Research Objectives:
Our primary objectives are to
- determine pesticide sorption/desorption
behavior onto soil particles of various sizes and physicochemical
characteristics
- enhance pesticide removal efficiency
using surfactant-aided soil washing and in-situ flushing,
by selecting the most appropriate surfactant for a contaminated
site.
The proposed studies is conducted at batch and column scales
to simulate soil washing and in-situ flushing respectively.
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Separation of primary size particles |
Low-energy separation procedure (gentle shaking
with water with no any chemicals being used as disperants and
repeated gravitational settling) is used to separate primary
soil particles, i.e. clay (<2 mm), silt (2 mm-50 mm), and
sand (50 mm-2 mm) size particles. To keep the change in the
properties of original clay particles as small as possible,
the amount of salt solution (CaCl2) added to flocculate the
clay fraction is kept to a minimum. The collected clay- and
silt-sized fractions are quickly frozen using liquid nitrogen
and then freeze-dried to get well separated size particles. |
Batch Experiments |
Sorption/desorption isotherms are determined in duplicate
by the batch equilibration technique. Batch experiment is an
important means to study a solute sorption behavior under equilibrium.
The vigor of shaking in batch systems is very important in the
mass transfer of reactive solutes between sorption sites inside
porous sorbents and bulk solution. The increase of the mass
transfer rate of the solute results in a faster establishment
of equilibrium. The supernatant is analyzed on a HPLC or on
a GC/MS/MS (Varian, 2100T) for the pesticides (Atrazine, Diuron
and Lindane), and on the DCA for the surfactants. All of these
analytical instruments are available in our lab. |
Column Experiments |
Columns are carefully packed with soils to minimize potential
preferential pathways. A 20 mm nylon mesh is strapped to the
bottom of the column to prevent the soils from falling out of
the column. C14-labelled pesticides are used to facilitate the
detection of the particle-bound pesticides. Pesticide concentrations
are quantified on a liquid scintillation analyzer (Beckman LS6500).
Both a total pesticide and a particle-bound pesticide concentration
are measured, being subsamples from the same effluent sample.
The operational defined ‘solution phase’ is taken
from the supernatant after centrifuging a 10ml subsamples at
4000 ×g for 30 minutes. The particle-bound pesticide concentration
is then calculated as the difference of the total amount and
the solution phase. |
Analysis of samples |
GC/MS/MS Specifications for the Varian Gas Chromatograph
- Mass Spectrometer (Saturn 2100T) can be found here.
HPLC - Shimadzu: info here
Liquid Scintillation Counter - Beckman: info here
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Other physicochemical characterization |
DCA Analyzer
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