Volume 12, Issue 2 - Special issue for International Chemical Engineering Congress 2013 (ICEC 2013), Guest editors: Mejdi Jeguirim and Lionel Limousy

The objective of this study is to investigate the use of photochemical systems (photolysis, H 2 O 2 /UV MP and NaOCl/UV MP ) to deplete monochloramine compound with a medium pressure lamp as an irradiation source (200–600 nm). First, it was found that the direct photolysis treatment was a suitable method to degrade the given compound and that this degradation was greatly enhanced by H 2 O 2 /UV MP . This could be attributed to radical • OH produced in great amount by the photolysis of H 2 O 2 . However, no big advantages were observed when we used NaOCl/UV MP system. Indeed, this process generated radical • OH (but in feeble amount) and also radical Cl • (to form chloramins) and leading consequently to a less degradation rate comparatively to that obtained with H 2 O 2 /UV MP . This could be explained by a competition between the two species: • OH and Cl • for the compound. In addition, kinetics data for the three systems were best represented by a pseudo-first-order model and the photodecomposition of NH 2 Cl has led to the formation of nitrite, nitrate without forming ammonia. It is essential to mention that • OH radicals produced from H 2 O 2 /UV MP and NaOCl/UV MP was detected by a photoluminescence (PL) technic using terephthalic acid (TA) as a probe molecule.

Matching experimental and theoretical approaches have often been fruitful in the investigation of complex biological processes. Here we develop a novel non-conventional model for the denitrification of waste water. Earlier models of the denitrification process were compiled by the International Association on Water Quality group. The Activated Sludge Models 1–3, which are the most frequently used all over the world, are presently not adapted towards the integration of both nitrous and nitric oxide emissions during the denitrification process. In the present work, a Generalized Mass Action model, based on Biochemical Systems Theory, was designed to simulate the nitrate reduction observed in specific experimental conditions. The model was implemented and analysed with the software package PLAS. Data from a representative experiment were chosen ( T =10°C, pH=7, C/N=3, with acetate as carbon source) to simulate greenhouse NO and N 2 O gas emissions, in order to test hypotheses about the corresponding bacterial metabolic pathways. The results show that the reduction of nitrate and nitrite is kinetically limiting and that nitrate reduction is limited by diffusion and support that distinct microbial subpopulations are involved in the denitrification pathway, which has consequences for NO emissions.

In wastewater treatment, waste removal and biomass activity are important processes which need to be monitored for a good process control. The difficulties in the interpretation of the total COD, BOD and VSS measurements encouraged the development of respirometric methods for assessing the kinetic constants. Respirometry is an important technique in assessing biological reaction in wastewater treatment. KLa$${K_L}a$$, depends on endogenous oxygen uptake rate (OURend), is a key constant in evaluating respirogram-specific parameters . Generally, OURend is assumed constant in the dissolved oxygen equations. However, it is not the case. Consequently, this paper deals with the influence of OURend calculations region on KLa$${K_L}a$$ determination, exogenous oxygen uptake rate (OURexo), total oxygen consumption and heterotrophic yield ( Y H ). It was shown that the value of OURend and KLa$${K_L}a$$ varied considerably, a maximum of 56%, depending on where to consider C fin , on the oxygen concentration variation curve. Even though, the variation on OURend and KLa$${K_L}a$$ is important its influence on Y o/ x and Y H is attenuated to 7.5% and 6%, respectively. This may be due to the local nature of the first parameters (OURend and KLa$${K_L}a$$) and the global nature of the later ones. Moreover, this can be seen through the variation of the calculated amount of oxygen consumed (QT hete ) which is of the order 7.6%.

The present work is interested in modeling the adsorption step for the process of Pressure Swing Adsorption (PSA) for hydrogen purification. This work aims at modeling the adsorption of one or more compounds in a mixture at different pressures ranging from 8 to 20 bars at ambient temperature. The flow was presented by the piston model with an axial dispersion. The equilibrium isotherm was expressed by the Langmuir model for the mono-component adsorption and the model of Langmuir extended for the multi-component adsorption. Moreover, two models of kinetic transfer between the gaseous and solid phases were considered, the first-order model based on the approximation of the Linear Driving Force (LDF) and a sophisticated model which is the Surface Diffusion model (SD). As a first step, the CH 4 /H 2 mixture adsorption on activated carbon was studied. In a second step, the adsorption of CH 4 /CO 2 /H 2 on activated carbon and of CH 4 /N 2 /H 2 on a 5A° molecular sieve was studied taking into consideration an interaction parameter for the extended Langmuir model. The simulation results obtained after the resolution of the equations of the model in a developed program, compared with the experimental results from previous works, show a rather satisfactory agreement on the level of stoichiometric time and kinetic mass transfer.

Activated carbons were prepared from date pits by physical activation with CO 2 and the textural properties were investigated by BET and D-R methods with N 2 and CO 2 adsorption isotherms. The interaction of the NO 2 with activated carbon was examined at ambient temperature and the effect of operating conditions such as temperature and inlet gas compositions was also examined. It was observed that the development of porosity with increasing time of activation favours the adsorption capacity of NO 2 . The maximum adsorption capacity reached was about 107 mg/g, which is higher than several activated carbon prepared from classical lignocellulosic biomass. However, a slight decrease of NO 2 adsorption capacity was observed with increasing temperature. The addition of oxygen into the inlet gas gave rise to an increase in amount adsorbed of NO 2 .