A n Overview of UV-based Advanced Oxidation Processes for Drinking Water Treatment S. R. Sarathy, 1 and M. Mohseni, 1 * Ph.D., P.Eng. 1 Department of Chemical & Biological Engineering University of British Columbia, 2360 East Mall, Vancouver, BC, Canada, V6T 1Z3 * Corresponding Author: E-mail: mmohseni@chml.ubc.ca ABSTRACT This paper begins by presenting the regulatory interest behind the growth of UV-based Advanced Oxidation Processes (AOPs). The main focus of the paper will be a detailed look at the use of four UV-based AOPs (direct photolysis, UV/H 2 O 2 , UV/O 3 , and UV/TiO 2 photocatalysis) in drinking water applications. For each treatment technology, the following are considered: (1) the general mechanism by which it achieves contaminant removal, (2) factors affecting its performance, (3) some relevant recent literature and research projects, and (4) some current commercial activities. Keywords: Ultraviolet radiation; advanced oxidation process; photocatalysis; photooxidation; drinking water. ?? | IUVA News / Vol. 7 No. 1 INTRODUCTION The practice of UV disinfection of water dates back to the early twentieth century. More recently, UV has begun to replace chlorine as a primary disinfectant (Oliver and Carey 1976) largely due to the fact that it has been demonstrated to be more effective at inactivating Cryptosporidium parvum and Giardia lamblia (Bukhari et al. 1999; Craik et al. 2001). With the increased use of UV in drinking water treatment plants, much attention has been placed on developing UV- based advanced oxidation processes (AOP) for the removal of taste and odor compounds, micropollutants, or natural organic matter (NOM) from raw drinking water (Parsons and Byrne 2004). An AOP typically involves the formation of hydroxyl radicals (•OH) that carry out the oxidation and degradation of target species. For UV-based AOPs this involves the addition of an oxidant or catalyst (e.g. O 3 , H 2 O 2 , TiO 2 ) that UV photolyzes or activates leading to the formation of •OH radicals (Bolton and Cater 2004; Legrini et al. 1993). UV-based AOPs date back to as early as 1899 when Bach (1899) observed the photolysis of carbonic acid. Much of the early work focused on the principles and theory behind photooxidation (i.e. quantum yields, reaction pathways). Currently, the main focus is on the full-scale application of AOPs, including reactor design and optimization. In the following, we present the drinking water regulations that have spurred the current interest in AOPs and discuss the current state of direct photolysis, UV/H 2 O 2 , UV/O 3 , and UV/TiO 2 photocatalysis in research and commercial drinking water applications. REGULATORY INTEREST Environmental and health organizations place strict regulations on the maximum allowable concentration (MAC) of a number of organic chemicals in potable water to protect consumer safety. Table 1 summarizes the water quality guidelines of the United States Environmental Protection Agency (USEPA), Health Canada, the European Union (EU), and the World Health Organization (WHO) for selected contaminants whose removal by AOPs has been studied. A certain class of halogenated derivates, namely disinfection by-products (DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), enter the potable water via reaction between chlorine and NOM. UV-based AOPs are capable of reducing the concentration of NOM while also achieving primary disinfection. Thus, the reduced chlorine demand for maintaining a residual in the distribution system leads to an overall decrease in the formation of DBPs. N-nitrosodimethylamine (NDMA) is a nitrosamine that is not currently regulated by national regulatory agencies. However, localized agencies such as the Ontario Ministry of Environment and the State of California have set drinking water guidelines of 0.009 ppb and 0.002 ppb NDMA, respectively. Because of its low molecular weight, low volatility, and poor adsorption characteristics, conventional treatment processes such as membranes, air stripping, and granular activated carbon (GAC) do not adequately remove NDMA. In addition, NDMA is not readily biodegradable so biological treatments are ineffective. Recently, much research has focussed on the removal of NDMA (Mitch et al. 2003) and commercial AOPs exist specifically for the removal of NDMA from drinking water. Mohseni Article 5/16/06 4:26 PM Page 1