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The purpose of including the silver in the ceramic filter is that it has an anti-bacterial action, it kills bacteria on contact. This increases the effectiveness of the filter against diarroheal diseases above that which could be expected from purely mechanical filtration, which relaxes quality control and tolerances required during the ceramic manufacture process.If chlorinated water is passed through the filter then the result will be the silver will be stripped from the ceramics. This will result in a reduction in the effectiveness of the filter in removing pathogens. If the water has been effectively chlorinated this will not be a problem, as pathogens will have been destroyed prior to filtration. According to the WHO Water Drinking Water Quality Guidelines there is insufficient data available to derive health based guideline values for water. However the guidelines do state that a concentration of 0.1 mg/L could be consumed over 70 years without adverse impact on human health. (pg. 434, https://www.who.int/water_sanitation_health/dwq/GDW12rev1and2.pdf?ua=1 ) The concentration of silver in the water will obviously depend on the concentration of the chlorine, the amount of silver initially present and the form of the silver in the ceramics. This will also determine how long it will take for the silver in the ceramics to be depleted/removed.The WASH Cluster should consider the following questions:Why is there a need to chlorinate the water when ceramic filters with an anti-bacteriological agent incorporated are being supplied? The only benefit that is likely to accrue from the addition of chlorine to the process is prevention of post collection and treatment disinfection due to the residual chlorine. If the filters are being used correctly, and the WASH agencies are providing effective training and hygiene promotion on the safe water chain and the correct use of the filters, then the risk of post collection or post treatment contamination should be negligible. The benefit of the residual chlorine is also questionable, as the effectiveness of the residual chlorine as a disinfectant reduces with time. In high ambient temperatures the residual effect will probably have quite a short lifespan.Why chlorinate the water pre-filtration? If the turbidity is high enough to interfere with the effectiveness of Chlorine as a disinfectant (a tubidity of < 1 NTU should be the target when a pre-treatment process stage such as flocculation & coagulation is incorporated in the treatment process)? The Sphere standard guideline value of <5 NTU is intended for use in the initial stages of an emergency. From the description given the the WHO Water Quality Guidelines guideline values for turbidity and effective disinfection would be more appropriate target in this context.It may be preferable in these circumstances for the WASH Cluster to consider increasing retention time in the process, by providing additional storage (point of collection, household etc), rather than chlorinating. If chlorination is deemed absolutely necessary then a strategy based on using point of use (POU) chlorination, following filtration using the ceramic filters may be most appropriate.The formation of chlorine by-products (CBP's) such as THM's is most likely if there are organics in the water. Thus the risks associated with CBP's is likely be greatest from the pond water sources. Again this risk is likely to be greatly reduced, or negligible if the water is chlorinated following filtration (or simple storage for 24 hours). The presence of THM's does not present an acute health risk. In the face of a risk of an AWD outbreak the best approach would be to chlorinate, and ignore the possiblity of CBP's. Of greatest concern here is that the presence of CBP's may render the treated water unpalatable, causing people to prefer water from untreated sources. This can occur at quite low concentrations of chlorine, as the water will smell and taste like a disinfectant.Based on the description then potentially the best strategy would be:Chlorinate bulk water supplies to provide residual disinfection through distribution networks. In this case the initial dosage of chlorine should be high enough to provide a 0.2-0.5 mg/L concentration at the tap. This will depend on the state of the system, leaks and points of ingress and the presence of organics in the network itself. Water entering the networks should have a turbidity of < 1 NTU prior to chlorination, which will require pre-treatment. This would probably entail coagulation and flocculation (Oxfam produces kits for coagulation and flocculation based around their storage tanks. Details for these can be found in the Oxfam Equipment Catalog;Providing filters and additional storage to users not being supplied by the bulk distribution networks;Where residual disinfection is felt to be critical (e.g. users not supplied with ceramic filters) provide POU chlorine products;Target users of ponds as priority for receiving ceramic filters;Budget for a minimum three months of hygiene promotion on the safe water chain and the use of any Point of Use Treatment products (Ceramic filters, Chlorine, combined coagulants and disinfection products) Ideally this needs to begin prior to a response;Plan bucket chlorination activities as a contingency in the event of an AWD outbreak for users collecting water from the wells. If budgets allow these should be the second priority users for receiving ceramic filters);M&E Activities on the effective use of the supplied products should be a continuous process;Provide capacity to store water for at least 24 hours (based on litres per person per day target and the number of members of the household);Hope this helpsJohn Cody------ Original Message ------From: admin@knowledgepoint.orgTo: extcody@yahoo.co.uk
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The purpose of including the silver in the ceramic filter is that it has an anti-bacterial action,
it kills bacteria on contact. This increases the effectiveness of the filter against diarroheal
diseases above that which could be expected from purely mechanical filtration, which relaxes quality
control and tolerances required during the ceramic manufacture
process.If
process.
If chlorinated water is passed through the filter then the result will be the silver will be stripped from the ceramics. This will result in a reduction in the effectiveness of the filter in removing pathogens. If the water has been effectively chlorinated this will not be a problem, as pathogens will have been destroyed prior to filtration. According to the WHO Water Drinking Water Quality Guidelines there is insufficient data available to derive health based guideline values for water.
However the guidelines do state that a concentration of 0.1 mg/L could be consumed over 70 years without adverse impact on human health. (pg. 434, https://www.who.int/water_sanitation_health/dwq/GDW12rev1and2.pdf?ua=1 )
The concentration of silver in the water will obviously depend on the concentration of the
chlorine, the amount of silver initially present and the form of the silver in the ceramics. This
will also determine how long it will take for the silver in the ceramics to be
depleted/removed.The
depleted/removed.
The WASH Cluster should consider the following
questions:Why
questions:
Why is there a need to chlorinate the water when ceramic filters with an anti-bacteriological
agent incorporated are being
supplied?
supplied?
The only benefit that is likely to accrue from the addition of chlorine to the process is
prevention of post collection and treatment disinfection due to the residual chlorine. If the
filters are being used correctly, and the WASH agencies are providing effective training and hygiene
promotion on the safe water chain and the correct use of the filters, then the risk of post
collection or post treatment contamination should be negligible. The benefit of the residual
chlorine is also questionable, as the effectiveness of the residual chlorine as a disinfectant
reduces with time. In high ambient temperatures the residual effect will probably have quite a short
lifespan.Why
lifespan.
Why chlorinate the water
pre-filtration?
pre-filtration?
If the turbidity is high enough to interfere with the effectiveness of Chlorine as a
disinfectant (a tubidity of < 1 NTU should be the target when a pre-treatment process stage such
as flocculation & coagulation is incorporated in the treatment process)? The Sphere standard
guideline value of <5 NTU is intended for use in the initial stages of an emergency. From the
description given the the WHO Water Quality Guidelines guideline values for turbidity and effective
disinfection would be more appropriate target in this
context.It
context.
It may be preferable in these circumstances for the WASH Cluster to consider increasing retention
time in the process, by providing additional storage (point of collection, household etc), rather
than chlorinating. If chlorination is deemed absolutely necessary then a strategy based on using
point of use (POU) chlorination, following filtration using the ceramic filters may be most
appropriate.The
appropriate.
The formation of chlorine by-products (CBP's) such as THM's is most likely if there are organics in
the water. Thus the risks associated with CBP's is likely be greatest from the pond water sources.
Again this risk is likely to be greatly reduced, or negligible if the water is chlorinated following
filtration (or simple storage for 24 hours). The presence of THM's does not present an acute health
risk. In the face of a risk of an AWD outbreak the best approach would be to chlorinate, and ignore
the possiblity of CBP's. Of greatest concern here is that the presence of CBP's may render the
treated water unpalatable, causing people to prefer water from untreated sources. This can occur at
quite low concentrations of chlorine, as the water will smell and taste like a
disinfectant.Based
disinfectant.
Based on the description then potentially the best strategy would
be:Chlorinate
be:
-
Chlorinate bulk water supplies to provide residual disinfection through distribution networks. In this case the initial dosage of chlorine should be high enough to provide a 0.2-0.5 mg/L concentration at the tap. This will depend on the state of the system, leaks and points of ingress and the presence of organics in the network itself. Water entering the networks should have a turbidity of < 1 NTU prior to chlorination, which will require pre-treatment. This would probably entail coagulation and flocculation (Oxfam produces kits for coagulation and flocculation based around their storage tanks. Details for these can be found in the Oxfam Equipment
Catalog;ProvidingCatalog; -
Providing filters and additional storage to users not being supplied by the bulk distribution
networks;Wherenetworks; -
Where residual disinfection is felt to be critical (e.g. users not supplied with ceramic filters) provide POU chlorine
products;Targetproducts; -
Target users of ponds as priority for receiving ceramic
filters;Budgetfilters; -
Budget for a minimum three months of hygiene promotion on the safe water chain and the use of any Point of Use Treatment products (Ceramic filters, Chlorine, combined coagulants and disinfection
products)products). Ideally this needs to begin prior to aresponse;Planresponse; -
Plan bucket chlorination activities as a contingency in the event of an AWD outbreak for users collecting water from the wells. If budgets allow these should be the second priority users for receiving ceramic
filters);M&Efilters); -
M&E Activities on the effective use of the supplied products should be a continuous
process;Provideprocess; -
Provide capacity to store water for at least 24 hours (based on litres per person per day target and the number of members of the
household);Hopehousehold).
Hope this
helpsJohn Cody------ Original Message ------From: admin@knowledgepoint.orgTo:
extcody@yahoo.co.uk
John Cody