Decontamination of porous surfaces*

The decontamination of materials is a challenging problem in a wide range of industrial, medical, urban and disaster-response applications. Attempts to decontaminate porous surfaces (e.g. concrete, tarmac and wood) can lead to a partial redistribution of the contaminant within the porous medium rather than a complete removal. This is of crucial importance in case of extremely harmful agents.

We present experiments modelling the surface-washing of porous substrates (obtained by sintering packed glass beads onto solid glass). The agent is simulated by a passive tracer introduced in the form of droplets, while a gravity-driven water film flows over an inclined porous plane. The contaminant mass transfer due to the cleansing flow is tracked by direct image analysis based on dye-attenuation (using three different illumination wavelengths), enabling study of the space-time evolution of the contaminant field within the porous medium. Additionally, an inline UV-Vis spectrometer measures the effluent from the washing.

Our experiments provide insights on the fundamental physics governing the cleaning process, such as the role of initial conditions (e.g., ingress of contaminant) and the impact of process parameters on the decontamination efficiency. Importantly, they demonstrate a decontamination-induced redistribution of the contaminant within the porous matrix that could increase the risk posed by the agent.