Modulating Nodal Outflows to Guarantee Sufficient Disinfectant Residuals in Water Distribution Networks

Abstract

This paper proposes the modulation of nodal outflows in water distribution networks (WDNs) to solve the problem of low disinfectant concentrations at critical dead-end nodes, in which low flow velocities and long residence times cause excessive disinfectant decay. The slight increase in nodal outflows at these sites, which can be obtained through the opening of a blowoff at the hydrant site, can help to address this problem with no need to increase disinfectant doses at the source(s) or of install additional disinfectant booster stations. The methodology is based on the combined use of optimization and flow routing/water quality modeling of WDNs. 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: the total volume of water delivered in the network (inclusive of supply, leakage, and additional nodal outflow considered for fixing disinfectant residuals); and the total mass of disinfectant injected into the network. The effectiveness of the methodology was proven on a real WDN, yielding insight into the economic feasibility of the solution.