Experimental investigation of the stability of the colmation zone around leaky sewers

Sewage exfiltration from a sanitary and combined sewer systems and its percolation into porous medium results in a clogged or colmation layer in the nearby soil. In order to develop a comprehensive understanding of raw sewage transport mechanisms in porous media, investigations were carried out on the micro-scale properties of the multiphase system. In our laboratory experiments, the role of surfactants as a major organic chemical compound in wastewater was evaluated by using a surfactant solution as an artificial wastewater percolating into a porous media, represented by using columns and Plexiglas model. We studied flows of water and surfactants solution in saturated porous medium to detect the dynamic effects by means of measuring pressure and permeability as well as by visualization of flow regions and consequence for porosity along interfaces between water and surfactants solution. The tests revealed that mechanisms at interfaces between fluids and solids as well as between water and surfactants solution (i.e. wastewater) are significantly influencing the flow behavior. At the interfaces surfactant molecules are adsorbed or accumulate, respectively, and subsequently inducing electrical charges to those layers, altering the properties of fluids and these interfaces. Depending on the conditions, channels might be narrowed and thus decreasing the flow rate with a later erosion and increase of flow rates, or the flow and thus the erosive capacity might become intensified along the interface between surfactants solution and neighbouring water. In conclusion, the results of tests proved the surfactants to be an important controlling factor in the hydraulic properties of wastewater percolating into soil