Photodecay of inorganic chloramines and disinfection by-products in synthetic and brine solution using UV irradiation

Abstract

Disinfection by-products (DBPs) such as chloramines, haloacetic acids (HAAs) and trihalomethane (THMs) are frequently detected in water and wastewater systems and their excess concentration can be detrimental to human health and many industrial operations. Therefore, it is imperative to evaluate their formation and speciation and decay kinetics in subsequent disinfection processes like UV treatment. UV Photodecay of monochloramine (NH2Cl), dichloramine (NHCl2) and trichloramine (NCl3) and decay kinetics of these compounds were assessed at different environmental conditions in synthetic and brine solutions. Results showed that the chloramine fractions and speciation were strongly dependent on solution pH and chlorine to ammonia molar ratios. Among the chloramines, NCl3 showed the fastest depletion with a quantum yield of 2.16 mol E−1. Kinetics study showed that the rate of photodecay and quantum yield of NCl3 was 8-times and 13-times higher than NHCl2 and NH2Cl, respectively. Addition of natural organic matter lead to formation of DBPs like THMs and HAAs in reaction mixture and the concentration of DBPs was found to increase post UV irradiation. DBP concentrations in present study were well below the regulatory value provided by US Environmental Protection Agency (US EPA). This investigation provides a better understanding of chloramine decay kinetics and aids in identification of DBPs that can potentially discharged from treatment plants employing UV photolysis.