Evaluating the effect of temperature induced water viscosity and density fluctuations on virus and DOC removal during river bank filtration - a scenario analysis
Derx, Julia; Farnleitner, Andreas H.; Zessner, Matthias; Pang, Liping; Schijven, Jack; Blaschke, Alfred P.
Riverbank filtration is considered an efficient method for removing contaminants from infiltrated surface water in the subsurface. Despite indications that changing water temperatures affect the biochemical and biological mediated removal processes of contaminants, the impact of temperature induced fluid viscosity and density effects on contaminant removal during riverbank filtration is not well understood. This paper investigates the viscosity and density effects associated with seasonal changes in groundwater temperature on virus and dissolved organic carbon (DOC) removal during riverbank filtration. Hypothetical aquifer and flood wave scenarios were assumed. Data on groundwater temperature were taken from an Austrian field site of the River Danube recorded during 2010/2011. Based on removal rates taken from previously published field experiments, virus and DOC transport was simulated for highly permeable gravel, fine gravel and fine sandy gravel material. Our simulations indicate that for DOC and a wide range of virus types the viscosity and density effects induced by water temperature changes can counteract with temperature dependent decay and inactivation rates. For particular situations, however, such as for receding floods during colder periods, our simulations indicate that fluid viscosity and density effects can result in a net decrease in the virus removal efficiency during colder periods. Persistent types of viruses (e.g. polio 1 or HAV) can be reduced less effectively and may travel by up to 25 % faster during warmer than during colder periods. Our simulations indicate that viscosity and density effects induced by temperature changes should be considered for studying and simulating virus or DOC removal and transport during riverbank filtration. The effects may be important specifically at field sites with a high river-aquifer exchange and large variations in groundwater temperature.