Effect of silver nanoparticles on nitrification by entrapped cells

Abstract

Effect of silver nanoparticles (AgNP) on nitrification by entrapped cells was investigated. The study consisted of the AgNP effect on nitrification performance and microorganism physiology. The influences of initial ammonia and AgNP concentrations on the nitrification performance by the entrapped cells were conducted using respirometric method. Two types (calcium alginate (CA) and polyvinyl alcohol (PVA)) and two sizes (small and large) of the entrapped cells were chosen. The test using the free cells was also performed for comparative purpose. For physiological effect, scanning electron microscopic (SEM) and transmission electron microscopic (TEM) observations of the microbial cells and matrices were performed. The result showed that the initial ammonia concentrations (28 and 70 mg-N/L) did not play the important role on the nitrification activity while the AgNP concentrations (0.05 to 5 mg/L) obviously affected on the nitrification (activities of 2 to 98 % compared to the control (no AgNPs). Both PVA- and CA- entrapped cells could lessen the problem but nitrification performance by the CA- entrapped cells (activities of 64-93%) was better than that of the PVA-entrapped cells (activities of 4 to 87 %). For both PVA- and CA- entrapped cells, large entrapped cells (activities of 44 to 93 %) performed better than small entrapped cells (activities of 4 to 89 %). The microscopic observation supported the respirometric result. Silver nanoparticles penetrated and damaged microbial cell membrane and cytoplasm resulting in decreased nitrification activity. The entrapment matrices could minimize the problem.