Sonolysis of trichloroethylene in aqueous solution: Volatile organic intermediates

The ultrasonic degradation of 3.34 mM trichloroethylene (TCE) in aqueous solution was measured at 20 and 520 kHz. As the degradation was energetically more efficient at 520 kHz, sonication at this frequency was further investigated. The effect of the saturating gas (air or argon) and the influence of the pH of the aqueous solution was studied. The degradation was fastest in basic solutions saturated with argon. TCE was not degraded in the bulk solution. During sonication volatile and non-volatile organic degradation products were formed. The most important volatile compounds were identified: C2HCl, C2Cl2, C4Cl2, C2Cl4, C4HCl3 (2), C4Cl4, C4HCl5 and C4Cl6. Those products are typical for pyrolysis of TCE and are an affirmation for the 'hot spot' theory. The kinetics of five of those volatile intermediates were determined by headspace analysis for air-saturated as well as for argon-saturated solutions. The intermediates considered are formed in single cavitation events and disappeared from the aqueous solution as well.