Applications of Ultrasound in NAPL Remediation:  Sonochemical Degradation of TCE in Aqueous Surfactant Solutions

Abstract

Surfactant-enhanced pump-and-treat technologies increase the efficiency of nonaqueous-phase liquids (NAPLs) removal from soils. However, high concentrations of surfactants in groundwater impose severe limitations to water treatment. In this paper, we explore the applicability of ultrasonic irradiation as an alternative method for surfactant recovery and contaminant degradation. The combined effects of temperature, initial substrate concentration, and concentration of added surfactant (sodium dodecyl sulfate, SDS) were analyzed for the sonolysis of trichloroethylene (TCE) in batch experiments at an ultrasonic frequency of 500 kHz and 77 W/L applied power density. In the range of 5-30 degrees C, TCE sonolysis becomes faster at higher temperatures, both in the absence and in the presence of surfactant. This indicates that gas-phase pyrolysis prevails over other chemical reactions in the liquid phase. Inhibition of TCE sonolysis was observed in the presence of surfactant at all SDS concentrations. Changes in the initial TCE concentration (from 250 microM to 1.2 mM) showed no effect on the degradation rates in the presence of SDS. For surfactant levels below its critical micelle concentration (cmc), the inhibition of TCE sonolysis exhibited a highly nonlinear dependence with increasing SDS concentration. A correlation was observed in this range between the relative inhibition of sonolysis and the decreasing surface tension of the solutions. Above the cmc up to an SDS concentration of 5%, the reaction rate decreased less markedly. Micellar sequestration of the contaminant seems to be the main reason for this additional inhibition. Bubble growth prior to collapse may incorporate some of the TCE dissolved in the micelles through their adsorption in the expanding bubble walls, thus partially overcoming the scavenging effect due to micellar entrapment of the contaminant.

Scale-Up of Sonochemical Reactors for Water Treatment

“…For all three studied substrates, degradation reactions in the Pilotstation followed pseudo-first-order kinetics. This is in agreement with previous experience in small reactors for these systems, where the primary degradation step in each case was described as 6,11,13 Reactions 1 and 2 take place in the gas-phase inside the cavitation bubbles, while reaction 3 occurs in solution. Table 1 summarizes the observed pseudo-firstorder rate constants, k -X , measured under the given experimental conditions for X ) DCM, TCE, and MO solutions with air saturation (i.e., without additional gas sparging), working both with the Pilotstation and with bench-scale reactors.…”

“…6,13 The reaction rate for the depletion of these molecules typically increases with the liquid temperature in proportion to their intrinsic vapor pressures, which indicates the predominance of high-temperature gas-phase pyrolysis reactions. 13 Since chlorinated methanes are not very susceptible to reaction with most oxidants in aqueous solution, sonolysis appears to be a convenient alternative to standard oxidative techniques. In this study, we used dichloromethane (DCM, CH 2 Cl 2 ) and trichloroethylene (TCE, C 2 HCl 3 ) as probes for volatile sonochemical targets.…”

PENGGUNAAN KATALIS ZnO-H2O2 UNTUK DEGRADASI ZAT WARNA RHODAMIN B DAN ALIZARIN-S

“…Gelombang ultrasonik yang digunakan dalam metoda sonolisis beroperasi pada frekuensi 20 -500 kHz [2] . Dengan metoda ini, zat warna organic dalam media air dapat diuraikan menggunakan getaran.…”

Kinetic analysis and energy efficiency of phenol degradation in a plasma-photocatalysis system

“…Most of them are biorefractory organic compounds, which are hard to be degraded by traditional methods of chemical oxidation and biological oxidation. In recent years, many advanced oxidation processes (AOPs) are widely used for organic compounds treatment [1][2][3][4][5]. Since some oxidation species with higher oxidation potential ( • OH, • O, H 2 O 2 and O 3 ) can be produced during the reaction processes, AOPs have virtues of thorough degradation and no secondary pollution.…”