Durand and Chereau (1988) developed an intermittently mixed bioreactor at INRA, in Dijon, France. It is 2 m long, 0.8 m wide and has an overall height of 2.3 m, with a working bed height of 1 m. This gives a working volume of approximately 1.8 m3, sufficient to hold a bed of approximately 1 ton of moist material. The mixing is provided by a number of screw augers (i.e., designed to lift the substrate as they turn) that are mounted on a carriage on top of the bioreactor (Fig. 10.3). This carriage travels from one end to the other at a top speed of 6.5 cm min-\ meaning that it takes 35 minutes to traverse the bioreactor for one end to the other. The screws rotate at a top speed 22 rpm. The agitation regime, in terms of the frequency and duration of mixing events, can be varied according to the needs of the process, as determined by the particular microorganism and substrate used. Further, if necessary, different agitators such as hollow screws or helicoid screws, can be fitted, depending on the mixing behavior of the solid medium to be used in the fermentation. The carriage has spray nozzles fitted onto its underside, allowing the addition of inoculum, water, nutrient or pH-correcting solutions during mixing. The aeration system has a maximum capacity of 1500 m3 h-1, which means that it is possible to aerate with over 13 volumes of air per bed volume per minute (i.e., over 13 vvm).
motors mounted on a carriage that moves back and forth r
flexible water hoses and power cables
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