Diesel Adsorption to Polyvinyl Chloride and Iron During Contaminated Water Flow and Flushing Tests

This paper presents an experimental and theoretical study of aqueous diesel contamination and decontamination of a polyvinyl chloride (PVC) surface and an iron (Fe) surface. A test apparatus designed for the purpose of studying adsorption of diesel from a flowing dilute diesel/water mixture was used to measure the mass of diesel adsorbed per unit surface area (the excess surface density) and the bulk concentration of the diesel in the flow using a fluorescence based measurement technique. Both bulk composition and the excess surface density measurements were achieved via a traverse of the fluorescent measurement probe perpendicular to the test surface. The diesel adsorption to each test surface was examined for three different Reynolds numbers between zero and 7000. Measurements for a given condition were made over a period of approximately 200 h for a diesel mass fraction of approximately 0.15 % in tap water. For a Reynolds number of approximately 7000, the largest excess layer thickness was approximately 4.4 μm, which was measured on a PVC surface. Averaging over all contaminating flow rates and exposure times, the excess layer thickness on the PVC surface was approximately 2.0 μm. Reynolds number had little or no effect on the accumulation of diesel on an iron surface, which was approximately 0.71 μm. The adsorbed diesel on the PVC and iron surfaces was removed by flushing with tap water. Models to predict excess layer thickness during flushing and contamination were developed. The models predict flushing times to within 7 h and predict the influence of pipe surface on contamination level.