The biosorption of cadmium metal ions by Saccharomyces cerevisiae and Kluyveromyces fragilis yeast cells was studied under various operating conditions in a batch system using shaker flasks and a 2-L double draft tube fluidized bioreactor system. The effects of key parameters such as solution pH, initial metal concentration, biosorbent concentration, and age of the biosorbent cells were investigated. The experiments were carried out at room temperature and pH values of 3.5, 4.5 and 5.0. Three biosorbent yeast cells concentrations (2.5, 5.0 and 7.5 g dry wt./L) were employed with aqueous solutions having initial cadmium concentrations of 50, 100 and 200 mg/L. The solution pH was found to play a critical role in the biosorption process and the metal uptake increased with an increase in pH value. The optimum pH was found to be 5.0. Also, increasing the metal concentration and decreasing the biosorbent concentration increased the final metal uptake per unit cell mass. At a sufficiently high cadmium concentration of 200 mg/L, the effect of initial metal concentration became the dominant factor, since the metal uptake became constant with respect to the initial metal concentration, regardless of pH value. The results showed that the effect of biosorbent concentration on metal uptake was less significant than those of the cadmium concentration and the pH. It was also found that the younger the yeast biosorbent, the higher the metal uptake capacity. Generally, the cadmium uptake was found to take place rapidly, whereby almost 90% uptake occurred within the first five minutes of exposure. The equilibrium of cadmium biosorption was investigated under the same operating conditions. The Langmuir and the Freundlich adsorption isotherms were used to fit the experimental data. However, both of these conventional adsorption models did not fit the experimental data accurately. The maximum uptake capacity was estimated to be close to 35 and 40 mg Cd/g DW cell for S. cerevisiae and K. fragilis, respectively at a pH value of 5.0.

Pulsation-assisted fluidization was employed in a square fluidized bed to enhance mixing properties. The gas-phase pulsation frequency was varied between 0.5 and 5.0 Hz. The fluidized bed hydrodynamics were studied with and without internals, in beds of different heights. From the measurement of pressure fluctuations, average cycle frequencies (ACF) and incoherent standard deviations (IOP) were calculated to quantify bubble characteristics, such as the bubble size. In addition, optical probe measurements were used to determine the local bubble fraction. When a fraction of the total flow is oscillated with an appropriate frequency, possible defluidization problems are prevented. A clear change in the bubble characteristics was observed when increasing the pulsation frequency up to 3.0 Hz. Higher pulsation frequencies, especially beyond 5.0 Hz, have no significant effect when compared to a steady, constant flow. Pulsation-assisted flow significantly increases bubble size, increases the ACF, and decreases bubble fraction. Moreover, the presence of internals slightly decreases the bubble size, slightly decreases the ACF, significantly decreases the bubble fraction, and influences the bubble pathway, especially at low superficial gas velocity. Finally, increasing the bed height has a less clear trend on the ACF, but it increases the bubble size using either steady or pulsed flow, with more significant increases in the latter case.

No abstract

Three different calibration techniques have been developed to greatly improve the accuracy of the solid holdup distributions obtained from electrical capacitance tomography (ECT) measurements. First, liquid mixtures are used to calibrate the ECT system. Second, the relative permittivity of solid particles is obtained by immersing the solids in different fluids: the solid relative permittivity corresponds to the point where the fluid relative permittivity matches the relative permittivity of the liquid-solid mixture. Third, the best relationship between solid holdup and electrical permittivity, over the required range of solid concentrations, is determined, for each particulate system, by suspending the particles in a viscous liquid honey.

Predicting the amount of attrition that will occur in a pneumatic transport system is very important in preventing product degradation. Considerable work has been performed on the mechanisms of attrition in fluidized beds; hence, they are well understood. On the other hand, there are fewer correlations that can be used to predict the attrition rate in pneumatic transport and spouted beds. In this study, polymethyl methacrylates particles were attrited in a pneumatic transport pilot plant and the experimental attrition rate was determined. The same particles were also used in a spouted bed with a sonic attrition jet and the attrition rate was measured. Finally, a fluidized bed correlation was applied to the spouted bed and a model was used to determine whether the attrition mechanism in pneumatic transport can be related to the attrition mechanism in the spouted bed.