The Chemical Engineering Journal and the Biochemical Engineering Journal最新文献

Colloidal gas aphrons (CGAs) were first reported by Sebba (J. Colloid Interface Sci., 35 (4) (1971) 643) as micro bubbles (10–100 μm), composed of a gaseous inner core surrounded by a thin surfactant film, which are created by intense stirring of a surfactant solution. Since then, these colloidal dispersions have been used for diverse applications (clarification of suspensions, removal of sulphur crystals, separation of organic dyes from wastewater, etc.). However, there have been no reports, as yet, of their direct application for protein recovery. In this study, CGAs are created from an anionic surfactant (AOT) and are characterised in terms of stability and gas hold-up for a range of process parameters relevant to their proposed use for protein recovery, at a later stage. A statistical experimental design was developed in order to study the effect of different factors (surfactant concentration, salt concentration, pH, time of stirring and temperature) on the stability and gas hold-up of CGAs. The analysis of results from the experimental design provides predictive statistical models. Stability was found to depend mainly on salt and surfactant concentration. Several interactions are shown to be significant including the time-temperature interaction. Gas hold-up was found to depend mainly on salt and surfactant concentration and time of stirring. Also, results from power measurements are presented and the minimum energy for the formation of CGAs, for one set of solution properties, is determined.

A simple algorithm for solving the hollow-fiber bioreactor design equations has been presented. This algorithm is quite general and is applicable to any nonlinear reaction occurring in the reactor spongy matrix. This can also be applied to other reactor types having similar configurations, like the wall-coated enzyme reactors.

Small diameter hydrocyclones have had an increasing use in performing difficult separations between phases, due to the large centrifugal forces generated in them. The potential use of hydrocyclones in the concentration of microbial suspensions is attractive as they are continuous, high capacity devices requiring low maintenance while having the additional benefit in that they can be readily sterilised.

Results are reported on the de-watering of Bakers' yeast in a 10 mm diameter hydrocyclone to quantify the separation process. The form of the model equation for recovery has been derived based on the non-equilibrium residence time theory. This is shown to represent experimental data in that increasing pressure and temperature exhibit a positive effect on both the recovery and the concentrating effect while an increase in the feed concentration exhibits a negative effect on these. In addition, the influence of cyclone geometry on the recovery and concentration ratio has been illustrated. Increasing the vortex diameter results in an increasing concentration ratio and a decreasing recovery. Increasing the diameter of the spigot shows the opposing trends.

Typical results from a single stage separation combine a recovery of 60% with a concentration ratio of 1.25 and a recovery of 30% with a concentration ratio of 2.0. Concomitant improvement of the recovery and concentration ratio will be attainable through the use of multi-stage hydrocyclone circuits.

Equilibrium studies on the extraction of lactic acid from aqueous solutions with tri-n-octylamine (TOA) in xylene were made in the temperature range 293–323 K. The formulation of the extracted species in the organic phase and the corresponding equilibrium constants were numerically determined at different temperatures. Also, the apparent thermodynamic functions were calculated. Finally, the effect of a water-insoluble organic acid, di(2-ethylhexyl)phosphoric acid (D2EHPA), on this extraction was investigated. Synergistic and antagonistic effects were observed in the presence of D2EHPA, mainly depending on the concentration ratio of D2EHPA to TOA.

The present work deals with modelling of anaerobic metabolism in a stratified biofilm consisting of two distinct layers of microorganisms in a fixed film reactor. The model is applied to steady state conditions and is based on substrate utilization kinetics and mass transport. The model assumes that the substrate is first metabolized by the outer acidogenic layer and the subsequent products are metabolized by the inner layer of methanogens to produce finally methane and carbon dioxide. The model considers slab geometry of the biofilm, Monod kinetics for growth rate of acidogens and the inhibition effect of volatile fatty acids on growth rate of methanogens. The diffusion equations are solved simultaneously using a modified form of the technique of orthogonal collocation on finite elements to obtain concentration profiles and the rate of methane production per unit volume of the biofilm is determined. Computer simulations are carried out to study the effect of various parameters on the rate of methane production and to investigate the existence of multiple steady states. The simulation shows that for a range of parameters values three steady states exist. It is shown that the upper steady state with highest rate of methane production may lead to unsatisfactory reactor performance.

In this study, Cu^II adsorption by Z. ramigera immobilized on Ca-alginate was investigated in a packed bed column test circuit using a stimulus-response technique. The mathematical model was described and solved using “parameter estimation by cybernetic moment technique”, and the adsorption rate constant of Cu^II ions on Z. ramigera immobilized on Ca-alginate was calculated. The Péclet numbers, which reflect the column flow characteristics in the cases of no diffusion and/or no adsorption, were calculated. The diffusional effects inside the pores of biomass immobilized on Ca-alginate matrices were investigated. The moment technique was used for evaluation of stimulus-response data of heavy metal-biosorbent interactions, to determine the process parameters.