Multiphase flow and enhanced biodegradation of dense non-aqueous phase liquids
Researcher: Drs. Ing. M. Langevoort
Promotor and supervisor: Prof.Dr.Ir S. M. Hassanizadeh
Funding source: TRIAS
Expected year of completion: 2008
Tetrachloroethylene (PCE) is a common and widespread contaminant of soil and groundwater.
It is classified as a dense non-aqueous phase liquid (DNAPL). These group of liquids are
immiscible with water and have a higher density than water. When spilled on the land surface, the
DNAPL will move down vertically in the unsaturated zone. When the liquid reaches the groundwater table, an
accumulation of DNAPL is nessecary to overcome the entry pressure to replace the water inside the pores. The DNAPL is
able to penetrate through permeable groundwater aquifers and will ultimately pool at a non-permeable
zone. Over the whole trajectory of the migrating DNAPL, a residual concentration will stay behind. A residual DNAPL
consists of immobile blobs of pure product. These drops of pure product, together with the pooled configuration of the DNAPL,
is a long-term source of groundwater contamination. Drinking water
wells may become contaminated.
A possible remediation method for a DNAPL contamination is biodegradation. In this
remediation technique micro-organisms are used to degrade the dissolved contaminants.
For some time, the study on the biodegradation of DNAPLs focussed only on the plume of dissolved components.
Degradation in the vicinity of pure phase was considered
not to be possible, because high concentrations of contaminant are toxic
to some micro-organisms.
Recently, the interest in biodegradation near DNAPL source zones has increased. A few experiments
have shown that PCE can be degraded under anaerobic
conditions at the solubility concentration.
To increase our knowledge on biodegradation near DNAPL source zones, we focus on the interactions between
flow and biodegradation. Although highly relevant for remediation actions,
the combined processes of flow and biodegradation near a DNAPL source have so far not
received much attention.
We investigate biodegradation of a PCE under anaerobic conditions with a groundwater culture from a
PCE-contaminated site with a continuous flow of water, mimicking natural
conditions in the subsurface. We plan to study biodegradation with a numerical model and with
batch, 1D and 2D experiments.
Small-scale experiments are designed to determine specific parameters for the
numerical model. Long-term 2D experiments, in a tank of dimensions 1 (h) by 2(l) by 0.05 m (d)
are performed with continuous horizontal water flow after a spill of DNAPL. This experiment will result
in a dataset that can be used for numerical model testing. Spatial and temporal variations in
flow and biodegradation will be studied by performing detailed measurements over a period
of several months.