Operability and feasibility of ethanol production by immobilizedZymomonas mobilis in a fluidized-bed bioreactor

Continuous Ethanol Production Using Immobilized-Cell/Enzyme Biocatalysts in Fluidized-Bed Bioreactor (FBR)

“…The average yield obtained, therefore, was 89% of the theoretical value. This was slightly lower than the yield obtained in other stud ies using immobilized Z. mobilis with glucose as substrate in an FBR (96% of the theoretical value) (Davison and Scott, 1988). …”

“…However, a drawback of this process is that the operating conditions cannot be optimized for both steps simultaneously. The maximum temperature at which Z. mobilis can ferment efficiently in a continuous process is 35°C (Davison and Scott, 1988), which is well below the optimum temperature of glucoamylase at 55°C (Genencor Product Data Sheet); hence a SSF process will suffer from low enzyme activity. In fact, it has been observed that in such a process, the enzymatic hydrolysis was indeed the rate-limiting step Kim et al, 1992).…”

“…Typical batch reactors, which are commonly used in industry, have volumetric ethanol productivity between 2 and 5 g/L-h (Silman, 1984;Bajpai and Margaritis, 1985). On a total reactor volume basis, volumetric productivity for continuous systems with high conversion is reported as 6-8 g/L-h for a free-cell CSTR, 10-16 g/L-h for an immobilized-cell CSTR, 10-30 g/L-h for a hollow fiber reactor, 16-40 g/L-h for vertical PBR, and 50-120 g/L-h for an immobilized-cell FBR (Godia et al, 1987;Davison and Scott, 1988). One very effective method is to use an immobilized biocatalyst that can be placed into a reaction environment that provides effective mass transport, such as fluidized bed.…”

“…One very effective method is to use an immobilized biocatalyst that can be placed into a reaction environment that provides effective mass transport, such as fluidized bed. Previous studies at ORNL using immobilized Zymomonas mobilis in FBR have shown that this system may be more than 10-50 times as productive as industrial benchmarks (Davison and Scott, 1988;Webb et al, 1995). Economic analysis with Fluor-Daniels showed that a continuous process employing the FBR technology to produce ethanol from corn-derived glucose would offer savings of three to six cents per gallon of ethanol compared to a typical batch process (Harshbarger et al, 1995).…”

Alternative Feedstocks Program Technical and Economic Assessment: Thermal/Chemical and Bioprocessing Components

“…Fluidized-bed reactor technology is being used for the simultaneous fermentation and separation of lactic acid (Davison and Thompson 1992), and producing ethanol <Davison and Scott 1988). A Significant improvement in retention time (five minutes rather than several hours) was achieved when fluidized bed reactors replaced conventional activated sludge systems in removing benzene, toluene, and xylene (BTX) from waste streams (Frank 1992;Hickey and Owens 1981).…”