Kanchan Arsenic Filters and the Future of Fe0-Based Filtration Systems for Single Household Drinking Water Supply
Round 1
Reviewer 1 Report
The communication provides interesting mixture of literature review on KAF point of use arsenic removal unit in combination with author’s critical remarks and suggestions on how the performance of this treatment unit can be improved. The communication can be seen as valuable contribution in search for affordable and sustainable household level arsenic removal treatment unit. The communication is therefore worth publishing, however, there is a space to improve it. Here are some general and specific comments and suggestions.
Objectives of the communication should be more clearly introduced.
Effect of ground water chemistry was not sufficiently addressed and in general underestimated, while it is well known that groundwater quality have pronounce effect on performance of all PoU water treatment units including the KAF.
Some of the conclusion are not supported by analyses presented earlier in the communication.
Risk associated with possible pollution of water to be treated due to use of not properly cleaned source of Fe0 (iron nails) not even mentioned.
Removal of other common groundwater impurities, some of direct health relevance (e.g. manganese) not addressed.
Short circuiting that very likely contribute to insufficient and difficult to predict performance of KAF underestimated.
Statements made are rather descriptive and not supported by specific results from reviewed publications.
Line 122 – unit for the acceptable levels should be µg/L and not mg/L
Lines 124-125. The effect of groundwater quality (As concentration and speciation, presence of competing compounds like phosphate, presence of ammonium and methane, that can consume dissolved oxygen and cause bio-fouling of Fe0 source, pH that is known to have strong effect of HFO arsenic adsorption capacity, etc.) on performance of KF was not sufficiently addressed.
The basic AF design parameters (e.g. filtration rate, zero iron bed depth, contact time) were not introduced and analysed in the communication.
The item 3 entitled “The design limitations of KAF”. The text provided, however, does not clearly presents limitation of KAF design.
Lines 192 – 200 – The effect of short circuiting caused by equal distribution of feed flow over the KFA surface area was considered to be of minor importance, while it is obvious that unequal feed flow distribution will cause preferential streams and caused insufficient contact of arsenic containing water and the Fe0 filter bed resulting in poor arsenic removal.
It should be more strongly stated that possible design improvements of the next generation(s) of KAF should be based on proper laboratory and field pilot studies, before providing filters to population for drinking water production.
Under conclusions several statements were made that were not supported by discussion or analyses in the previous text of the communication.
The communication strongly stated that inefficiency of the conventional KAF are the consequence of design mistakes. Design mistakes are, however, not clearly presented and analysed in the communication. At the same time the effect of groundwater quality were underestimated or completely ignored (e.g. presence of high levels of ammonium and possibly methane that are known to consume oxygen in the process of their biological oxidation).
Line from 188: The statement “Clearly, complete immersion of iron nails is not likely to play any detrimental role in the performance of a KAF” is rather speculative and not supported by deeper analyses. It is known that e.g. groundwater in Nepal (and several other countries affected by arsenic presence in groundwater) often contains higher levels of ammonium and/or methane. When such groundwater is passing through immersed Fe0 filter bed, it will become anoxic and dissolved oxygen could become unavailable for oxidation of immersed Fe0.
Lines from 224: Recommendations for more efficient KAFs
Recommendation to use less dense Fe0 materials (e.g., iron coils, iron foam, scrap iron, steel wool) could be beneficial in particular case but will for sure not be sufficient to improve performance of KAF when complex groundwater (with high levels of e.g. ammonium, methane) is used as source.
Line 258 Conclusions: Information provided in the communication do not support the statement in the conclusion “that it is still unclear if the original KAF design is viable upon modification is still unclear”. It is obvious that KAF even with suggested improvements is not an appropriate solution for all types of arsenic contaminated groundwater.
Author Response
Many thanks for this evaluation! We are also VERY VERY thankful for the specific comments and suggestions which have (i) made our manuscript expressing our original idea the best, and (ii) are very useful for our next works, including a literature review in preparation. Really many thanks again.
To summarize the responses, we have (i) given more details in presenting the non tested modification of the original KAF as for Figure 1, and (ii) added a new section (“Questioning the suitability of KAF” - section 5). We have tried to do this in the most collegiate manner and hope that colleagues will understand that we are not destroying their efforts but mainly thinking on common progress. Indeed there is no need to invent a new concept to test and disseminate frugal technologies. Using the KAF concept is regarded by us (since 2012) as a model. It is just unfortunate that even Mr. Ngai is still insisting on testing and testing the same wrong device. Therefore, we are very thankful (again and again) for the suggestions of the reviewers, which will put the needed pressure on colleagues to realize their mistakes.
Sincerely,
Dr. Noubactep
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper is good in my opinion. Maybe I would add some comment on the use of mechanical separation for water treatment, citing
Calabrò, Francesco. "Modeling the effects of material chemistry on water flow enhancement in nanotube membranes." Mrs Bulletin 42.4 (2017): 289.
Lee, Kah Peng, Tom C. Arnot, and Davide Mattia. "A review of reverse osmosis membrane materials for desalination—development to date and future potential." Journal of Membrane Science 370.1-2 (2011): 1-22.
Author Response
Many thanks for this evaluation, both references are properly considered in the revision.
