Simple deterministic model of the hydraulic buffer effect in septic tanks

Abstract

Septic tanks are widely used in on-site wastewater treatment systems. In addition to anaerobic pretreatment, hydraulic buffering is one of the roles attributed to septic tanks. However, there is still no tool for assessing it, especially in dynamic conditions. For gravity fed-system, it could help both researchers and system designers. This technical note reports a simple mechanistic model based on the assumption of flow transition between the septic tank and the outflow pipe. The only parameter of this model was calibrated using computational fluid dynamics (CFD) modeling for a wide range of discharge rates. The resulting model highlights that a septic tank plays a hydraulic buffer role when faced with sudden and large discharge flow, but this role tends to disappear when input hydrographs are smoother. In those cases, there is an observable lag between the input hydrograph and outflow hydrograph.

Enhancing the ventilation of sewers by using inhaled air in the vertical stack of a building

“…A hydraulic jump was then generated in the connection, which caused the evolution of the air and positive pressure. Septic tanks are widely used in on-site wastewater treatment systems (Forquet & Dufresne 2015), and when the building was linked to a septic tank, the air ran directly out of the exhaust port of the septic tank. The septic tank, which was not used to its full potential, subsequently exploded, partially because of the ventilation.…”