NANO SILVER URBAN WATER TREATMENT
The effectiveness of silver ions (silver ions) (generated from silver salts [silver nitrate, silver chloride (AgCl)] or produced by electrolysis) was tested against a variety of bacteria; Inactivation was mainly assessed by a log10 reduction in bacterial counts. Initial bacterial concentrations ranged from 3.5 cells/mL to 1.5 x 107 cells/mL. Single studies have examined the effects of silver nitrate on phages (De Gusseme et al., 2010) and Cryptosporidium cysts (Abebe et al., 2015).
Hwang et al. (2007) examined the efficacy of silver ions (up to 100 µg/L), derived from silver nitrate, against Legionella pneumophila, Pseudomonas aeruginosa and Escherichia coli (all at 1.5 x 107 cells). cells/mL) in synthetic drinking water (pH). 7, temperature 25 ᵒC – chemical composition determined in Hwang et al., 2006). After a three-hour exposure to the highest concentration of silver, the following log10 reductions were reported:
- Reduce 2,4 log10 – L. pneumophila;
- Reduce 4 log10 – P. aeruginosa;
- Reduce 7 log10 – E. coli
Similar work was done by Huang et al. (2008), in which the effectiveness of silver ions, derived from silver chloride, against 3 × 106 colony-forming units (cfu)/mL of P. aeruginosa, Stenotrophomonas maltophilia and Acinetobacter baumannii was investigated. . P. aeruginosa was found to be reduced by 5 log10 with 80 µg/L Ag (the highest concentration used) after 12 h. S. maltophilia was more sensitive to Ag, with a decrease of 5 log10 after 6 h of exposure to 80 µg/L. However, for A. baumannii, a 5 log10 reduction was seen only after 72 h of exposure to 80 µg/L Ag.
Silvestry-Rodriguez et al. (2007) investigated the inactivation of P. aeruginosa and Aeromonas hydrophila with silver in tap water, to evaluate the possibility of using silver as a secondary disinfectant to replace or reduce chlorine levels. Dechlorinated municipal water (taken from groundwater) was inoculated with 106 cfu/mL bacteria and silver nitrate was added at a concentration of 100 µg/L (0.1 ppm). Experiments were performed at pH 7 and pH 9 at 24 ᵒC for both bacterial species and at 4 ᵒC for P. aeruginosa. In addition, 3 mg/L of humic acid was added to dechlorinated tap water (to simulate surface water). Inactivation of bacteria depends on time and temperature; after 8 to 9 h of exposure to 100 µg/L silver at 24 ᵒC, both bacteria were reduced by more than 6 log10 (at 4 ᵒC, P. aeruginosa decreased by 4.5 log10 after only 24 h). Silver was found to be nearly as effective in reducing bacteria in the presence of humic acid (5.5 log10 reduction for P. aeruginosa at pH 7.24 ᵒC after 8 h in the presence of 3 mg/L humic acid) . This group also considered the possibility of silver exposure (100 µg/L) to reduce biofilm formation in drinking water distribution systems (Silvestry-Rodriguez et al., 2008). In this role, silver was found to be ineffective and there was no difference between the treatment of silver and the control
NANO SILVER HOSPITAL WATER TREATMENT
Silver ionization is commonly used to control Legionella in hot water distribution systems, especially in hospital environments. The studies covered in this subsection are often related to the systems in use and therefore tend to evaluate samples for the presence/absence of the organism of interest, rather than using tests quantitative test to determine log10 reduction. It is generally assumed that ion levels should be regularly monitored and maintained at regulatory concentrations (USEPA, 2015; WHO, 2007); Published studies suggest that levels between 0.01 and 0.08 mg/L of silver are required to maximize efficacy (Cachafeiro et al., 2007; Lin et al., 2011). Save et al. (1998) examined the intermittent use of a single silver ionization system in the hot water systems of two buildings. Twenty remote sites in each building were tested for Legionella before ionization began and then monthly after installation. Elimination of Legionella takes 4 to 12 weeks. After discontinuation of sterilization (16 weeks), no colony regeneration occurs for 6 to 12 weeks (depending on the sampling site) in the first building and 8 to 12 weeks in the second building . The control (non-ionized) building remained positive for Legionella throughout the study period.
In 2003, Stout & Yu (2003) reported on a survey of the first 16 hospitals in the US to install silver ionization systems to control Legionella. Prior to installation, all hospitals reported hospital-acquired Legionnaires’ cases and 75% had tried other sterilization methods. Two postal surveys (1995 and 2000) collected information on environmental monitoring of
Legionella, identification of hospital-acquired legionellosis, monitoring and maintenance of the silver ionization system. Legionella surveillance was conducted in 15 of 16 hospitals at both time points, although the frequency of surveillance was markedly lower in the second survey (9/16 hospitals reported monthly or quarterly surveillance). in 1995, compared with only 4/16 hospitals reporting quarterly surveillance in 2000). Routine monitoring (unspecified) of silver levels was reported by 15/16 hospitals in 1995; no information was presented for the 2000 survey. Infiltration of water sites distant from Legionella occurred less frequently after the installation of silver ionizers (between 7 and 8 hospitals reported levels). positivity of surveillance sites was 0 and the rest of the hospitals reported positivity of 30% or less). A single case (immediately after installation) of hospital-acquired Legionnaires’ disease was reported from the surveyed hospitals following silver ionization.
THE POTENTIAL OF NANO SILVER FOR HOUSEHOLD DRINKING WATER TREATMENT
The potential of nano silver to disinfect household POU drinking water is currently being explored extensively, mainly in conjunction with filtration. The media or substrates used for nanoparticles vary widely and include coatings on polyurethane foam (Jain & Pradeep, 2005), glass fibers (Nangmenyi et al., 2009), copolymer beads (Gangadharan et al., 2009). , 2010), paper (Dankovich & Gray, 2011), polystyrene beads (Mthombeni et al., 2012), alginate composite beads (Lin et al., 2013), ceramics (Lv et al., 2009), titiania (Lv et al., 2009), Liu et al., 2012), synthetic activated carbon combining magnetite (Valušová et al., 2012) and a bacterial carrier (De Gusseme et al., 2010; 2011). Since the focus here is on silver’s effectiveness in disinfecting water, only studies that can distinguish this from filtration efficiency, for example, are reviewed below. In addition to considering the LRV of microorganisms exposed to the test material, some studies have also conducted to determine the zone of inhibition.
Jain & Pradeep (2005) coated polyurethane foam with trisodium citrate stabilized silver nanoparticles. The antibacterial efficacy was assessed by adding nanosilver treated or untreated microfoams to the E. coli suspension (105–106 cfu/mL) and assessing the bacterial growth after the subsequent time. contact for 5 or 10 minutes. No bacterial growth was observed in the samples exposed to the nano silver treated polyurethane, while the untreated polyurethane samples showed “significant growth”. In addition, no growth of E. coli bacteria was detected on the agar plates below the nano silver – treated foam pads in the inhibition test region. A prototype filter was created using the treated foam, which was found to be effective in eliminating the growth of E. coli bacteria, but no comparable data were available for unfiltered foam. processing, making it difficult to determine the contribution of silver processing.
The main authors of this publication are:
- Lorna Fewtrell, Aberystwyth University, UK
- Ruth Bevan, IEH Consulting, UK
Several individuals have contributed to the development of this document by participating in meetings, peer review and/or providing insights and writing. Including:———-
- Mari Asami, National Institute of Public Health, Japan
- Sophie Boisson, WHO, Switzerland
- Julie Bourdon-Lacombe, Health Canada, Canada
- Joe Brown, Consultant, Georgia Institute of Technology, United States of America (USA)
- Enrique Calderon, Agua y Saneamientos Argentinos, Argentina
- Philip Callan, Consulting, Australia
- Joesph Cotruvo, Joseph Cotruvo and Associates LLC, USA
- David Cunliffe, Department of Health South Australia, Australia
- Lesley D’Anglada, United States Environmental Protection Agency (USEPA), USA
- Ana Maria de Roda Husman, National Institute of Public Health and Environment (RIVM), Netherlands
- Alexander Eckhardt, Umweltbundesamt (Federal Environment Agency), Germany
- John Fawell, Visiting Professor, Cranfield University, UK
- Charles Gerba, University of Arizona, USA
- Michèle Giddings, Health Canada, Canada
- Akihiko Hirose, National Institute of Health Sciences, Japan
- Paul Hunter, University of East Anglia, UK
- Daniel Lantagne, Tufts University, USA
- France Lemieux, Health Canada, Canada
- Batsirai Majuru, WHO, Switzerland
- Yoshihiko Matsui, Hokkaido University, Japan
- Peter Marsden, Drinking Water Inspector, UK
- Rory Moses McKeown, WHO, Switzerland
- Gertjan Medema, KWR Water Cycle Research Institute and Delft University of Technology, Netherlands
- Bette Meek, University of Ottawa, Canada
- Maggie Montgomery, WHO, Switzerland
- Choon Nam Ong, National University of Singapore, Singapore
- Santhini Ramasamy, USEPA, USA
- William Robertson, Watermicrobe Consulting, Canada
- Steve Schira, Liquitech, USA
- Shane Snyder, University of Arizona, USA
- Mark Sobsey, University of North Carolina at Chapel Hill, USA
- David Swiderski, Aquor/Global Water Council, USA
- Anca-Maria Tugulea, Health Canada, Canada
- Gordon Yasvinski, Health Canada, Canada
Reference source: Silver as a drinking-water disinfectant
