Efficacy of Flushing and Chlorination in Removing Microorganisms from a Pilot Drinking Water Distribution System
Round 1
Reviewer 1 Report
General comments:
This study tested methods for cleaning and disinfecting surfaces inside drinking water distribution pipes. It seems like very useful applied research, since we have fewer controls for distribution system risks relative to the treatment facility. It would benefit from minor revisions to streamline the paper and clarify a few small issues. I noticed but didn’t address minor editing issues (e.g., extra words, missing punctuation), which can probably be dealt with by the authors later.
Maybe use “incident” instead of “calamity” (could be minor leak), or a “crack/break” specifically if this is the intended meaning
Maybe a “model” distribution system instead of “pilot”?
Consider standardizing use of efficiency, effectivity, and efficacy.
Specific comments:
Abstract:
Line 26 – hard to understand that you were comparing natural and cultured biofilms based on the earlier explanation of the methods (lines 21-22 suggest all surfaces were treated the same)
Line 30 – both suspected and confirmed contamination events?
Introduction:
Paragraph 1 – not necessarily free of all pathogens; probably considered free of monitored pathogens, but more often we rely on indicators correlated with pathogen presence
Lines 64-74 – I found this discussion confusing and would break into a second paragraph here. Is the Canadian study suggestive of treatment issues or regrowth due to insufficient disinfection (along the lines of my comment on paragraph 1)? Reference 9 also needs more explanation… Campylobacter found in what media? Livestock found where? Public water supply versus what other source? Not sure what the household water treatment studies add… suggesting there is no residual risk from the distribution system? Maybe some of these studies could be deleted if tangential or don’t fit with the flow of logic earlier in the paragraph.
Line 79 – which study? (add in-text reference)
Line 84 – consider adding a little more text on the relative infectious dose of different types of pathogens (e.g., bacteria versus viruses versus protozoa)
Line 89 – efficiency or effectiveness? Efficiency might consider time, costs, or energy use. Maybe “efficacy” is appropriate given the laboratory setting (also see caption of Figure 4A)
Line 94 – include citation, not clear if this was the same study (19)
Lines 98-106 – good description!
Line 109-111 – hard to follow this sentence, consider revising
Materials and Methods:
Paragraph 1 - Is a bacteriophage adequately representative of the characteristics/sensitivity of a human virus (e.g., norovirus)? (add brief explanation to text)
Line 174 – 7 cm starting from the end of the 20-m pipe?
Figure 1 – I like the diagram but most of the text is too small to read, suggest making it bigger or deleting from the diagram and adding a legend. Also add a common scale if it’s to scale, this (20 m) only appears on the lower one. Need to mark as A, B, C if described this way in the text.
Line 230 – actively or passively circulated? What normal phenomenon did this simulate?
Line 238 – same time points as earlier paragraph? (please specify)
Line 246 – please specify the material of the excavated pipes (e.g., PVC)
Results and Discussion:
Line 326-327 – or could be in equilibrium (i.e., the same number of microorganisms attaching and releasing)?
Line 322-323 and 327-332 – this is helpful discussion but I wonder if the variation is literally caused by the experimental set-up or is just natural variation and would be observed in any case. It seems we’re also seeking a presence/absence answer in practice settings, so changes in counts might matter less.
Line 346-347 – this seems like an important finding (consider highlighting in abstract or conclusions)
Lines 357-363 – a bit repetitive
Line 381 – Consider adding separate bit of explanation (here or elsewhere) referring to whether would have (a) expected any different results with other pipe materials or (b) recommend using other materials for future experiments.
Line 402 – consider defining in lay terms what one volume unit is equal to (either here or on first use)
Figures 5 and 6 – this combination of graphics is a little hard to follow, consider combining As and Bs in one figure, and the Cs and D in another
Line 538 – consider describing the procedure for “ice pigging” and/or naming a few other common techniques, such as scraping or pressure washing. Perhaps briefly summarize what factors the preferred method depends on (e.g., age, material, type of contamination).
Author Response
Reviewer 1
Review Report Form
Open Review
(x) I would not like to sign my review report
( ) I would like to sign my review report
English language and style
( ) Extensive editing of English language and style required
(x) Moderate English changes required
( ) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style
Yes | Can be improved | Must be improved | Not applicable | |
Does the introduction provide sufficient background and include all relevant references? | ( ) | (x) | ( ) | ( ) |
Is the research design appropriate? | (x) | ( ) | ( ) | ( ) |
Are the methods adequately described? | ( ) | (x) | ( ) | ( ) |
Are the results clearly presented? | ( ) | (x) | ( ) | ( ) |
Are the conclusions supported by the results? | (x) | ( ) | ( ) | ( ) |
Comments and Suggestions for Authors
General comments:
This study tested methods for cleaning and disinfecting surfaces inside drinking water distribution pipes. It seems like very useful applied research, since we have fewer controls for distribution system risks relative to the treatment facility. It would benefit from minor revisions to streamline the paper and clarify a few small issues. I noticed but didn’t address minor editing issues (e.g., extra words, missing punctuation), which can probably be dealt with by the authors later.
Response: Manuscript was checked to change ‘en’ into ‘and’ and the use of ‘,’ and ‘.’ in numbers was improved.
Maybe use “incident” instead of “calamity” (could be minor leak), or a “crack/break” specifically if this is the intended meaning
Response: Calamity changed to incident at several places in the manuscript
Maybe a “model” distribution system instead of “pilot”?
Response: A model is indeed a more appropriate description than pilot, this has been changed in the manuscript.
Consider standardizing use of efficiency, effectivity, and efficacy.
Response: Efficiency and effectivity have both been replaced with efficacy.
Specific comments:
Abstract:
Line 26 – hard to understand that you were comparing natural and cultured biofilms based on the earlier explanation of the methods (lines 21-22 suggest all surfaces were treated the same)
Response: Information is added (line 22-23) that the pipes contain a natural or cultured biofilm
Line 30 – both suspected and confirmed contamination events?
Response: Information is added (line 32-33) that it mainly concerns confirmed contamination events
Introduction:
Paragraph 1 – not necessarily free of all pathogens; probably considered free of monitored pathogens, but more often we rely on indicators correlated with pathogen presence
Response: Sentence rephrased (line 38-40) to ‘Due to extensive purification of ground water or surface water, pathogenic microorganisms and indicator organisms are absent in detectable levels in treated drinking water’.
Lines 64-74 – I found this discussion confusing and would break into a second paragraph here. Is the Canadian study suggestive of treatment issues or regrowth due to insufficient disinfection (along the lines of my comment on paragraph 1)? Reference 9 also needs more explanation… Campylobacter found in what media? Livestock found where? Public water supply versus what other source? Not sure what the household water treatment studies add… suggesting there is no residual risk from the distribution system? Maybe some of these studies could be deleted if tangential or don’t fit with the flow of logic earlier in the paragraph.
Response: The paragraph was not split in two, as all discussed studies concerns the possible risks of contamination of drinking water during repair works or distribution. However, some less relevant information was removed and the paragraph was rephrased (lines 66-79).
Line 79 – which study? (add in-text reference)
Response: The reference has been added and the sentenced slightly rephrased (line 88-91)
Line 84 – consider adding a little more text on the relative infectious dose of different types of pathogens (e.g., bacteria versus viruses versus protozoa)
Response: Short information with references added on lines 95-97
Line 89 – efficiency or effectiveness? Efficiency might consider time, costs, or energy use. Maybe “efficacy” is appropriate given the laboratory setting (also see caption of Figure 4A)
Response: Efficiency changed to efficacy in the entire manuscript and in caption of Figure 4A.
Line 94 – include citation, not clear if this was the same study (19)
Response: Text added to clarify that it concerns the same study (line 95-96)
Lines 98-106 – good description!
Response: Thank you
Line 109-111 – hard to follow this sentence, consider revising
Response: Sentence was rephrased to ‘In this paper we used a pilot-scale pipe-loop system, in which a biofilm was cultured, to study i) the influence of the waiting time between flushing of the system and sampling the water and ii) the effect of the distance between sampling point and point of contamination. (line 120-123)
Materials and Methods:
Paragraph 1 - Is a bacteriophage adequately representative of the characteristics/sensitivity of a human virus (e.g., norovirus)? (add brief explanation to text)
Response: Bacteriophage are considered as indicators of enteric viruses as their morphological and biological characteristics more closely math enteric viruses (compared to, for example, faecal indicator bacteria). A short explanation has been added to the text (line 137-138) and a reference has been included.
Line 174 – 7 cm starting from the end of the 20-m pipe?
Response: Sentence rephrased to ‘Analyses of the biofilm were performed by swabbing roughly 7 cm of pipe wall biofilm (all sides), 1-2 cm pipe wall biofilm at the start of the pipe segment was not swabbed. For swabbing multiple sterile cotton swabs were used.’ Line: 189-191.
Figure 1 – I like the diagram but most of the text is too small to read, suggest making it bigger or deleting from the diagram and adding a legend. Also add a common scale if it’s to scale, this (20 m) only appears on the lower one. Need to mark as A, B, C if described this way in the text.
Response: Figure 1 has been improved.
Line 230 – actively or passively circulated? What normal phenomenon did this simulate?
Response: actively circulated using a pump. 0,1 m/s is the average flow in the Dutch drinking water distribution system. Information has been added (line 246-247).
Line 238 – same time points as earlier paragraph? (please specify)
Response: time points for chlorine measurements (line 255) and sampling of water and biofilm are added (line 256-259).
Line 246 – please specify the material of the excavated pipes (e.g., PVC)
Response: all pipes are PVC, information added on line 265
Results and Discussion:
Line 326-327 – or could be in equilibrium (i.e., the same number of microorganisms attaching and releasing)?
Response: Could be a possibility (added: line 352-354), although in general biofilm and water have differing microbial populations.
Line 322-323 and 327-332 – this is helpful discussion but I wonder if the variation is literally caused by the experimental set-up or is just natural variation and would be observed in any case. It seems we’re also seeking a presence/absence answer in practice settings, so changes in counts might matter less.
Response: Added that natural variation could also be a cause (line 348). In practice it is indeed about presence/absence, however in these experiments we also want to look at the dynamics as high numbers of microorganisms were used. Therefore, this point was not included in the text.
Line 346-347 – this seems like an important finding (consider highlighting in abstract or conclusions)
Response: Added to conclusions (number 3, lines 584-585) and abstract (lines 24-25)
Lines 357-363 – a bit repetitive
Response: Part of the text has been removed or rephrased (line 386 - 387).
Line 381 – Consider adding separate bit of explanation (here or elsewhere) referring to whether would have (a) expected any different results with other pipe materials or (b) recommend using other materials for future experiments.
Response: Literature study shows that the pipe material mainly influences the formation rate and probably composition of the biofilm. Once a biofilm is formed it appears that microorganisms will bind to it. The material of the pipe wall on which the biofilm was formed seems of less or no importance. The text has been rephrased (lines: 386-388).
Line 402 – consider defining in lay terms what one volume unit is equal to (either here or on first use)
Response: Explanation added in the material & methods section (lines 256-258)
Figures 5 and 6 – this combination of graphics is a little hard to follow, consider combining As and Bs in one figure, and the Cs and D in another
Response: Figures 5 and 6 have been changed according to the suggestions. The text has been adapted to this.
Line 538 – consider describing the procedure for “ice pigging” and/or naming a few other common techniques, such as scraping or pressure washing. Perhaps briefly summarize what factors the preferred method depends on (e.g., age, material, type of contamination).
Response: An short explanation of ice pigging was added (lines 570-572).
Submission Date
22 March 2019
Date of this review
08 Apr 2019 22:26:26
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript is both interesting and highly relevant to the water industry, providing practical information for operators of drinking water distribution networks about how to optimally prevent network contamination following repair work and mains bursts.
Suggestions/comments-
provide further information in methodology about how the network pipes were extracted for the natural biofilm experiments e.g. was this done aseptically? were they kept moist and refrigerated etc.
lines 322-323 unsure what is meant by "This result was only seen once and therefore suggests that this may be variation caused by the large set up of the experiments".
In future experiments It would be interesting to look at the affect of a different concentration of chlorine on removal, particularly a concentration that is usually seen in chlorinated networks (0.5 - 1 mg/L).
A few typos including use of "en" instead of "and"
Author Response
Reviewer 2
Review Report Form
Open Review
(x) I would not like to sign my review report
( ) I would like to sign my review report
English language and style
( ) Extensive editing of English language and style required
( ) Moderate English changes required
(x) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style
Yes | Can be improved | Must be improved | Not applicable | |
Does the introduction provide sufficient background and include all relevant references? | (x) | ( ) | ( ) | ( ) |
Is the research design appropriate? | (x) | ( ) | ( ) | ( ) |
Are the methods adequately described? | (x) | ( ) | ( ) | ( ) |
Are the results clearly presented? | (x) | ( ) | ( ) | ( ) |
Are the conclusions supported by the results? | (x) | ( ) | ( ) | ( ) |
Comments and Suggestions for Authors
The manuscript is both interesting and highly relevant to the water industry, providing practical information for operators of drinking water distribution networks about how to optimally prevent network contamination following repair work and mains bursts.
Suggestions/comments-
provide further information in methodology about how the network pipes were extracted for the natural biofilm experiments e.g. was this done aseptically? were they kept moist and refrigerated etc.
Response: Additional information is added (lines 269-273).
lines 322-323 unsure what is meant by "This result was only seen once and therefore suggests that this may be variation caused by the large set up of the experiments".
Response: We want to suggest that due to the large set up of the pilot system more variation can occur compared to small scale laboratory experiments (e.g. in bottles). In response to the comments of reviewer 1 also the option of ‘natural variation’ was added on line 348.
In future experiments It would be interesting to look at the effect of a different concentration of chlorine on removal, particularly a concentration that is usually seen in chlorinated networks (0.5 - 1 mg/L).
Response: This is indeed an interesting question. However, as the research question was focused on the efficacy of shock chlorination, low chlorine concentrations were not considered in this study.
A few typos including use of "en" instead of "and"
Response: changed ‘en’ for ‘and’ on several places.
Submission Date
22 March 2019
Date of this review
04 Apr 2019 07:01:49
Author Response File: Author Response.docx
