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The objective o f this chapter was the economic comparison of a conventional bioprocessing plant based on stainless steel equipment with one based on disposable equipment. Although the NPV values indicate the conventional option to be the most attractive ($76M for disposables and $103M for conventional), the difference at only 25% is probably sufficiently close to make disposables a viable alternative, especially when considering the other advantages o f disposable plants outlined in the introduction, e.g. time savings and flexibility.

The lower capital investment o f the disposable option results in increased flexibility for the disposable plants since changes in the process or the product result in a reduced financial loss, which is o f great interest for start-up companies. It also allows for an earlier decision to build which may result in earlier entry to market. This effect benefits strongly the disposables option since a reduction in time to market has a high impact on the NPV ratio, as shown in the results o f the sensitivity analysis (Figure 4.8).

Turning now to consider the differences between the two modes o f processing it is clear that staff costs have only a marginal effect on the way the conventional and the disposable options compare. This means that even if the staff requirements o f a disposable plant are less than those o f a conventional plant that would only result in a slight increase o f the NPV ratio. Similarly a decrease o f 25% in the capital investment would result in a variation o f less than 5% on the NPV ratio, showing insensitivity to this variable. Materials costs are shown to be more influential leading to the need for a more detailed evaluation o f the impact o f this variable on the NPV ratio. Indeed the examples given in section 4.4.3 show that materials costs may be reduced by even more than 25%, in favour o f the disposable option. For example an overall 10 fold decrease in the cost o f membranes is probably an attainable target and results in identical NPVs for both options. This cost reduction could be achieved by making use o f disposable dialysis cartridges. Also the cost o f membranes can be expected to decrease once a market for disposable equipment has been established and economies o f scale develop, as in the medical device market.

A final difficulty encountered in the analysis o f disposable bioprocessing is to establish the degree o f similarity between disposables-based plants and conventional designs. The fermentation step is an example o f how the different engineering features o f a disposable plant could have a detrimental impact on product yield. Although the impact on yield may happen in different ways, an analysis o f the sensitivity in Figure 4.11 shows that this is expected to affect the obtainable NPV by less than 20%.

Figure 4.12A and Figure 4.13 show that the reduction in the achievable yield given by a disposables-based option and associated both with a lower level o f biomass production in the fermentation and a reduced chromatographic performance has only a

limited impact on the NPV that is realised. By contrast the loss o f yield due to less productive cells has a dramatic impact on the NPV (Figure 4.12B). This is however a less likely scenario.

The analysis shows that any fall in NPV can easily be overcome when producers of disposable equipment start responding to an increasing demand in their products with higher production scales and hence lower prices. Effectively, a 50% reduction in the yield o f the fermentation can be compensated for by a 50% reduction in the cost o f the materials (Figure 4.12A and B). This is even more striking in the case o f the chromatography (Figure 4.13) where even a 50% loss in yield can be overcome by a saving o f 25% in the materials costs; a margin that appears highly probable as the disposables approach starts to gain acceptance.

It has to be noted that the use o f a chemical engineering model for the calculation o f the running costs indicated disposable plants as the more attractive option (section 4.3.2), with lower operating costs and consequently a higher NPV. This result is contrary to what could be intuitively predicted from the definition o f a disposables- based plant where the increase in the variable costs associated with disposable equipment would be expected to have a higher impact on the NPV. This is because this model places more emphasis on costs such as depreciation and utilities, which are reduced in a disposables approach, rather than on raw materials and consumables. The biochemical engineering model for running costs presented in section 4.3.2 was considered more appropriate and was therefore used for the NPV calculations. This does, however, show how critical it is to identify an appropriate running costs model, a common problem found in biotech costing studies.

In conclusion, a disposables-based plant with the same features as its conventional equivalent is economically and conceptually attractive as it may be o f easier and quicker implementation and with a comparable overall investment required. N ot only does it present a NPV which is close to that o f a conventional option, the difference can actually be nullified with the use o f intrinsically disposable equipment or by achieving shorter times to market.

the mechanism o f performance decay in the lysate clarification step o f the case study process. Chapters 7 and 8 will then focus on experimental strategies to reduce the membrane area required in biopharmaceutical processes.