Assessment of MS-2 phage and salt tracers to characterize axial dispersion in water distribution systems

The present study investigates the axial dispersion and retardation patterns of viruses in a pressurized water distribution pipe using MS-2 as a surrogate. The results were obtained by using computational fluid dynamics (CFD), along with a hydraulic and water quality model. These models included the plug flow assumption and were first used to estimate transport mechanisms along a pipe. These prediction-model results were compared to experimental data using sodium chloride as a chemical tracer. Significant axial dispersion and retardation (or tailing) was found to exist under laminar flow conditions with high dispersion coefficients (E) estimated by CFD runs and salt tracer experiments. A similar dispersion pattern was also observed for MS-2, along with a long tailing pattern, which is particularly unique. The commonly used water quality model showed no axial dispersion (E = 0) under any flow regimes; thus, the plug flow assumption could produce significant errors in predicting the transport phenomena of chemical and biological constituents in water distribution systems. On the other hand, the dispersion curves predicted by the plug flow model and CFD are in good agreement with the experimental data in the turbulent flow regime, although using computational methods to predict microbial retardation is intrinsically difficult. Because the MS-2 demonstrated considerable temporal retardation and because its detection limit is much lower than that of the salt tracer, MS-2 should make an excellent tracer for characterizing viral transport in water distribution systems.