Alternate Case 2: Batch Operation
To evaluate the impact of the semicontinuous processing strategy on the rrBChE COGS, we adapted the semicontinuous operation models to examine the process costs associated with the equivalent facility operated in a traditional two-stage batch mode. Here, each production bioreactor operation results in a single cycle of growth, expression, and harvest before CIP, steam-in-place (SIP), and introduction of a fresh inoculum. Five sets of seed train and production bioreactors are required to maintain base case production capacity. Each harvest produces 0.2 kg of pure rrBChE, as the entire 20,000 L culture is collected at the time of harvest. To minimize the size of the decanter, 80% of the spent medium is removed in the bioreactor via gravity sedimentation, and the remaining 15% is removed by the decanter to match the overall 95% medium removal in the semicontinuously-operated base case. Otherwise, the performance of all other downstream steps remains unchanged.
COGS and CAPEX of the two-stage batch operation cases are listed in Table 3. Most notably, OPEX contributions are more heavily weighted by the upstream (52%), as compared to the base case. A comparison of the two-stage semicontinuous and two-stage batch mode operation OPEX contributions is shown in Figure 5 and a comparison of CAPEX contributions is shown in Figure 6.