Bongbeen Yim

Sonochemical degradation of chlorophenols in water

Sonochemical degradation of dilute aqueous solutions of 2-, 3- and 4-chlorophenol and pentachlorophenol has been investigated under air or argon atmosphere. The degradation follows first-order kinetics in the initial state with rates in the range 4.5-6.6 microM min-1 under air and 6.0-7.2 microM min-1 under argon at a concentration of 100 microM of chlorophenols. The rate of OH radical formation from water is 19.8 microM min-1 under argon and 14.7 microM min-1 under air in the same sonolysis conditions. The sonolysis of chlorophenols is effectively inhibited, but not completely, by the addition of t-BuOH, which is known to be an efficient OH radical scavenger in aqueous sonolysis. This suggests that the main degradation of chlorophenols proceeds via reaction with OH radicals; a thermal reaction also occurs, although its contribution is small. The addition of appropriate amounts of Fe(II) ions accelerates the degradation. This is probably due to the regeneration of OH radicals from hydrogen peroxide, which would be formed from recombination of OH radicals and which may contribute a little to the degradation. The ability to inhibit bacterial multiplication of pentachlorophenol decreases with ultrasonic irradiation.

Sonolysis of alkylphenols in aqueous solution with Fe(II) and Fe(III).

The sonolytic degradation of alkylphenols (APs), such as butylphenol, pentylphenol, octylphenol, and nonylphenol (NP), in water was investigated at a sound frequency of 200 kHz with an acoustic intensity of 6 W cm(-2) under argon, oxygen, and air atmospheres. The sonolytic degradation rate of the APs under the conditions of the present study depended upon their alkyl chain length. The decrease in the degradation rate by the radical scavenging effect was in the range of about 48-82% for APs in the presence of 3 mM 2-methyl-2-propanol. The free radicals play a significant role in the sonolytic degradation process of the APs. In the presence of Fe(II) and Fe(III), the pseudo-first-order rate constants for the sonolytic degradation of 30 microM NP as a function of the concentration of Fe(II) and Fe(III) were estimated under argon and oxygen. The maximum rate constants were observed at 50 microM Fe(II) (0.139 +/- 0.008 min(-1)) and 100 microM Fe(III) (0.103 +/- 0.001 min(-1)) under oxygen. The total organic carbon concentration (TOC) was investigated under same conditions. TOC decreased in the range of about 50-70% during the sonication in the presence of Fe(II) and Fe(III) under argon and oxygen. The sonochemical effects by the addition of Fe(II) and Fe(III) as catalyst during the sonication under the proper atmosphere result in a remarkable enhancement of degradation and mineralization.

Inactivation of Saccharomyces cerevisiae by ultrasonic irradiation

We have investigated the inactivation of Saccharomyces cerevisiae (yeast cells) by ultrasonic irradiation. The amplitude on the vibration face contacting the sample solution was used as an indication of the ultrasonic power intensity. The effects of the amplitude on the vibration face and the initial cell numbers on the sonolytic inactivation of yeast cells have been investigated using a horn-type sonicator (27.5 kHz). The inactivation of the yeast cells by ultrasonic irradiation shows pseudo first-order behavior. The inactivation rate constant varied from 0.0007 to 0.145 s(-1) when the amplitude on the vibration face was in the range of 1-7 microm(p-p). The change in the inactivation rate constant as a function of the amplitude on the vibration face was similar to that of the OH radical formation rate under the same conditions. The threshold of this sonicator was 3 microm(p-p) with the amplitude on the vibration face. The initial cell numbers (from 10(2) to 10(5) mL(-1)) had an influence on the inactivation of the yeast cells by ultrasonic irradiation. The inactivation rate constants varied from 0.023 to 6.4 x 10(-3) s(-1), and the inactivation by ultrasonic irradiation was fastest at the lowest initial cell numbers. In a squeeze-film-type sonicator (26.6 kHz), 90% inactivation of the yeast cells was achieved by ultrasonic irradiation for 60 min.

Sonolysis of Chlorobenzene in Fenton Type Aqueous Systems

The influence of ultrasounds (200 kHz frequency) on the decomposition of chlorobenzene (CB) in a water solution (around 100 ppm concentration) containing iron or palladium sulfates was investigated. The intermediates of the sonolysis were identified, thus allowing a deeper insight into the degradation mechanism. It was established that CB degradation starts by pyrolysis inside the cavitation bubbles. The initial sonolysis product is benzene, formed in a reaction occurring outside the cavitation from phenyl radicals and the hydrogen atoms sonolytically generated from the water. Polyphenols as products of the CB sonochemical degradation are reported for the first time. The palladium salt was found to be a useful and sensitive indicator for differentiating the sites and mechanisms of the product formation. An alternative mechanism for the CB sonolysis is advanced, explaining the formation of phenols, polyphenols, chlorophenols and benzene.

Sonolysis of surfactants in aqueous solutions: an accumulation of solute in the interfacial region of the cavitation bubbles.

The sonolysis of surfactants (such as sodium dodecylbenzenesulfonate (DBS), sodium dodecylsulfate (SDS), and polyethylene glycol monostearate), sodium 4-toluenesulfonate (STS), and 1-hexanol in aqueous solutions was investigated under an argon atmosphere with ultrasound of 200 kHz in order to compare the scavenging efficiency of the hydroxyl radical and the accumulation in the gas-liquid interfacial region of the cavitation bubbles. The degradation rate of the solute follows the order 1-hexanol > DBS and SDS > STS. The scavenging efficiency of the hydroxyl radical by non-volatile surfactants was much greater than that of the non-volatile and hydrophilic solute (e.g., STS). The surfactant was accumulated in a relatively high ratio in the interfacial region. The degradation of surfactants occurred by reaction with the hydroxyl radical and also by pyrolysis at high temperature. On the other hand, STS, due to its non-volatile and hydrophilic properties, was principally present in the bulk solution and the degradation by pyrolysis was not observed at the investigated concentration ranges.

Sonochemical degradation of chlorinated hydrocarbons using a batch and continuous flow system

The sonochemical degradation of chlorinated hydrocarbons such as 1,1,1-trichloroethane, trichloroethylene and tetrachloroethylene in aqueous solution was carried out in the batch and continuous flow systems at an ultrasonic frequency of 100kHz under an air atmosphere. In the batch experiment, the rate of degradation follows the order 1,1,1-trichloroethane>tetrachloroethylene>trichloroethylene, and the chlorinated hydrocarbon were readily degraded by ultrasonic irradiation. The experiments in the continuous flow system were performed in the range of volumetric flow rate from 7 to 30 x 10(-3)lmin(-1). The conversion of the chlorinated hydrocarbons at a steady-state of reactor depended on the volumetric flow rate. The yield of Cl(-) (as a measurement of mineralization of chlorinated hydrocarbons) was 70-90% of the chlorine atoms in the parent chlorinated hydrocarbon molecules. From the viewpoint of the scale-up process, the sonochemical degradation of trichloroethylene was simulated in a three stage reactor, and the conversion (>99%) in a third stage reactor was showed the good results that can be satisfied a desired water quality standard.