Carine Julcour-Lebigue

Degradation of paracetamol by catalytic wet air oxidation and sequential adsorption - Catalytic wet air oxidation on activated carbons

The concern about the fate of pharmaceutical products has raised owing to the increasing contamination of rivers, lakes and groundwater. The aim of this paper is to evaluate two different processes for paracetamol removal. The catalytic wet air oxidation (CWAO) of paracetamol on activated carbon was investigated both as a water treatment technique using an autoclave reactor and as a regenerative treatment of the carbon after adsorption in a sequential fixed bed process. Three activated carbons (ACs) from different source materials were used as catalysts: two microporous basic ACs (S23 and C1) and a meso- and micro-porous acidic one (L27). During the first CWAO experiment the adsorption capacity and catalytic performance of fresh S23 and C1 were higher than those of fresh L27 despite its higher surface area. This situation changed after AC reuse, as finally L27 gave the best results after five CWAO cycles. Respirometry tests with activated sludge revealed that in the studied conditions the use of CWAO enhanced the aerobic biodegradability of the effluent. In the ADOX process L27 also showed better oxidation performances and regeneration efficiency. This different ageing was examined through AC physico-chemical properties.

An executive review of sludge pretreatment by sonication.

Ultrasonication (US), which creates hydro-mechanical shear forces in cavitation, is an advanced technology in sludge pretreatment. However, there are many factors affecting the efficacy of cavitation and ultrasonication disintegration of sludge as a consequence. The objective of this work is to present an extensive review of evaluation approaches of sludge US pretreatment efficiency. Besides, optimization methodologies of related parameters, the differences of optimum values and the similarities of affecting trends on cavitation and sludge pretreatment efficiency were specifically pointed out, including ambient conditions, ultrasonic properties, and sludge characteristics. The research is a prerequisite for optimization of sludge US pretreatment efficiency in lab-scale and practical application. There is not-yet a comprehensive method to evaluate the efficiency of sludge US pretreatment, but some main parameters commonly used for this purpose are degree of sludge disintegration, proteins, particle size reduction, etc. Regarding US parameters, power input PUS, intensity IUS, and frequency FS seem to have significant effects. However, the magnitude of the effect of PUS and probe size in terms of IUS has not been clearly detailed. Investigating very low FS seems interesting but has not yet been taken into consideration. In addition, static pressure effect has been marginally studied only and investigation on the effect of pH prior to US process has been restricted. Their effects therefore should be varied separately and simultaneously with other related parameters, i.e. process conditions, ultrasonic properties, and sludge characteristics, to optimize sludge US pretreatment process.

Competitive Adsorption of p-Hydroxybenzoic Acid and Phenol on Activated Carbon: Experimental Study and Modeling

AbstractThe competitive adsorption of phenol and p-hydroxybenzoic acid (4HBA) has been investigated on activated carbon (AC) for a wide range of concentrations under unbuffered conditions. The results show a preferential adsorption of 4HBA, which can be explained by the lower solubility of 4HBA and the electrostatic interactions between the AC and the ionic form of the molecule in this range of pH. The Langmuir isotherm was found suitable to describe the single-component adsorptions, indicating a monolayer adsorption in accordance with the microporous nature of the AC. Then the empirical extended Langmuir model and the predictive ideal adsorption solution theory model have been compared for competitive adsorption. When using parameter values optimized for single pollutants, both models show rather poor agreement with mixture data. However, after fitting the extended Langmuir parameters with the whole data set, better results can be obtained, showing that there is some peculiar behavior of the mixture unde...

Optimization of hydrostatic pressure at varied sonication conditions – power density, intensity, very low frequency – for isothermal ultrasonic sludge treatment

This work aims at investigating for the first time the key sonication (US) parameters: power density (DUS), intensity (IUS), and frequency (FS) - down to audible range, under varied hydrostatic pressure (Ph) and low temperature isothermal conditions (to avoid any thermal effect). The selected application was activated sludge disintegration, a major industrial US process. For a rational approach all comparisons were made at same specific energy input (ES, US energy per solid weight) which is also the relevant economic criterion. The decoupling of power density and intensity was obtained by either changing the sludge volume or most often by changing probe diameter, all other characteristics being unchanged. Comprehensive results were obtained by varying the hydrostatic pressure at given power density and intensity. In all cases marked maxima of sludge disintegration appeared at optimum pressures, which values increased at increasing power intensity and density. Such optimum was expected due to opposite effects of increasing hydrostatic pressure: higher cavitation threshold then smaller and fewer bubbles, but higher temperature and pressure at the end of collapse. In addition the first attempt to lower US frequency down to audible range was very successful: at any operation condition (DUS, IUS, Ph, sludge concentration and type) higher sludge disintegration was obtained at 12 kHz than at 20 kHz. The same values of optimum pressure were observed at 12 and 20 kHz. At same energy consumption the best conditions - obtained at 12 kHz, maximum power density 720 W/L and 3.25 bar - provided about 100% improvement with respect to usual conditions (1 bar, 20 kHz). Important energy savings and equipment size reduction may then be expected.

SONICATION PRETREATMENT OF SLUDGE: PRELIMINARY STUDY OF SLUDGE CONDITIONS

The objective of this work was to investigate effects of sludge conditions serving sludge ultrasonication ( US) . First, it is confirmed specific energy input ( ES ) plays a key role in sludge disintegration ( DD COD ) . An optimal total solid concentration of 28 g/L was found to be convenient for sludge US pretreatment. Besides , secondary sludge showed the highest disintegration, followed by digested and mixed sludge regardless of temperature ( T ) control during US . Additionally, pH adjustment -addition of low NaOH dose (22-40 mg NaOH /g TS ) could be useful, that significantly improved COD release under subsequent US while resulting in a suitable pH value for anaerobic digestion afterwards.

SLUDGE PARTICLE SIZE REDUCTION UNDER ALKALINE, ULTRASONIC, THERMAL, AND COMBINED PRETREATMENTS

Sludge particle size reduction ( PSR ) via pretreatment stage has been believed to accelerate the hydrolysis of sludge anaerobic digestion and enhance the degradation of organic matters. It is therefore one of important factors used to describe the effect of pretreatment on sludge. This work aimed at investigating the evolution of PSR under individual and combined pretreatment methods, including ultrasound ( US ), thermal, and alkaline pretreatments. Different conditions of temperature and pressure were applied to compare and optimize the PSR efficiency. In addition, the relationship between sludge PSR and COD release in the aqueous phase was taken into detailed consideration for the first time. Apart from analysis of Mastersizer 2000 particle size distribution, effects of US and temperature rise on particle size and morphological parameters were also examined by image processing of sludge photographs from Morphologi G3. US pretreatment showed the most predominant role in reducing sludge particle size compared to other methods. The variations of the volume moment mean diameter of different sludge types were dependent on ultrasonic specific energy input ( ES ). Moreover, the PSR was slightly improved in adiabatic conditions and applied pressure as compared to standard conditions. Besides, alkaline addition prior to US further accelerated the PSR . However, the strong reduction of mean particle size observed in the early stage of the process (low ES ) was insufficient to affect COD solubilisation. It is therefore necessary combine with other factors (chemical, biological parameters), not only base on PSR for process optimization.