, this picture is to highlight the spiral tray structure 3D printed inside the shaft.

Regarding Figure 8, this picture is to show the experimental shaft water circulation structure built in the laboratory, and the various parts of the structure are marked.

The figures in the article may appear a little blurry. I have uploaded the originals of these figures to the 《Water》 journal website.

1. Introduction：In order to effectively connect pipelines at different heights, engineers designed special structures such as ordinary drop wells and deeper vertical shafts to ensure the efficiency and safe operation of the system [12].

2. Conclusion needed to be more elaborated
   Conclusion lacks in corelation with prospects of socail aspected of the outcome
   results needed to be more compared and corelated with sustainability

Answer: Thank you for your comments. I have made some changes based on your comments. The modified content is as follows:

4. Conclusions：This paper focuses on a shaft project in St. Petersburg and innovatively introduces a spiral tray structure into the design. Detailed simulation experiments were conducted us-ing ANSYS finite element analysis to assess the impact of the spiral tray on the hydrogen sulfide degassing rate. The simulation results indicated that the degassing rate of hydro-gen sulfide fluctuated between 0.05% and 0.22%. To further validate the reliability of the simulation, a proportional experimental model was constructed in the laboratory, where systematic testing determined the hydrogen sulfide degassing rate to be between 0.1% and 0.4%.

The findings reveal that as the concentration of sulfide ions in water increases, the rate at which hydrogen sulfide is released into the shaft significantly rises. Additionally, an increase in the inflow velocity of water also accelerates the hydrogen sulfide release rate. This phenomenon was not only confirmed under laboratory conditions but also ob-served during actual shaft operations. Therefore, by controlling the concentration of hy-drogen sulfide in the water and reducing the turbulence of the water flow during re-al-world shaft operations, the release of hydrogen sulfide can be effectively minimized, thereby enhancing the efficiency and safety of the shaft's operation.

The results of this study are of significant theoretical importance and demonstrate broad practical application prospects. By appropriately adjusting the design parameters of the shaft, such as controlling water flow velocity and sulfide ion concentration, the safe and stable operation of the shaft can be ensured, while significantly reducing the negative impact of hydrogen sulfide on the surrounding environment and human health. These findings provide a robust scientific basis for optimizing the design and operation of shaft projects and can be applied to similar engineering projects.

More importantly, this study reveals the potential contribution of shaft projects to achieving sustainable development goals. By effectively reducing hydrogen sulfide emis-sions, this research not only helps to mitigate the environmental impact of engineering projects but also offers practical solutions for reducing air pollution and protecting the ecological environment. These research outcomes are not only widely applicable in the field of shaft engineering but also provide important references for the design, construc-tion, and operation of other similar infrastructure projects. This innovative integration of design and environmental protection represents the future direction of engineering tech-nology development and offers new ideas and methods for achieving sustainable devel-opment goals.

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

In this study, the authors investigate the vertical shafts with helical tray structures in drainage systems to analyze the release of hydrogen sulfide gas dissolved in water from this type of structure. The authors used simulation approaches and laboratory experiments to assess the hydrogen sulfide gas release rate.  

Despite this, the methodology used in the simulation and experimental pilot could generate unjustified results, especially concerning the choice of solvent type and/or the proposed helical system?!

Moreover, the redaction of the paper still require amelioration in order to valorize this work.  

Here are some comments and questions:

Abstract

-        Lines 18-19 : “Combining simulation …. is found to be 0.05%-0.4%” Rephrase this sentence as follows: “ Combining simulation and laboratory experiments, the hydrogen sulfide gas release rate from water in this structure is 0.05%-0.4%.

Introduction

-        Lines 33-34 : “Methane, a colorless …concentration in the air reaches” . Rephrase this sentence as follows: “rephrase this sentence as follows: “Methane, a colorless, odorless, and flammable gas, can cause explosions when its concentration in the air reaches a certain level”.

Mathematical and experimental models

-        Line 74, 86: In the choice of boundary conditions, why did you not propose wastewater with some known average turbidity, instead of water? does this not influence the deductions from the considered mathematical equations?

-        Line 132: Is the experimental model in helical tray structure considered the same one used in reality in pipeline structures? if so, you must add this argument in the text! if not, you must justify such choice?

-        Line 142: the choice of sodium sulfide nonahydrate as solvent is not convincing, given the possible reactions of sulfides with other compounds of raw wastewater. Why not use filtered raw wastewater?!

3. Research and analysis of results

The authors did not discuss the results obtained and did not make a comparison with previous works. The work appears as a simple description of the results obtained based on both a simulation approach and a proposed experimental system, without any thought on the control solutions of hydrogen sulfide gas release.

Author Response

Reviewer #2: has major comments the need o be addressed. The comments that need addressing are as follows:

Answer: I would like to thank the reviewer for all the pertinent questions and suggestions made. All the points that needed corrections were considered and the manuscript was improved through the incorporation of the suggested changes.

1. 1.-Lines 18-19 : “Combining simulation …. is found to be 0.05%-0.4%” Rephrase this sentence as follows: “ Combining simulation and laboratory experiments, the hydrogen sulfide gas release rate from water in this structure is 0.05%-0.4%.
   

Answer: Thank you for your valuable comments. I have modified it according to your comments.

Abstract -Lines 18-19:Combining simulation and laboratory experiments, the hydrogen sulfide gas release rate from water in this structure is 0.05%-0.4%

2. -Lines 33-34 : “Methane, a colorless …concentration in the air reaches” . Rephrase this sentence as follows: “rephrase this sentence as follows: “Methane, a colorless, odorless, and flammable gas, can cause explosions when its concentration in the air reaches a certain level”.

Answer: Thank you for your valuable comments. I have modified it according to your comments.

Abstract -Lines 33-34: Methane, a colorless, odorless, and flammable gas, can cause explosions when its concentration in the air reaches a certain leve

3. 3. -Line 74, 86: In the choice of boundary conditions, why did you not propose wastewater with some known average turbidity, instead of water? does this not influence the deductions from the considered mathematical equations?

Answer: Thank you for your question. The selection of the model solution is justified by conducting a laboratory experiment rather than a field experiment. The precise determination of sulfides in wastewater can only be accurately performed on-site.

The equations describe only the hydraulic process of water flow in the drop shaft. The flow of wastewater is rapid, with turbulence being the prevailing factor, leading to the degassing of molecular hydrogen sulfide. For this reason, when modeling, turbulent diffusion of hydrogen sulfide molecules in the flow and their subsequent release into the air are considered.

4. 4.-Line 132: Is the experimental model in helical tray structure considered the same one used in reality in pipeline structures? if so, you must add this argument in the text! if not, you must justify such choice?

Answer: Thank you for your question. There are examples of using such a design in sewerage systems. A similar structure was used in a sewer project in Japan. Also, in patent searches, shaft designs are found that provide for a spiral flow trajectory.

5. 5.-        Line 142: the choice of sodium sulfide nonahydrate as solvent is not convincing, given the possible reactions of sulfides with other compounds of raw wastewater. Why not use filtered raw wastewater?!

Answer: Thank you for your question. Key factors determining the possibility of hydrogen sulfide release in wastewater include the concentration of sulfides and hydrogen sulfide, pH, cation composition, and degree of turbulence. This study investigates the influence of the hydraulic regime on the degassing process of hydrogen sulfide from wastewater flow. The composition of wastewater can vary widely, and the experiment aimed to minimize factors affecting the equilibrium of S²⁻, HS⁻, and H₂S. The research focused on determining the intensity of molecular hydrogen sulfide release at a specified concentration of S²⁻ ions in the model solution. The information obtained will subsequently enable the assessment of potential gas release when the actual sulfide concentration is measured at the wastewater inlet to the facility (drop shaft).

6. 6.The authors did not discuss the results obtained and did not make a comparison with previous works. The work appears as a simple description of the results obtained based on both a simulation approach and a proposed experimental system, without any thought on the control solutions of hydrogen sulfide gas release.

Answer: Thank you for your question. I have discussed the results based on your question and considered the solution for controlling hydrogen sulfide gas release. The revised content is as follows:

3. Research and analysis of results:Based on the above analysis, the study indicates that with the increase in flow rate and the con-centration of sulfide ions in the water, the concentration of hydrogen sulfide gas reaching the monitoring point significantly rises. This phenomenon suggests that during vigorous water movement, the degassing effect of the water intensifies with the in-crease in sulfide ion concentration. Compared to previous studies, our experimental re-sults further validate the behavior of hydrogen sulfide transport and release in flowing water bodies. While existing research has shown that hydrogen sulfide release is closely related to water pH and sulfide ion concentration, this study particularly highlights the significant impact of increased flow rate on degassing efficiency at the same sulfide ion concentration. However, despite these results providing critical insights into the release mechanism of hydrogen sulfide, controlling its release in real-world environments still requires further investigation. Future studies could explore optimizing hydrogen sulfide control strategies by adjusting water pH, flow rate, and sulfide ion concentration, as well as introducing chemical inhibitors. These control measures could not only reduce hydro-gen sulfide emissions but also mitigate potential environmental impacts, offering more effective solutions.

Round 2

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

The authors adequately addressed my comments, and now all the critical points are clarified. Thus I can recommend this manuscript for publication.

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

Comments and Suggestions for Authors

This study is interesting but there are some shortcomings in the paper. 

-the literature review should be enhanced and a different point of view should be added. H2S is a indirect GHG. So, please mention about GHG emission. It should be highlighted. This perspective could increase the quality of the paper. You could use this reference:

*Yapıcıoğlu, P. S., & Yeşilnacar, M. İ. (2024). Decarbonization potential of geothermal energy: A new approach. In Decarbonization Strategies and Drivers to Achieve Carbon Neutrality for Sustainability (pp. 85-96). Elsevier.

https://www.sciencedirect.com/science/article/abs/pii/B978044313607800002X

Also please add IPCC 2022 and EU Green deal as the reference. 

-Please add the verification and validation of your study using sensitivity analysis. You should validate the simulation results.

-Please add the limitation and boundaries of your research as a section. Please highlight. 

-Also add the originality of your research apart from the previous studies clearly.

Comments on the Quality of English Language

This study is interesting but there are some shortcomings in the paper. 

-the literature review should be enhanced and a different point of view should be added. H2S is a indirect GHG. So, please mention about GHG emission. It should be highlighted. This perspective could increase the quality of the paper. You could use this reference:

*Yapıcıoğlu, P. S., & Yeşilnacar, M. İ. (2024). Decarbonization potential of geothermal energy: A new approach. In Decarbonization Strategies and Drivers to Achieve Carbon Neutrality for Sustainability (pp. 85-96). Elsevier.

https://www.sciencedirect.com/science/article/abs/pii/B978044313607800002X

Also please add IPCC 2022 and EU Green deal as the reference. 

-Please add the verification and validation of your study using sensitivity analysis. You should validate the simulation results.

-Please add the limitation and boundaries of your research as a section. Please highlight. 

-Also add the originality of your research apart from the previous studies clearly.

Author Response

Reviewer #1:

also stated the paper has a number of short comings.

1.The literature review needs to be enhanced

Answer: I would like to thank the reviewer for all the pertinent questions and suggestions made. All the points that needed corrections were considered and the manuscript was improved through the incorporation of the suggested changes.

I modified the shortcomings of the article based on the comments and optimized the literature review.

Reviewer 2 Report

Comments and Suggestions for Authors

The chosen research topic seems to be an interesting (and helpful, especially in terms of design) topic. The research conducted in combination with the proposed simulation could provide a more comprehensive view of the topic in question. Unfortunately, the preparation of the article is inadequate.

The title - “Research and Prevention of Harmful Gases in Special Struc- 2 tures of Urban Deep Drainage Systems” - The title does not match the data presented. No section on prevention (only mentioned).

Abstract - “Using ANSYS software, simulations of the shafts will be conducted employing the standard k-ε turbulence model and Eulerian multiphase flow method to simulate the shaft's operation and obtain various parameters of hydrogen sulfide release. Concurrently, a scale model constructed in the laboratory will be used to study and analyze the release of hydrogen sulfide gas dissolved in water from this type of structure.” – The simulation results were not presented or discussed in the article (only mentioned).

The lack of line numbering makes the review difficult. Below you will find only a few initial references.

A "hydrogen sulfide gas detector" was used in the investigation - no information is available on the measurement method.

Experimental results are discussed unreliably.

The drawings show diagrams with parameters - without legend or explanation. E.g. Figure 11 - Volume Fraction [%]

“In summary, based on the comparison of detection location data with the initial concentration, the degassing rate of hydrogen sulfide ranges from 0.1% to 0.4%.” – no information, how was it calculated?

The article needs to be cleaned up for a more comprehensive review. My suggestion is:

Consider what the main idea of the article is?

Describe the methodology in detail?

Present the results of the simulations and tests performed.

Compare the data obtained and draw conclusions.

Author Response

Reviewer #2: the paper has many flaws. The major comments of reviewer # 2 that need to be addressed are as follows:

Answer: I would like to thank the reviewer for all the pertinent questions and suggestions made. All the points that needed corrections were considered and the manuscript was improved through the incorporation of the suggested changes.

a.Simulation results were mentioned in the abstract. but not not presented or discussed in the article (only mentioned).

Answer: This is a good view from the reviewer. Based on the reviewer's comments, I discussed the simulation results in more detail.

3.2. Simulation Analysis of Hydrogen Sulfide Release: Based on the curves exported from ANSYS (Figure 11), in Figure 11(a), with an inflow velocity of 0.05 m/s, the sulfur ion volume fraction released into the air and reaching the monitoring point is 0.05% at a sulfur ion concentration of 10 mg/l in water, 0.1% at 20 mg/l, and 0.18% at 40 mg/l. In Figure 11(b), with an inflow velocity of 0.075 m/s, the sulfur ion volume fraction is 0.06% at 10 mg/l, 0.15% at 20 mg/l, and 0.20% at 40 mg/l. In Figure 11(c), with an inflow velocity of 0.1 m/s, the sulfur ion volume fraction is 0.08% at 10 mg/l, 0.18% at 20 mg/l, and 0.22% at 40 mg/l.

Based on the charts and data analysis, it is evident that as the flow rate and concen-tration increase, the hydrogen sulfide concentration reaching the monitoring point also increases. This demonstrates that during vigorous water movement, the degassing effect of the water increases with the concentration of sulfur ions in the water. Comparing the data at the monitoring point with the initial concentration, the degassing rate of hydrogen sulfide is determined to be 0.05% to 0.22%.

b A "hydrogen sulfide gas detector" was used in the investigation - no information is available on the measurement method.

Answer: This is a good view from the reviewer. I added a description of how the "hydrogen sulfide gas detector" works and how it measures.

2.2.3. Experimental circulation system: The gas detector employs solid-state metal oxide semiconductor sensing technology, uti-lizing a sensor composed of two thin films—one as a heating element and the other as a hydrogen sulfide-sensitive gas sensor. Both films are vacuum-deposited on a silicon chip. The heating element raises the operating temperature of the gas sensor to a level where it can react to hydrogen sulfide gas. The metal oxide on the gas sensor dynamically displays changes in hydrogen sulfide concentration with high sensitivity, ranging from parts per billion to percent levels. This technology ensures that the detector remains stable and du-rable in most industrial environments for over a decade.

3.3. Experimental Analysis of Hydrogen Sulfide Gas Release: The experiment utilizes a gas detector for measurement. To prevent large amounts of hydrogen sulfide gas from being released into the air and affecting the data, the gas detec-tor is placed in a sealed box, which is connected to an opening at the top of the shaft with a gas transmission tube.

1. Experimental results are discussed unreliably.

Answer: I re-discussed the experimental results.

3.3. Experimental Analysis of Hydrogen Sulfide Gas Release: The experiment utilizes a gas detector for measurement. To prevent large amounts of hydrogen sulfide gas from being released into the air and affecting the data, the gas detec-tor is placed in a sealed box, which is connected to an opening at the top of the shaft with a gas transmission tube. The gas detector data is shown in Figure 12. In Figure 12(a), with an inflow velocity of 0.05 m/s and a sulfur ion concentration of 10 mg/l in water, the hydrogen sulfide concen-tration measured by the gas detector fluctuates between 0.01 mg/m³ and 0.09 mg/m³. At a sulfur ion concentration of 20 mg/l, it fluctuates between 0.03 mg/m³ and 0.14 mg/m³, and at 40 mg/l, it fluctuates between 0.05 mg/m³ and 0.27 mg/m³. In Figure 12(b), with an in-flow velocity of 0.075 m/s, the measured hydrogen sulfide concentration fluctuates be-tween 0.02 mg/m³ and 0.12 mg/m³ at 10 mg/l, between 0.05 mg/m³ and 0.16 mg/m³ at 20 mg/l, and between 0.06 mg/m³ and 0.35 mg/m³ at 40 mg/l. In Figure 12(c), with an inflow velocity of 0.1 m/s, the measured hydrogen sulfide concentration fluctuates between 0.03 mg/m³ and 0.15 mg/m³ at 10 mg/l, between 0.07 mg/m³ and 0.19 mg/m³ at 20 mg/l, and between 0.07 mg/m³ and 0.40 mg/m³ at 40 mg/l.

In summary, it is known that under the same velocity conditions, the concentration of hydrogen sulfide gas released into the air increases with the increase of sulfur ion concen-tration in the water. This demonstrates that at a determined pH value, the degassing rate of water increases with the increase of sulfur ion concentration in the water.

According to the data depicted in Figure (13), in Figure (13)a, with a sulfur ion con-centration of 10mg/l, the hydrogen sulfide gas concentration detected reached a maximum of 0.15mg/m³ as the inflow velocity increased; in Figure (13)b, with a sulfur ion concentra-tion of 20mg/l, the detected hydrogen sulfide gas concentration reached a maximum of 0.20mg/m³ as the inflow velocity increased; in Figure (13)c, with a sulfur ion concentration of 40mg/l, the detected hydrogen sulfide gas concentration reached a maximum of 0.40mg/m³ as the inflow velocity increased.

In summary, for solutions with identical sulfur ion concentrations, the concentration of hydrogen sulfide gas released into the air increases with the increase in water inflow velocity. This demonstrates that at a determined pH value, the degassing rate of water in-creases with the increase in water inflow velocity.

In summary, and based on the comparison between detection location data and ini-tial concentration calculations, the degassing rate of hydrogen sulfide is determined to be 0.1%-0.4%.

d.The drawings show diagrams with parameters - without legend or explanation. E.g. Figure 11 - me  [%.

Answer: This set of chart data is the volume fraction data of hydrogen sulfide gas derived from ANSYS software, and the vertical axis parameters represent the percentage of volume fraction.

e.Based on the comparison of detection location data with the initial concentration, the degassing rate of hydrogen sulfide ranges from 0.1% to 0.4%.” – no information, how was it calculated?

Answer: This is a good view from reviewer. I forgot to add the formula before, and based on my tutor’s past research, I added the following formula.

2.2.2. Experimental water parameters: The degassing rate of hydrogen sulfide gas should be:

Where D is the degassing rate;  represents the hydrogen sulfide concentration data measured by the gas detector;  denotes the volume of hydrogen sulfide gas released into the gas detector;  is the concentration of hydrogen sulfide in the solution; and  is the volume of the aqueous solution.

f.T he simulation results were not presented or discussed in the article (only mentioned).

Answer: Based on the reviewer's comments, I discussed the simulation results in more detail.

3.2. Simulation Analysis of Hydrogen Sulfide Release: Based on the curves exported from ANSYS (Figure 11), in Figure 11(a), with an inflow velocity of 0.05 m/s, the sulfur ion volume fraction released into the air and reaching the monitoring point is 0.05% at a sulfur ion concentration of 10 mg/l in water, 0.1% at 20 mg/l, and 0.18% at 40 mg/l. In Figure 11(b), with an inflow velocity of 0.075 m/s, the sulfur ion volume fraction is 0.06% at 10 mg/l, 0.15% at 20 mg/l, and 0.20% at 40 mg/l. In Figure 11(c), with an inflow velocity of 0.1 m/s, the sulfur ion volume fraction is 0.08% at 10 mg/l, 0.18% at 20 mg/l, and 0.22% at 40 mg/l.

Based on the charts and data analysis, it is evident that as the flow rate and concen-tration increase, the hydrogen sulfide concentration reaching the monitoring point also increases. This demonstrates that during vigorous water movement, the degassing effect of the water increases with the concentration of sulfur ions in the water. Comparing the data at the monitoring point with the initial concentration, the degassing rate of hydrogen sulfide is determined to be 0.05% to 0.22%.