Laboratory Investigation into the Effect of Silver Application on the Bacterial Removal Efficacy of Filter Material for Use on Locally Produced Ceramic Water Filters for Household Drinking Water Treatment

Abstract

Locally produced ceramic water filters (CWF) are an effective technology to treat pathogen-contaminated drinking water at the household level. CWF manufacturers apply silver to filters during production, although the silver type and concentration vary and evidence-based silver application guidelines have not been established. We evaluated the effects of three concentrations of two silver species on effluent silver concentration, E. coli removal, and viable bacteria retained on the surface and contained in the pores of ceramic disks manufactured with clay imported from three CWF factories using sawdust as the burn-out material. Additionally, we evaluated performance using water with three chemistry characteristics (Na+–NaCl, Ca2+–CaCl2, and humic acid as natural organic matter) of disks made from the different clays using either sawdust or rice husk as the burn-out material. Results showed the following: (1) Silver desorption from disks coated with silver nitrate (Ag+) was greater than desorption of silver nanoparticles (nAg) for all disks. (2) Effluent silver concentration, E. coli removal, and viable bacteria retention were dose-dependent on the amount of silver applied. (3) Nither water chemistry conditions (inorganic or organic compounds) nor burn-out material showed an effect on any of the parameters evaluated at the silver concentration tested. The recommendation for filter manufacturers to use only nAg and at a higher concentration than currently recommended is discussed.

Comment on “A re-assessment of the safety of silver in household water treatment: rapid systematic review of mammalian in vivo genotoxicity studies”

“…Ceramic water filters are locally manufactured in more than 50 countries worldwide [ 5 ], are considered one of the most promising household water treatment methods [ 6 ], and application of silver nanoparticles (nAg or AgNP) or silver nitrate (AgNO 3 ) has been shown to reduce biofilm formation within, and improve the microbiological efficacy of, ceramic water filters [ 7 ]. There are benefits and drawbacks to either form of silver applied to ceramic filters; silver nitrate can be purchase locally and is less expensive, while silver nanoparticles must be imported.…”

“…There are benefits and drawbacks to either form of silver applied to ceramic filters; silver nitrate can be purchase locally and is less expensive, while silver nanoparticles must be imported. However silver nitrate elutes more quickly, and silver concentrations in treated drinking water are more likely to exceed World Health Organization guidelines if applied at concentrations sufficient to improve disinfection performance [ 4 , 7 ]. Thus, silver nanoparticles are recommended for use in ceramic filter factories [ 5 ].…”

Microwave-assisted incorporation of silver nanoparticles in paper for point-of-use water purification

“…With other filter media, such as ceramic water filters, the relevance of understanding the interactions between dissolved substances in water sources and nanoparticle is gaining attention. 26 …”

Ceramic Water Filters: A Point-of-Use Water Treatment Technology to Remove Bacteria from Drinking Water in Longhai City, Fujian Province, China

“…In addition to filtration, the development of a biofilm on the surface of the CWF aids in the removal of pathogens. Silver nitrate and/or silver nanoparticles are also utilized as disinfectants in some cases (Oyanedel-Craver and Smith, 2008;Vinka, et al, 2008;Yakub and Soboyejo, 2012;Rayner et al, 2013). Hence, the combination of filtration, disinfection and biofilm development result in significant removal of microorganisms from source water during CWF operation.…”