Silver and zinc oxide nanoparticle disinfection in water treatment applications: synergy and water quality influences

Abstract

The synergistic potential of silver and zinc oxide nanoparticles for water disinfection was investigated herein. By causing cell death through membrane interactions, oxidative killing, and DNA deactivation, metallic nanoparticles may be integrated with point-of-use water treatment systems for applications in rural and remote geographies. Disinfection efficacy was evaluated in batch-phase experiments under both synthetic and real water conditions, where synthetic water was varied by pH and dissolved oxygen levels. Ceramic pot filters with comparative nanoparticle concentrations were also investigated. In all cases, combinations of silver and zinc nanoparticles resulted in improved disinfection in comparison to either metal in isolation. In batch experiments, dissolved oxygen proved to be particularly impactful, with kinetic rates reducing approximately 45% when in low oxygen environment (<3 mg/L) versus high oxygen (>8 mg/L). Log removal values (LRVs) were further, on average, 31% lower in real water than synthetic water after 300 min, though silver–zinc combinations were still superior to either metal alone. In filters, those impregnated with 67% silver and 33% zinc achieved average LRVs of 2.7 and 2.9 after 60 min of filtration and 24 h of storage, respectively, while those with only silver achieved average LRVs of 2.0 and 3.1 at those same times.

Impact of Low-Levels of Silver, Zinc and Copper Nanoparticles on Bacterial Removal and Potential Synergy for Point-of-Use Water Treatment Solutions

“…Moreover, silver's high cost (1.66 USD/g Ag NPs) increases the total cost of the filter, reducing its affordability, and encouraging the study of alternative disinfectants to be used instead of silver or in combination with silver (Yang et al, 2020;Argenol Laboratories, 2022). In the recent years, copper and zinc nanoparticles and ions have been studied as alternatives for Ag NPs in ceramic water filters (Ehdaie et al, 2020;Venis & Basu, 2021;. These metals are less expensive than silver and have a higher threshold for safe release into drinking water of 1 mg/L for copper, and 5 mg/L for Zinc (USEPA, 2022a).…”

“…For example, the longest studied sampling point was up to 24 hours for the Ag-Zn combination, and the Ag-Cu combination while to-date the Zn-Cu combination has not been studied in the water field (Al-Issai et al, 2019;Sicairos-Ruelas et al, 2019;Ehdaie et al, 2020;Soliman et al, 2020;Venis, & Basu, 2021;Zazouli et al, 2021). Such studies, though valuable, do not well inform on the role of these combinations as disinfectants over potential storage periods.…”

Towards an Improved Ceramic Water Filter Paradigm: From Design Optimization to Participatory Implementation

“…The same concentrations of Ag + and Zn 2+ alone achieved LRVs of 1.0 and -0.5 (i.e., growth), respectively. Similarly,Venis and Basu (2021) showed clear Ag-Zn synergy when a combined 1 mg/L of AgNPs with ZnO achieved superior disinfection over 5 hours of mixing than either MNP at the same concentration in isolation. Silver supplementation with ZnO is thus a particularly encouraging approach to potentially reducing required Ag concentrations for CWF impregnation.…”

“…filter disks (CWFDISKS) and one ceramic water filter pot(CWFPOT) were evaluated in this research, which were manufactured at the Wine to Water East Africa facility in Arusha, Tanzania in 2019 and 2015, respectively. Please see(Venis and Basu 2021) for a detailed description of the production process.…”

“…MNP that has garnered recent interest is Zinc Oxide (ZnO), which is available at a significantly lower cost than silver and has demonstrated efficacy as a treatment to diarrheal illness(Venis and Basu 2021, Sigma-Aldrich 2022, Malik, et al 2013. For instance,Huang et al (2018) found that ceramic disk filters painted with ZnO solutions of 8 and 41 mg/L achieved LRVs of 1.4 and 1.5, respectively, showing no significant effect immediately after filtration.…”