Use of zero-valent iron nanoparticles in inactivating microbes Minghui Diao 1 , Maosheng Yao* State Key Joint Laboratory of Environmental Simulation and Pollution Control College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China article info Article history: Received 19 May 2009 Received in revised form 20 August 2009 Accepted 26 August 2009 Available online 8 September 2009 Keywords: Nanoscale zero-valent iron particles Bacteria Fungi Inactivation abstract Nanoscale zero-valent iron (NZVI) particles were investigated in inactivating gram-positive Bacillus subtilis var. niger and gram-negative Pseudomonas fluorescens bacteria, and the fungus Aspergillus versicolor. NZVI particles were synthesized using NaBH 4 and Fe(NO 3 ) 3 $9H 2 O, and the microbial suspensions were subjected to the treatments of NZVI particle suspensions with concentrations of 0.1, 1 and 10 mg/ml for 5 min. Field emission scanning electron microscope (FE-SEM) was used to characterize the synthesized NZVI particles, suspensions and the surface morphologies of the treated agents. FE-SEM images showed that the NZVI particles were spherical with a fairly uniform size of about 20–30 nm, and the iron precipitates FeO(OH) appeared in needle-shape aggregates. When treated directly with NZVI particles under aerobic condition, the surfaces of microbes were quickly coated with needle-shape yellow-brown iron oxides. In this study, complete inactivation was achieved both for B. subtilis var. niger and P. fluorescens when treated with 10 mg/ml NZVI particles with vigorous shaking under aerobic condition. When NZVI particle concentration decreased to 1, 0.1 mg/ml, there was still a complete inacti- vation for P. fluorescens, while for B. subtilis var. niger the inactivation decreased to 95%, 80%, respectively. However, no inactivation was observed for the fungus A. versicolor when treated the same manner. Physical coating, disruption of membrane and generation of reactive oxygen species have played major roles in the inactivation observed. ª 2009 Elsevier Ltd. All rights reserved. 1. Introduction Inadequate access to safe and clean water is highlighted as one of the most pervasive problems afflicting people throughout the world (Shannon et al., 2008). Montgomery and Elimelech (2007) have indicated that millions of people die annually, e.g., 3900 children a day, from diseases transmitted through contaminated water or human excreta. Among the pollutants, those water-borne bacteria, fungi and viruses pose a great threat (World Health Organization, 2003, Geneva). In addition, during waste water treatment, the generated biosolids contain a variety of microorganisms (Li et al., 2007; Paez-Rubio et al., 2007) including disease causing pathogens such as bacteria (Salmonella sp., Vibrio cholerae), protozoa (Giardia lamblia), and viruses (Hepatitis and Norwalk) (Li et al., 2007). When these biosolids are disposed on land, those microbial species can be aerosolized and transported over great distances, thus presenting serious health problems (Paez-Rubio et al., 2007). Therefore, there is a great need for the biological pre-treatment for the drinking or waste water, which helps minimize the associated biological health hazards. Over the past years, numerous studies have been under- taken to investigate methods and techniques in removing and * Corresponding author. Tel.: þ86 10 6276 7282. E-mail address: Yao@PKU.edu.cn (M. Yao). 1 M. Diao is now in the Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA. Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres 0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2009.08.051 water research 43 (2009) 5243–5251