Separation of zinc oxide nanoparticles in water stream by membrane filtration Neha Mehta, Subhankar Basu and Arun Kumar ABSTRACT Zinc oxide (ZnO) nanoparticles are used for the synthesis of various materials. The nanoparticles, when entering into the environment, affect aquatic life. Their antibacterial properties deter the biological treatment process of wastewater treatment plants. The study focuses on the effectiveness of ultrafiltration (UF) membranes for the removal of ZnO nanoparticles. In this study, a commercial membrane was used for the separation of ZnO nanoparticles in the presence of natural organic matter (NOM) and alkalinity. Membrane flux and retention were studied for different concentrations of ZnO (1 mg/L, 10 mg/L, and 100 mg/L). Bare and fouled membranes were studied using a scanning electron microscope (SEM), energy-dispersive X-ray (EDX), and atomic force microscopy (AFM). At higher concentrations (>10 mg/L), ZnO nanoparticles tend to aggregate and increase in size, resulting in 95 to 98% retention. Further, the presence of NOM and alkalinity enhances particle–particle interactions and thereby promotes nanoparticle aggregation, which shows better retention even at lower concentrations (1–10 mg/L). Neha Mehta Arun Kumar Department of Civil Engineering, Indian Institute of Technology Delhi (IITD), New Delhi 110 016, India Subhankar Basu (corresponding author) The Energy and Resources Institute (TERI), Darbari Seth Block, IHC Complex, Lodhi Road, New Delhi 110003, India E-mail: sbasu@teri.res.in Key words | alkalinity, natural organic matter, retention, ultrafiltration, zinc oxide INTRODUCTION Nanoparticles are used in the preparation of a variety of materials due to their extraordinarily large reaction surface, e.g., cosmetics, paints, medicines and drugs, drug delivery sys- tems, super hydrophobic and super hydrophilic surfaces, water treatment applications, electronics, optics, textiles, etc. However, the impact of nanomaterials on living beings is still in the early stage of research. Separate work on the tox- icity of these materials on individual species indicates that continuous use of these materials and their discharge into the environment will eventually affect the living population (Angelica et al. ; Bolis et al. ; Grimaldi et al. ). Zinc oxide (ZnO) is one of the toxic nanoparticles tested among silver (Ag), fullerenes and nano copper oxide (nano- CuO), and carbon nanotubes (CNTs), titanium dioxide (TiO 2 ), and iron oxide (Fe 3 O 4 )(Kahru & Dobourgier ). ZnO is used for the synthesis of nanocombs, nanorings, nanohelixes, nanosprings, nanobelts, nanowires, nanocages, nanosensors, nanocantilevers, sunscreens, cosmetics, coating applications in optoelectronics, sensors, transducers, and bio- medical sciences (Wang ; Dange et al. ). Studies on ZnO nanoparticles in an aquatic environment show that ZnO released into water bodies affects aquatic life, especially if it is in Zn þ2 ions (Bian et al. ). It reduces the efficiency of the phy- sico-chemical treatment process of coagulation–flocculation in water treatment by providing stability to pollutants (Brar et al. ; Omar et al. ). It has antibacterial properties (Huang et al. ; Li et al. ) which affect the biological treatment process (Brar et al. ). Many adverse effects of nanosized ZnO on mammals, plants, phytoplankton, and even human cell lines have been reported (Xia et al. ; Lin & Xing ). The fate of nanomaterials in natural systems depends on water quality parameters such as pH, ionic strength, and natural organic matter (NOM). As NOM occurs in surface water as complex organic matter at concentrations ranging from 1 mg/L to 100 mg/L (Wall & Choppin ), it is important to consider its effect in understanding the fate 148 © IWA Publishing 2016 Journal of Water Reuse and Desalination | 06.1 | 2016 doi: 10.2166/wrd.2015.069 Downloaded from https://iwaponline.com/jwrd/article-pdf/6/1/148/377243/jwrd0060148.pdf by guest on 02 December 2018