Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres Comparative disinfection efficiency of pulsed and continuous-wave UV irradiation technologies Zuzana Bohrerova a , Hilla Shemer b , Robert Lantis c , Christopher A. Impellitteri d , Karl G. Linden e,Ã a Department of Civil and Environmental Engineering, Duke University, Durham, NC 27708, USA b Rabin Desalination Laboratory, Department of Chemical Engineering, Technion, Haifa 32000, Israel c LightStream Technologies, Herndon, VA, USA d USEPA, National Risk Management Research Laboratory, Cincinnati, OH, USA e Department of Civil, Environmental, and Architectural Engineering, University of Colorado at Boulder, Boulder, CO 80309, USA article info Article history: Received 11 October 2007 Received in revised form 29 March 2008 Accepted 1 April 2008 Available online 4 April 2008 Keywords: T4 phage T7 phage E. coli Low-pressure UV Medium-pressure UV Water treatment abstract Pulsed UV (PUV) is a novel UV irradiation system that is a non-mercury lamp-based alternative to currently used continuous-wave systems for water disinfection. PUV polychromatic irradiation disinfection efficiency was compared to that from continuous- wave monochromatic low-pressure (LP) and polychromatic medium-pressure (MP) UV systems, using two types of actinometry (ferrioxalate and iodide–iodate) and an absolute spectral emission method for fluence measurement. All three methods were in good agreement. Once accurate and reliable methods for fluence measurement were estab- lished, the inactivation of Escherichia coli and pathogen surrogates phage T4 and T7 were investigated under each technology. Inactivation was significantly faster using PUV irradiation compared to LP or MP UV lamps at equivalent fluence levels. A significant fraction of the enhanced PUV inactivation efficiency was due to wavelengths greater than 295 nm. & 2008 Elsevier Ltd. All rights reserved. 1. Introduction Concerns over the use of chlorine as a primary disinfectant have led to stricter regulations on chlorinated disinfection byproducts. Furthermore, recently enacted regulations (e.g., the Long-Term 2 Enhanced Surface Water Treatment Rule) require improved treatment of some important water- borne pathogens (e.g., Cryptosporidium). Thus, a number of alternative disinfectants have been researched and imple- mented, such as ozone and ultraviolet light (UV). Within UV water disinfection, conventional technology is based on continuous-wave mercury vapor lamps in either low- pressure (monochromatic at 253.7 nm) or medium-pressure (polychromatic in the UV and visible light range) formats. Pulsed UV (PUV) sources are a relatively new lamp technology that has had limited application to water treatment but has been used for UV sterilization of food and pharmaceutical packaging (Dunn et al., 1997, 1995; Jun et al., 2003; Krishnamurthy et al., 2004; Rowan et al., 2001; Wekhof, 2002; Wekhof et al., 2001). PUV lamps are mercury-free and do not require a warm-up period (instant-on). A high power electrical pulse is discharged in microsecond bursts to produce intense light pulses. The discharge is in a rare gas (e.g. xenon or krypton) that is non-toxic. Pulsed lamps can be either of the flashlamp type or a surface discharge (SD) type. SD lamps employ a plasma discharge on the outside of a ARTICLE IN PRESS 0043-1354/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2008.04.001 Ã Corresponding author. Tel.: +1 303 492 4798; fax: +1 303 492 7317. E-mail addresses: bohrerz@duke.edu (Z. Bohrerova), shilla@duke.edu (H. Shemer), LightStream@CleanTechInventures.com (R. Lantis), Impellitteri.Christopher@epamail.epa.gov (C.A. Impellitteri), karl.linden@colorado.edu (K.G. Linden). WATER RESEARCH 42 (2008) 2975– 2982