Efficiency of a Gas‐Liquid Contactor for the Oxygenation of Activated Sludge: Assessment of Mass Transfer Coefficient

The aim of this work is to investigate a co‐current air‐liquid downward flow bubble column with air entrainment by liquid injection nozzle in order to use it as an aerator in activated sludge treatment plants. The study concerns the determination of mass transfer efficiency by measuring the mass transfer coefficient, k_La, both in clean water and in activated sludge. In clean water, this parameter is determined by three methods, i.e., gassing out method, absorption with chemical reaction and off‐gas method. In activated sludge medium, k_La values are measured by two methods, i.e., sludge reoxygenation and the hydrogen‐peroxide method. The values of k_La obtained in clean water are compared to those obtained in sludge, enabling the assessment of the α factor, i.e., ratio of oxygen transfer coefficient sludge/clean water. The results are in good agreement with those reported previously in the literature.     

Study of the combustion efficiency of polymers using a pyrolysis–combustion flow calorimeter

The combustion efficiency of various polymeric materials was studied using a pyrolysis–combustion flow calorimeter (PCFC). Decreasing the combustion temperature in a PCFC leads to partial combustion and lower heat release rates. Combustion efficiency versus combustion temperature was modeled using a phenomenological equation and model parameters were related to the chemical structures of eight pure polymers. The flame inhibition effect was evaluated for two classical approaches in flame retardancy by plotting the combustion efficiency versus the combustion temperature. In the first one (the reactive approach), polystyrenes with different chemical groups substituted on the aromatic ring were studied. In the second one (the additive approach), three well-known flame retardants were incorporated into an ABS matrix: ammonium polyphosphate, tetrabromobisphenol A (TBBA), and a TBBA/antimony trioxide system. Results confirm the flame inhibition effect of halogenated compounds in both approaches. Finally, a correlation between peaks of heat release rate (pHRR) in a cone calorimeter and in a PCFC was attempted. Predicting pHRR in a cone calorimeter using a PCFC appears possible when no barrier effect is expected, if PCFC tests are carried out at a precise combustion temperature, for which the combustion efficiencies in both tests are the same.     

Influence of dust particles on the hydrodynamic behavior and mass transfer in droplet column

Bubble columns are commonly used in industry for polluted gas treatment. Based on the same principle, the droplet column which is not widely known in the literature, uses much higher gas velocities, up to 14 m/s. This study concerns the hydrodynamics and mass transfer in this apparatus, in presence or absence of solid particles. Our results have demonstrated the impact of dusts on mass transfer performance giving rise to an increase in the k_L a_L coefficient with decreasing particle size. However, no influence of dust on the hydrodynamics of the column has been demonstrated within the studied particle size range. A study of liquid holdups obtained by three different methods is also carried out. Our results are comparable, thus validating the methods used.     

Importance of retronasal and orthonasal olfaction for odor aversion memory in rats.

The role of odors in food memory formation, especially for aversions, has long been considered secondary to taste. However, the importance of odor ingestion in conditioned odor aversion (COA) has recently challenged this assumption (B. M. Slotnick, F. Westbrook, & F. M. C. Darling, 1997). The aim of the present study was to evaluate the respective role of orthonasal and retronasal olfactory experience in COA acquisition, long-term retention, extinction, and spontaneous recovery. To this end, the odor was presented either close to the drinking spout (orthonasal stimulation) or close to and mixed with the drinking water (eliciting both orthonasal and retronasal stimulation). The authors brought evidence that odor ingestion was crucial for COA acquisition, especially when odor presentation and gastric malaise were separated by long delays. On the contrary, once formed, a distal (orthonasal) odor recognition was sufficient for COA to be retrieved. COA was odor specific and long lasting (more than 50 days). Moreover, results brought evidence for a spontaneous recovery of odor aversion tested 57 days after its extinction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A study of oxygen absorption kinetics in ionic Cu(I) aqueous solutions

We developed the oxidation reaction of Cu(I) ion in aqueous hydrochloric solution by oxygen in a gas-lift capillary bubble column. The method of gas-liquid absorption with chemical reaction was used. Test data confirmed that the rate constant of the reaction is strongly affected by solution compositions, and that chloride ions induce an inhibition effect. The kinetical orders found are equal to 1 and 2 for oxygen and Cu(I) respectively. The influence of temperature on reaction rate constant showed the existence of a maximum value between 303 and 313K. The effect of gas-liquid of gas-liquid system on the liquid-side mass transfer coefficient k_L was also investigated.     

Interactive DE for solving combined security environmental economic dispatch considering FACTS technology

This paper presents an efficient interactive differential evolution (IDE) to solve the multi-objective security environmental/economic dispatch (SEED) problem considering multi shunt flexible AC transmission system (FACTS) devices. Two sub problems are proposed.The first one is related to the active power planning to minimize the combined total fuel cost and emissions, while the second is a reactive power planning (RPP) using multi shunt FACTS device based static VAR compensator (SVC) installed at specified buses to make fine corrections to the voltage deviation, voltage phase profiles and reactive power violation. The migration operation inspired from biogeography-based optimization (BBO) algorithm is newly introduced in the proposed approach, thereby effectively exploring and exploiting promising regions in a space search by creating dynamically new efficient partitions. This new mechanism based migration between individuals from different subsystems makes the initial partitions to react more by changing experiences. To validate the robustness of the proposed approach, the proposed algorithm is tested on the Algerian 59-bus electrical network and on a large system, 40 generating units considering valve-point loading effect. Comparison of the results with recent global optimization methods show the superiority of the proposed IDE approach and confirm its potential for solving practical optimal power flow in terms of solution quality and convergence characteristics.     

Artificial bee colony optimization for economic dispatch with valve point effect

In recent years, various heuristic optimization methods have been proposed to solve economic dispatch (ED) problem in power systems. This paper presents the well-known power system ED problem solution considering valve-point effect by a new optimization algorithm called artificial bee colony (ABC). The proposed approach has been applied to various test systems with incremental fuel cost function, taking into account the valve-point effects. The results show that the proposed approach is efficient and robust when compared with other optimization algorithms reported in literature.     

CO2 and H2 detection with a CHx/porous silicon-based sensor

There has been great interest in the last years in gas sensors based on porous silicon (PS). Recently, a gas sensing device based on a hydrocarbon CH_x/porous silicon structure has been fabricated. The porous samples were coated with hydrocarbon groups deposited in a methane argon plasma. We have experimentally demonstrated that the structure can be used for detecting a low concentration of ethylene, ethane and propane gases [Gabouze N, Belhousse S, Cheraga H. Phy State Solidi (C), in press].In this paper, the CH_x/PS/Si structure has been used as a sensing material to detect CO₂ and H₂ gases. The sensitivity of the devices, response time and impedance response to different gas exposures (CO₂, H₂) have been investigated.The results show that current-voltage and impedance-voltage characteristics are modified by the gas reactivity on the PS/CH_x surface and the sensor shows a rapid and reversible response to low concentrations of the gases studied at room temperature.     

Experimental Study on a Co-current Gas–Liquid Down Flow Contactor with Gas Entrainment by a Liquid Jet

Two-phase flow co-current vertical downflow reactor with gas entrainment by a liquid jet is investigated in an air–water system. Experiments are carried out in order to clarify the flow behavior of the reactor under various conditions. Gas entrainment flow rates and gas holdup are quantified experimentally and their dependency on the liquid jet flow rates are shown. The experimental program also included determination of liquid phase residence time distribution (RTD) characteristics for different liquid jet flow rates. The result of the analysis of the liquid phase RTD curves justified the tank-in-series model flow for the liquid phase. On the basis of these analyses, the reactor hydrodynamics are modeled by the tank-in-series model including dead zones. Good agreement is obtained between theoretical and experimental results assuming the reactor is operating as perfectly mixed. The volumetric mass transfer coefficient k_La_Lis determined experimentally by a “gasing out” method. The interfacial area is deduced from the bubble diameter measurements which are determined by visualization experiments.