Automation complexity
Another important feature of single-use systems is that their installation is simplified because the need for cleaning and
sterilization are reduced. This reduction again translates into reduced requirements for clean steam, clean-in-place, and
waste collection and treatment. Although any reduction is important, it is really this elimination of entire systems that
accounts for large cost savings because it is no longer necessary to install distribution systems.
The traditional stainless-steel system needs to be cleaned and sterilized, so instrumentation is necessary to allow the timely
and safe execution of all the associated controls and monitoring efforts. It is therefore important to focus on system complexity
when evaluating cost advantages. Seen from an engineering perspective, an efficient way of evaluating complexity is to estimate
the number of in–out (IO) points (i.e., communications points in the automation system for valve control or temperature monitoring,
for example). A high number of IOs signifies a complex system with high installation and qualification costs.
Each check (e.g., valve positions, temperatures, pressure, and timers) requires several IOs. A stainless-steel system needs
significantly more IOs than do single-use systems that arrive precleaned and presterilized. Single-use systems only require
IOs necessary for running the process in question.
Figure 3
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NNE Pharmaplan compared the number of IOs for various stainless-steel and single-use bioreactors for simple and complex designs,
which differ in their degree of automation because some manual operations are definitely possible in stainless steel systems
(1). As demonstrated in Figure 3, single-use systems show a potential for dramatic reductions—at least 50%—in the number of
IOs. At an average price of approximately $3000 per IO, these reductions can translate to significant savings in installation
costs.
Operation costs
In many cases—not including high batch-frequency operations—single-use technology compares favorably to stainless-steel equipment
in terms of cost. This favorability obtains with respect to investment cost, but also with respect to variable costs when
we include the cost of the capital required to operate a comparable stainless steel system. Amortization and interest over
time must be added to variable costs, and many case studies show these to exceed the variable costs related to increased amount
of consumables used in a single-use design.
The costs of cleaning chemicals and water-for-injection (WFI) are often included in feasibility studies. These costs are seldom
the deciding factor because they are usually low compared with those of other consumables and with the cost of capital in
general. This analysis is perhaps counterintuitive because of the large volumes of resources involved in cleaning and rinsing.
This apparent paradox occurs because the cleaning chemicals are common and relatively inexpensive, because WFI is not used
for all cleaning solutions, and because WFI from an on-site generation and distribution system is much cheaper than WFI bought
as a laboratory material. In an authoritative study on disposables costs, Barnoon estimates that $0.05/L for WFI costs is
realistic for large-scale operations (2).
Estimates about reductions in operator time are sometimes introduced into the comparison, and typical values include a roughly
20% reduction for single-use systems (3). This number is somewhat anecdotal, however, because few published case studies exist.
Although personnel costs are important, such estimates may be realistic only for single facility functions (e.g., washing
and sterilization) but not for the entire facility because cleaning, sterilization, and maintenance are, after all, not constant
activities. It should therefore be possible to allocate resources from other areas during peak load periods.
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