Effect of dissolved oxygen and chemical oxygen demand to nitrogen ratios on the partial nitrification/denitrification process in moving bed biofilm reactors

Partial nitrification was reported to be technically feasible and economically favorable, especially for wastewater with high ammonium concentration or low C/N ratio. In this study, the effect of dissolved oxygen (DO) and influent ratio of chemical oxygen demand to nitrogen (COD/N) ratio on biological nitrogen removal from synthetic wastewater was investigated. Experiments were conducted in moving bed biofilm reactors (MBBRs) on partial nitrification process in pilot-plant configuration for 300 days. DO levels were changed from 0.04 to 0.12 and 0.42 to 3.4 mg/l in the anoxic (R1) and aerobic (R2) reactors, respectively. The optimum DO for partial nitrification was between 1-1.5 mg/l in the aerobic reactor (R2). Influent COD/N ratios between 20 and 2 g COD/g-N were tested by changing the nitrogen loading rate (NLR) supplied to the pilot plant. During operational conditions when the DO concentration in aerobic reactor was above 1 mg/l, near complete organic carbon removal occurred in the total MBBRs system. The effluent total nitrogen concentration in the operational conditions (1.7-2.1 mg O2/l and NH+ 4-N=35.7 mg N/l) was obtained in the range of 0.85-2 mg/l. The highest nitrite accumulation (50%- 52%) took place at the DO concentration of 1-1.5 mg/l and increased with decreasing COD/N ratio in aerobic reactor (R2). This study showed that the average nitrification rate at various COD/N ratios is about 0.96 gN/m2 per day while the maximum nitrification rate is about 2 gN/m2 per day at COD/N ratios lower than 6. The experimental COD/N ratio for denitrification was close to complete sum of NO2 - and NO3 - (NOx) removal efficiency (about 99%) at COD/N ratio equal 14 in the operational conditions in the anoxic reactor (R1)

Multi-Component Adsorption of Benzene, Toluene, Ethylbenzene, and Xylene from Aqueous Solutions by Montmorillonite Modified with Tetradecyl Trimethyl Ammonium Bromide

Multicomponent adsorption of benzene, toluene, ethylbenzene, and xylene (BTEX) was assessed in aqueous solutions by montmorillonite modified with tetradecyl trimethyl ammonium bromide (TTAB-Mt). Batch experiments were conducted to determine the influences of parameters including loading rates of surfactant, contact time, pH, adsorbate concentration, and temperature on the adsorption efficiency. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) were used to determine the adsorbent properties. Results showed that the modification of the adsorbent via the surfactant causes structural changes of the adsorbent. It was found that the optimum adsorption condition achieves with the surfactant loading rate of 200 of the cation exchange capacity (CEC) of the adsorbent for a period of 24 h. The sorption of BTEX by TTAB-Mt was in the order of B < T < E < X . The experimental data were fitted by many kinetic and isotherm models. The results also showed that the pseudo-second-order kinetic model and Freundlich isotherm model could, respectively, be fitted to the experimental data better than other available kinetic and isotherm models. The thermodynamic study indicated that the sorption of BTEX with TTAB-Mt was achieved spontaneously and the adsorption process was endothermic as well as physical in nature. The regeneration results of the adsorbent also showed that the adsorption capacity of adsorbent after one use was 51 to 70 of original TTAB-Mt

Removal of turbidity from water by dissolved air flotation and conventional sedimentation systems using poly aluminum chloride as coagulant

Flotation is a method in which particles in liquid phase are transported to the surface by air bubbles. In this experimental study, a comparison has been made between conventional sedimentation and dissolved air flotation (DAF) systems to remove turbidity from water. Initially, optimal operational conditions for each system utilized using water artificially turbid with Kaolin. For each system, samples were taken at 20-min interval after the system reached its optimal operational conditions. Parameters, such as turbidity, alkalinity, temperature, pH, and total suspended solids, were measured. For 20, 30-50 and 90-110NTU, turbidity average removal efficiencies in DAF system were 14.7, 11.1 and 10.9, respectively, larger than the conventional sedimentation system. The effect of coagulant dose indicated that DAF system with lower dosage of coagulant have higher removal efficiency. On the other hand, the results showed that due to increased efficiency of DAF system, solid concentration of sludge produced in this system was more than the sedimentation system (p<0.01). However, operation of DAF system needs accurate control devices and experienced technical staff to operate the system

Removal of benzene, toluene, ethylbenzene and xylene (BTEX) from aqueous solutions by montmorillonite modified with nonionic surfactant: Equilibrium, kinetic and thermodynamic study

The adsorption characteristics of benzene, toluene, ethylbenzene and xylene (BTEX) from aqueous solutions by montmorillonite (Mt) modified with poly ethylene glycol (PEG-Mt) were investigated. The batch adsorption technique was used to assess the influence of various parameters such as loading rates of the surfactant, contact time, pH, adsorbate concentration, solution ion strength and temperature on the BTEX sorption capacity by PEG-Mt. The raw and modified Mt was specified with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The XRD results showed that the interlayer spacing of the raw montmorillonite (12.10 angstrom) was increased by PEG surfactant modification (17.48 angstrom). The adsorption capacity of the PEG-Mt was increased by increasing the surfactant loading until 200 cation exchange capacity (CEC) of the clay. The equilibrium was achieved at the contact time of 24 h. The adsorption capacity of the adsorbent was in order of B < T < E < X. The experimental data were analyzed by Langmuir, Freundlich and D-R isotherm models. The results indicated that the data were best fitted with the Freundlich isotherm. The D-R isotherm model also showed that the adsorptive behavior of these compounds has physical nature. The obtained data for BTEX adsorption onto the PEG-Mt were also fitted through the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The correlation coefficients values (R-2) showed that the adsorption kinetic described well by the pseudo-second-order model. The thermodynamic study also indicated that the uptake of BTEX by the adsorbent was spontaneous, endothermic and favorable at higher temperatures. (c) 2012 Elsevier B.V. All rights reserved

Recherche de particules supersymétriques dans les canaux dimuons avec le détecteur DØ au TeVatron

Le Modèle Standard de la Physique des Particules décrit les particules élémentaires, qui constituent la matière, et leurs interactions. Malgré ses succès expérimentaux, il est certain que ce modèle ne peut être qu'une approximation d'une théorie plus fondamentale. La théorie supersymétrique est un candidat attractif pour étendre le Modèle Standard. Cette théorie prédit l'existence de nouvelles particules appelées superpartenaires. La thèse décrit de façon succinte les principaux aspects théoriques et phénoménologiques avant de faire le point sur l'état des recherches auprès du collisionneur électron-positron LEP et du collisionneur hadronique TeVatron pendant le Run I. L'analyse se concentre ensuite sur la recherche des squarks et des gluinos, superpartenaires des quarks et gluons, qui devraient être produits abondamment au TeVatron. Dans leur désintégration en cascade, ces particules produisent en majorité des jets de hadrons et dans une moindre mesure, des leptons. Les topologies avec leptons compensent en partie leur manque de statistique par une meilleure rejection du bruit de fond. Les canaux conduisant dans l'état final à deux muons, au moins deux jets de hadrons, et de l'énergie transverse manquante sont analysés en détail dans les données accumulées jusqu'à présent par l'expérience D0 au cours du Run II (soit pour une luminosité intégrée de 170 pb^-1 ). Aucun excès d'événements n'ayant été observé des limites inférieures sur la masse des squarks et gluinos ont pu être établies pour un set de valeurs des paramètres du Modèle de Super-Gravité minimal.The Standard Model of Particles Physics describes the elementary particles, which compose matter, and their interactions. Despite of its experimental success, it is clear that this model is only an approximation of a more fundamental theory. Supersymmetry is an attractive way to extend the Standard Model. This theory predicts the existence of new particles called superpartners. The thesis describes shortly the main theoretical and phenomenological features before giving the status of the searches at the electron-positron collider LEP and at the hadron collider TeVatron during the Run I period. The analysis points then to the search for squarks and gluinos, the superpartners of quarks and gluons, which should be produced copiously at a hadron collider. In their cascade decay, these particles produce mainly hadron jets and less frequently leptons. However, the topologies with leptons compensate their small statistics by a better rejection against back-ground. The channels leading to the final state with two muons, at least two jets and missing transverse energy are analyzed in detail with data presently accumulated by the D0 experiment during Run II (that is 170 pb^-1 integrated luminosity). No excess of events has been observed, lower limits on the mass of squarks and gluinos have been set for a region of parameters in the minimal Super Gravity Model.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Optimised exergy efficiency of a combined flash spray desalinator recovering discharge thermal energy

This study focuses on an individualised exergy analysis approach for optimising the exergy efficiencies of the high irreversible components for a new discharge thermal energy combined desalination (DTECD) system. DTECD is a newly introduced energy recovery system to use the latent heat of waste steam. It is a combination of closed and open thermodynamic cycles, which cogenerates power and pure water. Based on the extra steam in an ammonia plant, two scenarios were modelled with respect to the exergy performance, which were individualised to find the irreversibility of each component. The results showed that exergy efficiency of the entire system is about 50%. Also, it was found that the working fluid evaporator and vacuum flash desalinator were the most exergy destructive equipment in the closed power cycle and open water cycle, respectively. The performance of the DTECD system utilising a vacuum single-stage spray flash evaporator is compared with similar technologies. Finally, recommendations are provided as to how the exergy efficiencies of these low-efficiency pieces of equipment can be optimised by changing the operating parameters such as vacuum pressure and working fluid concentration