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Formation of organic chloramines during water disinfection – chlorination versus chloramination
Wontae Leea,*, Paul Westerhoffb
HDR Engineering Inc., 3200 East Camelback Road, Suite 350, Phoenix, AZ 85018, USA Department of Civil and Environmental Engineering,Arizona State University, Tempe, AZ 85287-5306, USA
Article history: Received 10 October 2008 Received in revised form 4 February 2009 Accepted 9 February 2009 Published online 20 February 2009 Keywords: Organic chloramines Chlorination Chloramination Disinfection Organic nitrogen
Many of the available studies on formation of organic chloramines during chlorination orchloramination have involved model organic nitrogen compounds (e.g., amino acids), but not naturally occurring organic nitrogen in water. This study assessed organic chloramine formation during chlorination and chloramination of 16 natural organic matter (NOM) solutions and 16 surface waters which contained dissolved organic nitrogen (DON). Chlorination rapidly formed organic chloramines within 10min, whereas chloramination formed organic chloramination much more slowly, reaching the maximum concentration between 2 and 120 h after the addition of monochloramine into the solutions containing DON. The average organic chloramine formation upon addition of free chlorine and monochloramine into the NOM solutions were 0.78 mg-Cl2/mg-DON at 10 min and 0.16 mg-Cl2/mg-DON at 24 h, respectively.Organic chloramine formation upon chlorination and chloramination increased as the dissolved organic carbon/dissolved organic nitrogen (DOC/DON) ratio decreased (i.e., DON contents increased). Chlorination of molecular weight (10,000 Da) fractionated water showed that molecular weight of DON would not impact the amount of organic chloramines produced. Comparison of three different disinfectionschemes at water treatment plants (free chlorine, preformed monochloramine, and chlorine/ammonia additions) indicated organic chloramine formation could lead to a possible overestimation of disinfection capacity in many chloraminated water systems that add chlorine followed by an ammonia addition to form monochloramine. ª 2009 Elsevier Ltd. All rights reserved.
Chlorine andchloramines are the most widely used disinfectants in water treatment plants and distribution systems because they are effective, relatively inexpensive, and remain active within the systems for a considerable length of time. Dissolved organic nitrogen (DON) can react with free chlorine (Calvert, 1940; Morris, 1967) or inorganic chloramines (Snyder and Margerum, 1982; Isaac and Morris, 1983) to formorganic chloramines, which have little or no bactericidal activity (Feng, 1966; Wolfe et al., 1985). Therefore, understanding the
distribution of chlorine between free chlorine, inorganic chloramines, and organic chloramines is important for adequate disinfection of pathogens during water treatment and prevention of microbial regrowth in the water distribution systems. With large numbers ofwater utilities in the U.S. switching from free chlorine to chloramines in order to comply with the Stage 2 Disinfectants and Disinfection Byproduct Rule, a better understanding of organic chloramine formation is critical to proper management of these disinfection systems. The general nature of the reactions between DON and free chlorine (HOCl) or monochloramine (NH2Cl, dominant (>95%)
*Corresponding author. Tel.: þ1 602 522 7700; fax: þ1 602 522 7707. E-mail address: email@example.com (W. Lee). 0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2009.02.009
water research 43 (2009) 2233–2239
inorganic chloramine species at typical water treatment conditions pH 7–9) is represented by Eqs. (1) and (2), respec-
R1 H2NC–R2 +...