A NEW APPROACH FOR WATER QUALITY NETWORK MODELLING

This study developed a new approach for water quality network modelling to enable estimation of monochloramine residual in real drinking water distribution systems using Bentley commercial hydraulic package (Water GEMS). The approach is based on using surrogate chemical and microbiological factors that affect chloramine decay rate. The model is based on an organic character (SUVA) as chemical factor, a laboratory measure of the microbiological decay of monochloramine (Fm) as microbiological factor, initial monochloramine concentration to the network, and hydraulic retention time (HRT) of the water samples through the distribution systems. The applicability of the proposed model for estimation of monochloramine residual was tested on a large regional chloraminated water distribution system in Australia through statistical test analysis between the experimental and estimated data. It was found that the developed model can recognise the nitrified locations in studied water distribution system, and therefore this modelling approach has the potential to be used by water treatment operators as a decision support tool in order to manage chloramine disinfection. INTRODUCTION Chloramine is commonly used as a disinfectant instead of chlorine to meet regulations regarding formation of disinfection by-products (DBPs) in drinking water, particularly in Australia and the USA (Krasner, 2009, Sarker et al., 2015, Sawade et al., 2016). The chloramine dose is crucial to ensure the water is safe to drink, but also needs to be considered based on taste and odour problems arising from use of high chloramine doses. Maintaining a chloramine residual throughout the water distribution system is important in ensuring microbiologically safe water is supplied at the customer’s tap (Fitzgerald et al., 2006). Modelling of disinfectant residual in treated water distribution systems is aimed at creating a better understanding of the effect of water quality on the disinfection consumption and can serve as a decision making tool for effective water quality control (Abdullah et al., 2009, Gnos et al., 2013). In chloraminated drinking water systems, monochloramine decay occurs due to chemical and microbiological reactions (Sathasivan et al., 2005). To manage disinfection residuals in drinking water, it is important to discriminate between chemical and microbiological decay processes. Chemical factors affecting monochloramine decay include DOM measured as dissolved organic carbon (DOC) concentration, pH, nitrite, organic nitrogen compounds, chlorine to ammonia ratio and temperature (Zhang et al., 2010, Sathasivan et al., 2005, Cook, 2012). In addition, the presence of dead microbial cells and abiotic particles in water may also affect monochloramine decay. The impact of microbiological decay on monochloramine decay can be determined by the analysis of Fm. ISSN 2206-1991 Volume 3 No 2 2018 doi.org/10.21139/wej.2018.009 A CASE STUDY OF A REGIONAL CHLORAMINATED DISTRIBUTION SYSTEM