Kinetics and Equilibrium Biosorption of Nano-ZnO Particles on Periphytic Biofilm under Different Environmental Conditions

Abstract

As engineered nanoparticles (ENPs) were widely used in industry and commerce, increasing amounts of ENPs are expected to enter aquatic environment where their fate and potential impacts are unknown. Understanding the interaction between ENPs and periphytic biofilm, ubiquitous in the natural water environment, will help to better predict the behavior and fate of ENPs in aquatic media. This study focuses on ZnO NPs biosorption mechanism by periphytic biofilm dominated by bacteria and diatoms. Batch experiments were performed, in which the effect of pH, natural organic matter (NOM), extracellular polymeric substances (EPS) and temperature on the biosorption were investigated. The biosorption of ZnO NPs were found to be pH dependent, and more biosorption was observed under neutral and acidic conditions. Increasing concentration of NOM negatively affected on the biosorption of ZnO NPs onto periphytic biofilm due to the adsorption of NOM molecules on the surface of nanoparticles and the resulting steric stabilization of the particles suspension. The removal of loosely bound EPS enhanced the biosorption capacity of periphytic biofilm. The biosorption of nano-ZnO on the biofilm was related to electrostatic force of attraction, confirmed from the zeta potential study. The biosorption of ZnO NPs on biofilm was correlated better with Langmuir isotherms as compared to Freundlich isotherms under the concentration range studied. The biosorption process was thermodynamically feasible and spontaneous. The present study shows that periphytic biofilm can be employed for an environmentally benign and effective biosorbent for removal of ZnO NPs.

Keywords: engineered nanoparticles, biosorption, natural biofilm, NOM, EPS