34    THE EFFECTS OF A SURFACTANT ON
POST-EXTRACTION TREATMENT OF PCE
CONTAMINATED WATER
Stefanie R. Lange, Research Associate
Clifford R. Lange, Assistant Professor
Department of Civil Engineering
Auburn University
Auburn, Alabama 36830
INTRODUCTION
Remediation of contaminated groundwater has long been a concern of environmental engineers and scientists. One category of environmentally important contaminants is chlorinated hydrocarbons. Chlorinated hydrocarbons in the environment are generally present in the form of
Dense Non-Aqueous Phase Liquids (DNAPLs) because of their high molecular weight and relatively low solubility in water. High densities combined with low viscosities make remediation of
chlorinated solvents difficult.' One specific chlorinated hydrocarbon of interest is tetrachloroeth-
ylene, also known as perchloroethylene (PCE), which is a solvent used in dry cleaning and de-
greasing. PCE has been a commonly encountered contaminant at remediation sites due to industrial discharges, municipal waste treatment plant discharges, and spills.
Pump and treat extraction has been the most widely used form of aquifer remediation for PCE
contaminated groundwater sites. However, large pumping volumes and long pumping times are
required to effectively remediate these sites. Recently, investigations have been conducted to assess the feasibility of surfactant enhanced pump and treat techniques. These investigators have
demonstrated that Surfactant Enhanced Aquifer Remediation (SEAR) can greatly reduce the volume of water required to flush PCE from a contaminated groundwater site.1
Surfactants are able to increase the apparent solubility and mobility of PCE.2 This allows the
PCE to go into solution and decreases liquid surface tension causing the PCE to be more readily
transported out of the groundwater through pumping. However, little research has been done
concerning the treatment of these wastes containing surfactants after they have been pumped out
of the groundwater.
The presence of surfactants in a wastewater solution complicates the mechanisms controlling
the adsorption of PCE onto granular activated carbon. It is hypothesized that competition exists
between the carbon and the surfactant micelles for PCE adsorption. PCE bound in surfactant micelles can pass through a carbon column without being adsorbed. The surfactants also block the
pore structure of the activated carbon, resulting in reduced absorbent surface area. It has been
observed that the rate of PCE adsorption by sand is controlled by intraparticle-pore diffusion,1
indicating that the potential for fouling of pores by surfactants can have a negative affect. Additionally, the surfactant can coat the surface of the carbon, which will alter the surface properties
of the absorbent.4
Surfactant in wastewater solutions also present problems for air stripping due to changes in
solubility and the generation of foaming. Further, surfactants alter the rate of mass transfer into
the gas bubble, reducing the mass transfer coefficient,5 and thereby slowing the air stripping
process.
52nd Purdue Industrial Waste Conference Proceedings. 1997. Ann Arbor Press. Chelsea. Michigan 48118. Printed in
U.S.A.
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