1. Does activated silver prevent recontamination in reservoirs of ceramic water filters?
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 laboratory tests with 3 configurations (Control, Silver in Reservoir, Silver in Reservoir & tap)
WQ assement in field conditions in rural Kenya
Influence of water handling and hygiene 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 until bacterial inactivation achieved
E.coli & total coliforms, every 12h membrane filtration, 100ml samples
Intact bacteria, every 12h flow cytometry, 500l samples
Silver diffusion over 13 days storage Absorption spectroscopy (AAS), 10ml sample a b c
Water Quality
C: control,no silver
SR:
Silver in Reservoir
SRT: Silver in
Reservoir & Tap
Reservoir
Tap
Experiment 1
(3 conf.)
6L Spiked Tap Water
0 (n=1)
5cm (n=1)
5cm
3cm (n=3)
Experiment 2
(5 conf.)
6L CB water
0 (n=2)
3cm
1.5cm (n=3)
3cm (n=1)
Experiment 3
(4 conf.)
1L CB water & 5L Tap water
5cm (n=2)
8cm (n=1)
Experiment 4
3L CB water & 3L Tap water

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 experimentsa
Storage in ceramic filters in laboratory
Configurations a,b,c & CS filter
E.coli & total coliforms, every 12h membrane filtration, 100ml samples
Household survey
3 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 coliforms membrane 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
Disinfection efficiency and regrowth during storage in ceramic filters in the laboratory included a batch with filters containing a colloidal silver coating. All configurations achieved at least 3 Log removal of E. coli, measured 4 hours after filling the filter and at least 1.8 Log removal of total coliforms. Filters with activated silver in the reservoir and the tap as well as filters with a coating of colloidal silver achieved 3.57 Log resp. 4.7 Log removal of total coliform. No regrowth of coliforms was observed in any of the filters with colloidal silver coating. Regrowth of E. coli as well as total coliforms was observed in all other configurations except for the setup with activated silver in the reservoir and in the tap, where E. coli did not grow, but the highest regrowth was observed for total coliforms.

12. Water Quality in household ceramic filtersns
t(107.8)=-5.6 p=0.000 ns
Brown-Forsythe F(2)=1.5 p=0.024 ns
This slide displays counts of E. coli and total coliforms in raw water and filtered water in ceramic filters used by 90 households living in a rural area near Kisumu, Kenya. The graph displays means of 3 household visits. Mean bacterial concentrations in groups between visits were statistically not different. Anova analysis revealed a statistically significant difference in the concentration of E. coli in filtered water between the three groups (C=control, filter without Silver, R= Silver in reservoir and RT= Silver in reservoir and tap) with Brown-Forsythe F(2)=1.449, p= Planned contrasts in Anova analysis revealed that the means counts of total coliforms in filtered water were significantly different between control group and the groups with activated silver in the filters: t(107.8)=-5.588, p= No statistically significant difference in counts of total coliforms in filtered water was found between group R and group RT. Anova analysis did not detected any statistically significant difference of mean counts of E. coli and total coliforms in raw water in the three groups.

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