Revised Chlorine Mass Balance for Chlorine Loss Assessment in Water Distribution Networks

Water and energy balances in water distribution networks (WDNs) are commonly used for managing water and energy losses, respectively. Recently, a new approach, the chlorine mass balance, has been proposed to assess chlorine losses within WDNs. However, previous research did not account for changes in chlorine masses in pipes and tanks within the networks (∆MN). In this study, we introduce ∆MN as a new component in the revised chlorine mass balance and assess its significance by utilizing a simple WDN model with a downstream tank. Our findings reveal that the hourly magnitude of ∆MN can be comparable to the other two primary components: the chlorine mass delivered to users, and chlorine mass losses by reactions. This underscores the importance of ∆MN for the short-term assessments, particularly in cases involving intermittent water supply and pressure-loss events. During non-supply periods, chlorine concentrations in stagnant water within pipes and tanks decrease due to reactions, resulting in negative ∆MN. When water supply resumes, a portion of the input chlorine mass is used to restore chlorine levels in WDNs, resulting in positive ∆MN. ∆MN fluctuates between positive and negative values with an average value around zero in continuously operating general WDNs. Therefore, if the balance is assessed over a long period with many cycles of periodic patterns, ∆MN becomes less significant.