Y. Gonthier

Ultrasonic treatment of an aerobic activated sludge in a batch reactor

Low-frequency and high-intensity ultrasonic treatment of sewage plant sludge disrupts the flocs and lyses the bacterial cells. This results in a substantial reduction in the volume of the flocs and a release of both inter and intracellular materials. The evolution of the particles size (flocs and isolated microorganisms) is evaluated by a Malvern Mastersizer granulometer and the release of material is quantified by measuring the chemical oxygen demand and the proteins solubilized in the solution. In the first part, the disruption of the particles was undertaken with low concentrated sludge from an aeration tank in order to comprehend better the mechanisms and to modelize them. In the second part, the influence of the initial concentration is studied by working with higher concentrated sludge from a settler. Ultrasonic treatment also causes a change in the settleability and filterability of the sludge which the effects are evaluated in the last part.

Wastewater pretreatment with ultrasonic irradiation to reduce toxicity

Abstract In order to industrialize an ultrasonic process for wastewater treatment, several works were undertaken. The first one was the study of pentachlorophenol degradation [E. Gonze, Y. Gonthier, P. Boldo and A. Bernis, Can. J. Chem. Eng. 75 (1997) 245]. Association of high-frequency ultrasound transducers was investigated [E. Gonze, Y. Gonthier, P. Boldo and A. Bernis, Entropie 204 (1997) 21] and the mapping of ultrasonic fields in various reactors was studied [E. Gonze, Y. Gonthier, P. Boldo and A. Bernis, Chem. Eng. Sci. 53 (1998) 523; V. Renaudin, N. Gondrexon, P. Boldo, C. Petrier, A. Bernis and Y. Gonthier, Ultrasonics Sonochem. 1 (1994) S81]. The third step presented here consists of considering the ultrasonic process as a preoxidation treatment before a classical biological purification. During the ultrasonic irradiation of a sodium pentachlorophenate solution (NaPCP), the concentration of NaPCP, the acute toxicity effects on bacteria ( Vibrio fischeri ) and on daphnids ( Daphnia magna ) as well as the biodegradability of the pollutant solution were simultaneously monitored. Experimental results provide evidence that an ultrasonic treatment is an efficient preoxidation step.

Degradation of pentachlorophenol aqueous solutions using a continuous flow ultrasonic reactor: experimental performance and modelling

The degradation of aqueous solutions of pentachlorophenol (PCP) in a three-stage sonochemical reactor operating in the continuous flow mode has been investigated. The experimental reactor may be considered as a series of three high-frequency ultrasonic units. The influence of several parameters such as ultrasonic power, reactor volume and volumetric feed flow rate on the reactor performance is reported. Application of classical basic chemical engineering principles leads to a model that enables us to predict the PCP concentration within the reactor. In steady state, experimental conversion rates are shown to be in good agreement with model predictions.

Standing Waves in a High Frequency Sonoreactor : Visualization and Effects

Various high-frequency (500 kHz) devices were investigated to determine the optimal geometry of sonoreactors used for wastewater treatment. Several complementary measurements (distribution of residence time, jacketed thermocouple, chemiluminescence of luminol, direct piezoelectric effect, calorimetry, sodium pentachlorophenate degradation) were used to characterize the acoustic field. These measurements evaluate either local or global physical or chemical ultrasonic activity. It was shown that in some specific reactors, standing waves can settle in the liquid, causing high energy spots to appear at pressure antinodes. It was found that these conditions provide greater sonochemical efficiency.

Experimental study of the hydrodynamic behaviour of a high frequency ultrasonic reactor

In relation to design and modeling of sonochemical reactors, the hydrodynamic behaviour of a high-frequency ultrasonic reactor has been investigated. Residence time distribution (RTD) measurements have been performed by means of a tracer method. The influence of ultrasound on the response to an inlet pulse was evidenced. It was shown that the reactor behaves like a completely stirred tank reactor (CSTR) as soon as ultrasonic irradiation operates. Preliminary observations on acoustic streaming occurring within the reactor will also be presented.

Degassing effect and gas-liquid transfer in a high frequency sonochemical reactor

With a view to determining the parameters required to describe and to optimize sonochemical reactors, we have investigated gas-liquid transfer in a high frequency ultrasonic reactor. The effect of the sonicated volume and ultrasonic power on the dissolved dioxygen concentration in the reactor have been studied. Degassing action caused by cavitation bubbles and absorption caused by the acoustic fountain were shown. The study of the absorption phase leads to a model presented in this paper. The dissolved dioxygen concentration at equilibrium in the reactor which results from these two effects was shown to be constant in all cases.

Method for determining the chemically active zones in a high-frequency ultrasonic reactor

Abstract In order to determine the optimal geometry of the high-frequency sonoreactors to be used for degradation of organic compounds in aqueous solutions, a method based on the chemiluminescence of luminol (which reacts specifically with OH radicals) is applied to visualize the zones where the sonochemical reactions are the most active. The spatial distribution of the light intensity emitted by these reactions is measured inside the reactor with an optical fibre fitted on a photomultiplier. To determine the relative ultrasonic energy distribution, the temperature is measured at different points of the reactor with a thermocouple probe embedded in an absorbing material. The zones where the energy density is the highest were shown not to correspond with those where chemiluminescence reactions are the most efficient.

High frequency ultrasound as a pre- or a post-oxidation for paper mill wastewaters and landfill leachate treatment

Abstract The ultrasonic process is investigated to remove refractory pollutants. The particular case of sodium pentachlorophenate is studied as a model molecule and several raw paper mill wastewaters and a landfill leachate are chosen as real industrial wastewaters. As the sonication requires a lot of energy, it is investigated as a pre- or a post-treatment in combination with biodegradation. For that, global indicators of the environmental pollution (COD, TOC, toxicity and biodegradability) are examined. The results show that ultrasound can decrease toxicity and enhance biodegradability. The amount of energy supplied and the position of the chemical treatment (pre- or post-treatment) are discussed.

Velocity study in an ultrasonic reactor.

In order to determine the parameters required to describe and to optimize sonochemical reactors, we have investigated the water flow inside such a reactor. With this aim, the experimental velocity field has been measured by tomography laser. The influence of certain parameters such as the electric power, the water height and the fluid viscosity has been evaluated. At the same time, the water movement has been studied theoretically using Nyborgs model. We have tried to improve this model by considering a three-dimensional velocity.

Etude de la cinetique de degradation du chlorophenol en solution aqueuse par les ultrasons

Abstract This study deals with the ultrasonic degradation of chlorophenol in aqueous solution at 530 kHz. The use of high frequency ultrasound enables reducing by 50% in 30 minutes the chlorophenol concentration without any additional product. The influence of sonified volume and ultrasonic consumed power is analysed. The experiments were carried out in batch reactor at constant temperature. The reactional volume was visualized with a chemiluminescence reaction.