BACKGROUND: An inexpensive and readily available agroindustrial substrate such as rice bran can be used to produce cheap commercial enzymes by solid-state fermentation. This work investigates the production of food-grade proteases by solid-state fermentation using readily available Thai rice bran.

A liquid–solid fluidized bed reactor was used to carry out sulfate reduction with a mixed culture of sulfate reducing bacteria. The bacteria were immobilized on porous glass beads. Stable fluidized bed operation with these biofilm‐coated beads was possible. The low specific gravity of the hydrated beads allowed operation at low liquid recirculation rates. H2S level in the reactor was controlled by N2 sparging, which also served as the location for liquid feed and removal. Ethanol was used as the electron donor/carbon source for the bacteria. Sulfate reduction rates up to 6.33 g sulfate L−1 day−1 were attained in the reactor at a hydraulic retention time of 5.1 h. The effect of hydraulic retention time and biomass loading on the beads, on reactor performance, and efficiency were examined. The efficiency of sulfate reduction increases considerably as the hydraulic retention increases, until the bacteria became very strongly substrate‐limited at 55h HRT. The effect of bead biomass loading on bed expansion at various liquid superficial velocities was studied. A model for the reactor was developed. Simulations of the continuous flow experiments indicate that the model can describe the system well, and thus could be used in the design/scale‐up of such reactors. The model suggests that a significant increase in the sulfate reduction capacity of the system is possible by increasing the volume of the bed relative to the total liquid volume of the system. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 70: 370–380, 2000.

A mixed culture of sulfate-reducing bacteria containing the species Desulfovibrio desulfuricans was used to study sulfate-reduction stoichiometry and kinetics using ethanol as the carbon source. Growth yield was lower, and kinetics were slower, for ethanol compared to lactate. Ethanol was converted into acetate and no significant carbon dioxide production was observed. A mathematical model for growth of sulfate-reducing bacteria on ethanol was developed, and simulations of the growth experiments on ethanol were carried out using the model. The pH variation due to sulfate reduction, and hydrogen sulfide production and removal by nitrogen sparging, were examined. The modeling study is distinct from earlier models for systems using sulfate-reducing bacteria in that it considers growth on ethanol, and analyzes pH variations due to the product-formation reactions.

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