Disinfection Byproducts (Dbps)

Chapter 1 Introduction

1.1 Background

Disinfection is applied to water as well as wastewater treatment as a finishing step so as to destroy pathogens but the cause of concern regarding the disinfection process is the formation of disinfection byproducts (DBPs) due to the reaction of disinfectants with precursors present in water. Disinfectants are powerful oxidants that oxidize the organic matter present in water forming DBPs. Chlorine, ozone, chlorine dioxide, and chloramines are the most common disinfectants used and each of these produces its own set of DBPs in water (Richardson, 2003). DBPs so formed pose a threat to human health because of their potential to cause cancer and reproductive/developmental

Most of the soluble organic matter present in effluents from biological treatment processes form part of SMPs, so they are a major cause of concern not only in terms of meeting effluent standards but also as a precursor for formation of DBPs (Barker & Stuckey, 1999). SMPs are classified into two categories named as Utilization Associated Products (UAPs) and Biomass Associated Products (BAPs). UAPs are the ones which are associated with substrate metabolism and biomass growth whereas BAPs are associated with biomass decay and are produced at a rate proportional to the concentration of biomass (Barker & Stuckey, 1999). Molecular weight of SMPs ranges from 50 kDa and this generally depends upon the operating conditions of the treatment provided. Also process parameters like hydraulic retention

By applying Beer Lambert law, the absorbance at a certain wavelength can be used to predict the concentration of an analyte (Matilainen et al., 2011). Absorbance by a molecule is dependent upon its structure and absorption at a particular range shows a specific bonding arrangement. Conjugated systems such as aromatic molecules show maximum absorbtivities in the UV range (200-400 nm).

UV absorption is found to be greater for humic acids because of the presence of aromatic structures and greater molecular size. 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.,