The use of antibacterial activity of ZnO nanoparticles in the treatment of municipal wastewater Fatemeh Elmi, Heshmatollah Alinezhad, Zahra Moulana, Fatemeh Salehian, Sahar Mohseni Tavakkoli, Fariba Asgharpour, Horrieh Fallah and Maryam Mitra Elmi ABSTRACT Nanotechnology holds great potential in advanced water and wastewater treatment to improve treatment efficiency. Zinc oxide nanoparticles (ZnO NPs) have received considerable attention due to their unique antibacterial activities toward various microorganisms that are commonly found in the environment. In the present study, ZnO NPs were synthesized through both mechano-chemical and sol–gel methods. The synthesized ZnO NPs were characterized through X-ray diffraction and transmission electron microscopy techniques. Then, their antibacterial activities against separated wastewater bacteria were evaluated by determining the zone inhibitor, the minimum inhibitory concentration, and the minimum bactericidal concentration. The results were compared with those obtained from wastewater after chlorine disinfection and ultraviolet (UV) disinfection. These studies demonstrated that the antibacterial activity of ZnO NPs depends on the type and the strain of bacteria. They have also demonstrated that the activity increases as the concentration of ZnO NPs increases. Overall, the experimental results suggest that ZnO NPs can potentially be an antibacterial reagent to treat wastewater. They can particularly be applied as a complementary method with UV disinfection. Thus, they can be developed as antibacterial agents to improve wastewater quality. Fatemeh Elmi Heshmatollah Alinezhad Fatemeh Salehian Sahar Mohseni Tavakkoli Department of Chemistry, University of Mazandaran, PO Box: 47416–95447, Babolsar, Iran Zahra Moulana Infectious Diseases and Tropical Medicine Research Center, Babol University of Medical Sciences, Gang Afrooz Street, Babol, Iran Fariba Asgharpour Horrieh Fallah Paramedical Faculty, Babol University of Medical Sciences, Gang Afrooz Street, Babol, Iran Maryam Mitra Elmi (corresponding author) Cellular and Molecular Biology Research Center, Babol University of Medical Sciences, Gang Afrooz Street, Babol, Iran E-mail: m.elmi@mubabol.ac.ir Key words | antibacterial, chlorine, disinfection, UV, wastewater, ZnO nanoparticle INTRODUCTION The growth of population and human civilization forces the world’s scientists to look for efficient ways to treat water and wastewater. Some physical, chemical, and biological methods can be applied for the disinfection of water and wastewater. Since the late 1940s, chlorination has been con- sidered to have a major role in inactivating waterborne pathogens in many countries. However, many halogenated disinfection by-products (DBPs) have been characterized during chlorination (Zhang et al. a, b), which have been shown to be mutagenic, and can increase the risk of cancer (Monarca et al. ). Also, chlorine residuals are toxic to marine life (Ward & DeGraeve ). An effec- tive alternative to chlorination is the disinfection of water and wastewater through ultraviolet (UV) irradiation to inac- tivate a variety of microorganisms (Chang et al. ; Das ; Bergmann et al. ; Hijnen et al. ). However, the germicidal efficiency of UV irradiation strongly depends on the total suspended solids in effluent, which will reduce germicidal efficiency or UV effect (Chang et al. ), although low-pressure UV produces undesirable DBPs (Bergmann et al. ; Hijnen et al. ). Despite the fact that municipal wastewater contains a variety of pathogenic organisms of human origin, it is used for the irrigation of plants. Therefore, it is highly necessary to come up with an advanced method of disinfection to reuse the municipal wastewater in agriculture (Mujeriego & Asano ). To overcome the limitations of traditional disinfection methods, research has focused on developing alternative ones (Qu et al. ). Many nanomaterials, such as nano- Ag, nano-ZnO, nano-TiO 2 , and carbon nanotubes have the potential to be used in the disinfection of water and wastewater (Li et al. ; Vahabi et al. ; Baruah et al. ). They display antimicrobial properties without strong oxidation. Therefore, they have a lower tendency 763 © IWA Publishing 2014 Water Science & Technology | 70.5 | 2014 doi: 10.2166/wst.2014.232 Downloaded from https://iwaponline.com/wst/article-pdf/70/5/763/471352/763.pdf by guest on 03 November 2018