Removal of Nano-Zinc Oxide (nZnO) from Simulated Waters by C/F/S—Focusing on the Role of Synthetic Coating, Organic Ligand, and Solution Chemistry

Increased usage of nano-zinc oxide (nZnO) in different commercial fields has raised serious concerns regarding their discharge into the water streams containing natural and synthetic coating agents. Moreover, utilization of ground and surface water for drinking purposes is a common approach in many countries. Therefore, the removal of nZnO particles from water is essential to minimize the risk to the environment. The present research investigated the removal of nZnO from complex water matrices by conventional coagulation-flocculation-sedimentation (C/F/S) process using polyaluminum chloride (PACl) as coagulants. The result showed that removal of uncoated nZnO through sedimentation was efficient in waters containing divalent cations in the absence of dissolved organic matter (DOM). For the water containing higher salt concentration, PACl coagulant showed better removal performance with increasing coagulant dosage; however, synthetic organic coating agent and DOM significantly decreased the removal up to 75%. The surface potential of studied waters indicated that the addition of PACl affects the charge potential of nZnO particles resulting in charge neutralization. The result of the particle size analyzer revealed the presence of smaller particles with size of 430 nm even after C/F/S process, which may increase the possibility of particles release into aquatic environment. The results of the present study may help in understating the removal behavior of other coated nanoparticles during conventional water treatment.