Experimental study and mathematical modeling of gaseous toluene biofiltration by thermophilic active compost

The main goal of this work was to develop a mathematical model of the process of toluene biofiltration by thermophilic active compost. The model parameters were determined in laboratory-scale experiments with a biofilter, as well as in microcosm experiments. Our experiments have shown that there are two distinctive shapes of compost particles: flat and round ones. The retention time distribution was also determined experimentally. The experimental results of the kinetics, retention time distribution and particle shape were used to develop a mathematical model of the process. Toluene and oxygen concentration profiles were calculated as a function of the particle depth. It has been shown that the oxygen concentration is always is excess and therefore, no anaerobic zones can be expected. A significant intraparticle mass-transfer resistance was predicted for the case of round particles while the effect of internal mass-transfer was not that important in the flat particles. The toluene concentration profile as a function of the bioreactor axial coordinate was calculated and compared to the experimental data.     

Design and experimental study of immobilized soil bioreactor for in-well biodegradation of pentach rophenol in groundwater

A novel system for in-situ biological treatment of pentachlorophenol in groundwater is proposed in this work. It is based on the concept of soil immobilization, which has already been shown to be very efficient when applied to bioreactor engineering. For this paper, we used immobilized soil to develop a bioreactor system for an in-situ (in-well) biodegradation of pentachlorophenol (PCP). The process was carried out at 9dGC, a temperature typical for groundwater. The volumetric PCP degradation efficiency in the new system was very high – up to 400 mg/(L.h). The effect of some physicochemical parameters (temperature, substrate concentration) on the biodegradation kinetics was studied. The results obtained show that the application of soil immobilization to the in-situ biodegradation of groundwater contaminated with PCP is very promising.     

Efficient temporal shaping of ultrashort pulses with birefringent crystals

We report on a simple and robust technique to temporally shape ultrashort pulses. A number of birefringent crystals with appropriate crystal length and orientation form a crystal set. When a short pulse propagates through the crystal set, the pulse is divided into numerous pulses, producing a desired temporal shape. Flexibility in the final pulse shape is achieved through varying initial pulse duration, divided-pulse number, the polarization-mode delay, and energy distribution of the divided pulses. The energy efficiency of the technique is near 100% for a pulse train of alternating polarizations, and 50% for a linearly polarized pulse train.     

Application of surface-renewal-stretch model for interface mass transfer

A new surface-renewal-stretch (SRS) model was developed to correlate experimental data for the time-average overall mass transfer coefficient, K_L,av, in liquid-liquid and gas-liquid mass transfer systems. The model is based on the equation of continuity, which includes both turbulent and convective mass transfer at the liquid-liquid and gas-liquid interfaces. The model incorporates Dankwerts surface-renewal model with the penetration theory for surface stretch proposed by Angelo et al. [Angelo, J.B., Lightfoot, E.N., Howard, D.W., 1996. Generalization of the penetration theory for surface stretch: application to forming and oscillation drops. A.I.Ch.E. Journal 12 (4) 751-760]. We used our new SRS mass transfer model to correlate successfully the existing interface mass transfer experimental data from published literature. As a result, the experimental mass transfer coefficient data was predicted with a high degree of accuracy.     

Wall Effects for the Free Rise of Solid Spheres in Moderately Viscous Liquids

For the first time ever, the influence of wall effects on the free rise of a buoyant solid sphere in a square column in a non‐Newtonian (pseudoplastic) fluid was determined. It was found that in most cases, as the column width decreased, the terminal rise velocity of the sphere would decrease as well. It was also discovered that wall effects could change the rising sphere trajectory. Spheres that displayed a spiraling trajectory in larger columns would display a more linear trajectory in smaller columns. Occasionally, due to this change in trajectory, the solid sphere terminal velocity would increase as the column width decreased. This phenomenon (the positive wall effect) has not been reported for falling spheres in Newtonian or non‐Newtonian fluids.     

Influence of dissolved hydrocarbons on volumetric oxygen mass transfer coefficient in a novel airlift contactor

Hydrocarbon compounds are sparsely soluble in aqueous systems but, nonetheless, their presence can influence significantly mass transfer behavior in gas-liquid systems. water-p-xylene and water-p-xylene-naphthalene mixtures were employed in order to determine the influence of dissolved hydrocarbons on mass transfer of oxygen from air bubbles to water. The surface renewal-stretch model has been modified for predicting the volumetric mass transfer coefficient, (K_La)_h, in the presence of surface contaminant molecules, including hydrocarbon compounds and surfactants. Theory and experimental oxygen transfer results were found to be in satisfactory agreement with average absolute deviation of 15%. Pendant drop and contact angle measurements by axisymmetric drop shape analysis were carried out to determine the reduction in surface tension of water due to the addition of p-xylene and naphthalene. Molecular orientation caused by instantaneous attraction of the polar moieties of the organic compounds toward the water interface has been found to be the main cause of reduction in surface tension. It was predicated that changes in gas-liquid mass transfer behavior resulted from surface contamination and that the significant parameter was the reduction in surface tension.     

Hydrodynamic characteristics of a trickling bed of peat moss used for biofiltration of wastewater

The retention time distribution of liquid in a trickling bed of peat moss was studied. Two different flow regimes have been detected. This is due to the fractal-like structure of peat moss. At low velocities, the liquid flows through the aggregates of peat moss particles. In this case, the tracer is distributed evenly in all the volume of the liquid because of the small characteristic time of diffusion. When the superficial liquid velocity is high, the liquid mainly flows between the solid aggregates and only a small amount of tracer penetrates the liquid inside and between the particles forming the aggregates. The results obtained are important for modelling the process of biofiltration with peat moss, a new system for environmental protection.     

EQUATIONS FOR CALCULATION OF THE TERMINAL VELOCITY AND DRAG COEFFICIENT OF SOLID SPHERES AND GAS BUBBLES

An analysis of the correlations proposed in the literature for calculation of the drag coefficient (C_D) and the terminal velocity of a falling rigid sphere has been made. Among the correlations describing C_D vs. Re, that of Turton and Levenspiel fits the experimental data almost perfectly. However, it is not explicit in the terminal velocity. The available explicit correlations do not fit the experimental data well. The present paper shows that a simple and precise explicit correlation can be developed if C_D is related to the Archimedes instead of the Reynolds number. The precision of the correlation proposed is similar to that of the Turton and Levenspiel (1986), while it is explicit in the terminal velocity. On the basis of this correlation, a model is proposed to calculate the drag coefficients and the terminal velocities of free falling or rising spherical particles in an infinite fluid as well as gas bubbles with any volume and shape rising in a contaminated liquid.     

Modeling,Simulation, and Optimization of Hybrid Fe(II)/Fe(III) Redox Flow Fuel Cell System

The kinetic parameters of ferrous iron oxidation, covering both lag and growth phases at low pH, were determined using a free suspended culture of the bacterium Leptospirillum ferriphilum. A mathematical model was developed to simulate the dynamics of a continuous bioreactor used for operation of a novel hybrid Fe(II)/Fe(III) redox flow fuel cell system. By changing the current load within a predefined range, three runs were performed to predict time‐varying ferrous iron concentration, bacterial cell concentration, and pH as the major output variables of simulation program. The model was experimentally validated through three runs. It was found out that the key variable in dynamic analysis of the bioreactor was the current load applied. To optimize the bioreactor and the fuel cell conditions for a normal‐steady‐state operation, the optimal current profile for a transient phase was determined. A selected optimal policy was also implemented and validated during the mini‐pilot‐scale system experiments. © 2013 American Institute of Chemical Engineers AIChE J, 59: 1844–1854, 2013