Green synthesis of zinc oxide nanoparticles for inactivation of antibiotic-resistant bacteria in real prawn farm wastewater

Antibiotic-resistant bacteria are widespread in prawn farm wastewater, contaminating water resources and threatening human health. This paper describes the synthesis of zinc oxide nanoparticles through a green technique using Nymphaea leaf extract to inactivate antibiotic-resistant bacteria in the prawn farm wastewater. NLE has not been previously reported for the synthesis of zinc oxide nanoparticles. The Nymphaea leaf extract and zinc oxide nanoparticles were characterized, and the optimization of the effect of parameters of zinc oxide nanoparticles loading (0.01–0.1 g/L), pH (7–9), and reaction time (30–60 min) on the inactivation of antibiotic-resistant bacteria of gram-negative Escherichia coli and gram-positive Bacillus cereus was determined using central composite design of response surface methodology. Nymphaea leaf extract contains terpenoids, flavonoids, tannins, phenols, and glycosides. Zinc oxide nanoparticles were spherical, evenly distributed, less agglomerated with small particles (31.2–80.5 nm), and nearly homogeneous grain size distribution on the surface. It has a hexagonal wurtzite crystalline structure with a crystallite size of 42.6 nm. The p-value of < 0.05 displayed the best fitting of the data to the quadratic model with a 95% confidence level. The best inactivation of 99.18% and 97.39% for Escherichia coli and Bacillus cereus in prawn farm wastewater was obtained at optimum zinc oxide loading of 0.1 g/L, pH 7, and 30 min of reaction time. Escherichia coli and Bacillus cereus were inactivated by damaging the bacterial cell wall. The green zinc oxide nanoparticles efficiently inactivated Escherichia coli and Bacillus cereus growth in prawn farm wastewater. Zinc oxide nanoparticles can be used to inactivate other bacteria in other types of wastewaters.