Abstract
The formation of bacterial regrowth and disinfection by-products is ubiquitous in chlorinated water distribution systems (WDSs) operated with organic loads. A generic, easy-to-use mechanistic model describing the fundamental processes governing the interrelationship between chlorine, 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 processes that cannot be experimentally determined were neglected. The effects of source water characteristics and water residence time on controlling bacterial regrowth and Trihalomethane (THM) formation in two well-tested systems under chlorinated and non-chlorinated conditions were analyzed by applying the model. The results established that a 100% increase in the free chlorine concentration 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 parameter 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.
Highlights
The focus during the operation of water distribution systems (WDSs) is to maintain the risk of trade-off between protection against opportunistic pathogens and the disinfection by-products (DBPs) [1]
This paper explicitly addresses this issue by developing a mechanistic model to aid the WDSs design and operation using EPANET-MSX [13]
265 and 1 were found to be 2.75 log scale and 0.72 log scale, respectively (Figure 4a). This indicated the significance of the bacteriological quality of the source water in influencing the degree of bacterial regrowth under similar growth environments, which could be attributed to the first-order dependence of the bacterial concentration in the growth reaction term represented by Monod formulation in Equation (4)
Summary
The focus during the operation of water distribution systems (WDSs) is to maintain the risk of trade-off between protection against opportunistic pathogens and the disinfection by-products (DBPs) [1]. The later model proposed by [6] successfully overcame many of the aforementioned drawbacks of the PICCOBIO model These researchers simplified the mathematical expressions to define the multispecies processes concerning bacterial regrowth inside distribution pipes. A similar work, utilizing a Cellular Automata-based model (CA-MSRT model), was recently reported by [11] Both the 1-D models (WU-MSRT and CA-MSRT) considered Trihalomethanes (THMs) as the surrogate for DBPs in WDSs and utilized the concepts of bacterial regrowth, biofilm formation, and the dynamics of chlorine decay and natural organic matter (NOM).
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