Potential susceptibility inhibitory effect of Ag and ZnO engineered nanoparticles on bacterial strains: effect of pH and temperature

Abstract

The economic and social benefits of metallic silver (n-Ag) and zinc oxide (n-ZnO) engineered nanoparticles (ENPs) applications in medical, technological, environmental remediation, consumer products, among other have widely been demonstrated. Conversely, concerns have been owing to these ENMs widely unknown environmental and public health effects. Until now, ENMs have been traced into the wastewater treatment plants (WWTPs); however, their impacts to the treatment systems are yet to be fully elucidated. The WWTPs main goal is to reduce the pollution level of urban and industrial wastewaters, prior to discharge into the environment. One way of achieving this objective is by exploiting diverse microbial ecology such as bacteria, fungi and protozoa – which are essential in secondary wastewater treatment processes. However, the benefits of biological treatment processes can be reversed or dramatically diminished when ENMs are introduced into WWTPs. This because certain ENMs can adversely affect the performance of wastewater treatment processes by various mechanisms, for example, inhibition of microorganisms in the secondary treatment process due to their antibacterial properties. Our study investigated the potential impacts of n-Ag and n-ZnO ENPs (i) to microbial populations, (ii) to the resistance limits of wastewater bacteria after exposure, and (iii) to the nutrient removal efficacy from the effluent. Using the disc diffusion techniques, the wells were impregnated with n-Ag and n-ZnO at concentrations varying between 1 and 100 mg/L and incubated for 24-h to ascertain the growth inhibition of selected wastewater bacterial strains (Bacillus licheniformis, Brevibacillus laterosporus, Pseudomonas putida). Our findings on bacterial growth rates, lethal limits, and tolerance limits were found to be dependent on abiotic factors such as temperature and pH changes.