Riverbank filtration: modeling fate of dissolved organic carbon, transport of Escherichia coli and coupling with aquifer storage to address temporal water scarcity

Abstract

Riverbank filtration (RBF) is an accepted method of treatment for water supply from rivers which markedly improves the source water quality. Pumping water from wells adjacent to water body induces surface water to infiltrate through the aquifer attenuating contaminants present in the source water. This study used field data from an operating RBF system located along the Rhine River in Düsseldorf, Germany, and carried out focused research on the fate of dissolved organic carbon and on transport of E. coli. Furthermore, a novel application of RBF and aquifer storage and recovery (ASR) was considered in a study to address seasonal water scarcity in the Albany region of the Georgia in US. A reactive transport model (PHT3D) was developed to study the fate of dissolved organic carbon incorporating transient boundary conditions. Modeling residence times showed that high floods in the river reduced the travel time to the RBF well to 8 days, while low flows increased it to about 60 days. Aerobic processes with some partial denitrification occured in the aquifer. The temporal changes in the breakthrough of dissolved oxygen were best reproduced when the temperature dependency of the biogeochemical processes was explicitly considered. The results showed that seasonal temperature changes superimposed by changes in residence time strongly affected the extent of redox reactions along the flow path. Microbial transport is modeled in groundwater using the advection-dispersion transport equation adding on the processes of attachment, detachment and inactivation processes. The rates defined by these processes are velocity dependent and cannot be used directly for a transient RBF model. An approach to handle such transient conditions is developed using colloid filtration theory and the concepts of single collector contact efficiency and verified on a benchmark 1-D study. The model is extended to the Rhine River RBF system. The transport of E-coli and coliforms was successfully modeled. The RBF-ASR study showed the viability of obtaining excess river flows through RBF and storing it a deeper aquifer to be recovered later. Geochemical changes were also investigated. The overall study contributes to our understanding of the various processes involved in RBF and subsurface flows.