Silver Nanoparticles as Inhibition Agents of Cooling Tower Microorganisms

Abstract

Silver nanoparticles are widely studied and the antibacterial activity is well-known. Although several methods of synthesis have been described, this article reports the simplest procedure using low cost reagents and a low consumption of energy, where silver nitrate is reduced by nitrate ions in an aqueous solution from pH 10.60 to 11.02. A relatively controlled dispersion of sizes was achieved and particles presented sizes between 49 and 76 nm dependent on the pH. Solutions of these particles were used to incubate a mixture of Pseudomona spp. ATCC and Pseudomona spp. recovered from a water well. All the particles were affective against inhibition of these bacteria after 3 hours of incubation. Specifically, 49 nm particles reached suitable efficiency after 120 minutes even if they were diluted 50 or 10%, whereas particles with 65 nm demonstrated  having an efficient inhibitory effect on Pseudomona spp. at 10 or 100% of concentration after 140 minutes of incubation. Results obtained with both sizes proved that the contact time (140 minutes) to reduce the colony forming units (CFU) per milliliter (x105) to values lower than 1 is an adequate time for applications in water treatments of cooling towers. Additionally, the procedure here followed with low cost and low energy, facilitates the design of advanced antimicrobial treatments for cooling towers at industrial levels.