Soft elastic tubular reactor: An unconventional bioreactor for high-solids operations

Abstract

Many bioreactors for solid state (SSF) and high-solids load fermentations have been developed in order to obtain valuable bioproducts. In general, it is emphasized the necessity for design improvements in reactor mixing, heat transfer, and gaseous mass transfer. A soft-elastic tubular reactor (SETR) was built and its behavior in terms of aeration, mixing, and temperature control was evaluated. Although soft-elastic reactors have been explored for some time, this was the first time they were thoroughly investigated for fermentation use. Depending on the applied parameters, such as aeration, mixing rate, and media characteristics (liquid viscosity, solid, sludge), KLa ranged between 1 and 40 h−1, a well-mixed state was attained between 0.3 and 60 min, and the temperature reached operational stability within 20 min. Soybeans were fermented by Bacillus subtilis subsp. natto as a proof of concept (moisture content from 66 wt% up to 80 wt%). The proposed SETR demonstrated that temperature, mixing, and aeration could be modified to meet the needs of the process, and while more research is needed, it might be regarded as a new option for solid state or high-load substrate processes.