Environmental Engineering Reference
In-Depth Information
sensing is also important, of course, in validating models during development. Especially
important is the potential of on-line sensing to allow precise, automated, feedback control
devices to maintain reactor homeostasis.
Instantaneous results are shown on the left, time averages on the right.
Figure 2. Distribution of fluid velocity (arrows) and oxygen distribution (color).
Conventional reactor sensors are often not ideal for bioprocess measurements, however,
due to their vulnerabilities to interference by biofilm growth, inabilities to resolve
overlapping signals generated in complex culture media, and inabilities to be sterilized to
avoid contaminating culture media, for example [26, 27], and ongoing research into sensor
design is important to the future of bioprocessing.
At the same time, sufficient progress has been made in several key areas that a number of
important variables may be monitored adequately. Dissolved oxygen and pH, for example,
are frequently monitored on-line using electrochemical sensors contained within steam-
sterilizable glass electrodes [28]. Dissolved oxygen may also be measured by a recently-
commercialized method based on fluorescence quenching [29]; available sensors are
described at www.oceanoptics.com and www.fluorometrix.com. On-line measurements of
cell mass are also desirable and can now be made indirectly by electrical or optical means:
capacitance and permittivity measurements, for example, provide electrical quantitation [30],
