Water displacement by surfactant solution: an experimental study to represent wastewater loss from sewers to saturated soil

Leakage of wastewater from sewer lines may result in contamination of soil and groundwater. Our investigation dealt with the effects of surfactant as one of the constituents of wastewater on the infiltration process of wastewater through soil. To that aim, in a laboratory experiment, a column was uniformly packed with glass beads of 0.25–0.50 mm diameter and equipped with sensors to measure local fluid pressure at three observation points along the direction of flow. The artificial laboratory wastewater was created by adding a commercially available detergent to degassed tap water producing surfactant concentrations between 8 and 16 mg l^-1. The displacement process of degassed tap water by such a particle-free artificial wastewater was studied by loading the surfactant solution into the saturated glass beads column. Short-term pressure changes were observed while the interface between water and surfactant solution passed the observation points within the column. The pressure peaks increased for higher surfactant concentrations. The theory of growing interface between surfactant solution and clean water by aggregation of monomers to a double layer could be supported by the column experiments.