Modeling bacterial regrowth and trihalomethane formation in water distribution systems

The formation of bacterial regrowth and disinfection by-products is ubiquitous in chlorin-ated water distribution systems (WDSs) operated with organic loads. A generic, easy-to-use mech-anistic model describing the fundamental processes governing the interrelationship between chlo-rine, total organic carbon (TOC), and bacteria to analyze the spatiotemporal water quality variations in WDSs was developed using EPANET-MSX. The representation of multispecies reactions was simplified to minimize the interdependent model parameters. The physicochemical/biological pro-cesses that cannot be experimentally determined were neglected. The effects of source water char-acteristics and water residence time on controlling bacterial regrowth and Trihalomethane (THM) formation in two well-tested systems under chlorinated and non-chlorinated conditions were ana-lyzed by applying the model. The results established that a 100% increase in the free chlorine con-centration and a 50% reduction in the TOC at the source effectuated a 5.87 log scale decrement in the bacteriological activity at the expense of a 60% increase in THM formation. The sensitivity study showed the impact of the operating conditions and the network characteristics in determining pa-rameter sensitivities to model outputs. The maximum specific growth rate constant for bulk phase bacteria was found to be the most sensitive parameter to the predicted bacterial regrowth.