Renzo Di Felice

Hydrodynamics of liquid fluidisation

Abstract Theoretical and empirical approaches to the fluid dynamic description of liquid fluidised beds are reviewed, together with the relevant experimental evidence. Attention has been focused, in the main, on steady- and unsteady-state phenomena relating to monocomponent fluidised beds, with one section devoted to binary-solid systems, the particles differing in size and/or in density.

Treatment of benzene-contaminated airstreams in laboratory-scale biofilters packed with raw and sieved sugarcane bagasse and with peat

Three identical upflow laboratory-scale biofilters, inoculated with thebenzene-degrading strain Pseudomonas sp. NCIMB 9688 but filled up with different packing media (PM), specifically raw sugarcane bagasse, sieved sugarcane bagasse and peat, were employed to eliminate benzene from waste air. Biofilters performances were evaluated by continuous runs in parallel at different influent benzene concentrations, sequentially stepped up through three different superficial gas velocities (31, 61, and 122 m h-1). The peat-packed biofilter exhibited the best performances over the whole experimentation, ensuring removal efficiency of 100% for influent benzeneconcentrations ≤0.05 g m-3, regardless of the superficial gas velocity, and up to 0.4 g m-3 at 31 m h-1. Maximum elimination capacities ofbiofilters packed with raw and sieved sugarcane bagasse and with peat were 3.2, 6.4 and 26 g mPM-3 h-1 at 6.1, 12 and 31 g mPM-3 h-1 loading rates, resulting in 52, 53 and 84% removals, respectively. The bacterial concentrationdistribution along the medium was shown to depend on the benzene loading rate and a correlation between specific benzene elimination rate and biomass concentration was established for biofilters packed with sieved sugarcane bagasse and peat. The macrokinetics of the process were also studied using the profiles of benzene and biomassconcentrations, collected under different conditions over the height of both biofilters, and a zeroth-order kinetic model was shown to describe successfully the degradation process.

Empirical Relationships for the Terminal Settling Velocity of Spheres in Cylindrical Columns

The terminal settling velocity of spherical particles was experimentally investigated in cylindrical columns in the range of Reynolds numbers 2≤Re t ∞≤185 and of particle-to-column diameter ratios, λ, about 0.1 to 0.9. It was observed that none of the existing equations relating the terminal settling velocity, u t , to the diameter ratio, λ, is fully satisfactory. For this reason two new empirical calculation methods are proposed which enable the determination of u t in the whole range of both Reynolds number, Re t ∞, and diameter ratio, λ.

Terminal settling velocity and bed-expansion characteristics of biofilm-coated particles.

Fluid dynamic behavior of biofilm-coated particles in ambient water has been investigated. New experimental results are presented and compared with published data. From experimental measurements of the single particle terminal settling velocity the corresponding drag coefficient was found to be larger (by a factor of 1.6) than that for a smooth, rigid sphere at the same Reynolds number. A new simple correlation describing this finding is suggested. For multiparticle systems the Richardson-Zaki equation, derived empirically for rigid particles, provided a satisfactory description of biological beds. Of the two numerical parameters characterizing the expansion law, i. e. the slope n and the extrapolation to voidage equal one ui, the first was found to be similar to that suggested by Richardson and Zaki (1954), whereas ui gave results smaller than the single-particle terminal settling velocity, in contrast with the mentioned work but in agreement with more recently published behavior.

Mechanisms of biofilm detachment in fluidized bed reactors

Biofilm detachment in liquid fluidized bed biological reactors was investigated to point out how different mechanisms influence the process. Erosion due to liquid shear and abrasion due to collisions of particles were considered as possible mechanisms of biomass detachment in liquid fluidized beds. A dimensional analysis technique allowed the identification of the significant parameters affecting the process. The influence of these parameters was established on a lab-scale reactor. An empirical model was proposed to correlate the experimental data and to analyze the effect of some characteristic quantities, such as particle Reynolds number, biomass fraction, liquid shear stress and solid concentration, on the detachment rate. Detachment rate strongly increased with fluid velocity while, owing to modifications in biofilm structure and morphology during the biological growth, it slightly decreased with liquid shear stress.

An experimental model of biofilm detachment in liquid fluidized bed biological reactors.

Dimensional analysis was applied for the description of biofilm detachment in liquid fluidized bed biological reactors. This technique allowed the identification of the significant parameters influencing detachment mechanisms and suggested suitable experiments for the characterization of involved phenomena. The influence of the significant variables was established on a lab-scale reactor and an empirical model was proposed to correlate experimental results. The detachment rate was strongly dependent on liquid velocity, while the influence of other parameters, such as solid hold-up and liquid shear stress, was found to be less important.

Estimation of viscosity of highly viscous fermentation media containing one or more solutes

Abstract Viscosity and density data are collected at different temperatures for aqueous solutions of glucose, carboxymethyl cellulose (CMC), or both the solutes and used to check the form of a predictive model proposed in this study for viscosity estimation of mixtures of non-electrolyte solutes in Newtonian fermentation broths. The model, which derives from the well-known Guzman–Andrade equation and is based on the Eyring theory, supposes a separate contribution of each solute to total viscosity, which linearly increases with solute concentration and exponentially decreases with temperature. Percentage deviations between theoretical and experimental viscosity values of both, the binary and ternary mixtures, are usually

Phosphorus removal in fluidized bed biological reactor (FBBR)

Abstract The biological phosphorus removal in fluidized bed biological reactor (FBBR) has been investigated. The feasibility of excess phosphorus uptake, assured by exposition of biomass to anaerobic-aerobic conditions, has been demonstrated on a bench-scale biofilm reactor working as sequencing batch reactor (SBR) and the limiting parameters have been established. Although the reactor worked effectively, it took several weeks for both acclimatization of biomass and selection of a biofilm rich in poly-P-bacteria. The highest phosphate uptake rates have been observed when strict anaerobic conditions were reached during the anaerobic phase. Using a fluidized bed, a thin biofilm, characterized by high surface/volume ratio and hence highly disposed toward substrate uptake, has been obtained and the overall phosphorus abatement, referred to the biomass present in the reactor, proved particularly effective.

Catalytic ceramic membrane in a three-phase reactor for the competitive hydrogenation–isomerisation of methylenecyclohexane

Abstract Hydrogenation and oxidation reactions can be carried out in very mild conditions using a three-phase catalytic reactor. The challenge is to overcome the diffusion resistance that affects this type of reactor. The catalytic membrane reactor (CMR), where the membrane is used not only as physical selective barrier but also as a chemical reactor, can be an efficient alternative to more conventional systems in improving the contact among solid catalyst, gas and liquid. The performances of different catalytic membranes were explored in the hydrogenation–isomerisation of methylenecyclohexane, in a temperature range between 288 and 343 K. Comparisons between a classic batch stirred tank and CMR were also carried out. Various characteristics of the reacting system, such as the overall process rate, the effect of temperature, the reaction order with reference to the substrate and the hydrogen and reaction selectivity were studied.

Fluid-particle Drag Force in Binary-solid Suspensions

The drag force on a particle in a multiparticle suspension is a function of the particle-fluid relative velocity and of the particle volume concentration. Its determination heavily relies on experimental observations, as theoretical support is still limited to viscous flow regime and dilute solid concentrations. When uniform particle suspensions are considered, there is a certain abundance of experimental data available which has permitted the proposition of simple and reliable relationships for the determination of the drag force: these relationships are normally expressed through the use of the so-called “voidage function”, i.e. a function by which the drag force on an isolated particle has to be multiplied in order to obtain the drag force on a particle in a multiparticle suspension. The extension of the approach mentioned above to suspensions made up of particles differing in size and density has been attempted here and new simple relationships are presented for the case of binary-solid systems. The basic idea draws an analogy between binary-solid suspension and single-particle suspensions thereby making possible the use of well established results. The simple relationships obtained for the estimation of the drag force on a particle in a binary-solid suspension have been tested, with satisfactory success, against experimental data available in literature.