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Title:Ozone-bromide-NOM interactions in water treatment
Author(s):Song, Rengao
Doctoral Committee Chair(s):Minear, Roger A.
Department / Program:Civil and Environmental Engineering
Discipline:Civil and Environmental Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Civil
Engineering, Sanitary and Municipal
Environmental Sciences
Engineering, Environmental
Abstract:Ozonation (O$\sb3$) of waters containing bromide (Br$\sp{-}$) results in Br$\sp{-}$ oxidation to first hypobromite ion (OBr$\sp{-}$) and its conjugate acid (HOBr), and eventually bromate (BrO$\sb{3\sp{-}}$), a suspected carcinogen. Natural organic matter (NOM) reads with HOBr/OBr$\sp{-}$ to form organic bromine (TOBr).
Ozone-bromide-NOM interactions are studied with true-batch reactors, which facilitate elucidation of the kinetics for ozone decomposition, bromate formation, and TOBr formation. In order to study influential factors independently the research employs NOM isolates, separated and concentrated by ultrafiltration (UF) and reverse osmosis (RO) membrane methods. A parametric study, involving an orthogonal matrix, is performed to study important variables. Kinetic data are obtained for ozone decomposition, bromate and TOBr formation.
Both molecular ozone and hydroxyl radical (HO$\cdot$) are critical to the formation of BrO$\sb{3\sp{-}}$. A HO$\cdot$ radical scavenger, tertiary butanol, is employed to delineate the direct ozone oxidation pathway. With the help of kinetic modeling, it can be concluded that bromate forms through three major pathways: the direct ozonation pathway, the direct ozonation/indirect ozonation combination pathway, and the indirect ozonation/direct ozonation combination pathway. Thus, the overall conversion of bromide to bromate depends on both molecular ozone residual and HO$\cdot$ radical concentrations. Experimental results also indicate that the two combination pathways which involve HO$\cdot$ radicals are very influential in bromate formation. The relative importance of an individual pathway contributing for bromate formation depends on water quality and treatment variables.
A linear relationship is observed between the ozone utilization time (OUT) and bromate formation. This simple linear relationship suggests a constant driving force for bromate formation and a strong dependency of bromate formation upon ozone decomposition. Therefore, it is necessary to understand the factors controlling ozone decomposition. In the absence of NOM (e.g. Milli-Q water), an overall first order decay represents the ozone disappearance. In the presence of NOM, a two-step decay model is formulated where the first more rapid ozone decay is followed by a subsequent slower first order decay. NOM exerts a significant ozone demand and also scavenges HO$\cdot$ radical and its daughter-radicals, which is evidenced by low bromate formation in the presence of NOM compared to that of Milli-Q water system. Ozonation of NOM also generates a significant amount of hydrogen peroxide $\rm(H\sb2O\sb2)$ which effectively reduces bromine to bromide.
Besides playing an important role in bromate formation, bromine-NOM interactions lead to rapid bromine reduction and substitution/addition to NOM and thus decrease concentrations of aqueous bromine for bromate formation.
Various water quality and water treatment variables affect ozone decay, and bromate and TOBr formation. These variables influence the BrO$\sb{3\sp{-}}$ and TOBr levels primarily through NOM-O$\sb3$, NOM-HO$\cdot$, NOM-bromine, and $\rm H\sb2 O\sb2$-bromine interactions. These interactions affect ozone residuals, HO$\cdot$ radical concentrations, and bromine concentrations, thus influence bromate and TOBr formation.
Both deterministic and empirical models for bromate formation (in the absence and presence of NOM, respectively) are presented. These models are tools for understanding the bromate formation mechanisms and the influences of water quality and treatment variables on bromate formation.
Issue Date:1996
Rights Information:Copyright 1996 Song, Rengao
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9702670
OCLC Identifier:(UMI)AAI9702670

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