Development and temperature gradient online monitoring of a vehicular rotary solid‐state bioreactor: a novel device for large‐scale preparation of Aspergillus niger spore inoculum

Abstract

AbstractBACKGROUNDMechanical cultivation of Aspergillus niger spores at industrial scales as the fermentationinoculum in citric acid plants is difficult to achieve: in solid‐state cultivation, intense mechanical agitation or continuous mixing to reduce damage to the filamentous microbes is not feasible, but inadequate mixing or static cultivation would cause serious inner‐bed temperature gradients. It is therefore necessary to develop novel bioreactors coordinating the conflict between microbe protection and heat transfer, by globally investigating the inner‐bed temperature profile, an investigation that has not been reported upon previously.RESULTSA novel vehicular rotary solid‐state bioreactor was developed combining the characteristics of both a vertical packed bed and a horizontal rotating drum. Moderate and intermittent rotary mixing based on the characteristic posture‐shifting function ensured high spore yields of 3.1 × 1012 per batch (22‐cm‐thick bed, using a rich medium) and 1.3 × 1012 per batch (15‐cm‐thick bed, using a poor medium and two‐stage temperature control strategy). The two‐stage temperature control strategy effectively depressed the upper limit of bed temperature under 37.0 °C. A 16‐point temperature measuring system provided online 4D data of the culture bed including time, temperature, radius and height, globally displaying the inner‐bed temperature gradients. A cylindrical air distributor benefits inner bed radial air flow distribution, but did not affect the spore yield and average moisture content of the solid culture.CONCLUSIONSThe novel devices and methods realized large‐scale production of A. niger spores by coordinating moderate mixing and inner bed temperature field monitoring and control; they also possessed application value for other filamentous microbes. © 2019 Society of Chemical Industry