Slurry Processing

A slurry bioreactor functions only with a pretreated feedstock; therefore, the bioreac-tor is necessarily integrated with washing-separation operations and includes a de-watering operation at the end of the process (Kleijntjens, 1991; Robra et al., 1998).

A typical setup of an integrated (slurry) bioprocess is shown in Figure 11.5. First, the feedstock is screened using a wet vibrating screen to remove the debris (typical size >2-6 mm). Second, sand fractions are removed by one or more separation techniques such as sieves, hydrocyclones, Humphrey spirals, flotation cells, jigs, and up-flow columns; a typical separation diameter (the so-called cutpoint) for the hydrocyclone depicted is 63 pm (Cullinane et al., 1990). In the cyclone the slurry flow is split into a sand fraction (particle size >63 pm) at the bottom and a fine fraction at the top (<63 pm).

Fig. 11.5 Typical setup for a slurry bioprocess using a batch-operated aerated stirred-tank reactor (typical solids holdup is 20 wt%).

The top flow of the cyclone, containing the contaminated fines, is fed to the bio-reactor (a stirred tank is shown, but any of the three types in Figure 11.2 can be chosen). The final operation results in a dewatered product containing the fines and a flow of process water.

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