Hydraulic performance of vaulted pumps placed in septic tanks used with on-site wastewater systems

The article presents a hydraulic study performed with pumps placed inside a septic tank using pump vaults. A large number of households rely on on-site wastewater treatment systems to treat sewage before discharging effluent back into the environment. Occasionally, these systems fail and must be replaced or greatly modified. In addition, some geographic locations cannot naturally handle septic systems due to soil types and structure. Under these circumstances, use of mound systems and low pressure pipe systems is becoming increasingly popular. However, these systems require use of pumps, which can add significant cost to the system and have the potential to "short circuit" the treatment process if not designed properly. Results illustrate the degree to which the pumps, placed inside pump vaults, affect hydraulic characteristics of the septic tank. The results are presented in terms of the Reynolds number (indicating the degree of turbulence), comparisons to critical velocities (i.e., scour velocity), and analysis of capacity reductions. It is concluded that pumps can effectively be placed inside septic tanks, thus eliminating relatively expensive external dosing chambers, without negatively affecting designed performance of the septic system.