Wider presence of accelerated chemical chloramine decay in severely nitrifying conditions K. C. Bal Krishna, Arumugam Sathasivan and Scott Garbin ABSTRACT Popularity of chloramine has been dampened by nitrification, which is believed to highly accelerate chloramine decay. This can seriously compromise the primary goal of using chloramine as a secondary disinfectant. Our previous laboratory-scale studies showed that highly accelerated chemical decay of chloramine was caused by soluble microbial products (SMPs) released by microbes under severely nitrifying conditions. To understand whether a similar phenomenon exists in full-scale distribution systems, samples were collected from four full-scale systems supplied from different water sources and have been compared with results obtained from laboratory-scale systems. The results verified that the acceleration typical in severely nitrified water is common in full- scale chloraminated systems under severely nitrifying conditions. K. C. Bal Krishna Arumugam Sathasivan (corresponding author) Department of Civil Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia E-mail: A.Sathasivan@uws.edu.au Arumugam Sathasivan School of Computing, Engineering and Mathematics, University of Western Sydney, Locked Bag 1797, Penrith NSW 2751, Australia Scott Garbin Water Corporation, PO Box 100, Leederville, WA 6902, Australia Key words | chloramine, distribution system, mild nitrification, severe nitrification INTRODUCTION Since the early 1900s, chlorine and chloramine have been used as secondary disinfectants to suppress the harmful microbes in water distribution systems. Due to increased concern over chlorinated disinfection by-products and fast decay characteristics, many water utilities were forced to employ chloramine instead of chlorine. In addition, chlora- mine is considered to be more effective in reducing heterotrophic bacterial growth and in improving water taste and odour in the system (Norton & LeChevallier ). Therefore, chloramine is a common choice for many water utilities. However, chloramine is an inherently unstable disinfec- tant. It decays by itself even in the absence of oxidizable matters ( Jafvert & Valentine ) and reacts with chlora- mine demanding matters present in the systems. In each decay process, free ammonia is liberated from chloramine, which is an energy source for indigenous nitrifiers. Free ammonia leads to biological instability by promoting nitrifier growth in the distribution system, resulting in nitrification. Nitrification is a microbial conversion of ammonia to nitrite by ammonia-oxidizing bacteria (AOB) and nitrite to nitrate by nitrite-oxidizing bacteria (NOB). Presence of autotrophic nitrifying bacteria in the distribution system is a probable health risk because it may lead to increased coliform regrowth, high disinfectant demands, corrosion of distri- bution system materials and water quality deterioration (Regan ; Pintar & Slawson ). Eventually this can compromise the primary aim of achieving secondary disin- fection in distribution systems. Based on the nitrite level produced by AOB and the chloramine decay rate, Sathasivan et al.() defined mildly and severely nitrifying stages in bulk water samples. The stage when chloramine decay was reasonably stable and the nitrite level was less than 0.010 mg-N/L was referred to as the mildly nitrifying stage. The stage when nitrite reached a high level (more than 0.10 mg-N/L) and chloramine decay excessively accelerated (total decay was about one order higher than in the mildly nitrifying stage) was defined as the severely nitrifying stage. Hence, the onset of severe nitrification is undesirable for water utilities. 1090 © IWA Publishing 2013 Water Science & Technology: Water Supply | 13.4 | 2013 doi: 10.2166/ws.2013.093 Downloaded from https://iwaponline.com/ws/article-pdf/13/4/1090/415024/1090.pdf by guest on 26 May 2020