Chlorine Disinfection Project Report

CONTENTS

Chapter 1 Introduction 1

1.1 Background 1

1.2 Objectives 2

1.3 Scope of Project 2

1.4 Structure of Report 2

Chapter 2 Literature Review 4

2.1 Introduction 4

2.2 Chemistry of Chlorine as a Disinfectant 4

2.3 Alternative Disinfectants 7

2.3.1 Chloramines 7

2.3.2 Chlorine dioxide 7

2.3.3 Ozone 8

2.4 DBP Precursors 8

2.4.1 Natural Organic Matter (NOM) 8

2.4.2 Soluble Microbial Products (SMPs) 9

2.4.3 Bromide & Iodide 9

2.4.4 Dissolved Organic Nitrogen (DON) 10

2.5 Classification of Disinfection Byproducts (DBPs) 10

2.5.1 Trihalomethanes (THMs) 10

2.5.2 Haloacetic Acids (HAAs) 10

2.5.3 Trihaloacetaldehydes (THAlds) 10

2.5.4 Halopropanones (HPNs) 10

2.5.5 N-DBPs: 10

2.5.6 Total Organic Halogen (TOX) 11

2.6 Kinetics of DBP formation 11

2.7

At similar concentrations of chlorine and bromine, bromine incorporation into THMs and HAAs is preferred over chlorine incorporation. This is because HOBr is 20 times stronger oxidant than HOCl so reacts faster with NOM shifting the distribution of THMs and HAAs to more brominated species. Ratio of applied chlorine to bromine plays an important role in the speciation of THMs and HAAs (Uyak & Toroz, 2007). Increase in bromide ion concentration first results in the formation of mixed choro-bromo species to fully brominated ones (Hua et al., 2006). It has been reported that brominated DBPs so formed are more carcinogenic as compared to the chlorinated ones (Uyak & Toroz, 2007). Water and wastewater treatment processes remove organic carbon but bromide ion is quite resistant to be removed by these and hence ultimately ratio of bromide ion to total organic carbon (TOC) increases. This increases the fraction of brominated DBPs (Roccaro et al.,

Also humic acids results in the production of more TOX, THMs, HAAs and haloacetonitriles as compared to the fulvic fraction of the same source (Ates et al., 2007). UV absorbance can also be correlated with DBP formation as activated aromatic structures like phenolics and aromatic amines substituted with nucleophilic groups serve as primary sites attacked by chlorine as well as other disinfectants. UV absorbance technique is practically easy to implement as only a small amount of sample without any intense sample preparation can be used for characterising DOM (Ates et al.,