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Oxygen Mass Transfer (oxygen + mass_transfer)
Selected AbstractsCell growth and Trametes versicolor laccase production in transformed Pichia pastoris cultured by solid-state or submerged fermentationsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2010Marcos López Abstract BACKGROUND: Growth kinetics of Pichia pastoris and heterologous expression of Trametes versicolor laccase were compared. This is the first study of its kind between solid-state yeast cultures done on polyurethane foam (PUF) and submerged liquid fermentations (SmF). RESULTS: The maximum values of biomass were similar for SSF (solid-state fermentation) and SmF experiments when the BOD (biochemical oxygen demand) was lower than 100 g L,1. For higher BOD levels, the maximum values of biomass were 55 g L,1 (SSF) and 35 g L,1 (SmF). Micrographs of PUF preparations showed yeast growing within liquid lamellae, thinner than 100 µm, forming large horizontal aggregates. Yeast aggregates were much smaller in SmF than in SSF experiments; however, laccase expression was lower in PUF than in SmF, unless the methanol concentration was increased to 63 g L,1, which was inhibitory only to the SmF system. CONCLUSION: The results show that oxygen mass transfer is more efficient in SSF, which is related to the higher area/volume ratio compared with SmF. Induction differences may also be due to hindered diffusion of methanol within large yeast aggregates. Copyright © 2009 Society of Chemical Industry [source] Carrier effects on oxygen mass transfer behavior in a moving-bed biofilm reactorASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Jie Ying Jing Abstract This study investigates the carrier effects on the oxygen mass transfer behavior of a gas,liquid biofilm surface, and aims to provide evidence for parameter optimization in the practical operation of a moving-bed biofilm reactor (MBBR) during the coking-plant wastewater process. By using the dynamic oxygen dissolution method, the volumetric oxygen mass transfer coefficient KLa was measured by varying the suspended carrier stuffing rate and the intensity of aeration. Within the range of fluidizable flow rate, the efficiency of oxygen mass transfer increased with suspended carrier stuffing rate, and KLa reached its peak value when the stuffing rate was 40%. KLa has an increasing trend with an increase of the aeration intensity, but high aeration intensity was not favorable for reactor operation. Better oxygen mass transfer effect and higher oxygen transfer efficiency could be achieved when the aeration intensity was 0.3 m3 h,1 and the suspended carrier stuffing rate was 30,50%. The possible mechanisms that can account for carrier effects on oxygen mass transfer are the changes in the gas,liquid interfacial area. The ammonia nitrogen removal performance of the coking-plant wastewater in MBBR was satisfied by using the above-suggested conditions. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Effect of particle,particle shearing on the bioleaching of sulfide mineralsBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2002N. Chong Abstract The biological leaching of sulfide minerals, used for the production of gold, copper, zinc, cobalt, and other metals, is very often carried out in slurry bioreactors, where the shearing between sulfide particles is intensive. In order to be able to improve the efficiency of the bioleaching, it is of significant importance to know the effect of particle shearing on the rate of leaching. The recently proposed concept of ore immobilization allowed us to study the effect of particle shearing on the rate of sulfide (pyrite) leaching by Thiobacillus ferrooxidans. Using this concept, we designed two very similar bioreactors, the main difference between which was the presence and absence of particle,particle shearing. It was shown that when the oxygen mass transfer was not the rate-limiting step, the rate of bioleaching in the frictionless bioreactor was 2.5 times higher than that in a bioreactor with particle friction (shearing). The concentration of free suspended cells in the frictionless bioreactor was by orders of magnitude lower than that in the frictional bioreactor, which showed that particle friction strongly reduces the microbial attachment to sulfide surface, which, in turn, reduces the rate of bioleaching. Surprisingly, it was found that formation of a layer of insoluble iron salts on the surface of sulfide particles is much slower under shearless conditions than in the presence of particle,particle shearing. This was explained by the effect of particle friction on liquid,solid mass transfer rate. The results of this study show that reduction of the particle friction during bioleaching of sulfide minerals can bring important advantages not only by increasing significantly the bioleaching rate, but also by increasing the rate of gas,liquid oxygen mass transfer, reducing the formation of iron precipitates and reducing the energy consumption. One of the efficient methods for reduction of particle friction is ore immobilization in a porous matrix. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng80: 349,357, 2002. [source] | ||||||||||