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Effect of Silver Inserts on Recontamination in Ceramic Water Filters

This study aims to assess the effectiveness of silver inserts with chemically-etched surfaces in preventing regrowth and recontamination in ceramic water filters. Laboratory and field tests were conducted to evaluate the impact of silver on water quality. The results indicate a protective effect of silver in reducing contamination levels, but further experiments are needed to determine its effectiveness on different types of bacteria and water quality parameters.

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Effect of Silver Inserts on Recontamination in Ceramic Water Filters

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  1. Does activated silver prevent recontamination in reservoirs of ceramic water filters? 10.10.2016 • Regula Meierhofer • Pascal Rubli • Jared Oremo • Aloyce Odhiambo Eawag: Swiss Federal Institute of Aquatic Science and Technology

  2. Can activated Silver reduce recontamination risks? Goal Assess if the application of an insert made of elementary silver with a chemically etched surface reduces the risk of regrowth and recontamination in during the storage of treated drinking water in ceramic filters? Method WQ laboratorytestswith 3 configurations (Control, Silver in Reservoir, Silver in Reservoir & tap) WQ assement in fieldconditions in rural Kenya Influenceofwaterhandlingandhygiene in rural households in Kenya Material Silver wire with a chemically etched surface • oxidizes and transforms the ionic surface structure • regions with crystalline and amorphous silver compound are built up that are in contact with elementary silver wire • in contact with water low concentrations of silver ions are released

  3. Methodology laboratory experiments • Storage untilbacterialinactivationachieved • E.coli & total coliforms, every 12hmembranefiltration, 100ml samples • Intactbacteria, every 12hflowcytometry, 500l samples • Silverdiffusionover 13 daysstorageAbsorption spectroscopy (AAS), 10ml sample a b c

  4. Coliform inactivation in spiked tap water (pretest)

  5. Coliform inactivation in creek water C= Control (n=2), EC= E.coli, TC=Total coliforms SR=3cm Silversan in Bucket (n=3), SRT= 3cm Silversan in Bucket & 1.5cm Silversan in Tap (n=3) SRX=5cm Silversan in Bucket (n=1), SRTX= 5cm Silversan in Bucket & 3cm Silversan in Tap (n=1) Volume: 5L, Temp: 20°C

  6. Coliform inactivation in 1:5 creek/ tap water C= Control (n=2), EC= E.coli, TC= Total coliforms SR=5cm Silversan in Bucket (n=2), SRA= 8cm Silversan in Bucket (n=3) SRT= 5cm Silversan in Bucket & 3cm Silversan in Tap (n=3) Volume: 6L, Temp: 20°C

  7. Coliform inactivation in 1:1 creek/ tap water C= Control (n=2), EC= E.coli, TC=Total coliforms SR=5cm Silversan in Bucket (n=2), SRA= 8cm Silversan in Bucket (n=3) SRT= 5cm Silversan in Bucket & 3cm Silversan in Tap (n=3) Volume: 6L, Temp: 20°C

  8. Total intact bacteria in 1:1 creek/ tap water C= Control (n=2), SR=5cm Silversan in Bucket (n=2), SRA= 8cm Silversan in Bucket (n=3) SRT= 5cm Silversan in Bucket & 3cm Silversan in Tap (n=3) Volume: 6L, Temp: 20°C

  9. Silver diffusion over 13 days 1:1 creek/ tap water, mean Chloride concentration: 34.5 mg Cl/L Diffusion in H2O dest.: 403 µg/L after 13 days WHO standard for silver in drinking water: 100µg Ag/L

  10. Methodology field experiments a • Storage in ceramicfilters in laboratory • Configurationsa,b,c & CS filter • E.coli & total coliforms, every 12hmembranefiltration, 100ml samples • Householdsurvey • 3 groups @ 30 Households a) control, no silver b) 5cm silver in Reservoir, c) 5cm silver in Reservoir & 3 cm in tap • BL & 3 visits over 7 weeks • E.coli & total coliformsmembrane filtration, 100ml samples • Quantitative interviews on water handling and hygiene b c d

  11. Regrowth of coliforms in ceramic filters Laboratory in Kenya, creek water

  12. Water Quality in household ceramic filters ns t(107.8)=-5.6 p=0.000 ns Brown-Forsythe F(2)=1.5 p=0.024 ns

  13. Influence of water handling and hygiene on water quality Multifvariate regression to assess water handling & hygiene on LRV(Only factors included that were significant in bivariate analysis) - group membership (type of filter used) - the water source used the last time water was collected, - cleaning the inside of the ceramic pot with a brush, - cleaning of the ceramic pot outside with a utensil, - condition of the water storage container, - type of household’s toilet - number of washing hands with soap yesterday 1st model: LRV E.coli as outcome variable:- group membership (B=0.3, SE=0.095, =0.196**, p=0.002, R2=0.051) 2nd model: LRV total coliforms as outcome variable:- group membership (B=0.96, SE=0.098,  =0.5***, p=0.000)- cleaning pot inside with brush (B=0.39, SE=0.196,  =0.12*, p=0.046)

  14. Conclusions Experiments indicate a protective effect of elemtary silver with a chemically etched surface on water quality However, mean contamination levels of treated water in reservoirs of ceramic filters measured during the field trials were in WHO’s low risk category (1-10 E. coli/100ml) only for group 3 with activated silver in the tap and in the reservoirs The observed effect cannot be extended to all classes of bacteria Further experiments are required to determine the influence of different water quality parameters on the effectiveness of activated silver in reducing recontamination risks

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