Inactivation of bacteria from contaminated streams in Limpopo, South Africa by silver- or copper-nanoparticle paper filters

Abstract

There is an urgent need for inexpensive point-of-use methods to purify drinking water in developing countries to reduce the incidence of illnesses caused by waterborne pathogens. Previously, our work showed the deactivation of laboratory-cultured bacteria by percolation through a thick paper sheet containing either silver (Ag) or copper (Cu) nanoparticles (NP). In this study, these paper filters containing AgNPs or CuNPs have been tested with water sourced from contaminated streams in Limpopo, South Africa. Following the percolation of the contaminated stream water through the metal nanoparticle (MNP) papers, the water quality of the filtered effluent was evaluated with respect to the colony counts of total coliform and E. coli bacteria, turbidity, and either silver or copper ions. Influent total coliform bacteria concentrations from the stream water in Limpopo ranged from 250 CFU/100 mL to 1,750,000 CFU/100 mL. With the less contaminated stream water (250 - 15,000 CFU/100 mL), both AgNP and CuNP papers showed complete inactivation of the coliform bacteria. With the surface water with higher coliform bacteria levels (500,000 - 1,000,000 CFU/100 mL), both the AgNP and CuNP papers showed similar results with a slightly higher bacteria reduction of log10 5.1 for the AgNP papers than the log10 4.8 reduction for the CuNP papers. E. coli results followed similar trends. For most water purification experiments, the metal release from the sheets was minimal, with values under 0.1 ppm for Ag and 1.0 ppm for Cu (the current US EPA and WHO drinking water limits for Ag and Cu, respectively). These results show good potential for the use of paper embedded with silver and/or copper nanoparticles as effective point-of-use water purifiers.

Incorporation of copper nanoparticles into paper for point-of-use water purification

“…membrane filtration, which separates the effluent water from the bacteria cells immediately following filtration through the CuNP paper. This work also showed strong antibacterial activity of the CuNP papers, which supports the idea that bacterial inactivation is due to the direct contact with CuNPs during filtration through the CuNP paper (Dankovich et al, 2014). Other researchers have examined the specific mechanism of copper inactivation of bacteria and suggest that the copper ions cause irreversible damage to bacterial membranes by increasing membrane permeability and destabilizing the cells (Esperito Santo et al, 2011).…”

“…However, from other studies, it appears copper ions can rapidly inactivate bacteria from a few minutes (Esperito Santo et al, 2011; Molteni et al, 2010; Jia et al, 2012) to several hours (Varkey and Dlamini, 2012), depending upon the environmental conditions. In this particular study, we cannot conclude whether dissolved copper or copper absorbed by the bacterial cells contributes to bacterial inactivation, but in subsequent work, which is published elsewhere (Dankovich et al, 2014), we used another method to test for bacterial viability, i.e. membrane filtration, which separates the effluent water from the bacteria cells immediately following filtration through the CuNP paper.…”

“…Potential uses include disaster relief and emergency response, backpacking filters, and rural household filters for developing countries. In our subsequent work, we have evaluated longer term use for this filter papers, which shows the potential for repeat usage with natural water sources (Dankovich et al, 2014). Future work will clarify the extent to how much water a single paper filter can purify.…”

“…Paper and cotton fabrics are very abundant and regularly used in water filtration. Recently, for POU applications, we have designed a paper sheet embedded with silver nanoparticles to purify drinking water contaminated with bacteria (Dankovich and Gray, 2011a; Dankovich, 2014). As a more affordable alternative to silver, researchers have turned to using copper to purify drinking water (Sudha et al, 2012; Stout and Yu, 2003; Varkey and Dlamini, 2012).…”

Zeolite Cotton in Tube: A Simple Robust Household Water Treatment Filter for Heavy Metal Removal

“…Anti-bacterial test. Silver has been well known as an anti-bacterial agent for centuries 46 . After exchanged into the zeolite framework, silver-zeolite also possessed disinfection function.…”