Evelyne Gonze

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.

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.

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.

Treatment of Diesel Particles Using an Electrostatic Agglomerator Under Negative DC Corona: A Modeling and Experimental Study

The aim of this paper is to characterize an electrostatic agglomerator with an innovative shape intended to collect diesel particles. The agglomerator consists of a tube-type electrofilter with a porous collecting electrode supplied by a negative dc operating voltage. The end of the device is closed, so all the treated gas passes through the collecting electrode. The stocking surface is very small, and the collecting electrode acts as a simple agglomerator. The specific electrical consumption is approximately 1 J/L for a 95% reduction in particle number. This agglomerator requires an extremely short residence time, in the same order of magnitude as the particle electrical charging time. The reentrained agglomerates clearly have micronic size and are very little in number, so that their characterization cannot be done easily by classical granulometers such as electrical low-pressure impactor or scanning mobility particle sizer. An approach to modeling the reentrained number distribution is proposed, which permits to confirm and explain many of the experimental results. Discrepancies between experimental results and numerical model predictions show that particle filtration may be highly enhanced by a dendrite layer actively maintained by an electric field.

Numerical Model of Current–Voltage Curve for the Wire-Cylinder Electrostatic Precipitators in Negative Voltage in the Presence of Nonpolar Gases

The aim of this paper is to develop a numerical model that takes into account the share of the electric current produced by free electrons when an electrostatic precipitator (ESP) with a wire-cylinder geometry is supplied with a negative voltage and the carrier gas is nonpolar. This model improves the understanding of ESPs and highlights the parameters that affect the process behavior and the generation of free electrons. It takes into account the current stemming from the presence of free electrons. For this reason, a coefficient was developed and was expressed as a function of the temperature, pressure, and composition of the carrier gas. Experimental results obtained by other authors and laboratory measurements were compared with the model. The set of results showed that the numerical model developed in this paper is valid only in the presence of nonpolar gases.