Trichloroethylene contaminated soil clean-up using surfactant-based separation technology and bioremediation

Abstract

Surfactant-based separation technology and bioremediation was integrated to enhance the removal of trichloroethylene (TCE) from soil. In this system, cloud point extraction by non-ionic surfactant was conducted to separate high amount of TCE into the surfactant-rich phase and then bioremediation was integrated into the system by adding bacteria to co-metabolize the remaining TCE. Six surfactant systems including SURFONIC TDA-5, SURFONIC TDA-6, SURFONIC L24-7, NEODOL 91-5, NEODOL 91-6 without electrolyte addition and DTAB/DOWFAX (2:1 molar ratio) with 0.8 M NaCI were studied. These surfactants induced a phase separation with the surfactant-rich phase presented on top of the solution thus preventing the accumulation of surfactant on soil particles. The results found that SURFONIC TDA-6, SURFONIC L24-7, an NEODOL 91-6 did not inhibit TCE degradability of either Rhodococcus sp. L4 or Phodococcus sp. P3 bacteria while others killed the bacteria. Rhodococcus sp. L4 degraded TCE effectively in the presence of SURFONIC TDA-6, in which more than 58% of 10 ppm TCE was reduced within 24 hours compared to only 30% of TCE removal in control treatment (without the bacteria), SURFONIC TDA-6 was then selected for determining the optimal condition for TCE extraction consisting of equilibrium time, contact time between surfactant solution and soil and initial concentration of surfactant. The optimal condition for TCE extraction by cloud point technique were as followed; 72 hours of equilibrium time, 1 lour of contact time between soil and surfactant solution, and 70 mM of initial concentration of surfactant. These acquired conditions were later applied to compare the effectiveness of three TCE treatment processes including: (1) bioremediation, (2) surfactant extraction and (3) integrated technique. TCE removal efficiency was determined from the remaining TCE concentration in soil after treatment. The TCE removal efficiency of 100 ppm TCE contaminated soil by bioremediation, surfactant extraction and integrated technique were about 74%, 74% and 94%, respectively. Morever, TCE was mineralized as showed by the increase of chloride ions after remediation by bioremediation and integrated technique. When increased the amount of initial TCE to 300 ppm, the removal efficiency of the integrated technique was about 94% which was around 30% higher than either technique alone. The result found that soil remediation by the integrated technique had the highest TCE removal efficiency.