Flowing Blow-Offs: A Solution to Maintain Adequate Disinfectant Residuals of Dead-End Nodes in WDNs

Abstract

Flushing plans within a water distribution network (WDN) provide a tool for improving disinfectant residuals and removing stagnant water. The problem of low disinfectant residuals occurs in areas of a WDN such as dead-end nodes, in which low flow conditions and long residence times lead to excessive decay of the disinfectant upstream from users. Here, a methodology is presented to maintain adequate disinfectant residuals in WDNs that have numerous dead-end nodes. The slight increase in nodal outflows at these sites, which can be obtained through the opening of a blow-off at the hydrant site, can help in tackling this problem. The methodology is based on the combined use of optimization and of flow routing/water quality modelling. The concentration of disinfectant at the source(s) and the values of nodal emitter coefficients at the critical dead-end nodes are the decisional variables to be optimized. Two objective functions are considered in the optimization, namely the total volume of water delivered in the network and the total mass of disinfectant injected into the network. The effectiveness of the methodology is proven on a real WDN, yielding an insight into the economic feasibility of the solution.