Bacterial Regrowth Model for Water Distribution Systems Incorporating Alternating Split-Operator Solution Technique

This paper presents a new mathematical model of bacterial regrowth in distribution systems, which combines hydraulic calculations, inclusive of dispersion, with a description of the following microbial processes: free and attached growth, detachment, endogenous respiration, and inactivation by chlorine. The microbial process description has been simplified from previous models based on a sensitivity analysis. The alternating split-operator algorithm is used to solve this model. This method differs from previous approaches by decoupling the transport and reaction processes, allowing a choice among numerical algorithms that is best suited for each part of the model. The proposed solution resolves sharp fronts of a concentration profile more accurately than traditional finite difference methods. The results of the model are also compared against EPANET to show the importance of accounting for dispersion, as would occur during low water demand conditions when velocity is low. Use of the model to understand the interaction among key parameters affecting bacterial regrowth is illustrated for a simple hypothetical network.