REACTIVE TRANSPORT OF ORGANIC CONTAMINANTS IN GROUNDWATER: IMPORTANCE OF MIXING AND FRINGE BIODEGRADATION PROCESSES

摘要

The release of organic pollutants in groundwater triggers many processes such as redox reactions, sorption, ion exchange and precipitation/dissolution reactions. The most important processes contributing to the contaminants' mass removal and, therefore, determining the fate and transport of the pollutants are microbially mediated degradation reactions. In this study focus is on biodegradation reactions taking place at the fringe of oxidizable organic contaminant plumes. In these zones dissolved contaminants, electron acceptors and nutrients are brought into contact by diffusive/dispersive mixing, thus creating favourable conditions for the degradation activity of the microorganisms. Mixing processes in saturated porous media and mixing-controlled fringe reactions were investigated both at the laboratory bench scale, by performing well-controlled tank experiments with conservative and reactive compounds, and at the typical field scale. The latter investigation was conducted by numerical simulations of contamination scenarios carried out with the main goal of identifying the relevant parameters which have a strong influence on migration and natural attenuation of organic contaminants. The influence of different parameters such as transverse dispersivity, thickness of the contamination source, recharge and mixing enhancement through flow focusing in high permeability zones were assessed.