Nearfield water quality of the Metro WWTP effluent mixing zone in the Mississippi River under Summer conditions

Abstract

A side channel discharge such as that from the Metro Wastewater Treatment Plant (WWTP) into the Mississippi River interacts with the river flow in several ways before the two become fully mixed. Among the flow and mixing processes generally to be considered are: (a) Jet effects due to the momentum of the discharge. (b) Lateral displacement of river flow by the effluent input. Conservation of mass requires that the streamlines in the river are displaced towards the center to make room for the effluent flow rate in the river. (c) Downstream advection by the river flow. (d) Transverse turbulent mixing due to bed shear and secondary flow in the river. (e) Buoyant spreading caused by the density difference between effluent water and river water. The density depends on water temperature and total solids content. (f) Vertical turbulent mixing by the river due to bed shear. (g) Mixing by tug boats and barge traffic.