A Study of Pollutant and Bacterial Transport through Porous Media for in-situ Bioremediation Applications

Abstract

Polycyclic Aromatic Hydrocarbons are considered to be priority pollutants by USEPA and other agencies. Their accumulation in groundwater and subsurface environment has necessitated development of treatment methods to control their bioaccumulation in the living environment. Ex-situ techniques have been tried for decades to treat the pollutants, but they are cost-prohibitive and tedious. In-situ techniques offer potential advantages to this cause. The in-situ techniques designed currently lack a comprehensive understanding of transport processes occurring in subsurface soil region. Understanding the same will allow us to engineer an effective design to treat hydrophobic organic contaminants. Their special properties need modelling studies to correlate their behaviour with conservative solutes. This will enable us to optimise the infiltration rate and remediation volume and geometry for specific regions. Naturally occurring and genetically modified bacteria are capable of degrading highly recalcitrant compounds. But the hydrophobic nature of the contaminants makes it necessary to use special delivery mechanisms to facilitate the interaction between the two. Surfactant and microbubble suspensions are favoured due to the improved flow properties observed. This study attempts to explore and identify key components that determine the transport behaviour of contaminants and bacteria in porous media, in order to increase our understanding of the underlying processes. Foam transport forms an important aspect in this study. Foam is a favourable medium for transport as it provides simultaneous bioaugmentation and biostimulation. The transport parameters need to be characterised to optimise our treatment systems. This area has been identified as the knowledge gap which we try to close in. This study also introduces novel in-situ measurement technique for monitoring bacterial population without the need for invasive sampling techniques. The study is still in its initial stages and, hence, considerable scope lays ahead to modify and improve on the current design of experimental setup and remediation strategies. However, this study provides a proof-of-concept for the operation of these innovative techniques. Bacterial transport is not studied in extensive detail due to certain limitations encountered over the course of the project.