Contents lists available at ScienceDirect Food and Chemical Toxicology journal homepage: www.elsevier.com/locate/foodchemtox A comparative study of the disinfection efficacy of H 2 O 2 /ferrate and UV/ H 2 O 2 /ferrate processes on inactivation of Bacillus subtilis spores by response surface methodology for modeling and optimization Atiyeh Rajabi Matin a , Samira Yousefzadeh b,a , Ehsan Ahmadi c,d , Amirhossein Mahvi a , Mahmood Alimohammadi a , Hassan Aslani e,f , Ramin Nabizadeh a,g,* a Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran b Department of Environmental Health Engineering, Aradan School of Public Health and Paramedical, Semnan University of Medical Sciences, Semnan, Iran c Department of Environmental Health, School of Health, Kashan University of Medical Sciences, Kashan, Iran d Students' Scientific Research Center (SSRC), Tehran University of Medical Sciences, Tehran, Iran e Health and Environment Research Center, Tabriz University of Medical Sciences, Tabriz, Iran f Department of Environmental Health Engineering, School of Public Health, Tabriz University of Medical Sciences, Tabriz, Iran g Center for Air Pollution Research (CAPR), Institute of Environmental Research (IER), Tehran University of Medical Sciences, Tehran, Iran ARTICLE INFO Keywords: Disinfection Bacillus subtilis spores UV radiation/ H2O2 /ferrate Response surface methodology (RSM) Central composite design (CCD) ABSTRACT Although chlorination can inactivate most of the microorganisms in water but protozoan parasites like C. parvum oocysts and Giardia cysts can resist against it. Therefore, many researches have been conducted to find a novel method for water disinfection. Present study evaluated the synergistic effect of H2O2 and ferrate followed by UV radiation to inactivate Bacillus subtilis spores as surrogate microorganisms. Response surface metho- dology(RSM) was employed for the optimization for UV/H2O2/ferrate and H2O2/ferrate processes. By using central composite design(CCD), the effect of three main parameters including time, hydrogen peroxide, and ferrate concentrations was examined on process performance. The results showed that the combination of UV, H2O2 and ferrate was the most effective disinfection process in compare with when H2O2 and ferrate were used. This study indicated that by UV/H2O2/ferrate, about 5.2 log reductions of B. subtilis spores was inactivated at 9299 mg/l of H2O2 and 0.4 mg/l of ferrate concentrations after 57 min of contact time which was the optimum condition, but H2O2/ferrate can inactivate B. subtilis spores about 4.7 logs compare to the other process. Therefore, the results of this research demonstrated that UV/H2O2 /ferrate process is a promising process for spore inactivation and water disinfection. 1. Introduction Giardiasis is a global disease and Giardia lamblia cyst can survive for a long time even at low temperature in water. Cryptosporidiosis out- breaks have been reported since 1983 in America (Craun et al., 2010). More prevalence of Giardiasis and Cryptosporidiosis has been observed in industrialized countries. The main symptoms of these protozoa are mild to severe diarrhea and possibly shorten the life of those who are at the risk of immune deficiency such as AIDS. About 1.5 million people are estimated to die every year from diarrhea as the result of inadequate sanitation and drinking unsafe water. Based on the data, the major reason for this type of disease is water contamination with sewage and low efficiency of water treatment systems. According to the latest re- ports, 748 million people did not access to drinking water in 2012 (Tsydenova et al., 2015). According to the above description, there is a vital need to remove and inactivate these pathogens and their related diseases. Therefore disinfection process is one of the most important steps in water and wastewater treatment facilities (Yousefzadeh et al., 2014). Nowadays, among many disinfectants used for water and waste- water disinfection, chlorination is more common. But although chlor- ination can inactivate most of the microorganisms in water such as Escherichia coli, but protozoan parasites such as Cryptosporidium parvum oocysts and Giardia cysts can resist against it. On the other hand, sci- entists concern about the cancer potential of chlorine by producing disinfection by-products (DBPs) during drinking water treatment (Chu et al., 2013). Therefore, in recent years, many studies have been con- ducted to find novel methods for water disinfection. Consequently, it is https://doi.org/10.1016/j.fct.2018.04.002 Received 22 December 2017; Received in revised form 14 March 2018; Accepted 1 April 2018 * Corresponding author. Department of Environmental Health Engineering, Floor Number 5, Ghods Ave., Enghelab St., P.O. Box 14155-6446, Enghelab Sq., Tehran, Iran. E-mail address: rnabizadeh@gmail.com (R. Nabizadeh). Food and Chemical Toxicology 116 (2018) 129–137 Available online 03 April 2018 0278-6915/ © 2018 Elsevier Ltd. All rights reserved. T