The Influence of Nanoparticle–Cell Ratios on the Disinfection of Escherichia Coli by Silver and Zinc Oxide in Low Concentrations

Silver nanoparticles (AgNPs) embedded within ceramic water filters have gained popularity as a methodology for improved disinfection over filtration alone, though concerns exist regarding their cost, health, and ecological impacts. Research into the replacement and/or supplementation of AgNPs with less expensive NP alternatives is therefore of interest. The influence of NP and microbial contaminant concentrations on disinfection performance, however, require further exploration and elucidation. This research thus investigates the potential synergistic disinfection of AgNP and zinc oxide (ZnO) at various co-application concentrations when challenged by three levels of Escherichia Coli contamination. In this study, 1 L of water with dissolved organics, micronutrients, and E. Coli in concentrations of 102, 103, or 105 CFU/mL was treated with AgNPs and/or ZnO. AgNPs concentrations ranged from 0.5 to 20 ppb, and ZnO concentrations ranged from 50 to 1000 ppb under dark conditions. E. coli samples were enumerated over a 72-h period. The results demonstrate that both NP and bacterial concentration significantly influenced outcomes. For example, 10 ppb AgNP alone did not achieve any disinfection under any bacterial loading over 72 h. However, log removal values (LRVs) of − 0.86, − 1.06, and + 0.01 were measured in water with 102, 103, and 105 CFU/mL, respectively, when combined with 75 ppb ZnO and − 2.62, − 2.17, and − 3.06 when combined with 1000 ppb ZnO, respectively; a negative LRV indicates bacterial inhibition, while a positive LRV indicates bacterial growth. This study therefore illustrates that co-application of AgNP-ZnO holds potential for implementation in the design of low-cost water treatment solutions that utilize nanoparticles for disinfection if influent bacterial concentrations are managed appropriately.