Effect of Particle Concentration and Pipe Materials on the Formation of Biofilms in Drinking Water Distribution Systems

Round 1

Reviewer 1 Report

Summary

This manuscript touches on a topic that is extremely important in public drinking water systems, namely the presence and composition of microbial communities in distribution pipes (biofilms). The study investigates the effects of particle abundance in the water and rotational speed of the water relative to the pipes in two different pipe materials, ductile iron and polyvinyl chloride. Studies like these are useful for understanding how biofilms develop in drinking water systems, as these biofilms have large potential for causing erosional issues within the drinking water system, as well as potential negative health impacts from the biological components themselves. The study is therefore appropriate for publication and I see no reason to reject the article. There are some improvements to the scope and application that would be beneficial:

Regarding application of the study:

The paper as it is written is missing the application. How will results from this study aid stakeholders responsible for distributing water? Should there be more efforts to regulate particle content or rotational speed within drinking water systems? Addressing these questions would significantly improve the scope of the conclusions.

Regarding the particle experiment:

Needs more information on the size distribution of the particles. It's not entirely clear how a particle is defined in this work. How big are the particles, what are their compositions, how do these compare to particles found in drinking water systems?

Is it possible that the composition of the particles would affect the biofilm development, such as the abundance of organic vs. inorganic particle types. What would the authors suggest a drinking water distribution system do about the particle content?

Numerically, what is the range, mean, median of particle contents in drinking water systems. How do we know that the parameters chosen in this study are relatable to those found in production systems?

Regarding rotation speed:

I did not understand the purpose of the rotational speed experiments, and I'm not sure if I fully understand what the authors are referring to by rotational speed and how this is related to the physical conditions occurring during water transport. How might this be controlled in a drinking water distribution system? What are typical rotation speeds for systems in production?

Author Response

1. The significance of this article is that the secondary pollution of the biofilm in the pipe network is more serious, so the impact of particulate matter in one of the pipe networks on it is studied, and the number of microorganisms decreases with the increase of particulate matter, which is the same as we assume that the increase of particulate matter will increase the number of microorganisms on the contrary, so further research is needed to provide some clues on how to control the growth of microorganisms from this aspect.

2. Because the experiments we have done have a relatively large range of research concepts on particulate matter, generally 0~100nm particulate matter, and there is no research on the impact of different particle sizes or different properties on microorganisms. If I have better thinking in the future, I will do related research.

3. Rotation speed experiment is to simulate the influence of particles on microorganisms at different flow rates in different time periods in the real pipe network.

Reviewer 2 Report

The manuscript concerns the important issue of “Effect of Particle Concentration and Pipe Materials on the Formation of Biofilms in Drinking Water Distribution Systems”. The simulative system of DWDS ran for 12 h every day from June 2018 to September 76 2019. The following remarks should be referred to: The state of the art should clearly show the knowledge gaps identified. Line 65, the previous mentioned studies should be cited. Line 109: The upper script of the units should be checked, eg. In water distribution system experiments, the temperature was 20 ℃, pH was 7.5 108 and flow rate was 0.15 m3/h. Authors do not explain well, where is the novelty of the distingusihed method. Please reason both the novelty and the relevance of your paper goals. Are there concrete steps that can be recommended and how generalizable are the findings? How in practice the results of the presented analysis can be used? This should be discussed in the point concerning discussion of the results. Conclusion is not sufficiently described. It is more like summary of information, what can be read in previous chapters.

Author Response

1. The significance of this article is that the secondary pollution of the biofilm in the pipe network is more serious, so the impact of particulate matter in one of the pipe networks on it is studied, and the number of microorganisms decreases with the increase of particulate matter, which is the same as we assume that the increase of particulate matter will increase the number of microorganisms on the contrary, so further research is needed to provide some clues on how to control the growth of microorganisms from this aspect.

2. Because the experiments we have done have a relatively large range of research concepts on particulate matter, generally 0~100nm particulate matter, and there is no research on the impact of different particle sizes or different properties on microorganisms. If I have better thinking in the future, I will do related research.

3. Rotation speed experiment is to simulate the influence of particles on microorganisms at different flow rates in different time periods in the real pipe network.

4. Due to my own mistakes, I made the wrong time for the experiment. It should be from June 2020 to September 2021. The reason for this time period is because it takes so long for the growth cycle of microorganisms to stabilize.
5. And I will modification the artical conclusion like this:

   Since the secondary pollution of biofilms in pipelines is a problem that we urgently need to solve, but if we research the turbidity indicators in the pipeline network water, it will be relatively macro and difficult to analyze, so the impact of particulates in the pipeline network on the formation of biofilms is studied. The experimental results show that the impact of its particulate matter on biological production is: as the particulate matter increases, the number of organisms decreases. This is the opposite of our expectation. Therefore, it provides information on how to reduce the number of biofilms in the pipe network.

Round 2

Reviewer 2 Report

Figures are too small.

More information about future work should be added.

Please explain your answer: If I have better thinking in the future, I will do related research.

Please reason both the novelty and the relevance of your paper goals.

Could be considered for publication as a case report.

Author Response

Our future work wants to continue to study the impact of particulate matter in the pipeline network on biofilms and to know and study how to control and reduce the formation of biofilms in the pipeline network to cause secondary pollution to drinking water.

And please see the case report document for other answers.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Extensive editing of English language and style required.