A Study on Antimicrobial Effects of Nanosilver for Drinking Water Disinfection by Xu Yang

Author:Xu Yang
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

2.4 Continuous Disinfection System with Silver Nanoparticles

Many efforts have been put in application of AgNPs in continuous flow-through system. Review of previous literature shows that AgNPs has been successfully incorporated in many materials or devices to serve as disinfectants, such as polymer foam (Jain and Pradeep 2005), ceramic materials (Oyanedel-Craver and Smith 2008; Lv et al. 2009), filter paper (Dankovich and Gray 2011) and membrane (Zodrow et al. 2009; De Gusseme et al. 2011). Detailed review is presented below.

Polyurethane (PU) foams were soaked in Ag@citrate NPs suspension for coating overnight by Jain and Pradeep (2005). After saturated coating, such AgNPs-contained PU foams were washed repeatedly to remove any adsorbed ions and then air-dried. With a flow rate of 0.5 L/min, 120 L of E. coli-contaminated tap water (105 CFU/mL) were passing through the PU foams and no E. coli colonies were found in further enumeration. Effective as this material may be, the authors failed to answer one key question: how much AgNPs were incorporated in PU foam after soaking and washing. Lack of quantification of AgNPs in PU foam may jeopardize the reproducibility of the entire experiment. And due to the same reason, it was impossible to discuss whether or not this material was economically beneficial.

With similar ‘soak-and-absorb’ method, Lv and coworkers synthesized AgNPs-contained ceramic composite (Lv et al. 2009). The highlight of this study was that modification of amino groups on the ceramic surface by using 3-aminopropyltriethoxysilane was conducted to ensure a better absorbance of AgNPs. Results indicated that such ceramic composite was also able to inactivate all the initial E. coli (105 CFU/mL for 500 mL) at a flow rate of 10 mL/min. This ‘soak-and-absorb’ strategy was easy to control but difficult to quantify the AgNPs usage. On top of this ‘soak-and-absorb’ strategy, Oyanedel-Craver and Smith (2008) provided another method to fix AgNPs onto ceramic filter: painting. Straightforward as it was, concentrate suspension of AgNPs was painted on the filter surface for economical usage of AgNPs. These two ways of fixing AgNPs on the surface did not make a significant difference in terms of disinfection performances. Over 6 log inactivation of E. coli were achieved for at least 90 min. Ionic silver release was monitored and the concentrations of all the samples were lower than 0.1 mg/L, which was in compliance with WHO and USEPA recommendations (WHO 2006).

Dankovich and Gray synthesized nanosilver in situ with the presence of filter paper in order to generate a bactericidal filter paper (Dankovich and Gray 2011). Water spiked with bacteria was vertically passing through such filter paper with simply gravity. It was noted that more than 7 log removal of E. coli and 3 log of Enterococci faecalis were achieved. The researchers also monitored the concentration of releasing Ag+ to make sure it was not higher than 0.1 mg/L. The combination of AgNPs and a paper sheet shed some light on the development of light, cheap, portable and point-of-use water purification device.

Besides antibacterial performance, antiviral effects of AgNPs-involved continuous system were also studied.

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