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REMEDIATION OF GROUNDWATER CONTAMINATION BY COMBINED FLUSHING AND MPPE WATER TREATMENT: SUMMARY AND CONCLUSIONSRamsay, Loren; Jens Brandt Jorgensen, WaterTech A/S. Danish Environmental Protection Agency, Denmark. Environmental Project No 725, p 7-8, 2002 [The above title refers to an English summary. The body of the publication is in Danish. Danish title: Afværge af grundvandsforurening ved kombination af Flushing og MPPE-vandrensning]
Flushing is a remediation technique well-suited for aggressive subsurface
treatment of a NAPL-contaminated source area. The method is based on pump-and-
treat technology and makes use of chemicals (surfactants, cosolvents, or
chemical complexes) added to the aquifer via injection wells. The chemicals
change the physical-chemical properties of the NAPL and promote contaminant
dissolution and/or mobilization, which enables the removal of the contaminants
from extraction wells. Macro Porous Polymer Extraction (MPPE) technology makes
use of small hydrophobic particles of plastic placed in a column through which
contaminated water is pumped for treatment. A liquid immobilized in the pore
structure of the particles removes the contaminants by liquid-liquid
extraction. When the column is saturated with contamination, the particles can
be regenerated by steam treatment. MPPE has performed well in cases where the
concentration of contaminants is high. Flushing typically results in high
contaminant concentrations, so combining flushing and MPPE is a logical step.
This summary briefly presents two case studies of flushing and MPPE used
together to address PCE contamination at former dry-cleaner sites. The first
case involved a pilot-scale project--cosolvent flushing with ethanol combined
with extracted water treatment by MPPE. The second case involved a 16-day
demonstration that applied a flushing mixture of rape seed oil, fatty acids,
and glycerol. Approximately 900 cubic meters of ground water were extracted,
with an average PCE concentration of 36 mg/L before MPPE treatment and 3 mg/L
afterward. Nearly 29 kg of PCE was removed during the demonstration project.
Recovery of the surfactant was 82%. Because the PCE concentration in the
extracted water did not increase after surfactant injection, the value of the
flushing was limited. The MPPE water treatment method was able to remove the
PCE from the water/surfactant mixture with good efficiency.
MPPE water treatment has functioned as intended in the investigated
cases. The disadvantages of combining the technologies include the fact that
flushing is a "coarse" method that only removes part of the contamination, so
often it is necessary to supplement the method with other approaches for
polishing. Flushing also risks spreading the contamination through
mobilization. In addition, incomplete recovery will leave some of the chemical
additive to remain in the ground water. MPPE is not competitive in situations
where the contaminant concentrations are limited. Future prospects for use of
flushing/MPPE in Denmark are good because the combined methods are suitable
for an initial aggressive remediation of chlorinated solvent NAPL. For more
information, visit http://www.mst.dk/udgiv/Publikationer/2002/87-7972-282 -
2/pdf/87-7972-283-0.pdf
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